ABSTRACT
This chapter describes conserved and species-specific features of melatonin rhythm-generating systems. The source of circulating melatonin is the pineal gland, which can be considered to be the melatonin factory. One functional advantage of an endogenous clock which drives melatonin synthesis — as opposed to a simple light-off/dark-on system — is that the clock prevents high levels of melatonin synthesis from occurring during the day if animals are in darkness. The anatomical organization of the rhythm-generating system is essentially identical in all mammals. The clock that drives pineal melatonin synthesis is in the suprachiasmatic nucleus, which is connected to the pineal gland by a neural pathway passing through central and peripheral structures. Finally, an understanding of the molecules and molecular mechanisms involved in the regulation of melatonin production will provide new pharmacological targets for drugs which modulate circadian rhythms.
