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George SZ, Horn ME. Acute Intermittent Hypoxia Did Not Alter Pain Sensitivity or Pain Intensity Ratings for Individuals with Chronic Low Back Pain: A Pilot Study. J Pain Res 2024; 17:421-429. [PMID: 38328018 PMCID: PMC10848823 DOI: 10.2147/jpr.s433685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 01/25/2024] [Indexed: 02/09/2024] Open
Abstract
Aims and Objective The purpose of this pilot study was to explore whether AIH produces changes in pain sensitivity or in reports of self-reported pain intensity for individuals with low back pain. Methods In a quasi-experimental, cross-over design we compared participants (n = 9) exposed to normal room air and hypoxia using a commercially available gas blender. The treatment period consisted of 5 consecutive days of randomly assigned to AIH or room air. For the participants initially randomized to AIH there was cross-over to receive 5 more consecutive days of room air. Therefore, this design allowed for between group and within subject assessment of AIH effects. Pain sensitivity was assessed with quantitative sensory testing (QST) for posterior superior iliac spine pressure threshold, plantar thermal threshold, and peak pain ratings. Self-reported pain intensity for low back pain was assessed via the Brief Pain Inventory. Results There were no between group differences for AIH and room air in pain sensitivity or self-reported pain intensity. In the within subject analyses larger effect sizes favoring AIH were detected for plantar measures of pain sensitivity but not for self-reported pain intensity. Conclusion This study, while presenting null findings, describes an initial step in determining whether AIH can be used to increase pain relief. Based on this pilot study we offer guidance for future research including study design, AIH dosage, participant selection, and using AIH in combination with non-pharmacologic treatments.
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Affiliation(s)
- Steven Z George
- Duke Clinical Research Institute, Duke University, Durham, NC, USA
- Departments of Orthopaedic Surgery and Population Health Science, Duke University, Durham, NC, USA
| | - Maggie E Horn
- Departments of Orthopaedic Surgery and Population Health Science, Duke University, Durham, NC, USA
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2
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Miller S, Lopez EJ, Grittner JML, Dougherty BJ. Low level CO 2 supplementation maintains isocapnia and reveals ventilatory long-term facilitation in rats. Respir Physiol Neurobiol 2024; 320:104185. [PMID: 37935342 PMCID: PMC10842720 DOI: 10.1016/j.resp.2023.104185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Revised: 10/23/2023] [Accepted: 10/30/2023] [Indexed: 11/09/2023]
Abstract
Acute, intermittent hypoxia (AIH) induces ventilatory long-term facilitation (vLTF) in awake, freely behaving rats under poikilocapnic and isocapnic experimental conditions. Establishing pre-clinical methods for vLTF induction that more closely align with successful protocols in humans and anesthetized rats would minimize dissonance in experimental findings and improve translational aspects of vLTF. Here, we tested several levels of low-dose CO2 supplementation during and after AIH to determine 1) the lowest amount of inspired CO2 that would maintain isocapnia in rats during a vLTF protocol, and 2) the net impact of supplemental CO2 on vLTF expression. Rats received one of four levels of inspired CO2 (0%, 0.5%, 1% or 2%) administered during AIH and for the 60 min following AIH to quantify vLTF. Our findings indicated that 2% inspired CO2 was sufficient to maintain isocapnia across the AIH protocol and reveal significant vLTF. These findings provide evidence-based support for using 2% supplemental CO2 during and after AIH when assessing vLTF in rats.
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Affiliation(s)
- Shawn Miller
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Edgar Juarez Lopez
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Jessica M L Grittner
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA; Graduate Program in Rehabilitation Science, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Brendan J Dougherty
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA.
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Thakre PP, Fuller DD. Pattern sensitivity of ampakine-hypoxia interactions for evoking phrenic motor facilitation in anesthetized rat. J Neurophysiol 2024; 131:216-224. [PMID: 38116608 DOI: 10.1152/jn.00315.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 12/13/2023] [Accepted: 12/18/2023] [Indexed: 12/21/2023] Open
Abstract
Repeated hypoxic episodes can produce a sustained (>60 min) increase in neural drive to the diaphragm. The requirement of repeated hypoxic episodes (vs. a single episode) to produce phrenic motor facilitation (pMF) can be removed by allosteric modulation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors using ampakines. We hypothesized that the ampakine-hypoxia interaction resulting in pMF requires that ampakine dosing precedes the onset of hypoxia. Phrenic nerve recordings were made from urethane-anesthetized, mechanically ventilated, and vagotomized adult male Sprague-Dawley rats during isocapnic conditions. Ampakine CX717 (15 mg/kg iv) was given immediately before (n = 8), during (n = 8), or immediately after (n = 8) a 5-min hypoxic episode (arterial oxygen partial pressure 40-45 mmHg). Ampakine before hypoxia (Aprior) resulted in a sustained increase in inspiratory phrenic burst amplitude (i.e., pMF) reaching +70 ± 21% above baseline (BL) after 60 min. This was considerably greater than corresponding values in the groups receiving ampakine during hypoxia (+28 ± 47% above BL, P = 0.005 vs. Aprior) or after hypoxia (+23 ± 40% above BL, P = 0.005 vs. Aprior). Phrenic inspiratory burst rate, heart rate, and systolic, diastolic, and mean arterial pressure (mmHg) were similar across the three treatment groups (all P > 0.3, treatment effect). We conclude that the presentation order of ampakine and hypoxia impacts the magnitude of pMF, with ampakine pretreatment evoking the strongest response. Ampakine pretreatment may have value in the context of hypoxia-based neurorehabilitation strategies.NEW & NOTEWORTHY Phrenic motor facilitation (pMF) is evoked after repeated episodes of brief hypoxia. pMF can also be induced when an allosteric modulator of AMPA receptors (ampakine) is intravenously delivered immediately before a single brief hypoxic episode. Here we show that ampakine delivery before hypoxia (vs. during or after hypoxia) evokes the largest pMF with minimal impact on arterial blood pressure and heart rate. Ampakine pretreatment may have value in the context of hypoxia-based neurorehabilitation strategies.
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Affiliation(s)
- Prajwal P Thakre
- Department of Physical Therapy, University of Florida, Gainesville, Florida, United States
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
| | - David D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, Florida, United States
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
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4
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Ruyle BC, Lima-Silveira L, Martinez D, Cummings KJ, Heesch CM, Kline DD, Hasser EM. Paraventricular nucleus projections to the nucleus tractus solitarii are essential for full expression of hypoxia-induced peripheral chemoreflex responses. J Physiol 2023; 601:4309-4336. [PMID: 37632733 DOI: 10.1113/jp284907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Accepted: 07/13/2023] [Indexed: 08/28/2023] Open
Abstract
The hypothalamic paraventricular nucleus (PVN) is essential to peripheral chemoreflex neurocircuitry, but the specific efferent pathways utilized are not well defined. The PVN sends dense projections to the nucleus tractus solitarii (nTS), which exhibits neuronal activation following a hypoxic challenge. We hypothesized that nTS-projecting PVN (PVN-nTS) neurons contribute to hypoxia-induced nTS neuronal activation and cardiorespiratory responses. To selectively target PVN-nTS neurons, rats underwent bilateral nTS nanoinjection of retrogradely transported adeno-associated virus (AAV) driving Cre recombinase expression. We then nanoinjected into PVN AAVs driving Cre-dependent expression of Gq or Gi designer receptors exclusively activated by designer drugs (DREADDs) to test the degree that selective activation or inhibition, respectively, of the PVN-nTS pathway affects the hypoxic ventilatory response (HVR) of conscious rats. We used immunohistochemistry for Fos and extracellular recordings to examine how DREADD activation influences PVN-nTS neuronal activation by hypoxia. Pathway activation enhanced the HVR at moderate hypoxic intensities and increased PVN and nTS Fos immunoreactivity in normoxia and hypoxia. In contrast, PVN-nTS inhibition reduced both the HVR and PVN and nTS neuronal activation following hypoxia. To further confirm selective pathway effects on central cardiorespiratory output, rats underwent hypoxia before and after bilateral nTS nanoinjections of C21 to activate or inhibit PVN-nTS terminals. PVN terminal activation within the nTS enhanced tachycardic, sympathetic and phrenic (PhrNA) nerve activity responses to hypoxia whereas inhibition attenuated hypoxia-induced increases in nTS neuronal action potential discharge and PhrNA. The results demonstrate the PVN-nTS pathway enhances nTS neuronal activation and is necessary for full cardiorespiratory responses to hypoxia. KEY POINTS: The hypothalamic paraventricular nucleus (PVN) contributes to peripheral chemoreflex cardiorespiratory responses, but specific PVN efferent pathways are not known. The nucleus tractus solitarii (nTS) is the first integration site of the peripheral chemoreflex, and the nTS receives dense projections from the PVN. Selective GqDREADD activation of the PVN-nTS pathway was shown to enhance ventilatory responses to hypoxia and activation (Fos immunoreactivity (IR)) of nTS neurons in conscious rats, augmenting the sympathetic and phrenic nerve activity (SSNA and PhrNA) responses to hypoxia in anaesthetized rats. Selective GiDREADD inhibition of PVN-nTS neurons attenuates ventilatory responses, nTS neuronal Fos-IR, action potential discharge and PhrNA responses to hypoxia. These results demonstrate that a projection from the PVN to the nTS is critical for full chemoreflex responses to hypoxia.
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Affiliation(s)
- Brian C Ruyle
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
| | - Ludmila Lima-Silveira
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Diana Martinez
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Kevin J Cummings
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Cheryl M Heesch
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - David D Kline
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA
| | - Eileen M Hasser
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA
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Panza GS, Kissane DM, Puri S, Mateika JH. The hypoxic ventilatory response and hypoxic burden are predictors of the magnitude of ventilatory long-term facilitation in humans. J Physiol 2023; 601:4611-4623. [PMID: 37641466 PMCID: PMC11006398 DOI: 10.1113/jp285192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 08/16/2023] [Indexed: 08/31/2023] Open
Abstract
Mild intermittent hypoxia initiates progressive augmentation (PA) and ventilatory long-term facilitation (vLTF) in humans. The magnitude of these forms of plasticity might be influenced by anthropometric and physiological variables, as well as protocol elements. However, the impact of many of these variables on the magnitude of respiratory plasticity has not been established in humans. A meta-analysis was completed using anthropometric and physiological variables obtained from 124 participants that completed one of three intermittent hypoxia protocols. Simple correlations between the aggregate variables and the magnitude of PA and vLTF standardized to baseline was completed. Thereafter, the variables correlated to PA or vLTF were input into a multilinear regression equation. Baseline measures of the hypoxic ventilatory response was the sole predictor of PA (R = 0.370, P = 0.012). Similarly, this variable along with the hypoxic burden predicted the magnitude of vLTF (R = 0.546, P < 0.006 for both variables). In addition, the magnitude of PA was strongly correlated to vLTF (R = 0.617, P < 0.001). Anthropometric measures do not predict the magnitude of PA and vLTF in humans. Alternatively, the hypoxic ventilatory response was the sole predictor of PA, and in combination with the hypoxic burden, predicted the magnitude of vLTF. These influences should be considered in the design of mild intermittent hypoxia protocol studies in humans. Moreover, the strong correlation between PA and vLTF suggests that a common mechanistic pathway may have a role in the initiation of these forms of plasticity. KEY POINTS: Mild intermittent hypoxia initiates progressive augmentation (PA) and ventilatory long-term facilitation (vLTF) in humans. Many of the anthropometric and physiological variables that could impact the magnitude of these forms of plasticity are unknown. Anthropometric and physiological variables were measured from a total of 124 participants that completed one of three distinct intermittent hypoxia protocols. The variables correlated to PA or vLTF were input into a multilinear regression analysis. The hypoxic ventilatory response was the sole predictor of PA, while this variable in addition to the average hypoxic burden predicted the magnitude of vLTF. A strong correlation between PA and vLTF was also revealed. These influences should be considered in the design of mild intermittent hypoxia protocol studies in humans. Moreover, the strong correlation between PA and vLTF suggests that a common mechanistic pathway may have a role in the initiation of these forms of plasticity.
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Affiliation(s)
- Gino S Panza
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, USA
- Department of Health Care Sciences, Program of Occupational Therapy, Wayne State University, Detroit, MI, USA
| | - Dylan M Kissane
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, USA
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Shipra Puri
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, USA
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
| | - Jason H Mateika
- John D. Dingell Veterans Affairs Medical Center, Detroit, MI, USA
- Department of Physiology, Wayne State University School of Medicine, Detroit, MI, USA
- Department of Internal Medicine, Wayne State University School of Medicine, Detroit, MI, USA
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Marciante AB, Mitchell GS. Increased spinal adenosine impairs phrenic long-term facilitation in aging rats. J Appl Physiol (1985) 2023; 134:1537-1548. [PMID: 37167263 PMCID: PMC10281789 DOI: 10.1152/japplphysiol.00197.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 04/26/2023] [Accepted: 05/08/2023] [Indexed: 05/13/2023] Open
Abstract
Moderate acute intermittent hypoxia (mAIH) elicits a form of spinal, respiratory motor plasticity known as phrenic long-term facilitation (pLTF). In middle-aged male and geriatric female rats, mAIH-induced pLTF is attenuated through unknown mechanisms. In young adults, mAIH activates competing intracellular signaling cascades, initiated by serotonin 2 and adenosine 2A (A2A) receptors, respectively. Spinal A2A receptor inhibition enhances mAIH-induced pLTF, meaning, serotonin dominates, and adenosine constrains mAIH-induced plasticity in the daily rest phase. Thus, we hypothesized elevated basal adenosine levels in the ventral cervical spinal cord of aged rats shifts this balance, undermining mAIH-induced pLTF. A selective A2A receptor antagonist (MSX-3) or vehicle was delivered intrathecally at C4 in anesthetized young (3-6 mo) and aged (20-22 mo) Sprague-Dawley rats before mAIH (3,5-min episodes; arterial Po2 = 45-55 mmHg). In young males, spinal A2A receptor inhibition enhanced pLTF (119 ± 5%) vs. vehicle (55 ± 9%), consistent with prior reports. In old males, pLTF was reduced to 25 ± 11%, but A2A receptor inhibition increased pLTF to levels greater than in young males (186 ± 19%). Basal adenosine levels in ventral C3-C5 homogenates are elevated two- to threefold in old vs. young males. These findings advance our understanding of age as a biological variable in phrenic motor plasticity and will help guide translation of mAIH as a therapeutic modality to restore respiratory and nonrespiratory movements in older populations afflicted with clinical disorders that compromise movement.NEW & NOTEWORTHY Advanced age undermines respiratory motor plasticity, specifically phrenic long-term facilitation (pLTF) following moderate acute intermittent hypoxia (mAIH). We report that spinal adenosine increases in aged male rats, undermining mAIH-induced pLTF via adenosine 2A (A2A) receptor activation, an effect reversed by selective spinal adenosine 2A receptor inhibition. These findings advance our understanding of mechanisms that impair neuroplasticity, and the ability to compensate for the onset of lung or neural injury with age, and may guide efforts to harness mAIH as a treatment for clinical disorders that compromise breathing and other movements.
