Restricted feeding entrains liver clock without participation of the suprachiasmatic nucleus

Background: There are two main stimuli that entrain the circadian rhythm, t he light-dark cycle (LD) and restricted feeding (RF). Light-induced entrain ment requires induction of the Per1 and Per2 genes in the suprachiasmatic n ucleus (SCN), the locus of a main oscillator. In this experiment, we determ ined whether RF resets the expression of circadian clock genes in the mouse liver with or without participation of the SCN. Results: Mice were allowed access to food for 4 h during the daytime (7 h a dvance of feeding time) under LD or constant darkness (DD). The peaks of mP er1, mPer2, D-site-binding protein (Dbp) and cholesterol 7 alpha -hydroxyla se (Cyp7A) mRNA in the liver were advanced 6-12 h after 6 days of RF, where as those in SCN were unaffected. The advance of mPer expression in the live r by RF was still observed in SCN-lesioned mice. A 7 h advance in the LD cy cle advanced the peaks of clock gene expression in both the liver and SCN, whereas, a shift in the LD did not move the phase of the liver clock when t he shift was carried out under a fixed RF schedule during the night-time. Conclusions: These results suggest that restricted feeding strongly entrain ed the expression of circadian clock genes in the liver without the partici pation of an SCN clock function.