Central melanocortins modulate mesocorticolimbic activity and food seeking behavior in the rat.

The hypothalamic melanocortin system is known for its role in regulating energy homeostasis through it actions within hypothalamic brain centers. However, emerging evidence suggests that this system regulates addictive behaviors through signaling within mesolimbic neurons. Here, we hypothesized the melanocortin system modulates feeding behavior through its actions on mesolimbic neurons. In particular, we predicted that central administration of the melanocortin antagonist agouti-related peptide (AgRP) would activate midbrain dopamine neurons, increase mesolimbic dopamine turnover, and alter food seeking behaviors. We found that intraventricular administration of agouti-related peptide increased neuronal activation within midbrain dopamine neurons in addition to increasing dopamine turnover in the medial prefrontal cortex. Additionally, using the conditioned place preference paradigm to assay food seeking behavior, we report that central injection of agouti-related peptide attenuates the acquisition of a conditioned place preference for sucrose, but not high fat diet. These results suggest that the melanocortin system is capable of regulating mesocorticolimbic activity and food seeking behavior.

Comparison of hydrogenated vegetable shortening and nutritionally complete high-fat diet on limited access-binge behavior in rats.

Previous studies have suggested that intermittent exposure to hydrogenated vegetable shortening yields a binge/compensate pattern of feeding in rats. The present study was designed to assess whether rats would exhibit similar patterns of intake when given intermittent access to a nutritionally complete high-fat diet. Four groups of rats received varying exposure to either hydrogenated vegetable shortening or high-fat diet for 8 consecutive weeks. Animals were given daily and intermittent access to determine if the binge/compensate pattern of feeding was frequency dependent. At the conclusion of the study, body composition and plasma leptin levels were assessed to determine effects of diet and binge/compensate intake on endocrine alterations. As predicted, animals receiving intermittent access to high-fat diet displayed the binge/compensate pattern of feeding and appeared to compensate as a result of the caloric overload accompanying a particular binge episode. In addition, exposure to either shortening or high-fat diet led to alterations in body composition, while only exposure to shortening altered plasma leptin levels. These results suggest that binge-intake behavior occurs on a nutritionally complete high-fat diet and that this regimen is capable of altering both body composition and endocrine profile.