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Affiliation(s)
- Alexandria B Marciante
- Department of Physical Therapy & McKnight Brain Institute, Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
| | - Gordon S Mitchell
- Department of Physical Therapy & McKnight Brain Institute, Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
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7
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La Rosa G, Avola M, Di Gregorio T, Calabrò RS, Onesta MP. Gait Recovery in Spinal Cord Injury: A Systematic Review with Metanalysis Involving New Rehabilitative Technologies. Brain Sci 2023; 13:brainsci13050703. [PMID: 37239175 DOI: 10.3390/brainsci13050703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Revised: 04/13/2023] [Accepted: 04/19/2023] [Indexed: 05/28/2023] Open
Abstract
Gait recovery is a fundamental goal in patients with spinal cord injury to attain greater autonomy and quality of life. Robotics is becoming a valid tool in improving motor, balance, and gait function in this patient population. Moreover, other innovative approaches are leading to promising results. The aim of this study was to investigate new rehabilitative methods for gait recovery in people who have suffered spinal cord injuries. A systematic review of the last 10 years of the literature was performed in three databases (PubMed, PEDro, andCochrane). We followed this PICO of the review: P: adults with non-progressive spinal cord injury; I: new rehabilitative methods; C: new methods vs. conventional methods; and O: improvement of gait parameters. When feasible, a comparison through ES forest plots was performed. A total of 18 RCTs of the 599 results obtained were included. The studies investigated robotic rehabilitation (n = 10), intermittent hypoxia (N = 3) and external stimulation (N = 5). Six studies of the first group (robotic rehabilitation) were compared using a forest plot for 10MWT, LEMS, WISCI-II, and SCIM-3. The other clinical trials were analyzed through a narrative review of the results. We found weak evidence for the claim that robotic devices lead to better outcomes in gait independence compared to conventional rehabilitation methods. External stimulation and intermittent hypoxia seem to improve gait parameters associated with other rehabilitation methods. Research investigating the role of innovative technologies in improving gait and balance is needed since walking ability is a fundamental issue in patients with SCI.
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Affiliation(s)
| | - Marianna Avola
- Consorzio Siciliano di Riabilitazione, 95100 Catania, Italy
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Marciante AB, Mitchell GS. Mild inflammation impairs acute intermittent hypoxia-induced phrenic long-term facilitation by a spinal adenosine-dependent mechanism. J Neurophysiol 2023; 129:799-806. [PMID: 36883762 PMCID: PMC10069977 DOI: 10.1152/jn.00035.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 02/23/2023] [Accepted: 02/23/2023] [Indexed: 03/09/2023] Open
Abstract
Inflammation undermines neuroplasticity, including serotonin-dependent phrenic long-term facilitation (pLTF) following moderate acute intermittent hypoxia (mAIH: 3, 5-min episodes, arterial Po2: 40-50 mmHg; 5-min intervals). Mild inflammation elicited by a low dose of the TLR-4 receptor agonist, lipopolysaccharide (LPS; 100 µg/kg, ip), abolishes mAIH-induced pLTF by unknown mechanisms. In the central nervous system, neuroinflammation primes glia, triggering ATP release and extracellular adenosine accumulation. As spinal adenosine 2 A (A2A) receptor activation impairs mAIH-induced pLTF, we hypothesized that spinal adenosine accumulation and A2A receptor activation are necessary in the mechanism whereby LPS impairs pLTF. We report that 24 h after LPS injection in adult male Sprague Dawley rats: 1) adenosine levels increase in ventral spinal segments containing the phrenic motor nucleus (C3-C5; P = 0.010; n = 7/group) and 2) cervical spinal A2A receptor inhibition (MSX-3, 10 µM, 12 µL intrathecal) rescues mAIH-induced pLTF. In LPS vehicle-treated rats (saline, ip), MSX-3 enhanced pLTF versus controls (LPS: 110 ± 16% baseline; controls: 53 ± 6%; P = 0.002; n = 6/group). In LPS-treated rats, pLTF was abolished as expected (4 ± 6% baseline; n = 6), but intrathecal MSX-3 restored pLTF to levels equivalent to MSX-3-treated control rats (120 ± 14% baseline; P < 0.001; n = 6; vs. LPS controls with MSX-3: P = 0.539). Thus, inflammation abolishes mAIH-induced pLTF by a mechanism that requires increased spinal adenosine levels and A2A receptor activation. As repetitive mAIH is emerging as a treatment to improve breathing and nonrespiratory movements in people with spinal cord injury or ALS, A2A inhibition may offset undermining effects of neuroinflammation associated with these neuromuscular disorders.NEW & NOTEWORTHY Mild inflammation undermines motor plasticity elicited by mAIH. In a model of mAIH-induced respiratory motor plasticity (phrenic long-term facilitation; pLTF), we report that inflammation induced by low-dose lipopolysaccharide undermines mAIH-induced pLTF by a mechanism requiring increased cervical spinal adenosine and adenosine 2 A receptor activation. This finding advances the understanding of mechanisms impairing neuroplasticity, potentially undermining the ability to compensate for the onset of lung/neural injury or to harness mAIH as a therapeutic modality.
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Affiliation(s)
- Alexandria B Marciante
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
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Ostrowski D, Heesch CM, Kline DD, Hasser EM. Nucleus tractus solitarii is required for the development and maintenance of phrenic and sympathetic long-term facilitation after acute intermittent hypoxia. Front Physiol 2023; 14:1120341. [PMID: 36846346 PMCID: PMC9949380 DOI: 10.3389/fphys.2023.1120341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 01/26/2023] [Indexed: 02/11/2023] Open
Abstract
Exposure to acute intermittent hypoxia (AIH) induces prolonged increases (long term facilitation, LTF) in phrenic and sympathetic nerve activity (PhrNA, SNA) under basal conditions, and enhanced respiratory and sympathetic responses to hypoxia. The mechanisms and neurocircuitry involved are not fully defined. We tested the hypothesis that the nucleus tractus solitarii (nTS) is vital to augmentation of hypoxic responses and the initiation and maintenance of elevated phrenic (p) and splanchnic sympathetic (s) LTF following AIH. nTS neuronal activity was inhibited by nanoinjection of the GABAA receptor agonist muscimol before AIH exposure or after development of AIH-induced LTF. AIH but not sustained hypoxia induced pLTF and sLTF with maintained respiratory modulation of SSNA. nTS muscimol before AIH increased baseline SSNA with minor effects on PhrNA. nTS inhibition also markedly blunted hypoxic PhrNA and SSNA responses, and prevented altered sympathorespiratory coupling during hypoxia. Inhibiting nTS neuronal activity before AIH exposure also prevented the development of pLTF during AIH and the elevated SSNA after muscimol did not increase further during or following AIH exposure. Furthermore, nTS neuronal inhibition after the development of AIH-induced LTF substantially reversed but did not eliminate the facilitation of PhrNA. Together these findings demonstrate that mechanisms within the nTS are critical for initiation of pLTF during AIH. Moreover, ongoing nTS neuronal activity is required for full expression of sustained elevations in PhrNA following exposure to AIH although other regions likely also are important. Together, the data indicate that AIH-induced alterations within the nTS contribute to both the development and maintenance of pLTF.
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Affiliation(s)
- Daniela Ostrowski
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States,Department of Biology, Truman State University, Kirksville, MO, United States
| | - Cheryl M. Heesch
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States
| | - David D. Kline
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, United States
| | - Eileen M. Hasser
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, United States,*Correspondence: Eileen M. Hasser,
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10
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Initiating daily acute intermittent hypoxia (dAIH) therapy at 1-week after contusion spinal cord injury (SCI) improves lower urinary tract function in rat. Exp Neurol 2023; 359:114242. [PMID: 36240880 DOI: 10.1016/j.expneurol.2022.114242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2022] [Revised: 09/15/2022] [Accepted: 10/05/2022] [Indexed: 11/07/2022]
Abstract
Spinal cord injury (SCI) above the level of the lumbosacral spinal cord produces lower urinary tract (LUT) dysfunction, resulting in impairment of urine storage and elimination (voiding). While spontaneous functional recovery occurs due to remodeling of spinal reflex micturition pathways, it is incomplete, indicating that additional strategies to further augment neural plasticity following SCI are essential. To this end, acute intermittent hypoxia (AIH) exposure has been proposed as a therapeutic strategy for improving recovery of respiratory and other somatic motor function following SCI; however, the impact of AIH as a therapeutic intervention to improve LUT dysfunction remains to be determined. Therefore, we examined the effects of daily AIH (dAIH) on both spontaneous micturition patterns and reflex micturition event (rME) behaviors in adult female Sprague-Dawley rats with mid-thoracic moderate contusion SCI. For these experiments, dAIH gas exposures (five alternating 3 min 12% O2 and 21% O2 episodes) were delivered for 7 consecutive days beginning at 1-week after SCI, with awake micturition patterns being evaluated weekly for 2-3 sessions before and for 4 weeks after SCI and rME behaviors elicited by continuous infusion of saline into the bladder being evaluated under urethane anesthesia at 4-weeks after SCI; daily normoxia (dNx; 21% O2 episodes) served as a control. At 1-week post-SCI, both an areflexic phenotype (i.e., no effective voiding events) and a functional voiding phenotype (i.e., infrequent voiding events with large volumes) were observed in spontaneous micturition patterns (as expected), and subsequent dAIH, but not dNx, treatment led to recovery of spontaneous void frequency pattern to pre-SCI levels; both dAIH- and dNx-treated rats exhibited slightly increased void volumes. At 4-weeks post-SCI, rME behaviors showed increased effectiveness in voiding in dAIH-treated (compared to dNx-treated) rats that included an increase in both bladder contraction pressure (delta BP; P = 0.014) and dynamic voiding efficiency (P = 0.018). Based on the voiding and non-voiding bladder contraction behaviors (VC and NVC, respectively) observed in the BP records, bladder dysfunction severity was classified into mild, moderate, and severe phenotypes, and while rats in both treatment groups included each severity phenotype, the primary phenotype observed in dAIH-treated rats was mild and that in dNx-treated rats was moderate (P = 0.044). Taken together, these findings suggest that 7-day dAIH treatment produces beneficial improvements in LUT function that include recovery of micturition pattern, more efficient voiding, and decreased NVCs, and extend support to the use of dAIH therapy to treat SCI-induced LUT dysfunction.
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Thakre PP, Rana S, Benevides ES, Fuller DD. Targeting drug or gene delivery to the phrenic motoneuron pool. J Neurophysiol 2023; 129:144-158. [PMID: 36416447 PMCID: PMC9829468 DOI: 10.1152/jn.00432.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 11/19/2022] [Accepted: 11/19/2022] [Indexed: 11/24/2022] Open
Abstract
Phrenic motoneurons (PhrMNs) innervate diaphragm myofibers. Located in the ventral gray matter (lamina IX), PhrMNs form a column extending from approximately the third to sixth cervical spinal segment. Phrenic motor output and diaphragm activation are impaired in many neuromuscular diseases, and targeted delivery of drugs and/or genetic material to PhrMNs may have therapeutic application. Studies of phrenic motor control and/or neuroplasticity mechanisms also typically require targeting of PhrMNs with drugs, viral vectors, or tracers. The location of the phrenic motoneuron pool, however, poses a challenge. Selective PhrMN targeting is possible with molecules that move retrogradely upon uptake into phrenic axons subsequent to diaphragm or phrenic nerve delivery. However, nonspecific approaches that use intrathecal or intravenous delivery have considerably advanced the understanding of PhrMN control. New opportunities for targeted PhrMN gene expression may be possible with intersectional genetic methods. This article provides an overview of methods for targeting the phrenic motoneuron pool for studies of PhrMNs in health and disease.
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Affiliation(s)
- Prajwal P Thakre
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
- Breathing Research and Therapeutics Center, Gainesville, Florida
| | - Sabhya Rana
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
- Breathing Research and Therapeutics Center, Gainesville, Florida
| | - Ethan S Benevides
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
- Breathing Research and Therapeutics Center, Gainesville, Florida
| | - David D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
- Breathing Research and Therapeutics Center, Gainesville, Florida
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12
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Trumbower RD, Barth S, Tuthill C, Slocum C, Shan G, Zafonte R, Mitchell GS. Caffeine Enhances Intermittent Hypoxia-Induced Gains in Walking Function for People with Chronic Spinal Cord Injury. J Neurotrauma 2022; 39:1756-1763. [PMID: 35686460 PMCID: PMC9734018 DOI: 10.1089/neu.2022.0120] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Incomplete spinal cord injury (iSCI) often results in lifelong walking impairments that limit functional independence. Thus, treatments that trigger enduring improvement in walking after iSCI are in high demand. Breathing brief episodes of low oxygen (i.e., acute intermittent hypoxia, AIH) enhances breathing and walking function in rodents and humans with chronic iSCI. Pre-clinical studies found that AIH also causes the accumulation of extracellular adenosine that undermines AIH-induced functional plasticity. Pharmacologically blocking adenosine A2a receptors (A2aR) prior to AIH resulted in a dramatic improvement in motor facilitation in rodents with iSCI; however, a similar beneficial effect in humans is unclear. Thus, we conducted a double-blind, placebo-controlled, crossover randomized study to test the hypothesis that a non-selective A2aR antagonist (i.e., caffeine) enhances AIH-induced effects on walking function in people with chronic (≥1yr) iSCI. We enrolled 12 participants to receive daily (5 days) caffeine or placebo (4 mg/kg) 30 min before breathing 15, 1.5-min low oxygen (AIH; FIO2 = 0.10) or SHAM (FIO2 = 0.21) episodes with 1-min intervals. We quantified walking function as the change in the 10-meter walk test (speed) and 6-min walk test (endurance) relative to baseline, on Day 5 post-intervention, and on follow-up Days 12 and 19. Participants walked faster (Day 19; p < 0.001) and farther (Day 19; p = 0.012) after caffeine+AIH and the boost in speed persisted more than after placebo+AIH or caffeine+SHAM (Day 19; p < 0.05). These results support our hypothesis that a caffeine pre-treatment to AIH training shows promise as a strategy to augment walking speed in persons with chronic iSCI.
