P2RX3 and obesity due to melanocortin 4 receptor deficiency: Experimental animal models of high-fat diet-induced obesity show an increased expression of muscarinic M2 and M3 and purinergic P2X3 receptors in the urothelium and the smooth muscle, as well as the TRPV1 and inducible NO synthase proteins in the urothelium [12, 25].