Abstract
The circadian clock in the suprachiasmatic nucleus (SCN) is composed of multiple single-cell circadian oscillators, and a challenge now is to learn how individual cells are assembled to create an integrated tissue pacemaker that can orchestrate the temporal programs of whole organisms. By measuring SCN gene expression (in situ hybridization) as an assay of clock activity, we have found that assembled cellular oscillators can assume different configurations within the SCN, giving rise to unusual locomotor activity patterns. Thus, in hamsters maintained in constant light, splitting of the single circa-24 hr activity bout into two circa-12 hr components appears to be the consequence of a paired SCN that is reorganized into two oppositely-phased, left- and right-sided circadian pacemakers. In rats exposed to an artificially short light-dark cycle, the simultaneous expression of two stable circadian motor activity rhythms with different period lengths corresponds to the desynchronization of circadian pacemakers in the ventrolateral and dorsomedial subdivisions of the SCN (as previously defined by regional differences in their cyto- and chemo-architecture and topography of afferents and efferents). These kinds of reconfigurations (left/right, dorsal/ventral) of regional oscillators should provide a powerful approach for understanding intercellular coupling, tissue organization, and differential outputs of the SCN in intact, behaving animals. [J Physiol Sci. 2006;56 Suppl:S6]
