Resetting Process of Peripheral Circadian Gene Expression after the Combined Reversal of Feeding Schedule and Light/Dark Cycle Via a 24-h Light Period Transition in Rats

To investigate the effect of light cue on the resetting of theperipheral clocks, we examined the resetting processes of clockgenes (Per1, Per2, Bmal1, Cry1, Dec1, and Rev-erbα) in the liverand heart of rats after the feeding and light-dark (LD) reversalvia a 24-h light period transition. The liver clock was reset quicklywithin 3 days, while the heart clock needed a longer time courseof 5-7 days to be completely re-entrained. Moreover, the reentrainment of Per1 and Per2 in the liver clock was more rapidthan that of the other four clock genes, suggesting the importantrole of these two clock genes in initiating the circadian resettingof the hepatic clock. However, the resetting rates of these twoclock genes were as similar as the others in the heart clock.Therefore, the resetting mechanisms underlining these twoperipheral clocks may be totally distinct. Furthermore, the reentrainment of the liver and heart clocks were relativelylengthened after the feeding and LD reversal via a light periodtransition compared to a dark period transition, suggesting asimultaneous shift of feeding schedule and the LD cycle mayfacilitate the circadian resetting in rats.