Social interaction: responses to chlordiazepoxide and the loss of isolation-reared effects with paired-housing

This study investigated the action of chlordiazepoxide (CDP), on the social interaction (SI) of adult rats maintained in one of three housing conditions: (i) group-reared, (ii) isolated from weaning or (iii) paired during adulthood after initial isolation at weaning (pair-housed former isolates; PHFIs). Group-reared rats and PHFIs rats were housed in pairs starting 21 days prior to the first experiment. For these two groups, CDP (2.5 and 5.0 mg/kg) increased SI in unfamiliar, but not familiar (cagemate) pairings. In rats isolated throughout, SI was markedly increased and this was unaffected by CDP. Isolated rats also exhibited increased motor activity (MA) during SI tests, and the MA of both isolates and PHFIs was reduced by CDP. Finally, levels of aggression were very low except in isolates, where a relatively modest increase in aggression was reversed by either pairing or CDP. To summarise, isolation-induced increases in SI and aggression were reversed by pairing, but pairing only attenuated isolation-induced increases in MA. Although CDP reduced the elevated aggression and MA of isolated rats, it had no effect on their elevated SI scores. These data question the permanence of anxiety-related, isolation-induced behavioural changes and stand in contrast to the irreversible anxiogenic profile reported for isolation-reared rats in the elevated X-test.