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A Primer on Hypotussic Cough: Mechanisms and Assessment. CURRENT OTORHINOLARYNGOLOGY REPORTS 2023. [DOI: 10.1007/s40136-023-00446-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
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Musselwhite MN, Shen TY, Rose MJ, Iceman KE, Poliacek I, Pitts T, Bolser DC. THE INFLUENCE OF CO 2 ON SPATIOTEMPORAL FEATURES OF MECHANICALLY INDUCED COUGH IN ANESTHETIZED CATS. Respir Physiol Neurobiol 2022; 307:103964. [PMID: 36174962 DOI: 10.1016/j.resp.2022.103964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 08/10/2022] [Accepted: 09/19/2022] [Indexed: 11/27/2022]
Abstract
Effective cough requires a significant increase in lung volume used to produce the shear forces on the airway to clear aspirated material. This increase in tidal volume during cough, along with an increase in tidal frequency during bouts of paroxysmal cough produces profound hyperventilation and thus reduces arterial CO2. While there are several reports in the literature regarding the effects of hypercapnia, hyperoxia, and hypoxia on cough, there is little research quantifying the effects of hypocapnia on the cough reflex. We hypothesized that decreased CO2 would enhance coughing. In 12 spontaneously breathing adult male cats, we compared bouts of prolonged mechanically stimulated cough, in which cough induced hyperventilation (CHV) was allowed to occur, with isocapnic cough trials where we maintained eupneic end-tidal CO2 by adding CO2 to the inspired gas. Isocapnia slightly increased cough number and decreased esophageal pressures with no change in EMG magnitudes or phase durations. The cough-to-eupnea transition was also analyzed between CHV, isocapnia, and a third group of animals that were mechanically hyperventilated to apnea. The transition to eupnea was highly sensitive to added CO2, and CHV apneas were much shorter than those produced by mechanical hyperventilation. We suggest that the cough pattern generator is relatively insensitive to CHV. In the immediate post-cough period, the appearance of breathing while CO2 is very low suggests a transient reduction in apneic threshold following a paroxysmal cough bout.
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Affiliation(s)
- M Nicholas Musselwhite
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida. 1333 Center Dr, Gainesville, Florida, 32603, United States of America.
| | - Tabitha Y Shen
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida. 1333 Center Dr, Gainesville, Florida, 32603, United States of America
| | - Melanie J Rose
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida. 1333 Center Dr, Gainesville, Florida, 32603, United States of America
| | - Kimberly E Iceman
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville. 511 S Floyd St, MDR 616, Louisville, Kentucky, 40202, United States of America
| | - Ivan Poliacek
- Comenius University in Bratislava, Jessenius Faculty of Medicine in Martin, Institute of Medical Biophysics. Malá hora 4A, 036 01 Martin-Záturčie, Slovakia
| | - Teresa Pitts
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville. 511 S Floyd St, MDR 616, Louisville, Kentucky, 40202, United States of America.
| | - Donald C Bolser
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida. 1333 Center Dr, Gainesville, Florida, 32603, United States of America
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Musselwhite MN, Shen TY, Rose MJ, Iceman KE, Poliacek I, Pitts T, Bolser DC. Differential effects of acute cerebellectomy on cough in spontaneously breathing cats. PLoS One 2021; 16:e0253060. [PMID: 34153070 PMCID: PMC8216514 DOI: 10.1371/journal.pone.0253060] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 05/27/2021] [Indexed: 11/29/2022] Open
Abstract
The role of the cerebellum in controlling the cough motor pattern is not well understood. We hypothesized that cerebellectomy would disinhibit motor drive to respiratory muscles during cough. Cough was induced by mechanical stimulation of the tracheobronchial airways in anesthetized, spontaneously breathing adult cats (8 male, 1 female), and electromyograms (EMGs) were recorded from upper airway, chest wall, and abdominal respiratory muscles. Cough trials were performed before and at two time points after total cerebellectomy (10 minutes and >1 hour). Unlike a prior report in paralyzed, decerebrated, and artificially ventilated animals, we observed that cerebellectomy had no effect on cough frequency. After cerebellectomy, thoracic inspiratory muscle EMG magnitudes increased during cough (diaphragm EMG increased by 14% at 10 minutes, p = 0.04; parasternal by 34% at 10 minutes and by 32% at >1 hour, p = 0.001 and 0.03 respectively). During cough at 10 minutes after cerebellectomy, inspiratory esophageal pressure was increased by 44% (p = 0.004), thyroarytenoid (laryngeal adductor) muscle EMG amplitude increased 13% (p = 0.04), and no change was observed in the posterior cricoarytenoid (laryngeal abductor) EMG. Cough phase durations did not change. Blood pressure and heart rate were reduced after cerebellectomy, and respiratory rate also decreased due to an increase in duration of the expiratory phase of breathing. Changes in cough-related EMG magnitudes of respiratory muscles suggest that the cerebellum exerts inhibitory control of cough motor drive, but not cough number or phase timing in response to mechanical stimuli in this model early after cerebellectomy. However, results varied widely at >1 hour after cerebellectomy, with some animals exhibiting enhancement or suppression of one or more components of the cough motor behavior. These results suggest that, while the cerebellum and behavior-related sensory feedback regulate cough, it may be difficult to predict the nature of the modulation based on total cerebellectomy.
