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Mille T, Bonilla A, Guillaud E, Bertrand SS, Menuet C, Cazalets JR. Muscarinic cholinergic modulation of cardiovascular variables in spinal cord injured rats. Exp Neurol 2023; 363:114369. [PMID: 36878399 DOI: 10.1016/j.expneurol.2023.114369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 02/16/2023] [Accepted: 02/28/2023] [Indexed: 03/07/2023]
Abstract
Spinal cord injury (SCI) leads not only to major impairments in sensorimotor control but also to dramatic dysregulation of autonomic functions including major cardiovascular disturbances. Consequently, individuals with SCI endure daily episodic hypo/hypertension and are at increased risk for cardiovascular disease. Several studies have suggested that an intrinsic spinal coupling mechanism between motor and sympathetic neuronal networks exist and that propriospinal cholinergic neurons may be responsible for a synchronized activation of both somatic and sympathetic outputs. We therefore investigated in the present study, the effect of cholinergic muscarinic agonists on cardiovascular parameters in freely moving adult rats after SCI. Female Sprague-Dawley rats were implanted with radiotelemetry sensors for long-term in vivo monitoring of blood pressure (BP). From BP signal, we calculated heart rate (HR) and respiratory frequency. We first characterized the physiological changes occurring after a SCI performed at the T3-T4 level in our experimental model system. We then investigated the effects on BP, HR and respiration, of the muscarinic agonist oxotremorine using one variant that crossed the blood brain barrier (Oxo-S) and one that does not (Oxo-M) in both Pre- and Post-SCI animals. After SCI, both HR and respiratory frequency increased. BP values exhibited an immediate profound drop before progressively increasing over the three-week post-lesion period but remained below control values. A spectral analysis of BP signal revealed the disappearance of the low frequency component of BP (0.3-0.6 Hz) referred to as Mayer waves after SCI. In Post-SCI animals, central effects mediated by Oxo-S led to an increase in HR and MAP, a slowdown in respiratory frequency and to an increased power in the 0.3-0.6 Hz frequency band. This study unravels some of the mechanisms by which muscarinic activation of spinal neurons could contribute to partial restoration of BP after SCI.
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Affiliation(s)
- Théo Mille
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Aurélie Bonilla
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Etienne Guillaud
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Sandrine S Bertrand
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Clément Menuet
- Institut de Neurobiologie de la Méditerranée, INMED UMR 1249, INSERM, Aix-Marseille Université, Marseille, France
| | - Jean-René Cazalets
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France.
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Ghali MGZ. Dynamic changes in arterial pressure following high cervical transection in the decerebrate rat. J Spinal Cord Med 2021; 44:399-410. [PMID: 31525149 PMCID: PMC8081319 DOI: 10.1080/10790268.2019.1639974] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Objective: Spinal transection has variable effects on arterial pressure, with some investigators demonstrating a precipitous decline and others reporting only a minimal decrease below normal. Recovery of arterial pressure following spinalization occurs with varying time courses - in some cases over days and in others over weeks to months. Given these findings, we sought to systematically test the hypothesis that in the unanesthetized decerebrate rat, arterial pressure would recover to pre-transection values over an acute time course.Design: Experiments were performed on a total of six Sprague-Dawley unanesthetized decerebrate adult male rats. In four rats, we determined dynamic changes in arterial pressure and heart rate in response to C1 transection.Results: Immediately following spinal cord injury, there were significant decreases in systolic blood (SBP) and mean arterial pressure (MAP), but not diastolic blood pressure (DBP). SBP, DBP, and MAP were significantly greater 170 min post-transection compared to immediate and 5 min-post transection values and were not statistically significantly different from pre-transection control. Heart rate decreased significantly following transection, but not immediately following the spinal cord injury. Lung inflation elicited depressor responses in all animals tested (n = 4 animals) and in three animals resulted in bradycardia. Hypercapnia tests effected a decrease in arterial pressure and heart rate (n = 3 animals).Conclusions: We demonstrate that in the unanesthetized decerebrate spinalized animal, arterial pressure is reduced by spinal transection and recovers over an acute time course to pre-transection values.
