Abe H, Honma S, Honma K-i. Daily restricted feeding resets the circadian clock in the suprachiasmatic nucleus of CS mice. Am J Physiol Regul Integr Comp Physiol 292: R607-R615, 2007. First published September 21, 2006; doi:10.1152/ajpregu.00331.2006.-Circadian rhythms in clock gene expressions in the suprachiasmatic nucleus (SCN) of CS mice and C57BL/6J mice were measured under a daily restricted feeding (RF) schedule in continuous darkness (DD), and entrainment of the SCN circadian pacemaker to RF was examined. After 2-3 wk under a light-dark cycle with free access to food, animals were released into DD and fed for 3 h at a fixed time of day for 3-4 wk. Subsequently, they returned to having free access to food for 2-3 wk. In CS mice, wheel-running rhythms entrained to RF with a stable phase relationship between the activity onset and feeding time, and the rhythms started to free run from the feeding time after the termination of RF. mPer1, mPer2, and mBMAL1 mRNA rhythms in the SCN showed a fixed phase relationship with feeding time, indicating that the circadian pacemaker in the SCN entrained to RF. On the other hand, in C57BL/6J mice, wheel-running rhythms free ran under RF, and clock gene expression rhythms in the SCN showed a stable phase relation not to feeding time but to the behavioral rhythms, indicating that the circadian pacemaker in the SCN did not entrain. These results indicate that the SCN circadian pacemaker of CS mice is entrainable to RF under DD and suggest that CS mice have a circadian clock system that can be reset by a signal associated with feeding time.biological rhythm; food entrainment; clock gene; behavior; brain CIRCADIAN RHYTHMS UNDER A RESTRICTED feeding (RF) schedule, in which the food available time is restricted for several hours in a day, have been well studied in rats and mice (for a review, see Refs. 24 and 31). RF induces prefeeding increases in locomotor activity and adrenal corticosterone secretion 2-3 h prior to the feeding time (food-anticipatory activity). The food-anticipatory activity has been suggested to be regulated by the circadian clock because the food-anticipatory activity appears only under RF in which the feeding interval is near 24 h (circadian range). However, RF had no entraining (synchronizing) effect on oscillation components of activity rhythm driven by the circadian pacemaker located in the hypothalamic suprachiasmatic nucleus (SCN). The food-anticipatory activity was not affected by SCN bilateral lesions, which disrupted the free-running component of circadian behavioral rhythms (29,30). Moreover, the circadian expression rhythms of clock genes, such as mPer1 and mPer2 in the SCN were unchanged by RF (8,13,32,34). These findings suggested that RF cannot reset the SCN central pacemaker, and food-anticipatory activity is regulated by another oscillator(s) that entrains to the RF (food-entrainable oscillator) located outside the SCN.On the other hand, one recent study reported that the SCNdriven behavioral rhythm and mPER2 protein rhythm in the SCN of sev...