Social enrichment during early life attenuates specific behavioral alterations induced by early life stress in an age- and sex-dependent manner

Early social stress (ESI) interferes with neurodevelopmental processes and can lead to long-lasting emotional, cognitive, and hormonal alterations in adolescent and adulthood. Communal nesting (CN) provides a socially stimulating environment, which was shown to affect social and anxiety-like behaviors. This study investigates whether the postnatal rearing conditions could affect reward-related processing for natural rewards, compulsive tendencies, sensorimotor gating and corticosterone levels in adolescence and adult rats of both sexes. The results obtained in a paradigm of food self-administration showed that adolescent and adult rats reared in standard (SH) condition showed a greater propensity for natural reward compared to CN condition, and this effect is highlighted in the ESI condition although to a different extent in the two sexes. Notably, ESI-induced effect was reverted by CN condition. In the marble burying test, differences were noted only in adolescent males, with an increase in the number of marbles buried by SH-ESI rats vs SH-not isolated (control) group. Moreover, ESI reduced % prepulse inhibition (PPI) in adolescent SH rats, an effect that in males was long-lasting and reverted by CN. Finally, female rats showed higher plasma corticosterone levels, independently from housing and stress conditions. Altogether, our findings indicate that early life social isolation and communal nesting have long-lasting effects on sensorimotor gating, reward-seeking, and compulsive-like behaviors, with males and females showing different vulnerabilities in these domains. Specifically, we demonstrated for the first time that a socially enriched condition may play a "protective" role toward early stress-induced reward-related responses, emotional changes and cognitive deficit.