Early life adversity reduces affiliative behavior towards a distressed cagemate and leads to sex-specific alterations in corticosterone responses.

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both mice 20 or 90 minutes after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.