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Affiliation(s)
- M. Nicholas Musselwhite
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida, United States of America
- * E-mail: (MNM); (TP)
| | - Tabitha Y. Shen
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida, United States of America
| | - Melanie J. Rose
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida, United States of America
| | - Kimberly E. Iceman
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, Kentucky, United States of America
| | - Ivan Poliacek
- Comenius University in Bratislava, Jessenius Faculty of Medicine in Martin, Institute of Medical Biophysics, Martin, Slovak Republic
| | - Teresa Pitts
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, Kentucky, United States of America
- * E-mail: (MNM); (TP)
| | - Donald C. Bolser
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida, United States of America
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Romano V, Reddington AL, Cazzanelli S, Mazza R, Ma Y, Strydis C, Negrello M, Bosman LWJ, De Zeeuw CI. Functional Convergence of Autonomic and Sensorimotor Processing in the Lateral Cerebellum. Cell Rep 2021; 32:107867. [PMID: 32640232 PMCID: PMC7351113 DOI: 10.1016/j.celrep.2020.107867] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 05/12/2020] [Accepted: 06/16/2020] [Indexed: 01/24/2023] Open
Abstract
The cerebellum is involved in the control of voluntary and autonomic rhythmic behaviors, yet it is unclear to what extent it coordinates these in concert. We studied Purkinje cell activity during unperturbed and perturbed respiration in lobules simplex, crus 1, and crus 2. During unperturbed (eupneic) respiration, complex spike and simple spike activity encode the phase of ongoing sensorimotor processing. In contrast, when the respiratory cycle is perturbed by whisker stimulation, mice concomitantly protract their whiskers and advance their inspiration in a phase-dependent manner, preceded by increased simple spike activity. This phase advancement of respiration in response to whisker stimulation can be mimicked by optogenetic stimulation of Purkinje cells and prevented by cell-specific genetic modification of their AMPA receptors, hampering increased simple spike firing. Thus, the impact of Purkinje cell activity on respiratory control is context and phase dependent, highlighting a coordinating role for the cerebellar hemispheres in aligning autonomic and sensorimotor behaviors. During unperturbed respiration, Purkinje cells signal ongoing sensorimotor processing After perturbation, mice advance their simple spike activity, whisking, and inspiration Altering simple spike activity affects the impact of whisker stimulation on respiration Cerebellar coordination of autonomic and sensorimotor behaviors is context dependent
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Affiliation(s)
- Vincenzo Romano
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands
| | | | - Silvia Cazzanelli
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands
| | - Roberta Mazza
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands
| | - Yang Ma
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands
| | - Christos Strydis
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands
| | - Mario Negrello
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands.
| | - Laurens W J Bosman
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands.
| | - Chris I De Zeeuw
- Department of Neuroscience, Erasmus MC, 3015 GE Rotterdam, the Netherlands; Netherlands Institute for Neuroscience, Royal Academy of Arts and Sciences, 1105 BA Amsterdam, the Netherlands
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Olsen WL, Rose M, Golder FJ, Wang C, Hammond JC, Bolser DC. Intra-Arterial, but Not Intrathecal, Baclofen and Codeine Attenuates Cough in the Cat. Front Physiol 2021; 12:640682. [PMID: 33746778 PMCID: PMC7973226 DOI: 10.3389/fphys.2021.640682] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 02/15/2021] [Indexed: 11/15/2022] Open
Abstract
Centrally-acting antitussive drugs are thought to act solely in the brainstem. However, the role of the spinal cord in the mechanism of action of these drugs is unknown. The purpose of this study was to determine if antitussive drugs act in the spinal cord to reduce the magnitude of tracheobronchial (TB) cough-related expiratory activity. Experiments were conducted in anesthetized, spontaneously breathing cats (n = 22). Electromyograms (EMG) were recorded from the parasternal (PS) and transversus abdominis (TA) or rectus abdominis muscles. Mechanical stimulation of the trachea or larynx was used to elicit TB cough. Baclofen (10 and 100 μg/kg, GABA-B receptor agonist) or codeine (30 μg/kg, opioid receptor agonist) was administered into the intrathecal (i.t.) space and also into brainstem circulation via the vertebral artery. Cumulative doses of i.t. baclofen or codeine had no effect on PS, abdominal muscle EMGs or cough number during the TB cough. Subsequent intra-arterial (i.a.) administration of baclofen or codeine significantly reduced magnitude of abdominal and PS muscles during TB cough. Furthermore, TB cough number was significantly suppressed by i.a. baclofen. The influence of these drugs on other behaviors that activate abdominal motor pathways was also assessed. The abdominal EMG response to noxious pinch of the tail was suppressed by i.t. baclofen, suggesting that the doses of baclofen that were employed were sufficient to affect spinal pathways. However, the abdominal EMG response to expiratory threshold loading was unaffected by i.t. administration of either baclofen or codeine. These results indicate that neither baclofen nor codeine suppress cough via a spinal action and support the concept that the antitussive effect of these drugs is restricted to the brainstem.
