This study examined the effects of temperature and chronic hypoxia (CH) on pH/CO2- sensitive fictive breathing, and central pH/CO2 chemosensitivity, in cane toads (Bufo marinus). Toads were exposed to CH (10% or 15% O2) or control conditions (21% O2) for 10 days at either room temperature (controls), 10°C or 30°C following which in vitro brainstem-spinal cord preparations were used to examine central pH/CO2-sensitive fictive breathing (i.e., motor output from respiratory nerves which is the neural correlate of breathing). A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation (TFV). Cold temperature reduced and hot temperature increased fR and TFV under control conditions. CH attenuated fictive breathing independently of temperature. Additional experiments in which the aCSF temperature was varied indicate that the effects of temperature acclimation result from neural plastic changes within respiratory control centres in the brain.

This study examined the effects of temperature and chronic hypoxia (CH) on pH/CO2- sensitive fictive breathing, and central pH/CO2 chemosensitivity, in cane toads (Bufo marinus). Toads were exposed to CH (10% or 15% O2) or control conditions (21% O2) for 10 days at either room temperature (controls), 10°C or 30°C following which in vitro brainstem-spinal cord preparations were used to examine central pH/CO2-sensitive fictive breathing (i.e., motor output from respiratory nerves which is the neural correlate of breathing). A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation (TFV). Cold temperature reduced and hot temperature increased fR and TFV under control conditions. CH attenuated fictive breathing independently of temperature. Additional experiments in which the aCSF temperature was varied indicate that the effects of temperature acclimation result from neural plastic changes within respiratory control centres in the brain.

Les fonctions locomotrices et posturales sont contrôlées par un ensemble de réseaux neuronaux qui doivent interagir afin de produire un comportement locomoteur optimal, adaptable aux contraintes internes et externes de l’organisme. Le maintien d’un équilibre dynamique au cours de la locomotion repose sur des processus internes de coordination entre les réseaux nerveux spinaux et supraspinaux qui commandent les différents segments du corps (membres, tête et tronc). C’est dans ce contexte que nous nous sommes intéressés aux interactions entre la fonction locomotrice et la fonction posturale, sur des préparations réduites de tronc cérébral-moelle épinière de rats nouveau-nés, au sein desquelles les CPGs locomoteurs spinaux et les noyaux vestibulaires sont intacts. Des approches combinées électrophysiologiques, pharmacologiques, neuroanatomique et lésionnelles nous ont permis de mettre en évidence une partie des mécanismes à l’origine du couplage entre les différents réseaux neuronaux étudiés. Dans cette étude nous avons montré que les réseaux locomoteurs lombaires contrôlent l’activité des réseaux thoraciques axiaux, de manière à produire une activation coordonnée des réseaux moteurs des membres et du tronc. Cette coordination est sous influence des entrées supraspinales. Les amines induisent une organisation temporelle spécifique de l’activité des réseaux thoraco-lombo-sacrés, et les informations en provenance des noyaux vestibulaires influencent le rythme locomoteur. Ces données apportent des éléments nouveaux concernant les processus neuronaux à l’origine de la coordination des réseaux moteurs et posturaux. / Locomotor and postural functions are controlled by a set of neural networks that must interact to produce optimal locomotor behavior, adaptable to internal and external constraints of the body. Maintaining a dynamic balance during locomotion is based on internal coordination processes between spinal and supraspinal neuronal networks controlling different parts of the body (limbs, head and trunk). In this context, we have interested in the interactions between locomotor and postural functions, in spinal and supraspinal networks. The experiments were conducted on isolated brainstem-spinal cord preparations from neonatal rats, in which the spinal locomotor CPGs and the vestibular nuclei are intact. Electrophysiological, pharmacological, and neuroanatomical approaches allowed us to highlight some of the mechanisms involved in the coupling of the different neural networks. In this study we showed that the lumbar locomotor networks control the activity of axial thoracic networks, in order to produce a coordinated activation of motors networks of limbs and trunk. This coordination is modulated by amines and information from the vestibular nuclei. These data provide new evidence for spinal mechanisms involved in the coordination of motor and postural networks.

No description available.

