Individual housing during the play period results in changed responses to and consequences of a psychosocial stress situation in rats.

In the present study, the consequences of individual rearing during the play period on adult responses to aggression were investigated in a complex social setting. In a group of either socially or individually reared rats, an aggressor was repeatedly introduced. Separate control groups of individually and socially reared rats were not exposed to an aggressor. To allow an interpretation of the altered reactivity to aggression in terms of (in)efficient or (in)adequate behavior, not only the responses in the presence of the aggressor but also the consequences of the altered reactivity on subsequent behavior in the absence of the aggressor were observed. We demonstrated that a higher number of injuries, more agitation of the aggressor, and more ultrasonic distress vocalizations accompanied the altered responses of individually reared rats in the presence of the aggressor. In the absence of the aggressor, individually reared rats displayed less social stress-reducing behaviors (play and social grooming) than socially reared rats. It was concluded that individually reared rats display a less adequate response to aggression in this social context. Copyright 2002 Wiley Periodicals, Inc.