zif268, arc mRNA were analyzed by Q-RT-PCR. As shown in Fig. 3a (F = 22.233), b (F = 23.655), the levels of these genes decreased on days 1 and 3 after stimulation and increased at days 7 and 15 after stimulation. We also analyzed the expression of c-Fos protein. Similar to those of zif268 and arc, the expression of c-Fos protein decreased at day 3 and increased at day 15 after stimulation (Fig. 3c, d, F = 4.73). c-Fos-positive cells were labeled and counted as described in "Methods" section. As shown in Fig. 3e, f (F = 5.287), the number of c-Fos-positive cells in intruder mice decreased significantly at days 3 and 7 after stimulation compared with those in the control mice, and then increased to the same levels as those in the control mice at day 15 after stimulation. These results suggest that vHIP is inhibited by aggressive stimulation at the beginning of aggression (from day 1 to day 3), and then gradually recovered (from day 7 to day 15).Fig. 3Response of vHIP to social defeat stress. a mRNA levels of zif268 in vHIP tissues from intruder mice decreased at days 1 and 3 after stimulation and increased at days 7 and 15 after stimulation compared with those in the control mice, one way ANOVA with Tukey’s test was used, F = 22.233, p < 0.05, **p < 0.01 compared with the control, n = 8. b mRNA levels of arc in vHIP tissues from intruder mice decreased at days 1 and 3 after stimulation and increased at days 7 and 15 after stimulation compared with those in the control mice, one way ANOVA with Tukey’s test was used, F = 23.655, p < 0.05, ** p < 0.01 compared with the control, n = 8. c Representative Western blot image of c-Fos. d Statistical analysis of c-Fos expression, one way ANOVA with Tukey’s test was used, F = 4.73, *p < 0.05, compared with the control, n = 8. e The representative images of c-Fos staining in vHIP. Squares in the upper images indicate areas that are shown magnified in the bottom images. Blue arrows indicate c-Fos-positive cells. f Cell counts in the vHIP, one way ANOVA with Tukey’s test was used, F = 5.287, *p < 0.05 compared with control, n = 4