LEP and obesity due to melanocortin 4 receptor deficiency: Exposure to a high fat diet (HFD) can induce both obesity and a diabetic (insulin resistant) state in rodents, which means that models of obesity and diabetes are highly overlapping: consumption of a HFD or use of leptin deficient (ob/ob) or leptin receptor deficient (db/db) mice, which do not respond appropriately to this satiety hormone, have recently been used to examine CNS effects.