INS and obesity due to melanocortin 4 receptor deficiency: POMC p110β (but not p110α KO) KO: leptin resistance, obesity, loss of insulin- and leptin-stimulated neuronal firing. AgRP p110β (but not p110α KO) KO: increased leptin sensitivity, resistance to diet-induced obesity.POMC PI3K KO mice: disrupted leptin and insulin-induced POMC neuronal firing.