A Novel Method for Chronic Social Defeat Stress in Female Mice

Abstract

Historically, preclinical stress studies have often omitted female subjects, despite evidence that women have higher rates of anxiety and depression. In rodents, many stress susceptibility and resilience studies have focused on males as one commonly used paradigm-chronic social defeat stress-has proven challenging to implement in females. We report a new version of the social defeat paradigm that works in female mice. By applying male odorants to females to increase resident male aggressive behavior, we find that female mice undergo repeated social defeat stress and develop social avoidance, decreased sucrose preference, and decreased time in the open arms of the elevated plus maze relative to control mice. Moreover, a subset of the female mice in this paradigm display resilience, maintaining control levels of social exploration and sucrose preference. This method produces comparable results to those obtained in male mice and will greatly facilitate studying female stress susceptibility.

Figure 1

Resident male mice attack female intruders paired with male scent. (a) Experimental timeline. (b) Rates of aggression and mounting during resident–intruder sessions (n=39 mice, 10 sessions per mouse) for all sessions (upper charts), and split by estrous phase (lower charts). (c) Day 1 plasma corticosterone responses to aggression (Wilcoxon-rank sum, **P<0.01; n=25 and 39 for control and stressed animals, respectively). Error bars represent SEM. (d) Number of aggressive interactions over 10 days of social defeat, for each animal (n=39). Error bars represent 1.5 × the interquartile range (IQR).

Figure 2

Repeated social defeat results in social avoidance. (a) Time spent interacting with an empty cup (non-social target) and a novel mouse (social target) after chronic social defeat stress (Kruskal–Wallis, χ²=15.3; P=0.0015, Wilcoxon-rank sum, ***P<0.001; control n=25, stressed n=30). (b) Right, social interaction ratios for control and stressed mice (Wilcoxon-rank sum, ***P<0.001; control n=25, stressed n=30). Left, heat maps indicating time spent in the interaction chamber for example control and stress mice. (c) Social interaction ratios for control (n=25), susceptible (n=17, social interaction ratios <1), and resilient (n=13, social interaction ratios >1) mice. (d) Time spent in the interaction zone with social target for control (n=25), susceptible (n=17), and resilient (n=13) mice (Kruskal–Wallis χ²=20.7; P<0.00003, Wilcoxon-rank sum, ***P<0.001). (e) Top, the percent of resilient and susceptible mice. Bottom, the cumulative distribution of SI values for control (black line) and stressed mice. Blue line indicates susceptible and red line indicates resilient mice. Error bars represent SEM.

Figure 3

Repeated social defeat results in decreased sucrose preference and open arm exploration. (a) Sucrose preference for control, susceptible and resilient mice (Kruskal–Wallis, χ²=8.6; Wilcoxon-rank sum, **P<0.01; n=24, 10, 16). (b) Time spent by control and stressed mice in the open arms of the elevated plus maze (Wilcoxon-rank sum, *P<0.05; n=14, 21). (c) Time spent in the EPM by susceptible and resilient mice (not significant (n.s.); n=8, 14). Error bars represent SEM.

Figure 4

Neither number of aggressive encounters nor estrous cycle determines susceptible outcome. (a) Left, cumulative distribution of days of aggression for susceptible and resilient mice (Kolmogorov–Smirnov test, P=0.63). Right, distribution of aggressive days grouped by susceptible vs resilient (n=13–18). (b) Social interaction times for control and chronically stressed mice across estrous phase (not significant (n.s.); n=6–11). Error bars represent SEM.