1
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Xie Y, Zhang L, Guo S, Peng R, Gong H, Yang M. Changes in respiratory structure and function after traumatic cervical spinal cord injury: observations from spinal cord and brain. Front Neurol 2023; 14:1251833. [PMID: 37869136 PMCID: PMC10587692 DOI: 10.3389/fneur.2023.1251833] [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: 07/02/2023] [Accepted: 09/18/2023] [Indexed: 10/24/2023] Open
Abstract
Respiratory difficulties and mortality following severe cervical spinal cord injury (CSCI) result primarily from malfunctions of respiratory pathways and the paralyzed diaphragm. Nonetheless, individuals with CSCI can experience partial recovery of respiratory function through respiratory neuroplasticity. For decades, researchers have revealed the potential mechanism of respiratory nerve plasticity after CSCI, and have made progress in tissue healing and functional recovery. While most existing studies on respiratory plasticity after spinal cord injuries have focused on the cervical spinal cord, there is a paucity of research on respiratory-related brain structures following such injuries. Given the interconnectedness of the spinal cord and the brain, traumatic changes to the former can also impact the latter. Consequently, are there other potential therapeutic targets to consider? This review introduces the anatomy and physiology of typical respiratory centers, explores alterations in respiratory function following spinal cord injuries, and delves into the structural foundations of modified respiratory function in patients with CSCI. Additionally, we propose that magnetic resonance neuroimaging holds promise in the study of respiratory function post-CSCI. By studying respiratory plasticity in the brain and spinal cord after CSCI, we hope to guide future clinical work.
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Affiliation(s)
- Yongqi Xie
- School of Rehabilitation Medicine, Capital Medical University, Beijing, China
| | - Liang Zhang
- School of Rehabilitation Medicine, Capital Medical University, Beijing, China
| | - Shuang Guo
- School of Rehabilitation Medicine, Capital Medical University, Beijing, China
- Department of Rehabilitation, Guangdong Provincial People's Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China
| | - Run Peng
- School of Rehabilitation Medicine, Capital Medical University, Beijing, China
| | - Huiming Gong
- School of Rehabilitation Medicine, Capital Medical University, Beijing, China
- Department of Spinal and Neural Functional Reconstruction, China Rehabilitation Research Center, Beijing, China
| | - Mingliang Yang
- School of Rehabilitation Medicine, Capital Medical University, Beijing, China
- Department of Spinal and Neural Functional Reconstruction, China Rehabilitation Research Center, Beijing, China
- Center of Neural Injury and Repair, Beijing Institute for Brain Disorders, Beijing, China
- Beijing Key Laboratory of Neural Injury and Rehabilitation, Beijing, China
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2
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Kawamura K, Kobayashi M, Tomita K. Routine hypercapnic challenge after cervical spinal hemisection affects the size of phrenic motoneurons. Sci Rep 2023; 13:13905. [PMID: 37626145 PMCID: PMC10457361 DOI: 10.1038/s41598-023-40505-x] [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: 11/18/2022] [Accepted: 08/11/2023] [Indexed: 08/27/2023] Open
Abstract
After an individual experiences a cervical cord injury, the cell body's adaptation to the smaller size of phrenic motoneurons occurs within several weeks. It is not known whether a routine hypercapnic load can alter this adaptation of phrenic motoneurons. We investigated this question by using rats with high cervical cord hemisection. The rats were divided into four groups: control, hypercapnia, sham, and sham hypercapnia. Within 72 h post-hemisection, the hypercapnia groups began a hypercapnic challenge (20 min/day, 4 times/week for 3 weeks) with 7% CO2 under awake conditions. After the 3-week challenge, the phrenic motoneurons in all of the rats were retrogradely labeled with horseradish peroxidase, and the motoneuron sizes in each group were compared. The average diameter, cross-sectional area, and somal surface area of stained phrenic motoneurons as analyzed by software were significantly smaller in only the control group compared to the other groups. The histogram distribution was unimodal, with larger between-group size differences for motoneurons in the horizontal plane than in the transverse plane. Our findings indicate that a routine hypercapnic challenge may increase the input to phrenic motoneurons and alter the propensity for motoneuron adaptations.
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Affiliation(s)
- Kenta Kawamura
- Department of Physical Therapy, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ami-Machi, Inashiki-Gun, Ibaraki, 300-0394, Japan.
- Graduate School of Health Science, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ami-Machi, Inashiki-Gun, Ibaraki, 300-0394, Japan.
| | - Masaaki Kobayashi
- Graduate School of Health Science, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ami-Machi, Inashiki-Gun, Ibaraki, 300-0394, Japan
| | - Kazuhide Tomita
- Department of Physical Therapy, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ami-Machi, Inashiki-Gun, Ibaraki, 300-0394, Japan
- Graduate School of Health Science, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ami-Machi, Inashiki-Gun, Ibaraki, 300-0394, Japan
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3
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Fogarty MJ, Dasgupta D, Khurram OU, Sieck GC. Chemogenetic inhibition of TrkB signalling reduces phrenic motor neuron survival and size. Mol Cell Neurosci 2023; 125:103847. [PMID: 36958643 PMCID: PMC10247511 DOI: 10.1016/j.mcn.2023.103847] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 03/07/2023] [Accepted: 03/16/2023] [Indexed: 03/25/2023] Open
Abstract
Brain derived neurotrophic factor (BDNF) signalling through its high-affinity tropomyosin receptor kinase B (TrkB) is known to have potent effects on motor neuron survival and morphology during development and in neurodegenerative diseases. Here, we employed a novel 1NMPP1 sensitive TrkBF616 rat model to evaluate the effect of 14 days inhibition of TrkB signalling on phrenic motor neurons (PhMNs). Adult female and male TrkBF616 rats were divided into 1NMPP1 or vehicle treated groups. Three days prior to treatment, PhMNs in both groups were initially labeled via intrapleural injection of Alexa-Fluor-647 cholera toxin B (CTB). After 11 days of treatment, retrograde axonal uptake/transport was assessed by secondary labeling of PhMNs by intrapleural injection of Alexa-Fluor-488 CTB. After 14 days of treatment, the spinal cord was excised 100 μm thick spinal sections containing PhMNs were imaged using two-channel confocal microscopy. TrkB inhibition reduced the total number of PhMNs by ∼16 %, reduced the mean PhMN somal surface areas by ∼25 %, impaired CTB uptake 2.5-fold and reduced the estimated PhMN dendritic surface area by ∼38 %. We conclude that inhibition of TrkB signalling alone in adult TrkBF616 rats is sufficient to lead to PhMN loss, morphological degeneration and deficits in retrograde axonal uptake/transport.
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Affiliation(s)
- Matthew J Fogarty
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA
| | - Debanjali Dasgupta
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA
| | - Obaid U Khurram
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA
| | - Gary C Sieck
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN 55905, USA.
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4
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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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Michel-Flutot P, Efthimiadi L, Djerbal L, Deramaudt TB, Bonay M, Vinit S. AMPK-Nrf2 Signaling Pathway in Phrenic Motoneurons following Cervical Spinal Cord Injury. Antioxidants (Basel) 2022; 11:antiox11091665. [PMID: 36139739 PMCID: PMC9495920 DOI: 10.3390/antiox11091665] [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: 07/28/2022] [Revised: 08/24/2022] [Accepted: 08/25/2022] [Indexed: 12/03/2022] Open
Abstract
High spinal cord injuries (SCI) induce the deafferentation of phrenic motoneurons, leading to permanent diaphragm paralysis. This involves secondary injury associated with pathologic and inflammatory processes at the site of injury, and at the level of phrenic motoneurons. In the present study, we evaluated the antioxidant response in phrenic motoneurons involving the AMPK-Nrf2 signaling pathway following C2 spinal cord lateral hemi-section in rats. We showed that there is an abrupt reduction in the expression of phosphorylated AMPK and Nrf2 at one hour post-injury in phrenic motoneurons. A rebound is then observed at one day post-injury, reflecting a return to homeostasis condition. In the total spinal cord around phrenic motoneurons, the increase in phosphorylated AMPK and Nrf2 occurred at three days post-injury, showing the differential antioxidant response between phrenic motoneurons and other cell types. Taken together, our results display the implication of the AMPK-Nrf2 signaling pathway in phrenic motoneurons’ response to oxidative stress following high SCI. Harnessing this AMPK-Nrf2 signaling pathway could improve the antioxidant response and help in spinal rewiring to these deafferented phrenic motoneurons to improve diaphragm activity in patients suffering high SCI.
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Fuller DD, Rana S, Smuder AJ, Dale EA. The phrenic neuromuscular system. HANDBOOK OF CLINICAL NEUROLOGY 2022; 188:393-408. [PMID: 35965035 PMCID: PMC11135908 DOI: 10.1016/b978-0-323-91534-2.00012-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The phrenic neuromuscular system consists of the phrenic motor nucleus in the mid-cervical spinal cord, the phrenic nerve, and the diaphragm muscle. This motor system helps sustain breathing throughout life, while also contributing to posture, coughing, swallowing, and speaking. The phrenic nerve contains primarily efferent phrenic axons and afferent axons from diaphragm sensory receptors but is also a conduit for autonomic fibers. On a breath-by-breath basis, rhythmic (inspiratory) depolarization of phrenic motoneurons occurs due to excitatory bulbospinal synaptic pathways. Further, a complex propriospinal network innervates phrenic motoneurons and may serve to coordinate postural, locomotor, and respiratory movements. The phrenic neuromuscular system is impacted in a wide range of neuromuscular diseases and injuries. Contemporary research is focused on understanding how neuromuscular plasticity occurs in the phrenic neuromuscular system and using this information to optimize treatments and rehabilitation strategies to improve breathing and related behaviors.
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Affiliation(s)
- David D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, FL, United States; McKnight Brain Institute, University of Florida, Gainesville, FL, United States; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, United States.
| | - Sabhya Rana
- Department of Physical Therapy, University of Florida, Gainesville, FL, United States; McKnight Brain Institute, University of Florida, Gainesville, FL, United States; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, United States
| | - Ashley J Smuder
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, United States; Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States
| | - Erica A Dale
- McKnight Brain Institute, University of Florida, Gainesville, FL, United States; Breathing Research and Therapeutics Center, University of Florida, Gainesville, FL, United States; Department of Physiology and Functional Genomics, University of Florida, Gainesville, FL, United States
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7
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Kaufman MR, Ferro N, Paulin E. Phrenic nerve paralysis and phrenic nerve reconstruction surgery. HANDBOOK OF CLINICAL NEUROLOGY 2022; 189:271-292. [PMID: 36031309 DOI: 10.1016/b978-0-323-91532-8.00003-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Phrenic nerve injury results in paralysis of the diaphragm muscle, the primary generator of an inspiratory effort, as well as a stabilizing muscle involved in postural control and spinal alignment. Unilateral deficits often result in exertional dyspnea, orthopnea, and sleep-disordered breathing, whereas oxygen or ventilator dependency can occur with bilateral paralysis. Common etiologies of phrenic injuries include cervical trauma, iatrogenic injury in the neck or chest, and neuralgic amyotrophy. Many patients have no identifiable etiology and are considered to have idiopathic paralysis. Diagnostic evaluation requires radiographic and pulmonary function testing, as well as electrodiagnostic assessment to quantitate the nerve deficit and determine the extent of denervation atrophy. Treatment for symptomatic diaphragm paralysis has traditionally been limited. Medical therapies and nocturnal positive airway pressure may provide some benefit. Surgical repair of the nerve injury to restore functional diaphragmatic activity, termed phrenic nerve reconstruction, is a safe and effective alternative to static repositioning of the diaphragm (diaphragm plication), in properly selected patients. Phrenic nerve reconstruction has increasingly become a standard surgical treatment for diaphragm paralysis due to phrenic nerve injury. A multidisciplinary approach at specialty referral centers combining diagnostic evaluation, surgical treatment, and rehabilitation is required to achieve optimal long-term outcomes.