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Reed MD, English M, English C, Huff A, Poliacek I, Musselwhite MN, Howland DR, Bolser DC, Pitts T. The Role of the Cerebellum in Control of Swallow: Evidence of Inspiratory Activity During Swallow. Lung 2019; 197:235-240. [PMID: 30680516 DOI: 10.1007/s00408-018-00192-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Accepted: 12/29/2018] [Indexed: 10/27/2022]
Abstract
Anatomical connections are reported between the cerebellum and brainstem nuclei involved in swallow such as the nucleus tractus solitarius, nucleus ambiguus, and Kölliker-fuse nuclei. Despite these connections, a functional role of the cerebellum during swallow has not been elucidated. Therefore, we examined the effects of cerebellectomy on swallow muscle recruitment and swallow-breathing coordination in anesthetized freely breathing cats. Electromyograms were recorded from upper airway, pharyngeal, laryngeal, diaphragm, and chest wall muscles before and after complete cerebellectomy. Removal of the cerebellum reduced the excitability of swallow (i.e., swallow number), and muscle recruitment of the geniohyoid, thyroarytenoid, parasternal (chestwall), and diaphragm muscles, but did not disrupt swallow-breathing coordination. Additionally, diaphragm and parasternal muscle activity during swallow is reduced after cerebellectomy, while no changes were observed during breathing. These findings suggest the cerebellum modulates muscle excitability during recruitment, but not pattern or coordination of swallow with breathing.
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Affiliation(s)
- Mitchell D Reed
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, KY, USA
| | - Mason English
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, KY, USA
| | - Connor English
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, KY, USA
| | - Alyssa Huff
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, KY, USA.,Department of Physiology, College of Medicine, University of Louisville, Louisville, KY, USA
| | - Ivan Poliacek
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA.,Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Martin, Slovakia
| | - M Nicholas Musselwhite
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
| | - Dena R Howland
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, KY, USA.,Research Service, Robley Rex Veterans Affairs Medical Center, Louisville, KY, USA
| | - Donald C Bolser
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
| | - Teresa Pitts
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, College of Medicine, University of Louisville, Louisville, KY, USA.
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Brainstem mechanisms underlying the cough reflex and its regulation. Respir Physiol Neurobiol 2017; 243:60-76. [DOI: 10.1016/j.resp.2017.05.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 05/16/2017] [Accepted: 05/17/2017] [Indexed: 12/12/2022]
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Audrit KJ, Delventhal L, Aydin Ö, Nassenstein C. The nervous system of airways and its remodeling in inflammatory lung diseases. Cell Tissue Res 2017; 367:571-590. [PMID: 28091773 DOI: 10.1007/s00441-016-2559-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Accepted: 12/13/2016] [Indexed: 12/20/2022]
Abstract
Inflammatory lung diseases are associated with bronchospasm, cough, dyspnea and airway hyperreactivity. The majority of these symptoms cannot be primarily explained by immune cell infiltration. Evidence has been provided that vagal efferent and afferent neurons play a pivotal role in this regard. Their functions can be altered by inflammatory mediators that induce long-lasting changes in vagal nerve activity and gene expression in both peripheral and central neurons, providing new targets for treatment of pulmonary inflammatory diseases.
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Affiliation(s)
- Katrin Julia Audrit
- Institute of Anatomy and Cell Biology, Aulweg 123, 35385, Giessen, Germany.,German Center for Lung Research (DZL), Giessen, Germany
| | - Lucas Delventhal
- Institute of Anatomy and Cell Biology, Aulweg 123, 35385, Giessen, Germany.,German Center for Lung Research (DZL), Giessen, Germany
| | - Öznur Aydin
- Institute of Anatomy and Cell Biology, Aulweg 123, 35385, Giessen, Germany.,German Center for Lung Research (DZL), Giessen, Germany
| | - Christina Nassenstein
- Institute of Anatomy and Cell Biology, Aulweg 123, 35385, Giessen, Germany. .,German Center for Lung Research (DZL), Giessen, Germany.
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Zhang XY, Wang JJ, Zhu JN. Cerebellar fastigial nucleus: from anatomic construction to physiological functions. CEREBELLUM & ATAXIAS 2016; 3:9. [PMID: 27144010 PMCID: PMC4853849 DOI: 10.1186/s40673-016-0047-1] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Accepted: 03/31/2016] [Indexed: 12/16/2022]
Abstract
Fastigial nucleus (FN) is the phylogenetically oldest nucleus in the cerebellum, a classical subcortical motor coordinator. As one of the ultimate integration stations and outputs of the spinocerebellum, the FN holds a key position in the axial, proximal and ocular motor control by projecting to the medial descending systems and eye movement related nuclei. Furthermore, through topographic connections with extensive nonmotor systems, including visceral related nuclei in the brainstem, hypothalamus, as well as the limbic system, FN has also been implicated in regulation of various nonsomatic functions, such as feeding, cardiovascular and respiratory, defecation and micturition, immune, as well as emotional activities. In clinic, FN lesion or dysfunction results in motor deficits including spinocerebellar ataxias, and nonmotor symptoms. In this review, we summarize the cytoarchitecture, anatomic afferent and efferent connections, as well as the motor and nonmotor functions of the FN and the related diseases and disorders. We suggest that by bridging the motor and nonmotor systems, the cerebellar FN may help to integrate somatic motor and nonsomatic functions and consequently contribute to generate a coordinated response to internal and external environments.
