Posthypoxic Reoxygenation-Induced Neurotoxicity Prevented by Free Radical Scavenger and NMDA/non-NMDA Antagonist in Tandem as Revealed by Dynamic Changes in Glucose Metabolism with Positron Autoradiography

Abstract

Using a positron autoradiography technique, dynamic changes in the cerebral glucose metabolic rate (CMRglc) induced by hypoxia/reoxygenation were investigated in living brain slices. After incubating fresh rat brain slices (300 μm thick) with [18F]2-fluoro-2-deoxy-d-glucose ([18F]FDG) in oxygenated Krebs–Ringer solution at 36°C, serial two-dimensional time-resolved images of [18F]FDG uptake in the slices were obtained on imaging plates. As compared to the unloaded control values, with hypoxia-loading [18F]FDG uptake increased markedly, suggesting enhanced glycolysis. The net influx constant (K) of [18F]FDG at pre-hypoxia-loading and after reoxygenation with loading hypoxia for various periods of time was quantitatively evaluated by applying the Patlak graphical method to the image data. Regardless of the brain region, with hypoxia of ≤10-min duration, the K value returned to the preloading level, whereas with hypoxia of ≥20 min duration only partial or no recovery was seen, indicating irreversible neuronal damage. The 30-min administration of either N-methyl-d-aspartate (NMDA)/non-NMDA antagonist or a free radical scavenger at the same time as reoxygenation after 20 min hypoxia showed a neuroprotective effect inhibiting the decrease in the post-hypoxia-loading K value. In contrast, no such neuroprotective effect was evident with administration of either of these agents only during hypoxia loading, possibly indicating that immediately after reoxygenation neuronal damage was induced mediated by excitatory amino acids and free radicals in tandem. These results demonstrate that serial quantitative evaluation of CMRglc using this technique may be of use in investigating the brain tissue injury associated with hypoxia/reoxygenation as well as clarifying the underlying mechanisms and protective effect of various drugs against such injury.