Exposure to a high-fat high-sugar diet causes strong up-regulation of proopiomelanocortin and differentially affects dopamine D1 and D2 receptor gene expression in the brainstem of rats

A strong link between obesity and dopamine (DA) has been established by studies associating body weight status to variants of genes related to DA signalling. Human and animal studies investigating this relationship have so far focused mainly on the role of DA within the mesolimbic pathway. The aim of this study was to investigate potential DA receptor dysregulation in the brainstem, where these receptors play a potential role in meal termination, during high-fat high-sugar diet (HFHS) exposure. Expression of other key genes, including proopiomelanocortin (POMC), was also analyzed. We randomized rats into three groups; ad libitum access to HFHS (n=24), restricted HFHS access (n=10), or controls (chow-fed, n=10). After 5 weeks, brainstem gene expression was investigated by qRT-PCR. We observed an increase in POMC expression in ad libitum HFHS-fed rats compared to chow-fed controls (p<. 0.05). Further, expression of DA D2 receptor mRNA was down-regulated in the brainstem of the HFHS ad libitum-fed rats (p<. 0.05), whereas expression of the DA D1 receptor was upregulated (p<. 0.05) in these animals compared to chow-fed rats. In control experiments, we observed no effect relative to chow-fed controls on DA-receptor or POMC gene expression in the hypothalamus of HFHS diet-exposed rats, or in the brainstem of acutely food deprived rats. The present findings suggest brainstem POMC to be responsive to palatable foods, and that DA dysregulation after access to energy-dense diets occurs not only in striatal regions, but also in the brainstem, which could be relevant for overeating and for the development and maintenance of obesity.