Investigating the role of ghrelin in food anticipatory activity of a scheduled treat

Rim Khazall (2015)R. Khazall, H. MacKay, A. Abizaid

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Food availability constitutes an environmental variable that can influence circadian rhythms. For instance, laboratory rodents exposed to restricted feeding schedules (i.e.schedules where food is available only a few hours during the day) results in changes in locomotor activity that include an increase in locomotor activity in anticipation of the oncoming meal. Interestingly, these behaviours are not only expressed under negative energy balance. Exposure to palatable foods is also associated with increases in food anticipatory behavior in rats and mice. Ghrelin, a hormone associated with feeding and metabolism, has also been implicated in the expression of food anticipatory behavior in mice and rats, but it’s not known if ghrelin is also associated with increased anticipatory behaviors to scheduled snacks. To determine if this is the case, we conducted experiments where male CD-1 mice were housed in locomotor activity boxes. After a 7 day baseline period of ad lib access to a standard laboratory chow, experimental mice were given daily 2hr access to commercial chocolate chip cookie dough in the middle of their light cycle (ZT6-ZT8) for 15 days. Results showed that experimental mice exhibited a significant increase in locomotor activity in anticipation of the cookie dough. This increase in anticipatory activity was maintained several days after access to the treat was terminated. The experimental mice also consumed more calories than controls, but did not gain more weight than controls, nor did they differ from the controls in plasma levels of glucose, corticosterone,or ghrelin. In a second experiment the experimental period was extended to 21 days and a 6 day re-exposure period was added, in which the animals were reintroduced to the cookie dough following the recovery period. As previously observed, mice that had limited access to cookie dough demonstrated a significant increase in anticipatory locomotor activity throughout the experimental period, which was maintained throughout recovery and was re-established during the re-exposure period. Body weight, food intake and plasma levels of ghrelin and glucose did not differ between the groups. These results suggest that CD-1 mice display robust locomotor activity in anticipation of a scheduled snack, and that behaviour continues for days following the last day of cookie dough exposure. The maintenance of treat anticipation after the cookie dough is no longer presented, however, is not associated with plasma ghrelin concentrations.