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Affiliation(s)
- Michael George Zaki Ghali
- Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA
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Bezdudnaya T, Lane MA, Marchenko V. Pharmacological disinhibition enhances paced breathing following complete spinal cord injury in rats. Respir Physiol Neurobiol 2020; 282:103514. [PMID: 32750492 PMCID: PMC9793860 DOI: 10.1016/j.resp.2020.103514] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Revised: 07/12/2020] [Accepted: 07/29/2020] [Indexed: 12/30/2022]
Abstract
Respiratory dysfunction is one of the most devastating and life-threatening deficits that occurs following cervical spinal cord injury (SCI). Assisted breathing with mechanical ventilators is a necessary part of care for many cervical injured individuals, but it is also associated with increased risk of secondary complications such as infection, muscle atrophy and maladaptive plasticity. Pre-clinical studies with epidural stimulation (EDS) have identified it as an alternative/additional method to support adequate lung ventilation without mechanical assistance. The full potential of EDS, however, may be limited by spinal inhibitory mechanisms within the injured spinal cord. The goal of the present work is to assess the potential improvement for EDS in combination with pharmacological disinhibition of spinal circuits following complete high cervical SCI. All experiments were performed in decerebrate, unanesthetized, non-paralyzed (n = 13) and paralyzed (n = 8) adult Sprague-Dawley rats 6 h following a complete C1 transection. The combination of high-frequency EDS (HF-EDS) at the C4 spinal segment with intrathecal delivery of GABA and glycine receptors antagonists (GABAzine and strychnine, respectively) resulted in significantly increased phrenic motor output, tidal volume and amplitude of diaphragm electrical activity compared to HF-EDS alone. Thus, it appears that spinal fast inhibitory mechanisms limit phrenic motor output and present a new neuropharmacological target to improve paced breathing in individuals with cervical SCI.
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Affiliation(s)
- T Bezdudnaya
- Drexel University College of Medicine, Department of Neurobiology & Anatomy, 2900 W Queen Lane, Philadelphia, PA, 19129, United States
| | - M A Lane
- Drexel University College of Medicine, Department of Neurobiology & Anatomy, 2900 W Queen Lane, Philadelphia, PA, 19129, United States
| | - V Marchenko
- Drexel University College of Medicine, Department of Neurobiology & Anatomy, 2900 W Queen Lane, Philadelphia, PA, 19129, United States; Medical College of Wisconsin, Department of Anesthesiology, 8701 W Watertown Plank Rd, Wauwatosa, WI, 53226, United States.
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Milanez MIO, Silva AM, Perry JC, Faber J, Nishi EE, Bergamaschi CT, Campos RR. Pattern of sympathetic vasomotor activity induced by GABAergic inhibition in the brain and spinal cord. Pharmacol Rep 2020; 72:67-79. [PMID: 32016845 DOI: 10.1007/s43440-019-00025-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 09/05/2019] [Accepted: 10/11/2019] [Indexed: 10/25/2022]
Abstract
BACKGROUND Knowledge of the central areas involved in the control of sympathetic vasomotor activity has advanced in the last few decades. γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mammal nervous system, and a microinjection of bicuculline, an antagonist of GABA type A (GABA-A) receptors, into the paraventricular nucleus of the hypothalamus (PVN) alters the pattern of sympathetic activity to the renal, splanchnic and lumbar territories. However, studies are needed to clarify the role of GABAergic inputs in other central areas involved in the sympathetic vasomotor activity. The present work studied the cardiovascular effects evoked by GABAergic antagonism in the PVN, RVLM and spinal cord. METHODS AND RESULTS Bicuculline microinjections (400 pMol in 100 nL) into the PVN and rostral ventrolateral medulla (RVLM) as well as intrathecal administration (1.6 nmol in 2 µL) evoked an increase in blood pressure, heart rate, and renal and splanchnic sympathetic nerve activity (rSNA and sSNA, respectively), inducing a higher coherence between rSNA and sSNA patterns. However, some of these responses were more intense when the GABA-A antagonism was performed in the RVLM than when the GABA-A antagonism was performed in other regions. CONCLUSIONS Administration of bicuculline into the RVLM, PVN and SC induced a similar pattern of renal and splanchnic sympathetic vasomotor burst discharge, characterized by a low-frequency (0.5 Hz) and high-amplitude pattern, despite different blood pressure responses. Thus, the differential control of sympathetic drive to different targets by each region is dependent, in part, on tonic GABAergic inputs.
