The Effect of Zinc on Brain Enzymes with Special Reference to Enzymohistochemical Changes in Ammon’s Horn

Changes in brain enzymes produced by zinc were histochemically studied to elucidate the effect of zinc on function of the central nervous system. Since systemically or intracerebral1y injected 65Zn showed a characteristic distribution in Ammon's horn, attention was focused on histochemical changes in this region. The observations may be summarized as follows : 1) The activities of cytochrome oxidase, succinic dehydrogenase, DPN-and TPN-diaphorase were inhibited by systemic or intracerebral injection of zinc. Particulary the activities of DPN-and TPN-diaphorase were strongly inhibited. These findings indicate that zinc inhibits the oxidative process in the brain. 2) Intracerebral injection of zinc diminished cholinesterase activity in the layer of mossy fibers in 4-5 days, when the injected 65Zn showed distinct localization in this layer. 3) The activities of monoamine oxidase and acid phosphatase remained unchanged. 4) A little larger dose of zinc produced tonic extensor seizures with running or hopping movements in 4-5 days after intracerebra1 injection. Relationship between the behavioral changes and the histochemical changes in brain enzymes produced by zinc is discussed briefly.