P2X2 and P2Y1 immunofluorescence in rat neostriatal medium‐spiny projection neurones and cholinergic interneurones is not linked to respective purinergic receptor function

The presence of ionotropic P2X receptors, targets of ATP in fast synaptic transmission, as well as metabotropic P2Y receptors, known to activate K+ currents in cultured neostriatal neurones, was investigated in medium-spiny neurones and cholinergic interneurones contained in neostriatal brain slices from 5–26-day-old rats. In these cells, adenosine-5′-triphosphate (ATP) (100–1000 μM), 2-methylthioadenosine-5′-triphosphate (2MeSATP), α,β-methyleneadenosine-5′-triphosphate (α,βmeATP, 30–300 μM, each) and adenosine-5′-O-(3-thiotriphosphate (ATPγS) (100 μM) failed to evoke P2X receptor currents even when 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 μM), apyrase (10 U ml−1) or intracellular Cs+ was used to prevent occluding effects of the ATP breakdown product adenosine, desensitisation of P2X receptors by endogenous ATP and an interference with the activation of K+ channels, respectively. P2X receptor agonists were also ineffective in outside-out patches withdrawn from the brain slice tissue. Muscimol (10 μM) evoked GABAA receptor-mediated currents under all these conditions. When used as a control, locus coeruleus neurones responded with P2X receptor-mediated currents to ATP (300 μM), 2MeSATP and α,βmeATP (100 μM, each). ATP and adenosine-5′-diphosphate (ADP) (100 μM, each) did not activate K+ currents in the neostriatal neurones. Despite the observed lack of function, P2X2 and P2Y1 immunofluorescence was found in roughly 50% of the medium-spiny neurones and cholinergic interneurones. A role of ATP in synaptic transmission to striatal medium-spiny neurones and cholinergic interneurones appears unlikely, however, the otherwise silent P2X and P2Y receptors may gain functionality under certain yet unknown conditions. British Journal of Pharmacology (2004) 143, 119–131. doi:10.1038/sj.bjp.0705916