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Popp NM, Holmes TC, Streeter KA. Diaphragm stimulation elicits phrenic afferent-induced neuromuscular plasticity. Respir Physiol Neurobiol 2023; 310:104014. [PMID: 36642318 PMCID: PMC9945879 DOI: 10.1016/j.resp.2023.104014] [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: 07/21/2022] [Revised: 12/29/2022] [Accepted: 01/08/2023] [Indexed: 01/15/2023]
Abstract
We hypothesized that activation of phrenic afferents induces diaphragm motor plasticity. In anesthetized and spontaneously breathing rats we delivered 40 Hz, low threshold (twitch and 1.5X twitch threshold), inspiratory-triggered stimulation to the left hemidiaphragm for 30 min to activate ipsilateral phrenic afferents. Diaphragm amplitude ipsilateral and contralateral to stimulation were increased for 60 min following both currents compared to time controls not receiving stimulation. Diaphragm stimulation was repeated in laminectomy controls or following a unilateral C3-C6 dorsal rhizotomy to eliminate phrenic afferent volleys. Laminectomy controls expressed neuromuscular plasticity post-stimulation. In contrast, ipsilateral and contralateral diaphragm amplitude following dorsal rhizotomy was lower than laminectomy controls and no different than time controls, suggesting diaphragm motor plasticity was not induced post-rhizotomy. Our results indicate that diaphragm stimulation induces a novel form of plasticity in the phrenic motor system which requires phrenic afferent activation. Respiratory motor plasticity elicited by diaphragm stimulation may have value as a therapeutic strategy to improve diaphragm output in neuromuscular conditions.
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Affiliation(s)
- Nicole M Popp
- Department of Physical Therapy, Marquette University, Milwaukee, WI, United States
| | - Taylor C Holmes
- Department of Physical Therapy, Marquette University, Milwaukee, WI, United States
| | - Kristi A Streeter
- Department of Physical Therapy, Marquette University, Milwaukee, WI, United States.
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Galer EL, Huang R, Madhavan M, Wang E, Zhou Y, Leiter JC, Lu DC. Cervical Epidural Electrical Stimulation Increases Respiratory Activity through Somatostatin-Expressing Neurons in the Dorsal Cervical Spinal Cord in Rats. J Neurosci 2023; 43:419-432. [PMID: 36639888 PMCID: PMC9864577 DOI: 10.1523/jneurosci.1958-21.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 09/21/2022] [Accepted: 09/29/2022] [Indexed: 12/12/2022] Open
Abstract
We tested the hypothesis that dorsal cervical epidural electrical stimulation (CEES) increases respiratory activity in male and female anesthetized rats. Respiratory frequency and minute ventilation were significantly increased when CEES was applied dorsally to the C2-C6 region of the cervical spinal cord. By injecting pseudorabies virus into the diaphragm and using c-Fos activity to identify neurons activated during CEES, we found neurons in the dorsal horn of the cervical spinal cord in which c-Fos and pseudorabies were co-localized, and these neurons expressed somatostatin (SST). Using dual viral infection to express the inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADD), hM4D(Gi), selectively in SST-positive cells, we inhibited SST-expressing neurons by administering Clozapine N-oxide (CNO). During CNO-mediated inhibition of SST-expressing cervical spinal neurons, the respiratory excitation elicited by CEES was diminished. Thus, dorsal cervical epidural stimulation activated SST-expressing neurons in the cervical spinal cord, likely interneurons, that communicated with the respiratory pattern generating network to effect changes in ventilation.SIGNIFICANCE STATEMENT A network of pontomedullary neurons within the brainstem generates respiratory behaviors that are susceptible to modulation by a variety of inputs; spinal sensory and motor circuits modulate and adapt this output to meet the demands placed on the respiratory system. We explored dorsal cervical epidural electrical stimulation (CEES) excitation of spinal circuits to increase ventilation in rats. We identified dorsal somatostatin (SST)-expressing neurons in the cervical spinal cord that were activated (c-Fos-positive) by CEES. CEES no longer stimulated ventilation during inhibition of SST-expressing spinal neuronal activity, thereby demonstrating that spinal SST neurons participate in the activation of respiratory circuits affected by CEES. This work establishes a mechanistic foundation to repurpose a clinically accessible neuromodulatory therapy to activate respiratory circuits and stimulate ventilation.
