Fighting, nonagonistic social behavior, and exploration in isolation-reared rats

Sixty hooded Long-Evans rats were assigned to one of three conditions: isol ation-rearing (from 14-30 days of age), brief isolation (from 28-30 days of age), and normal (no isolation). From day 14 to day 21, the isolation-rear ed animals were maintained in an incubator set at 35 degrees C to prevent h ypothermia and were separated from each other by Plexiglas. They learned to nourish themselves by lapping milk that continuously flowed down one side of the enclosure. Thereafter, they were housed in standard hanging wire cag es. Unlike previous studies of isolation at this age, there were no signifi cant weight differences between the isolation-reared group and the two cont rol groups. At 30 days of age, the three groups were compared on fighting ( serious and play), nonagonistic social behaviors (following and crawling un der):, and exploratory behavior (open-field ambulation). The isolation-rear ed group was significantly different from the normal group on all measures (isolates were higher on all measures except exploration). The isolation-re ared animals showed significantly more serious fighting (aggression) than t he brief isolation animals, whereas these two groups did not differ on othe r behaviors. This methodology allows for the study of isolation-rearing wit hout the nutritional confounds found in previous research and shows an effe ct on aggression that is not accounted for by recent isolation. (C) 1999 Wi ley-Liss, Inc.