Coronal slices of rat brain were incubated for 40 min in 300 microM kainate (KA) or 500 microM N-methyl-D-aspartate (NMDA). Histological examination showed neuronal degeneration accompanied by significant losses in the activity of neuron-specific enolase (NSE; EC 126.96.36.199) (-23% KA; -26% NMDA). The activity of the glial enzyme glutamine synthetase (GS; EC 188.8.131.52) was also reduced (-32% KA; -27% NMDA). Pre-incubation with 100 microM L-NG-nitroarginine (L-N-ARG), an inhibitor of nitric oxide (NO) synthase (EC 1.14.23.-), for 20 min attenuated the toxicity of toxicity of NMDA, but not KA. NSE levels after successive incubation in L-N-ARG and NMDA were 95% of controls incubated in Krebs bicarbonate medium only (GS activity 89% of controls). In contrast, pre-incubation with L-N-ARG prior to the addition of KA resulted in neuronal degeneration and significant reductions in NSE levels and GS activities. These observations suggest that the unrestricted function of NO synthase is significant in mediating NMDA neurotoxicity whereas KA toxicity is associated with alternative mechanisms not linked to NO production.