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Affiliation(s)
- Erika L Galer
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
- Department of Molecular Cellular and Integrative Physiology, University of California Los Angeles, Los Angeles 90095, California
| | - Ruyi Huang
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
| | - Meghna Madhavan
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
| | - Emily Wang
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
| | - Yan Zhou
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
| | - James C Leiter
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
- Research Service, White River Junction VA Medical Center, White River Junction 05009, Vermont
| | - Daniel C Lu
- Department of Neurosurgery, University of California Los Angeles, Los Angeles 90095, California
- Department of Molecular Cellular and Integrative Physiology, University of California Los Angeles, Los Angeles 90095, California
- Brain Research Institute, University of California Los Angeles, Los Angeles 90095, California
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Streeter KA, Sunshine MD, Davenport PW, Fuller DD. Phrenic afferent activation modulates cardiorespiratory output in the adult rat. J Neurophysiol 2021; 126:2091-2103. [PMID: 34788165 PMCID: PMC8715055 DOI: 10.1152/jn.00433.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 11/10/2021] [Accepted: 11/12/2021] [Indexed: 11/22/2022] Open
Abstract
Phrenic afferents project to brainstem areas responsible for cardiorespiratory control and the mid-cervical spinal cord containing the phrenic motor nucleus. Our purpose was to quantify the impact of small- and large-diameter phrenic afferent activation on phrenic motor output. Anesthetized and ventilated rats received unilateral phrenic nerve stimulation while contralateral phrenic motor output and blood pressure were recorded. Twelve currents of 40-Hz inspiratory-triggered stimulation were delivered (20 s on, 5 min off) to establish current response curves. Stimulation pulse width was varied to preferentially activate large-diameter phrenic afferents (narrow pulse width) and recruit small-diameter fibers (wide pulse width). Contralateral phrenic amplitude was elevated immediately poststimulation at currents above 35 µA for wide and 70 µA for narrow pulse stimulation when compared with animals not receiving stimulation (time controls). Wide pulse width stimulation also increased phrenic burst frequency at currents ≥35 µA, caused a transient decrease in mean arterial blood pressure at currents ≥50 µA, and resulted in a small change in heart rate at 300 µA. Unilateral dorsal rhizotomy attenuated stimulation-induced cardiorespiratory responses indicating that phrenic afferent activation is required. Additional analyses compared phrenic motor amplitude with output before stimulation and showed that episodic activation of phrenic afferents with narrow pulse stimulation can induce short-term plasticity. We conclude that the activation of phrenic afferents 1) enhances contralateral phrenic motor amplitude when large-diameter afferents are activated, and 2) when small-diameter fibers are recruited, the amplitude response is associated with changes in burst frequency and cardiovascular parameters.NEW & NOTEWORTHY Acute, inspiratory-triggered stimulation of phrenic afferents increases contralateral phrenic motor amplitude in adult rats. When small-diameter afferents are recruited, the amplitude response is accompanied by an increase in phrenic burst frequency, a transient decrease in mean arterial blood pressure, and a slight increase in heart rate. Repeated episodes of large-diameter phrenic afferent activation may also be capable of inducing short-term plasticity.
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Affiliation(s)
- Kristi A Streeter
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin
- Center for Research and Rehabilitation, University of Florida, Gainesville, Florida
| | - Michael D Sunshine
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- Center for Research and Rehabilitation, University of Florida, Gainesville, Florida
| | - Paul W Davenport
- Center for Research and Rehabilitation, University of Florida, Gainesville, Florida
- Department of Physiological Sciences, University of Florida, Gainesville, Florida
| | - David D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- Center for Research and Rehabilitation, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
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Sunshine MD, Sutor TW, Fox EJ, Fuller DD. Targeted activation of spinal respiratory neural circuits. Exp Neurol 2020; 328:113256. [PMID: 32087253 DOI: 10.1016/j.expneurol.2020.113256] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 01/31/2020] [Accepted: 02/18/2020] [Indexed: 12/30/2022]
Abstract
Spinal interneurons which discharge in phase with the respiratory cycle have been repeatedly described over the last 50 years. These spinal respiratory interneurons are part of a complex propriospinal network that is synaptically coupled with respiratory motoneurons. This article summarizes current knowledge regarding spinal respiratory interneurons and emphasizes chemical, electrical and physiological methods for activating spinal respiratory neural circuits. Collectively, the work reviewed here shows that activating spinal interneurons can have a powerful impact on spinal respiratory motor output, and can even drive rhythmic bursting in respiratory motoneuron pools under certain conditions. We propose that the primary functions of spinal respiratory neurons include 1) shaping the respiratory pattern into the final efferent motor output from the spinal respiratory nerves; 2) coordinating respiratory muscle activation across the spinal neuraxis; 3) coordinating postural, locomotor and respiratory movements, and 4) enabling plasticity of respiratory motor output in health and disease.
