A comparison of the effects of haloperidol on dopamine turnover in the striatum, olfactory tubercule and median eminence.

A sensitive radioenzymatic procedure was used to quantify the effect of haloperidol on dopamine concentrations and rates of turnover in rat striatum, olfactory tubercle and median eminence, regions containing terminals of nigrostriatal, mesolimbic and tuberoinfundibular neurons, respectively. Haloperidol (2.5 mg/kg s.c.) did not alter the steady-state concentrations of dopamine in any of these brain regions at any time. Haloperidol increased dopamine turnover in the striatum and olfactory tubercle 2 and 8 hours after adminstration. The rate of dopamine turnover was increased only in the median eminence 16 and 24 hours after the administration of haloperidol, and effect which was blocked by hypophysectomy. Two other antipsychotic agents, clozapine and thioridazine, also increased dopamine turnover in the median eminence 16 hours after the first of two injections. These results provide evidence for the existence of hormonal neuronal feedback modulation of tuberoinfundibular dopaminergic neurons in contrast to the neuronal feedback modulation of nigrostriatal and mesolimbic neurons.