NPY and obesity due to melanocortin 4 receptor deficiency: Still, leptin is suggested to exert anti-obesity effects by signaling through “long form” leptin receptors (ObR) abundantly present on both orexigenic neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons and anorexigenic pro-opiomelanocortin (POMC) neurons in the Arc.