Abstract

The mechanisms associated with the neurotoxic response caused by kainate (KA) were examined in cerebellar granule cell cultures. Under the conditions studied, millimolar concentrations of quisqualate, (RS)-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, glutamate and N-methyl-D-aspartate did not cause significant cytolysis. In contrast, KA induced complete cell death, which was antagonized by 6,7-dinitroquinoxaline-2,3-dione, quisqualate, (RS)-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and glutamate. This neurotoxic effect was dependent on the dose of KA and the age of the cultures. Two separate components of KA-induced neurotoxicity were observed and differentiated according to morphological changes, time of onset and ionic dependence. For acute neurotoxicity, release of lactate dehydrogenase measured after 30 min of KA exposure, became apparent between 8 and 11 days in culture and was dependent on both Cl- and Na+. However, vulnerability to acute toxicity did not correlate with [3H]KA receptor expression with receptor-mediated Cl- influx. On the other hand, delayed toxicity, as determined by lactate dehydrogenase release 24 hr after KA exposure, was dependent on Cl-. This delayed neurotoxicity induced by KA shares time course features with N-methyl-D-aspartate-mediated toxicity. Yet in contrast to studies reported for N-methyl-D-aspartate, glutamate was ineffective as an agonist, measured by its ability to elicit a neurotoxic response, and the KA delayed response did not appear to be dependent upon the presence of extracellular Ca++, during the exposure to KA.