EFFECT OF SOMATOSTATIN ON CIRCADIAN-RHYTHMS OF FIRING AND 2-DEOXYGLUCOSE UPTAKE IN RAT SUPRACHIASMATIC SLICES

In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus appe ars to act as a circadian clock. The SCN vasoactive intestinal polypep tide-like immunoreactive neurons, which may act to mediate photic info rmation in the SCN, receive input from neurons immunoreactive for soma tostatin (SST). Therefore we investigated the role of SST as a transmi tter for entrainment by analyzing the phase-resetting effect of SST on the circadian rhythm of SCN firing activity. Perfusion of SST increas ed 2-deoxyglucose uptake at circadian time (CT) 18, but not at CT6. A 1-h or 15-min treatment with SST produced phase delays when it was adm inistered at CT13-14 and phase advances at CT22-23. Thus SST-induced p hase changes are similar to those for light pulses to animals under co nstant darkness. The present findings suggest that SST is a transmitte r for mediating information of entrainment to circadian clocks within the SCN.