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Fogarty MJ, Sieck GC. Spinal cord injury and diaphragm neuromotor control. Expert Rev Respir Med 2020; 14:453-464. [PMID: 32077350 PMCID: PMC7176525 DOI: 10.1080/17476348.2020.1732822] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 02/18/2020] [Indexed: 12/22/2022]
Abstract
Introduction: Neuromotor control of diaphragm muscle and the recovery of diaphragm activity following spinal cord injury have been narrowly focused on ventilation. By contrast, the understanding of neuromotor control for non-ventilatory expulsive/straining maneuvers (including coughing, defecation, and parturition) is relatively impoverished. This variety of behaviors are achieved via the recruitment of the diverse array of motor units that comprise the diaphragm muscle.Areas covered: The neuromotor control of ventilatory and non-ventilatory behaviors in health and in the context of spinal cord injury is explored. Particular attention is played to the neuroplasticity of phrenic motor neurons in various models of cervical spinal cord injury.Expert opinion: There is a remarkable paucity in our understanding of neuromotor control of maneuvers in spinal cord injury patients. Dysfunction of these expulsive/straining maneuvers reduces patient quality of life and contributes to severe morbidity and mortality. As spinal cord injury patient life expectancies continue to climb steadily, a nexus of spinal cord injury and age-associated comorbidities are likely to occur. While current research remains concerned only with the minutiae of ventilation, the major functional deficits of this clinical cohort will persist intractably. We posit some future research directions to avoid this scenario.
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Affiliation(s)
- Matthew J Fogarty
- 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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Porzionato A, Stocco E, Guidolin D, Agnati L, Macchi V, De Caro R. Receptor-Receptor Interactions of G Protein-Coupled Receptors in the Carotid Body: A Working Hypothesis. Front Physiol 2018; 9:697. [PMID: 29930516 PMCID: PMC6000251 DOI: 10.3389/fphys.2018.00697] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2018] [Accepted: 05/18/2018] [Indexed: 12/15/2022] Open
Abstract
In the carotid body (CB), a wide series of neurotransmitters and neuromodulators have been identified. They are mainly produced and released by type I cells and act on many different ionotropic and metabotropic receptors located in afferent nerve fibers, type I and II cells. Most metabotropic receptors are G protein-coupled receptors (GPCRs). In other transfected or native cells, GPCRs have been demonstrated to establish physical receptor–receptor interactions (RRIs) with formation of homo/hetero-complexes (dimers or receptor mosaics) in a dynamic monomer/oligomer equilibrium. RRIs modulate ligand binding, signaling, and internalization of GPCR protomers and they are considered of relevance for physiology, pharmacology, and pathology of the nervous system. We hypothesize that RRI may also occur in the different structural elements of the CB (type I cells, type II cells, and afferent fibers), with potential implications in chemoreception, neuromodulation, and tissue plasticity. This ‘working hypothesis’ is supported by literature data reporting the contemporary expression, in type I cells, type II cells, or afferent terminals, of GPCRs which are able to physically interact with each other to form homo/hetero-complexes. Functional data about cross-talks in the CB between different neurotransmitters/neuromodulators also support the hypothesis. On the basis of the above findings, the most significant homo/hetero-complexes which could be postulated in the CB include receptors for dopamine, adenosine, ATP, opioids, histamine, serotonin, endothelin, galanin, GABA, cannabinoids, angiotensin, neurotensin, and melatonin. From a methodological point of view, future studies should demonstrate the colocalization in close proximity (less than 10 nm) of the above receptors, through biophysical (i.e., bioluminescence/fluorescence resonance energy transfer, protein-fragment complementation assay, total internal reflection fluorescence microscopy, fluorescence correlation spectroscopy and photoactivated localization microscopy, X-ray crystallography) or biochemical (co-immunoprecipitation, in situ proximity ligation assay) methods. Moreover, functional approaches will be able to show if ligand binding to one receptor produces changes in the biochemical characteristics (ligand recognition, decoding, and trafficking processes) of the other(s). Plasticity aspects would be also of interest, as development and environmental stimuli (chronic continuous or intermittent hypoxia) produce changes in the expression of certain receptors which could potentially invest the dynamic monomer/oligomer equilibrium of homo/hetero-complexes and the correlated functional implications.
