Behavior, sleep and melatonin.

The focus of most behavioral studies on melatonin relate to sleep, arousal levels and circadian rhythms of alertness. It has also been suggested that melatonin administration can reduce anxiety (Golus and King, 1981), affect learning (Datta and King, 1980), and exacerbate symptoms in patients suffering from severe depression (Carman et al., 1976). For a variety of reasons the effects of exogenous melatonin on sleep and circadian rhythms seem most likely to reflect the actual physiological functions of the endogenous hormone; however, definitive relationships between melatonin secretion and these effects have not yet been established. Administration of melatonin to humans in pharmacologic doses produces acute hypnotic-like effects (Vollrath et al., 1981; Lieberman et al., 1984). Available evidence suggests that melatonin may participate in the physiological regulation of sleep, particularly in determining the phase of circadian rhythms of sleep and sleepiness (Redman et al., 1983; Wurtman and Lieberman, 1985).