Histochemical Localization of Superoxide Dismutase Activity in Rat Brain

Histochemical localization of superoxide anion (O2·−) scavenging activity in rat brain was visualized by the tissue-blotting technique. The activity was thought to mainly depend on Cu/Zn-SOD, because the localization of the activity was identical with the immunohistochemistry of Cu/Zn-SOD and the localization of its mRNA in the brain. Moreover, the activity was dramatically decreased after treatment of Cu (I) chelater. The activity was detected in pyramidal cells of the cortex, granular, and mitral cells of the olfactory bulbs, pyramidal cell layer CA1 to CA3, and dentate gyrus of hippocampus formation and granular cells of the cerebellum. Moreover, the activity was detected in the pontine nuclei of brain stem. Olfactory bulbs, hippocampus, and cerebellum were believed to be bestowed high brain functions, i.e., long-term potentiation and long-term depression. A part of the function was regulated by a retrograde neurotransmitter, nitric oxide (·NO). Our findings suggest that the SOD is colocalized with NO synthase in olfactory bulbs, hippocampus, and cerebellum, where ·NO plays the important roles. In contrast, low SOD activity was observed in the axonal neurofiber bundles, although the regions contain a lot of membrane lipids, which was thought to be peroxidized by O2·− and related radicals such as ·OH in the regions. From these findings, it was suggested that the SOD did not only play a role in protecting the neurons from endogenously formed O2·−, but also play a role in preservation of beneficial natures of ·NO in the brain.