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Affiliation(s)
- Matthew R Kaufman
- Institute for Advanced Reconstruction, Shrewsbury, NJ, United States; Division of Plastic and Reconstructive Surgery, UCLA Medical Center, Los Angeles, CA, United States.
| | - Nicole Ferro
- Institute for Advanced Reconstruction, Shrewsbury, NJ, United States
| | - Ethan Paulin
- Institute for Advanced Reconstruction, Shrewsbury, NJ, United States
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8
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Chiu TT, Lee KZ. Impact of cervical spinal cord injury on the relationship between the metabolism and ventilation in rats. J Appl Physiol (1985) 2021; 131:1799-1814. [PMID: 34647826 DOI: 10.1152/japplphysiol.00472.2021] [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] [Indexed: 11/22/2022] Open
Abstract
Cervical spinal cord injury typically results in respiratory impairments. Clinical and animal studies have demonstrated that respiratory function can spontaneously and partially recover over time after injury. However, it remains unclear whether respiratory recovery is associated with alterations in metabolism. The present study was designed to comprehensively examine ventilation and metabolism in a rat model of spinal cord injury. Adult male rats received sham (i.e., laminectomy) or unilateral mid-cervical contusion injury (height of impact rod: 6.25 or 12.5 mm). Breathing patterns and whole body metabolism (O2 consumption and CO2 production) were measured using a whole body plethysmography system conjugated with flow controllers and gas analyzer at the acute (1 day postinjury), subchronic (2 wk postinjury), and chronic (8 wk postinjury) injury stages. The results demonstrated that mid-cervical contusion caused a significant reduction in the tidal volume. Although the tidal volume of contused animals can gradually recover, it remains lower than that of uninjured animals at the chronic injury stage. Although O2 consumption and CO2 production were similar between uninjured and contused animals at the acute injury stage, these two metabolic parameters were significantly reduced in contused animals at the subchronic to chronic injury stages. Additionally, the relationships between ventilation, metabolism, and body temperature were altered by cervical spinal cord injury. These results suggest that cervical spinal cord injury causes a complicated reconfiguration of ventilation and metabolism that may enable injured animals to maintain a suitable homeostasis for adapting to the pathophysiological consequences of injury.NEW & NOTEWORTHY Ventilation and metabolism are tightly coupled to maintain appropriate energy expenditure under physiological conditions. Our findings demonstrate that cervical spinal cord injury results in the differential reduction of ventilation and metabolism at the various injury stages and leads to alterations in the relationship between ventilation and metabolism. These results from an animal model provide fundamental knowledge for understanding how cervical spinal cord injury impacts energy homeostasis.
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Affiliation(s)
- Tzu-Ting Chiu
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan
| | - Kun-Ze Lee
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan.,Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung, Taiwan
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9
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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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10
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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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11
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Gonzalez-Rothi EJ, Lee KZ. Intermittent hypoxia and respiratory recovery in pre-clinical rodent models of incomplete cervical spinal cord injury. Exp Neurol 2021; 342:113751. [PMID: 33974878 DOI: 10.1016/j.expneurol.2021.113751] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 04/24/2021] [Accepted: 05/06/2021] [Indexed: 10/21/2022]
Abstract
Impaired respiratory function is a common and devastating consequence of cervical spinal cord injury. Accordingly, the development of safe and effective treatments to restore breathing function is critical. Acute intermittent hypoxia has emerged as a promising therapeutic strategy to treat respiratory insufficiency in individuals with spinal cord injury. Since the original report by Bach and Mitchell (1996) concerning long-term facilitation of phrenic motor output elicited by brief, episodic exposure to reduced oxygen, a series of studies in animal models have led to the realization that acute intermittent hypoxia may have tremendous potential for inducing neuroplasticity and functional recovery in the injured spinal cord. Advances in our understanding of the neurobiology of acute intermittent hypoxia have prompted us to begin to explore its effects in human clinical studies. Here, we review the basic neurobiology of the control of breathing and the pathophysiology and respiratory consequences of two common experimental models of incomplete cervical spinal cord injury (i.e., high cervical hemisection and mid-cervical contusion). We then discuss the impact of acute intermittent hypoxia on respiratory motor function in these models: work that has laid the foundation for translation of this promising therapeutic strategy to clinical populations. Lastly, we examine the limitations of these animal models and intermittent hypoxia and discuss how future work in animal models may further advance the translation and therapeutic efficacy of this treatment.
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Affiliation(s)
- Elisa J Gonzalez-Rothi
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
| | - Kun-Ze Lee
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan; Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung, Taiwan.
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12
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Rana S, Mantilla CB, Sieck GC. Glutamatergic input varies with phrenic motor neuron size. J Neurophysiol 2019; 122:1518-1529. [PMID: 31389739 DOI: 10.1152/jn.00430.2019] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Like all skeletal muscles, the diaphragm muscle accomplishes a range of motor behaviors by recruiting different motor unit types in an orderly fashion. Recruitment of phrenic motor neurons (PhMNs) is generally assumed to be based primarily on the intrinsic properties of PhMNs with an equal distribution of descending excitatory inputs to all PhMNs. However, differences in presynaptic excitatory input across PhMNs of varying sizes could also contribute to the orderly recruitment pattern. In the spinal cord of Sprague-Dawley rats, we retrogradely labeled PhMNs using cholera toxin B (CTB) and validated a robust confocal imaging-based technique that utilizes semiautomated processing to identify presynaptic glutamatergic (Glu) terminals within a defined distance around the somal membrane of PhMNs of varying size. Our results revealed an ~10% higher density of Glu terminals at PhMNs in the lower tertile of somal surface area. These smaller PhMNs are likely recruited first to accomplish lower force ventilatory behaviors of the diaphragm as compared with larger PhMNs in the upper tertile that are recruited to accomplish higher force expulsive behaviors. These results suggest that differences in excitatory synaptic input to PhMNs may also contribute to the orderly recruitment of diaphragm motor units.NEW & NOTEWORTHY The distribution of excitatory glutamatergic synaptic input to phrenic motor neurons differs across motor neurons of varying size. These findings support the size principle of motor unit recruitment that underlies graded force generation in a muscle, which is based on intrinsic electrophysiological properties of motor neurons resulting from differences in somal surface area. A higher density of glutamatergic inputs at smaller, more excitable motor neurons substantiates the earlier and more frequent recruitment of these units.
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Affiliation(s)
- Sabhya Rana
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota
| | - Carlos B Mantilla
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Gary C Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
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13
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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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14
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Zholudeva LV, Iyer N, Qiang L, Spruance VM, Randelman ML, White NW, Bezdudnaya T, Fischer I, Sakiyama-Elbert SE, Lane MA. Transplantation of Neural Progenitors and V2a Interneurons after Spinal Cord Injury. J Neurotrauma 2018; 35:2883-2903. [PMID: 29873284 DOI: 10.1089/neu.2017.5439] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
There is growing interest in the use of neural precursor cells to treat spinal cord injury (SCI). Despite extensive pre-clinical research, it remains unclear as to which donor neuron phenotypes are available for transplantation, whether the same populations exist across different sources of donor tissue (e.g., developing tissue vs. cultured cells), and whether donor cells retain their phenotype once transplanted into the hostile internal milieu of the injured adult spinal cord. In addition, while functional improvements have been reported after neural precursor transplantation post-SCI, the extent of recovery is limited and variable. The present work begins to address these issues by harnessing ventrally derived excitatory pre-motor V2a spinal interneurons (SpINs) to repair the phrenic motor circuit after cervical SCI. Recent studies have demonstrated that Chx10-positive V2a SpINs contribute to anatomical plasticity within the phrenic circuitry after cervical SCI, thus identifying them as a therapeutic candidate. Building upon this discovery, the present work tests the hypothesis that transplantation of neural progenitor cells (NPCs) enriched with V2a INs can contribute to neural networks that promote repair and enhance respiratory plasticity after cervical SCI. Cultured NPCs (neuronal and glial restricted progenitor cells) isolated from E13.5 Green fluorescent protein rats were aggregated with TdTomato-mouse embryonic stem cell-derived V2a INs in vitro, then transplanted into the injured cervical (C3-4) spinal cord. Donor cells survive, differentiate and integrate with the host spinal cord. Functional diaphragm electromyography indicated recovery 1 month following treatment in transplant recipients. Animals that received donor cells enriched with V2a INs showed significantly greater functional improvement than animals that received NPCs alone. The results from this study offer insight into the neuronal phenotypes that might be effective for (re)establishing neuronal circuits in the injured adult central nervous system.
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Affiliation(s)
- Lyandysha V Zholudeva
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
| | - Nisha Iyer
- 3 Wisconsin Institute for Discovery, University of Wisconsin, Madison, Wisconsin
| | - Liang Qiang
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
| | - Victoria M Spruance
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
| | - Margo L Randelman
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
| | - Nicholas W White
- 4 Department of Biomedical Engineering, University of Texas, Austin, Texas
| | - Tatiana Bezdudnaya
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
| | - Itzhak Fischer
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
| | | | - Michael A Lane
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, Pennsylvania.,2 Spinal Cord Research Center, College of Medicine, Drexel University, Philadelphia, Pennsylvania
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15
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Warren PM, Campanaro C, Jacono FJ, Alilain WJ. Mid-cervical spinal cord contusion causes robust deficits in respiratory parameters and pattern variability. Exp Neurol 2018; 306:122-131. [PMID: 29653187 PMCID: PMC6333202 DOI: 10.1016/j.expneurol.2018.04.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 03/24/2018] [Accepted: 04/06/2018] [Indexed: 02/08/2023]
Abstract
Mid-cervical spinal cord contusion disrupts both the pathways and motoneurons vital to the activity of inspiratory muscles. The present study was designed to determine if a rat contusion model could result in a measurable deficit to both ventilatory and respiratory motor function under “normal” breathing conditions at acute to chronic stages post trauma. Through whole body plethysmography and electromyography we assessed respiratory output from three days to twelve weeks after a cervical level 3 (C3) contusion. Contused animals showed significant deficits in both tidal and minute volumes which were sustained from acute to chronic time points. We also examined the degree to which the contusion injury impacted ventilatory pattern variability through assessment of Mutual Information and Sample Entropy. Mid-cervical contusion significantly and robustly decreased the variability of ventilatory patterns. The enduring deficit to the respiratory motor system caused by contusion was further confirmed through electromyography recordings in multiple respiratory muscles. When isolated via a lesion, these contused pathways were insufficient to maintain respiratory activity at all time points post injury. Collectively these data illustrate that, counter to the prevailing literature, a profound and lasting ventilatory and respiratory motor deficit may be modelled and measured through multiple physiological assessments at all time points after cervical contusion injury.
