Abstract

When food-access is restricted to a consistent time of day (restricted feeding), rodents reorganize many circadian behaviors around the mealtime. The suprachiasmatic nucleus (SCN) is the master circadian pacemaker, while the oval nucleus of the bed nucleus of the stria terminalis (BNST-OV) and the central nucleus of the amygdala (CEA) are important in stress, motivation and feeding. All these regions express the 'clock protein' Period2 (PER2) with a circadian rhythm. Restricted feeding changes PER2 expression patterns in the BNST-OV and CEA, but not in the SCN. To test the relative importance of motivational and homeostatic variables on PER2 expression in the BNST-OV and CEA, we contrasted daily restricted feeding (containing homeostatic and motivational components) with daily restricted treats (no weight loss, a motivational challenge only). Restricted feeding was comprised of fasted animals receiving repeated daily access to chocolate Ensure, whereas restricted treats consisted of sated animals receiving similar Ensure-access. In restricted feeding groups, the daily pattern of running wheel activity was consistently reorganized. However, in restricted treat groups, behavioral reorganization was more variable. Daily oscillations of PER2 expression in the BNST-OV and CEA were altered only under restricted-feeding, but not restricted-treat conditions. In contrast, cFOS expression in both the BNST-OV and CEA was enhanced in response to Ensure-access regardless of whether it was presented to fasted or sated rats. These findings suggest that some aspect of the homeostatic challenge associated with restricted feeding is important for shifting circadian PER2 expression in these areas of the central extended amygdala.