Effect of feeding on peripheral circadian rhythms and behaviour in mammals.

Although feeding time is a dominant cue for circadian rhythms in mammalian peripheral tissue, the effect of feeding and fasting on circadian gene expression and behaviour is unknown. Here we report that fasting does not affect the phase of rhythmic mRNA expression levels of the clock genes, mPer1, mPer2 and of the clock controlled gene, mDBP. However, the levels of each of these genes were significantly altered in different ways and recovered by feeding. We also found that feeding enhances phase-shifting to a new light-dark cycle of rhythmic mPer2 mRNA expression in the heart. Furthermore, feeding enhances the phase-shifting to new light-dark cycle of behaviour more than fasting. Our data indicate that feeding is an important cue for circadian behaviour rhythms as well as for the photo-entrainment of peripheral clock gene expression.