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Affiliation(s)
- Philippa M Warren
- Department of Neurosciences, MetroHealth Medical Center, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Cara Campanaro
- Division of Pulmonary Critical Care and Sleep Medicine and Louis Stokes VA Medical Center, Department of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Frank J Jacono
- Division of Pulmonary Critical Care and Sleep Medicine and Louis Stokes VA Medical Center, Department of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Warren J Alilain
- Department of Neurosciences, MetroHealth Medical Center, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; Spinal Cord and Brain Injury Research Centre, University of Kentucky, Lexington, KY 40536, USA.
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16
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Bezdudnaya T, Hormigo KM, Marchenko V, Lane MA. Spontaneous respiratory plasticity following unilateral high cervical spinal cord injury in behaving rats. Exp Neurol 2018; 305:56-65. [PMID: 29596845 DOI: 10.1016/j.expneurol.2018.03.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Revised: 01/23/2018] [Accepted: 03/23/2018] [Indexed: 01/25/2023]
Abstract
Unilateral cervical C2 hemisection (C2Hx) is a classic model of spinal cord injury (SCI) for studying respiratory dysfunction and plasticity. However, most previous studies were performed under anesthesia, which significantly alters respiratory network. Therefore, the goal of this work was to assess spontaneous diaphragm recovery post-C2Hx in awake, freely behaving animals. Adult rats were chronically implanted with diaphragm EMG electrodes and recorded during 8 weeks post-C2Hx. Our results reveal that ipsilateral diaphragm activity partially recovers within days post-injury and reaches pre-injury amplitude in a few weeks. However, the full extent of spontaneous ipsilateral recovery is significantly attenuated by anesthesia (ketamine/xylazine, isoflurane, and urethane). This suggests that the observed recovery may be attributed in part to activation of NMDA receptors which are suppressed by anesthesia. Despite spontaneous recovery in awake animals, ipsilateral hemidiaphragm dysfunction still persists: i) Inspiratory bursts during basal (slow) breathing exhibit an altered pattern, ii) the amplitude of sighs - or augmented breaths - is significantly decreased, and iii) the injured hemidiaphragm exhibits spontaneous events of hyperexcitation. The results from this study offer an under-appreciated insight into spontaneous diaphragm activity and recovery following high cervical spinal cord injury in awake animals.
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Affiliation(s)
- Tatiana Bezdudnaya
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA.
| | - Kristiina M Hormigo
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
| | - Vitaliy Marchenko
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
| | - Michael A Lane
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
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17
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Cornelison RC, Gonzalez-Rothi EJ, Porvasnik SL, Wellman SM, Park JH, Fuller DD, Schmidt CE. Injectable hydrogels of optimized acellular nerve for injection in the injured spinal cord. Biomed Mater 2018; 13:034110. [PMID: 29380749 PMCID: PMC5911159 DOI: 10.1088/1748-605x/aaab82] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
OBJECTIVE Spinal cord injury (SCI) affects a quarter million individuals in the United States, and there is currently no clinical treatment. Both fresh and acellular peripheral nerve grafts can induce spinal axon regeneration and support functional recovery in experimental injury models. Nonetheless, a scaffold that can be injected into a spinal contusion would be far less invasive to apply. We aimed to develop the first injectable acellular nerve graft for promoting repair after contusion SCI. APPROACH We report a method to enzymatically solubilize optimized acellular (OA) nerve-a decellularized peripheral nerve graft developed in our laboratory and currently used clinically-to obtain an injectable solution that undergoes thermal gelation under physiological conditions. We quantified multiple physical and compositional properties of this novel material as well as tested its efficacy at acute and chronic time points following cervical contusion SCI. MAIN RESULTS This injectable optimized acellular (iOA) nerve graft retains native chemical cues such as collagens and glycosaminoglycans. By varying hydrogel concentration, the rheological properties and compressive modulus of iOA were similar to that previous reported for rat central nervous tissue. iOA solution was compatible with rat Schwann cells in culture, and hydrogel injection into a rat cervical contusion model significantly reduced the ratio of M1:M2 macrophages after one week, favoring regenerative phenotypes (p < 0.05). Furthermore, while iOA treatment did not affect locomotor or respiratory recovery over an eight week period, the percentage of axonal coverage increased at the distal tissue interface (p < 0.05), suggesting enhanced axonal extension within this region. SIGNIFICANCE Our data indicate that this novel injectable form of acellular nerve grafts is amenable for use after contusion SCI and may bolster a simultaneous therapy by acutely modulating the inflammatory milieu and supporting axonal growth.
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Affiliation(s)
- R. Chase Cornelison
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611
| | | | - Stacy L. Porvasnik
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611
| | - Steven M. Wellman
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611
| | - James H. Park
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611
| | - David D. Fuller
- Department of Physical Therapy, University of Florida, Gainesville, FL 32611
| | - Christine E. Schmidt
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611
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18
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Morton AB, Mor Huertas A, Hinkley JM, Ichinoseki-Sekine N, Christou DD, Smuder AJ. Mitochondrial accumulation of doxorubicin in cardiac and diaphragm muscle following exercise preconditioning. Mitochondrion 2018; 45:52-62. [PMID: 29474837 DOI: 10.1016/j.mito.2018.02.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Revised: 11/22/2017] [Accepted: 02/15/2018] [Indexed: 12/22/2022]
Abstract
Doxorubicin (DOX) is a highly effective anthracycline antibiotic. Unfortunately, the clinical use of DOX is limited by the risk of deleterious effects to cardiac and respiratory (i.e. diaphragm) muscle, resulting from mitochondrial reactive oxygen species (ROS) production. In this regard, exercise is demonstrated to protect against DOX-induced myotoxicity and prevent mitochondrial dysfunction. However, the protective mechanisms are currently unclear. We hypothesized that exercise may induce protection by increasing the expression of mitochondria-specific ATP-binding cassette (ABC) transporters and reducing mitochondrial DOX accumulation. Our results confirm this finding and demonstrate that two weeks of exercise preconditioning is sufficient to prevent cardiorespiratory dysfunction.
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Affiliation(s)
- Aaron B Morton
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States
| | - Andres Mor Huertas
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States
| | - J Matthew Hinkley
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States
| | | | - Demetra D Christou
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States
| | - Ashley J Smuder
- Department of Exercise Science, University of South Carolina, Columbia, SC, United States.
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19
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Bezdudnaya T, Marchenko V, Zholudeva LV, Spruance VM, Lane MA. Supraspinal respiratory plasticity following acute cervical spinal cord injury. Exp Neurol 2017; 293:181-189. [PMID: 28433644 PMCID: PMC5510885 DOI: 10.1016/j.expneurol.2017.04.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 04/06/2017] [Accepted: 04/10/2017] [Indexed: 12/20/2022]
Abstract
Impaired breathing is a devastating result of high cervical spinal cord injuries (SCI) due to partial or full denervation of phrenic motoneurons, which innervate the diaphragm - a primary muscle of respiration. Consequently, people with cervical level injuries often become dependent on assisted ventilation and are susceptible to secondary complications. However, there is mounting evidence for limited spontaneous recovery of respiratory function following injury, demonstrating the neuroplastic potential of respiratory networks. Although many studies have shown such plasticity at the level of the spinal cord, much less is known about the changes occurring at supraspinal levels post-SCI. The goal of this study was to determine functional reorganization of respiratory neurons in the medulla acutely (>4h) following high cervical SCI. Experiments were conducted in decerebrate, unanesthetized, vagus intact and artificially ventilated rats. In this preparation, spontaneous recovery of ipsilateral phrenic nerve activity was observed within 4 to 6h following an incomplete, C2 hemisection (C2Hx). Electrophysiological mapping of the ventrolateral medulla showed a reorganization of inspiratory and expiratory sites ipsilateral to injury. These changes included i) decreased respiratory activity within the caudal ventral respiratory group (cVRG; location of bulbospinal expiratory neurons); ii) increased proportion of expiratory phase activity within the rostral ventral respiratory group (rVRG; location of inspiratory bulbo-spinal neurons); iii) increased respiratory activity within ventral reticular nuclei, including lateral reticular (LRN) and paragigantocellular (LPGi) nuclei. We conclude that disruption of descending and ascending connections between the medulla and spinal cord leads to immediate functional reorganization within the supraspinal respiratory network, including neurons within the ventral respiratory column and adjacent reticular nuclei.
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Affiliation(s)
- Tatiana Bezdudnaya
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
| | - Vitaliy Marchenko
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
| | - Lyandysha V Zholudeva
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
| | - Victoria M Spruance
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA
| | - Michael A Lane
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, 2900 W Queen Lane, Philadelphia, PA 19129, USA.
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20
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Zholudeva LV, Karliner JS, Dougherty KJ, Lane MA. Anatomical Recruitment of Spinal V2a Interneurons into Phrenic Motor Circuitry after High Cervical Spinal Cord Injury. J Neurotrauma 2017; 34:3058-3065. [PMID: 28548606 DOI: 10.1089/neu.2017.5045] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
More than half of all spinal cord injuries (SCIs) occur at the cervical level, often resulting in impaired respiration. Despite this devastating outcome, there is substantial evidence for endogenous neuroplasticity after cervical SCI. Spinal interneurons are widely recognized as being an essential anatomical component of this plasticity by contributing to novel neuronal pathways that can result in functional improvement. The identity of spinal interneurons involved with respiratory plasticity post-SCI, however, has remained largely unknown. Using a transgenic Chx10-eGFP mouse line (Strain 011391-UCD), the present study is the first to demonstrate the recruitment of excitatory interneurons into injured phrenic circuitry after a high cervical SCI. Diaphragm electromyography and anatomical analysis were used to confirm lesion-induced functional deficits and document extent of the lesion, respectively. Transneuronal tracing with pseudorabies virus (PRV) was used to identify interneurons within the phrenic circuitry. There was a robust increase in the number of PRV-labeled V2a interneurons ipsilateral to the C2 hemisection, demonstrating that significant numbers of these excitatory spinal interneurons were anatomically recruited into the phrenic motor pathway two weeks after injury, a time known to correspond with functional phrenic plasticity. Understanding this anatomical spinal plasticity and the neural substrates associated with functional compensation or recovery post-SCI in a controlled, experimental setting may help shed light onto possible cellular therapeutic candidates that can be targeted to enhance spontaneous recovery.
