The effect of chronic treatment (twice daily for 21 days) with low doses of l-sulpiride (2 mg/kg i.p.) on the apomorphine-induced inhibition of A10 and A9 dopaminergic neurons was compared with the effect of chronic administration of the classic antidepressant desipramine (20 mg/kg i.p. daily for 21 days). Intravenous administration of apomorphine (0.01-0.04 mg/kg), to rats treated chronically with l-sulpiride, produced a reduction of the spontaneous firing rate of A9 dopaminergic neurons not significantly different from that observed in control (saline-treated) rats. In contrast, apomorphine at the same doses was more potent in inhibiting A10 firing in control rats than in l-sulpiride-treated subjects. On the other hand, desipramine-treated rats were found normosensitive (as compared to saline-treated rats) to the inhibitory properties of apomorphine in both A9 and A10 dopaminergic neurons. It is suggested that chronic l-sulpiride-induced reduction of autoreceptor sensitivity in the A10 region may contribute to its clinical antidepressant effect.