The chronobiotic properties of melatonin.

In mammals, the exact role of melatonin (Mel) in the circadian timing system remains to be determined. However, exogenously administered Mel, as reported in the present mini-review, has been shown to affect the circadian clock. The sites and mechanisms of action involved in this "chronobiotic" effect of Mel have begun to be characterized. The suprachiasmatic nuclei (SCN) appear to be an important site for the entrainment effect of Mel and the presence of Mel receptors appears to be a prerequisite. However, the pharmacological dose of Mel needed to entrain circadian rhythms means that very probably other sites and mechanisms also play a role.