Distribution of dopamine D-2 receptors in the rat striatal complex and its comparison with acetylcholinesterase

The distribution of D-2 dopamine receptors in the rat striatal complex was studied with autoradiography after specific in vivo labeling with the dopamine agonist [3H]N-n-propylnorapomorphine and subsequent irreversible fixation. This labeling technique allows the visualization of D-2 receptors at the cellular level by light microscopic emulsion autoradiography. During the preparation of emulsion autoradiograms, the recovery of the label was 75%, the specific and the aspecific label being equally affected. The distribution of label before and after the loss of radioactive label occurred, did not show differences. In rat neostriatum, dopamine D-2 receptors are not homogeneously distributed: in the caudate-putamen the density is laterally higher than medially. Moreover, there exists a mosaic-like pattern of receptor density. In the ventral striatum, comprising the fundus striati, nucleus accumbens septi and olfactory tubercle, the receptor density is lower than in the caudate-putamen, except for the core regions in the islands of Calleja and the rim of these islands, which contain high (as high as the lateral caudate-putamen) and a moderate density of receptors, respectively. In caudate-putamen and lateral nucleus accumbens it appeared that the intensity of acetylcholinesterase staining parallels more or less the distribution of dopamine D-2 receptors. In medial nucleus accumbens and in olfactory tubercle, the high intensity of acetylcholinesterase is not paralleled by a high D-2 receptor labeling density. This receptor labeling density does not seem to be matched by differences in densities of medium-sized neuronal cell bodies.