Antidepressants given repeatedly increase the behavioural effect of dopamine D-2 agonist.

The effects of single or repeated doses of antidepressant drugs (imipramine, amitriptyline, citalopram, mianserin) on rat locomotor hyperactivity induced by quinpirole, a dopamine D-2 receptor agonist, was investigated. Single doses of antidepressants do not change the effect of quinpirole, but enhance it when they are administered repeatedly. This enhancement is inhibited by (+/-)-sulpiride, a dopamine D-2 receptor antagonist. The results obtained indicate that the enhancement of dopaminergically-stimulated hyperactivity induced by repeated doses of antidepressants is mediated by dopamine D-2 receptors.