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Affiliation(s)
- Lyandysha V Zholudeva
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University , Philadelphia, Pennsylvania.,2 The Spinal Cord Research Center, College of Medicine, Drexel University , Philadelphia, Pennsylvania
| | - Jordyn S Karliner
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University , Philadelphia, Pennsylvania.,2 The Spinal Cord Research Center, College of Medicine, Drexel University , Philadelphia, Pennsylvania.,3 Department of Neuroscience, Ursinus College , Collegeville, Pennsylvania
| | - Kimberly J Dougherty
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University , Philadelphia, Pennsylvania.,2 The Spinal Cord Research Center, College of Medicine, Drexel University , Philadelphia, Pennsylvania
| | - Michael A Lane
- 1 Department of Neurobiology and Anatomy, College of Medicine, Drexel University , Philadelphia, Pennsylvania.,2 The Spinal Cord Research Center, College of Medicine, Drexel University , Philadelphia, Pennsylvania
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21
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Navarrete-Opazo A, Dougherty BJ, Mitchell GS. Enhanced recovery of breathing capacity from combined adenosine 2A receptor inhibition and daily acute intermittent hypoxia after chronic cervical spinal injury. Exp Neurol 2017; 287:93-101. [PMID: 27079999 PMCID: PMC5193117 DOI: 10.1016/j.expneurol.2016.03.026] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 02/29/2016] [Accepted: 03/31/2016] [Indexed: 01/16/2023]
Abstract
Daily acute intermittent hypoxia (dAIH) improves breathing capacity after C2 spinal hemisection (C2HS) in rats. Since C2HS disrupts spinal serotonergic innervation below the injury, adenosine-dependent mechanisms underlie dAIH-induced functional recovery 2weeks post-injury. We hypothesized that dAIH-induced functional recovery converts from an adenosine-dependent to a serotonin-dependent, adenosine-constrained mechanism with chronic injury. Eight weeks post-C2HS, rats began dAIH (10, 5-min episodes, 10.5% O2; 5-min intervals; 7days) followed by AIH 3× per week (3×wAIH) for 8 additional weeks with/without systemic A2A receptor inhibition (KW6002) on each AIH exposure day. Tidal volume (VT) and bilateral diaphragm (Dia) and T2 external intercostal motor activity were assessed in unanesthetized rats breathing air and during maximum chemoreflex stimulation (MCS: 7% CO2, 10.5% O2). Nine weeks post-C2HS, dAIH increased VT versus time controls (p<0.05), an effect enhanced by KW6002 (p<0.05). dAIH increased bilateral Dia activity (p<0.05), and KW6002 enhanced this effect in contralateral (p<0.05) and ipsilateral Dia activity (p<0.001), but not T2 inspiratory activity. Functional benefits of combined AIH plus systemic A2A receptor inhibition were maintained for 4weeks. Thus, in rats with chronic injuries: 1) dAIH improves VT and bilateral diaphragm activity; 2) VT recovery is enhanced by A2A receptor inhibition; and 3) functional recovery with A2A receptor inhibition and AIH "reminders" last 4weeks. Combined dAIH and A2A receptor inhibition may be a simple, safe, and effective strategy to accelerate/enhance functional recovery of breathing capacity in patients with respiratory impairment from chronic spinal injury.
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Affiliation(s)
- A Navarrete-Opazo
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, USA; Teletón Children Rehabilitation Institute, Alameda 4620, Santiago, Chile
| | - B J Dougherty
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, USA
| | - G S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, USA; Department of Physical Therapy, University of Florida, Gainesville, FL 32610, USA.
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22
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Sandhu MS, Ross HH, Lee KZ, Ormerod BK, Reier PJ, Fuller DD. Intraspinal transplantation of subventricular zone-derived neural progenitor cells improves phrenic motor output after high cervical spinal cord injury. Exp Neurol 2017; 287:205-215. [PMID: 27302679 PMCID: PMC6154390 DOI: 10.1016/j.expneurol.2016.06.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2016] [Revised: 06/06/2016] [Accepted: 06/09/2016] [Indexed: 01/30/2023]
Abstract
Following spinal cord injury (SCI), intraspinal transplantation of neural progenitor cells (NPCs) harvested from the forebrain sub-ventricular zone (SVZ) can improve locomotor outcomes. Cervical SCI often results in respiratory-related impairments, and here we used an established model cervical SCI (C2 hemisection, C2Hx) to confirm the feasibility of mid-cervical transplantation of SVZ-derived NPCs and the hypothesis that that this procedure would improve spontaneous respiratory motor recovery. NPCs were isolated from the SVZ of enhanced green fluorescent protein (GFP) expressing neonatal rats, and then intraspinally delivered immediately caudal to an acute C2Hx lesion in adult non-GFP rats. Whole body plethysmography conducted at 4 and 8wks post-transplant demonstrated increased inspiratory tidal volume in SVZ vs. sham transplants during hypoxic (P=0.003) or hypercapnic respiratory challenge (P=0.019). Phrenic nerve output was assessed at 8wks post-transplant; burst amplitude recorded ipsilateral to C2Hx was greater in SVZ vs. sham rats across a wide range of conditions (e.g., quiet breathing through maximal chemoreceptor stimulation; P<0.001). Stereological analyses at 8wks post-injury indicated survival of ~50% of transplanted NPCs with ~90% of cells distributed in ipsilateral white matter at or near the injection site. Peak inspiratory phrenic bursting after NPC transplant was positively correlated with the total number of surviving cells (P<0.001). Immunohistochemistry confirmed an astrocytic phenotype in a subset of the transplanted cells with no evidence for neuronal differentiation. We conclude that intraspinal transplantation of SVZ-derived NPCs can improve respiratory recovery following high cervical SCI.
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Affiliation(s)
- M S Sandhu
- University of Florida, Department of Physical Therapy, P.O. Box 100154, Gainesville, FL 32610-0154, United States
| | - H H Ross
- University of Florida, Department of Physical Therapy, P.O. Box 100154, Gainesville, FL 32610-0154, United States
| | - K Z Lee
- University of Florida, Department of Physical Therapy, P.O. Box 100154, Gainesville, FL 32610-0154, United States
| | - B K Ormerod
- University of Florida, Department of Biomedical Engineering, P.O. Box 116131, Gainesville, FL 32611-6131, United States
| | - P J Reier
- University of Florida, Department of Neuroscience, P.O. Box 100244, Gainesville, FL 32610-0244, United States
| | - D D Fuller
- University of Florida, Department of Physical Therapy, P.O. Box 100154, Gainesville, FL 32610-0154, United States.
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23
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Neuroprotective and Neurorestorative Processes after Spinal Cord Injury: The Case of the Bulbospinal Respiratory Neurons. Neural Plast 2016; 2016:7692602. [PMID: 27563469 PMCID: PMC4987469 DOI: 10.1155/2016/7692602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 06/29/2016] [Indexed: 11/18/2022] Open
Abstract
High cervical spinal cord injuries interrupt the bulbospinal respiratory pathways projecting to the cervical phrenic motoneurons resulting in important respiratory defects. In the case of a lateralized injury that maintains the respiratory drive on the opposite side, a partial recovery of the ipsilateral respiratory function occurs spontaneously over time, as observed in animal models. The rodent respiratory system is therefore a relevant model to investigate the neuroplastic and neuroprotective mechanisms that will trigger such phrenic motoneurons reactivation by supraspinal pathways. Since part of this recovery is dependent on the damaged side of the spinal cord, the present review highlights our current understanding of the anatomical neuroplasticity processes that are developed by the surviving damaged bulbospinal neurons, notably axonal sprouting and rerouting. Such anatomical neuroplasticity relies also on coordinated molecular mechanisms at the level of the axotomized bulbospinal neurons that will promote both neuroprotection and axon growth.
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24
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Turner SM, ElMallah MK, Hoyt AK, Greer JJ, Fuller DD. Ampakine CX717 potentiates intermittent hypoxia-induced hypoglossal long-term facilitation. J Neurophysiol 2016; 116:1232-8. [PMID: 27306673 DOI: 10.1152/jn.00210.2016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 06/10/2016] [Indexed: 01/26/2023] Open
Abstract
Glutamatergic currents play a fundamental role in regulating respiratory motor output and are partially mediated by α-amino-3-hydroxy-5-methyl-isoxazole-propionic acid (AMPA) receptors throughout the premotor and motor respiratory circuitry. Ampakines are pharmacological compounds that enhance glutamatergic transmission by altering AMPA receptor channel kinetics. Here, we examined if ampakines alter the expression of respiratory long-term facilitation (LTF), a form of neuroplasticity manifested as a persistent increase in inspiratory activity following brief periods of reduced O2 [intermittent hypoxia (IH)]. Current synaptic models indicate enhanced effectiveness of glutamatergic synapses after IH, and we hypothesized that ampakine pretreatment would potentiate IH-induced LTF of respiratory activity. Inspiratory bursting was recorded from the hypoglossal nerve of anesthetized and mechanically ventilated mice. During baseline (BL) recording conditions, burst amplitude was stable for at least 90 min (98 ± 5% BL). Exposure to IH (3 × 1 min, 15% O2) resulted in a sustained increase in burst amplitude (218 ± 44% BL at 90 min following final bout of hypoxia). Mice given an intraperitoneal injection of ampakine CX717 (15 mg/kg) 10 min before IH showed enhanced LTF (500 ± 110% BL at 90 min). Post hoc analyses indicated that CX717 potentiated LTF only when initial baseline burst amplitude was low. We conclude that under appropriate conditions ampakine pretreatment can potentiate IH-induced respiratory LTF. These data suggest that ampakines may have therapeutic value in the context of hypoxia-based neurorehabilitation strategies, particularly in disorders with blunted respiratory motor output such as spinal cord injury.
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Affiliation(s)
- S M Turner
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida; McKnight Brain Institute, University of Florida, Gainesville, Florida; and Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida
| | - M K ElMallah
- Department of Pediatrics, Division of Pulmonary Medicine, College of Medicine, University of Florida, Gainesville, Florida
| | - A K Hoyt
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida
| | - J J Greer
- Department of Physiology, University of Alberta, Edmonton, Canada
| | - D D Fuller
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida; McKnight Brain Institute, University of Florida, Gainesville, Florida; and Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida
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Gonzalez-Rothi EJ, Armstrong GT, Cerreta AJ, Fitzpatrick GM, Reier PJ, Lane MA, Judge AR, Fuller DD. Forelimb muscle plasticity following unilateral cervical spinal cord injury. Muscle Nerve 2016; 53:475-8. [PMID: 26662579 PMCID: PMC4733411 DOI: 10.1002/mus.25007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/04/2015] [Indexed: 12/22/2022]
Abstract
INTRODUCTION Motor dysfunction and muscle atrophy are well documented in the lower extremity after spinal cord injury. However, the extent and time course of myoplastic changes in forelimb musculature is not clear. METHODS Forelimb muscle morphology and fiber type were evaluated after high cervical hemilesion injury in rats. RESULTS There was significant atrophy of the ipsilateral extensor carpi radialis longus (ECRL) muscle at 2 weeks postinjury, which was subsequently reversed at 8 weeks postinjury. The triceps muscle showed minimal evidence of atrophy after spinal injury. No significant changes in fiber type were observed. CONCLUSIONS These findings indicate a robust capacity for spontaneous myoplasticity after C2 hemisection injury but highlight differential capacity for plasticity within the forelimb muscles.
