Inhibition of Bax translocation to mitochondria protects oligodendrocytes against AMPA and kainate receptor-mediated damage. Cultured rat oligodendrocytes were pretreated with furosemide (20 μm), a blocker of Bax translocation to mitochondria, and then incubated with agonists for 15 min. A, Cell viability was assayed 24 h later using calcein-AM. Furosemide significantly reduced cell death induced by AMPA or kainate receptor activation. B, ROS generation quantified with DCFDA (20 μm) in response to AMPA and kainate (KA) was inhibited by furosemide. C, Western blot analysis of Bax expression in the mitochondrial fraction showed an increase triggered by AMPA and kainate receptor activation, which was abolished with furosemide (20 μm, pretreatment for 30 min). COX-IV levels were measured as a normalization control. D, Toxicity assays were performed in cultured oligodendrocytes derived from Bax^+/+ or Bax^−/− mice. AMPA or kainate receptors were activated for 15 min in the absence or presence of furosemide (20 μm, pretreatment for 30 min) and viability was quantified 24 h later. Cell death was significantly inhibited by furosemide in wild-type oligodendrocytes but had no effect on Bax^−/− oligodendrocytes. E, F, Pretreatment of cells with a blocker of the mitochondrial permeability transition pore (BkA, 5 μm, 30 min) before excitotoxic signal induction did not reduce cell death (E) or ROS production (F) caused by activation of AMPA and kainate receptors. *p < 0.05, **p < 0.01, ***p < 0.001 (cells treated with furosemide vs control cells); ^#p < 0.05, ^###p < 0.001 (Bax^−/− vs Bax^+/+ cells for the same treatment).