抄録
Most organisms show circadian rhythms in their physiological functions, which were driven by the pacemaker located, in mammals, in the suprachiasmatic nucleus of the hypothalamus (SCN). In rodents, the fetal SCN(s) already show circadian rhythmicity which is entrained by their maternal rhythms. The maternal signals are also dominant to entrain the pups' circadian pacemaker for several days after birth, which, however, are gradually replaced by the photic signal. In this study, we compared the responses to non-photic stimuli between newborn and adult SCN to examine the development of clock function in the SCN. [Method] Adult (8-42 weeks old) and newborn (6 days old) Bmal1-luc transgenic mice were used, in which firefly luciferase was expressed under control of clock gene Bmal1 promoter. Their SCN slices were cultured in serum-free medium containing 0.1mM luciferin, and bioluminescence was monitored continuously. Culture medium was exchanged at different phases of Bmal1-luc rhythms and the phase responses to medium exchange were examined. [Result and Discussion] In adult SCN, the phase of Bmal1-luc rhythm was not influenced by medium exchange at any phase, whereas, in newborn SCN, medium exchange induced phase-dependent phase shifts. In addition, about 25% of new born SCN exhibited bimodal rhythms in a day, which merged during the course of culturing. Such bimodality was never seen in adult SCN. These results can be explained in terms of coupling among neuronal oscillators which was much weaker in newborn SCN than in adult SCN. [J Physiol Sci. 2007;57 Suppl:S139]
