Modulation of NMDA receptor current in layer V pyramidal neurons of the rat prefrontal cortex by P2Y receptor activation

Current responses to N-methyl-D-aspartate (NMDA) in layer V pyramidal neurons of the rat prefrontal cortex were potentiated by the P2 receptor agonists adenosine 5′-triphosphate (ATP) and uridine 5′-triphosphate (UTP). The failure of these nucleotides to induce inward current on fast local superfusion suggested the activation of P2Y rather than P2X receptors. The potentiation by ATP persisted in a Ca²⁺-free superfusion medium but was abolished by 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N′,N′- tetraacetic acid tetrakis(acetoxymethyl) ester, cyclopiazonic acid, 7-nitroindazole, fluoroacetic acid, bafilomycin, and tetanus toxin, indicating that an astrocytic signaling molecule may participate. Because the metabotropic glutamate receptor (mGluR) agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) (group I/II) and (RS)-3,5-dihydroxyphenylglycine (group I) both imitated the effect of ATP and the group I mGluR antagonist 1-aminoindan-1,5- dicarboxylic acid or a combination of selective mGluR₁ (7-(hydroxyimino)-cyclopropa[b]chromen-1a-carboxylate) and mGluR₅ (2-methyl-6-(phenylethynyl)pyridine) antagonists abolished the facilitation by ATP, it was concluded that the signaling molecule may be glutamate. Pharmacological tools known to interfere with the transduction cascade of type I mGluRs (guanosine 5′-O-(3-thiodiphosphate), U-73122, xestospongin C, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, calmodulin kinase II [CAMKII] inhibitor peptide) depressed the actions of both ATP and ACPD. Characterization of the P2Y receptor by agonists (ATP and UTP), antagonists (suramin and pyridoxal-phosphate-6-azophenyl-2′,4′- disulfonic acid), and knockout mice (P2Y₂^-/-) suggested that the nucleotides act at the P2Y₄ subtype. In conclusion, we propose that exogenous and probably also endogenous ATP release vesicular glutamate from astrocytes by P2Y₄ receptor activation. This glutamate then stimulates type I mGluRs of layer V pyramidal neurons and via the G _q/phospholipase C/inositol 1,4,5-trisphosphate/Ca²⁺/CAMKII transduction pathway facilitates NMDA receptor currents.