Feeding cues alter clock gene oscillations and photic responses in the suprachiasmatic nuclei of mice exposed to a light/dark cycle.

The suprachiasmatic nuclei (SCN) of the hypothalamus contain the master mammalian circadian clock, which is mainly reset by light. Temporal restricted feeding, a potent synchronizer of peripheral oscillators, has only weak influence on light-entrained rhythms via the SCN, unless restricted feeding is coupled with calorie restriction, thereby altering phase angle of photic synchronization. Effects of daytime restricted feeding were investigated on the mouse circadian system. Normocaloric feeding at midday led to a predominantly diurnal (60%) food intake and decreased blood glucose in the afternoon, but it did not affect the phase of locomotor activity rhythm or vasopressin expression in the SCN. In contrast, hypocaloric feeding at midday led to 2-4 h phase advances of three circadian outputs, locomotor activity rhythm, pineal melatonin, and vasopressin mRNA cycle in the SCN, and it decreased daily levels of blood glucose. Furthermore, Per1 and Cry2 oscillations in the SCN were phase advanced by 1 and 3 h, respectively, in hypocalorie- but not in normocalorie-fed mice. The phase of Per2 and Bmal1 expression remained unchanged regardless of feeding condition. Moreover, the shape of behavioral phase-response curve to light and light-induced expression of Per1 in the SCN were markedly modified in hypocalorie-fed mice compared with animals fed ad libitum. The present study shows that diurnal hypocaloric feeding affects not only the temporal organization of the SCN clockwork and circadian outputs in mice under light/dark cycle but also photic responses of the circadian system, thus indicating that energy metabolism modulates circadian rhythmicity and gating of photic inputs in mammals.