Measurement in vivo of dopamine receptor density I: Effect of endogenous dopamine on spiroperidol binding

Non-invasive localization of brain dopamine (DA) receptors has been achieved by us and others using gamma emitting derivatives of the DA antagonist spiroperidol (SP). To accurately characterize this localization, the authors have previously described an equilibrium binding model involving SP and DA for a single DA receptor. It is the purpose of this study to establish experimentally the significance of endogenous DA on the ability of SP to bind a group of DA receptors. Several mice were administered different doses of SP. To one group of mice L-dopa was given with peripheral decarboxylase inhibitor, RO-4-4602, in order to elevate brain DA levels while a separate group served as control. /sup 3/H-SP binding and DA levels were measured in each brain sample. The results reflect a significant competition between DA and SP for caudate DA binding sites