Post-weaning social isolation increases reward-seeking behavior in a sex-specific manner in mice

Social isolation is a growing concern in public health. Although isolation at any age is harmful, previous studies have shown that isolation during adolescence, correlating with critical periods of brain development, can impair cognitive function and increase the risk for psychiatric illness later in life. In this study, we utilized a mouse model of adolescent social isolation (SI) and compared performance of isolated and group-housed mice on touchscreen-based continuous performance test (CPT) and fixed ratio/progressive ratio (FR/PR) tasks in adulthood. SI increased sensitivity in the CPT in male mice and had no effect in female mice. The increase in sensitivity was consistent across time bins within the 45-minute testing session and there were no SI effects on reaction times or reward retrieval latencies. A possible confound for performance in the CPT would be SI-induced changes in reward-seeking or motivation for the strawberry milk reward. We next compared the SI mice to their group-housed littermate controls on both FR and PR schedules of reinforcement and found that male SI mice earned significantly more reinforcers on FR schedules of reinforcement and had higher breakpoints on PR schedules compared to their group-housed littermates. SI had no effect on FR or PR performance in female mice. These data indicate that SI during adolescence has striking, sex-specific effects on reward-seeking behavior in adult mice and may provide a useful behavioral model for studying the link between SI and risk for neuropsychiatric disorders.