Clonidine as a sensitizing agent in the forced swimming test for revealing antidepressant activity.

The forced swimming test (FST) in mice has failed to predict antidepressant activity for drugs having beta adrenoreceptor agonist activity and for serotonin uptake inhibitors. We investigated the potential for clonidine to render the FST sensitive to antidepressants by using a behaviorally inactive dose of this agent (0.1 mg/kg). All antidepressants studied (tricyclics, 5-HT uptake inhibitors, iprindole, mianserin, viloxazine, trazodone) showed either activity at lower doses or activity at previously inactive doses. The effect appeared specific because it did not appear with drugs other than antidepressants (diazepam, chlorpromazine, sulpiride, atropine), except for amphetamine and apomorphine which have a strong effect on the dopaminergic system. The use of behaviorally subactive doses of clonidine may thus provide an important means of increasing the sensitivity of the forced swimming test.