EFFECTS OF SINGLE RESTRAINT ON THE DEFENSIVE BEHAVIOR OF MALE AND FEMALE RATS

The effects of single aversive stimulation due to restraint (RT) on be havioral responses to unfamiliar conspecifics were studied in male and female rats. The Resident-intruder paradigm was adopted, RT animals a nd their controls playing the role of intruders. Introductory and agon istic behaviors of both intruders and residents were recorded. In male s, RT increased both the number of subjects which showed freezing and freezing duration, and this was independent of the amount of aggressio n received by the residents. By contrast, no change was found in activ e defense. Increased passive defense was not paralleled by a complete inhibition of aggression. The latter was rare, but not absent, and occ urred in RT males as often as in their controls. Females never showed freezing and, unlike males, resorted to a fully active defensive strat egy. RT females were the preferential targets of residents' high-inten sity aggression, but showed the same rate of defensive responding as c ontrol females. The crucial role played in studies of social behavior by testing conditions and mutual influences between the behavior of ex perimental subjects and residents are discussed.