Ritanserin-induced changes in sleep-waking phases in rats.

Ten male Wistar rats were chronically implanted with conventional electrodes for sleep-waking stages detection. Three 12-hour electroencephalographic (EEG) registrations were performed once a week, after i.p. injection of the serotonin-2 (5-HT2) antagonist ritanserin at two doses (0.63 mg/kg and 2.5 mg/kg) and after ritanserin vehicle. The goal of the present study was to examine the effects of ritanserin on sleep-waking phases, and to obtain additional data about the participation of 5-HT2 receptors in the regulation of sleep and wake behaviour. Six sleep-waking stages were detected: active waking, quiet waking, light slow-wave sleep, deep slow-wave sleep, intermediate stage of sleep and paradoxical sleep. Each of the 12-h postdrug EEG records was divided into 3 consecutive 4-hour periods and the sleep-waking stages were scored visually for every minute of the whole postdrug period. The three periods were compared in order to evaluate the effect of ritanserin in dynamics. The results obtained showed a significant decrease in wakefulness and paradoxical sleep, a significant increase in slow-wave sleep (mainly the deep slow-wave sleep) and in the intermediate stage of sleep. These changes in the sleep-waking phases occurred in a dose-dependent manner, the larger the dose of ritanserin, the stronger the effect of ritanserin. The changes were more pronounced during the first 4-h period and then a restoration in the sleep-waking phases took place except for the paradoxical sleep.