These results were surprising in light of the fact that Sim1 neurons account for most if not all neurons of the PVH [21] and bilateral electrolytic ablation of the PVH leads to reduced energy expenditure, and lack of diet induced thermogenesis [27], [28] in addition to increased food intake, and obesity [27]–[29]. This evidence concerns the gene SIM1 and obesity due to melanocortin 4 receptor deficiency.