N-omega-nitro-L-arginine methyl ester protects retinal neurons against N-methyl-D-aspartate-induced neurotoxicity in vivo

We investigated whether the inhibition of nitric oxide (NO) synthesis with N(o)mega-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase, affects N-methyl-D-aspartate (NMDA)-induced neurotoxicity in the rat retina in vivo. A single intravitreal injection of NMDA damaged the ganglion cell layer and the inner plexiform layer without affecting the other retinal layers 7 days after injection. Intravitreal injection of (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate (MK-801) with NMDA significantly reduced NMDA-induced degeneration of the retina. NMDA-induced degeneration was also prevented by intravitreal injection of L-NAME but not of D-NAME. The protective effect of L-NAME was antagonized by L-arginine. These results suggest that NO plays an important role in NMDA-induced excitotoxic degeneration in the retina.