Daily rhythms in physiological and behavioral processes are controlled by a network of
circadian clocks, reset by inputs and delivering circadian signals to the brain and peripheral
organs. In mammals, at the top of the network is a master clock located in the
suprachiasmatic nuclei (SCN) of the hypothalamus, mainly reset by ambient light. The
nocturnal synthesis and release of melatonin by the pineal gland are tightly controlled by the
SCN clock and inhibited by light exposure. Several roles of melatonin in the circadian …