Effect of ritanserin on sleep stages and sleep EEG in the rat.

Ritanserin (1.0 and 2.5 mg/kg i.p.) was administered to rats before the start, of the light period, and sleep was recorded during the subsequent 12 h. The higher dose reduced sleep in the first 3 h. Both doses caused a more prolonged suppression of REM sleep. Spectral analysis of the EEG in non-REM sleep showed an increase of power density in the low frequency range (1.5-6 Hz) and a depression in the high frequency range (8-25 Hz). Since these changes differ from those previously observed after sleep deprivation, it is premature to conclude that the drug induces a physiological sleep intensification.