Chronic mitochondrial inhibition induces glutamate-mediated corticomotoneuron death in an organotypic culture model

There is growing evidence that mitochondrial dysfunction is an important fa ctor in a cascade of neurotoxic events as observed during pathogenesis of v arious neurodegenerative diseases. In the neurodegenerative disease amyotro phic lateral sclerosis (ALS) both spinal and cortical motoneurons degenerat e, but in experimental studies most attention so far has been focussed on t he spinal motoneurons, In order to study the role of mitochondrial dysfunct ion in the pathways leading to cortical (upper) motoneuron (CMN) death, a l ong-term culture system of rat cortical explants was used. CMNs were visual ized by immunocytochemical labeling with antibodies directed against nonpho sphorylated neurofilament, SMI-32, and for their identification we also use d their location in layer V of the explant, their size, and their morpholog ical appearance. In this model the effect of mitochondrial inhibition was s tudied through chronic malonate treatment. For 2 weeks, low doses of comple x II inhibitor malonate were added to the cultures twice a week. The malona te-induced chronic mitochondrial inhibition resulted in a dose-dependent in crease of CMN death in the slices. Neuroprotection was achieved with the NM DA antagonist MK-801 and the non-NMDA antagonist CNQX indicating the involv ement of glutamate in the malonate-induced CMN death. Furthermore, our data indicate that chronic mitochondrial inhibition results in CMN death, which is mediated by glutamate excitotoxicity via both non-NMDA and NMDA recepto rs, In this respect the present in vitro approach may act as a model for un derstanding mechanisms underlying CMN death in ALS. (C) 2001 Academic Press .