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Affiliation(s)
- Elisa J. Gonzalez-Rothi
- Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - Gregory T. Armstrong
- Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - Anthony J. Cerreta
- Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - Garrett M. Fitzpatrick
- Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - Paul J. Reier
- Department of Neuroscience, College of Medicine, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - Michael A. Lane
- Department of Neuroscience, College of Medicine, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - Andrew R. Judge
- Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
| | - David D. Fuller
- Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, P.O. Box 100154, 100 S. Newell Drive, Gainesville, FL 32610, USA
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Reorganization of Respiratory Descending Pathways following Cervical Spinal Partial Section Investigated by Transcranial Magnetic Stimulation in the Rat. PLoS One 2016; 11:e0148180. [PMID: 26828648 PMCID: PMC4734706 DOI: 10.1371/journal.pone.0148180] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2015] [Accepted: 01/14/2016] [Indexed: 01/24/2023] Open
Abstract
High cervical spinal cord injuries lead to permanent respiratory deficits. One preclinical model of respiratory insufficiency in adult rats is the C2 partial injury which causes unilateral diaphragm paralysis. This model allows the investigation of a particular population of respiratory bulbospinal axons which cross the midline at C3-C6 spinal segment, namely the crossed phrenic pathway. Transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to study supraspinal descending respiratory pathways in the rat. Interestingly, a lateral C2 injury does not affect the amplitude and latency of the largest motor-evoked potential recorded from the diaphragm (MEPdia) ipsilateral to the injury in response to a single TMS pulse, compared to a sham animal. Although the rhythmic respiratory activity on the contralateral diaphragm is preserved at 7 days post-injury, no diaphragm activity can be recorded on the injured side. However, a profound reorganization of the MEPdia evoked by TMS can be observed. The MEPdia is reduced on the non-injured rather than the injured side. This suggests an increase in ipsilateral phrenic motoneurons excitability. Moreover, correlations between MEPdia amplitude and spontaneous contralateral diaphragmatic activity were observed. The larger diaphragm activity correlated with a larger MEPdia on the injured side, and a smaller MEPdia on the non-injured side. This suggests, for the first time, the occurrence of a functional neuroplasticity process involving changes in motoneuron excitability balance between the injured and non-injured sides at a short post-lesional delay.
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Satkunendrarajah K, Nassiri F, Karadimas SK, Lip A, Yao G, Fehlings MG. Riluzole promotes motor and respiratory recovery associated with enhanced neuronal survival and function following high cervical spinal hemisection. Exp Neurol 2015; 276:59-71. [PMID: 26394202 DOI: 10.1016/j.expneurol.2015.09.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 08/03/2015] [Accepted: 09/19/2015] [Indexed: 10/23/2022]
Abstract
Cervical spinal cord injury (SCI) can result in devastating functional deficits that involve the respiratory and hand function. The mammalian spinal cord has limited ability to regenerate and restore meaningful functional recovery following SCI. Riluzole, 2-amino-6-trifluoromethoxybenzothiazole, an anti-glutamatergic drug has been shown to reduce excitotoxicity and confer neuroprotection at the site of injury following experimental SCI. Based on promising preclinical studies, riluzole is currently under Phase III clinical trial for the treatment of SCI (ClinicalTrials.gov: NCT01597518). Riluzole's anti-glutamatergic role has the potential to regulate neuronal function and provide neuroprotection and influence glutamatergic connections distal to the initial injury leading to enhanced functional recovery following SCI. In order to investigate this novel role of riluzole we used a high cervical hemisection model of SCI, which interrupts all descending input to motoneurons innervating the ipsilateral forelimb and diaphragm muscles. Following C2 spinal cord hemisection, animals were placed into one of two groups: one group received riluzole (8 mg/kg) 1 h after injury and every 12 h thereafter for 7 days at 6 mg/kg, while the second group of injured rats received vehicle solution for the same duration of time. A third group of sham injured rats underwent a C2 laminectomy without hemisection and served as uninjured control rats. Interestingly, this study reports a significant loss of motoneurons within the cervical spinal cord caudal to C2 hemisection injury. Disruption of descending input led to a decrease in glutamatergic synapses and motoneurons caudal to the injury while riluzole treatment significantly limited this decline. Functionally, Hoffmann reflex recordings revealed an increase in the excitability of the remaining ipsilateral cervical motoneurons and significant improvements in skilled and unskilled forelimb function and respiratory motor function in the riluzole-treated animals. In conclusion, using a C2 hemisection injury model, this study provides novel evidence of motoneuron loss caudal to the injury and supports riluzole's capacity to promote neuronal preservation and function of neural network caudal to the SCI resulting in early and sustained functional improvements.
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Affiliation(s)
- K Satkunendrarajah
- Department of Genetics and Development, Toronto Western Research Institute, and Spinal Program, Krembil Neuroscience Center, University Health Network, Toronto, Ontario, Canada
| | - F Nassiri
- Department of Genetics and Development, Toronto Western Research Institute, and Spinal Program, Krembil Neuroscience Center, University Health Network, Toronto, Ontario, Canada
| | - S K Karadimas
- Department of Surgery, University of Toronto, Ontario, Canada
| | - A Lip
- Department of Genetics and Development, Toronto Western Research Institute, and Spinal Program, Krembil Neuroscience Center, University Health Network, Toronto, Ontario, Canada
| | - G Yao
- Department of Genetics and Development, Toronto Western Research Institute, and Spinal Program, Krembil Neuroscience Center, University Health Network, Toronto, Ontario, Canada
| | - M G Fehlings
- Department of Genetics and Development, Toronto Western Research Institute, and Spinal Program, Krembil Neuroscience Center, University Health Network, Toronto, Ontario, Canada; Department of Surgery, University of Toronto, Ontario, Canada.
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Navarrete-Opazo A, Vinit S, Dougherty BJ, Mitchell GS. Daily acute intermittent hypoxia elicits functional recovery of diaphragm and inspiratory intercostal muscle activity after acute cervical spinal injury. Exp Neurol 2015; 266:1-10. [PMID: 25687551 PMCID: PMC4716671 DOI: 10.1016/j.expneurol.2015.02.007] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Revised: 01/14/2015] [Accepted: 02/06/2015] [Indexed: 01/31/2023]
Abstract
A major cause of mortality after spinal cord injury is respiratory failure. In normal rats, acute intermittent hypoxia (AIH) induces respiratory motor plasticity, expressed as diaphragm (Dia) and second external intercostal (T2 EIC) long-term facilitation (LTF). Dia (not T2 EIC) LTF is enhanced by systemic adenosine 2A (A2A) receptor inhibition in normal rats. We investigated the respective contributions of Dia and T2 EIC to daily AIH-induced functional recovery of breathing capacity with/without A2A receptor antagonist (KW6002, i.p.) following C2 hemisection (C2HS). Rats received daily AIH (dAIH: 10, 5-min episodes, 10.5% O2; 5-min normoxic intervals; 7 successive days beginning 7days post-C2HS) or daily normoxia (dNx) with/without KW6002, followed by weekly (reminder) presentations for 8weeks. Ventilation and EMGs from bilateral diaphragm and T2 EIC muscles were measured with room air breathing (21% O2) and maximum chemoreceptor stimulation ( MCS 7% CO2, 10.5% O2). dAIH increased tidal volume (VT) in C2HS rats breathing room air (dAIH+vehicle: 0.47±0.02, dNx+vehicle: 0.40±0.01ml/100g; p<0.05) and MCS (dAIH+vehicle: 0.83±0.01, dNx+vehicle: 0.73±0.01ml/100g; p<0.001); KW6002 had no significant effect. dAIH enhanced contralateral (uninjured) diaphragm EMG activity, an effect attenuated by KW6002, during room air breathing and MCS (p<0.05). Although dAIH enhanced contralateral T2 EIC EMG activity during room air breathing, KW6002 had no effect. dAIH had no statistically significant effects on diaphragm or T2 EIC EMG activity ipsilateral to injury. Thus, two weeks post-C2HS: 1) dAIH enhances breathing capacity by effects on contralateral diaphragm and T2 EIC activity; and 2) dAIH-induced recovery is A2A dependent in diaphragm, but not T2 EIC. Daily AIH may be a useful in promoting functional recovery of breathing capacity after cervical spinal injury, but A2A receptor antagonists (e.g. caffeine) may undermine its effectiveness shortly after injury.
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Affiliation(s)
- A Navarrete-Opazo
- Department of Comparative Biosciences University of Wisconsin-Madison, Madison, WI 53706, USA
| | - S Vinit
- Department of Comparative Biosciences University of Wisconsin-Madison, Madison, WI 53706, USA
| | - B J Dougherty
- Department of Comparative Biosciences University of Wisconsin-Madison, Madison, WI 53706, USA
| | - G S Mitchell
- Department of Comparative Biosciences University of Wisconsin-Madison, Madison, WI 53706, USA.
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Navarrete-Opazo AA, Vinit S, Mitchell GS. Adenosine 2A receptor inhibition enhances intermittent hypoxia-induced diaphragm but not intercostal long-term facilitation. J Neurotrauma 2014; 31:1975-84. [PMID: 25003645 DOI: 10.1089/neu.2014.3393] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Acute intermittent hypoxia (AIH) elicits diaphragm (Dia) and second external intercostal (T2 EIC) long-term facilitation (LTF) in normal unanesthetized rats. Although AIH-induced phrenic LTF is serotonin dependent, adenosine constrained in anesthetized rats, this has not been tested in unanesthetized animals. Cervical (C2) spinal hemisection (C2HS) abolishes phrenic LTF because of loss of serotonergic inputs 2 weeks post-injury, but LTF returns 8 weeks post-injury. We tested three hypotheses in unanesthetized rats: (1) systemic adenosine 2aA (A2A) receptor inhibition with intraperitoneal (IP) KW6002 enhances Dia and T2 EIC LTF in normal rats; (2) Dia and T2 EIC LTF are expressed after chronic (8 weeks), but not acute (1 week) C2HS; and (3) KW6002 enhances Dia and T2 EIC LTF after chronic (not acute) C2HS. Electromyography radiotelemetry was used to record Dia and T2 EIC activity during normoxia (21% O2), before and after AIH (10, 5-min 10.5% O2, 5-min intervals). In normal rats, KW6002 enhanced DiaLTF versus AIH alone (33.1±4.6% vs. 22.1±6.4% baseline, respectively; p<0.001), but had no effect on T2 EIC LTF (p>0.05). Although Dia and T2 EIC LTF were not observed 2 weeks post-C2HS, LTF was observed in contralateral (uninjured) Dia and T2 EIC 8 weeks post-C2HS (18.7±2.7% and 34.9±4.9% baseline, respectively; p<0.05), with variable ipsilateral expression. KW6002 had no significant effects on contralateral Dia (p=0.447) or T2 EIC LTF (p=0.796). We conclude that moderate AIH induces Dia and T2 EIC LTF after chronic, but not acute cervical spinal injuries. A single A2A receptor antagonist dose enhances AIH-induced Dia LTF in normal rats, but this effect is not significant in chronic (8 weeks) C2HS unanesthetized rats.
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Lee KZ, Chang YS. Recovery of the pulmonary chemoreflex and functional role of bronchopulmonary C-fibers following chronic cervical spinal cord injury. J Appl Physiol (1985) 2014; 117:1188-98. [PMID: 25257870 DOI: 10.1152/japplphysiol.00723.2014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Persistent impairment of pulmonary defense reflexes is a critical factor contributing to pulmonary complications in patients with spinal cord injuries. The pulmonary chemoreflex evoked by activation of bronchopulmonary C-fibers has been reported to be abolished in animals with acute cervical hemisection (C2Hx). The present study examined whether the pulmonary chemoreflex can recover during the chronic injury phase and investigated the role of bronchopulmonary C-fibers on the altered breathing pattern after C2Hx. In the first protocol, bronchopulmonary C-fibers were excited by intrajugular capsaicin administration in uninjured and complete C2Hx animals 8 wk postsurgery. Capsaicin evoked pulmonary chemoreflexes in both groups, but the reflex intensity was significantly weaker in C2Hx animals. To examine whether spared spinal white matter tissue contributes to pulmonary chemoreflex recovery, the reflex was evaluated in animals with different extents of lateral injury. Linear regression analyses revealed that tidal volume significantly correlated with the extent of spared tissue; however, capsaicin-induced apnea was not related to injury severity when the ipsilateral-to-contralateral white matter ratio was <50%. In the second protocol, the influence of background bronchopulmonary C-fiber activity on respiration was investigated by blocking C-fiber conduction via perivagal capsaicin treatment. The rapid shallow breathing of C2Hx animals persisted after perivagal capsaicin treatment despite attenuation of pulmonary chemoreflexes. These results indicate that the pulmonary chemoreflex can recover to some extent following spinal injury, but remains attenuated even when there is moderate spinal tissue sparing, and that altered breathing pattern of C2Hx animals cannot be attributed to endogenous activation of bronchopulmonary C-fibers.
