Effects of isolated housing and chronic antidepressant treatment on cooperative social behaviour in rats.

Pair-housed, water-deprived rats were trained to run in a two-way shuttle box, using water reinforcement. Animals were tested either singly or in pairs; in the paired condition, the animals were required to shuttle in close physical proximity. Paired performance, but not single performance was severely disrupted by single housing for 3-7 weeks. Performance of singly-housed animals could be restored either by re-housing in pairs (30 days) or by chronic (30 day) treatment with the antidepressants imipramine or fluoxetine. Chronic imipramine was also prophylactically active in preventing the deterioration in performance of singly-housed animals. The superior paired performance of pair-housed animals and of imipramine-treated singly-housed animals, was abolished by the 5-HT antagonist metergoline. Metergoline had relatively little effect on single running: the DA antagonist pimozide disrupted paired and single running equally. The results suggest a role for 5-HT in cooperative performance and in the action of antidepressant drugs in this paradigm.