DRD2 and obesity due to melanocortin 4 receptor deficiency: Similarly, comparisons between mice bred for excessive exercise or obesity revealed that NAc dopamine content was increased in high running compared to obese and control mice, while Drd1, Drd2, and adenylate cyclase 5 (Adcy5) mRNAs were downregulated 92, 80, and 91%, respectively, in obese compared to control mice (78).