Activity of NMDA receptors is controlled by converging signals from GPCRs and receptor tyrosine kinases. PACAP regulates NMDAR responses by stimulating Galphas subunit and PKA as well as Galphaq subunits and PKC. In CA1 neurons PACAP38 enhanced synaptic NMDA, and evoked NMDAR currents via activation of the PAC1R, Galphaq and PKC. Enhancement is isolated CA1 neurons was selectively mediated by NR2A containing NMDARs. Signaling was blocked by intracellular applications of the Src inhibitory peptide, Src(40-58). Immunoblots confirmed biochemical activation of Src. A Galphaq pathway is responsible for this enhancement as it was attenuated by RGS2 as it was in PLCbeta1 knockout mice. It was also blocked by preventing elevations in intracellular Ca2+, and it was eliminated by inhibiting PKC and CAKbeta/Pyk2. Peptides which mimic binding sites for Fyn or Src on RACK1 enhance NMDARs but their effects were blocked by Src(40-58) implying that Src is the ultimate regulator of NMDARs.