Hypoxia and Hyperoxia Both Increase Superoxide Production in Nucleus Tractus Solitarius (NTS) Neurons in Rat Brain Tissue Slices

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Maintaining brain slices in 95%O2 produces hyperoxia, oxidative stress and increased cell death, whereas decreasing control O2 to 20-40% significantly decreases both oxidative stress and cell death (J. Neurophysiol. 98:1030-41, 2007) and maintains neuronal excitability (Matott et al., this meeting). In this study, beginning at 20-40%O2, we tested the hypothesis that acute hyperoxia and hypoxia both increase the rate of superoxide (·O2-) production in NTS neurons. Medullary slices (400µm, weaned rats, 36-37oC) were maintained using 2-sided superfusion. Intracellular ·O2- production was measured using dihydroethidium (DHE, 2.5µM) added to the superfusate. The rate of ·O2- production (fluorescence intensity units/min, FIU/min) increased during hypoxia (40/20%(0%O2) and was blocked by myxothiazol (10µM; inhibits ·O2- produced by mitochondrial Complex III). ·O2- production also increased during hyperoxia (20(95%O2), but to a lesser extent than during hypoxia, and was not blocked by myxothiazol. We propose that NTS neurons undergo redox stimulation and/or stress via increased ·O2- production during both hypoxia (Complex III) and hyperoxia (Complex I ?). We also hypothesize that the smaller increase in FIUDHE/min during hyperoxia reflects increased production of ·NO during hyperoxia, which reacts with ·O2- (and thus consumes ·O2-) to yield peroxynitrite. ONR N000140710890, NIH R01 HL 56683-10.


Presented at the 2009 Federation of American Societies for Experimental Biology (FASEB) Science Research Conference.

Presentation Number 1038.8.

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