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Affiliation(s)
- Randy D. Trumbower
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA.,Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA.,Address correspondence to: Randy D. Trumbower, PT, PhD, Department of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation Hospital, 1575 Cambridge Street, Cambridge, MA 02138, USA
| | - Stella Barth
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
| | - Christopher Tuthill
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA
| | - Chloe Slocum
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
| | - Guogen Shan
- Department of Biostatistics, College of Medicine, University of Florida, Gainesville, Florida, USA
| | - Ross Zafonte
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA.,Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
| | - Gordon S. Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy, College of Medicine, University of Florida, Gainesville, Florida, USA
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13
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Locke KC, Randelman ML, Hoh DJ, Zholudeva LV, Lane MA. Respiratory plasticity following spinal cord injury: perspectives from mouse to man. Neural Regen Res 2022; 17:2141-2148. [PMID: 35259820 PMCID: PMC9083159 DOI: 10.4103/1673-5374.335839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Revised: 09/18/2021] [Accepted: 10/20/2021] [Indexed: 12/03/2022] Open
Abstract
The study of respiratory plasticity in animal models spans decades. At the bench, researchers use an array of techniques aimed at harnessing the power of plasticity within the central nervous system to restore respiration following spinal cord injury. This field of research is highly clinically relevant. People living with cervical spinal cord injury at or above the level of the phrenic motoneuron pool at spinal levels C3-C5 typically have significant impairments in breathing which may require assisted ventilation. Those who are ventilator dependent are at an increased risk of ventilator-associated co-morbidities and have a drastically reduced life expectancy. Pre-clinical research examining respiratory plasticity in animal models has laid the groundwork for clinical trials. Despite how widely researched this injury is in animal models, relatively few treatments have broken through the preclinical barrier. The three goals of this present review are to define plasticity as it pertains to respiratory function post-spinal cord injury, discuss plasticity models of spinal cord injury used in research, and explore the shift from preclinical to clinical research. By investigating current targets of respiratory plasticity research, we hope to illuminate preclinical work that can influence future clinical investigations and the advancement of treatments for spinal cord injury.
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Affiliation(s)
- Katherine C. Locke
- Department of Neurobiology & Anatomy, Drexel University, Philadelphia, PA, USA
- Marion Murray Spinal Cord Research Center, Philadelphia, PA, USA
| | - Margo L. Randelman
- Department of Neurobiology & Anatomy, Drexel University, Philadelphia, PA, USA
- Marion Murray Spinal Cord Research Center, Philadelphia, PA, USA
| | - Daniel J. Hoh
- Lillian S. Wells Department of Neurosurgery, University of Florida, Gainesville, FL, USA
| | - Lyandysha V. Zholudeva
- Marion Murray Spinal Cord Research Center, Philadelphia, PA, USA
- Cardiovascular Disease, Gladstone Institutes, San Francisco, CA, USA
| | - Michael A. Lane
- Department of Neurobiology & Anatomy, Drexel University, Philadelphia, PA, USA
- Marion Murray Spinal Cord Research Center, Philadelphia, PA, USA
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14
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Dean JB, Stavitzski NM. The O2-sensitive brain stem, hyperoxic hyperventilation, and CNS oxygen toxicity. Front Physiol 2022; 13:921470. [PMID: 35957982 PMCID: PMC9360621 DOI: 10.3389/fphys.2022.921470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 06/27/2022] [Indexed: 11/13/2022] Open
Abstract
Central nervous system oxygen toxicity (CNS-OT) is a complex disorder that presents, initially, as a sequence of cardio-respiratory abnormalities and nonconvulsive signs and symptoms (S/Sx) of brain stem origin that culminate in generalized seizures, loss of consciousness, and postictal cardiogenic pulmonary edema. The risk of CNS-OT and its antecedent “early toxic indications” are what limits the use of hyperbaric oxygen (HBO2) in hyperbaric and undersea medicine. The purpose of this review is to illustrate, based on animal research, how the temporal pattern of abnormal brain stem responses that precedes an “oxtox hit” provides researchers a window into the early neurological events underlying seizure genesis. Specifically, we focus on the phenomenon of hyperoxic hyperventilation, and the medullary neurons presumed to contribute in large part to this paradoxical respiratory response; neurons in the caudal Solitary complex (cSC) of the dorsomedial medulla, including putative CO2 chemoreceptor neurons. The electrophysiological and redox properties of O2-/CO2-sensitive cSC neurons identified in rat brain slice experiments are summarized. Additionally, evidence is summarized that supports the working hypothesis that seizure genesis originates in subcortical areas and involves cardio-respiratory centers and cranial nerve nuclei in the hind brain (brainstem and cerebellum) based on, respectively, the complex temporal pattern of abnormal cardio-respiratory responses and various nonconvulsive S/Sx that precede seizures during exposure to HBO2.
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15
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Effects of acute intermittent hypoxia on corticospinal excitability within the primary motor cortex. Eur J Appl Physiol 2022; 122:2111-2123. [PMID: 35752660 PMCID: PMC9381468 DOI: 10.1007/s00421-022-04982-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 06/01/2022] [Indexed: 11/29/2022]
Abstract
Purpose Acute intermittent hypoxia (AIH) is a safe and non-invasive treatment approach that uses brief, repetitive periods of breathing reduced oxygen air alternated with normoxia. While AIH is known to affect spinal circuit excitability, the effects of AIH on cortical excitability remain largely unknown. We investigated the effects of AIH on cortical excitability within the primary motor cortex. Methods Eleven healthy, right-handed participants completed two testing sessions: (1) AIH (comprising 3 min in hypoxia [fraction of inspired oxygen ~ 10%] and 2 min in normoxia repeated over five cycles) and (2) normoxia (NOR) (equivalent duration to AIH). Single- and paired-pulse transcranial magnetic stimulations were delivered to the primary motor cortex, before and 0, 25, and 50 min after AIH and normoxia. Results The mean nadir in arterial oxygen saturation was lower (p < 0.001) during the cycles of AIH (82.5 ± 4.9%) than NOR (97.8 ± 0.6%). There was no significant difference in corticospinal excitability, intracortical facilitation, or intracortical inhibition between AIH and normoxia conditions at any time point (all p > 0.05). There was no association between arterial oxygen saturation and changes in corticospinal excitability after AIH (r = 0.05, p = 0.87). Conclusion Overall, AIH did not modify either corticospinal excitability or excitability of intracortical facilitatory and inhibitory circuits within the primary motor cortex. Future research should explore whether a more severe or individualised AIH dose would induce consistent, measurable changes in corticospinal excitability. Supplementary Information The online version contains supplementary material available at 10.1007/s00421-022-04982-8.
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16
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Thakre PP, Sunshine MD, Fuller DD. Spinally delivered ampakine CX717 increases phrenic motor output in adult rats. Respir Physiol Neurobiol 2022; 296:103814. [PMID: 34775071 PMCID: PMC9235873 DOI: 10.1016/j.resp.2021.103814] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/01/2021] [Accepted: 11/07/2021] [Indexed: 02/03/2023]
Abstract
Ampakines are synthetic molecules that allosterically modulate AMPA-type glutamate receptors. We tested the hypothesis that delivery of ampakines to the intrathecal space could stimulate neural drive to the diaphragm. Ampakine CX717 (20 mM, dissolved in 10 % HPCD) or an HPCD vehicle solution were delivered via a catheter placed in the intrathecal space at the fourth cervical segment in urethane-anesthetized, mechanically ventilated adult male Sprague-Dawley rats. The electrical activity of the phrenic nerve was recorded for 60-minutes following drug application. Intrathecal application of CX717 produced a gradual and sustained increase in phrenic inspiratory burst amplitude (n = 10). In contrast, application of HPCD (n = 10) caused no sustained change in phrenic motor output. Phrenic burst rate, heart rate, and mean arterial pressure were similar between CX717 and HPCD treated rats. We conclude that intrathecally delivered ampakines can modulate phrenic motor output. This approach may have value for targeted induction of spinal neuroplasticity in the context of neurorehabiliation.
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Affiliation(s)
- Prajwal P. Thakre
- Department of Physical Therapy, University of Florida, Gainesville, FL,Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL,McKnight Brain Institute, University of Florida, Gainesville, FL
| | - Michael D. Sunshine
- Department of Physical Therapy, University of Florida, Gainesville, FL,Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL,McKnight Brain Institute, University of Florida, Gainesville, FL
| | - David D. Fuller
- Department of Physical Therapy, University of Florida, Gainesville, FL,Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL,McKnight Brain Institute, University of Florida, Gainesville, FL,Corresponding author: David D. Fuller, Department of Physical Therapy, University of Florida, 1149 Newell Drive, Gainesville, FL 32611
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17
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Daily acute intermittent hypoxia enhances serotonergic innervation of hypoglossal motor nuclei in rats with and without cervical spinal injury. Exp Neurol 2022; 347:113903. [PMID: 34699788 PMCID: PMC8848979 DOI: 10.1016/j.expneurol.2021.113903] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2021] [Revised: 10/17/2021] [Accepted: 10/20/2021] [Indexed: 01/03/2023]
Abstract
Intermittent hypoxia elicits protocol-dependent effects on hypoglossal (XII) motor plasticity. Whereas low-dose, acute intermittent hypoxia (AIH) elicits serotonin-dependent plasticity in XII motor neurons, high-dose, chronic intermittent hypoxia (CIH) elicits neuroinflammation that undermines AIH-induced plasticity. Preconditioning with repeated AIH and mild CIH enhance AIH-induced XII motor plasticity. Since intermittent hypoxia pre-conditioning could enhance serotonin-dependent XII motor plasticity by increasing serotonergic innervation density of the XII motor nuclei, we tested the hypothesis that 3 distinct intermittent hypoxia protocols commonly studied to elicit plasticity (AIH) or simulate aspects of sleep apnea (CIH) differentially affect XII serotonergic innervation. Sleep apnea and associated CIH are common in people with cervical spinal injuries and, since repetitive AIH is emerging as a promising therapeutic strategy to improve respiratory and non-respiratory motor function after spinal injury, we also tested the hypotheses that XII serotonergic innervation is increased by repetitive AIH and/or CIH in rats with cervical C2 hemisections (C2Hx). Serotonergic innervation was assessed via immunofluorescence in male Sprague Dawley rats, with and without C2Hx (beginning 8 weeks post-injury) exposed to 28 days of: 1) normoxia; 2) daily AIH (10, 5-min 10.5% O2 episodes per day; 5-min normoxic intervals); 3) mild CIH (5-min 10.5% O2 episodes; 5-min intervals; 8 h/day); and 4) moderate CIH (2-min 10.5% O2 episodes; 2-min intervals; 8 h/day). Daily AIH, but neither CIH protocol, increased the area of serotonergic immunolabeling in the XII motor nuclei in both intact and injured rats. C2Hx per se had no effect on XII serotonergic innervation density. Thus, daily AIH may increases XII serotonergic innervation and function, enhancing the capacity for serotonin-dependent, AIH-induced plasticity in upper airway motor neurons. Such effects may preserve upper airway patency and/or swallowing ability in people with cervical spinal cord injuries and other clinical disorders that compromise breathing and airway defense.
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18
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Vose AK, Welch JF, Nair J, Dale EA, Fox EJ, Muir GD, Trumbower RD, Mitchell GS. Therapeutic acute intermittent hypoxia: A translational roadmap for spinal cord injury and neuromuscular disease. Exp Neurol 2022; 347:113891. [PMID: 34637802 PMCID: PMC8820239 DOI: 10.1016/j.expneurol.2021.113891] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 09/29/2021] [Accepted: 10/03/2021] [Indexed: 01/03/2023]
Abstract
We review progress towards greater mechanistic understanding and clinical translation of a strategy to improve respiratory and non-respiratory motor function in people with neuromuscular disorders, therapeutic acute intermittent hypoxia (tAIH). In 2016 and 2020, workshops to create and update a "road map to clinical translation" were held to help guide future research and development of tAIH to restore movement in people living with chronic, incomplete spinal cord injuries. After briefly discussing the pioneering, non-targeted basic research inspiring this novel therapeutic approach, we then summarize workshop recommendations, emphasizing critical knowledge gaps, priorities for future research effort, and steps needed to accelerate progress as we evaluate the potential of tAIH for routine clinical use. Highlighted areas include: 1) greater mechanistic understanding, particularly in non-respiratory motor systems; 2) optimization of tAIH protocols to maximize benefits; 3) identification of combinatorial treatments that amplify plasticity or remove plasticity constraints, including task-specific training; 4) identification of biomarkers for individuals most/least likely to benefit from tAIH; 5) assessment of long-term tAIH safety; and 6) development of a simple, safe and effective device to administer tAIH in clinical and home settings. Finally, we update ongoing clinical trials and recent investigations of tAIH in SCI and other clinical disorders that compromise motor function, including ALS, multiple sclerosis, and stroke.
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Affiliation(s)
- Alicia K Vose
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA; Brooks Rehabilitation, Jacksonville, FL 32216, USA
| | - Joseph F Welch
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA; Brooks Rehabilitation, Jacksonville, FL 32216, USA
| | - Jayakrishnan Nair
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
| | - Erica A Dale
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, FL 32610, USA
| | - Emily J Fox
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA; Brooks Rehabilitation, Jacksonville, FL 32216, USA
| | - Gillian D Muir
- Department of Biomedical Sciences, WCVM, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada
| | - Randy D Trumbower
- Spaulding Rehabilitation Hospital, Harvard Medical School, Boston, MA, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA.
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19
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Randelman M, Zholudeva LV, Vinit S, Lane MA. Respiratory Training and Plasticity After Cervical Spinal Cord Injury. Front Cell Neurosci 2021; 15:700821. [PMID: 34621156 PMCID: PMC8490715 DOI: 10.3389/fncel.2021.700821] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 08/11/2021] [Indexed: 12/30/2022] Open
Abstract
While spinal cord injuries (SCIs) result in a vast array of functional deficits, many of which are life threatening, the majority of SCIs are anatomically incomplete. Spared neural pathways contribute to functional and anatomical neuroplasticity that can occur spontaneously, or can be harnessed using rehabilitative, electrophysiological, or pharmacological strategies. With a focus on respiratory networks that are affected by cervical level SCI, the present review summarizes how non-invasive respiratory treatments can be used to harness this neuroplastic potential and enhance long-term recovery. Specific attention is given to "respiratory training" strategies currently used clinically (e.g., strength training) and those being developed through pre-clinical and early clinical testing [e.g., intermittent chemical stimulation via altering inhaled oxygen (hypoxia) or carbon dioxide stimulation]. Consideration is also given to the effect of training on non-respiratory (e.g., locomotor) networks. This review highlights advances in this area of pre-clinical and translational research, with insight into future directions for enhancing plasticity and improving functional outcomes after SCI.
