[3H]205-501, a non-catechol dopaminergic agonist, labels selectively and with high affinity dopamine D2 receptors

[3H]205-501, a noncatechol dopaminergic agonist, is presented as a ligand with high affinity (KD approximately 1 nM) and high selectivity for dopamine receptors. pKi values of dopaminergic agonists derived from competition isotherms in the [3H]205-501 binding assay correlate very well with their potency in the acetylcholine release assay, which is controlled by dopamine D2 receptors. There is however no correlation with their potency stimulating adenylate cyclase, a process controlled by dopamine D1 receptors. Thus [3H]205-501 is the first agonist ligand selective for dopamine D2 receptors.