Differential effect of neuroleptic drugs on dopamine turnover in the extrapyramidal and limbic system

In gallamine-immobilized cats, the caudate nucleus and the nucleus accumbens septi were perfused by means of a push-pull cannula and dopamine was measured in the perfusate. Chlorpromazine (10 mg kg(-1)) and clozapine (20 mg kg(-1)), administered intravenously, enhanced the release of dopamine. The effect of chlorpromazine was similar in both regions whereas that of clozapine was more pronounced in the nucleus accumbens than in the caudate nucleus. Furthermore, in the rat, sulpiride, clozapine and thioridazine increased the homovanillic acid concentration in striatum and limbic system to a similar extent. However, following probenecid administration, the net effect of these drugs on homovanillic acid accumulation was more marked in the limbic system than in the striatum whereas haolperidol and chlorpromazine had a similar effect in the two regions. It is concluded that, in contrast to haloperidol and chlorpromazine, sulpiride, clozapine and thioridazine may preferentially affect the limbic dopaminergic transmission. This possibly accounts for the fact that sulpiride, clozapine and thioridazine display an antipsychotic action and yet cause less extrapyramidal side effects than haloperidol and chlorpromazine.