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Affiliation(s)
- Michael D Sunshine
- Department of Physical Therapy, University of Florida, United States of America; McKnight Brain Institute, University of Florida, United States of America; Rehabilitation Science PhD Program, University of Florida, United States of America; Center for Respiratory Research and Rehabilitation, University of Florida, United States of America
| | - Tommy W Sutor
- Department of Physical Therapy, University of Florida, United States of America; Rehabilitation Science PhD Program, University of Florida, United States of America; Center for Respiratory Research and Rehabilitation, University of Florida, United States of America
| | - Emily J Fox
- Department of Physical Therapy, University of Florida, United States of America; Center for Respiratory Research and Rehabilitation, University of Florida, United States of America; Clinical Research Center, Brooks Rehabilitation, Jacksonville, FL, United States of America
| | - David D Fuller
- Department of Physical Therapy, University of Florida, United States of America; McKnight Brain Institute, University of Florida, United States of America; Center for Respiratory Research and Rehabilitation, University of Florida, United States of America.
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Nair J, Streeter KA, Turner SMF, Sunshine MD, Bolser DC, Fox EJ, Davenport PW, Fuller DD. Anatomy and physiology of phrenic afferent neurons. J Neurophysiol 2017; 118:2975-2990. [PMID: 28835527 DOI: 10.1152/jn.00484.2017] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Revised: 08/17/2017] [Accepted: 08/17/2017] [Indexed: 12/23/2022] Open
Abstract
Large-diameter myelinated phrenic afferents discharge in phase with diaphragm contraction, and smaller diameter fibers discharge across the respiratory cycle. In this article, we review the phrenic afferent literature and highlight areas in need of further study. We conclude that 1) activation of both myelinated and nonmyelinated phrenic sensory afferents can influence respiratory motor output on a breath-by-breath basis; 2) the relative impact of phrenic afferents substantially increases with diaphragm work and fatigue; 3) activation of phrenic afferents has a powerful impact on sympathetic motor outflow, and 4) phrenic afferents contribute to diaphragm somatosensation and the conscious perception of breathing. Much remains to be learned regarding the spinal and supraspinal distribution and synaptic contacts of myelinated and nonmyelinated phrenic afferents. Similarly, very little is known regarding the potential role of phrenic afferent neurons in triggering or modulating expression of respiratory neuroplasticity.
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Affiliation(s)
- Jayakrishnan Nair
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
| | - Kristi A Streeter
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
| | - Sara M F Turner
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
| | - Michael D Sunshine
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
| | - Donald C Bolser
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
| | - Emily J Fox
- Department of Physical Therapy, College of Public Health and Health Professions, University of Florida, Gainesville, Florida.,McKnight Brain Institute, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and.,Brooks Rehabilitation, Jacksonville, Florida
| | - Paul W Davenport
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
| | - David 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.,Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida; and
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Brainstem areas activated by intermittent apnea in awake unrestrained rats. Neuroscience 2015; 297:262-71. [DOI: 10.1016/j.neuroscience.2015.04.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Revised: 03/24/2015] [Accepted: 04/03/2015] [Indexed: 11/21/2022]
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Socolovsky M, di Masi G, Bonilla G, Paez MD, Robla J, Cabrera CC. The phrenic nerve as a donor for brachial plexus injuries: is it safe and effective? Case series and literature analysis. Acta Neurochir (Wien) 2015; 157:1077-86; discussion 1086. [PMID: 25833303 DOI: 10.1007/s00701-015-2387-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Accepted: 02/26/2015] [Indexed: 10/23/2022]
Abstract
BACKGROUND Controversy exists surrounding the use of the phrenic nerve for transfer in severe brachial plexus injuries. The objectives of this study are: (1) to present the experience of the authors using the phrenic nerve in a single institution; and (2) to thoroughly review the existing literature to date. METHODS Adult patients with C5-D1 and C5-C8 lesions and a phrenic nerve transfer were retrospectively included. Patients with follow-up shorter than 18 months were excluded. The MRC muscle strength grading system was used to rate the outcome. Clinical repercussions relating to sectioning of the phrenic nerve were studied. An intense rehabilitation program was started after surgery, and compliance to this program was monitored using a previously described scale. Statistical analysis was performed with the obtained data. RESULTS Fifty-one patients were included. The mean time between trauma and surgery was 5.7 months. Three-quarters of the patients had C5-D1, with the remainder C5-C8. Mean post-operative follow-up was 32.5 months A MRC of M4 was achieved in 62.7% patients, M3 21.6%, M2 in 3.9%, and M1 in 11.8%. The only significant differences between the two groups were in graft length (9.8 vs. 15.1 cm, p = 0.01); and in the rehabilitation compliance score (2.86 vs. 2.00, p = 0.01). CONCLUSIONS Results of phrenic nerve transfer are predictable and good, especially if the grafts are short and the rehabilitation is adequate. It may adversely affect respiratory function tests, but this rarely correlates clinically. Contraindications to the use of the phrenic nerve exist and should be respected.
