Abstract: Objective: To study the influence of different doses of manganese on the glutamatic neuron content and the activity of succinate dehydrogenase(SDH) in rats so as to explore the cell molecular mechanism of manganese-induced excitotoxicity.Methods: Forty Wistar rats were divided into four groups at random by weight.Group one was injected 0.9% sodium chloride and the second to fourth groups were respectively given i.p of 10,50,250 μmol/kg MnCl₂.The capacity of the injection was all 5 ml/kg.After 15 days' administration,the brain tissue of 4 rats in each group was removed after the rats were perfused 4% ploymerisatum from the left ventricles,and the glutamatic neuron content was determined by immunohistochemical method(SABC).The other 6 rats in each group were executed,and the striatum and pallium were incised to determine the activity of SDH.Results: Compared with the control group,the percentage of positive areaAa(%) and integral optical density(IOD)of glutamate immunocreative cells in the striatum of the rats increased significantly,and the percentage of positive area of glutamate immunocreative cell in pallium increased significantly in 50 μmol/kg MnCl₂ group;the percentage of positive area and integral optical density of glutamate immunocreative cells in striatum and pallium increased significantly in 250 μmol/kg MnCl₂ group(P<0.01);The activity of SDH in the striatum of the rats decreased significantly in 10 μmol/kg MnCl₂ group(P<0.05);The activity of SDH in the striatum and pallium of the rats decreased significantly in 50 μmol/kg and 250 μmol/kg MnCl₂ group(P<0.01).Conclusions: Mn can decrease the activity of SDH and increase the glutamatic neuron content,which may lead to activation of glutamic acid receptor and promote excitotoxicity.