BACKGROUND:Phytoestrogen,derived from plants,is an estrogen-like element,and is effective and safe for estrogen replacement.OBJECTIVE:To compare the interventional effects of genistein and 17 β-estradiol on leing and memory and synaptophysin(SYN)expression in the hippocampus of ovariectomized rats.DESIGN:Randomized controlled animal study.SETTING:Department of Neurology,the Third Affiliated Hospital,Xiangya Medical College,Central South University.rnMATERIALS:130 healthy female Sprague Dawley(SD)rats,6 months old and weighing(293.1±10.2)g,were provided by the Second Xiangya Hospital of Central South University.This animal experiment received confirmed consent from the local ethics committee.All rats were randomly divided into 5 groups,including baseline group(n＝10),sham operation group(n＝30),ovariectomlzed group(n＝30),genistein group(n＝ 30),and 17 β-estradiol group(n＝30).Rats in the latter four groups were observed for 3 weeks(n＝10)and for 15 weeks(n＝20)after model establishment.METHODS:This study was performed at the Department of Endocrinology,the Second Affiliated Hospital,Xiangya Medical College,Central South University from August 2005 to January 2006.Animals were not submitted to any treatment in the baseline group,but anesthetized and sacrificed at the 7 months of age.After anesthesia in the ovariectomized,genistein,and 17 β-estradiol groups,both ovaries were separated and resected to establish an ovariectomized model.The same volume of fat was resected in the sham operation group.After surgery,rats were intraperitoneally injected with 5 mg/kg genistein in the genistein group,10 μ g/kg 17 β-estradiol in the 17 β-estradiol group,and 0.1 mL/100 g dimethyl sulfoxide (DMSO)/polyethylene glycol(PEG)-200 stock solution in the sham peration and ovariectomized groups once a day until one day before sacrifice.MAIN OUTCOME MEASURES:①Leing and memory changes of SD rats were detected using water maze behavioral testing 3 and 15 weeks after surgery.②SYN expression in the hippocampus was measured using immunohistochemistry. RESULTS:A total of 16 out of 130 rats died due to infection,and 114 rats were included in the final analysis.①Comparison of water maze results from the five groups:by 3 and 15 weeks after surgery, escape latency was prolonged and platform-crossing times decreased in the ovariectomized group compared to the baseline,genistein,17 β-estradiol,and sham operation groups(t＝4.17--14.64,P＜0.05).However, there were no significant differences in escape latency and platform-crossing times among the sham operation,genistein,and 17 β-estradiol groups(P＜0.05).②Distribution and quantity of SYN immunoreactive products in hippocampus:SYN-immunoreactive cells stained darkly in the baseline and sham operation groups,but were lightly stained in the genistein,17 β-estradiol,and ovariectomized groups.In particular,SYN-immunoreactive cells stained lightly in the ovariectomized group 15 weeks after surgery. SYN correction gray values in hippocampal sub-regions,especially in the mossy fiber layer of the CA3 region,of the ovariectomized group was lower compared to the baseline,sham operation,17 β-estradiol,and genistein groups(t＝12.57-23.92,P＜0.05)15 weeks after surgery.However,there were no significant differences in SYN correction gray values among the baseline,sham operation,17 β-estradiol and genistein groups(P＜0.05).CONCLUSION:Genistein or 17 β-estradiol supplemental therapy antagonizes memory deterioration,due to endogenous estrogen deficiency and blocks the decrease of SYN expression in the hippocampus.The effect of genistein is similar to 17 β-estradiol.