Autoradiographic visualization of dopamine D-2 receptors in the monkey brain using the selective benzamide drug [3H]raclopride.

Using the novel substituted benzamide drug [3H]raclopride in combination with in vitro receptor autoradiography, the distribution of dopamine D-2 receptors was studied in the monkey brain. Highest densities of D-2 receptors are present in dopamine-rich areas and the distribution shows the following rank order: caudatus and putamen greater than nucleus accumbens greater than olfactory tubercle greater than substantia nigra (pars compacta) greater than insular cortex greater than piriform and entorhinal cortex greater than substantia nigra (pars reticulata). In all of these areas [3H]raclopride binding was blocked by dopamine (1 microM) and by D-2 receptor antagonists such as (+)-butaclamol, eticlopride and raclopride, while the D-1 receptor antagonist SCH 23390 (1 microM) reduced [3H]raclopride binding by 15-20% in some restricted parts of the caudatus and putamen exclusively.