P2RX2 and obesity due to melanocortin 4 receptor deficiency: The participation of purinergic receptors (P1: A1, A2a, A2b, A3) [18–34], (P2: P2X2, P2X3, P2X7, P2Y1, P2Y13) [35–52], and neuronal pathways bearing these receptors [53, 54] has been confirmed in different AP-sensitive conditions (pain, inflammation, myocardial ischemia, obesity, cerebral ischemia).