Group I Metabotropic Glutamate Receptor NMDA Receptor Coupling and Signaling Cascade Mediate Spinal Dorsal Horn NMDA Receptor 2B Tyrosine Phosphorylation Associated with Inflammatory Hyperalgesia
Journal of Neuroscience
Hindpaw inflammation induces tyrosine phosphorylation (tyr-P) of the NMDA receptor (NMDAR) 2B (NR2B) subunit in the rat spinal dorsal horn that is closely related to the initiation and development of hyperalgesia. Here, we show that in rats with Freund's adjuvantinduced inflammation, the increased dorsal horn NR2B tyr-P is blocked by group I metabotropic glutamate receptor (mGluR) antagonists [7-(hydroxyimino)cyclopropa[b] chromen-1a-carboxylate ethyl ester (CPCCOEt) and
... thyl-6-(phenylethynyl)-pyridine (MPEP), by the Src inhibitor CGP 77675, but not by the MAP kinase inhibitor 2Ј-amino-3Ј-methoxyflavone. Analysis of the calcium pathways shows that the in vivo NR2B tyr-P is blocked by an IP 3 receptor antagonist 2-aminoethoxydiphenylborate (2APB) but not by antagonists of ionotropic glutamate receptors and voltage-dependent calcium channels, suggesting that the NR2B tyr-P is dependent on intracellular calcium release. In a dorsal horn slice preparation, the group I (dihydroxyphenylglycine), but not group II [(2R,4R)-4-aminopyrrolidine-2,3-dicarboxylate] and III [L-AP 4 (L-(ϩ)-2-amino-4-phosphonobutyric acid)], mGluR agonists, an IP 3 receptor (D-IP 3 ) agonist, and a PKC (PMA) activator, induces NR2B tyr-P similar to that seen in vivo after inflammation. Coimmunoprecipitation indicates that Shank, a postsynaptic density protein associated with mGluRs, formed a complex involving PSD-95 (postsynaptic density-95), NR2B, and Src in the spinal dorsal horn. Double immunofluorescence studies indicated that NR1 is colocalized with mGluR5 in dorsal horn neurons. mGluR5 also coimmunoprecipitates with NR2B. Finally, intrathecal pretreatment of CPCCOEt, MPEP, and 2APB attenuates inflammatory hyperalgesia. Thus, inflammation and mGluR-induced NR2B tyr-P sharesimilarmechanisms.ThegroupImGluR-NMDARcouplingcascadeleadstophosphorylationoftheNMDARandappearsnecessaryforthe initiation of spinal dorsal horn sensitization and behavioral hyperalgesia after inflammation.