Comparative analysis of procedural variations in the social defeat stress paradigm in mice: effects of post-defeat housing conditions and aggressor exposure duration

The chronic social defeat stress (CSDS) paradigm is widely used to model psychosocial stress in rodents. Procedural variations across studies may contribute to diverse behavioral outcomes, underscoring the need to clarify the experimental conditions that influence specific behaviors toward establishing a valid animal model. In this study, we examined the effects of post-defeat housing conditions and aggressor exposure duration, two procedural parameters in the CSDS paradigm, on behavior. Adult male C57BL/6 J mice were subjected to chronic SDS for 10 consecutive days under different conditions varying in (i) post-defeat housing (complete separation from an ICR aggressor vs. cohabitation with the aggressor under sensory contact) and (ii) duration of direct contact with aggressor (short exposure: 5 min vs. long exposure: 10 min). A battery of behavioral tests to assess social interaction and anxiety- and depression-related behaviors was conducted after the CSDS procedures. The proportion of mice classified as susceptible or resilient after CSDS did not differ significantly between the post-defeat housing (separation and cohabitation) groups or between the short- and long-contact duration groups. Regardless of the experimental condition, susceptible mice showed increased body weight, reduced social interaction, and decreases in the distance traveled and time spent in center area in the open field test compared with non-stressed controls, whereas no marked differences were observed in behavioral measures in the forced swim and tail suspension tests. Procedural variations led to differences in behavioral outcomes, with both the cohabitation and long-contact duration groups showing reduced distance traveled and less time spent in the center area in the open field test compared with the separation and short-contact duration groups, respectively. These results demonstrate that procedural variations in the CSDS paradigm shape certain behavioral phenotypes, suggesting that cohabitation and long duration of direct contact with aggressor are effective conditions for producing more pronounced and reproducible behavioral changes. These findings highlight the importance of carefully controlling procedural parameters to obtain reproducible CSDS mouse models and that the stress-induced behavioral changes consistently observed represent characteristic features of this model.