Introduction: Diabetes mellitus increased the blood glucose level, oxidative stress and production of free radicals that leads to create Amyloid plaque and Alzheimer,s Disease. In this investigation the effects of metformin one of the important drugs for diabetes on memory deficiency and number of CA1 pyramidal neurons in STZ - induced Alzheimeric rats were studied. Methods: The experimental groups consist of control group, STZ group(3mg/kg) and care group with STZ(3mg/kg) and metformin( 200mg/kg dose in once, one week, three weeks and eleven weeks period).ICV administration of STZ was down in the first and the third day of the surgery and received metformin (ip) starting one day before the surgery to the end of care period. The animals memory were examined with passive avoidance test and the number of intact neurons in CA1 area in experimental groups were counted. The statistical analysis were performed using SPSS software and one-way analysis of variance and prism software. Results: Injections of STZ significantly reduced memory retention(p<0.001) and intact neurons in CA1 area(P<0.001) compared to the control group. Metformin in once(P<0.001), one week(P<0.001), and three weeks(p<0.01) period improved the effects of STZ on memory loss and increased the number of intact neurons(p<0.001) in CA1 area compared to the STZ group. Eleven weeks metformin can not improved the memory and the number of intact neurons significantly. Conclusion: The chronic use of metformin in long time in diabetic patients lead to memory deficiency.
