[Effects of melatonin on circadian time keeping system].

This paper is intended to provide an overview of a physiological role of melatonin (MLT) in sleep-wake regulation. In human MLT studies, MLT has significantly increased sleepiness and fatigue during the daytime but not at night, which indicates time-dependent sleep-promoting effect of MLT. Op the other hand, MLT is known to have phase-shifting effect of biological clock. Phase response curve (PRC) for MLT administration was introduced in human studies. Successful melatonin treatments for circadian rhythm sleep-disorders based on PRC have been reported. MLT is known to decrease core body temperature. Effects of MLT on sleep-wake cycle may be mediated by a combination of sleep-promoting and phase-shifting actions and may involve the temperature lowering effect.