Effects of Phytoestrogen on Learning and Memory in Ovariectomized Rats and the Underlying Mechanism

Objective: To investigate the effects of genstein,a kind of phytoestrogen(PE) derived from a soy diet,on capabilities of learning and memory in ovariectomized rats,and to explore the underlying mechanism.Methods: Fifty female Sprague Dawley rats were randomly divided into 5 groups: sham-operation group,ovariectomized group;and low(25 mg/kg),medium(50 mg/kg) and high(100 mg/kg) doses of genstein groups,10 in each.Three genstein groups were given 25,50,and 100 mg/kg genstein in 1 week after operation,respectively,and the sham-operation and ovariectomized groups were given equivalent volume of the vehicle in which genstein was dissolved.After 4-week treatment,Morris water maze test were used to observe the ability of learning and memory.The number of apoptosis neurons in the hippocampus was detected by flow cytometry.Results: The ovariectomized group had significantly prolonged average latency as compared with the sham-operation group(P0.05);the average latency of 3 doses of genstein groups was significantly shortened as compared with the ovariectomized group(P0.05);but no significant difference was found among low,medium and high doses of genstein groups(P0.05).The apoptosis of neurons in the hippocampus of the ovariectomized group was greater than that in the sham ovariectomized group(P0.01).Treatment with 4-week different doses of genstein in the experiment groups significantly decreased the apoptosis of neurons in the hippocampus as compared with the ovariectomized group(P0.05),but no significant difference was noted among the 3 experimental groups and the sham-operation group(P0.05).Conclusions: Genstein can enhance the capabilities of learning and memory of the ovariectomized rats.This improvement may be due to the decrease in the number of apoposis neurons in the hippocampus.