Autoradiographic localization of the putative D4 dopamine receptor in rat brain

The putative dopamine D4 receptor protein in rat brain was labelled and quantified autoradiographically using two selective benzamides: [3H]YM-09151-2 which labels D2, D3 and D4 dopamine receptors and [3H]Raclopride which labels D2 and D3. The difference in densities of both ligands at saturable concentrations, show a regional distribution for the putative D4 receptor in the following rank order: hippocampus > caudate putamen > olfactory tubercle = substancia nigra > nucleus accumbens core > cerebral cortex > cerebellum. A calculated value of 0.34 pmol/mg protein was attributable to D4 receptor maximum capacity in caudate putamen and was obtained after subtracting the Bmax of the ligands. Our results show that the distribution of D4 receptor only partially overlaps with the D4 mRNA localization reported earlier and is not only associated to limbic structures but to motor areas as well.