Differential c-Fos expression in cholinergic, monoaminergic, and GABAergic cell groups of the pontomesencephalic tegmentum after paradoxical sleep deprivation and recovery.

Multiple lines of evidence indicate that neurons within the pontomesencephalic tegmentum are critically involved in the generation of paradoxical sleep (PS). From single-unit recording studies, evidence suggests that unidentified but "possibly" cholinergic tegmental neurons discharge at higher rates during PS than during slow wave sleep or even waking and would thus play an active role, whereas "presumed" monoaminergic neurons cease firing during PS and would thus play a permissive role in PS generation. In the present study performed on rats, c-Fos immunostaining was used as a reflection of neuronal activity and combined with immunostaining for choline acetyltransferase (ChAT), serotonin (Ser), tyrosine hydroxylase (TH), or glutamic acid decarboxylase (GAD) for immunohistochemical identification of active neurons during PS recovery ( approximately 28% of recording time) as compared with PS deprivation (0%) and PS control (approximately 15%) conditions. With PS recovery, there was a significant increase in ChAT+/c-Fos+ cells, a significant decrease in Ser+/c-Fos+ and TH+/c-Fos+ cells, and a significant increase in GAD+/c-Fos+ cells. Across conditions, the percent PS was correlated positively with tegmental cholinergic c-Fos+ cells, negatively with raphe serotonergic and locus coeruleus noradrenergic c-Fos+ cells, and positively with codistributed and neighboring GABAergic c-Fos+ cells. These results support the hypothesis that cholinergic neurons are active, whereas monoaminergic neurons are inactive during PS. They moreover indicate that GABAergic neurons are active during PS and could thus be responsible for inhibiting neighboring monoaminergic neurons that may be essential in the generation of PS.