REDOX CHANGES IN PERFUSATES FOLLOWING INTRACEREBRAL PENETRATION OF MICRODIALYSIS PROBES

Microdialysis probe insertion into rat cerebral cortex significantly a ffects the levels of redox-active substances in brain extracellular fl uid. Ascorbic acid levels are high immediately after probe insertion, decline rapidly, and then rise as the rat recovers from anesthesia 5-8 hours after surgery. Uric acid is at a low level for 5 hours and then rapidly increases in parallel with ascorbic acid. High ascorbic acid levels immediately after probe insertion are likely due to a shift fro m intracellular to extracellular fluids, whereas the delayed increase in uric acid may be due to increased enzymatic formation. After remova l from the brain, hydrogen peroxide (H2O2) in microdialysis samples pr oduces catalase-sensitive oxidative chemiluminescence. Microdialysis s amples also produce high level catalase-resistant chemiluminescence as sociated with ascorbic acid levels after penetration injury. Although ascorbic acid is likely an antioxidant at concentrations estimated to be in brain extracellular fluid, it may have prooxidant effects when c omplexed with transition metals released into the neuronal microenviro nment during traumatic brain injury.