Endocrine Abstracts

Circadian rhythms in behaviours and gene expression are driven by the autonomously rhythmic cells of the hypothalamic suprachiasmatic nucleus (SCN). In nocturnal rodents, restricting a daily meal to the lights-on phase, leads to entrainment of behaviour and gene expression in many extra-SCN hypothalamic nuclei and peripheral tissues. This anticipatory activity is independent of the SCN and is likely to arise from the activities of multiple hypothalamic centres including the dorsomedial (DMH). Here, we used digital video recording to monitor the behaviour of lean and 45% High Fat Fed (HFF) Han Wistar rats. Rats were maintained in a 12 h:12 h Light/Dark cycle (lights on at 6am) and were subject to day time restricted feeding (RF) for 28 days (meal provided 09:00 a.m.-13:00 p.m). Hypothalamic neuronal activation was measured by immunohistochemistry for c-Fos protein. Lean RF rats displayed the characteristic increase in cage activity and meal anticipatory hopper approaches, whereas HFF RF rats lacked meal anticipation, as determined by the lack of hopper approaching in the time preceding the scheduled meal. Immunohistochemistry data showed that HFF RF rats had 77% lower c-Fos expression in the SCN and 37% lower c-Fos expression in the DMH compared to lean RF rats. Consistent with other studies, we found a meal anticipatory rise in plasma corticosterone in the chow RF rats, whereas a post-anticipatory peak of plasma corticosterone levels was detected in HFF RF rats. Taken together, these findings suggest that neuronal activation in both the light-entrainable and food-entrainable oscillators are altered by high fat feeding. In addition this loss of meal anticipatory behaviour is associated with an altered regulation of plasma corticosterone.