MC4R and obesity due to melanocortin 4 receptor deficiency: This rationale, coupled with the observation that Mc4r expression is seen in vagal fibers (likely originating from the DMV) that innervate the liver, stomach, and duodenum (Gautron et al., 2010), indicates that the observed changes in GI vagal efferent signaling may underlie the pathophysiological autonomic changes pivotal for the development and maintenance of obesity produced by the loss of the Mc4r.