P1 or adenosine receptors (ARs) are a family of G protein–coupled receptors (GPCRs) with 4 subtypes: A1, A2A, A2B, and A3. P2 receptors are subgrouped into the ligand-gated ion channel receptors P2X with 7 receptor subtypes: P2X1, P2X2, P2X3, P2X4, P2X5, P2X6, P2X7, and P2Y, which are G protein-coupled metabotropic receptors with 8 subtypes: P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14 (Figure 1).4 Burnstock has recently published an excellent review article on purinergic receptors, their distributions, and functions revealing the importance of these receptors in physiological system.5 Purinergic receptors play major roles in CNS disorders including Alzheimer disease (AD), Parkinson disease (PD), Huntington disease (HD), frontotemporal dementia (FD), amyotrophic lateral sclerosis (ALS), multiple scleroses (MS), traumatic brain injury (TBI), stroke, cerebral ischemia, epilepsy, psychiatric diseases, sleep disorder, and neuropathic pain.1,3,6,7