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Pate KM, Davenport PW. Tracheal occlusion conditioning causes stress, anxiety and neural state changes in conscious rats. Exp Physiol 2012; 98:819-29. [PMID: 23024371 DOI: 10.1113/expphysiol.2012.068924] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Evidence from human and animal studies indicates that mechanical loads to breathing are stressful stimuli and evoke compensatory behaviours. Conditioning of stressful stimuli is known to cause changes in basal stress levels and behaviour. Individuals with respiratory obstructive diseases repeatedly experience bouts of airway obstruction, which may act as a form of conditioning, and often have affective disorders, such as anxiety and depression. It is unknown whether the development of affective disorders in these individuals results from the unexpected recurring respiratory perturbations. To investigate this possibility, we developed a model to elicit tracheal occlusion (TO) in conscious rats and exposed them to 10 days of TO conditioning. We hypothesized that healthy, conscious animals exposed to TO conditioning would develop stress and anxiety and would have modulated neural activity in respiratory, stress, discriminative and affective neural regions. Following TO conditioning, rats had increased basal corticosterone levels, greater adrenal weights and elevated anxiety levels compared with animals not receiving TO. Significant increases in cytochrome oxidase staining were found in brainstem respiratory nuclei, periaqueductal grey, dorsal raphe, thalamus and insular cortex. These results suggest that healthy animals develop stress and anxiety responses to respiratory load conditioning via inescapable tracheal occlusions, which may be mediated through state changes in specific brain nuclei.
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Affiliation(s)
- K M Pate
- Department of Medicine, National Jewish Health, 1400 Jackson Street, Denver, CO 80206, USA.
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Pate KM, Davenport PW. Tracheal occlusions evoke respiratory load compensation and neural activation in anesthetized rats. J Appl Physiol (1985) 2011; 112:435-42. [PMID: 22074720 DOI: 10.1152/japplphysiol.01321.2010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Airway obstruction in animals leads to compensation and avoidance behavior and elicits respiratory mechanosensation. The pattern of respiratory load compensation and neural activation in response to intrinsic, transient, tracheal occlusions (ITTO) via an inflatable tracheal cuff are unknown. We hypothesized that ITTO would cause increased diaphragm activity, decreased breathing frequency, and activation of neurons within the medullary and pontine respiratory centers without changing airway compliance. Obstructions were performed for 2-3 breaths followed by a minimum of 15 unobstructed breaths with an inflatable cuff sutured around the trachea in rats. The obstruction procedure was repeated for 10 min. The brains of obstructed and control animals were removed, fixed, sectioned, and stained for c-Fos. Respiratory pattern was measured from esophageal pressure (P(es)) and diaphragm electromyography (EMG(dia)). The obstructed breaths resulted in a prolonged inspiratory and expiratory time, an increase in EMG(dia) amplitude, and a more negative P(es) compared with control breaths. Neurons labeled with c-Fos were found in brain stem and suprapontine nuclei, with a significant increase in c-Fos expression for the occluded experimental group compared with the control groups in the nucleus ambiguus, nucleus of the solitary tract, lateral parabrachial nucleus, and periaqueductal gray matter. The results of this study demonstrate tracheal occlusion-elicited activation of neurons in brain stem respiratory nuclei and neural areas involved in stress responses and defensive behaviors, suggesting that these neurons mediate the load compensation breathing pattern response and may be part of the neural pathway for respiratory mechanosensation.
