Blockade of in vivo binding of 125I-labeled 3-iodobenzamide (IBZM) to dopamine receptors by D2 antagonist and agonist.

The in vivo binding of [125I]3-iodobenzamide (IBZM), a substituted benzamide, to DA receptor binding sites in the caudate nucleus, nucleus accumbens, and olfactory tubercle was investigated by using ex vivo autoradiography. The in vivo binding of IBZM seems to be selective to D2 dopamine receptors, since the binding was blocked by pretreatment of animals with D2 agonist LY-171555 or antagonist YM-09151-2. Furthermore, in vitro binding assays in striatal membranes confirmed that IBZM binding was highly selective to D2 sites. Thus, IBZM, when labeled with 123I (T1/2: 13h; 159 kev), could be a potential ligand for imaging D2 dopamine receptors by single photon emission computerized tomography procedures.