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Affiliation(s)
- Xiao-Yang Zhang
- State Key Laboratory of Pharmaceutical Biotechnology and Department of Biological Science and Technology, School of Life Sciences, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023 China
| | - Jian-Jun Wang
- State Key Laboratory of Pharmaceutical Biotechnology and Department of Biological Science and Technology, School of Life Sciences, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023 China
| | - Jing-Ning Zhu
- State Key Laboratory of Pharmaceutical Biotechnology and Department of Biological Science and Technology, School of Life Sciences, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023 China
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Recessive spinocerebellar ataxia with paroxysmal cough attacks: a report of five cases. THE CEREBELLUM 2014; 13:215-21. [PMID: 24097205 DOI: 10.1007/s12311-013-0526-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hereditary ataxias are a heterogeneous group of neurological diseases characterized by progressive cerebellar syndrome and numerous other features, which result in great diversity of ataxia subtypes. Despite the characterization of a number of both autosomal dominant and autosomal recessive ataxias, it is thought that a large group of these conditions remains to be identified. In this study, we report the characterization of five patients (three Mexicans and two Italians) who exhibit a peculiar form of recessive ataxia associated with coughing. The main clinical and neurophysiological features of these patients include cerebellar ataxia, paroxysmal cough, restless legs syndrome (RLS), choreic movements, atrophy of distal muscles, and oculomotor disorders. Brain magnetic resonance imaging (MRI) revealed cerebellar atrophy, while video polysomnography (VPSG) studies showed a severe pattern of breathing-related sleep disorder, including sleep apnea, snoring, and significant oxygen saturation in the absence of risk factors. All patients share clinical features in the peripheral nervous system, including reduction of amplitude and prolonged latency of sensory potentials in median and sural nerves. Altogether, clinical criteria as well as molecular genetic testing that was negative for different autosomal dominant and autosomal recessive ataxias suggest the presence of a new form of recessive ataxia. This ataxia, in which cerebellar signs are preceded by paroxysmal cough, affects not only the cerebellum and its fiber connections, but also the sensory peripheral nervous system and extracerebellar central pathways.
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Lee A, Chen ML, Abeshaus S, Poliakov A, Ojemann JG. Posterior fossa tumors and their impact on sleep and ventilatory control: A clinical perspective. Respir Physiol Neurobiol 2013; 189:261-71. [DOI: 10.1016/j.resp.2013.05.027] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Revised: 04/23/2013] [Accepted: 05/22/2013] [Indexed: 11/28/2022]
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Cough-related neurons in the nucleus tractus solitarius of decerebrate cats. Neuroscience 2012; 218:100-9. [DOI: 10.1016/j.neuroscience.2012.05.053] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 05/21/2012] [Accepted: 05/21/2012] [Indexed: 01/09/2023]
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Abstract
Following systemic administration, centrally acting antitussive drugs are generally assumed to act in the brainstem to inhibit cough. However, recent work in humans has raised the possibility of suprapontine sites of action for cough suppressants. For drugs that may act in the brainstem, the specific locations, types of neurones affected, and receptor specificities of the compounds represent important issues regarding their cough-suppressant actions. Two medullary areas that have received the most attention regarding the actions of antitussive drugs are the nucleus of the tractus solitarius (NTS) and the caudal ventrolateral respiratory column. Studies that have implicated these two medullary areas have employed both microinjection and in vitro recording methods to control the location of action of the antitussive drugs. Other brainstem regions contain neurones that participate in the production of cough and could represent potential sites of action of antitussive drugs. These regions include the raphe nuclei, pontine nuclei, and rostral ventrolateral medulla. Specific receptor subtypes have been associated with the suppression of cough at central sites, including 5-HT1A, opioid (mu, kappa, and delta), GABA-B, tachykinin neurokinin-1 (NK-1) and neurokinin-2, non-opioid (NOP-1), cannabinoid, dopaminergic, and sigma receptors. Aside from tachykinin NK-1 receptors in the NTS, relatively little is known regarding the receptor specificity of putative antitussive drugs in particular brainstem regions. Our understanding of the mechanisms of action of antitussive drugs would be significantly advanced by further work in this area.
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Affiliation(s)
- D C Bolser
- Department of Physiological Sciences, University of Florida, College of Veterinary Medicine, Gainesville, FL 32610-0144, USA.
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Jakus J, Poliacek I, Halasova E, Murin P, Knocikova J, Tomori Z, Bolser DC. Brainstem circuitry of tracheal-bronchial cough: c-fos study in anesthetized cats. Respir Physiol Neurobiol 2007; 160:289-300. [PMID: 18055277 DOI: 10.1016/j.resp.2007.10.014] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Revised: 10/15/2007] [Accepted: 10/23/2007] [Indexed: 11/15/2022]
Abstract
The c-fos gene expression method was used to localize brainstem neurons functionally related to the tracheal-bronchial cough on 13 spontaneously breathing, pentobarbitone anesthetized cats. The level of Fos-like immunoreactivity (FLI) in 6 animals with repetitive coughs (170+/-12) induced by mechanical stimulation of the tracheobronchial mucosa was compared to FLI in 7 control non-stimulated cats. Thirty-four nuclei were compared for the number of labeled cells. Enhanced cough FLI was found bilaterally at following brainstem structures, as compared to controls: In the medulla, FLI was increased in the medial, interstitial and ventrolateral subnuclei of the solitary tract (p < 0.02), in the retroambigual nucleus of the caudal medulla (p < 0.05), in the ambigual, paraambigual and retrofacial nuclei of the rostral medulla along with the lateral reticular nuclei, the ventrolateral reticular tegmental field (p < 0.05), and the raphe nuclei (p < 0.05). In pons, increased FLI was detected in the lateral parabrachial and Kölliker-Fuse nuclei (p < 0.01), in the posteroventral cochlear nuclei (p < 0.01), and the raphe midline (p < 0.05). Within the mesencephalon cough-related FLI was enhanced at the rostral midline area (p < 0.05), but a decrease was found at its caudal part in the periaqueductal gray (p < 0.02). Results of this study suggest a large medullary - pontine - mesencephalic neuronal circuit involved in the control of the tracheal-bronchial cough in cats.
