BLOCKADE OF NITRIC-OXIDE FORMATION DOES NOT PREVENT GLUTAMATE-INDUCED NEUROTOXICITY IN NEURONAL CULTURES FROM RAT HIPPOCAMPUS

This study examined the role of nitric oxide (NO) in glutamate-induced, N-methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity in rat hippocampal neuronal cultures grown under serum-free conditions. Formation of cGMP was used as an indirect measure of NO formation. Neuronal cell degeneration was monitored by measuring the release of lactate dehydrogenase (LDH). Neuronal cells showed a 4-fold increase in cGMP formation and release of LDH upon exposure to 30-mu-M glutamate. cGMP formation was fully inhibited by 1-mu-M nitro-arginine (N-Arg), 100-mu-M hemoglobin or 1-mu-M MK-801. In the presence of 1-mu-M MK-801, glutamate induced neither cGMP formation nor neuronal cell degeneration. However, when NO formation was inhibited by means of 100-mu-M N-Arg, glutamate still induced neurotoxicity. Therefore, in serum-free hippocampal cultures glutamate neurotoxicity occurs notwithstanding complete inhibition of the NO-synthase enzyme by N-Arg. Our data provide evidence that NO, synthesized upon glutamate exposure, has not a primary toxic action in pure hippocampal neuronal cultures.