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Affiliation(s)
- Maycon I O Milanez
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, Ground Floor, CEP 04023-060, São Paulo, SP, Brazil
| | - Adilson M Silva
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, Ground Floor, CEP 04023-060, São Paulo, SP, Brazil
| | - Juliana C Perry
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, Ground Floor, CEP 04023-060, São Paulo, SP, Brazil
| | - Jean Faber
- Department of Neurology and Neurosurgery, Universidade Federal de São Paulo, Escola Paulista de Medicina, São Paulo, Brazil
| | - Erika E Nishi
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, Ground Floor, CEP 04023-060, São Paulo, SP, Brazil
| | - Cássia T Bergamaschi
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, Ground Floor, CEP 04023-060, São Paulo, SP, Brazil
| | - Ruy R Campos
- Cardiovascular Division, Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, Ground Floor, CEP 04023-060, São Paulo, SP, Brazil.
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Abstract
Variability in cardiovascular spectra was first described by Stephan Hales in 1733. Traube and Hering initially noted respirophasic variation of the arterial pressure waveform in 1865 and Sigmund Mayer noted a lower frequency oscillation of the same in anesthetized rabbits in 1876. Very low frequency oscillations were noted by Barcroft and Nisimaru in 1932, likely representing vasogenic autorhythmicity. While the origins of Traube Hering and very low frequency oscillatory variability in cardiovascular spectra are well described, genesis mechanisms and functional significance of Mayer waves remain in controversy. Various theories have posited baroreflex and central supraspinal mechanisms for genesis of Mayer waves. Several studies have demonstrated the persistence of Mayer waves following high cervical transection, indicating a spinal capacity for genesis of these oscillations. We suggest a general tendency for central sympathetic neurons to oscillate at the Mayer wave frequency, the presence of multiple Mayer wave oscillators throughout the brainstem and spinal cord, and possible contemporaneous genesis by baroreflex and vasomotor mechanisms.
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Affiliation(s)
- George Zaki Ghali
- United States Environmental Protection Agency, Arlington, VA; Department of Toxicology, Purdue University, West Lafayette, IN, USA
| | - Michael George Zaki Ghali
- Department of Neurological Surgery, Houston Methodist Hospital, Houston, TX; Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Emil Zaki Ghali
- Department of Medicine, Inova Alexandria Hospital, Alexandria, VA, USA; Department of Cardiothoracic Surgery, El Gomhoureya General Hospital, Alexandria, Egypt
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Bowman BR, Bokiniec P, McMullan S, Goodchild AK, Burke PGR. Somatostatin 2 Receptors in the Spinal Cord Tonically Restrain Thermogenic, Cardiac and Other Sympathetic Outflows. Front Neurosci 2019; 13:121. [PMID: 30842723 PMCID: PMC6391348 DOI: 10.3389/fnins.2019.00121] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Accepted: 02/04/2019] [Indexed: 12/25/2022] Open
Abstract
The anatomical and functional characterization of somatostatin (SST) and somatostatin receptors (SSTRs) within the spinal cord have been focused in the dorsal horn, specifically in relation to sensory afferent processing. However, SST is also present within the intermediolateral cell column (IML), which contains sympathetic preganglionic neurons (SPN). We investigated the distribution of SSTR2 within the thoracic spinal cord and show that SSTR2A and SSTR2B are expressed in the dorsal horn and on SPN and non-SPN in or near the IML. The effects of activating spinal SSTR and SSTR2 were sympathoinhibition, hypotension, bradycardia, as well as decreases in interscapular brown adipose tissue temperature and expired CO2, in keeping with the well-described inhibitory effects of activating SSTR receptors. These data indicate that spinal SST can decrease sympathetic, cardiovascular and thermogenic activities. Unexpectedly blockade of SSTR2 revealed that SST tonically mantains sympathetic, cardiovascular and thermogenic functions, as activity in all measured parameters increased. In addition, high doses of two antagonists evoked biphasic responses in sympathetic and cardiovascular outflows where the initial excitatory effects were followed by profound but transient falls in sympathetic nerve activity, heart rate and blood pressure. These latter effects, together with our findings that SSTR2A are expressed on GABAergic, presumed interneurons, are consistent with the idea that SST2R tonically influence a diffuse spinal GABAergic network that regulates the sympathetic cardiovascular outflow. As described here and elsewhere the source of tonically released spinal SST may be of intra- and/or supra-spinal origin.
