P2X2 purinoreceptor protein in hypothalamic neurons associated with the regulation of food intake.

Purines such as ATP act as extracellular messengers through specific purinergic receptors. Three different classes of purinergic receptors have been identified and termed P1, P2X and P2Y. The purinergic receptor subunit P2X2 is a ligand-gated ion channel that is widely expressed by neurons in the central nervous system. The aim of this study was to study the cellular localization and to identify the chemical phenotypes of ionotropic P2X2 receptor (P2X2R)-containing neurons in the rat mediobasal hypothalamus by immunohistochemistry using three different P2X2R antisera, with special reference to neurons that influence food intake and body weight. P2X2R immunoreactivity was mainly observed in cell bodies and neural extensions located in the ventromedial part of the hypothalamic arcuate nucleus, a subregion of the nucleus with a weak blood-brain barrier (BBB). At the subcellular level, P2X2R immunoreactivity was located to the periphery of individual cells, likely representing the plasma membrane. Many P2X2R-immunoreactive cell bodies in the arcuate nucleus contained the orexigenic peptides neuropeptide Y (NPY) and agouti-related protein (AgRP), and the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD). In contrast, P2X2R immunoreactive cell bodies of the arcuate nucles only occasionally contained the anorexigenic peptides α-melanocyte-stimulating hormone (α-MSH) or cocaine- and amphetamine-regulated transcript (CART), or the opioid peptide dynorphin (DYN). There was no evidence for colocalization of P2X2R with somatostatin or neuronal nitric oxide synthase (nNOS) in neurons of the arcuate nucleus. In the parvocellular part of the paraventricular nucleus, P2X2R was demonstrated in some corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH) and CART-containing neurons. In some cell bodies of the lateral hypothalamic area P2X2R was colocalized with DYN. The presence of P2X2R immunoreactivity in primarily orexigenic NPY/AgRP/GABA-containing neurons of the arcuate nucleus suggests that extracellular ATP has a regulatory action on this neuronal population located in a strategic position of the brain.