[Modulation by the GABA of the ventro-oral-pontine reticular REM sleep-inducing neurons]

From a multidisciplinary study in our laboratory we have compiled numerous findings on the role played by the inhibitory neurotransmitter GABA in the ventral part of the oral pontine reticular nucleus (vRPO), REM sleep induction and maintenance brainstem structure. Functional GABA in the vRPO is located in a few small and scattered neuronal bodies, and in an abundant number of synaptic terminals: 30% of all synaptic terminals in vRPO are GABAergic. These terminals form inhibitory, symmetric synapses on the soma and different segments of the dendritic tree of the vRPO neurons, mainly in those of large diameter. In unitary intracellular studies, in vitro, we have demonstrated that GABA produces hyperpolarization of the vRPO neurons. In vivo experiments in freely moving cats, local microinjections of the GABA(A) receptor agonist muscimol decreased REM sleep. The different densities of GABA-immunoreactions and the diverse and complex morphological ultrastructure of the vRPO GABAergic terminals suggest that they have different origins and physiologic functions. There are GABAergic projections to the vRPO from diencephalic structures related with the other phases of the sleep-wakefulness cycle: wakefulness and non-REM sleep, which may be anatomical substrata for the GABAergic inhibition of the vRPO REM sleep-inducing neurons during these other phases.