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Affiliation(s)
| | - Elena Stocco
- Department of Neuroscience, University of Padua, Padua, Italy
| | - Diego Guidolin
- Department of Neuroscience, University of Padua, Padua, Italy
| | - Luigi Agnati
- Department of Diagnostic, Clinical Medicine and Public Health, University of Modena and Reggio Emilia, Modena, Italy
| | - Veronica Macchi
- Department of Neuroscience, University of Padua, Padua, Italy
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Xu S, Zhu W, Shao M, Zhang F, Guo J, Xu H, Jiang J, Ma X, Xia X, Zhi X, Zhou P, Lu F. Ecto-5'-nucleotidase (CD73) attenuates inflammation after spinal cord injury by promoting macrophages/microglia M2 polarization in mice. J Neuroinflammation 2018; 15:155. [PMID: 29788960 PMCID: PMC5964922 DOI: 10.1186/s12974-018-1183-8] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 04/29/2018] [Indexed: 12/15/2022] Open
Abstract
Background Immune activation, specifically activation of macrophages and resident microglia, leading to inflammation is a key component in the progression of spinal cord injury (SCI). Macrophages/microglia exist in two states—the classically activated M1 phenotype that confers pro-inflammatory effects or the alternatively activated M2 phenotype that confers anti-inflammatory effects. Ecto-5′-nucleotidase (CD73) is an immunosuppressive molecule intricately involved in adaptive and innate immune responses and is able to dephosphorylate AMP to adenosine. However, it is not known if CD73 is able to modulate the macrophages/microglia transformation between the M1 and M2 phenotypes. Methods We used gene-deficient mice to determine the role of CD73 in macrophages/microglia polarization post-SCI in vivo. We used small interference RNA (siRNA) or pcDNA3.1 to inhibit or overexpress CD73 in BV2 cells to verify anterior discovery in vitro. A combination of molecular and histological methods was used to detect the macrophages/microglia polarization and explore the mechanism both in vivo and in vitro. Results We found that SCI induced the upregulation of CD73 expression. CD73 deficient mice were noted to demonstrate overwhelming immune responses, few anti-inflammatory phenotype macrophages/microglia, and had a poorer locomotor recovery in comparison to wild-type mice that were also inflicted with SCI. In vitro studies found that CD73 suppression inhibited the expression of characteristic microglial anti-inflammatory polarization markers in BV2 cells, while the converse was noted in CD73 overexpression. Subsequent experiments confirmed that CD73 promoted microglia alternative activation by stimulating p38 MAPK. Conclusion We were able to conclude that CD73 imparts neuroprotective effects by mediating macrophages/microglia polarization. These findings allow for better understanding of the modulatory factors involved in triggering the change in macrophages/microglia phenotypes, therefore uncovering additional molecules and pathways that may be targeted in the innovation of novel SCI therapies. Electronic supplementary material The online version of this article (10.1186/s12974-018-1183-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Shun Xu
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Wei Zhu
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Minghao Shao
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Fan Zhang
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Ji Guo
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Haocheng Xu
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Jianyuan Jiang
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Xiaosheng Ma
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Xinlei Xia
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China
| | - Xiuling Zhi
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Fudan University, No.138, Yixueyuan Road, Shanghai, 200032, China
| | - Ping Zhou
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Fudan University, No.138, Yixueyuan Road, Shanghai, 200032, China.
| | - Feizhou Lu
- Department of Orthopedics, Huashan Hospital, Fudan University, No.12, Wulumuqi middle Road, Jingan District, Shanghai, 200040, China. .,The Fifth People's Hospital of Shanghai, Fudan University, Shanghai, China.
