MITOCHONDRIAL TRANSMEMBRANE POTENTIAL AND FREE-RADICAL PRODUCTION IN EXCITOTOXIC NEURODEGENERATION

Excitotoxic cell death is involved in many forms of acute and chronic neurodegeneration. We induced excitotoxic cell death in cultured rat h ippocampal neurons by brief exposure to two selective glutamate recept or agonists with different neurotoxic potencies, N-methyl-D-aspartate (NMDA) and kainate (KA). Digital video imaging was performed during ex posure to the agonists to monitor free radical production and changes in mitochondrial transmembrane potential, Psi(m). Brief exposure to NM DA (10 min) induced significant cell death in the hippocampal neurons reaching a maximum at a concentration of 300 mu M (57.2+/-2.6% cell de ath; P<0.001). In parallel imaging experiments we found that exposure to NMDA (300 mu M, 10 min) induced a significant increase in superoxid e production monitored with the oxidation-sensitive probe, hydroethidi ne (increase of 280+/-33% above baseline, P<0.001). Rhodamine-123-base d imaging revealed a loss of Psi(m) in 70.1+/-10.1% of the hippocampal neurons during the exposure to NMDA. In contrast to NMDA, brief expos ure to KA (10 min) produced limited neurotoxicity reaching a maximum a t a concentration of 100 mu M (10.2+/-4.0% cell death: P<0.05. Exposur e to KA (100 mu M, 10 min) also caused a significant increase in super oxide production. This increase, however, was significantly less prono unced than that produced by NMDA (increase of 94+/-17% above baseline: P<0.001 compared to controls or NMDA-exposed cultures). Moreover, rho damine-123-based imaging revealed that KA (100 mu M) caused a collapse of Psi(m) in only 13.5+/-1.4% of the hippocampal neurons. In conclusi on, the present study demonstrates that early changes in intracellular superoxide production and Psi(m) relate to neuronal survival outcome in excitotoxic cell death.