The motivation to obtain sugar pellets is attenuated in the ghrelin receptor knock-out rat

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 676-684-Central Regulation of Appetite & Feeding
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-684
Samantha Joy King*, Logan Seaman and Alfonso Abizaid
Carleton University, Ottawa, ON, Canada
A role for ghrelin in the motivation to obtain palatable food sources has been supported by many recent studies. In the absence of a negative energy balance, which typically drives food procurement, ghrelin appears able to increase the saliency of palatable food stimuli and thus increase the amount of work an animal is willing to perform to obtain food. Increased consumption of such foods can lead to a number of unhealthy consequences, including but not limited to obesity. Ghrelin acts on the growth hormone secretagogue receptor 1A (GHSR-1A) in the central nervous system to exert its orexigenic effects. In the current study, we used a recently developed GHSR knock out (KO) rat to examine the role of ghrelin in the motivation to obtain food reinforcers of both average and high palatability.

Food restricted GHSR-KO  (n=10) and wild-type (WT) rats (n=10) were trained to bar press on a fixed ratio 1 (FR1) schedule of reinforcement, followed by FR4, and finally a progressive ratio (PR) schedule for purified grain-based pellets. The procedure was repeated for purified chocolate-flavored, sugar, and high-fat chocolate pellets, respectively. We hypothesized that an absence of intact ghrelin signaling in KO rats would attenuate the amount of effort produced to obtain reinforcers, an effect that is likely to be exaggerated when the pellet is highly palatable. An analysis of the cost-benefit ratio as measured by breakpoint was conducted. Results show that while the KO and WT rats performed similarly to eachother on a PR schedule to obtain grain, chocolate flavor and high-fat chocolate pellets, when pressing for sugar pellets, the KO rats failed to increase their rate of bar pressing. Interestingly, both WT and KO rats exhibited less effort to obtain the high-fat chocolate reinforcer (though the amount of calories earned was comparable). In the presence of a sweet reinforcer the GHSR KO rat does not escalate its responding as is typical for a hungry animal. As sugar is known to be a highly palatable reinforcer, these results highlight that the absence of GHSR can influence the incentive value attributed to food rewards.

Nothing to Disclose: SJK, LS, AA

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