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Pulmonary outcomes following specialized respiratory management for acute cervical spinal cord injury: a retrospective analysis. Spinal Cord 2017; 55:559-565. [PMID: 28220822 PMCID: PMC5457341 DOI: 10.1038/sc.2017.10] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Revised: 12/29/2016] [Accepted: 01/05/2017] [Indexed: 12/25/2022]
Abstract
Study Design Retrospective analysis. Objectives To identify multivariate interactions of respiratory function that are sensitive to spinal cord injury level and pharmacological treatment to promote strategies that increases successful liberation from mechanical ventilation. Setting United States regional spinal cord injury (SCI) treatment center. Methods Retrospective chart review of patients consecutively admitted to Santa Clara Valley Medical Center (SCVMC) between May 2013 and December 2014 for ventilator weaning with C1-5 AIS A or B SCI, < 3 months from injury and who had a tracheostomy in place. A non-linear, categorical principal component analysis (NL-PCA) was performed to test the multivariate interaction of respiratory outcomes from patients (N=36) being weaned off ventilator support after acute SCI with (N=15) or without (N=21) theophylline treatment. Results 36 patients met inclusion criteria (2 C1, 5 C2, 11 C3, 14 C4, 4 C5). The NL-PCA returned 3 independent components that accounted for 95% of the variance in the dataset. Multivariate general linear models (GLM) hypothesis tests revealed a significant syndromic interaction between theophylline treatment and SCI level (Wilks’ Lambda, p=0.028, F(12,64)=2.116, η2=0.256, 1−β=0.838), with post-hoc testing demonstrating a significant interaction on PC1, explained by a positive correlation between improved forced vital capacity and time it took to reach 16 hours of ventilator free breathing. Thirty-three patients (92%) achieved 16 hours ventilator-free breathing (VFB), 30 (83%) achieved 24 hours VFB. Conclusions We suspect that some portion of the high success rate of ventilator weaning may be attributable to theophylline use in higher cervical SCI; in addition to our aggressive regimen of high volume ventilation, medication optimization, and pulmonary toilet (positive pressure treatments and mechanical insufflation-exsufflation).
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Heitzmann D, Buehler P, Schweda F, Georgieff M, Warth R, Thomas J. The in vivo respiratory phenotype of the adenosine A1 receptor knockout mouse. Respir Physiol Neurobiol 2015; 222:16-28. [PMID: 26593641 DOI: 10.1016/j.resp.2015.11.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Revised: 11/09/2015] [Accepted: 11/09/2015] [Indexed: 10/22/2022]
Abstract
The nucleoside adenosine has been implicated in the regulation of respiration, especially during hypoxia in the newborn. In this study the role of adenosine A1 receptors for the control of respiration was investigated in vivo. To this end, respiration of unrestrained adult and neonatal adenosine A1 receptor knockout mice (A1R(-/-)) was measured in a plethysmographic device. Under control conditions (21% O2) and mild hypoxia (12-15% O2) no difference of respiratory parameters was observed between adult wildtype (A1R(+/+)) and A1R(-/-) mice. Under more severe hypoxia (6-10% O2) A1R(+/+) mice showed, after a transient increase of respiration, a decrease of respiration frequency (fR) and tidal volume (VT) leading to a decrease of minute volume (MV). This depression of respiration during severe hypoxia was absent in A1R(-/-) mice which displayed a stimulated respiration as indicated by the enhancement of MV by some 50-60%. During hypercapnia-hyperoxia (3-10% CO2/97-90 % O2), no obvious differences in respiration of A1R(-/-) and A1R(+/+) was observed. In neonatal mice, the respiratory response to hypoxia was surprisingly similar in both genotypes. However, neonatal A1R(-/-) mice appeared to have more frequently periods of apnea during hypoxia and in the post-hypoxic control period. In conclusion, these data indicate that the adenosine A1 receptor is an important molecular component mediating hypoxic depression in adult mice and it appears to stabilize respiration of neonatal mice.
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Affiliation(s)
- Dirk Heitzmann
- Medizinische Klinik, University hospital Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, D-68167 Mannheim, Germany
| | - Philipp Buehler
- University children's hospital, Steinwiesstr. 75, CH-8032 Zürich, Switzerland
| | - Frank Schweda
- Institute of Physiology, University of Regensburg, D-93053 Regensburg, Germany
| | - Michael Georgieff
- Department of Anaesthesiology, University of Ulm, D-89075 Ulm, Germany
| | - Richard Warth
- Institute of Physiology, University of Regensburg, D-93053 Regensburg, Germany
| | - Joerg Thomas
- University children's hospital, Steinwiesstr. 75, CH-8032 Zürich, Switzerland.
