Mitochondrial impairment reduces the threshold for in vivo NMDA-mediated neuronal death in the striatum.

There may be important relationships between glutamate receptor activation and neurotoxicity in neurodegenerative diseases. Previous experiments using cultured neurons have demonstrated a correlation between the metabolic status of neurons and their sensitivity to glutamate receptor-mediated cytotoxicity (Novelli et al. Brain Res. 451, 205, 1988). To examine such a relationship in vivo, we first established a dose-response curve for N-methyl-D-aspartate (NMDA)-induced neuronal death in the rat striatum. We then examined the interaction between metabolic impairment and infusion of NMDA at a dose below the threshold for neurotoxicity. Metabolic impairment was induced by intraperitoneal delivery of 3-nitropropionic acid (3-NP), an inhibitor of mitochondrial complex II (succinic dehydrogenase). Twelve hours after 3-NP delivery we performed stereotactic infusion of NMDA or vehicle into the striatum. During mitochondrial impairment, a relatively nonneurotoxic dose of NMDA (15 nmol) produced a lesion that was significantly larger than that caused by this dose under normal metabolic conditions. At a dose normally below the threshold for neurotoxicity, metabolic impairment significantly increased the likelihood of neuronal death in the striatum by a factor of 5. Lesions were characterized by neuronal loss with gliosis and sparing of traversing fiber bundles. These results demonstrate that metabolic impairment reduces the threshold for glutamate receptor-mediated neurotoxicity in vivo. This potentiation may have implications for understanding the role of "neuronal stress" produced by glutamate receptor activation in neurodegenerative diseases and normal aging.