Time and concentration dependency of the toxicity of excitatory amino acids on cerebral neurones in primary culture.

The cytotoxicity of the glutamate receptor agonists, N-methyl-d-aspartate (NMDA), kainate (KA) and (RS)-?-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) on cultured cerebral cortex neurones was monitored as a function of exposure time and concentration by following the release into the culture medium of the cytoplasmic enzyme lactate dehydrogenase from the neurones. Chronic exposure of the cells to different concentrations of the agonists showed that AMPA was the most potent excitotoxin (ED(50) 10 ?M) followed in potency by NMDA (ED(50) 65 ?M) and KA (ED(50) 100 ?M). Experiments in which the neurones were exposed for different periods of time to fixed concentrations of the agonists showed that after short exposure times (1-3 min) cells survived for more than 24 h after removal of the agonists but after longer exposure times (5-10 min) cells survived for time periods ranging from 25 min to 6 h depending upon the exposure time and the nature of the agonist. The results of the latter experiments indicate that even short exposure times trigger processes in the cell membranes which even after removal of the excitotoxin will lead to neuronal death.