Behavioral and neural alterations of the ventral tegmental area by exposure to junk food in rats

The brain reward system is essential for regulating appetitive and consummatory behaviors in response to various incentive stimuli. Junk food, characterized by its high palatability, is particularly associated with the potential for excessive consumption. While prior studies indicate that excessive junk food intake can impact reward circuitry, the precise mechanisms underlying these effects remain elusive. Furthermore, it is unclear whether the functionality of this neural system is similarly altered in response to other natural rewards. In this study, we used fiber photometry combined with a behavioral reward test to investigate the effects of six weeks of excessive cafeteria (CAF) diet consumption on ventral tegmental area (VTA) neural activity and behavioral responses to food and sexual rewards in female rats. Our findings demonstrate that prolonged exposure to a CAF diet reduced the exploration and consumption of food rewards. These behavioral changes were accompanied by attenuated neural activity in the VTA. Similarly, reductions in VTA activity were observed in response to a sexual partner, although no significant behavioral differences were detected during sexual interactions. Moreover, a two-week reversal diet of standard chow proved insufficient to restore VTA neural activity in CAF-exposed animals, which continued to exhibit decreased VTA responses to both food rewards and sexual partners. Our results suggest that prolonged junk food exposure induces desensitization of the VTA, resulting in reduced responsiveness to natural rewards.