Dissociation of Per1 and Bmal1 circadian rhythms in the suprachiasmatic nucleus in parallel with behavioral outputs

Significance The circadian clock in the suprachiasmatic nucleus (SCN) regulates seasonality in physiology and behavior, which is best characterized by the change in the activity time of behavioral rhythms. In nocturnal rodents, the activity time was shortened in long summer days and lengthened in short winter days because of the change in the phase relationship of activity onset and offset, for which different circadian oscillators are predicted. Taking advantage of in vivo monitoring of clock gene expression in freely moving mice, we demonstrated that the circadian rhythms of Per1 and Bmal1 in the SCN are associated differentially with the phase shifts of activity onset and offset, respectively, suggesting the existence of two oscillations with different molecular mechanisms in timing of circadian behavior.