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Affiliation(s)
- Belinda R Bowman
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Phillip Bokiniec
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia.,Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Simon McMullan
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Ann K Goodchild
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Peter G R Burke
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia.,Neuroscience Research Australia, Sydney, NSW, Australia
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Sourioux M, Bertrand SS, Cazalets JR. Cholinergic-mediated coordination of rhythmic sympathetic and motor activities in the newborn rat spinal cord. PLoS Biol 2018; 16:e2005460. [PMID: 29985914 PMCID: PMC6053244 DOI: 10.1371/journal.pbio.2005460] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 07/19/2018] [Accepted: 06/22/2018] [Indexed: 02/07/2023] Open
Abstract
Here, we investigated intrinsic spinal cord mechanisms underlying the physiological requirement for autonomic and somatic motor system coupling. Using an in vitro spinal cord preparation from newborn rat, we demonstrate that the specific activation of muscarinic cholinergic receptors (mAchRs) (with oxotremorine) triggers a slow burst rhythm in thoracic spinal segments, thereby revealing a rhythmogenic capability in this cord region. Whereas axial motoneurons (MNs) were rhythmically activated during both locomotor activity and oxotremorine-induced bursting, intermediolateral sympathetic preganglionic neurons (IML SPNs) exhibited rhythmicity solely in the presence of oxotremorine. This somato-sympathetic synaptic drive shared by MNs and IML SPNs could both merge with and modulate the locomotor synaptic drive produced by the lumbar motor networks. This study thus sheds new light on the coupling between somatic and sympathetic systems and suggests that an intraspinal network that may be conditionally activated under propriospinal cholinergic control constitutes at least part of the synchronizing mechanism.
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Affiliation(s)
| | | | - Jean-René Cazalets
- Université de Bordeaux, CNRS UMR 5287, Bordeaux, France
- * E-mail: (JRC); (SSB)
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8
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Kandukuri DS, Phillips JK, Tahmindjis M, Hildreth CM. Effect of anaesthetic and choice of neuromuscular blocker on vagal control of heart rate under laboratory animal experimental conditions. Lab Anim 2017; 52:280-291. [PMID: 28862524 DOI: 10.1177/0023677217725365] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Neuromuscular-blocking agents are commonly used in laboratory animal research settings. Due to actions of cholinergic receptors at locations other than the motor end-plate, these agents have a strong propensity to modulate autonomic outflow and may therefore not be desirable in studies examining autonomic function. This study aimed to compare the effect of two non-depolarizing neuromuscular-blocking agents, pancuronium and cisatracurium, on blood pressure, heart rate and non-invasive indices of autonomic function (heart rate variability, systolic blood pressure variability and baroreflex sensitivity) under two different types of anaesthesia in Lewis rats. Pancuronium produced a profound vagolytic response characterized by tachycardia, reduction in heart rate variability and baroreflex sensitivity under urethane anaesthesia, and with minimal effect under isoflurane anaesthesia. Conversely, cisatracurium produced no evidence of vagolytic action under either urethane or isoflurane anaesthesia. Therefore, for studies interested in examining autonomic function, particularly baroreflex or vagal function, neuromuscular blockade would be best achieved using cisatracurium.
