Sulpiride endowed with dopamine (DA)-antagonist properties, does not antagonize neostriatal DA-sensitive adenylyl cyclase activity either in vitro or in vivo. Sulpiride however is able to displace radioactive ligands, which label DA-receptors, from their specific binding sites. On these bases sulpiride has been proposed as a selective antagonist at dopamine-D2 receptors. We have characterized 3H(-)sulpiride stereospecific binding in various rat brain areas. In particular, 3H(-)sulpiride binding was found to be saturable, stereospecific and maximally enriched in the synaptic membrane fraction prepared from dopaminergic brain areas. Among a variety of compound tested only DA, DA-agonists and DA-antagonists were competitors for 3H(-)sulpiride specific binding sites. The results suggest that 3H(-)sulpiride may be an useful tool for the characterization and localization of dopamine D2-receptors.
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