The effects of different doses of E2 pre-treatment on apoptosis of PC12 cell after OGD-R as assessed by flow cytometric analysis. (A) The cell populations of annexin V-FITC+/PI–(Quadrant 4) were considered to represent apoptotic cells. The cell apoptosis rate in the control, DMSO, 10 nM, 20 nM, 10 μM and 20 μM groups is 9.8%, 9.4%, 3.9%, 4.4%, 16.9% and 18.7%, respectively. (B) The cell apoptosis rate in 10 nM and 20 nM E2 group significantly decreased. And the cell apoptosis rate of 10 μM and 20 μM E2 group significantly increased (* p < 0.01 v.s. the control and DMSO groups, #p < 0.05 v.s. the control and DMSO groups).