Hypnotic activity of melatonin: involvement of semicarbazide hydrochloride, blocker of synthetic enzyme for GABA.

AIM To assess the effect of semicarbazide hydrochloride (SCZ), the blocker of synthetic enzyme for GABA, on the hypnotic activity of melatonin. METHODS Righting reflex method in mice and electroencephalography (EEG) in rats were used to determine effects of SCZ on sleep and hypnotic activity of melatonin. RESULTS Melatonin displayed a marked hypnotic activity both in righting reflex experiment and EEG recording. SCZ had no influence on sleep parameters in mice and rats when it was used alone. However, it blocked the sleep-potentiation effect of melatonin in mice. SCZ also inhibited melatonin-induced increase in total sleep time, slow wave sleep time, and paradoxical sleep time, and prevented melatonin-induced decrease in awake time in rats. CONCLUSION SCZ antagonized the hypnotic activity of melatonin. It is thought that the hypnotic activity of melatonin is mediated by GABAergic system.