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Affiliation(s)
- Kun-Ze Lee
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan; Institute of Medical Science and Technology, National Sun Yat-sen University, Kaohsiung, Taiwan; Center for Neuroscience, National Sun Yat-sen University, Kaohsiung, Taiwan; and Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung, Taiwan
| | - Yu-Shuo Chang
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan
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Mantilla CB, Greising SM, Stowe JM, Zhan WZ, Sieck GC. TrkB kinase activity is critical for recovery of respiratory function after cervical spinal cord hemisection. Exp Neurol 2014; 261:190-5. [PMID: 24910201 DOI: 10.1016/j.expneurol.2014.05.027] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Revised: 05/27/2014] [Accepted: 05/30/2014] [Indexed: 01/24/2023]
Abstract
Neuroplasticity following spinal cord injury contributes to spontaneous recovery over time. Recent studies highlight the important role of brain-derived neurotrophic factor (BDNF) signaling via the high-affinity tropomyosin-related kinase (Trk) receptor subtype B (TrkB) in recovery of rhythmic diaphragm activity following unilateral spinal hemisection at C2 (C2SH). We hypothesized that TrkB kinase activity is necessary for spontaneous recovery of diaphragm activity post-C2SH. A chemical-genetic approach employing adult male TrkB(F616A) mice (n=49) was used to determine the impact of inhibiting TrkB kinase activity by the phosphoprotein phosphatase 1 inhibitor derivative 1NMPP1 on recovery of ipsilateral hemidiaphragm EMG activity. In mice, C2SH was localized primarily to white matter tracts comprising the lateral funiculus. The extent of damaged spinal cord (~27%) was similar regardless of the presence of functional recovery, consistent with spontaneous recovery reflecting neuroplasticity primarily of contralateral spared descending pathways to the phrenic motor pools. Ipsilateral hemidiaphragm EMG activity was verified as absent in all mice at 3days post-C2SH. By 2weeks after C2SH, ipsilateral hemidiaphragm EMG activity was present in 39% of vehicle-treated mice compared to 7% of 1NMPP1-treated mice (P=0.03). These data support the hypothesis that BDNF/TrkB signaling involving TrkB kinase activity plays a critical role in spontaneous recovery of diaphragm activity following cervical spinal cord injury.
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Affiliation(s)
- Carlos B Mantilla
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA; Department of Anesthesiology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
| | - Sarah M Greising
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
| | - Jessica M Stowe
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
| | - Wen-Zhi Zhan
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
| | - Gary C Sieck
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA; Department of Anesthesiology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
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Keomani E, Deramaudt TB, Petitjean M, Bonay M, Lofaso F, Vinit S. A murine model of cervical spinal cord injury to study post-lesional respiratory neuroplasticity. J Vis Exp 2014. [PMID: 24894020 DOI: 10.3791/51235] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
A cervical spinal cord injury induces permanent paralysis, and often leads to respiratory distress. To date, no efficient therapeutics have been developed to improve/ameliorate the respiratory failure following high cervical spinal cord injury (SCI). Here we propose a murine pre-clinical model of high SCI at the cervical 2 (C2) metameric level to study diverse post-lesional respiratory neuroplasticity. The technique consists of a surgical partial injury at the C2 level, which will induce a hemiparalysis of the diaphragm due to a deafferentation of the phrenic motoneurons from the respiratory centers located in the brainstem. The contralateral side of the injury remains intact and allows the animal recovery. Unlike other SCIs which affect the locomotor function (at the thoracic and lumbar level), the respiratory function does not require animal motivation and the quantification of the deficit/recovery can be easily performed (diaphragm and phrenic nerve recordings, whole body ventilation). This pre-clinical C2 SCI model is a powerful, useful, and reliable pre-clinical model to study various respiratory and non-respiratory neuroplasticity events at different levels (molecular to physiology) and to test diverse putative therapeutic strategies which might improve the respiration in SCI patients.
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Affiliation(s)
- Emilie Keomani
- UFR des sciences de la santé - Simone Veil, Université de Versailles Saint-Quentin-en-Yvelines
| | - Thérèse B Deramaudt
- UFR des sciences de la santé - Simone Veil, Université de Versailles Saint-Quentin-en-Yvelines
| | - Michel Petitjean
- UFR des sciences de la santé - Simone Veil, Université de Versailles Saint-Quentin-en-Yvelines; Service de Physiologie - Explorations fonctionnelles, Hôpital Ambroise Paré
| | - Marcel Bonay
- UFR des sciences de la santé - Simone Veil, Université de Versailles Saint-Quentin-en-Yvelines; Service de Physiologie - Explorations fonctionnelles, Hôpital Ambroise Paré
| | - Frédéric Lofaso
- UFR des sciences de la santé - Simone Veil, Université de Versailles Saint-Quentin-en-Yvelines; Services de Physiologie, Explorations Fonctionnelles, Réanimation Médicale et Centre d'Investigation Clinique et d'Innovation Technologique (Unité Inserm 805), Université de Versailles Saint-Quentin-en-Yvelines
| | - Stéphane Vinit
- UFR des sciences de la santé - Simone Veil, Université de Versailles Saint-Quentin-en-Yvelines;
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Warren PM, Alilain WJ. The challenges of respiratory motor system recovery following cervical spinal cord injury. PROGRESS IN BRAIN RESEARCH 2014; 212:173-220. [DOI: 10.1016/b978-0-444-63488-7.00010-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Lee KZ, Dougherty BJ, Sandhu MS, Lane MA, Reier PJ, Fuller DD. Phrenic motoneuron discharge patterns following chronic cervical spinal cord injury. Exp Neurol 2013; 249:20-32. [PMID: 23954215 DOI: 10.1016/j.expneurol.2013.08.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Revised: 07/30/2013] [Accepted: 08/06/2013] [Indexed: 11/29/2022]
Abstract
Cervical spinal cord injury (SCI) dramatically disrupts synaptic inputs and triggers biochemical, as well as morphological, plasticity in relation to the phrenic motor neuron (PhMN) pool. Accordingly, our primary purpose was to determine if chronic SCI induces fundamental changes in the recruitment profile and discharge patterns of PhMNs. Individual PhMN action potentials were recorded from the phrenic nerve ipsilateral to lateral cervical (C2) hemisection injury (C2Hx) in anesthetized adult male rats at 2, 4 or 8 wks post-injury and in uninjured controls. PhMNs were phenotypically classified as early (Early-I) or late inspiratory (Late-I), or silent according to discharge patterns. Following C2Hx, the distribution of PhMNs was dominated by Late-I and silent cells. Late-I burst parameters (e.g., spikes per breath, burst frequency and duration) were initially reduced but returned towards control values by 8wks post-injury. In addition, a unique PhMN burst pattern emerged after C2Hx in which Early-I cells burst tonically during hypocapnic inspiratory apnea. We also quantified the impact of gradual reductions in end-tidal CO2 partial pressure (PETCO2) on bilateral phrenic nerve activity. Compared to control rats, as PETCO2 declined, the C2Hx animals had greater inspiratory frequencies (breaths∗min(-1)) and more substantial decreases in ipsilateral phrenic burst amplitude. We conclude that the primary physiological impact of C2Hx on ipsilateral PhMN burst patterns is a persistent delay in burst onset, transient reductions in burst frequency, and the emergence of tonic burst patterns. The inspiratory frequency data suggest that plasticity in brainstem networks is likely to play an important role in phrenic motor output after cervical SCI.
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Affiliation(s)
- Kun-Ze Lee
- Department of Biological Sciences, College of Science, National Sun Yat-sen University, #70 Lien-Hai Rd., Kaohsiung 804, Taiwan; Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, PO Box 100154, 100 S. Newell Dr, Gainesville, FL 32610, USA
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Hoh DJ, Mercier LM, Hussey SP, Lane MA. Respiration following spinal cord injury: evidence for human neuroplasticity. Respir Physiol Neurobiol 2013; 189:450-64. [PMID: 23891679 DOI: 10.1016/j.resp.2013.07.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 07/01/2013] [Accepted: 07/01/2013] [Indexed: 12/17/2022]
Abstract
Respiratory dysfunction is one of the most devastating consequences of cervical spinal cord injury (SCI) with impaired breathing being a leading cause of morbidity and mortality in this population. However, there is mounting experimental and clinical evidence for moderate spontaneous respiratory recovery, or "plasticity", after some spinal cord injuries. Pre-clinical models of respiratory dysfunction following SCI have demonstrated plasticity at neural and behavioral levels that result in progressive recovery of function. Temporal changes in respiration after human SCI have revealed some functional improvements suggesting plasticity paralleling that seen in experimental models-a concept that has been previously under-appreciated. While the extent of spontaneous recovery remains limited, it is possible that enhancing or facilitating neuroplastic mechanisms may have significant therapeutic potential. The next generation of treatment strategies for SCI and related respiratory dysfunction should aim to optimize these recovery processes of the injured spinal cord for lasting functional restoration.
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Affiliation(s)
- Daniel J Hoh
- Department of Neuroscience, College of Medicine, University of Florida, McKnight Brain Institute, Gainesville, FL 32611, USA; Neurological Surgery, College of Medicine, University of Florida, McKnight Brain Institute, Gainesville, FL, 32611, USA
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Nichols NL, Punzo AM, Duncan ID, Mitchell GS, Johnson RA. Cervical spinal demyelination with ethidium bromide impairs respiratory (phrenic) activity and forelimb motor behavior in rats. Neuroscience 2012; 229:77-87. [PMID: 23159317 DOI: 10.1016/j.neuroscience.2012.10.066] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Revised: 10/13/2012] [Accepted: 10/16/2012] [Indexed: 10/27/2022]
Abstract
Although respiratory complications are a major cause of morbidity/mortality in many neural injuries or diseases, little is known concerning mechanisms whereby deficient myelin impairs breathing, or how patients compensate for such changes. Here, we tested the hypothesis that respiratory and forelimb motor functions are impaired in a rat model of focal dorsolateral spinal demyelination (ethidium bromide, EB). Ventilation, phrenic nerve activity and horizontal ladder walking were performed 7-14 days post-C2 injection of EB or vehicle (SHAM). EB caused dorsolateral demyelination at C2-C3 followed by significant spontaneous remyelination at 14 days post-EB. Although ventilation did not differ between groups, ipsilateral integrated phrenic nerve burst amplitude was significantly reduced versus SHAM during chemoreceptor activation at 7 days post-EB but recovered by 14 days. The ratio of ipsi- to contralateral phrenic nerve amplitude correlated with cross-sectional lesion area. This ratio was significantly reduced 7 days post-EB versus SHAM during baseline conditions, and versus SHAM and 14-day groups during chemoreceptor activation. Limb function ipsilateral to EB was impaired 7 days post-EB and partially recovered by 14 days post-EB. EB provides a reversible model of focal, spinal demyelination, and may be a useful model to study mechanisms of functional impairment and recovery via motor plasticity, or the efficacy of new therapeutic interventions to reduce severity or duration of disease.
