The role of ghrelin in reinstatement of food seeking

V. St-Onge, A. Abizaid

Location: Halls B-H
Presentation Time: Wednesday, Nov 13, 2013, 8:00 AM – 9:00 AM
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Relapse to preferred high fat foods is a primary concern for people undergoing weight-reduction diets. Recent studies suggest that the orexigenic hormone ghrelin can bind to dopaminergic cells in the ventral tegmental area (VTA), a key structure in the brain’s reward system, and increase the incentive value of such foods. The current study examined the effects of intra-VTA ghrelin infusions in an operant conditioning task in which reinstatement of food seeking following a period of abstinence is considered analogous to the relapse phenomenon. Thirty Long-Evans rats were single-caged and put on a reverse dark-light cycle. The rats underwent 12 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 chocolate-flavored high-fat food pellet, under a fixed ratio (1) schedule. After an extinction period, stereotaxic surgery was performed wherein rats were implanted with a subcutaneous osmotic mini-pump that delivered either saline, ghrelin, or the ghrelin receptor antagonist ([D-Lys-3]-GHRP-6) directly into the VTA for 14 consecutive days. Following a 7 day recovery period, lever pressing responses were reinstated by either pre-exposure to the food pellets (food priming), contingent presentations of the CS, or an overnight fast. While drug treatment did not affect food priming- or fasting-induced reinstatement, we found that ghrelin-treated rats pressed significantly more than rats who received a ghrelin receptor antagonist in response to CS presentation. Similarly, ghrelin-treated rats pressed more than saline-treated rats in response to the CS, although this difference did not reach statistical significance. This effect was not due to differences in locomotion since all groups obtained similar scores on this measure. These results support previous findings implicating a role of ghrelin signaling in cue-potentiated feeding. Importantly, ghrelin receptors within the VTA appear to be mediating these effects.