Decreased rates of operant food self-administration are associated with reward deficits in high-fat feeding mice.

PURPOSE: Highly palatable foods behave as appetitive reinforcers and tend to be consumed compulsively. Nevertheless, the motivation for this kind of diets in experimental diet-induced obesity models has not been well established. Our hypothesis is that obesity caused by a regular consumption of high-fat diet (HFD) occurs concomitantly with the inhibition of food reward. The ultimate goal of our study was to further analyze the extent to which the perception of food as an appetitive reinforcer is a necessary condition for obesity.
METHODS: We have evaluated the influence of HFD on operant food self-administration (FSA) during a whole light-dark (12-12-h) cycle in mice that consumed HFD either during 1, 4 or 8 weeks. The study has been complemented by a two-bottle free-choice assay between tap water and sweetened drinks.
RESULTS: These data show that both 4- and 8-week HFD treatments induced a significant decrease in operant FSA rate. Moreover, HFD impaired the sweetened-conditioned flavor preference in the two-bottle choice assay.
CONCLUSION: Our results, showing a reduction in how hard an animal is willing to work for food reinforcers, provide evidence that chronic consumption of HFD negatively contributes to the incentive motivation to acquire food/drink reinforcers. We demonstrate that energy homeostasis imbalance triggered by HFD is associated with the inhibition of hedonic feeding.