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Affiliation(s)
- Margo Randelman
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States.,Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Lyandysha V Zholudeva
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States.,Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States.,Gladstone Institutes, San Francisco, CA, United States
| | - Stéphane Vinit
- INSERM, END-ICAP, Université Paris-Saclay, UVSQ, Versailles, France
| | - Michael A Lane
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States.,Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States
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20
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Thakre PP, Sunshine MD, Fuller DD. Ampakine pretreatment enables a single hypoxic episode to produce phrenic motor facilitation with no added benefit of additional episodes. J Neurophysiol 2021; 126:1420-1429. [PMID: 34495779 DOI: 10.1152/jn.00307.2021] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Repeated short episodes of hypoxia produce a sustained increase in phrenic nerve output lasting well beyond acute intermittent hypoxia (AIH) exposure (i.e., phrenic long-term facilitation; pLTF). Pretreatment with ampakines, drugs which allosterically modulate AMPA receptors, enables a single brief episode of hypoxia to produce pLTF, lasting up to 90 min after hypoxia. Here, we tested the hypothesis that ampakine pretreatment would enhance the magnitude of pLTF evoked by repeated bouts of hypoxia. Phrenic nerve output was recorded in urethane-anesthetized, mechanically ventilated, and vagotomized adult male Sprague-Dawley rats. Initial experiments demonstrated that ampakine CX717 (15 mg/kg iv) caused an acute increase in phrenic nerve inspiratory burst amplitude reaching 70 ± 48% baseline (BL) after 2 min (P = 0.01). This increased bursting was not sustained (2 ± 32% BL at 60 min, P = 0.9). When CX717 was delivered 2 min before a single episode of isocapnic hypoxia (5 min, [Formula: see text] = 44 ± 9 mmHg), facilitation of phrenic nerve burst amplitude occurred (96 ± 62% BL at 60 min, P < 0.001). However, when CX717 was given 2 min before three, 5-min hypoxic episodes ([Formula: see text] = 45 ± 6 mmHg) pLTF was attenuated and did not reach statistical significance (24 ± 29% BL, P = 0.08). In the absence of CX717 pretreatment, pLTF was observed after three (74 ± 33% BL at 60 min, P < 0.001) but not one episode of hypoxia (1 ± 8% BL at 60 min, P = 0.9). We conclude that pLTF is not enhanced when ampakine pretreatment is followed by repeated bouts of hypoxia. Rather, the combination of ampakine and a single hypoxic episode appears to be ideal for producing sustained increase in phrenic motor output.NEW & NOTEWORTHY Pretreatment with ampakine CX717 created conditions that enabled an acute bout of moderate hypoxia to evoke phrenic motor facilitation, but this response was not observed when ampakine pretreatment was followed by intermittent hypoxia. Thus, in anesthetized and spinal intact rats, the combination of ampakine and one bout of hypoxia appears ideal for triggering respiratory neuroplasticity.
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Affiliation(s)
- Prajwal P Thakre
- Department of Physical Therapy, University of Florida, Gainesville, Florida.,Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Michael D Sunshine
- Department of Physical Therapy, University of Florida, Gainesville, Florida.,Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - David D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, Florida.,Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
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21
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Hatano K, Matsuura R, Ohtsuka Y, Yunoki T. Enhancement of self-sustained muscle activity through external dead space ventilation appears to be associated with hypercapnia. Respir Physiol Neurobiol 2021; 295:103777. [PMID: 34425262 DOI: 10.1016/j.resp.2021.103777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 07/24/2021] [Accepted: 08/19/2021] [Indexed: 11/19/2022]
Abstract
We reported that external dead space ventilation (EDSV) enhanced self-sustained muscle activity (SSMA) of the human soleus muscle, which is an indirect observation of plateau potentials. However, the main factor for EDSV to enhance SSMA remains unclear. The purpose of the present study was to examine the effects of EDSV-induced hypercapnia, hypoxia, and hyperventilation on SSMA. In Experiment 1 (n = 11; normal breathing [NB], EDSV, hypoxia, and voluntary hyperventilation conditions) and Experiment 2 (n = 9; NB and normoxic hypercapnia [NH] conditions), SSMA was evoked by electrical train stimulations of the right tibial nerve and measured using surface electromyography under each respiratory condition. In Experiment 1, SSMA was significantly higher than that in the NB condition only in the EDSV condition (P < 0.05). In Experiment 2, SSMA was higher in the NH condition than in the NB condition (P < 0.05). These results suggest that the EDSV-enhanced SSMA is due to hypercapnia, not hypoxia or increased ventilation.
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Affiliation(s)
- Kei Hatano
- Graduate School of Education, Hokkaido University, Sapporo, Japan.
| | - Ryouta Matsuura
- Graduate School of Education, Joetsu University of Education, Japan
| | - Yoshinori Ohtsuka
- Department of Sports and Human Studies, Sapporo International University, Japan
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22
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How Are Adenosine and Adenosine A 2A Receptors Involved in the Pathophysiology of Amyotrophic Lateral Sclerosis? Biomedicines 2021; 9:biomedicines9081027. [PMID: 34440231 PMCID: PMC8392384 DOI: 10.3390/biomedicines9081027] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 08/03/2021] [Accepted: 08/12/2021] [Indexed: 12/19/2022] Open
Abstract
Adenosine is extensively distributed in the central and peripheral nervous systems, where it plays a key role as a neuromodulator. It has long been implicated in the pathogenesis of progressive neurogenerative disorders such as Parkinson’s disease, and there is now growing interest in its role in amyotrophic lateral sclerosis (ALS). The motor neurons affected in ALS are responsive to adenosine receptor function, and there is accumulating evidence for beneficial effects of adenosine A2A receptor antagonism. In this article, we focus on recent evidence from ALS clinical pathology and animal models that support dynamism of the adenosinergic system (including changes in adenosine levels and receptor changes) in ALS. We review the possible mechanisms of chronic neurodegeneration via the adenosinergic system, potential biomarkers and the acute symptomatic pharmacology, including respiratory motor neuron control, of A2A receptor antagonism to explore the potential of the A2A receptor as target for ALS therapy.
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23
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Barok R, Grittner JML, Dougherty BJ. The long-term impact of ovariectomy on ventilation and expression of phrenic long-term facilitation in female rats. Exp Physiol 2021; 106:2002-2012. [PMID: 34180081 PMCID: PMC8410681 DOI: 10.1113/ep089546] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 06/18/2021] [Indexed: 01/04/2023]
Abstract
NEW FINDINGS What is the central question of this study? Would ovariectomy cause prolonged changes in ventilation and sustained loss of acute, intermittent hypoxia-induced neuroplasticity or would these outcomes be restored with time? What is the main finding and its importance? Our main findings demonstrate that ovariectomy elicits minimal alteration in overall breathing function but impairs acute, intermittent hypoxia-induced plasticity for ≤ 12 weeks. ABSTRACT Sex hormones are necessary to enable respiratory neuroplasticity, including phrenic long-term facilitation (pLTF), a form of respiratory motor plasticity elicited by acute, intermittent hypoxia (AIH). Female rats exhibit a progressive increase in phrenic nerve amplitude after AIH characteristic of pLTF only during pro-oestrus, the stage of the oestrous cycle notable for elevated circulating oestradiol levels. Removal of the ovaries [ovariectomy (OVX)], the primary source of circulating oestradiol, also eliminates AIH-induced pLTF after 1 week. Ovariectomy is used routinely as a model to examine the impact of sex hormones on CNS structure and function, but the long-term impact of OVX is rarely examined. Extra-ovarian sites of oestradiol synthesis, including multiple CNS sites, have been identified and might possess the capacity to restore oestradiol levels, in part, over time, impacting respiratory function and the expression of respiratory neuroplasticity. We examined both ventilation in awake, freely behaving female rats, using barometric plethysmography, and the expression of AIH-induced pLTF in anaesthetized, ventilated female rats 2 and 12 weeks after OVX and compared them with age-matched ovarian-intact female rats. Our findings indicate that chronic OVX had little impact on baseline breathing or in the response to respiratory challenge (10% O2 , 5% CO2 , balance N2 ) during plethysmography. However, OVX rats at both 2 and 12 weeks demonstrated a persistent loss of AIH-induced pLTF relative to control animals (P < 0.01), suggesting that other sources of oestradiol synthesis were insufficient to restore pLTF. These data are consistent with our previous work indicating that oestradiol plays a key role in expression of AIH-induced respiratory neuroplasticity.
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Affiliation(s)
- Rebecca Barok
- Rehabilitation Science Graduate Program, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Jessica M L Grittner
- Rehabilitation Science Graduate Program, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Brendan J Dougherty
- Divisions of Physical Therapy and Rehabilitation Science, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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Malone IG, Nosacka RL, Nash MA, Otto KJ, Dale EA. Electrical epidural stimulation of the cervical spinal cord: implications for spinal respiratory neuroplasticity after spinal cord injury. J Neurophysiol 2021; 126:607-626. [PMID: 34232771 DOI: 10.1152/jn.00625.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Traumatic cervical spinal cord injury (cSCI) can lead to damage of bulbospinal pathways to the respiratory motor nuclei and consequent life-threatening respiratory insufficiency due to respiratory muscle paralysis/paresis. Reports of electrical epidural stimulation (EES) of the lumbosacral spinal cord to enable locomotor function after SCI are encouraging, with some evidence of facilitating neural plasticity. Here, we detail the development and success of EES in recovering locomotor function, with consideration of stimulation parameters and safety measures to develop effective EES protocols. EES is just beginning to be applied in other motor, sensory, and autonomic systems; however, there has only been moderate success in preclinical studies aimed at improving breathing function after cSCI. Thus, we explore the rationale for applying EES to the cervical spinal cord, targeting the phrenic motor nucleus for the restoration of breathing. We also suggest cellular/molecular mechanisms by which EES may induce respiratory plasticity, including a brief examination of sex-related differences in these mechanisms. Finally, we suggest that more attention be paid to the effects of specific electrical parameters that have been used in the development of EES protocols and how that can impact the safety and efficacy for those receiving this therapy. Ultimately, we aim to inform readers about the potential benefits of EES in the phrenic motor system and encourage future studies in this area.
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Affiliation(s)
- Ian G Malone
- Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida.,Breathing Research and Therapeutics Center (BREATHE), University of Florida, Gainesville, Florida
| | - Rachel L Nosacka
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida
| | - Marissa A Nash
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida
| | - Kevin J Otto
- Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida.,Breathing Research and Therapeutics Center (BREATHE), University of Florida, Gainesville, Florida.,J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, Florida.,Department of Neuroscience, University of Florida, Gainesville, Florida.,Department of Neurology, University of Florida, Gainesville, Florida.,Department of Materials Science and Engineering, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Erica A Dale
- Breathing Research and Therapeutics Center (BREATHE), University of Florida, Gainesville, Florida.,Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida.,Department of Neuroscience, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
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Tadjalli A, Seven YB, Sharma A, McCurdy CR, Bolser DC, Levitt ES, Mitchell GS. Acute morphine blocks spinal respiratory motor plasticity via long-latency mechanisms that require toll-like receptor 4 signalling. J Physiol 2021; 599:3771-3797. [PMID: 34142718 DOI: 10.1113/jp281362] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2021] [Accepted: 06/15/2021] [Indexed: 12/22/2022] Open
Abstract
KEY POINTS While respiratory complications following opioid use are mainly mediated via activation of mu opioid receptors, long-latency off-target signalling via innate immune toll-like receptor 4 (TLR4) may impair other essential elements of breathing control such as respiratory motor plasticity. In adult rats, pre-treatment with a single dose of morphine blocked long-term facilitation (LTF) of phrenic motor output via a long-latency TLR4-dependent mechanism. In the phrenic motor nucleus, morphine triggered TLR4-dependent activation of microglial p38 MAPK - a key enzyme that orchestrates inflammatory signalling and is known to undermine phrenic LTF. Morphine-induced LTF loss may destabilize breathing, potentially contributing to respiratory side effects. Therefore, we suggest minimizing TLR-4 signalling may improve breathing stability during opioid therapy. ABSTRACT Opioid-induced respiratory dysfunction is a significant public health burden. While respiratory effects are mediated via mu opioid receptors, long-latency off-target opioid signalling through innate immune toll-like receptor 4 (TLR4) may modulate essential elements of breathing control, particularly respiratory motor plasticity. Plasticity in respiratory motor circuits contributes to the preservation of breathing in the face of destabilizing influences. For example, respiratory long-term facilitation (LTF), a well-studied model of respiratory motor plasticity triggered by acute intermittent hypoxia, promotes breathing stability by increasing respiratory motor drive to breathing muscles. Some forms of respiratory LTF are exquisitely sensitive to inflammation and are abolished by even a mild inflammation triggered by TLR4 activation (e.g. via systemic lipopolysaccharides). Since opioids induce inflammation and TLR4 activation, we hypothesized that opioids would abolish LTF through a TLR4-dependent mechanism. In adult Sprague Dawley rats, pre-treatment with a single systemic injection of the prototypical opioid agonist morphine blocks LTF expression several hours later in the phrenic motor system - the motor pool driving diaphragm muscle contractions. Morphine blocked phrenic LTF via TLR4-dependent mechanisms because pre-treatment with (+)-naloxone - the opioid inactive stereoisomer and novel small molecule TLR4 inhibitor - prevented impairment of phrenic LTF in morphine-treated rats. Morphine triggered TLR4-dependent activation of microglial p38 MAPK within the phrenic motor system - a key enzyme that orchestrates inflammatory signalling and undermines phrenic LTF. Morphine-induced LTF loss may destabilize breathing, potentially contributing to respiratory side effects. We suggest minimizing TLR-4 signalling may improve breathing stability during opioid therapy by restoring endogenous mechanisms of plasticity within respiratory motor circuits.
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Affiliation(s)
- Arash Tadjalli
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, USA.,Department of Physical Therapy, University of Florida, Gainesville, FL, USA
| | - Yasin B Seven
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, USA.,Department of Physical Therapy, University of Florida, Gainesville, FL, USA
| | - Abhisheak Sharma
- Department of Pharmaceutics, University of Florida, Gainesville, FL, USA
| | | | - Donald C Bolser
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, USA.,Department of Physiological Sciences, University of Florida, Gainesville, FL, USA
| | - Erica S Levitt
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, USA.,Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, USA.,Department of Physical Therapy, University of Florida, Gainesville, FL, USA
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Novel Influences of Sex and APOE Genotype on Spinal Plasticity and Recovery of Function after Spinal Cord Injury. eNeuro 2021; 8:ENEURO.0464-20.2021. [PMID: 33536234 PMCID: PMC7986541 DOI: 10.1523/eneuro.0464-20.2021] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 12/30/2020] [Accepted: 01/22/2021] [Indexed: 12/16/2022] Open
Abstract
Spinal cord injuries can abolish both motor and sensory function throughout the body. Spontaneous recovery after injury is limited and can vary substantially between individuals. Despite an abundance of therapeutic approaches that have shown promise in preclinical models, there is currently a lack of effective treatment strategies that have been translated to restore function after spinal cord injury (SCI) in the human population. We hypothesized that sex and genetic background of injured individuals could impact how they respond to treatment strategies, presenting a barrier to translating therapies that are not tailored to the individual. One gene of particular interest is APOE, which has been extensively studied in the brain because of its allele-specific influences on synaptic plasticity, metabolism, inflammation, and neurodegeneration. Despite its prominence as a therapeutic target in brain injury and disease, little is known about how it influences neural plasticity and repair processes in the spinal cord. Using humanized mice, we examined how the ε3 and ε4 alleles of APOE influence the efficacy of therapeutic intermittent hypoxia (IH) in inducing spinally-mediated plasticity after cervical SCI (cSCI). IH is sufficient to enhance plasticity and restore motor function after experimental SCI in genetically similar rodent populations, but its effect in human subjects is more variable (Golder and Mitchell, 2005; Hayes et al., 2014). Our results demonstrate that both sex and APOE genotype determine the extent of respiratory motor plasticity that is elicited by IH, highlighting the importance of considering these clinically relevant variables when translating therapeutic approaches for the SCI community.