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Affiliation(s)
- Jan Jakus
- Department of Medical Biophysics, Comenius University Bratislava, Jessenius Faculty of Medicine, Malá Hora 4, 03754 Martin, Slovakia.
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Simonyan K, Saad ZS, Loucks TMJ, Poletto CJ, Ludlow CL. Functional neuroanatomy of human voluntary cough and sniff production. Neuroimage 2007; 37:401-9. [PMID: 17574873 PMCID: PMC2018653 DOI: 10.1016/j.neuroimage.2007.05.021] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2007] [Revised: 05/06/2007] [Accepted: 05/11/2007] [Indexed: 02/06/2023] Open
Abstract
Cough and sniff are both spontaneous respiratory behaviors that can be initiated voluntarily in humans. Disturbances of cough may be life threatening, while inability to sniff impairs the sense of smell in neurological patients. Cortical mechanisms of voluntary cough and sniff production have been predicted to exist; however, the localization and function of supramedullary areas responsible for these behaviors are poorly understood. We used functional magnetic resonance imaging to identify the central control of voluntary cough and sniff compared with breathing. We determined that both voluntary cough and sniff require a widespread pattern of sensorimotor activation along the Sylvian fissure convergent with voluntary breathing. Task-specific activation occurred in a pontomesencephalic region during voluntary coughing and in the hippocampus and piriform cortex during voluntary sniffing. Identification of the localization of cortical activation for cough control in humans may help potential drug development to target these regions in patients with chronic cough. Understanding the sensorimotor sniff control mechanisms may provide a new view on the cerebral functional reorganization of olfactory control in patients with neurological disorders.
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Affiliation(s)
- Kristina Simonyan
- Laryngeal and Speech Section, Medical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Building 10, Room 5D38, Bethesda, MD 20814-1416, USA.
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Zhu JN, Yung WH, Kwok-Chong Chow B, Chan YS, Wang JJ. The cerebellar-hypothalamic circuits: potential pathways underlying cerebellar involvement in somatic-visceral integration. ACTA ACUST UNITED AC 2006; 52:93-106. [PMID: 16497381 DOI: 10.1016/j.brainresrev.2006.01.003] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2005] [Revised: 12/19/2005] [Accepted: 01/13/2006] [Indexed: 12/13/2022]
Abstract
The cerebellum has been considered only as a classical subcortical center for motor control. However, accumulating experimental and clinical evidences have revealed that the cerebellum also plays an important role in cognition, for instance, in learning and memory, as well as in emotional behavior and in nonsomatic activities, such as visceral and immunological responses. Although it is not yet clear through which pathways such cerebellar nonsomatic functions are mediated, the direct bidirectional connections between the cerebellum and the hypothalamus, a high autonomic center, have recently been demonstrated in a series of neuroanatomical investigations on a variety of mammals and indicated to be potential pathways underlying the cerebellar autonomic modulation. The direct hypothalamocerebellar projections originate from the widespread hypothalamic nuclei/areas and terminate in both the cerebellar cortex as multilayered fibers and the cerebellar nuclei. Immunohistochemistry studies have offered fairly convincing evidence that some of these projecting fibers are histaminergic. It has been suggested that through their excitatory effects on cerebellar cortical and nuclear cells mediated by metabotropic histamine H(2) and/or H(1) receptors, the hypothalamocerebellar histaminergic fibers participate in cerebellar modulation of somatic motor as well as non-motor responses. On the other hand, the direct cerebellohypothalamic projections arise from all cerebellar nuclei (fastigial, anterior and posterior interpositus, and dentate nuclei) and reach almost all hypothalamic nuclei/areas. Neurophysiological and neuroimaging studies have demonstrated that these connections may be involved in feeding, cardiovascular, osmotic, respiratory, micturition, immune, emotion, and other nonsomatic regulation. These observations provide support for the hypothesis that the cerebellum is an essential modulator and coordinator for integrating motor, visceral and behavioral responses, and that such somatic-visceral integration through the cerebellar circuitry may be fulfilled by means of the cerebellar-hypothalamic circuits.