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Altered expression of adenosine A1 and A2A receptors in the carotid body and nucleus tractus solitarius of adult male and female rats following neonatal caffeine treatment. Brain Res 2009; 1287:74-83. [DOI: 10.1016/j.brainres.2009.06.064] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Revised: 06/12/2009] [Accepted: 06/19/2009] [Indexed: 12/26/2022]
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Nantwi KD. Recovery of respiratory activity after C2 hemisection (C2HS): involvement of adenosinergic mechanisms. Respir Physiol Neurobiol 2009; 169:102-14. [PMID: 19651244 DOI: 10.1016/j.resp.2009.07.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Revised: 07/14/2009] [Accepted: 07/14/2009] [Indexed: 11/18/2022]
Abstract
Consequences of spinal cord injury (SCI) depend on the level and extent of injury. Cervical SCI often results in a compromised respiratory system. Primary treatment of SCI patients with respiratory insufficiency continues to be with mechanical ventilatory support. In an animal model of SCI, an upper cervical spinal cord hemisection paralyzes the hemidiaphragm ipsilateral to the side of injury. However, a latent respiratory motor pathway can be activated to restore respiratory function after injury. In this review, restoration of respiratory activity following systemic administration of theophylline, a respiratory stimulant will be discussed. Pharmacologically, theophylline is a non-specific adenosine receptor antagonist, a phosphodiesterase inhibitor and a bronchodilator. It has been used in the treatment of asthma and other respiratory-related diseases such as chronic obstructive pulmonary disease (COPD) and in treatment of apnea in premature infants. However, the clinical use of theophylline to improve respiration in SCI patients with respiratory deficits is a more recent approach. This review will focus on the use of theophylline to restore respiratory activity in an animal model of SCI. In this model, a C2 hemisection (C2HS) interrupts the major descending respiratory pathways and paralyzes the ipsilateral hemidiaphragm. The review also highlights involvement of central and peripheral adenosine receptors in functional restitution. Biochemical binding assays that highlight changes in adenosine receptors after chronic theophylline administration are discussed as they pertain to understanding adenosine receptor-mediation in functional recovery. Finally, the clinical application of theophylline in SCI patients with respiratory deficits in particular is discussed.
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Affiliation(s)
- Kwaku D Nantwi
- Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI 48202, USA.
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Inskip JA, Ramer LM, Ramer MS, Krassioukov AV. Autonomic assessment of animals with spinal cord injury: tools, techniques and translation. Spinal Cord 2008; 47:2-35. [DOI: 10.1038/sc.2008.61] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Abstract
Acute intermittent hypoxia elicits a form of spinal, brain-derived neurotrophic factor (BDNF)-dependent respiratory plasticity known as phrenic long-term facilitation. Ligands that activate G(s)-protein-coupled receptors, such as the adenosine 2a receptor, mimic the effects of neurotrophins in vitro by transactivating their high-affinity receptor tyrosine kinases, the Trk receptors. Thus, we hypothesized that A2a receptor agonists would elicit phrenic long-term facilitation by mimicking the effects of BDNF on TrkB receptors. Here we demonstrate that spinal A2a receptor agonists transactivate TrkB receptors in the rat cervical spinal cord near phrenic motoneurons, thus inducing long-lasting (hours) phrenic motor facilitation. A2a receptor activation increased phosphorylation and new synthesis of an immature TrkB protein, induced TrkB signaling through Akt, and strengthened synaptic pathways to phrenic motoneurons. RNA interference targeting TrkB mRNA demonstrated that new TrkB protein synthesis is necessary for A2a-induced phrenic motor facilitation. A2a receptor activation also increased breathing in unanesthetized rats, and improved breathing in rats with cervical spinal injuries. Thus, small, highly permeable drugs (such as adenosine receptor agonists) that transactivate TrkB receptors may provide an effective therapeutic strategy in the treatment of patients with ventilatory control disorders, such as obstructive sleep apnea, or respiratory insufficiency after spinal injury or during neurodegenerative diseases.
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Vinit S, Gauthier P, Stamegna JC, Kastner A. High Cervical Lateral Spinal Cord Injury Results in Long-Term Ipsilateral Hemidiaphragm Paralysis. J Neurotrauma 2006; 23:1137-46. [PMID: 16866626 DOI: 10.1089/neu.2006.23.1137] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Although axon regeneration is limited in the central nervous system, partial lesions of the spinal cord induce neuroplasticity processes that can lead to spontaneous functional improvement. To determine whether such compensatory mechanisms occur in the respiratory system, we analyzed the incidence of partial injury of the cervical spinal cord on diaphragm activity in adult rats. We show that a section of the lateral area of the C2 cervical spinal cord induces complete phrenic nerve inactivation and ipsilateral hemidiaphragm paralysis, whereas medial or dorsolateral sections had only a moderate effect on respiratory activity. In the case of lateral hemisection, activity of the ipsilateral phrenic nerve was partially restored after a lapse of 3 months. No spontaneous diaphragm recovery was observed, however, even after a lapse of several months in the case of hemisection or lateral section. Ipsilateral hemidiaphragm activity could however be restored after transection of the contralateral phrenic nerve, by activation of the "crossed phrenic phenomenon" (involving activation of previously latent respiratory contralateral pathways crossing the midline). These data suggest that the respiratory system develops important long-term plasticity processes at the level of phrenic motoneuron innervation. However, they do not by themselves allow substantial diaphragm recovery, underscoring the continued need for developing repair strategies. These studies also validates the use of the respiratory system as a model to evaluate the functional incidence of repair strategies not only after hemisection but also after more limited sectioning restricted to the lateral side of the cervical cord.
