The study of biological clock responsible for suprachiasmatic nucleus-independent circadian rhythm induced by restricted feeding

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1.Effects of phase-shift of LD(light-dark) cycle and feeding time (Comparison between Wild-type mice(WT) and Cry 1&2 double mutant, behaviorally arrhythmic mice (DKO))After phase-shift of LD cycle, WT reentrained to the new LD cycle after several transient cycles while DKO immediately showed active phase during the dark period of the new LD cycle. In constant darkness (DD), both WT and DKO showed the anticipatory activity rhythm in response to restricted feeding, although in WT, suprachiasmatic nucleus(SCN)-dependent free-running component was also observed in their actograms. After phase-shift of the feeding time, the activity rhythm in response to the new feeding time was established within a couple of days in both WT and DKO. The rhythm which had established by the former feeding time, however, was also maintained for several cycles in both types of mice. This suggests that the molecular basis of the mechanisms for generation and entrainment of restricted feeding-induced rhythm is a … More t least in part different from that of SCN-dependent circadian rhythm.2.The entrainable range of SCN-dependent rhythm and restricted feeding-induced rhythm (WT vs.Cry1 mutant, short-period mice (SP))The actogram from both WT and SP showed SCN-dependent free-running component in DD irrespective of the period of given restricted feeding rhythms. Restricted feeding period ranging from 26h to 34h entrained all WT (N=6) and SP (N=8) mice except the fact that a half of SP mice failed to show clear feeding-induced rhythm when they were subjected to the 34 h feeding rhythm. This may suggest that upper entrainable limit of restricted feeding-induced rhythm of SP tends to be shorter than that of WT. LD cycles with the periods ranging from 26 h to 31 h under free access to food entrained all WT and SP mice. Further study using LD cycles with longer period is required to examine if upper entrainable limit of the period of LD cycle is shorter in SP mice than that in WT mice. Entraining mechanism of SCN-dependent activity rhythm of SP mouse, however, may be at least in part different from that in WT because, in the present study, the activity phase tended to be advanced as the period of LD cycle increases in SP mice. Less