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Affiliation(s)
- Jing-Ning Zhu
- Department of Biological Science and Technology and State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Mailbox 426, Nanjing University, 22 Hankou Road, Nanjing 210093, China
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Chen ML, Witmans MB, Tablizo MA, Jubran RF, Turkel SB, Tavaré CJ, Keens TG. Disordered respiratory control in children with partial cerebellar resections. Pediatr Pulmonol 2005; 40:88-91. [PMID: 15880401 DOI: 10.1002/ppul.20225] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
While the cerebellum is not traditionally thought of as having an important role in respiratory control, breathing involves cyclic motor acts that require cerebellar coordination. We postulate that children with partial cerebellar resections have disordered respiratory control due to altered synchronization of ventilatory muscles. We reviewed the records of 36 children following partial cerebellar resections due to neoplasms confined to the cerebellum. P aCO2 values were elevated in 19% of patients. Six patients had apneic or bradypneic events documented within the first month after resection. Two patients required intubation with assisted ventilation, and one needed assisted ventilation for 7.3 weeks. Those with apnea had lower oxygen saturations, and a longer need for supplemental oxygen. Patients with apnea were older than those without apnea. Swallowing, which uses many of the same muscles as those needed to maintain upper airway patency, was dysfunctional in 50% of those with apneas. We conclude that children with cerebellar resections have an increased incidence of apnea, hypoventilation, and hypoxemia not otherwise explained by pulmonary disease, and some require prolonged assisted ventilation. We speculate that these abnormalities are manifestations of altered respiratory control caused by dysfunctional cerebellar coordination of ventilatory muscles.
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Affiliation(s)
- Maida Lynn Chen
- Division of Pediatric Pulmonology, Children's Hospital Los Angeles, Los Angeles, California 90027, USA
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Fontana GA, Lavorini F, Geri P, Zanasi A, Piumelli R. Cough in children with congenital central hypoventilation syndrome. Pulm Pharmacol Ther 2005; 17:425-9. [PMID: 15564086 DOI: 10.1016/j.pupt.2004.09.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Accepted: 09/13/2004] [Indexed: 11/19/2022]
Abstract
Congenital central hypoventilation syndrome (CCHS) is defined as failure of the chemical (autonomic) control of breathing causing alveolar hypoventilation in the absence of pulmonary, cardiac, neuromuscular or patent brainstem lesions. Hypoventilation is predominant in non-rapid-eye-movement sleep, during which breathing is primarily under chemical control. Failure of the central integration of chemosensory inputs is proposed as the putative defect. A genetic basis for CCHS is supported by lines of evidence. In some diseases of the central nervous system there is more or less complete depression of the cough reflex, whereas spontaneous ventilation is generally preserved. Little is known regarding cough in CCHS patients. Parents consistently report that their children cough 'normally' during airway infections; in contrast, experimental lines of evidence suggest that CCHS children lack a cough response following inhalation of a tussigenic agent. Although several factors may account for the discrepancy, the possibility of a weakened or even absent cough reflex remains to be fully ascertained. Conceivably, a defective cough reflex, in conjunction with the well established lack of perception of respiratory discomfort, might result in an increased risk of potentially serious respiratory complications in CCHS patients.
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Affiliation(s)
- Giovanni A Fontana
- Dipartimento di Area Critica Medico Chirurgica, Sezione di Malattie dell'Apparato Respiratorio, Università degli Sudi di Firenze, Viale G. B., Morgagni, 85, 50134 Firenze, Italy.
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Xu F, Zhou T, Frazier DT. Purkinje cell degeneration elevates eupneic and hypercapnic ventilation in rats. THE CEREBELLUM 2005; 3:133-40. [PMID: 15543803 DOI: 10.1080/14734220310023332] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Previous studies have demonstrated that among cerebellar nuclei, the fastigial nucleus (FN) plays a major role in facilitation of respiration, especially during hypercapnia. Since the FN primarily receives inhibitory afferents from Purkinje cells (PCs), we hypothesized that degeneration of PCs would increase both eupneic and hypercapnic ventilation. Experiments were carried out on 20 animals (n=10 for both normal and PC-degenerated) that were divided into three groups based on the different preparations used, i.e., four pairs for the awake, three pairs for the anesthetized, and three other pairs initially for the awake and subsequently for the anesthetized. The awake normal and PCD rats were separately placed in an unrestrained whole-body plethysmograph and ventilatory parameters measured before (room air) and during hypercapnia (5% CO2 + 21% O2 + 74% N2) for 30 min. The anesthetized animals were exposed to the same level of hypercapnia applied for approximately 5 min. The results showed that both eupneic breathing and hypercapnia-induced ventilatory augmentation were significantly greater in the awake PCD rat than those observed in the normal one, primarily due to a remarkable elevation in VT with little changes in f. The same results were also observed in anesthetized preparations. A Fos protein Immunocytochemical approach was employed to determine the effect of degeneration on PCs and FN neuronal activity. Fos expression of PCs was very intensive in normal rats, but absent or diminished in PCD rats. In sharp contrast, FN Fos expression was obscure in normal rats, but very apparent in PCD rats. These data suggest that PCs play an inhibitory role in modulation of eupneic and hypercapnic ventilation via inhibiting FN neuronal activity.
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Affiliation(s)
- Fadi Xu
- Department of Pathophysiology, Lovelace Respiratory Research Institute, Albuquerque, New Mexico 87108, USA.
