Relative affinities of dopaminergic drugs at dopamine D2 and D3 receptors.

Quantitative autoradiography was used to evaluate the pharmacological profile of dopamine D2-like receptors labeled by [125I]iodosulpiride. Caudate/putamen, a brain region associated primarily with dopamine D2 receptor mRNA, was used as a prototypical D2 tissue; cerebellar lobule X (D3 mRNA associated), as a D3 tissue. 7-OH-DPAT ((+/-)-2-dipropylamino-7-hydroxy-1,2,3,4- tetrahydronaphthalene) exhibited selectively for cerebellar receptors (24-fold), followed by quinpirole (6-fold). Haloperidol and domperidone were 4- and 18-fold more potent at striatal receptors, respectively. These data are in close agreement with that derived from dopamine D2 and D3 receptor-expressing cell lines.