Fig. 2

Behavioral changes to different estrogen pretreatment regimes. a Changes of paw withdraw threshold with date in groups of OVX (blue), E-decrease (green) and E-increase (red) rats. The day of OVX surgery was defined as day 0, and the mechanical nociception tests started 2 days prior to OVX and lasted until day 41. Arrows indicate the doze and time of estrogen pellets implanted. 2.5-mg pellets were applied on day 20 to both E-increase and E-decrease group, and 0.25-mg pellets were applied in E-increase group only on day 33, 35, 37, 39, and 41 respectably. Data are shown as mean paw withdraw threshold (± SD) to three times of electronic von Frey stimuli. *P < 0.05 when compared with the OVX group, ^&P < 0.05 when compared with the E-decrease group. Significant differences (one-way ANOVA with Bonferroni’s multiple comparison test; P < 0.05) were detected in both estrogen replacement groups compared with the OVX group started from day 22 until the end of the experiment. And the PWT of the E-increase group significantly attenuated (one-way ANOVA with Bonferroni’s multiple comparison test; P < 0.01) starting from day 36 compared with that of the E-decrease group. b Grouped histographs show PWT difference among different groups at selected time points as day 8, day 28, and day 39 after OVX. Data are shown as mean paw withdraw threshold (± SD) to electronic von Frey stimuli. ^#P < 0.05 when compared with the control group, *P < 0.05 when compared with the OVX group, ^&P < 0.05 when compared with the E-decrease group, and ^%P < 0.05 compared with the E-increase group