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 17β-estradiol on learning and mem-ory 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. MATERIALS: 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),ovariectomized group (n = 30),genistein group (n = 30),and 17β-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 Hos-pital,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 17β-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 μg/kg 17β-estradiol in the 17β-estradiol group,and 0.1 mL/100 g dimethyl sulfoxide (DMSO)/polyethylene glycol (PEG)-200 stock solution in the sham operation and ovariectomized groups once a day until one day before sacrifice. MAIN OUTCOME MEASURES: ① Learning and memory changes of SD rats were detected using water maze behavioral testing 3 and 15 weeks after surgery. ② SYN expression in the hippocampus was meas-ured using immunohistochemistry. RESULTS: A total of 16 out of 130 rats died due to infection,and 114 rats were included in the final analy-sis. ① Comparison of water maze results from the five groups: by 3 and 15 weeks after surgery,escape la-tency was prolonged and platform-crossing times decreased in the ovariectomized group compared to the baseline,genistein,17β-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 17β-estradiol groups (P > 0.05). ② Distribution 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,17β-estradiol,and ovariectomized groups. In particular,SYN-immunoreactive cells stained lightly in the ovariectomized group 15 weeks after surgery. SYN correc-tion 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,17β-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,17β-estradiol and genistein groups (P > 0.05). CONCLUSION: Genistein or 17β-estradiol supplemental therapy antagonizes memory deterioration,due to endogenous estrogen deficiency and blocks the decrease of SYN expression in the hippocampus. The ef-fect of genistein is similar to 17β-estradiol.
