Neurotransmitters and the pharmacology of the suprachiasmatic nuclei.

The suprachiasmatic nucleus is the major component of the biological clock responsible for the generation and the regulation of circadian rhythms in behavioral and physiological functions. The SCN acts as an endogenous circadian pacemaker that becomes entrained to the light/dark cycle. Although many neuropeptides and neurotransmitters have been localized within and around the SCN, their role in the generation of the circadian signal still has to be elucidated. There are some data about the transmitters that are involved in the mechanism of entrainment. The way the SCN modulates the homeostatic control systems that are involved in the control of behaviour, also needs more clarification.