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Nadeau JR, Arnold BM, Johnston JM, Muir GD, Verge VMK. Acute intermittent hypoxia enhances regeneration of surgically repaired peripheral nerves in a manner akin to electrical stimulation. Exp Neurol 2021; 341:113671. [PMID: 33684407 DOI: 10.1016/j.expneurol.2021.113671] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2020] [Revised: 02/16/2021] [Accepted: 02/25/2021] [Indexed: 12/12/2022]
Abstract
The intrinsic repair response of injured peripheral neurons is enhanced by brief electrical stimulation (ES) at time of surgical repair, resulting in improved regeneration in rodents and humans. However, ES is invasive. Acute intermittent hypoxia (AIH) - breathing alternate cycles of regular air and air with ~50% normal oxygen levels (11% O2), considered mild hypoxia, is an emerging, promising non-invasive therapy that promotes motor function in spinal cord injured rats and humans. AIH can increase neural activity and under moderately severe hypoxic conditions improves repair of peripherally crushed nerves in mice. Thus, we posited an AIH paradigm similar to that used clinically for spinal cord injury, will improve surgically repaired peripheral nerves akin to ES, including an impact on regeneration-associated gene (RAG) expression-a predictor of growth states. Alterations in early RAG expression were examined in adult male Lewis rats that underwent tibial nerve coaptation repair with either 2 days AIH or normoxia control treatment begun on day 2 post-repair, or 1 h ES treatment (20 Hz) at time of repair. Three days post-repair, AIH or ES treatments effected significant and parallel elevated RAG expression relative to normoxia control at the level of injured sensory and motor neuron cell bodies and proximal axon front. These parallel impacts on RAG expression were coupled with significant improvements in later indices of regeneration, namely enhanced myelination and increased numbers of newly myelinated fibers detected 20 mm distal to the tibial nerve repair site or sensory and motor neurons retrogradely labeled 28 mm distal to the repair site, both at 25 days post nerve repair; and improved return of toe spread function 5-10 weeks post-repair. Collectively, AIH mirrors many beneficial effects of ES on peripheral nerve repair outcomes. This highlights its potential for clinical translation as a non-invasive means to effect improved regeneration of injured peripheral nerves.
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Affiliation(s)
- J R Nadeau
- Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK S7N 5E5, Canada; Biomedical Sciences, WCVM, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK S7N 5B4, Canada; Cameco MS Neuroscience Research Centre, University of Saskatchewan, Saskatoon, SK S7K 0M7, Canada
| | - B M Arnold
- Biomedical Sciences, WCVM, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK S7N 5B4, Canada; Cameco MS Neuroscience Research Centre, University of Saskatchewan, Saskatoon, SK S7K 0M7, Canada
| | - J M Johnston
- Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK S7N 5E5, Canada; Cameco MS Neuroscience Research Centre, University of Saskatchewan, Saskatoon, SK S7K 0M7, Canada
| | - G D Muir
- Biomedical Sciences, WCVM, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK S7N 5B4, Canada; Cameco MS Neuroscience Research Centre, University of Saskatchewan, Saskatoon, SK S7K 0M7, Canada
| | - V M K Verge
- Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK S7N 5E5, Canada; Cameco MS Neuroscience Research Centre, University of Saskatchewan, Saskatoon, SK S7K 0M7, Canada.
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Perim RR, El-Chami M, Gonzalez-Rothi EJ, Mitchell GS. Baseline Arterial CO 2 Pressure Regulates Acute Intermittent Hypoxia-Induced Phrenic Long-Term Facilitation in Rats. Front Physiol 2021; 12:573385. [PMID: 33716760 PMCID: PMC7943620 DOI: 10.3389/fphys.2021.573385] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 02/02/2021] [Indexed: 01/25/2023] Open
Abstract
Moderate acute intermittent hypoxia (mAIH) elicits a progressive increase in phrenic motor output lasting hours post-mAIH, a form of respiratory motor plasticity known as phrenic long-term facilitation (pLTF). mAIH-induced pLTF is initiated by activation of spinally-projecting raphe serotonergic neurons during hypoxia and subsequent serotonin release near phrenic motor neurons. Since raphe serotonergic neurons are also sensitive to pH and CO2, the prevailing arterial CO2 pressure (PaCO2) may modulate their activity (and serotonin release) during hypoxic episodes. Thus, we hypothesized that changes in background PaCO2 directly influence the magnitude of mAIH-induced pLTF. mAIH-induced pLTF was evaluated in anesthetized, vagotomized, paralyzed and ventilated rats, with end-tidal CO2 (i.e., a PaCO2 surrogate) maintained at: (1) ≤39 mmHg (hypocapnia); (2) ∼41 mmHg (normocapnia); or (3) ≥48 mmHg (hypercapnia) throughout experimental protocols. Although baseline phrenic nerve activity tended to be lower in hypocapnia, short-term hypoxic phrenic response, i.e., burst amplitude (Δ = 5.1 ± 1.1 μV) and frequency responses (Δ = 21 ± 4 bpm), was greater than in normocapnic (Δ = 3.6 ± 0.6 μV and 8 ± 4, respectively) or hypercapnic rats (Δ = 2.0 ± 0.6 μV and −2 ± 2, respectively), followed by a progressive increase in phrenic burst amplitude (i.e., pLTF) for at least 60 min post mAIH. pLTF in the hypocapnic group (Δ = 4.9 ± 0.6 μV) was significantly greater than in normocapnic (Δ = 2.8 ± 0.7 μV) or hypercapnic rats (Δ = 1.7 ± 0.4 μV). In contrast, although hypercapnic rats also exhibited significant pLTF, it was attenuated versus hypocapnic rats. When pLTF was expressed as percent change from maximal chemoreflex stimulation, all pairwise comparisons were found to be statistically significant (p < 0.05). We conclude that elevated PaCO2 undermines mAIH-induced pLTF in anesthetized rats. These findings contrast with well-documented effects of PaCO2 on ventilatory LTF in awake humans.
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Affiliation(s)
- Raphael R Perim
- Department of Physical Therapy, McKnight Brain Institute, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, United States
| | - Mohamed El-Chami
- Department of Physical Therapy, McKnight Brain Institute, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, United States
| | - Elisa J Gonzalez-Rothi
- Department of Physical Therapy, McKnight Brain Institute, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, United States
| | - Gordon S Mitchell
- Department of Physical Therapy, McKnight Brain Institute, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, United States
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Nichols NL, Mitchell GS. Mechanisms of severe acute intermittent hypoxia-induced phrenic long-term facilitation. J Neurophysiol 2021; 125:1146-1156. [PMID: 33566744 DOI: 10.1152/jn.00691.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Moderate acute intermittent hypoxia (mAIH; 35-55 mmHg PaO2) elicits phrenic long-term facilitation (pLTF) by a mechanism that requires activation of Gq protein-coupled serotonin type 2 receptors, MEK/ERK MAP kinase, and NADPH oxidase activity and is constrained by cAMP-PKA signaling. In contrast, severe AIH (sAIH; 25-35 mmHg PaO2) elicits Gs protein-coupled adenosine type 2 A receptor-dependent pLTF. Another Gs protein-coupled receptor, serotonin 7 receptors, elicits phrenic motor facilitation (pMF) by a mechanism that requires exchange protein activated by cyclic AMP (EPAC) and phosphatidylinositol 3-kinase/Akt (PI3K/Akt) activation and is constrained by NADPH oxidase activity. Here, we tested the hypothesis that the same downstream signaling mechanisms giving rise to serotonin 7 (vs. serotonin 2) receptor-induced pMF underlie sAIH-induced pLTF. In anesthetized rats, sAIH-induced pLTF was compared after pretreatment with intrathecal (C4) injections of inhibitors for: 1) EPAC (ESI-05); 2) MEK/ERK (UO126); 3) PKA (KT-5720); 4) PI3K/Akt (PI828); and 5) NADPH oxidase (apocynin). In partial agreement with our hypothesis, sAIH-induced pLTF was abolished by ESI-05 and PI828 and marginally enhanced by apocynin but, surprisingly, was abolished by UO126 and attenuated by KT-5720. Mechanisms of sAIH-induced pLTF reflect elements of both Gq and Gs pathways to pMF, likely as a consequence of the complex, cross-talk interactions between them.NEW & NOTEWORTHY Distinct mechanisms give rise to pLTF induced by moderate and severe AIH. We demonstrate that, unlike moderate AIH, severe AIH-induced pLTF requires EPAC and PI3K/Akt and is marginally constrained by NADPH oxidase activity. Surprisingly, sAIH-induced pLTF requires MEK/ERK activity similar to moderate AIH-induced pLTF and is reduced by PKA inhibition. We suggest sAIH-induced pLTF arises from complex interactions between dominant mechanisms characteristic of moderate versus severe AIH-induced pLTF.
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Affiliation(s)
- Nicole L Nichols
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
| | - Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
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Tadjalli A, Seven YB, Perim RR, Mitchell GS. Systemic inflammation suppresses spinal respiratory motor plasticity via mechanisms that require serine/threonine protein phosphatase activity. J Neuroinflammation 2021; 18:28. [PMID: 33468163 PMCID: PMC7816383 DOI: 10.1186/s12974-021-02074-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 01/05/2021] [Indexed: 01/05/2023] Open
Abstract
Background Inflammation undermines multiple forms of neuroplasticity. Although inflammation and its influence on plasticity in multiple neural systems has been extensively studied, its effects on plasticity of neural networks controlling vital life functions, such as breathing, are less understood. In this study, we investigated the signaling mechanisms whereby lipopolysaccharide (LPS)-induced systemic inflammation impairs plasticity within the phrenic motor system—a major spinal respiratory motor pool that drives contractions of the diaphragm muscle. Here, we tested the hypotheses that lipopolysaccharide-induced systemic inflammation (1) blocks phrenic motor plasticity by a mechanism that requires cervical spinal okadaic acid-sensitive serine/threonine protein phosphatase (PP) 1/2A activity and (2) prevents phosphorylation/activation of extracellular signal-regulated kinase 1/2 mitogen activated protein kinase (ERK1/2 MAPK)—a key enzyme necessary for the expression of phrenic motor plasticity. Methods To study phrenic motor plasticity, we utilized a well-characterized model for spinal respiratory plasticity called phrenic long-term facilitation (pLTF). pLTF is characterized by a long-lasting, progressive enhancement of inspiratory phrenic nerve motor drive following exposures to moderate acute intermittent hypoxia (mAIH). In anesthetized, vagotomized and mechanically ventilated adult Sprague Dawley rats, we examined the effect of inhibiting cervical spinal serine/threonine PP 1/2A activity on pLTF expression in sham-vehicle and LPS-treated rats. Using immunofluorescence optical density analysis, we compared mAIH-induced phosphorylation/activation of ERK 1/2 MAPK with and without LPS-induced inflammation in identified phrenic motor neurons. Results We confirmed that mAIH-induced pLTF is abolished 24 h following low-dose systemic LPS (100 μg/kg, i.p.). Cervical spinal delivery of the PP 1/2A inhibitor, okadaic acid, restored pLTF in LPS-treated rats. LPS also prevented mAIH-induced enhancement in phrenic motor neuron ERK1/2 MAPK phosphorylation. Thus, a likely target for the relevant okadaic acid-sensitive protein phosphatases is ERK1/2 MAPK or its upstream activators. Conclusions This study increases our understanding of fundamental mechanisms whereby inflammation disrupts neuroplasticity in a critical population of motor neurons necessary for breathing, and highlights key roles for serine/threonine protein phosphatases and ERK1/2 MAPK kinase in the plasticity of mammalian spinal respiratory motor circuits.
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Affiliation(s)
- Arash Tadjalli
- Breathing Research and Therapeutics Center, Department of Physical Therapy and The McKnight Brain Institute, College of Public Health & Health Professions, University of Florida, 1225 Center Drive, PO Box 100154, Gainesville, FL, 32610, USA
| | - Yasin B Seven
- Breathing Research and Therapeutics Center, Department of Physical Therapy and The McKnight Brain Institute, College of Public Health & Health Professions, University of Florida, 1225 Center Drive, PO Box 100154, Gainesville, FL, 32610, USA
| | - Raphael R Perim
- Breathing Research and Therapeutics Center, Department of Physical Therapy and The McKnight Brain Institute, College of Public Health & Health Professions, University of Florida, 1225 Center Drive, PO Box 100154, Gainesville, FL, 32610, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and The McKnight Brain Institute, College of Public Health & Health Professions, University of Florida, 1225 Center Drive, PO Box 100154, Gainesville, FL, 32610, USA.
