MELATONIN - THE KEY TO THE GATE OF SLEEP

This article reviews the evidence that melatonin, a hormone produced b y the pineal gland during the dark hours, plays a major role in the re gulation of the sleep-wake cycle. In recent years, our laboratory has been involved in a large-scale project aimed at investigating the role of endogenous melatonin in sleep-wake regulation and the effects of n onpharmacological levels of melatonin on sleep. Based on our finding o n the precise coupling between the endogenous nocturnal increase in me latonin secretion and the opening of the nocturnal sleep gate, we prop ose that the role of melatonin in the induction of sleep does not invo lve the active induction of sleep, but is rather mediated by an inhibi tion of a wakefulness-producing mechanism in the central nervous syste m. Our studies also suggest that exogenously administered melatonin ma y be beneficial in certain types of insomnia that are related to distu rbances in the normal secretion of the hormone.