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Affiliation(s)
- N L Nichols
- Department of Comparative Biosciences, University of Wisconsin, Madison, WI 53706, United States.
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Extensive respiratory plasticity after cervical spinal cord injury in rats: Axonal sprouting and rerouting of ventrolateral bulbospinal pathways. Exp Neurol 2012; 236:88-102. [DOI: 10.1016/j.expneurol.2012.04.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 03/14/2012] [Accepted: 04/11/2012] [Indexed: 01/10/2023]
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Dougherty BJ, Lee KZ, Gonzalez-Rothi EJ, Lane MA, Reier PJ, Fuller DD. Recovery of inspiratory intercostal muscle activity following high cervical hemisection. Respir Physiol Neurobiol 2012; 183:186-92. [PMID: 22705013 DOI: 10.1016/j.resp.2012.06.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 06/01/2012] [Accepted: 06/02/2012] [Indexed: 01/14/2023]
Abstract
Anatomical and neurophysiological evidence indicates that thoracic interneurons can serve a commissural function and activate contralateral motoneurons. Accordingly, we hypothesized that respiratory-related intercostal (IC) muscle electromyogram (EMG) activity would be only modestly impaired by a unilateral cervical spinal cord injury. Inspiratory tidal volume (VT) was recorded using pneumotachography and EMG activity was recorded bilaterally from the 1st to 2nd intercostal space in anesthetized, spontaneously breathing rats. Studies were conducted at 1-3 days, 2 wks or 8 wks following C2 spinal cord hemisection (C2HS). Data were collected during baseline breathing and a brief respiratory challenge (7% CO(2)). A substantial reduction in inspiratory intercostal EMG bursting ipsilateral to the lesion was observed at 1-3 days post-C2HS. However, a time-dependent return of activity occurred such that by 2 wks post-injury inspiratory intercostal EMG bursts ipsilateral to the lesion were similar to age-matched, uninjured controls. The increases in ipsilateral intercostal EMG activity occurred in parallel with increases in VT following the injury (R=0.55; P<0.001). We conclude that plasticity occurring within a "crossed-intercostal" circuitry enables a robust, spontaneous recovery of ipsilateral intercostal activity following C2HS in rats.
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Affiliation(s)
- B J Dougherty
- University of Florida, College of Medicine, McKnight Brain Institute, Department of Neuroscience, Gainesville, FL 32611, United States
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Nicaise C, Hala TJ, Frank DM, Parker JL, Authelet M, Leroy K, Brion JP, Wright MC, Lepore AC. Phrenic motor neuron degeneration compromises phrenic axonal circuitry and diaphragm activity in a unilateral cervical contusion model of spinal cord injury. Exp Neurol 2012; 235:539-52. [PMID: 22465264 DOI: 10.1016/j.expneurol.2012.03.007] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Accepted: 03/15/2012] [Indexed: 12/23/2022]
Abstract
Respiratory dysfunction is the leading cause of morbidity and mortality following traumatic spinal cord injury (SCI). Injuries targeting mid-cervical spinal cord regions affect the phrenic motor neuron pool that innervates the diaphragm, the primary respiratory muscle of inspiration. Contusion-type injury in the cervical spinal cord is one of the most common forms of human SCI; however, few studies have evaluated mid-cervical contusion in animal models or characterized consequent histopathological and functional effects of degeneration of phrenic motor neuron-diaphragm circuitry. In an attempt to target the phrenic motor neuron pool, two unilateral contusion injury paradigms were tested, a single injury at level C4 and a double injury both at levels C3 and C4, and animals were followed for up to 6 weeks post-injury. Both unilateral cervical injury paradigms are reproducible with no mortality or need for breathing assistance, and are accompanied by phrenic motor neuron loss, phrenic nerve axon degeneration, diaphragm atrophy, denervation and subsequent partial reinnervation at the diaphragm neuromuscular junction, changes in spontaneous diaphragm EMG recordings, and reduction in phrenic nerve compound muscle action potential amplitude. These findings demonstrate significant and chronically persistent respiratory compromise following mid-cervical SCI due to phrenic motor neuron degeneration. These injury paradigms and accompanying analyses provide important tools both for understanding mechanisms of phrenic motor neuron and diaphragm pathology following SCI and for evaluating therapeutic strategies in clinically relevant cervical SCI models.
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Affiliation(s)
- Charles Nicaise
- Department of Neuroscience, Farber Institute for Neurosciences, Thomas Jefferson University Medical College, Philadelphia, PA, 19107, USA
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Treatments to restore respiratory function after spinal cord injury and their implications for regeneration, plasticity and adaptation. Exp Neurol 2011; 235:18-25. [PMID: 22200541 DOI: 10.1016/j.expneurol.2011.12.018] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Revised: 11/18/2011] [Accepted: 12/09/2011] [Indexed: 02/04/2023]
Abstract
Spinal cord injury (SCI) often leads to impaired breathing. In most cases, such severe respiratory complications lead to morbidity and death. However, in the last few years there has been extensive work examining ways to restore this vital function after experimental spinal cord injury. In addition to finding strategies to rescue breathing activity, many of these experiments have also yielded a great deal of information about the innate plasticity and capacity for adaptation in the respiratory system and its associated circuitry in the spinal cord. This review article will highlight experimental SCI resulting in compromised breathing, the various methods of restoring function after such injury, and some recent findings from our own laboratory. Additionally, it will discuss findings about motor and CNS respiratory plasticity and adaptation with potential clinical and translational implications.
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Ferguson AR, Stück ED, Nielson JL. Syndromics: a bioinformatics approach for neurotrauma research. Transl Stroke Res 2011; 2:438-54. [PMID: 22207883 PMCID: PMC3236294 DOI: 10.1007/s12975-011-0121-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Revised: 10/14/2011] [Accepted: 10/18/2011] [Indexed: 12/25/2022]
Abstract
Substantial scientific progress has been made in the past 50 years in delineating many of the biological mechanisms involved in the primary and secondary injuries following trauma to the spinal cord and brain. These advances have highlighted numerous potential therapeutic approaches that may help restore function after injury. Despite these advances, bench-to-bedside translation has remained elusive. Translational testing of novel therapies requires standardized measures of function for comparison across different laboratories, paradigms, and species. Although numerous functional assessments have been developed in animal models, it remains unclear how to best integrate this information to describe the complete translational "syndrome" produced by neurotrauma. The present paper describes a multivariate statistical framework for integrating diverse neurotrauma data and reviews the few papers to date that have taken an information-intensive approach for basic neurotrauma research. We argue that these papers can be described as the seminal works of a new field that we call "syndromics", which aim to apply informatics tools to disease models to characterize the full set of mechanistic inter-relationships from multi-scale data. In the future, centralized databases of raw neurotrauma data will enable better syndromic approaches and aid future translational research, leading to more efficient testing regimens and more clinically relevant findings.
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Affiliation(s)
- Adam R. Ferguson
- Brain and Spinal Injury Center (BASIC), Department of Neurological Surgery, University of California, 1001 Potrero Avenue, Building 1, Room 101, San Francisco, CA 94110 USA
| | - Ellen D. Stück
- Brain and Spinal Injury Center (BASIC), Department of Neurological Surgery, University of California, 1001 Potrero Avenue, Building 1, Room 101, San Francisco, CA 94110 USA
| | - Jessica L. Nielson
- Brain and Spinal Injury Center (BASIC), Department of Neurological Surgery, University of California, 1001 Potrero Avenue, Building 1, Room 101, San Francisco, CA 94110 USA
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Dougherty BJ, Lee KZ, Lane MA, Reier PJ, Fuller DD. Contribution of the spontaneous crossed-phrenic phenomenon to inspiratory tidal volume in spontaneously breathing rats. J Appl Physiol (1985) 2011; 112:96-105. [PMID: 22033536 DOI: 10.1152/japplphysiol.00690.2011] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Spinal cord hemisection at C2 (C2HS) severs bulbospinal inputs to ipsilateral phrenic motoneurons causing transient hemidiaphragm paralysis. The spontaneous crossed-phrenic phenomenon (sCPP) describes the spontaneous recovery of ipsilateral phrenic bursting following C2HS. We reasoned that the immediate (next breath) changes in tidal volume (V(T)) induced by ipsilateral phrenicotomy during spontaneous breathing would provide a quantitative measure of the contribution of the sCPP to postinjury V(T). Using this approach, we tested the hypothesis that the sCPP makes more substantial contributions to V(T) when respiratory drive is increased. Pneumotachography was used to measure V(T) in anesthetized, spontaneously breathing adult male rats at intervals following C2HS. A progressive increase in V(T) (ml/breath) occurred over an 8 wk period following C2HS during both poikilocapnic baseline breathing and hypercapnic respiratory challenge (7% inspired CO(2)). The sCPP did not impact baseline breathing at 1-3 days postinjury since V(T) was unchanged after ipsilateral phrenicotomy. However, by 2 wk post-C2HS, baseline phrenicotomy caused a 16 ± 2% decline in V(T); a comparable 16 ± 4% decline occurred at 8 wk. Contrary to our hypothesis, the phrenicotomy-induced declines in V(T) (%) during hypercapnic respiratory stimulation did not differ from the baseline response at any postinjury time point (all P > 0.11). We conclude that by 2 wk post-C2HS the sCPP makes a meaningful contribution to V(T) that is similar across different levels of respiratory drive.
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Affiliation(s)
- Brendan J Dougherty
- Department of Physical Therapy, McKnight Brain Institute, College of Public Health and Health Professions, University of Florida, Gainesville, Florida, USA
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43
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Windelborn JA, Mitchell GS. Glial activation in the spinal ventral horn caudal to cervical injury. Respir Physiol Neurobiol 2011; 180:61-8. [PMID: 22041654 DOI: 10.1016/j.resp.2011.10.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 10/14/2011] [Accepted: 10/17/2011] [Indexed: 01/24/2023]
Abstract
Microglia and astrocytes play complex roles following spinal cord injury (SCI), contributing to inflammatory processes that both exacerbate injury and promote functional recovery by supporting neuro-protection and neuroplasticity. The crossed phrenic phenomenon (CPP) is an example of respiratory plasticity in which C(2) cervical hemisection (C(2)HS) strengthens crossed-spinal synaptic pathways to phrenic motor neurons ipsilateral to injury. We hypothesized that microglia and astrocytes are activated in the phrenic motor nucleus caudal and ipsilateral to C(2)HS, suggesting their potential for involvement in the CPP. To test this hypothesis, an incomplete cervical spinal hemisection (C(2) lateral injury; C(2)LI) was performed, and rats were allowed to recover for 1, 3, 14 or 28 days before collecting perfused spinal tissues. Microglia (via OX42) and astrocytes [via glial fibrillary acidic protein (GFAP)] were visualized with immunofluorescence microscopy in the C(4)-C(5) ventral horn, the region encompassing most of the phrenic motor nucleus. OX42-occupied fractional area ipsilateral to injury increased with C(2)LI (vs. sham) at 1 (12.5±1.8%, p<0.001), 3 (29.0±1.9%, p<0.001), 14 (26.1±3.1%, p<0.001) and 28 (19.2±2.0%, p<0.001) days post-C(2)LI. GFAP-occupied fractional area also increased with C(2)LI at 3 (24.4±3.2%, p<0.001) and 14 (16.8±8.3%, p=0.012) days, but not at 1 (6.2±3.9%, p=0.262) or 28 (10.6±3.9%, p=0.059) days post-C(2)LI. Thus, microglia and astrocytes are activated in the phrenic motor nucleus caudal to C(2)LI, suggesting that they play a role in functional deficits and/or recovery following spinal injury.