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Borkowski LF, Nichols NL. Differential mechanisms are required for phrenic long-term facilitation over the course of motor neuron loss following CTB-SAP intrapleural injections. Exp Neurol 2020; 334:113460. [PMID: 32916172 PMCID: PMC10823911 DOI: 10.1016/j.expneurol.2020.113460] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 08/28/2020] [Accepted: 09/01/2020] [Indexed: 01/25/2023]
Abstract
Selective elimination of respiratory motor neurons using intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB-SAP) mimics motor neuron death and respiratory deficits observed in rat models of neuromuscular diseases. This CTB-SAP model allows us to study the impact of motor neuron death on the output of surviving phrenic motor neurons. After 7(d) days of CTB-SAP, phrenic long-term facilitation (pLTF, a form of respiratory plasticity) is enhanced, but returns towards control levels at 28d. However, the mechanism responsible for this difference in magnitude of pLTF is unknown. In naïve rats, pLTF predominately requires 5-HT2 receptors, the new synthesis of BDNF, and MEK/ERK signaling; however, pLTF can alternatively be induced via A2A receptors, the new synthesis of TrkB, and PI3K/Akt signaling. Since A2A receptor-dependent pLTF is enhanced in naïve rats, we suggest that 7d CTB-SAP treated rats utilize the alternative mechanism for pLTF. Here, we tested the hypothesis that pLTF following CTB-SAP is: 1) TrkB and PI3K/Akt, not BDNF and MEK/ERK, dependent at 7d; and 2) BDNF and MEK/ERK, not TrkB and PI3K/Akt, dependent at 28d. Adult Sprague Dawley male rats were anesthetized, paralyzed, ventilated, and were exposed to acute intermittent hypoxia (AIH; 3, 5 min bouts of 10.5% O2) following bilateral, intrapleural injections at 7d and 28d of: 1) CTB-SAP (25 μg), or 2) un-conjugated CTB and SAP (control). Intrathecal C4 delivery included either: 1) small interfering RNA that targeted BDNF or TrkB mRNA; 2) UO126 (MEK/ERK inhibitor); or 3) PI828 (PI3K/Akt inhibitor). Our data suggest that pLTF in 7d CTB-SAP treated rats is elicited primarily through TrkB and PI3K/Akt-dependent mechanisms, whereas BDNF and MEK/ERK-dependent mechanisms induce pLTF in 28d CTB-SAP treated rats. This project increases our understanding of respiratory plasticity and its implications for breathing following motor neuron death.
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Affiliation(s)
- Lauren F Borkowski
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, United States of America
| | - Nicole L Nichols
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, United States of America.
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Wollman LB, Streeter KA, Fusco AF, Gonzalez-Rothi EJ, Sandhu MS, Greer JJ, Fuller DD. Ampakines stimulate phrenic motor output after cervical spinal cord injury. Exp Neurol 2020; 334:113465. [PMID: 32949571 DOI: 10.1016/j.expneurol.2020.113465] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Revised: 08/31/2020] [Accepted: 09/14/2020] [Indexed: 12/21/2022]
Abstract
Activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors increases phrenic motor output. Ampakines are a class of drugs that are positive allosteric modulators of AMPA receptors. We hypothesized that 1) ampakines can stimulate phrenic activity after incomplete cervical spinal cord injury (SCI), and 2) pairing ampakines with brief hypoxia could enable sustained facilitation of phrenic bursting. Phrenic activity was recorded ipsilateral (IL) and contralateral (CL) to C2 spinal cord hemisection (C2Hx) in anesthetized adult rats. Two weeks after C2Hx, ampakine CX717 (15 mg/kg, i.v.) increased IL (61 ± 46% baseline, BL) and CL burst amplitude (47 ± 26%BL) in 8 of 8 rats. After 90 min, IL and CL bursting remained above baseline (BL) in 7 of 8 rats. Pairing ampakine with a single bout of acute hypoxia (5-min, arterial partial pressure of O2 ~ 50 mmHg) had a variable impact on phrenic bursting, with some rats showing a large facilitation that exceeded the response of the ampakine alone group. At 8 weeks post-C2Hx, 7 of 8 rats increased IL (115 ± 117%BL) and CL burst amplitude (45 ± 27%BL) after ampakine. The IL burst amplitude remained above BL for 90-min in 7 of 8 rats; CL bursting remained elevated in 6 of 8 rats. The sustained impact of ampakine at 8 weeks was not enhanced by hypoxia exposure. Intravenous vehicle (10% 2-Hydroxypropyl-β-cyclodextrin) did not increase phrenic bursting at either time point. We conclude that ampakines effectively stimulate neural drive to the diaphragm after cervical SCI. Pairing ampakines with a single hypoxic exposure did not consistently enhance phrenic motor facilitation.
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Affiliation(s)
- L B Wollman
- Department of Physical Therapy, University of Florida, Gainesville, FL 32610, United States of America; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL 32610, United States of America
| | - K A Streeter
- Department of Physical Therapy, University of Florida, Gainesville, FL 32610, United States of America; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL 32610, United States of America
| | - A F Fusco
- Department of Physical Therapy, University of Florida, Gainesville, FL 32610, United States of America
| | - E J Gonzalez-Rothi
- Department of Physical Therapy, University of Florida, Gainesville, FL 32610, United States of America; McKnight Brain Institute, University of Florida, Gainesville, Florida 32610, United States of America; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL 32610, United States of America
| | - M S Sandhu
- Department of Physical Therapy, University of Florida, Gainesville, FL 32610, United States of America
| | - J J Greer
- Department of Physiology, University of Alberta, Edmonton, AB T6G2SE, Canada
| | - D D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, FL 32610, United States of America; McKnight Brain Institute, University of Florida, Gainesville, Florida 32610, United States of America; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL 32610, United States of America.
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Kelly MN, Smith DN, Sunshine MD, Ross A, Zhang X, Gumz ML, Esser KA, Mitchell GS. Circadian clock genes and respiratory neuroplasticity genes oscillate in the phrenic motor system. Am J Physiol Regul Integr Comp Physiol 2020; 318:R1058-R1067. [PMID: 32348679 DOI: 10.1152/ajpregu.00010.2020] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Circadian rhythms are endogenous and entrainable daily patterns of physiology and behavior. Molecular mechanisms underlie circadian rhythms, characterized by an ~24-h pattern of gene expression of core clock genes. Although it has long been known that breathing exhibits circadian rhythms, little is known concerning clock gene expression in any element of the neuromuscular system controlling breathing. Furthermore, we know little concerning gene expression necessary for specific respiratory functions, such as phrenic motor plasticity. Thus, we tested the hypotheses that transcripts for clock genes (Bmal1, Clock, Per1, and Per2) and molecules necessary for phrenic motor plasticity (Htr2a, Htr2b, Bdnf, and Ntrk2) oscillate in regions critical for phrenic/diaphragm motor function via RT-PCR. Tissues were collected from male Sprague-Dawley rats entrained to a 12-h light-dark cycle at 4 zeitgeber times (ZT; n = 8 rats/group): ZT5, ZT11, ZT17, and ZT23; ZT0 = lights on. Here, we demonstrate that 1) circadian clock genes (Bmal1, Clock, Per1, and Per2) oscillate in regions critical for phrenic/diaphragm function, including the caudal medulla, ventral C3-C5 cervical spinal cord, and diaphragm; 2) the clock protein BMAL1 is localized within CtB-labeled phrenic motor neurons; 3) genes necessary for intermittent hypoxia-induced phrenic/diaphragm motor plasticity (Htr2b and Bdnf) oscillate in the caudal medulla and ventral C3-C5 spinal cord; and 4) there is higher intensity of immunofluorescent BDNF protein within phrenic motor neurons at ZT23 compared with ZT11 (n = 11 rats/group). These results suggest local circadian clocks exist in the phrenic motor system and confirm the potential for local circadian regulation of neuroplasticity and other elements of the neural network controlling breathing.
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Affiliation(s)
- Mia N Kelly
- Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida.,Department of Physical Therapy, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Danelle N Smith
- Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida
| | - Michael D Sunshine
- Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida.,Department of Physical Therapy, University of Florida, Gainesville, Florida
| | - Ashley Ross
- Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida.,Department of Physical Therapy, University of Florida, Gainesville, Florida
| | - Xiping Zhang
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida
| | - Michelle L Gumz
- Department of Medicine, University of Florida, Gainesville, Florida
| | - Karyn A Esser
- Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida
| | - Gordon S Mitchell
- Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida.,Department of Physical Therapy, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida
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34
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Cummins EP, Strowitzki MJ, Taylor CT. Mechanisms and Consequences of Oxygen and Carbon Dioxide Sensing in Mammals. Physiol Rev 2019; 100:463-488. [PMID: 31539306 DOI: 10.1152/physrev.00003.2019] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Molecular oxygen (O2) and carbon dioxide (CO2) are the primary gaseous substrate and product of oxidative phosphorylation in respiring organisms, respectively. Variance in the levels of either of these gasses outside of the physiological range presents a serious threat to cell, tissue, and organism survival. Therefore, it is essential that endogenous levels are monitored and kept at appropriate concentrations to maintain a state of homeostasis. Higher organisms such as mammals have evolved mechanisms to sense O2 and CO2 both in the circulation and in individual cells and elicit appropriate corrective responses to promote adaptation to commonly encountered conditions such as hypoxia and hypercapnia. These can be acute and transient nontranscriptional responses, which typically occur at the level of whole animal physiology or more sustained transcriptional responses, which promote chronic adaptation. In this review, we discuss the mechanisms by which mammals sense changes in O2 and CO2 and elicit adaptive responses to maintain homeostasis. We also discuss crosstalk between these pathways and how they may represent targets for therapeutic intervention in a range of pathological states.
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Affiliation(s)
- Eoin P Cummins
- UCD Conway Institute, Systems Biology Ireland and the School of Medicine, University College Dublin, Belfield, Dublin, Ireland
| | - Moritz J Strowitzki
- UCD Conway Institute, Systems Biology Ireland and the School of Medicine, University College Dublin, Belfield, Dublin, Ireland
| | - Cormac T Taylor
- UCD Conway Institute, Systems Biology Ireland and the School of Medicine, University College Dublin, Belfield, Dublin, Ireland
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35
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Fields DP, Braegelmann KM, Meza AL, Mickelson CR, Gumnit MG, Baker TL. Competing mechanisms of plasticity impair compensatory responses to repetitive apnoea. J Physiol 2019; 597:3951-3967. [PMID: 31280489 DOI: 10.1113/jp277676] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Accepted: 06/03/2019] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS Intermittent reductions in respiratory neural activity, a characteristic of many ventilatory disorders, leads to inadequate ventilation and arterial hypoxia. Both intermittent reductions in respiratory neural activity and intermittent hypoxia trigger compensatory enhancements in inspiratory output when experienced separately, forms of plasticity called inactivity-induced inspiratory motor facilitation (iMF) and long-term facilitation (LTF), respectively. Reductions in respiratory neural activity that lead to moderate, but not mild, arterial hypoxia occludes plasticity expression, indicating that concurrent induction of iMF and LTF impairs plasticity through cross-talk inhibition of their respective signalling pathways. Moderate hypoxia undermines iMF by enhancing NR2B-containing NMDA receptor signalling, which can be rescued by exogenous retinoic acid, a molecule necessary for iMF. These data suggest that in ventilatory disorders characterized by reduced inspiratory motor output, such as sleep apnoea, endogenous mechanisms of compensatory plasticity may be impaired, and that exogenously activating respiratory plasticity may be a novel strategy to improve breathing. ABSTRACT Many forms of sleep apnoea are characterized by recurrent reductions in respiratory neural activity, which leads to inadequate ventilation and arterial hypoxia. Both recurrent reductions in respiratory neural activity and hypoxia activate mechanisms of compensatory plasticity that augment inspiratory output and lower the threshold for apnoea, inactivity-induced inspiratory motor facilitation (iMF) and long-term facilitation (LTF), respectively. However, despite frequent concurrence of reduced respiratory neural activity and hypoxia, mechanisms that induce and regulate iMF and LTF have only been studied separately. Here, we demonstrate that recurrent reductions in respiratory neural activity ('neural apnoea') accompanied by cessations in ventilation that result in moderate (but not mild) hypoxaemia do not elicit increased inspiratory output, suggesting that concurrent induction of iMF and LTF occludes plasticity. A key role for NMDA receptor activation in impairing plasticity following concurrent neural apnoea and hypoxia is indicated since recurrent hypoxic neural apnoeas triggered increased phrenic inspiratory output in rats in which spinal NR2B-containing NMDA receptors were inhibited. Spinal application of retinoic acid, a key molecule necessary for iMF, bypasses NMDA receptor-mediated constraints, thereby rescuing plasticity following hypoxic neural apnoeas. These studies raise the intriguing possibility that endogenous mechanisms of compensatory plasticity may be impaired in some individuals with sleep apnoea, and that exogenously activating pathways giving rise to respiratory plasticity may be a novel pharmacological strategy to improve breathing.
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Affiliation(s)
- Daryl P Fields
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI, USA
| | - Kendra M Braegelmann
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI, USA
| | - Armand L Meza
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI, USA
| | - Carly R Mickelson
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI, USA
| | - Maia G Gumnit
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI, USA
| | - Tracy L Baker
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI, USA
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36
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Tadjalli A, Mitchell GS. Cervical spinal 5-HT 2A and 5-HT 2B receptors are both necessary for moderate acute intermittent hypoxia-induced phrenic long-term facilitation. J Appl Physiol (1985) 2019; 127:432-443. [PMID: 31219768 DOI: 10.1152/japplphysiol.01113.2018] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Serotonin (5-HT) is a key regulator of spinal respiratory motor plasticity. For example, spinal 5-HT receptor activation is necessary for the induction of phrenic long-term facilitation (pLTF), a form of respiratory motor plasticity triggered by moderate acute intermittent hypoxia (mAIH). mAIH-induced pLTF is blocked by cervical spinal application of the broad-spectrum 5-HT-receptor antagonist, methysergide. However, methysergide does not allow distinctions between the relative contributions of different 5-HT receptor subtypes. Intravenous administration of the Gq protein-coupled 5-HT2A/2C receptor antagonist ketanserin blocks mAIH-induced pLTF when administered before, but not after, mAIH; thus, 5-HT2 receptor activation is necessary for the induction but not maintenance of mAIH-induced pLTF. However, systemic ketanserin administration does not identify the site of the relevant 5-HT2A/2C receptors. Furthermore, this approach does not differentiate between the roles of 5-HT2A versus 5-HT2C receptors, nor does it preclude involvement of other Gq protein-coupled metabotropic 5-HT receptors capable of eliciting long-lasting phrenic motor facilitation, such as 5-HT2B receptors. Here we tested the hypothesis that mAIH-induced pLTF requires cervical spinal 5-HT2 receptor activation and determined which 5-HT2 receptor subtypes are involved. Anesthetized, paralyzed, and ventilated adult male Sprague Dawley rats were pretreated intrathecally with cervical (~C3-C5) spinal injections of subtype selective 5-HT2A/2C, 5-HT2B, or 5-HT2C receptor antagonists before mAIH. Whereas cervical spinal 5-HT2C receptor inhibition had no impact on mAIH-induced pLTF, pLTF was no longer observed after pretreatment with either 5-HT2A/2C or 5-HT2B receptor antagonists. Furthermore, spinal pretreatment with an MEK/ERK MAPK inhibitor blocked phrenic motor facilitation elicited by intrathecal injections of 5-HT2A but not 5-HT2B receptor agonists. Thus, mAIH-induced pLTF requires concurrent cervical spinal activation of both 5-HT2A and 5-HT2B receptors. However, these distinct receptor subtypes contribute to phrenic motor facilitation via distinct downstream signaling cascades that differ in their requirement for ERK MAPK signaling. The demonstration that both 5-HT2A and 5-HT2B receptors make unique contributions to mAIH-induced pLTF advances our understanding of mechanisms that underlie 5-HT-induced phrenic motor plasticity.NEW & NOTEWORTHY Moderate acute intermittent hypoxia (mAIH) triggers a persistent enhancement in phrenic motor output, an effect termed phrenic long-term facilitation (pLTF). mAIH-induced pLTF is blocked by cervical spinal application of the broad-spectrum serotonin (5-HT) receptor antagonist methysergide, demonstrating the need for spinal 5-HT receptor activation. However, the exact type of 5-HT receptors required for initiation of pLTF remains unknown. To the best of out knowledge, the present study is the first to demonstrate that 1) spinal coactivation of two distinct Gq protein-coupled 5-HT2 receptor subtypes is necessary for mAIH-induced pLTF, and 2) these receptors contribute to pLTF via cascades that differ in their requirement for ERK MAPK signaling.
