Sulpiride blocks postsynaptic dopamine receptors in the nucleus accumbens

Intra-accumbens injection of sulpiride, tiapride, and metoclopramide antagonized locomotor hyperactivity induced by intraperitoneal administration of apomorphine in rats and measured over the first five minutes after introducing the animal to an open-field cage. Sulpiride was slightly more potent than tiapride which was more than 10 times more potent than metoclopramide and haloperidol. The threshold dose of sulpiride was as low as 0.001 microgram, bilaterally. Intra-accumbens injection of sulpiride also blocked exploratory hypermotility induced by bilateral intra-accumbens injections of apomorphine and picrotoxin. The threshold dose of sulpiride for blocking these two effects was about 0.01 microgram, bilaterally. Sulpiride was more than 10 times more potent than haloperidol in blocking this apomorphine-induced hypermotility. Haloperidol did not influence the picrotoxin hypermotility. The results obtained indicate strong postsynaptic dopamine antagonist properties of sulpiride, tiapride and metoclopramide.