Effects of puerarin on synaptic structural modification in hippocampus of ovariectomized mice

There is growing interest in whether phytoestrogens, especially isoflavones, affect cognitive function and have beneficial effects on neurodegenerative diseases. Previous work from our laboratory showed that puerarin (Pur), a major component of the Pueraria lobata isoflavones, displayed protective effects on learning and memory in ovariectomized (Ovx) female mice. In the present study, we investigated the effects of Pur on the synaptic structural modifications of the hippocampus in Ovx female mice. One week after ovariectomy or sham operation, female mice were given a 4-week treatment of Pur (50 or 100 mg/kg, I. G.) or estradiol benzoate (EB, 120 microg/kg, S. C.). The results from synaptic structural measurement and analysis did not show any differences in the hippocampal volumes, the synaptic numeric density, and the curvature of synaptic interface among Sham, Ovx, and Ovx plus EB or Pur replacement female mice. However, Pur replacement effectively normalized some structural changes induced by Ovx, reducing the width of the synaptic cleft, enlarging the thickness of postsynaptic density (PSD), and lengthening the synaptic active zone of the pre-existing synapses in the hippocampus CA1 area (P < 0.05 or P < 0.01). Furthermore, through Western blotting, we found that the immunocontent of the NMDA receptor subunit NR2 was not altered by Pur (108 % and 114 % of Ovx); however, the content of postsynaptic protein PSD-95 (145 % and 176 % of Ovx) and phosphorylation of NMDA receptor subunit NR2B (141 % and 172 % of Ovx) strongly increased in Ovx mice following treatment with Pur (50 or 100 mg/kg) for 4 weeks. These results suggest that Pur possesses phytoestrogen activity with 1,000 -fold lower activity than EB, and the beneficial effects of Pur on improving memory behavior of Ovx female mice are associated with the changes of synaptic structural modifications in the hippocampus.