Figure 1. Strong genetic background effect on the behavioral response to CSDS. A, Timeline of experiments. Each perpendicular line represents 1 d. B, SI ratios of the four strains in the SA test. Pie charts represent the proportion of resilient and susceptible mice in each mouse strain. 129, BALB, and D2 strains were highly susceptible to CSDS, while B6 strain was the most resilient to CSDS. Time spent in the IZ (C) and the corner zones (D) of the SA test during sessions with no social target (N) and a CD1 mouse as a social target (T). Susceptible mice of all strains spent less time in the IZ when the target was present compared to when it was not. E, Distance traveled during the no-target trial of the SA test. In the B6 strain, both susceptible and resilient mice had lower locomotor activity, while in the D2 strain only susceptible mice moved significantly less than controls; n (B–E, I) = 129: Con = 7, Res = 3, Sus = 13; C: Con = 34, Res = 10, Sus = 33; B6: Con = 72, Res = 70, Sus = 32; D2: Con = 39, Res = 2, Sus = 40. F, Distance traveled during the 5-min OF test. B6 resilient and D2 susceptible mice traveled significantly shorter distances than their same-strain control mice; n = 129: Con = 7, Res = 3, Sus = 13; C: Con = 18, Res = 6, Sus = 19; B6: Con = 20, Res = 19, Sus = 4; D2: Con = 19, Res = 1 (not analyzed), Sus = 22. G, Time B6 mice spent in the open area of the EZM. Susceptible mice spent significantly less time in the open zones compared to controls; n: Con = 20, Res = 29, Sus = 11. H, Immobility time of B6 mice during minutes 2–6 of the FST did not differ between groups; n = Con = 28, Res = 32, Sus = 21. I, Difference in body weight before and after CSDS. B6 defeated mice gained weight during CSDS similarly to their same-strain controls, BALB susceptible mice gained significantly less weight than controls, and both resilient and susceptible D2 mice lost weight. All figures depict mean ± 1 SEM; *p < 0.05, **p < 0.01, ***p < 0.001, see Extended Data Figure 1-1 for exact p values. D2: DBA/2NCrl strain; BALB: Balb/cAnNCrl; 129: 129S2/SvPasCrl; B6: C57BL/6NCrl; Con: control; Res: resilient; Sus: susceptible; mPFC: medial prefrontal cortex; BNST: bed nucleus of the stria terminalis; vHPC: ventral hippocampus.