EFFECTS OF FLUOXETINE ON PLAY DOMINANCE IN JUVENILE RATS

In a series of three studies, we investigated the influence of a selec tive serotonin reuptake inhibitor (fluoxetine) on the rough-and-tumble play of juvenile rats. In Experiment 1, both members of eight pairs o f solitary-housed juvenile rats received either vehicle, 2.5, 5, or 10 mg/kg fluoxetine in a counterbalanced within-subject design 20 min be fore being allowed to play for 5 min periods on four successive test d ays. The 5 and 10 mg/kg pretreatments significantly reduced incidence of pins during play without affecting dorsal contacts. In Experiment 2 , one member of each of 19 established play pairs received 5 mg/kg flu oxetine 20 min before play, while the other member received vehicle. D ominant rats showed no reduction in pins as a result of fluoxetine tre atment, but subordinate rats who received fluoxetine exhibited signifi cant reductions in pins. Subsequent dyadic analyses indicated that in pairs where the subordinate animal received fluoxetine, dominant anima ls maintained their pinning advantage over the 10 days of testing, but in pairs where the dominant animals received fluoxetine, this pinning asymmetry diminished. In Experiment 3, we replicated the above proced ure with inexperienced play pairs, to control for the effects of prior social learning. Fluoxetine treatment (5 mg/kg) significantly reduced both pins and dorsal contacts in all treated rats. The results indica te that fluoxetine can reduce the playful pins of juvenile rats, but t hat prior social learning mediates the strength of these effects. (C) 1996 Wiley-Liss, Inc.