9Introduction: Rough-and-tumble play presents opportunities for young mammals to test social skills in an affiliative context. Because serotonin (5HT) depletion can induce nonaffiliative or openly hostile behavior in adult rats’ and primates,’ we conducted an experiment to examine if serotonin depletion would also increase the agonistic nature of play behavior in juvenile rats.
Results: Taken together, these findings suggest that serotonin depletion can enhance individual differences in play behavior. These enhancements can, in turn, magnify behavioral asymmetries within a playing dyad. This finding is consistent with the observation that serotonin augmentation (via the administration of fluoxetine) reduces behavioral asymmetries in playing rat pairs, particularly when administered to the dominant ~artner.~These results also suggest that serotonergic manipulations change the quality of play interaction rather than simply reducing or enhancing the overall amount of play. If reciprocation is a mark of playfulness, then these changes may transform play into a more agonistic interaction that approaches the appearance of fighting. Dyadic analyses can help to illuminate these types of qualitative changes in social interaction.