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Affiliation(s)
- Divya Sarma Kandukuri
- 1 Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia
| | - Jacqueline K Phillips
- 1 Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia
| | - Mark Tahmindjis
- 2 Department of Clinical Medicine, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia
| | - Cara M Hildreth
- 1 Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia
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Ghali MGZ, Marchenko V. Patterns of Phrenic Nerve Discharge after Complete High Cervical Spinal Cord Injury in the Decerebrate Rat. J Neurotrauma 2016; 33:1115-27. [DOI: 10.1089/neu.2015.4034] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Michael George Zaki Ghali
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Vitaliy Marchenko
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania
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10
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Bowman BR, Goodchild AK. GABA and enkephalin tonically alter sympathetic outflows in the rat spinal cord. Auton Neurosci 2015; 193:84-91. [DOI: 10.1016/j.autneu.2015.08.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Revised: 07/24/2015] [Accepted: 08/19/2015] [Indexed: 12/29/2022]
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Müller-Ribeiro FCF, Dampney RAL, McMullan S, Fontes MAP, Goodchild AK. Disinhibition of the midbrain colliculi unmasks coordinated autonomic, respiratory, and somatomotor responses to auditory and visual stimuli. Am J Physiol Regul Integr Comp Physiol 2014; 307:R1025-35. [DOI: 10.1152/ajpregu.00165.2014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The midbrain superior and inferior colliculi have critical roles in generating coordinated orienting or defensive behavioral responses to environmental stimuli, and it has been proposed that neurons within the colliculi can also generate appropriate cardiovascular and respiratory responses to support such behavioral responses. We have previously shown that activation of neurons within a circumscribed region in the deep layers of the superior colliculus and in the central and external nuclei of the inferior colliculus can evoke a response characterized by intense and highly synchronized bursts of renal sympathetic nerve activity and phrenic nerve activity. In this study, we tested the hypothesis that, under conditions in which collicular neurons are disinhibited, coordinated cardiovascular, somatomotor, and respiratory responses can be evoked by natural environmental stimuli. In response to natural auditory, visual, or somatosensory stimuli, powerful synchronized increases in sympathetic, respiratory, and somatomotor activity were generated following blockade of GABAA receptors in a specific region in the midbrain colliculi of anesthetized rats, but not under control conditions. Such responses still occurred after removal of most of the forebrain, including the amygdala and hypothalamus, indicating that the essential pathways mediating these coordinated responses were located within the brain stem. The temporal relationships between the different outputs suggest that they are driven by a common population of “command neurons” within the colliculi.
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Affiliation(s)
- Flávia C. F. Müller-Ribeiro
- Australian School of Advanced Medicine, Macquarie University, New South Wales, Australia; and
- Laboratório de Hipertensão, Departamento de Fisiologia e Biofísica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Minas Gerais, Brazil; and
| | - Roger A. L. Dampney
- School of Medical Sciences (Physiology) and Bosch Institute, University of Sydney, New South Wales, Australia
| | - Simon McMullan
- Australian School of Advanced Medicine, Macquarie University, New South Wales, Australia; and
| | - Marco A. P. Fontes
- Laboratório de Hipertensão, Departamento de Fisiologia e Biofísica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Minas Gerais, Brazil; and
| | - Ann K. Goodchild
- Australian School of Advanced Medicine, Macquarie University, New South Wales, Australia; and
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12
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Shahid IZ, Rahman AA, Pilowsky PM. Intrathecal orexin A increases sympathetic outflow and respiratory drive, enhances baroreflex sensitivity and blocks the somato-sympathetic reflex. Br J Pharmacol 2011; 162:961-73. [PMID: 21054340 DOI: 10.1111/j.1476-5381.2010.01102.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Intrathecal (i.t.) injection of orexin A (OX-A) increases blood pressure and heart rate (HR), but the effects of OX-A on sympathetic and phrenic, nerve activity, and the baroreflex(es), somato-sympathetic and hypoxic chemoreflex(es) are unknown. EXPERIMENTAL APPROACH Urethane-anaesthetized, vagotomized and artificially ventilated male Sprague-Dawley rats were examined in this study. The effects of i.t. OX-A (20 nmol 10 µL⁻¹) on cardiorespiratory parameters, and responses to stimulation of the sciatic nerve (electrical), arterial baroreceptors (phenylephrine hydrochloride, 0.01 mg kg⁻¹ i.v.) and peripheral (hypoxia) chemoreceptors were also investigated. KEY RESULTS i.t. OX-A caused a prolonged dose-dependent sympathoexcitation, pressor response and tachycardia. The peak effect was observed at 20 nmol with increases in mean arterial pressure, HR and splanchnic sympathetic nerve activity (sSNA) of 32 mmHg, 52 beats per minute and 100% from baseline respectively. OX-A also dose-dependently increased respiratory drive, as indicated by a rise in phrenic nerve amplitude and a fall in phrenic nerve frequency, an increase in neural minute ventilation, a lengthening of the expiratory period, and a shortening of the inspiratory period. All effects of OX-A (20 nmol) were attenuated by the orexin receptor 1 antagonist SB 334867. OX-A significantly reduced both sympathoexcitatory peaks of somato-sympathetic reflex while increasing baroreflex sensitivity. OX-A increased the amplitude of the pressor response and markedly amplified the effect of hypoxia on sSNA. CONCLUSIONS Thus, activation of OX receptors in rat spinal cord alters cardiorespiratory function and differentially modulates sympathetic reflexes.
