Circadian function of suprachiasmatic nuclei: molecular and cellular biology.

Suprachiasmatic nuclei (SCN) contain a circadian oscillator that is normally synchronized by the light/dark cycle. Embryonic SCN grafted into the brain of an SCN-lesioned arrhythmic host define the period of the restored circadian locomotor rhythm. Gene expression of immediate-early genes, such as c-fos and jun-B, in the ventrolateral SCN is associated with circadian synchronization by light pulses and subjected to circadian control. Vasopressin and somatostatin gene expression in dorsomedial SCN show distinct circadian rhythms with higher peptide levels occurring during the day. It is currently unknown whether the circadian oscillator in SCN resides in a single cell or is a property of cellular network. Briefly presented are some model views about the circadian oscillator in SCN and the molecular and cellular approaches to the circadian function of the nucleus.