Metabolic entrainment to scheduled meals and treats in relation to corticosterone and ghrelin

R. Khazall, T. Rodrigues, N. Bashir, A. Abizaid
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Ghrelin, an orexignic gut hormone, is secreted in anticipation of food and is associated with the locomotor activity that precedes the presentation of food. While it is clear that anticipation occurs when food is only available during short periods of the day, some reports show that it also occurs in ad lib conditions in anticipation of scheduled treats. Here we attempted to replicate this and to determine if ghrelin plays a role in this form of entrainment. Following baseline measures, CD-1 male mice were assigned to one of 3 groups (n=8) : ad lib fed, restricted feeding schedule (food available from ZT 4-ZT8) (RF), and high fat treat (treat available from ZT4-ZT6) (HF). After 15 days, all mice were sacrificed and their blood was collected for hormonal analyses. As expected, mice in the RF group showed locomotor activity in anticipation of food, and this was associated with an inversion in circadian rhythms of metabolic rate. While mice in the HF group did not show a significant increase in anticipatory activity to the treat, they did over consume calories and shifted a portion of their caloric intake to the time when the treat was available. Furthermore, their circadian rhythms in metabolism were dampened. Ghrelin and corticosterone concentrations in anticipation of a meal were elevated in mice in the RF group compared to controls and with mice exposed to the scheduled treat. Interestingly a small but significant rise in both ghrelin and corticosterone was detected in HF mice compared to controls. These data shows that restricted feeding schedules entrain metabolic function as well as behavior and that scheduled treats, while not as effective in entraining behavior, they do affect circadian rhythms of food consumption and dampen rhythms in metabolism. Finally this occurs in correlation with increases in plasma ghrelin and corticosterone.