CHRONIC ADMINISTRATION OF L-SULPIRIDE AT LOW-DOSES REDUCES A10 BUT NOT A9 SOMATODENTRITIC DOPAMINE AUTORECEPTOR SENSITIVITY

The effect of chronic treatment (twice daily for 21 days) with low dos es 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 ch ronic 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 I-sulpiride, produ ced a reduction of the spontaneous firing rate of A9 dopaminergic neur ons not significantly different from that observed in control (saline- treated) rats. In contrast, apomorphine at the same doses was more pot ent in inhibiting A10 firing in control 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 a pomorphine in both A9 and A10 dopaminergic neurons. It is suggested th at chronic I-sulpiride-induced reduction of autoreceptor sensitivity i n the A10 region may contribute to its clinical antidepressant effect.