Increase of striatal dopamine turnover by drugs: interference with granular storage or receptor blackade?

Apomorphine completely antagonized the reserpine-induced enhancement of the striatal 3,4-dihydroxyphenylalanine (dopa) accumulation seen after administration of the decarboxylase inhibitor 3-hydroxybenzylhydrazine (NSD 1015). Reserpine-like drugs, e.g. Ro 4-1284 and Ro 4-9040, markedly enhanced the striatal dopa accumulation (due to NSD 1015) in normal animals but not in rats treated with reserpine plus apomorphine. Haloperidol enhanced the striatal dopa accumulation to a similar extent in normal and in reserpine-apomorphine-treated animals. Chlorpromazine also caused an enhancement of striatal dopa accumulation in both types of animals, but its potency was somewhat higher in normal rats than in those treated with reserpine plus apomorphine. In conclusion, reserpinized animals treated with apomorphine appear to be useful models for differentiating whether a drug enhances striatal DA turnover by interference with granular DA storage or by blockade of DA receptors. The latter seems to be the main mechanism of action of neuroleptic drugs.