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Affiliation(s)
- Arash Tadjalli
- Center for Respiratory Research and Rehabilitation, Department of Physical Therapy and the McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Gordon S Mitchell
- Center for Respiratory Research and Rehabilitation, Department of Physical Therapy and the McKnight Brain Institute, University of Florida, Gainesville, Florida
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McIntosh D, Dougherty BJ. Development of ventilatory long-term facilitation is dependent on estrous cycle stage in adult female rats. Respir Physiol Neurobiol 2019; 264:1-7. [PMID: 30898577 DOI: 10.1016/j.resp.2019.02.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 02/25/2019] [Accepted: 02/26/2019] [Indexed: 11/16/2022]
Abstract
Ventilatory long-term facilitation (vLTF) is a form of respiratory plasticity characterized by a progressive and sustained increase in minute ventilation over time following acute, intermittent hypoxia (AIH). Though vLTF has been repeatedly demonstrated in adult males (rats and humans), few studies have assessed vLTF in adult females and no studies have explored differential expression of vLTF across the normal female estrous cycle. We recently reported that AIH-induced plasticity of phrenic motor output (phrenic long-term facilitation, pLTF), a phenotypically similar form of respiratory plasticity presenting as a sustained increase in phrenic nerve amplitude, develops in adult female rats only during the proestrus stage of the estrous cycle, notable for high levels of serum estrogen. Here, we tested the hypothesis that AIH-induced vLTF would also be estrous-stage dependent; developing in female rats during proestrus, but not estrus. Barometric plethysmography in adult (4-5 months), normally cycling female rats revealed a progressive increase in minute ventilation for 60 min following AIH (5 × 5 min episodes; 10% O2) during proestrus indicative of vLTF, while estrus rats showed no changes in minute ventilation over the same time period. The development of vLTF in proestrus rats was driven by changes in tidal volume production versus respiratory frequency consistent with prior studies. These data are the first to investigate differential vLTF expression across the estrous cycle in adult female rats and highlight the importance of female estrous cycle stage as a critical physiological variable to consider in studies of AIH-induced plasticity.
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Affiliation(s)
- Danielle McIntosh
- University of Minnesota Medical School, Department of Rehabilitation Medicine, Divisions of Physical Therapy and Rehabilitation Science, 420 Delaware Street S.E. (MMC 388), Minneapolis, MN 55455, United States
| | - Brendan J Dougherty
- University of Minnesota Medical School, Department of Rehabilitation Medicine, Divisions of Physical Therapy and Rehabilitation Science, 420 Delaware Street S.E. (MMC 388), Minneapolis, MN 55455, United States.
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38
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Taranto-Montemurro L, Sands SA, Grace KP, Azarbarzin A, Messineo L, Salant R, White DP, Wellman DA. Neural memory of the genioglossus muscle during sleep is stage-dependent in healthy subjects and obstructive sleep apnoea patients. J Physiol 2018; 596:5163-5173. [PMID: 30022493 DOI: 10.1113/jp276618] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 07/16/2018] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS In most patients with obstructive sleep apnoea (OSA), there is a spontaneous resolution of the breathing disorders during slow wave sleep (SWS) for yet unknown reasons related to non-anatomical factors. Some recently identified forms of neural memory specific of upper airway muscles may play a role in this phenomenon. In the present study, we show for the first time that a form of memory of the genioglossus (tongue) muscle is greatly enhanced during SWS compared to non-rapid eye movement stage 2 sleep. The present study represents a step forward in understanding the mechanisms responsible for the spontaneous development of stable breathing during SWS in OSA patients and may help the discovery of novel therapeutic strategies for this disease. ABSTRACT Several studies have shown that obstructive sleep apnoea (OSA) improves during slow wave sleep (SWS) for reasons that remain unclear. Recent studies have identified forms of neural memory such as short-term potentiation or after-discharge that can occur in response to upper airway obstruction. Neural memory may play a role in the development of stable breathing during SWS by increasing upper airway muscles activity in this sleep stage. We hypothesize that the after-discharge of the genioglossus muscle following upper airway obstruction is enhanced during SWS compared to non-rapid eye movement stage 2 (N2). During sleep, we performed five-breath drops in continuous positive airway pressure (CPAP-drop) to simulate obstructive events and reflexively activate the genioglossus. Immediately afterwards, CPAP was returned to an optimal level. Once the post-drop ventilation returned to eupnoea, the genioglossus after-discharge was measured as the time it took for genioglossus activity to return to baseline levels. In total, 171 CPAP-drops were analysed from a group of 16 healthy subjects and 19 OSA patients. A mixed-model analysis showed that after-discharge duration during SWS was 208% (95% confidence interval = 112% to 387%, P = 0.022) greater than during N2 after adjusting for covariates (ventilatory drive, CPAP levels). There was also a non-significant trend for a -35% reduction in after-discharge duration following an arousal vs. no-arousal from sleep (95% confidence interval = -59.5% to 5%, P = 0.08). Genioglossus after-discharge is two-fold greater in SWS vs. N2, which could partly explain the breathing stabilization described in OSA patients during this sleep stage.
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Affiliation(s)
- Luigi Taranto-Montemurro
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA
| | - Scott A Sands
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA
| | - Kevin P Grace
- Department of Neurology, Beth Israel Deaconess Medical Center & Harvard Medical School, Boston, MA, USA
| | - Ali Azarbarzin
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA
| | - Ludovico Messineo
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA.,Respiratory Medicine and Sleep Laboratory, Department of Experimental and Clinical Sciences, University of Brescia, Italy
| | - Rebecca Salant
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA
| | - David P White
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA
| | - D Andrew Wellman
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham & Women's Hospital & Harvard Medical School, Boston, MA, USA
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O'Halloran KD, Burns DP. Breathing with neuromuscular disease: Does compensatory plasticity in the motor drive to breathe offer a potential therapeutic target in muscular dystrophy? Respir Physiol Neurobiol 2018; 265:49-54. [PMID: 29933052 DOI: 10.1016/j.resp.2018.06.009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Revised: 05/22/2018] [Accepted: 06/18/2018] [Indexed: 11/26/2022]
Abstract
Duchenne muscular dystrophy is a fatal neuromuscular disease associated with respiratory-related morbidity and mortality. Herein, we review recent work by our group exploring deficits and compensation in the respiratory control network governing respiratory homeostasis in a pre-clinical model of DMD, the mdx mouse. Deficits at multiple sites of the network provide considerable challenges to respiratory control. However, our work has also revealed evidence of compensatory neuroplasticity in the motor drive to breathe enhancing diaphragm muscle activity during increased chemical drive. The finding may explain the preserved capacity for mdx mice to increase ventilation in response to chemoactivation. Given the profound dysfunction in the primary pump muscle of breathing, we argue that activation of accessory muscles of breathing may be especially important in mdx (and perhaps DMD). Notwithstanding the limitations resulting from respiratory muscle dysfunction, it may be possible to further leverage intrinsic physiological mechanisms serving to compensate for weak muscles in attempts to preserve or restore ventilatory capacity. We discuss current knowledge gaps and the need to better appreciate fundamental aspects of respiratory control in pre-clinical models so as to better inform intervention strategies in human DMD.
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Affiliation(s)
- Ken D O'Halloran
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland.
| | - David P Burns
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland
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40
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Christiansen L, Urbin MA, Mitchell GS, Perez MA. Acute intermittent hypoxia enhances corticospinal synaptic plasticity in humans. eLife 2018; 7:e34304. [PMID: 29688171 PMCID: PMC5915172 DOI: 10.7554/elife.34304] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 03/12/2018] [Indexed: 01/02/2023] Open
Abstract
Acute intermittent hypoxia (AIH) enhances voluntary motor output in humans with central nervous system damage. The neural mechanisms contributing to these beneficial effects are unknown. We examined corticospinal function by evaluating motor evoked potentials (MEPs) elicited by cortical and subcortical stimulation of corticospinal axons and the activity in intracortical circuits in a finger muscle before and after 30 min of AIH or sham AIH. We found that the amplitude of cortically and subcortically elicited MEPs increased for 75 min after AIH but not sham AIH while intracortical activity remained unchanged. To examine further these subcortical effects, we assessed spike-timing dependent plasticity (STDP) targeting spinal synapses and the excitability of spinal motoneurons. Notably, AIH increased STDP outcomes while spinal motoneuron excitability remained unchanged. Our results provide the first evidence that AIH changes corticospinal function in humans, likely by altering corticospinal-motoneuronal synaptic transmission. AIH may represent a novel noninvasive approach for inducing spinal plasticity in humans.
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Affiliation(s)
- Lasse Christiansen
- Department of Neurological Surgery, The Miami Project to Cure ParalysisUniversity of MiamiMiamiUnited States
| | - MA Urbin
- Department of Neurological Surgery, The Miami Project to Cure ParalysisUniversity of MiamiMiamiUnited States
| | - Gordon S Mitchell
- Center for Respiratory Research and RehabilitationUniversity of FloridaGainesvilleUnited States
- Department of Physical TherapyUniversity of FloridaGainesvilleUnited States
- McKnight Brain InstituteUniversity of FloridaGainesvilleUnited States
| | - Monica A Perez
- Department of Neurological Surgery, The Miami Project to Cure ParalysisUniversity of MiamiMiamiUnited States
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41
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Wilkerson JER, Devinney M, Mitchell GS. Intermittent but not sustained moderate hypoxia elicits long-term facilitation of hypoglossal motor output. Respir Physiol Neurobiol 2017; 256:15-20. [PMID: 29074449 DOI: 10.1016/j.resp.2017.10.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Revised: 10/05/2017] [Accepted: 10/16/2017] [Indexed: 01/14/2023]
Abstract
Phrenic long-term facilitation (pLTF) is a form of serotonin-dependent respiratory motor plasticity induced by moderate acute intermittent hypoxia (AIH), but not by moderate acute sustained hypoxia (ASH) of similar cumulative duration. Thus, moderate AIH-induced pLTF is sensitive to the pattern of hypoxia. On the other hand, pLTF induced by severe AIH protocols is neither pattern sensitive nor serotonin dependent (it converts to an adenosine-dependent mechanism). Although moderate AIH also induces hypoglossal LTF (hLTF), no data are available concerning its sensitivity/insensitivity to the pattern of hypoxia. Since hLTF following moderate hypoxia is serotonin-dependent, we hypothesized that hLTF is pattern-sensitive, similar to serotonin-dependent pLTF. Integrated hypoglossal nerve activity was recorded in urethane-anesthetized, vagotomized, paralyzed, and ventilated rats exposed to isocapnic AIH (3, 5min episodes of 11% O2) or ASH (a single 25min episode of 11% O2). Similar to previous studies of pLTF, hypoglossal motor output was elevated for more than 1h following AIH (50±20%, p<0.01), but not ASH (-6±9%, p>0.05). Frequency LTF was not observed following either hypoxic exposure. Thus, in agreement with our hypothesis, hypoglossal LTF following moderate AIH is pattern-sensitive, similar to phrenic LTF.
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Affiliation(s)
- Julia E R Wilkerson
- Department of Comparative Biosciences University of Wisconsin Madison, WI, 53706, USA; Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Michael Devinney
- Department of Comparative Biosciences University of Wisconsin Madison, WI, 53706, USA; Department of Anesthesiology, Duke University, Durham, NC, 27710, USA
| | - Gordon S Mitchell
- Department of Comparative Biosciences University of Wisconsin Madison, WI, 53706, USA; Center for Respiratory Research and Rehabilitation Department of Physical Therapy and McKnight Brain Institute University of Florida, Gainesville, FL, 32610, USA.
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42
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Agosto-Marlin IM, Mitchell GS. Spinal BDNF-induced phrenic motor facilitation requires PKCθ activity. J Neurophysiol 2017; 118:2755-2762. [PMID: 28855298 DOI: 10.1152/jn.00945.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 07/19/2017] [Accepted: 08/29/2017] [Indexed: 11/22/2022] Open
Abstract
Spinal brain-derived neurotrophic factor (BDNF) is necessary and sufficient for certain forms of long-lasting phrenic motor facilitation (pMF). BDNF elicits pMF by binding to its high-affinity receptor, tropomyosin receptor kinase B (TrkB), on phrenic motor neurons, potentially activating multiple downstream signaling cascades. Canonical BDNF/TrkB signaling includes the 1) Ras/RAF/MEK/ERK MAP kinase, 2) phosphatidylinositol 3-kinase (PI3K)/Akt, and 3) PLCγ/PKC pathways. Here we demonstrate that spinal BDNF-induced pMF requires PLCγ/PKCθ in normal rats but not MEK/ERK or PI3K/Akt signaling. Cervical intrathecal injections of MEK/ERK (U0126) or PI3K/Akt (PI-828; 100 μM, 12 μl) inhibitor had no effect on BDNF-induced pMF (90 min after BDNF; U0126 + BDNF: 59 ± 14%, PI-828 + BDNF: 59 ± 8%, inhibitor vehicle + BDNF: 56 ± 7%; all P ≥ 0.05). In contrast, PKCθ inhibition with theta inhibitory peptide (TIP; 0.86 mM, 12 μl) prevented BDNF-induced pMF (90 min after BDNF; TIP + BDNF: -2 ± 2%; P ≤ 0.05 vs. other groups). Thus BDNF-induced pMF requires downstream PLCγ/PKCθ signaling, contrary to initial expectations.NEW AND NOTEWORTHY We demonstrate that BDNF-induced pMF requires downstream signaling via PKCθ but not MEK/ERK or PI3K/Akt signaling. These data are essential to understand the sequence of the cellular cascade leading to BDNF-dependent phrenic motor plasticity.
