BDNF and obesity due to melanocortin 4 receptor deficiency: Although studies suggest that MC4R signaling interacts with BDNF-TrkB signaling in the context of body weight regulation11,44, it is unlikely that Ntrk2 deletion in the PVH leads to obesity through the MC4R because the deletion did not reduce levels of Mc4r mRNA (Supplementary Fig. 4j, k).