Chronic antidepressant treatments enhance dopaminergic neurotransmission in the mesolimbic dopamine system. We suggested that this potentiation might underlie both the antidepressant therapeutic effect and the antidepressant-induced switch from depression to mania, which in turn, might be involved in the development of rapid cycling in bipolar patients. In this study, we investigated the changes occurring in the sensitivity of the mesolimbic dopamine system up to 40 days after antidepressant withdrawal. Male Sprague-Dawley rats were treated for 3 weeks with imipramine (20 mg/kg) and tested for motor activity 24 h, 12, 33 and 40 days after treatment withdrawal. Ambulatory activity and rearing counts were recorded after challenge with the dopamine D2-like receptor agonist quinpirole (0.15 mg/kg). Imipramine increased the motor response to quinpirole, 24 h after treatment discontinuation. No relevant differences between the groups were found after 12 and 33 days. After 40 days, a decreased level of rearing was observed in the group treated with imipramine. These results show a reversal of the imipramine-induced dopaminergic supersensitivity after 40 days of chronic imipramine withdrawal and suggest that the mood-switches observed in bipolar patients following antidepressant treatment and subsequent withdrawal, i.e. mania followed by rebound depression, might depend upon parallel changes in the mesolimbic dopamine system sensitivity.