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Shannon R, Baekey DM, Morris KF, Nuding SC, Segers LS, Lindsey BG. Production of reflex cough by brainstem respiratory networks. Pulm Pharmacol Ther 2004; 17:369-76. [PMID: 15564078 DOI: 10.1016/j.pupt.2004.09.022] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Accepted: 09/13/2004] [Indexed: 10/26/2022]
Abstract
Delineation of neural mechanisms involved in reflex cough is essential for understanding its many physiological and clinical complexities, and the development of more desirable antitussive agents. Brainstem networks that generate and modulate the breathing pattern are also involved in producing the motor patterns during reflex cough. Neurones of the ventrolateral medulla respiratory pattern generator mutually interact with neural networks in the pons, medulla and cerebellum to form a larger dynamic network. This paper discusses evidence from our laboratory and others supporting the involvement of the nucleus tractus solitarii, midline raphe nuclei and lateral tegmental field in the medulla, and the pontine respiratory group and cerebellum in the production of reflex cough. Gaps in our knowledge are identified to stimulate further research on this complicated issue.
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Affiliation(s)
- R Shannon
- Department of Physiology and Biophysics, MDC Box 8, University of South Florida Health Sciences Center, 12901 Bruce B. Downs Blvd. Tampa, FL 33612-4799, USA.
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Shannon R, Baekey DM, Morris KF, Nuding SC, Segers LS, Lindsey BG. Pontine respiratory group neuron discharge is altered during fictive cough in the decerebrate cat. Respir Physiol Neurobiol 2004; 142:43-54. [PMID: 15351303 DOI: 10.1016/j.resp.2004.05.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/05/2004] [Indexed: 01/06/2023]
Abstract
A network of neurons in the rostral dorsal lateral pons and pons/mescencephalic junction constitute the pontine respiratory group (PRG) and is essential for reflex cough. As a next step in understanding the role of the PRG in the expression of the cough reflex, we examined neuron firing rates during fictive cough in cats. Decerebrated, thoracotomized, paralyzed, cycle-triggered ventilated adult cats were used. Extracellular activity of many single neurons and phrenic and lumbar neurograms were monitored during fictive cough produced by mechanical stimulation of the intrathoracic trachea. Neurons were tested during control periods for respiratory modulation of firing rate by cycle-triggered histograms and statistical tests. Most respiratory modulated cells were continuously active with various superimposed respiratory patterns; major categories included inspiratory decrementing (I-Dec), expiratory decrementing (E-Dec) and expiratory augmenting (E-Aug). There were alterations in the discharge patterns of respiratory, as well as, non-respiratory modulated neurons during cough. The results suggest an involvement of the PRG in the configuration of the cough motor pattern.
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Affiliation(s)
- Roger Shannon
- Department of Physiology and Biophysics , University of South Florida Health Sciences Center, Tampa 33612-4799, USA.
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Harper RM, Macey PM, Henderson LA, Woo MA, Macey KE, Frysinger RC, Alger JR, Nguyen KP, Yan-Go FL. fMRI responses to cold pressor challenges in control and obstructive sleep apnea subjects. J Appl Physiol (1985) 2003; 94:1583-95. [PMID: 12514164 DOI: 10.1152/japplphysiol.00881.2002] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Obstructive sleep apnea (OSA) patients exhibit altered sympathetic outflow, which may reveal mechanisms underlying the syndrome. We used functional MRI (fMRI) in 16 control and 10 OSA subjects who were free of cardiovascular or mood-altering drugs to examine neural responses to a forehead cold pressor challenge, which elicits respiratory slowing, bradycardia, and enhanced sympathetic outflow. The magnitude of cold-induced bradycardia was smaller, and respiratory slowing showed greater intersubject variability and reached a nadir later in OSA patients. Both groups showed similar signal changes to cold stimulation in multiple brain sites. However, signal increases emerged in OSA over controls in anterior and posterior cingulate and cerebellar and frontal cortex, whereas signals markedly declined in the ventral thalamus, hippocampus, and insula rather than rising as in controls. Anomalous responses often paralleled changes in breathing and heart rate. Medullary, midbrain areas and lentiform and cerebellar dentate nuclei also showed lower signals in OSA cases. Cold pressor physiological responses are modified in OSA and may result from both diminished and exaggerated responses in multiple brain structures.
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Affiliation(s)
- Ronald M Harper
- Departments of Neurobiology, Radiology, and Neurology, School of Nursing, and Brain Research Institute, University of California at Los Angeles, Los Angeles, California 90095, USA.
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Abstract
Recent studies evaluating the effects of pulmonary afferents, chemoreceptors, and antitussive drugs on the cough motor pattern indicate that this reflex is regulated in a different manner than breathing. Furthermore, regulatory differences exist between tracheobronchial and laryngeal cough. We propose a functional model of the brainstem elements participating in the production of cough that accounts for these regulatory differences. The model incorporates known brainstem interneuronal pathways as well as novel regulatory elements for tracheobronchial and laryngeal cough. Each of these novel regulatory elements controls the excitability of a common motor pattern generation network. Given that cough and breathing are associated with profoundly different spatiotemporal alterations in motor drive to respiratory motoneurons, brainstem elements common to the generation of both behaviours must be capable of a high degree of plasticity.
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Affiliation(s)
- Donald C Bolser
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0144, USA.
