Short-term treatments with haloperidol or bromocriptine do not alter the density of the monoamine vesicular transporter in the substantia nigra.

[3H]dihydrotetrabenazine ([3H]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 colchicine (10 micrograms/2 microliters) into the medial forebrain bundle. This accumulation was measured after sustained 2-day pharmacological modifications of the central dopaminergic transmission. It was not modified after s.c. administration of either the direct dopamine (DA) receptor agonist bromocriptine (four injections of 4 or 6 mg/kg) or the DA receptor antagonist haloperidol (four injections of 0.5-1-1.5-2 mg/kg). Thus, it appears that these pharmacological modifications, imposed to the activity of the nigro-striatal dopaminergic system during 2 days, have no consequence on the rate of synthesis of its vesicles.