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Affiliation(s)
- Kathryn M Pate
- Physiological Sciences, University of Florida, Gainesville, Florida 32603, USA
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Côté MP, Amin AA, Tom VJ, Houle JD. Peripheral nerve grafts support regeneration after spinal cord injury. Neurotherapeutics 2011; 8:294-303. [PMID: 21360238 PMCID: PMC3101823 DOI: 10.1007/s13311-011-0024-6] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Traumatic insults to the spinal cord induce both immediate mechanical damage and subsequent tissue degeneration leading to a substantial physiological, biochemical, and functional reorganization of the spinal cord. Various spinal cord injury (SCI) models have shown the adaptive potential of the spinal cord and its limitations in the case of total or partial absence of supraspinal influence. Meaningful recovery of function after SCI will most likely result from a combination of therapeutic strategies, including neural tissue transplants, exogenous neurotrophic factors, elimination of inhibitory molecules, functional sensorimotor training, and/or electrical stimulation of paralyzed muscles or spinal circuits. Peripheral nerve grafts provide a growth-permissive substratum and local neurotrophic factors to enhance the regenerative effort of axotomized neurons when grafted into the site of injury. Regenerating axons can be directed via the peripheral nerve graft toward an appropriate target, but they fail to extend beyond the distal graft-host interface because of the deposition of growth inhibitors at the site of SCI. One method to facilitate the emergence of axons from a graft into the spinal cord is to digest the chondroitin sulfate proteoglycans that are associated with a glial scar. Importantly, regenerating axons that do exit the graft are capable of forming functional synaptic contacts. These results have been demonstrated in acute injury models in rats and cats and after a chronic injury in rats and have important implications for our continuing efforts to promote structural and functional repair after SCI.
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Affiliation(s)
- Marie-Pascale Côté
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, 2900 Queen Lane, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129 USA
| | - Arthi A. Amin
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, 2900 Queen Lane, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129 USA
| | - Veronica J. Tom
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, 2900 Queen Lane, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129 USA
| | - John D. Houle
- Department of Neurobiology and Anatomy, Spinal Cord Research Center, 2900 Queen Lane, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129 USA
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Respiratory related evoked potential measures of cerebral cortical respiratory information processing. Biol Psychol 2010; 84:4-12. [DOI: 10.1016/j.biopsycho.2010.02.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 01/28/2010] [Accepted: 02/10/2010] [Indexed: 11/22/2022]
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Davenport PW, Reep RL, Thompson FJ. Phrenic nerve afferent activation of neurons in the cat SI cerebral cortex. J Physiol 2010; 588:873-86. [PMID: 20064855 DOI: 10.1113/jphysiol.2009.181735] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Stimulation of respiratory afferents elicits neural activity in the somatosensory region of the cerebral cortex in humans and animals. Respiratory afferents have been stimulated with mechanical loads applied to breathing and electrical stimulation of respiratory nerves and muscles. It was hypothesized that stimulation of the phrenic nerve myelinated afferents will activate neurons in the 3a and 3b region of the somatosensory cortex. This was investigated in cats with electrical stimulation of the intrathoracic phrenic nerve and C(5) root of the phrenic nerve. The somatosensory cortical response to phrenic afferent stimulation was recorded from the cortical surface, contralateral to the phrenic nerve, ispilateral to the phrenic nerve and with microelectrodes inserted into the cortical site of the surface dipole. Short-latency, primary cortical evoked potentials (1 degrees CEP) were recorded with stimulation of myelinated afferents of the intrathoracic phrenic nerve in the contralateral post-cruciate gyrus of all animals (n = 42). The mean onset and peak latencies were 8.5 +/- 5.7 ms and 21.8 +/- 9.8 ms, respectively. The rostro-caudal surface location of the 1 degrees CEP was found between the rostral edge of the post-cruciate dimple (PCD) and the rostral edge of the ansate sulcus, medio-lateral location was between 2 mm lateral to the sagittal sulcus and the lateral end of the cruciate sulcus. Histological examination revealed that the 1 degrees CEP sites were recorded over areas 3a and 3b of the SI somatosensory cortex. Intracortical activation of 16 neurons with two patterns of neural activity was recorded: (1) short-latency, short-duration activation of neurons and (2) long-latency, long-duration activation of neurons. Short-latency neurons had a mean onset latency of 10.4 +/- 3.1 ms and mean burst duration of 10.1 +/- 3.2 ms. The short-latency units were recorded at an average depth of 1.7 +/- 0.5 mm below the cortical surface. The long-latency neurons had a mean onset latency of 36.0 +/- 4.2 ms and mean burst duration of 32.2 +/- 8.4 ms. The long-latency units were recorded at an average depth of 2.4 +/- 0.2 mm below the cortical surface. The results of the study demonstrated that phrenic nerve afferents have a short-latency central projection to the SI somatosensory cortex. The phrenic afferents activated neurons in lamina III and IV of areas 3a and 3b. The cortical representation of phrenic nerve afferents is medial to the forelimb, lateral to the hindlimb, similar to thoracic loci, hence the phrenic afferent SI site in the cat homunculus is consistent with body position (thoracic region) rather than spinal segment (C(5)-C(7)). The phrenic afferent activation of the somatosensory cortex is bilateral, with the ipsilateral cortical activation occurring subsequent to the contralateral. These results support the hypothesis that phrenic afferents provide somatosensory information to the cerebral cortex which can be used for diaphragmatic proprioception and somatosensation.
