MELATONIN AND S-20098 INCREASE REM-SLEEP AND WAKE-UP PROPENSITY WITHOUT MODIFYING NREM SLEEP HOMEOSTASIS

The pineal hormone melatonin has been implicated in the circadian regu lation of sleep. In a crossover design, we investigated the effect of acute administration of 5 mg melatonin and a melatonin agonist (S-2009 8, 5 and 100 mg) in healthy young men when given 5 h before bedtime on sleep structure and electroencephalogram (EEG) power density. Each tr ial comprised a baseline, a treatment, and a posttreatment sleep episo de. Relative to the placebo condition, all treatments phase advanced t he core body temperature rhythm [Krauchi, K., C. Cajochen, D. Mori, C. Hetsch, and A. Wirz-Justice. Sleep Res. 24: 526, 1995; and Krauchi, K ., C. Cajochen, D. Mori, and A. Wirz-Justice. Am. J. Physiol. 272 (Reg ulatory Integrative Comp. Physiol. 41): R1178-1188, 1997]. Rapid eye m ovement (REM) sleep was increased after both melatonin and S-20098. Th is increase in REM sleep was most pronounced in the first REM sleep ep isode. On the posttreatment night after melatonin and S-20098 administ ration, more wakefulness was present in the latter one-half of the sle ep episode. EEG power density between 0.25 and 20 Hz during either non -REM (NREM) or REM sleep did not differ from placebo. Thus a single ea rly evening dose of melatonin or the agonist S-20098 increases REM sle ep propensity and advances sleep termination while, at the same time, the EEG in NREM sleep remains unaffected.