Age-related effect of ritanserin on the sleep-waking phases in rats.

The age-related effect of the specific 5-hydroxytryptamine-2A/2C (5-HT(2A/2C)) antagonist ritanserin at two doses 0.63 mg/kg and 2.5 mg/kg) on six sleep-waking phases in young, middle-aged, and old male Wistar rats was electroencephalographically (EEG) examined. Only in the young and middle-aged rats, ritanserin enhanced slow wave sleep and reduced wakefulness in a dose-dependent manner. Ritanserin suppressed paradoxical sleep, such that this effect did not depend on the age. Although the effect of ritanserin on slow wave sleep was significantly smaller in the old compared to the young and the middle-aged rats, ritanserin produced an apparent sleep-improving effect in the old age group.