EFFECTS OF MELATONIN AND THE MELATONIN RECEPTOR AGONIST S-20098 ON THE VIGILANCE STATES, EEG SPECTRA, AND CORTICAL TEMPERATURE IN THE RAT

The effects of melatonin (3 mg/kg i.p.) and the melatonin receptor ago nist S-20098 (3 mg/kg i.p.) on the vigilance states, electroencephalog ram power spectra (0.25-25.0 Hz), and cortical temperature were determ ined in eight rats in the first 6-hr interval of the 12-hr light perio d. Compared to the vehicle injection both compounds reduced the power density in non-rapid eye movement sleep in the low frequency range (1- 8 Hz) but did not affect the vigilance states and brain temperature. T he present findings do not indicate that the stimulation of the melato nin receptor exerts a hypnotic effect at doses that had been shown to affect the circadian rest-activity rhythm.