The role of ghrelin in reward-based feeding and food anticipatory activity

V. St.-Onge, A. Abizaid

Location: Hall F-J
Presentation Time: Sunday, Oct 14, 2012, 4:00 PM – 5:00 PM
See details on OASIS

The incidence of obesity has more than doubled over the last 30 years, and this rise in prevalence is directly linked to increased consumption of energy-dense foods. Ghrelin, a gut-derived orexigenic hormone, has been shown to increase the incentive value of such foods in calorically sated animals, resulting in over-consumption and weight gain. This is highly reminiscent of situations in which individuals consume palatable desserts after eating filling meals. In addition, ghrelin is associated with a number of food-seeking behaviors, including the increase in locomotor activity that precedes a meal. In the current study, the role of ghrelin signaling in the dessert phenomenon and food anticipatory activity was assessed by comparing ghrelin receptor knock out rats (KO) to rats possessing an identical genetic background, with an intact ghrelin receptor gene (wildtype – WT) rats in a paradigm designed to model these behaviors. Specifically, KO and WT rats’ tendency to eat a palatable snack (cookie dough) when calorically sated was measured. Ten rats of each strain were exposed to a scheduled meal regimen during which free access to food was restricted to 4 hours per day (10am to 2pm) until they consumed most of their baseline daily intake during this interval. On the last day, the rats were exposed to 30 grams of cookie dough during the last hour of the meal. KO rats exhibited reduced locomotor activity one hour prior to meals compared to their WT counterparts. KO rats also consumed significantly less cookie dough per gram of body weight following their last meal compared to their WT counterparts, although regular chow consumption remained similar throughout the study. In an additional experiment, KO and WT rats’ motivation to obtain a high-fat food reward was further explored using an operant conditioning paradigm. Twelve rats of each strain underwent a total of 22 3-hour training sessions during which pressing a lever resulted in the presentation of a conditioned stimulus (CS – light + tone) and the delivery of a high-fat food pellet, under a fixed ratio (1) schedule. After an extinction period of 6 to 11 days, the lever pressing response was reinstated in 2 additional sessions by either pre-exposure to the food pellets or by contingent presentations of the CS. No strain differences were found in any of the behavioral endpoints of this experiment. Collectively, the results of this study suggest that ghrelin is involved in both food anticipatory behavior and overconsumption of readily available palatable foods. However, the absence of ghrelin signaling does not necessarily interfere with the motivation to acquire similar high-fat foods.