Presented at the Annual Meeting of the Society for Neuroscience, Los Angeles, 1998.

SEROTONERGIC INVOLVEMENT IN THE ROUGH-AND-TUMBLE PLAY OF JUVENILE RATS. S.M. Siviy*, M. Boustani, J.H. Birkholz & M. Pineault. Department of Psychology, Gettysburg College, Gettysburg, PA 17325.

Previous research suggests that serotonin may have an inhibitory influence on the play behavior of juvenile rats. To further evaluate the receptor selectivity and behavioral specificity of this putative influence, the effects of selective agonists at 5HT_1A, 5HT_1B, and 5HT₂/5HT_1C receptors were evaluated. Male, Sprague-Dawley rats were tested between the ages of 25 and 40 days of age and were isolated for 24 hours prior to a 5 minute opportunity to play. Play bouts were videotaped, allowing for a more detailed behavioral analysis. The effects of the following compounds on play were assessed in separate groups of rats: the full (R+) and partial (S-) enantiomers of the 5HT_1A agonist 8-OH-DPAT (0, 0.01, 0.03, 0.1, 0.3 mg/kg), the 5HT_1B agonist RU24969 (0, 0.03, 0.1, 0.3, 1.0 mg//kg) and the 5HT₂/5HT_1C agonist DOI (0, 0.01, 0.03, 0.1, 0.3 mg/kg). Low, autoreceptor-selective, doses of R(+)-8-OH-DPAT, but not S(-)-8-OH-DPAT, had a tendency to increase overall levels of playfulness, as measured by increases in pinning. Higher doses of both compounds reduced play. Pinning was also reduced at the higher doses of RU24969 and DOI. These data suggest that the most predominant effect of selective 5HT agonists is for a reduction in playfulness. Preliminary analysis of videotaped play bouts indicates that playful defense may be more sensitive to disruption by these compounds than playful attack, suggesting that responsiveness to playful overtures may be preferentially affected by serotonergic agonists.