Isolated during adolescence: long-term impact on social behavior, pain sensitivity, and the oxytocin system in male and female rats.

Background: Adolescent social isolation (ASI) has profound long-term effects on behavioral and neural development. Despite this, the specific long-term impact of ASI during different adolescent stages and across sexes remain underexplored.

Methods: Our study addresses this gap by examining the effects of early- and late- adolescent social isolation on both male and female rats. Rats were either isolated (or group-housed) starting from PD 21 (early) or PD 42 (late) for three weeks and then rehoused into groups. In adulthood (PD 90), rats underwent a battery of tests: elevated plus-maze, open field, novel object recognition, social interaction and social recognition memory and hotplate tests. Finally, we analyzed oxytocin receptor binding in several regions in the brains of a second cohort of rats.

Results: Both, male and female rats from the late adolescent social isolation (LASI) groups spent significantly less time interacting in the social interaction test. Additionally, we observed a general decrease in social recognition memory regardless of sex. Both male ASI groups demonstrated heightened thermal pain sensitivity, while the opposite was observed in early adolescent social isolation (EASI) female rats. In the brain, we observed changes in oxytocin receptor (OTR) binding in the paraventricular nucleus of the hypothalamus (PVN) and paraventricular nucleus of the thalamus (PVT) and central amygdala (CeA) with the largest changes in EASI and LASI female rats.

Conclusion: Our model demonstrates long-lasting alterations on behavior and oxytocin receptor binding levels following ASI providing insights into the long-term effects of ASI in a time- and sex-specific manner.