IN-VITRO ISCHEMIA PROMOTES GLUTAMATE-MEDIATED FREE-RADICAL GENERATIONAND INTRACELLULAR CALCIUM ACCUMULATION IN HIPPOCAMPAL PYRAMIDAL NEURONS

Ischemia-induced cell damage studies have revealed a complex mechanism that is thought to involve glutamate excitotoxicity, intracellular ca lcium increase, and free radical production. We provide direct evidenc e that free radical generation occurs in rat CAI pyramidal neurons of organotypic slices subjected to a hypoxic-hypoglycemic insult. The pro duction of free radicals is temporally correlated with intracellular c alcium elevation, as measured by injection of fluo-3 in individual pyr amidal cells, using patch electrodes. Free radical production (measure d as changes in the fluorescence emission of dihydrorhodamine 123) pea ked during reoxygenation and paralleled rising intracellular calcium. Electrophysiological whole-cell recordings revealed membrane potential depolarization and decreased input resistance during the ischemic ins ult. Glutamate receptor blockade resulted in decreased free radical pr oduction and markedly diminished intracellular calcium accumulation, a nd prevented neuronal depolarization and input resistance decrease dur ing the ischemic episode. These results provide evidence for a direct involvement of glutamate in oxidative damage resulting from ischemic e pisodes.