125I-spiperone: A novel ligand for D 2 dopamine receptors

Abstract

Listen

Translate article

125I-Spiperone binds with high affinity (K D 0.3 nM) to a single specific site (B max 34 pmol/g wet weight) in homogenates of rat corpus striatum. Specific binding is about 40–60 percent of total binding and is displaced stereo-specifically by butaclamol and clopenthixol. Neuroleptic drugs of various classes are potent inhibitors of 125I-spiperone binding (K i's 1–10 nM). Selective dopamine antagonists such as sulpiride (K i 50 nM) are dopamine agonists such as apomorphine (K i 200 nM) are also potent inhibitors. The drug specificity of 125I-spiperone binding correlates well with that of 3H-spiperone binding, providing good evidence that 125I-spiperone labels D 2 dopamine receptors in striatal membranes. 125I-Spiperone, with its high specific activity (2200 Ci/mmol) may prove to be a useful ligand in studies examining D 2 dopamine receptors in soluble preparations and by autoradiography. Furthermore iodinated spiperone may be useful in radioreceptor assays of neuroleptic drug levels and, in a 123I-labeled form, for imaging of dopamine receptors, in vivo , using single photon tomography.