Free radicals are highly reactive species, because they possess an unpaired electron in their molecular orbitals. Free radical reactivity and its resulting alternation of membrane function are considered one of the important factors contributing to development of the brain edema and irreversible ischemic brain injury. Intraischemic period (electron depletion) hydrogen abstraction from inner mitochondrial membrane lipid occurs by coenzyme Q semiquinone radical. On the other hand, it has been suggested that activation of O2 is essential for the initiation of postischemic lipid peroxidation by demonstrating little or no thiobarbituric acid reactive substances (TBARS) formation under 100% N2. The chapter demonstrates experiments; the rat brain surface emitted weak light promptly after embolization that lasted at least four hours, indicating the generation of excited species from an early stage of reoxygenation around multiple ischemic areas.
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