Contrôle nerveux de la respiration chez la lamproie

Respiration is an essential rhythmic motor activity maintained throughout life. Neural networks called “rhythm generators” are responsible to produce rhythmic muscular contractions necessary for respiration in all vertebrates. These neural networks have been studied in mammals, but their detailed organization remains unknown. We used the lamprey as an animal model of a basal vertebrate to study respiratory neural networks. An important advantage of this experimental model is that we can record both groups/or single neurons in an intact brainstem preparation in vitro. Two repiratory rhythms can be observed in the lamprey: a fast rhythm (main rhythm) and a slow rhythm. Past studies have demonstrated that the fast rhythm is generated at the rosto-lateral pole of the V motor nucleus, a region named the paratrigeminal respiratory group (pTRG); whereas the slow rhythm was shown to be generated in the caudal part of the rhombencephalon by a caudal respiratory group (CRG) of neurons.  The results of this thesis have first characterized anatomically and physiologically the connections between the pTRG on both sides of the brain, as well as the connections between the pTRG and the respiratory motoneurons. We found that the pTRG contains different populations of neurons: neurons projecting towards their contralateral homologue and neurons projecting towards the respiratory motoneurons exclusively of the same side, or both sides of the brain. Our recordings of pTRG neurons have demonstrated that the neural activity of the latter is in phase with the respiratory rhythm. We have also shown that these neurons possess a complex axonal arborisation, including bilateral projections   towards groups of respiratory motoneurons in the brainstem, as well as connections linking the pTRGs on both sides.  Secondly, we have characterized, for the first time, the localization and the partial organization of the neural networks underlying the generation of the slow respiratory rhythm. Anatomical experiments have revealed the presence of populations of neurons distributed along the respiratory motoneuronal columns in the caudal part of the rhombencephalon. More precisely in the medial and lateral tegmentum, in the rdV, in the region close to the sulcus limitans, as well as through and in close proximity of the motor nucleus VII, IX and X. These neurons send projections to the other side and to the pTRG. Physiological experiments have shown that the activation of the regions comprising the different populations of neurons of the CRG, along the respiratory motoneuronal columns, is able to produce long bursts of discharges characteristic of the slow rhythm. Conversely, the bilateral inactivation of approximately one third of the caudal rhombencephalon abolishes that rhythm (VIIm/IXm/Xm (rostral part) et Xm (caudal part)). Moreover, we have demonstrated that we could abolish the slow rhythm without affecting the fast rhythm, in an intact brainstem preparation in vitro. Finally, intracellular recordings have found that the CRG region possesses neurons that show a rhythmic activity in phase with the slow rhythm.  In summary, our results demonstrate that the pTRG possesses neuronal networks presenting connection patterns capable of supporting the bilateral synchronization of the fast respiratory rhythm, as well as neurons projecting to the pTRG on the other side, adding redundancy and stability to the respiratory system. At last, our results also   demonstrate that the slow rhythm is generated by neural networks distributed bilaterally along the motor nucleus of the VII, the IX and the X, covering the whole length of the caudal rhombencephalon of the lamprey. As for the pTRG, the projections from the CRG towards its contralateral homologue, as well as the projections towards the pTRG, assure the bilateral synchronisation of the slow rhythm and its interactions with the fast rhythm.

Keyphrases: respiration, CPG, CRG, pTRG