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Affiliation(s)
- Stéphane Vinit
- Laboratoire de Physiologie Neurovégétative, Université Paul Cézanne Aix-Marseille III, Marseille, France
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James E, Nantwi KD. Involvement of peripheral adenosine A2 receptors in adenosine A1 receptor-mediated recovery of respiratory motor function after upper cervical spinal cord hemisection. J Spinal Cord Med 2006; 29:57-66. [PMID: 16572566 PMCID: PMC1864794 DOI: 10.1080/10790268.2006.11753857] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
BACKGROUND/OBJECTIVE In an animal model of spinal cord injury, a latent respiratory motor pathway can be pharmacologically activated through central adenosine A1 receptor antagonism to restore respiratory function after cervical (C2) spinal cord hemisection that paralyzes the hemidiaphragm ipsilateral to injury. Although respiration is modulated by central and peripheral mechanisms, putative involvement of peripheral adenosine A2 receptors in functional recovery in our model is untested. The objective of this study was to assess the effects of peripherally located adenosine A2 receptors on recovery of respiratory function after cervical (C2) spinal cord hemisection. METHODS Respiratory activity was electrophysiologically assessed (under standardized recording conditions) in C2-hemisected adult rats with the carotid bodies intact (H-CBI; n=12) or excised (H-CBE; n=12). Animals were administered the adenosine A2 receptor agonist, CGS-21680, followed by the A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), or administered DPCPX alone. Recovered respiratory activity, characterized as drug-induced activity in the previously quiescent left phrenic nerve of C2-hemisected animals in H-CBI and H-CBE rats, was compared. Recovered respiratory activity was calculated by dividing drug-induced activity in the left phrenic nerve by activity in the right phrenic nerve. RESULTS Administration of CGS-21680 before DPCPX (n=6) in H-CBI rats induced a significantly greater recovery (58.5 +/- 3.6%) than when DPCPX (42.6 +/- 4.6%) was administered (n=6) alone. In H-CBE rats, prior administration of CGS-21680 (n=6) did not enhance recovery over that induced by DPCPX (n=6) alone. Recovery in H-CBE rats amounted to 39.7 +/- 3.7% and 38.4 + 4.2%, respectively. CONCLUSIONS Our results suggest that adenosine A2 receptors located in the carotid bodies can enhance the magnitude of adenosine A1 receptor-mediated recovery of respiratory function after C2 hemisection. We conclude that a novel approach of targeting peripheral and central adenosine receptors can be therapeutically beneficial in alleviating compromised respiratory function after cervical spinal cord injury.
