ABSTRACT
Objective:To explore the role of 17β-estradiol(17β-E2) derived from the hippocampus and gonad in the cognitive memory during the reconsolidation period of fear memory in rats with post-traumatic stress disorder(PTSD).Methods:The 8-week-old clean grade female SD rats were used for this study. Single prolonged stress combined with context fear conditioning was used to prepare the rat PTSD model.(1) Gonad estradiol experiment: 50 female rats were randomly divided into blank control group, model group, sham ovariectomy group, ovariectomy group, and ovariectomy+ estradiol group by random number table method, with 10 rats in each group. The rats in model group, sham ovariectomy group, ovariectomy group, and ovariectomy+ estradiol group were established PTSD model. Rats in ovariectomy group and ovariectomy+ estradiol group underwent ovariectomy, while rats in sham ovariectomy group only were removed adipose tissue of the same mass around the ovaries. And the rats in ovariectomy+ estradiol group were injected with 17β-E2(1 mg/kg, once a day for 14 days) 7 days after ovariectomy.(2) Hippocampal estradiol experiment: 40 female rats were randomly divided into blank control group, model group, hippocampal solvent control group and hippocampal estradiol inhibitor group by random number table method, with 10 rats in each group.The rats in model group, hippocampal solvent control group and hippocampal estradiol inhibitor group were established PTSD model.Rats in hippocampal estradiol inhibitor group were given letrozole once(bilateral, 0.5 μL per side) during the fear memory consolidation period) and rats in the hippocampus solvent control group were injected once with dimethyl sulfoxide in the hippocampus(bilateral, 0.5 μL per side) . The open field test and elevated cross maze test were used to evaluate the anxiety level and autonomous exploration ability, the freeze test was used to evaluate the fear memory, the new object recognition test was used to evaluate the non-spatial memory, and ELISA was used to detect serum 17β-E2 level. SPSS 25.0 software was used for data analysis, and one-way ANOVA was used for inter group comparisons, LSD test was used for further pairwise comparisons.Results:(1)In the gonad estradiol experiment, there were statistical differences in various indicators among the five groups of rats in the open field test, elevated cross maze test, freeze test, and new object recognition test( F=20.200, 12.702, 7.514, 10.094, 7.899, 13.211, all P<0.05). The number of upright times, central area activity time, distance and frequency of entering the open arm, and cognitive index of the model group rats were all lower than those of the blank control group(all P<0.05), and the freezing time was higher than that of the blank control group( P<0.05). The number of upright positions((11.20±1.55) times), central area activity time((11.33±1.80) s), distance((1.49±0.26) m) and times((10.00±1.50) times) entering the open arm, the freezing time((92.20±6.07) s) and cognitive index((60.40±3.71)%) in ovariectomy+ estradiol group were all higher than those of ovariectomy group((4.90±0.65) times, (4.31±1.07) s, (0.49±0.06) m, (3.10±0.62) times, (60.30±5.28) s, (32.60±8.08)%)(all P<0.05). (2) In the hippocampal estradiol experiment, there were statistical differences in various indicators among the four groups in the open field test, elevated cross maze test, freeze test, and new object recognition test( F=40.831, 5.553, 9.087, 5.848, 7.657, 9.191, all P<0.05). The numbers of upright positions, distance and frequency of entering open arms of the model group rats were lower than those of the blank control group(all P<0.05). The number of upright positions((3.00 ± 0.39) times), distance of entering open arm((1.17±0.37) m), freezing time((46.70±3.57)s), and cognition index((29.60±2.70)%) in the hippocampal estradiol inhibitor group were all lower than those in the hippocampal solvent control group((10.10±1.40) times, (4.02±0.79) m, (93.70±9.73) s, (54.20±5.08)%)(all P<0.05). Conclusion:17β-E2 derived from the hippocampus and gonad both had ameliorative effect on cognitive memory and anxiety-like behavior in the reconsolidation period of fear memory in PTSD model rats.