SOCIAL-ISOLATION INCREASES AGGRESSIVE-BEHAVIOR AND ALTERS THE EFFECTSOF DIAZEPAM IN THE RAT SOCIAL-INTERACTION TEST

Isolation rearing in the early stages of Life has been shown to modify a variety of behaviours in many animals and the responsitivity to psy chotropic drugs. The aims of the present study were to investigate the effects of isolation rearing on anxiety using the social interaction paradigm and to compare the effects of diazepam on social interaction behaviours in isolation and socially reared rats. Male Lister hooded r ats were reared from weaning either alone (isolation reared) or in gro ups of four (socially reared) for 6 weeks and then were tested for soc ial interaction. Both isolation and socially reared rats were exposed to the social interaction test either without drug treatment or follow ing saline or diazepam (1 and 2.5 mg/kg, i.p., 30 min before testing). The results demonstrate that under high light in an unfamiliar arena, the isolation compared to the socially reared rats showed a significa ntly (P < 0.01) higher level of social interaction, manifested as incr eases in aggressive and avoidance behaviours, and that this interactio n occur for a greater length of time during the test period (10 min). However, when the light level was decreased or when the arena was fami liar, active social interaction of isolation reared rats decreased but increased in the socially reared rats. In both conditions the isolati on reared rats displayed more aggressive behaviours, in particular bit ing and boxing the partners which did not occur with the socially rear ed rats. Pretreatment of diazepam (1 and 2.5 mg/kg, i.p.) caused a dos e-related reduction in aggressive behaviours in rats reared under both conditions but increased passive interactions in the socially reared rats. In contrast diazepam (2.5 mg/kg) reduced active interaction in t he isolation reared rats but had no effect on passive interaction. The se results indicate that isolation rearing increases aggressive behavi ours and alters the effects of diazepam.