Determination of dopamine D(4) receptor density in rat striatum using PB12 as a probe

N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (PB12), a potent and selective dopamine D(4) receptor ligand, was used as a probe for the direct determination of the dopamine D(4) receptor density in rat striatum as an alternative to the subtraction method. The experiment was performed using [(3)H]spiroperidol to label D(2), D(3) and D(4) receptors and PB12 to determine directly dopamine D(4) receptor specific binding. The determined B(max) value was 82 fmol/mg protein. The contribution of the dopamine D(4) receptor to the overall population of D(2)-like receptors was 63%; however, this value cannot be considered reliable because of the observed difference in the kinetic profiles of D(2), D(3) and D(4) receptors.