AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 5 1199-R1204, Copyright © 1993 by American Physiological Society
Effect of somatostatin on circadian rhythms of firing and 2-deoxyglucose uptake in rat suprachiasmatic slices
T. Hamada, S. Shibata, A. Tsuneyoshi, K. Tominaga and S. Watanabe
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyushu University 62, Fukuoka, Japan.
In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus appears
to act as a circadian clock. The SCN vasoactive intestinal polypeptide-like
immunoreactive neurons, which may act to mediate photic information in the
SCN, receive input from neurons immunoreactive for somatostatin (SST).
Therefore we investigated the role of SST as a transmitter for entrainment
by analyzing the phase-resetting effect of SST on the circadian rhythm of
SCN firing activity. Perfusion of SST increased 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 administered at CT13-14 and phase
advances at CT22-23. Thus SST-induced phase changes are similar to those
for light pulses to animals under constant darkness. The present findings
suggest that SST is a transmitter for mediating information of entrainment
to circadian clocks within the SCN.