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Affiliation(s)
- Elysia James
- Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan
| | - Kwaku D Nantwi
- Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan
- Please address correspondence to Kwaku D. Nantwi, PhD, Wayne State University, School of Medicine, Department of Anatomy and Cell Biology, 540 East Canfield Avenue, Detroit, MI 48202; phone: 313.577.7925; fax: 313.577.3125 (e-mail: )
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Bae H, Nantwi KD, Goshgarian H. Effects of carotid body excision on recovery of respiratory function in C2 hemisected adult rats. Exp Neurol 2005; 195:140-7. [PMID: 15919075 DOI: 10.1016/j.expneurol.2005.04.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2004] [Revised: 03/18/2005] [Accepted: 04/18/2005] [Indexed: 11/16/2022]
Abstract
In a previous study, we described the spontaneous recovery of respiratory motor function in adult rats subjected to a left C2 hemisection 6-16 weeks post-injury without any therapeutic intervention. We extend the previous findings by demonstrating in the present study that rats subjected to a left C2 hemisection with bilateral carotid body excision will also recover respiratory-related activity in the paralyzed ipsilateral hemidiaphragm. However, in this instance, recovery is significantly accelerated; i.e., it is evident as early as 2 weeks after spinal cord injury. Two experimental groups (and noninjured and sham-operated controls) of rats were employed in the study. H-CBE animals were subjected to a left C2 hemisection plus bilateral carotid body excision while H-CBI animals were subjected to a left C2 hemisection only. Carotid body excision was confirmed by the sodium cyanide test. The animals were allowed to survive for 2 weeks after hemisection. Thereafter, electrophysiologic assessment of respiratory activity was conducted in all animals. Spontaneous recovery of respiratory-related activity in the paralyzed hemidiaphragm (indicated by left phrenic nerve activity) was detected in all H-CBE animals while H-CBI animals did not express spontaneous recovery of diaphragmatic activity. The magnitude of recovered activity when expressed as a function of contralateral phrenic nerve activity was 48.8 +/- 3.8%. When expressed as a function of the homolateral phrenic nerve in noninjured animals, the magnitude amounted to 25.6 +/- 2.8%. Although the mechanisms responsible for the apparent early onset of spontaneous recovery are unknown, it is likely that a reorganization of the respiratory circuitry in the CNS may be involved. The significance of the findings is that it may be feasible to modulate the onset of functional recovery following cervical spinal cord injury by specifically targeting peripheral chemoreceptors.
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Affiliation(s)
- Han Bae
- Department of Otolaryngology, Wayne State University, School of Medicine, Detroit, MI 48202, USA
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Nantwi KD, Goshgarian HG. Adenosinergic mechanisms underlying recovery of diaphragm motor function following upper cervical spinal cord injury: potential therapeutic implications. Neurol Res 2005; 27:195-205. [PMID: 15829183 DOI: 10.1179/016164105x21977] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
OBJECTIVES In adult rats, a latent respiratory motor pathway can be pharmacologically activated with 1,3-dimethylxanthine (theophylline) to restore respiratory-related activity to a hemidiaphragm paralysed by an ipsilateral upper cervical (C2) spinal cord hemisection. The purpose of this review is to describe mechanisms that underlie theophylline-induced recovery of respiratory-related function following C2 hemisection and to underscore the therapeutic potential of theophylline therapy in spinal cord injured patients with respiratory deficits. METHODS Theophylline mediates recovery of respiratory-related activity via antagonism of central adenosine A(1) receptors. When administered chronically, the drug restores and maintains recovered function. Since theophylline is an adenosine receptor antagonist with affinity for both the adenosine A(1) and A(2) receptors, we assessed the relative contributions of each receptor to functional recovery. While A(1) receptor antagonism plays a predominant role, activation of the A(2) receptors by specific agonists subserves the A(1) receptor-mediated actions. That is, when an adenosine A(2) receptor agonist is administered first, it primes the system such that subsequent administration of the A(1) antagonist induces a greater degree of recovered respiratory activity than when the antagonist alone is administered. RESULTS Chronic oral administration of theophylline in C2 hemisected animals demonstrates that even when animals have been weaned from the drug, theophylline-induced recovered respiratory actions persist. This suggests that in clinical application, it may not be necessary to maintain patients on long-term theophylline. We have shown that recovery of respiratory-related activity in the ipsilateral phrenic nerve can occur spontaneously 3-4 months after C2 hemisection. Theophylline administration after this post-injury period obliterates/negates the recovery function. This indicates strongly that there is therapeutic window (more acutely after injury) for the initiation of theophylline therapy. We have also demonstrated that peripheral (carotid bodies) adenosine A(1) receptors can be selectively activated to modulate theophylline-induced CNS actions. Blocking central adenosine receptors while simultaneously activating peripheral adenosine receptors minimizes the potential of respiratory muscle fatigue with theophylline. DISCUSSION The significance of the current findings lies in the potential clinical application of theophylline therapy in spinal cord injured patients with respiratory deficits. The ultimate goal of theophylline therapy is to wean ventilator-dependent patients off ventilatory support. Thus far, our animal studies suggest that the onset of theophylline therapy must be soon after injury.
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Affiliation(s)
- Kwaku D Nantwi
- Department of Anatomy and Cell Biology, Wayne State University, School of Medicine, Detroit, MI 48201, USA.
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