HCRT and obesity due to melanocortin 4 receptor deficiency: Administration of orexin into the lateral ventricle stimulated food consumption in rodents (Sakurai et al., 1998), and ablation of orexin neurons or KO of the orexin gene in rodents attenuated food intake and obesity (Hara et al., 2005; Fujiki et al., 2006), suggesting that the orexinergic system contributes to food entrainment.