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Effects of amyloid ,(3-protein fragment 25-35, A(3P(25-35), on the membrane permeability of organic molecules were examined in the brain neurons dissociated from rats by using an argon laser (equipped in flow cytometer and laser microscope) and a combination of two fluorescent dyes, fluo-3-AM and ethidium bromide. Aj P(25-35) at concentrations of 1 pM or greater induced both leakage of fluo-3 from the neurons and permeation of ethidium across the membrane in a dose-dependent manner, although both dyes are highly impermeant to the intact plasma membrane. Thus, A(3P(25-35) seems to increase not only membrane permeability of inorganic ions such as Ca t+, Na+ and K+, as previously suggested, but also that of organic molecules. Therefore, the brain neuron membrane is suggested to lose its integrity in the presence of A f P(25-35) that leads to neuronal death.

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Effect of an extract of Ginkgo biloba leaves (EGb) on oxidative metabolism was studied using rat brain neurons and 2',7'-dichlorofluorescin fluorescence. lonomycin (100 nM to 1 ƒÊM), a Ca2+-iono phore, dose-dependently augmented the 2',7'-dichlorofluorescin fluorescence in the presence of external Ca2+, but not under the external Ca2+-free condition. Preincubation of neurons with EGb (3 ƒÊg/ml) greatly reduced the ionomycin-induced increase in 2',7'-dichlorofluorescin fluorescence. Results suggest that EGb may reduce the Ca2+-induced increase in the oxidative metabolism of brain neurons.