N-methyl-D-aspartate receptor-mediated mitochondrial Ca2+ overload in acute excitotoxic motor neuron death: A mechanism distinct from chronic neurotoxicity after Ca2+ influx

Mitochondrial uptake of Ca2+ has recently been found to play an important r ole in glutamate-induced neurotoxicity (GNT) as well as in the activation o f Ca2+-dependent molecules, such as calmodulin and neuronal nitric oxide sy nthase (nNOS), in the cytoplasm, Prolonged exposure to glutamate injures mo tor neurons predominantly through the activation of Ca2+/calmodulin-nNOS, a s previously reported, and is, in part, associated with the pathogenesis of amyotrophic lateral sclerosis (ALS), In the present study, we investigated how mitochondrial uptake of Ca2+ is involved in GNT in spinal motor neuron s. Acute excitotoxicity induced by exposure to 0.5 mM glutamate for 5 min w as found in both motor and nonmotor neurons in cultured spinal cords from r at embryos and was dependent on extracellular Ca2+ and on N-methyl-D-aspart ate (NWDA) receptor activation. Mitochondrial uncouplers markedly blocked a cute excitotoxicity, and membrane-permeable superoxide dismutase mimics att enuated acute excitotoxicity induced by glutamate and NMDA but not by alpha -amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) or kainate, Fluorime tric analysis showed that mitochondrial Ca2+ was elevated promptly with sub sequent accumulation of reactive oxygen species (ROS) in the mitochondria. An NMDA receptor antagonist and a mitochondrial uncoupler eliminated the in crease in fluorescence of mitochondrial Ca2+ and ROS indicators. These data indicate that acute excitotoxicity in spinal neurons is mediated by mitoch ondrial Ca2+ overload and ROS generation through the activation of NMDA rec eptors. This mechanism is different from that of chronic GNT. (C) 2001 Wile y-Liss, Inc.