SHORT-TERM TREATMENTS WITH HALOPERIDOL OR BROMOCRIPTINE DO NOT ALTER THE DENSITY OF THE MONOAMINE VESICULAR TRANSPORTER IN THE SUBSTANTIA-NIGRA

[H-3]dihydrotetrabenazine ([H-3]TBZOH) was used to label the monoamine vesicular transporter in the rat substantia nigra. An accumulation of neuronal vesicles in the substantia nigra pars compacta was observed after blockade of the fast axonal transport by a microinjection of col chicine (10 mu g/2 mu l) into the medial forebrain bundle. This accumu lation was measured after sustained 2-day pharmacological modification s of the central dopaminergic transmission. It was not modified after s.c. administration of either the direct dopamine (DA) receptor agonis t bromocriptine (four injections of 4 or 6 mg/kg) or the DA receptor a ntagonist haloperidol (four injections of 0.5-1-1.5-2 mg/kg). Thus, it appears that these pharmacological modifications, imposed to the acti vity of the nigro-striatal dopaminergic system during 2 days, have no consequence on the rate of synthesis of its vesicles.