Antagonism by NG-nitro-L-arginine of L-glutamate-induced neurotoxicity in cultured neonatal rat cortical neurons. Prolonged application enhances neuroprotective efficacy.

The effects of NG-nitro-L-arginine on L-glutamate-induced neurotoxicity have been evaluated on primary cultures of neonatal rat cortical neurons. Treatment of cultures with increasing concentrations of L-glutamate during 5 min produced a delayed neuronal death, as measured by lactate dehydrogenase release in the medium 24 h later. Maximal toxicity was obtained with 500 microM of L-glutamate. Substantial nitric oxide synthase activity was detected in these cortical cultures. Nitric oxide synthase activity and cellular L-glutamate-induced cyclic guanosine 3',5'-monophosphate accumulation were totally inhibited by 100 microM NG-nitro-L-arginine. Addition of NG-nitro-L-arginine (100 microM) to the medium either 5 min prior to and during L-glutamate exposure (500 microM, 5 min) or for 24 h after L-glutamate exposure decreased the amino acid-induced neurotoxicity by 23% (not significant) and 43%, respectively. When added 5 min before L-glutamate and just after L-glutamate removal and kept in contact with neurons for the following 24 h, NG-nitro-L-arginine (100 microM) antagonized by 74% the L-glutamate-induced neurotoxicity. This effect was not reversed by a co-application of L-arginine (1 mM). The neuroprotective effect of NG-nitro-L-arginine was concentration-dependent, a half-maximal inhibition of L-glutamate-induced neurotoxicity being observed with the addition (before and after L-glutamate) of 4 microM of the drug. These results suggest that the neuroprotective effect of NG-nitro-L-arginine previously observed in vivo is exerted at the neuronal level.(ABSTRACT TRUNCATED AT 250 WORDS)