Lesion of serotonergic neurons antagonizes clonidine-induced suppression of avoidance behavior and locomotor activity in rats

Abstract
The effects of clonidine on avoidance acquisition and locomotor activity were studied in male Wistar rats with 5,6-dihydroxytryptamine (5,6-DHT) lesions of the median raphe nucleus. Lesioned animals showed marked depletion in forebrain serotonin and 5-hydroxyindole acetic acid concentrations. Clonidine (0.2 mg/kg IP in a single daily dose for 6 consecutive days) inhibited avoidance acquisition and reduced locomotor activity in unlesioned rats. In 5,6-DHT rats clonidine failed to produce depressive effects. The resistance of raphe-lesioned rats to clonidine is discussed on the basis of possible interaction between noradrenergic and serotonergic brain systems.