Serotonin neurons and sleep. II. Time course of dorsal raphe discharge, PGO waves, and behavioral states.

This study documents the time course profiles for simultaneous measures of: the electrographic signs of sleep and wakefulness, ponto-geniculo-occipital (PGO) waves, and extracellular discharge potentials for single cells in the dorsal raphe nucleus (DRN). These measures were obtained from intact, undrugged cats across 177 sleep cycles. Ninety-one of these sleep cycles were recorded with no prior forced activity. Forced activity previously has been shown to powerfully alter the temporal organization of sleep by shortening the duration of both the sleep cycle and the ultradian rhythm of DRN discharge. The present paper evaluated the hypothesis that DRN discharge time course might regulate the sleep cycle. These experiments documented the phase relationship between the time course of DRN discharge and the electrographic signs of sleep. These phase relationship were examined by determining whether forced locomotor activity could dissociate the time course profile for behavioral states, PGO waves, and DRN discharge. The results revealed that the time course of DRN discharge and PGO waves were always phase-locked to the time course of the ultradian sleep cycle. Furthermore, the results show that changes in DRN discharge consistently precede changes in PGO waves, and behavioral state. Since a cause must precede an effect, these data are consistent with the hypothesis that the DRN may be causally involved in sleep cycle regulation. These temporal data also provide parameter values for the continued evaluation of cellularly based, mathematical models of sleep cycle control.