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Affiliation(s)
- Paul W Davenport
- Department of Physiological Sciences, Box 100144, HSC, University of Florida, Gainesville, FL 32610, USA.
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Chou YL, Davenport PW. Phrenic nerve afferents elicited cord dorsum potential in the cat cervical spinal cord. BMC PHYSIOLOGY 2005; 5:7. [PMID: 15877811 PMCID: PMC1131907 DOI: 10.1186/1472-6793-5-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Accepted: 05/06/2005] [Indexed: 11/10/2022]
Abstract
BACKGROUND The diaphragm has sensory innervation from mechanoreceptors with myelinated axons entering the spinal cord via the phrenic nerve that project to the thalamus and somatosensory cortex. It was hypothesized that phrenic nerve afferent (PnA) projection to the central nervous system is via the spinal dorsal column pathway. RESULTS A single N1 peak of the CDP was found in the C4 and C7 spinal segments. Three peaks (N1, N2, and N3) were found in the C5 and C6 segments. No CDP was recorded at C8 dorsal spinal cord surface in cats. CONCLUSION These results demonstrate PnA activation of neurons in the cervical spinal cord. Three populations of myelinated PnA (Group I, Group II, and Group III) enter the cat's cervical spinal segments that supply the phrenic nerve.
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Affiliation(s)
- Yang-Ling Chou
- Department of Physiological Sciences, Box 100144, HSC, University of Florida, Gainesville FL 32610, USA
| | - Paul W Davenport
- Department of Physiological Sciences, Box 100144, HSC, University of Florida, Gainesville FL 32610, USA
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Respiratory motor recovery after unilateral spinal cord injury: eliminating crossed phrenic activity decreases tidal volume and increases contralateral respiratory motor output. J Neurosci 2003. [PMID: 12657710 DOI: 10.1523/jneurosci.23-06-02494.2003] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
By 2 months after unilateral cervical spinal cord injury (SCI), respiratory motor output resumes in the previously quiescent phrenic nerve. This activity is derived from bulbospinal pathways that cross the spinal midline caudal to the lesion (crossed phrenic pathways). To determine whether crossed phrenic pathways contribute to tidal volume in spinally injured rats, spontaneous breathing was measured in anesthetized C2 hemisected rats at 2 months after injury with an intact ipsilateral phrenic nerve, or with ipsilateral phrenicotomy performed at the time of the SCI (i.e., crossed phrenic pathways rendered ineffective) (dual injury). Ipsilateral phrenicotomy did not alter the rapid shallow eupneic breathing pattern in C2 injured rats. However, the ability to generate large inspiratory volumes after either vagotomy or during augmented breaths was impaired if crossed phrenic activity was abolished. We also investigated whether compensatory plasticity in contralateral motoneurons would be affected by eliminating crossed phrenic activity. Thus, contralateral phrenic motor output was recorded in anesthetized, vagotomized, and mechanically ventilated rats with dual injury during chemoreceptor stimulation. Hypercapnia, hypoxia, and asphyxia increased contralateral phrenic burst amplitude in the dual injury group more than in rats with SCI alone. Dual injury rats also had elevated baseline burst frequency. Together, these results demonstrate a functional role of crossed phrenic activity after SCI. Moreover, by preventing ipsilateral phrenic motor recovery in rats with unilateral SCI, segmental and supraspinal changes could be induced in contralateral respiratory motor output beyond that seen with SCI alone.
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