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Affiliation(s)
- Ibis M Agosto-Marlin
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin; and
| | - Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin; and .,Center for Respiratory Research and Rehabilitation, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, Florida
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43
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Nichols NL, Craig TA, Tanner MA. Phrenic long-term facilitation following intrapleural CTB-SAP-induced respiratory motor neuron death. Respir Physiol Neurobiol 2017; 256:43-49. [PMID: 28822818 DOI: 10.1016/j.resp.2017.08.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 07/20/2017] [Accepted: 08/04/2017] [Indexed: 01/26/2023]
Abstract
Amyotrophic lateral sclerosis (ALS) is a devastating disease leading to progressive motor neuron degeneration and death by ventilatory failure. In a rat model of ALS (SOD1G93A), phrenic long-term facilitation (pLTF) following acute intermittent hypoxia (AIH) is enhanced greater than expected at disease end-stage but the mechanism is unknown. We suggest that one trigger for this enhancement is motor neuron death itself. Intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB-SAP) selectively kill respiratory motor neurons and mimic motor neuron death observed in SOD1G93A rats. This CTB-SAP model allows us to study the impact of respiratory motor neuron death on breathing without many complications attendant to ALS. Here, we tested the hypothesis that phrenic motor neuron death is sufficient to enhance pLTF. pLTF was assessed in anesthetized, paralyzed and ventilated Sprague Dawley rats 7 and 28 days following bilateral intrapleural injections of: 1) CTB-SAP (25 μg), or 2) un-conjugated CTB and SAP (control). CTB-SAP enhanced pLTF at 7 (CTB-SAP: 162 ± 18%, n = 8 vs. Control: 63 ± 3%; n = 8; p < 0.05), but not 28 days post-injection (CTB-SAP: 64 ± 10%, n = 10 vs. Control: 60 ± 13; n = 8; p > 0.05). Thus, pLTF at 7 (not 28) days post-CTB-SAP closely resembles pLTF in end-stage ALS rats, suggesting that processes unique to the early period of motor neuron death enhance pLTF. This project increases our understanding of respiratory plasticity and its implications for breathing in motor neuron disease.
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Affiliation(s)
- Nicole L Nichols
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, 65211, United States.
| | - Taylor A Craig
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, 65211, United States
| | - Miles A Tanner
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, 65211, United States
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Mechanisms of Enhanced Phrenic Long-Term Facilitation in SOD1G93A Rats. J Neurosci 2017; 37:5834-5845. [PMID: 28500219 DOI: 10.1523/jneurosci.3680-16.2017] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 04/08/2017] [Accepted: 05/05/2017] [Indexed: 12/13/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron disease, causing muscle paralysis and death from respiratory failure. Effective means to preserve/restore ventilation are necessary to increase the quality and duration of life in ALS patients. At disease end-stage in a rat ALS model (SOD1G93A ), acute intermittent hypoxia (AIH) restores phrenic nerve activity to normal levels via enhanced phrenic long-term facilitation (pLTF). Mechanisms enhancing pLTF in end-stage SOD1G93A rats are not known. Moderate AIH-induced pLTF is normally elicited via cellular mechanisms that require the following: Gq-protein-coupled 5-HT2 receptor activation, new BDNF synthesis, and MEK/ERK signaling (the Q pathway). In contrast, severe AIH elicits pLTF via a distinct mechanism that requires the following: Gs-protein-coupled adenosine 2A receptor activation, new TrkB synthesis, and PI3K/Akt signaling (the S pathway). In end-stage male SOD1G93A rats and wild-type littermates, we investigated relative Q versus S pathway contributions to enhanced pLTF via intrathecal (C4) delivery of small interfering RNAs targeting BDNF or TrkB mRNA, and MEK/ERK (U0126) or PI3 kinase/Akt (PI828) inhibitors. In anesthetized, paralyzed and ventilated rats, moderate AIH-induced pLTF was abolished by siBDNF and UO126, but not siTrkB or PI828, demonstrating that enhanced pLTF occurs via the Q pathway. Although phrenic motor neuron numbers were decreased in end-stage SOD1G93A rats (∼30% survival; p < 0.001), BDNF and phosphorylated ERK expression were increased in spared phrenic motor neurons (p < 0.05), consistent with increased Q-pathway contributions to pLTF. Our results increase understanding of respiratory plasticity and its potential to preserve/restore breathing capacity in ALS.SIGNIFICANCE STATEMENT Since neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), end life via respiratory failure, the ability to harness respiratory motor plasticity to improve breathing capacity could increase the quality and duration of life. In a rat ALS model (SOD1G93A ) we previously demonstrated that spinal respiratory motor plasticity elicited by acute intermittent hypoxia is enhanced at disease end-stage, suggesting greater potential to preserve/restore breathing capacity. Here we demonstrate that enhanced intermittent hypoxia-induced phrenic motor plasticity results from amplification of normal cellular mechanisms versus addition/substitution of alternative mechanisms. Greater understanding of mechanisms underlying phrenic motor plasticity in ALS may guide development of new therapies to preserve and/or restore breathing in ALS patients.
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Hormigo KM, Zholudeva LV, Spruance VM, Marchenko V, Cote MP, Vinit S, Giszter S, Bezdudnaya T, Lane MA. Enhancing neural activity to drive respiratory plasticity following cervical spinal cord injury. Exp Neurol 2017; 287:276-287. [PMID: 27582085 PMCID: PMC5121051 DOI: 10.1016/j.expneurol.2016.08.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 07/20/2016] [Accepted: 08/26/2016] [Indexed: 02/07/2023]
Abstract
Cervical spinal cord injury (SCI) results in permanent life-altering sensorimotor deficits, among which impaired breathing is one of the most devastating and life-threatening. While clinical and experimental research has revealed that some spontaneous respiratory improvement (functional plasticity) can occur post-SCI, the extent of the recovery is limited and significant deficits persist. Thus, increasing effort is being made to develop therapies that harness and enhance this neuroplastic potential to optimize long-term recovery of breathing in injured individuals. One strategy with demonstrated therapeutic potential is the use of treatments that increase neural and muscular activity (e.g. locomotor training, neural and muscular stimulation) and promote plasticity. With a focus on respiratory function post-SCI, this review will discuss advances in the use of neural interfacing strategies and activity-based treatments, and highlights some recent results from our own research.
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Affiliation(s)
- Kristiina M Hormigo
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Lyandysha V Zholudeva
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Victoria M Spruance
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Vitaliy Marchenko
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Marie-Pascale Cote
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Stephane Vinit
- Université de Versailles Saint-Quentin-en-Yvelines, INSERM U1179 End:icap, UFR des Sciences de la Santé - Simone Veil, Montigny-le-Bretonneux, France
| | - Simon Giszter
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Tatiana Bezdudnaya
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA
| | - Michael A Lane
- Spinal Cord Research Center, Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA, USA.
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Beckhauser TF, Francis-Oliveira J, De Pasquale R. Reactive Oxygen Species: Physiological and Physiopathological Effects on Synaptic Plasticity. J Exp Neurosci 2016; 10:23-48. [PMID: 27625575 PMCID: PMC5012454 DOI: 10.4137/jen.s39887] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Revised: 08/09/2016] [Accepted: 08/13/2016] [Indexed: 12/18/2022] Open
Abstract
In the mammalian central nervous system, reactive oxygen species (ROS) generation is counterbalanced by antioxidant defenses. When large amounts of ROS accumulate, antioxidant mechanisms become overwhelmed and oxidative cellular stress may occur. Therefore, ROS are typically characterized as toxic molecules, oxidizing membrane lipids, changing the conformation of proteins, damaging nucleic acids, and causing deficits in synaptic plasticity. High ROS concentrations are associated with a decline in cognitive functions, as observed in some neurodegenerative disorders and age-dependent decay of neuroplasticity. Nevertheless, controlled ROS production provides the optimal redox state for the activation of transductional pathways involved in synaptic changes. Since ROS may regulate neuronal activity and elicit negative effects at the same time, the distinction between beneficial and deleterious consequences is unclear. In this regard, this review assesses current research and describes the main sources of ROS in neurons, specifying their involvement in synaptic plasticity and distinguishing between physiological and pathological processes implicated.
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Affiliation(s)
- Thiago Fernando Beckhauser
- Physiology and Biophysics Department, Biomedical Sciences Institute, Sao Paulo University (USP), Butanta, Sao Paulo, Brazil
| | - José Francis-Oliveira
- Physiology and Biophysics Department, Biomedical Sciences Institute, Sao Paulo University (USP), Butanta, Sao Paulo, Brazil
| | - Roberto De Pasquale
- Physiology and Biophysics Department, Biomedical Sciences Institute, Sao Paulo University (USP), Butanta, Sao Paulo, Brazil
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Transporter Protein-Coupled DPCPX Nanoconjugates Induce Diaphragmatic Recovery after SCI by Blocking Adenosine A1 Receptors. J Neurosci 2016; 36:3441-52. [PMID: 27013674 DOI: 10.1523/jneurosci.2577-15.2016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 01/08/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Respiratory complications in patients with spinal cord injury (SCI) are common and have a negative impact on the quality of patients' lives. Systemic administration of drugs that improve respiratory function often cause deleterious side effects. The present study examines the applicability of a novel nanotechnology-based drug delivery system, which induces recovery of diaphragm function after SCI in the adult rat model. We developed a protein-coupled nanoconjugate to selectively deliver by transsynaptic transport small therapeutic amounts of an A1 adenosine receptor antagonist to the respiratory centers. A single administration of the nanoconjugate restored 75% of the respiratory drive at 0.1% of the systemic therapeutic drug dose. The reduction of the systemic dose may obviate the side effects. The recovery lasted for 4 weeks (the longest period studied). These findings have translational implications for patients with respiratory dysfunction after SCI. SIGNIFICANCE STATEMENT The leading causes of death in humans following SCI are respiratory complications secondary to paralysis of respiratory muscles. Systemic administration of methylxantines improves respiratory function but also leads to the development of deleterious side effects due to actions of the drug on nonrespiratory sites. The importance of the present study lies in the novel drug delivery approach that uses nanotechnology to selectively deliver recovery-inducing drugs to the respiratory centers exclusively. This strategy allows for a reduction in the therapeutic drug dose, which may reduce harmful side effects and markedly improve the quality of life for SCI patients.
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Pamenter ME, Powell FL. Time Domains of the Hypoxic Ventilatory Response and Their Molecular Basis. Compr Physiol 2016; 6:1345-85. [PMID: 27347896 DOI: 10.1002/cphy.c150026] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ventilatory responses to hypoxia vary widely depending on the pattern and length of hypoxic exposure. Acute, prolonged, or intermittent hypoxic episodes can increase or decrease breathing for seconds to years, both during the hypoxic stimulus, and also after its removal. These myriad effects are the result of a complicated web of molecular interactions that underlie plasticity in the respiratory control reflex circuits and ultimately control the physiology of breathing in hypoxia. Since the time domains of the physiological hypoxic ventilatory response (HVR) were identified, considerable research effort has gone toward elucidating the underlying molecular mechanisms that mediate these varied responses. This research has begun to describe complicated and plastic interactions in the relay circuits between the peripheral chemoreceptors and the ventilatory control circuits within the central nervous system. Intriguingly, many of these molecular pathways seem to share key components between the different time domains, suggesting that varied physiological HVRs are the result of specific modifications to overlapping pathways. This review highlights what has been discovered regarding the cell and molecular level control of the time domains of the HVR, and highlights key areas where further research is required. Understanding the molecular control of ventilation in hypoxia has important implications for basic physiology and is emerging as an important component of several clinical fields. © 2016 American Physiological Society. Compr Physiol 6:1345-1385, 2016.
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Affiliation(s)
| | - Frank L Powell
- Physiology Division, Department of Medicine, University of California San Diego, La Jolla, California, USA
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Dale EA, Fields DP, Devinney MJ, Mitchell GS. Phrenic motor neuron TrkB expression is necessary for acute intermittent hypoxia-induced phrenic long-term facilitation. Exp Neurol 2016; 287:130-136. [PMID: 27185271 DOI: 10.1016/j.expneurol.2016.05.012] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 03/17/2016] [Accepted: 05/06/2016] [Indexed: 10/21/2022]
Abstract
Phrenic long-term facilitation (pLTF) is a form of hypoxia-induced spinal respiratory motor plasticity that requires new synthesis of brain derived neurotrophic factor (BDNF) and activation of its high-affinity receptor, tropomyosin receptor kinase B (TrkB). Since the cellular location of relevant TrkB receptors is not known, we utilized intrapleural siRNA injections to selectively knock down TrkB receptor protein within phrenic motor neurons. TrkB receptors within phrenic motor neurons are necessary for BDNF-dependent acute intermittent hypoxia-induced pLTF, demonstrating that phrenic motor neurons are a critical site of respiratory motor plasticity.
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Affiliation(s)
- Erica A Dale
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, United States
| | - Daryl P Fields
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, United States; Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, United States
| | - Michael J Devinney
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, United States
| | - Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, United States; Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, United States.
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STIPICA I, PAVLINAC DODIG I, PECOTIC R, DOGAS Z, VALIC Z, VALIC M. Periodicity During Hypercapnic and Hypoxic Stimulus Is Crucial in Distinct Aspects of Phrenic Nerve Plasticity. Physiol Res 2016; 65:133-43. [DOI: 10.33549/physiolres.933012] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
This study was undertaken to determine pattern sensitivity of phrenic nerve plasticity in respect to different respiratory challenges. We compared long-term effects of intermittent and continuous hypercapnic and hypoxic stimuli, and combined intermittent hypercapnia and hypoxia on phrenic nerve plasticity. Adult, male, urethane-anesthetized, vagotomized, paralyzed, mechanically ventilated Sprague-Dawley rats were exposed to: acute intermittent hypercapnia (AIHc or AIHcO2), acute intermittent hypoxia (AIH), combined intermittent hypercapnia and hypoxia (AIHcH), continuous hypercapnia (CHc), or continuous hypoxia (CH). Peak phrenic nerve activity (pPNA) and burst frequency were analyzed during baseline (T0), hypercapnia or hypoxia exposures, at 15, 30, and 60 min (T60) after the end of the stimulus. Exposure to acute intermittent hypercapnia elicited decrease of phrenic nerve frequency from 44.25±4.06 at T0 to 35.29±5.21 at T60, (P=0.038, AIHc) and from 45.5±2.62 to 37.17±3.68 breaths/min (P=0.049, AIHcO2), i.e. frequency phrenic long term depression was induced. Exposure to AIH elicited increase of pPNA at T60 by 141.0±28.2 % compared to baseline (P=0.015), i.e. phrenic long-term facilitation was induced. Exposure to AIHcH, CHc, or CH protocols failed to induce long-term plasticity of the phrenic nerve. Thus, we conclude that intermittency of the hypercapnic or hypoxic stimuli is needed to evoke phrenic nerve plasticity.
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Affiliation(s)
| | | | | | | | | | - M. VALIC
- Department of Neuroscience, University of Split School of Medicine, Split, Croatia
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