Systems neuroscienceRole of the dorsal paragigantocellular reticular nucleus in paradoxical (rapid eye movement) sleep generation: a combined electrophysiological and anatomical study in the rat
Section snippets
The head-restrained rat method
The procedure (fixation of the head-restraining system and chronic implantation for the polygraphic recordings) has been previously described in detail (Boissard et al 2002, Gervasoni et al 1998). All experiments were conducted in agreement with the Guide for the Care and Use of Laboratory Animals (NIH Publication 80-23; authorization no. 03-505 of the French Ministry of Agriculture) and every effort was made to minimize the number of animals used and their suffering. Briefly, male
Classification of neurons by their behavior
The localization of each recorded neuron was estimated postmortem by assessing on brainstem sections the location of PSB or PHA-L deposit loci, corresponding to the area where cells were recorded. In this context, a sample of 41 neurons was recorded in the DPGi (n=9 rats, three PHA-L and six PSB injection sites) during at least one complete sleep–waking cycle (with W, SWS and PS). Neurons recorded outside the DPGi, i.e. in the vestibular nucleus or the gigantocellular reticular nucleus ventral
Discussion
We show for the first time that the DPGi contains neurons selectively activated during PS (tonic PS-on neurons). Moreover, using anterograde tract-tracing, we demonstrated that neurons of the DPGi simultaneously project to the main structures known to be involved in PS regulation, including the wake-promoting areas and the vlPAG. These original results highlight the role of the DPGi in PS regulation.
Noradrenergic neurons of the LC are silent during PS, due to a tonic GABAergic inhibition (
Conclusion
We highlighted here for the first time that the DPGi contains a population of PS-on neurons that may play a key role in the executive processes of PS generation, by inhibiting simultaneously the wake-promoting neurons and the vlPAG, two permissive systems for PS onset. Additional studies, such as the confirmation of the GABAergic phenotype of the PS-on neurons or the effects on PS of DPGi lesion, are necessary to test our hypothesis and to determine the mechanisms of activation of DPGi neurons
Acknowledgments
This work was supported by CNRS (FRE2469 and UMR5167) and Université C. Bernard Lyon I. R. Goutagny received a PhD grant from the “Région Rhône-Alpes” and the “Fondation pour la Recherche Médicale.” We thank S. Williams for his critical reading of the manuscript and R. Boissard and L. Leger for their help.
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