Effects of clonidine and yohimbine on the social play of juvenile rats.

The social play of juvenile rats was observed following administration of either the alpha-2-adrenergic agonist clonidine (0.1, 0.5, 1, 5, 10, and 50 micrograms/kg) or antagonist yohimbine (0.5, 1, 2, and 5 mg/kg). Using pins (one animal on its back with the other on top) as the dependent measure, we found that clonidine reliably reduced the amount of play at all but the lowest dose tested, while yohimbine had no effect at any but the highest dose. In addition, we tested a clonidine-yohimbine interaction to assess neurospecificity of the results. While yohimbine alone (0.5 mg/kg) had no effect on play, it partially reversed the clonidine-induced suppression, indicating that the effect may be mediated to some degree through an alpha-2-adrenergic mechanism.