NITRIC-OXIDE MEDIATES N-METHYL-D-ASPARTATE RECEPTOR-INDUCED ACTIVATION OF P21(RAS)

N-methyl-D-aspartate (NMDA) glutamate receptor-mediated increases in i ntracellular calcium;Ire thought to play a critical role in synaptic p lasticity. The mechanisms by which changes in cytoplasmic calcium tran smit the glutamate signal to the nucleus, which is ultimately importan t for long-lasting neuronal responses, are poorly understood. We show that NMDA receptor stimulation leads to activation of p21(ras) (Ras) t hrough generation of nitric oxide (NO) via neuronal NO synthase, The c ompetitive NO synthase inhibitor, L-nitroarginine methyl ester, preven ts Ras activation elicited by NMDA and this effect is competitively re versed by the NO synthase substrate, L-arginine. NMDA receptor stimula tion fails to activate Ras in neuronal cultures from mice lacking neur onal NO synthase. NMDA-induced Ras activation occurs through a cGMP-in dependent pathway as 1H-[1,2,4]oxadiazolo [4,3-alpha] quinoxalin-1-one (ODQ), a potent and selective inhibitor of guanylyl cyclase, has no e ffect on NMDA receptor-induced activation of Ras, and the cell-permeab le cGMP analog, 8Br-cGMP, does not activate Ras, Furthermore, NO direc tly activates immunoprecipitated Ras from neurons. NMDA also elicits t yrosine phosphorylation of extracellular signal-regulated kinases, a d ownstream effector pathway of Ras, through a NO/non-cGMP dependent mec hanism, thus supporting the physiologic relevance of endogenous NO reg ulation of Ras, These results suggest that Ras is a physiologic target of endogenously produced NO and indicates a signaling pathway for NMD A receptor activation that may be important for long-lasting neuronal responses.