Clonidine-induced sedation in rats: evidence for mediation by postsynaptic alpha 2-adrenoreceptors

The effect of low doses of clonidine on exploration and motility was investigated in rats after destruction of central noradrenergic systems by 6-hydroxydopamine (6-OHDA) or DSP-4. In accordance with previous results, clonidine decreased exploration and motility in control animals. This sedative effect of clonidine was potentiated in animals that suffered selective and extensive depletions of brain NA as a result of neonatal treatment with 6-OHDA. Depletion of NA by administration of DSP-4 to adult animals did not influence clonidine's sedative effects. Yohimbine, but not phentolamine, antagonized clonidine-induced hypomotility both in control and in neonatal 6-OHDA treated groups. The results suggest that clonidine-induced sedation is mediated by postsynaptic alpha 2-adrenoreceptors.