Le système nerveux central possède des réseaux de neurones capables de générer des commandes motrices rythmiques en l'absence d'informations sensorielles. Ces réseaux neuronaux sont communément appelés générateurs centraux de patron (CPG, central pattern generator) et sont impliqués dans plusieurs fonctions et comportements vitaux tels que la locomotion et la respiration. Dans certaines circonstances, ces réseaux neuronaux se doivent d'interagir afin de produire un comportement moteur adapté aux contraintes environnementales ainsi qu'aux exigences de l'organisme. C'est notamment le cas lors d'un effort physique où une augmentation du rythme respiratoire est rapidement observée pour subvenir aux besoins en oxygène de l'organisme. Dans ce contexte de neurosciences intégratives, mon travail doctoral a porté sur l'étude des mécanismes neurogènes responsables de l'interaction entre les CPG respiratoires du tronc cérébral et les CPG locomoteurs de la moelle épinière. Cette étude a été réalisée sur des préparations de tronc cérébral-moelle épinière isolée in vitro de rat nouveau-né (P0 à P2) au sein desquelles les centres respiratoires et locomoteurs sont conservés intacts. Par des approches électrophysiologique, pharmacologique, lésionnelle et neuroanatomique, les mécanismes de coordination entre ces sous-groupes neuronaux ont été étudiés. Dans ce contexte, un des principaux résultats de ce travail doctoral est la mise en évidence de l'existence d'une influence ascendante excitatrice issues des CPG locomoteurs spinaux sur les centres respiratoires, et plus particulièrement sur le groupe respiratoire parafacial, structure située dans le bulbe rachidien et impliquée dans la genèse de la commande respiratoire. Outre son implication dans la modulation du rythme respiratoire, cette influence ascendante module également l'activité des populations neuronales expiratoires des régions spinales thoraciques et lombaires. Ces données constituent la première mise en évidence de l'existence de neurones bi-fonctionnels au sein de la moelle-épinière chez le rat nouveau-né. / The central nervous system contains neural networks that can generate rhythmic motor drive in absence of sensory feedback. These neural networks are commonly called central pattern generators (CPG) and are involved in many vital functions and behaviors, such as locomotion or respiration. In certain circumstances, these neural networks must interact to produce motor behaviors adapted to environmental constraints and the basic needs of organism. This is the case during physical exercise when the respiratory frequency increases in order to satisfy the oxygen needs. In a context of integrative neurosciences, my doctoral work aimed at exploring the neurogenic mechanisms involved in the coordination between the medullary respiratory networks and the spinal locomotor CPG. To address this question, we used an isolated in vitro brain stem-spinal cord preparations from neonatal rats (0-2 days) in which the respiratory and the locomotor networks are kept intact. Using electrophysiological, pharmacological, lesional and neuroanatomical approaches, mechanisms involved in the coordination between locomotor and respiratory rhythms have been studied. The major finding of this doctoral work is the identification of an ascending excitatory influence from spinal locomotor CPG to the respiratory networks, acting particularly on the parafacial respiratory group, which is known to be engaged in the genesis of expiratory activity. In addition to the respiratory frequency modulation, this ascending influence also modulates the activity of spinal expiratory neurons located in lumbar and thoracic segments. These data provide the first evidence for the existence of bi-functional neurons in newborn rat spinal cord.

The aim of this thesis was to elucidate the role of carbonic anhydrase (CA) in the modulation of central pH/CO2-sensitive fictive breathing (measured using in vitro brainstem-spinal cord preparations) in leopard frogs (Rana pipiens) following exposure to chronic hypercapnia (CHC) and chronic hypoxia (CH). CHC caused an augmentation in fictive breathing compared to the controls (normoxic normocapnic). Addition of acetazolamide (ACTZ), a cell-permeant CA inhibitor, to the superfusate reduced fictive breathing in the controls and abolished the CHC-induced augmentation of fictive breathing. ACTZ had no effect on preparations taken from frogs exposed to CH. Addition of bovine CA to the superfusate did not alter fictive breathing in any group, suggesting that the effects of ACTZ were due to inhibition of intracellular CA. Taken together, these results indicate that CA is involved in central pH/CO2 chemoreception and the CHC-induced increase in fictive breathing in the leopard frog.

The aim of this thesis was to elucidate the role of carbonic anhydrase (CA) in the modulation of central pH/CO2-sensitive fictive breathing (measured using in vitro brainstem-spinal cord preparations) in leopard frogs (Rana pipiens) following exposure to chronic hypercapnia (CHC) and chronic hypoxia (CH). CHC caused an augmentation in fictive breathing compared to the controls (normoxic normocapnic). Addition of acetazolamide (ACTZ), a cell-permeant CA inhibitor, to the superfusate reduced fictive breathing in the controls and abolished the CHC-induced augmentation of fictive breathing. ACTZ had no effect on preparations taken from frogs exposed to CH. Addition of bovine CA to the superfusate did not alter fictive breathing in any group, suggesting that the effects of ACTZ were due to inhibition of intracellular CA. Taken together, these results indicate that CA is involved in central pH/CO2 chemoreception and the CHC-induced increase in fictive breathing in the leopard frog.