Abstract
The circadian rhythm of about 24 hours is a fundamental physiological function observed in almost all organisms from prokaryotes to humans. Identification of clock genes has allowed us to study the molecular bases for circadian behaviors and temporal physiological processes including autonomic nervous and neuroendocrine system. Although we know much about of molecular clock mechanism, we still do not fully understand how the molecular clock is coupled to the output pathways which controls circadian phenotypes. The neural output of the suprachiasmatic nucleus (SCN) in the mammalian hypothalamus is essential in the circadian regulation of behavioral activity. We have examined the downstream pathway of the central clock by means of real-time monitoring of multi-unit neural activity in feely moving mice. The results demonstrate that SCN neural activity is tightly coupled to environmental photic input that is relayed to the subparaventricular zone (SPZ), the neural activity rhythm in the SPZ being reversed in phase compared in the SCN. In Clock mutant mice exhibiting attenuated circadian locomotor rhythmicity, neural rhythmicity in the SCN and SPZ is affected in a similar manner. These results suggest that the SPZ plays a functional role in relaying circadian and photic signals from the SCN to centers involved in generating behavioral activity. [J Physiol Sci. 2008;58 Suppl:S20]
