Increased sympathetic tone in the absence of changes in BAT UCP1 gene expression was noted in lean, hypermetabolic M3 muscarinic acetylcholine receptor knockout mice [67], which are very similar to VGF mutant mice in phenotype, and also largely resistant to high fat diet-induced, gold-thio-glucose-induced and genetically (ob/ob)-induced obesity, hyperphagia, hyperinsulinemia, and hyperglycemia [17,18,21,67]. Here, UCP1 is linked to obesity due to melanocortin 4 receptor deficiency.