Social interactions in adolescent and adult Sprague-Dawley rats: impact of social deprivation and test context familiarity.

Interactions with peers become particularly important during adolescence, and age differences in social interactions have been successfully modeled in rats. To determine the impact of social deprivation on social interactions under anxiogenic (unfamiliar) or non-anxiogenic (familiar) test circumstances during ontogeny, the present study used a modified social interaction test to assess the effects of 5 days of social isolation or group housing on different components of social behavior in early [postnatal day (P) 28], mid (P35), or late (P42) adolescent and adult (P70) male and female Sprague-Dawley rats. As expected, testing in an unfamiliar environment suppressed social interactions regardless of age, housing, and sex. Social deprivation drastically enhanced all forms of social behavior in P28 animals regardless of test situation, whereas depriving older animals of social interactions had more modest effects and was restricted predominantly to play fighting -- an adolescent-characteristic form of social interactions. Social investigation -- more adult-typical form of social behavior was relatively resistant to isolation-induced enhancement and was elevated in early adolescent isolates only. These findings confirm that different forms of social behavior are differentially sensitive to social deprivation across ontogeny.