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Affiliation(s)
- I Z Shahid
- Australian School of Advanced Medicine, Macquarie University, Sydney, Australia
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13
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Garrison MK, Schmit BD. Flexor reflex decreases during sympathetic stimulation in chronic human spinal cord injury. Exp Neurol 2009; 219:507-15. [PMID: 19615998 DOI: 10.1016/j.expneurol.2009.07.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2009] [Revised: 06/29/2009] [Accepted: 07/06/2009] [Indexed: 11/18/2022]
Abstract
A better understanding of autonomic influence on motor reflex pathways in spinal cord injury is important to the clinical management of autonomic dysreflexia and spasticity in spinal cord injured patients. The purpose of this study was to examine the modulation of flexor reflex windup during episodes of induced sympathetic activity in chronic human spinal cord injury (SCI). We simultaneously measured peripheral vascular conductance and the windup of the flexor reflex in response to conditioning stimuli of electrocutaneous stimulation to the opposite leg and bladder percussion. Flexor reflexes were quantified using torque measurements of the response to a noxious electrical stimulus applied to the skin of the medial arch of the foot. Both bladder percussion and skin conditioning stimuli produced a reduction (43-67%) in the ankle and hip flexor torques (p<0.05) of the flexor reflex. This reduction was accompanied by a simultaneous reduction in vascular conductance, measured using venous plethysmography, with a time course that matched the flexor reflex depression. While there was an overall attenuation of the flexor reflex, windup of the flexor reflex to repeated stimuli was maintained during periods of increased sympathetic activity. This paradoxical depression of flexor reflexes and minimal effect on windup is consistent with inhibition of afferent feedback within the superficial dorsal horn. The results of this study bring attention to the possible interaction of motor and sympathetic reflexes in SCI above and below the T5 spinal level, and have implications for clinicians in spasticity management and for researchers investigating motor reflexes post SCI.
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Affiliation(s)
- M Kevin Garrison
- Marquette University, Department of Biomedical Engineering, P.O. Box 1881, Milwaukee, Wisconsin 53233, USA
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14
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Respiratory neuroplasticity and cervical spinal cord injury: translational perspectives. Trends Neurosci 2008; 31:538-47. [PMID: 18775573 DOI: 10.1016/j.tins.2008.07.002] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 07/10/2008] [Accepted: 07/17/2008] [Indexed: 12/18/2022]
Abstract
Paralysis of the diaphragm is a severe consequence of cervical spinal cord injury. This condition can be experimentally modeled by lateralized, high cervical lesions that interrupt descending inspiratory drive to the corresponding phrenic nucleus. Although partial recovery of ipsilateral diaphragm function occurs over time, recent findings show persisting chronic deficits in ventilation and phrenic motoneuron activity. Some evidence suggests, however, that spontaneous recovery can be enhanced by modulating neural pathways to phrenic motoneurons via synaptic circuitries which appear more complex than previously envisioned. The present review highlights these and other recent experimental multidisciplinary findings pertaining to respiratory neuroplasticity in the rat. Translational considerations are also emphasized, with specific attention directed at the clinical and interpretational strengths of different lesion models and outcome measures.
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