Melatonin and sleep: possible involvement of GABAergic mechanisms

Abstract

Pineal melatonin is synthezized and secreted in close association with the light/dark cycle. The temporal relatinship between the nocturnal rise in melatonin secretion and the "opening of the sleep gate" (i.e.the increase in sleep propensity at the begining of the night), compled with the sleep-promoting effects of exogenous melatonin, support the view that endogenous melatonin is involved in the rgulation of sleep. The sleep-promoting and sleep-wake rhythm-regulating effects of melatonin are atributed to its action on MT1 and MT2 melatonn receptors present in the suprachiasmatic nucleus (SNC) of the hypothalamus. Nearly all neurons in the SCN contain GABA and GABA driven mechaisms have been shown to play a key role in circadian coupling among regions and reurons in the SCN. Results are reviewed indicating that among the neurochemical effects fo melatonin in the jSCN, its interaction with the GABAergic system appears to be significant for coupling to sleep mechanisms