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Xu F, Frazier DT. Role of the cerebellar deep nuclei in respiratory modulation. CEREBELLUM (LONDON, ENGLAND) 2002; 1:35-40. [PMID: 12879972 DOI: 10.1080/147342202753203078] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The cerebellum contains three deep nuclei, i.e., the fastigial, interposed and lateral nucleus. Recent studies demonstrate that these nuclei play different roles in respiratory modulation. Activation of fastigial nuclear neurons predominantly increases ventilation via elevation of respiratory frequency and/or tidal volume. Ablation of the fastigial nucleus did not significantly alter eupneic breathing, but did markedly attenuate the respiratory response to medium and severe hypercapnia as well as hypoxia. The fastigial nucleus contains respiratory-modulated neurons and about 25% of these neurons do not show their respiratory-related phasic activity until exposed to hypercapnia. The fastigial nucleus also contains CO2/H+ chemosensitive sites that contributed to the respiratory response to hypercapnia. Therefore, it is concluded that fastigial nuclear facilitatory influence on chemoreflexes emerges during hypercapnia via recruiting intrinsic chemoreception and respiratory-modulated neurons. Full expression of the fastigial nucleus-mediated respiratory responses depends on the integrity of the medullary gigantocellular nucleus at least partially via monosynaptic projections. Additionally, the fastigial nucleus receives inhibitory inputs primarily from Purkinje cells located in the medial vermis and recent observations indicate that simulation of these Purkinje cells inhibits respiration. As compared to chemoreflexes, fastigial nuclear role in the respiratory mechanoreflexes is not significant. The studies related to the role of the interposed and lateral nucleus in eupneic breathing are limited and the results appear controversial. However, there is evidence to show that the interposed nucleus contains respiratory-modulated neurons and is involved in coughing motor control.
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Affiliation(s)
- Fadi Xu
- Department of Physiology, University of Kentucky, Lexington, Kentucky 40536, USA.
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Xu F, Zhang Z, Frazier DT. Microinjection of acetazolamide into the fastigial nucleus augments respiratory output in the rat. J Appl Physiol (1985) 2001; 91:2342-50. [PMID: 11641379 DOI: 10.1152/jappl.2001.91.5.2342] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The rostral fastigial nucleus (FNr) of the cerebellum facilitates the respiratory response to hypercapnia. We hypothesized that some FNr sites are chemosensitive to focal tissue acidosis and contribute, at least partially, to respiratory modulation. Minute ventilation (VE) was recorded in 21 anesthetized and spontaneously breathing rats. Acetazolamide (AZ; 50 microM) was microinjected unilaterally into the FNr while an isocapnic condition was maintained throughout the experiment. AZ (1 or 20 nl) injection into the FNr significantly elevated VE (46.0 +/- 6.7%; P < 0.05), primarily via an increase in tidal volume (31.7 +/- 3.8%; P < 0.05), with little effect on arterial blood pressure. This augmented ventilatory response was initiated at 6.3 +/- 0.8 min and reached the peak at 19.7 +/- 4.1 min after AZ administration. The same dose of AZ delivered into the interposed and lateral cerebellar nuclei, or vehicle injection into the FNr, failed to elicit detectable cardiorespiratory responses. To determine whether the ventilatory response to AZ injection into the FNr resulted from an increase in respiratory central drive, the minute phrenic nerve activity (MPN) was recorded in seven paralyzed and ventilated rats. Similar to VE, MPN was increased by 38.9 +/- 8.9% (P < 0.05) after AZ administration. Our results suggest that elevation of CO2/H+ within the FNr facilitates respiratory output, supporting the presence of ventilatory chemoreception in rat FNr.
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Affiliation(s)
- F Xu
- Department of Physiology, University of Kentucky, Lexington, Kentucky 40536, USA.
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Xu F, Frazier DT. Modulation of respiratory motor output by cerebellar deep nuclei in the rat. J Appl Physiol (1985) 2000; 89:996-1004. [PMID: 10956343 DOI: 10.1152/jappl.2000.89.3.996] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study was undertaken to determine what roles the various cerebellar deep nuclei (CDN) play in modulation of respiration, especially during chemical challenges. Experiments were carried out in 12 anesthetized, tracheotomized, paralyzed, and ventilated rats. The integrated phrenic nerve activity (integralPN) was recorded as an index of respiratory motor output. A stimulating electrode was sequentially placed into the fastigial nucleus (FN), the interposed nucleus, and the lateral nucleus. Only stimulation of the FN significantly altered respiration, primarily via increasing respiratory frequency associated with a pressor response. The evoked respiratory responses persisted after blocking the pressor response via pretreatment with phenoxybenzamine or use of transient stimulation (<2 s) but were abolished by microinjection of kainic acid into the FN. To test the involvement of FN neurons in respiratory chemoreflexes, ventilation with hypercapnic gases mixture and intravenous injection of sodium cyanide were applied before and after CDN lesions induced by kainic acid. CDN lesions did not significantly alter eupneic breathing, but FN lesions attenuated the respiratory response to hypercapnia and sodium cyanide. We conclude that, with respect to the CDN in the rat, FN neurons uniquely modulate respiration independent of cardiovascular effects and facilitate respiratory responses mediated by activation of CO(2) and O(2) receptors.
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Affiliation(s)
- F Xu
- Department of Physiology, University of Kentucky, Lexington, Kentucky 40536, USA.
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