Immediate early genes, including zif268, arc and c-fos were used as indices for the evaluation of neural activity. We detected the expression levels of these genes through Q-RT-PCR, Western blotting, and immunohistochemistry. First, we analyzed the mRNA levels of zif268 and arc by using Q-RT-PCR. As shown in Fig. 2a (F = 21.5), b (F = 26.7), the mRNA levels of zif268 and arc in intruder mice gradually increased at day 1, peaked at day 3, decreased at day 7, and were the same as those in control mice at day 15 after stimulation. Second, we examined c-Fos protein levels by using Western blotting. As shown in Fig. 2c, d (F = 5.6), c-Fos expression in intruder mice dramatically increased at day 3 and then slightly decreased at day 7. c-Fos protein levels in intruder mice on days 3 and 7 after stimulation were higher than those in control mice. c-Fos positive cells were labeled and counted as described in “Methods” section. As shown in Fig. 2e, f (F = 16.357), the number of c-Fos positive cells dramatically increased at day 3 after stimulation and then decreased. The above data suggests that aggressive stimulation facilitates BLA activation at the beginning of the stimulus (from day 1 to day 7). This response then diminished during the later stages of the stimulus (from day 7 to day 15).Fig. 2Response of BLA to social defeat stress. a mRNA levels of zif 268 and arc in BLA tissues gradually increased at day 1 after stimulation, peaked at day 3 after stimulation, and decreased at day 7 after stimulation compared with control mice, one way ANOVA with Tukey’s test was used, F = 21.5, *p < 0.05, **p < 0.01 compared with the control, n = 8. b mRNA levels of arc in BLA tissues gradually increased at day 1 after stimulation, peaked at day 3 after stimulation, and decreased at day 7 after stimulation compared with control mice, one way ANOVA with Tukey’s test was used, F = 26.7, *p < 0.05, **p < 0.01 compared with the control, n = 8. c Representative image of the Western blot of c-Fos. d Statistical analysis of c-Fos expression, one way ANOVA with Tukey’s test was used, F = 5.6, *p < 0.05, **p < 0.01 compared with the control, n = 8. e Representative images of c-Fos staining in BLA. Squares in the upper images indicate areas that are shown magnified in the bottom images. Blue arrows indicate c-Fos-positive cells. f Cell count in the BLA, one way ANOVA with Tukey’s test was used, F = 16.357, **p < 0.01 compared with the control, n = 4