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Affiliation(s)
- James A Windelborn
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Dr. West, Madison, WI 53706, USA.
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44
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Lane MA. Spinal respiratory motoneurons and interneurons. Respir Physiol Neurobiol 2011; 179:3-13. [DOI: 10.1016/j.resp.2011.07.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 07/03/2011] [Accepted: 07/07/2011] [Indexed: 01/30/2023]
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Respiratory function following bilateral mid-cervical contusion injury in the adult rat. Exp Neurol 2011; 235:197-210. [PMID: 21963673 DOI: 10.1016/j.expneurol.2011.09.024] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Revised: 08/27/2011] [Accepted: 09/13/2011] [Indexed: 11/22/2022]
Abstract
The consequences of spinal cord injury (SCI) are often viewed as the result of white matter damage. However, injuries occurring at any spinal level, especially in cervical and lumbar enlargement regions, also entail segmental neuronal loss. Yet, the contributions of gray matter injury and plasticity to functional outcomes are poorly understood. The present study addressed this issue by investigating changes in respiratory function following bilateral C(3)/C(4) contusion injuries at the level of the phrenic motoneuron (PhMN) pool which in the adult rat extends from C(3) to C(5/6) and provides innervation to the diaphragm. Despite extensive white and gray matter pathology associated with two magnitudes of injury severity, ventilation was relatively unaffected during both quiet breathing and respiratory challenge (hypercapnia). On the other hand, bilateral diaphragm EMG recordings revealed that the ability to increase diaphragm activity during respiratory challenge was substantially, and chronically, impaired. This deficit has not been seen following predominantly white matter lesions at higher cervical levels. Thus, the impact of gray matter damage relative to PhMNs and/or interneurons becomes evident during conditions associated with increased respiratory drive. Unaltered ventilatory behavior, despite significant deficits in diaphragm function, suggests compensatory neuroplasticity involving recruitment of other spinal respiratory networks which may entail remodeling of connections. Transynaptic tracing, using pseudorabies virus (PRV), revealed changes in PhMN-related interneuronal labeling rostral to the site of injury, thus offering insight into the potential anatomical reorganization and spinal plasticity following cervical contusion.
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Golder FJ, Fuller DD, Lovett-Barr MR, Vinit S, Resnick DK, Mitchell GS. Breathing patterns after mid-cervical spinal contusion in rats. Exp Neurol 2011; 231:97-103. [PMID: 21683697 PMCID: PMC3172815 DOI: 10.1016/j.expneurol.2011.05.020] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Revised: 05/12/2011] [Accepted: 05/22/2011] [Indexed: 12/13/2022]
Abstract
Respiratory failure is the leading cause of death after cervical spinal injury. We hypothesized that incomplete cervical spinal injuries would alter respiratory pattern and initiate plasticity in the neural control of breathing. Further, we hypothesized that the severity of cervical spinal contusion would correlate with changes in breathing pattern. Fourteen days after C4-C5 contusions, respiratory frequency and tidal volume were measured in unanesthetized Sprague Dawley rats in a whole body plethysmograph. Phrenic motor output was monitored in the same rats which were anesthetized, vagotomized, paralyzed and ventilated to eliminate and/or control sensory feedback that could alter breathing patterns. The extent of spinal injury was approximated histologically by measurements of the injury-induced cyst area in transverse sections; cysts ranged from 2 to 28% of spinal cross-sectional area, and had a unilateral bias. In unanesthetized rats, the severity of spinal injury correlated negatively with tidal volume (R(2)=0.85; p<0.001) and positively with breathing frequency (R(2)=0.65; p<0.05). Thus, the severity of C4-C5 spinal contusion dictates post-injury breathing pattern. In anesthetized rats, phrenic burst amplitude was decreased on the side of injury, and burst frequency correlated negatively with contusion size (R(2)=0.51; p<0.05). A strong correlation between unanesthetized breathing pattern and the pattern of phrenic bursts in anesthetized, vagotomized and ventilated rats suggests that changes in respiratory motor output after spinal injury reflect, at least in part, intrinsic neural mechanisms of CNS plasticity initiated by injury.
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Affiliation(s)
- FJ Golder
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
| | - DD Fuller
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
| | - MR Lovett-Barr
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
| | - S Vinit
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
| | - DK Resnick
- Department of Neurological Surgery, University of Wisconsin, Madison, Wisconsin
| | - GS Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin
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Phrenic motor unit recruitment during ventilatory and non-ventilatory behaviors. Respir Physiol Neurobiol 2011; 179:57-63. [PMID: 21763470 DOI: 10.1016/j.resp.2011.06.028] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Revised: 06/30/2011] [Accepted: 06/30/2011] [Indexed: 02/07/2023]
Abstract
Phrenic motoneurons are located in the cervical spinal cord and innervate the diaphragm muscle, the main inspiratory muscle in mammals. Similar to other skeletal muscles, phrenic motoneurons and diaphragm muscle fibers form motor units which are the final element of neuromotor control. In addition to their role in sustaining ventilation, phrenic motor units are active in other non-ventilatory behaviors important for airway clearance such as coughing or sneezing. Diaphragm muscle fibers comprise all fiber types and are commonly classified based on expression of contractile proteins including myosin heavy chain isoforms. Although there are differences in contractile and fatigue properties across motor units, there is a matching of properties for the motor neuron and muscle fibers within a motor unit. Motor units are generally recruited in order such that fatigue-resistant motor units are recruited earlier and more often than more fatigable motor units. Thus, in sustaining ventilation, fatigue-resistant motor units are likely required. Based on a series of studies in cats, hamsters and rats, an orderly model of motor unit recruitment was proposed that takes into consideration the maximum forces generated by single type-identified diaphragm muscle fibers as well as the proportion of the different motor unit types. Using this model, eupnea can be accomplished by activation of only slow-twitch diaphragm motor units and only a subset of fast-twitch, fatigue-resistant units. Activation of fast-twitch fatigable motor units only becomes necessary when accomplishing tasks that require greater force generation by the diaphragm muscle, e.g., sneezing and coughing.
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48
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Chronic assessment of diaphragm muscle EMG activity across motor behaviors. Respir Physiol Neurobiol 2011; 177:176-82. [PMID: 21414423 DOI: 10.1016/j.resp.2011.03.011] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2011] [Revised: 03/07/2011] [Accepted: 03/09/2011] [Indexed: 11/22/2022]
Abstract
The diaphragm muscle is the main inspiratory muscle in mammals. Quantitative analyses documenting the reliability of chronic diaphragm EMG recordings are lacking. Assessment of ventilatory and non-ventilatory motor behaviors may facilitate evaluating diaphragm EMG activity over time. We hypothesized that normalization of diaphragm EMG amplitude across behaviors provides stable and reliable parameters for longitudinal assessments of diaphragm activity. We found that diaphragm EMG activity shows substantial intra-animal variability over 6 weeks, with coefficient of variation (CV) for different behaviors ∼ 29-42%. Normalization of diaphragm EMG activity to near maximal behaviors (e.g., deep breathing) reduced intra-animal variability over time (CV ∼ 22-29%). Plethysmographic measurements of eupneic ventilation were also stable over 6 weeks (CV ∼ 13% for minute ventilation). Thus, stable and reliable measurements of diaphragm EMG activity can be obtained longitudinally using chronically implanted electrodes by examining multiple motor behaviors. By quantitatively determining the reliability of longitudinal diaphragm EMG analyses, we provide an important tool for evaluating the progression of diseases or injuries that impair ventilation.
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49
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Dunham KA, Siriphorn A, Chompoopong S, Floyd CL. Characterization of a graded cervical hemicontusion spinal cord injury model in adult male rats. J Neurotrauma 2011; 27:2091-106. [PMID: 21087156 DOI: 10.1089/neu.2010.1424] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Most experimental models of spinal cord injury (SCI) in rodents induce damage in the thoracic cord and subsequently examine hindlimb function as an indicator of recovery. In these models, functional recovery is most attributable to white-matter preservation and is less influenced by grey-matter sparing. In contrast, most clinical cases of SCI occur at the lower cervical levels, a region in which both grey-matter and white-matter sparing contribute to functional motor recovery. Thus experimental cervical SCI models are beginning to be developed and used to assess protective and pharmacological interventions following SCI. The objective of this study was to characterize a model of graded cervical hemicontusion SCI with regard to several histological and behavioral outcome measures, including novel forelimb behavioral tasks. Using a commercially available rodent spinal cord impactor, adult male rats received hemicontusion SCI at vertebral level C5 at 100, 200, or 300 kdyn force, to produce mild, moderate, or severe injury severities. Tests of skilled and unskilled forelimb and locomotor function were employed to assess functional recovery, and spinal cord tissue was collected to assess lesion severity. Deficits in skilled and unskilled forelimb function and locomotion relating to injury severity were observed, as well as decreases in neuronal numbers, white-matter area, and white-matter gliosis. Significant correlations were observed between behavioral and histological data. Taken together, these data suggest that the forelimb functional and locomotor assessments employed here are sensitive enough to measure functional changes, and that this hemicontusion model can be used to evaluate potential protective and regenerative therapeutic strategies.
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Affiliation(s)
- Kelly A Dunham
- Department of Physical Medicine and Rehabilitation, Center for Glial Biology in Medicine, University of Alabama-Birmingham, Birmingham, Alabama 35249, USA
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50
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Lee KZ, Fuller DD. Neural control of phrenic motoneuron discharge. Respir Physiol Neurobiol 2011; 179:71-9. [PMID: 21376841 DOI: 10.1016/j.resp.2011.02.014] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 02/23/2011] [Accepted: 02/25/2011] [Indexed: 01/09/2023]
Abstract
Phrenic motoneurons (PMNs) provide a synaptic relay between bulbospinal respiratory pathways and the diaphragm muscle. PMNs also receive propriospinal inputs, although the functional role of these interneuronal projections has not been established. Here we review the literature regarding PMN discharge patterns during breathing and the potential mechanisms that underlie PMN recruitment. Anatomical and neurophysiological studies indicate that PMNs form a heterogeneous pool, with respiratory-related PMN discharge and recruitment patterns likely determined by a balance between intrinsic MN properties and extrinsic synaptic inputs. We also review the limited literature regarding PMN bursting during respiratory plasticity. Differential recruitment or rate modulation of PMN subtypes may underlie phrenic motor plasticity following neural injury and/or respiratory stimulation; however, this possibility remains relatively unexplored.
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Affiliation(s)
- Kun-Ze Lee
- University of Florida, College of Public Health and Health Professions, McKnight Brain Institute, Department of Physical Therapy, PO Box 100154, 100 S. Newell Dr, Gainesville, FL 32610, United States
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