Opioid receptor ligand binding in the human striatum: II. Heterogeneous distribution of kappa opioid receptor labeled with [³H]bremazocine

Selective kappa opioid receptor autoradiography with [³H]bremazocine (BRM) was used to examine regional and subregional kappa receptor distribution patterns at five rostrocaudal levels through the human striatum. [³H]BRM binding densities were measured in the individual striatal nuclei and in subregions therein. The distribution of [³H]BRM binding sites was found to have a strongly heterogeneous character. At the regional level a rostral-to-caudal decrease in [³H]BRM binding densities was observed. Also, a dorsal-to-ventral differentiation was seen, with higher values in the ventral striatum, especially in the nucleus accumbens, and lower values in the dorsal parts of the caudate nucleus and putamen. These findings suggest an association of kappa receptor function with limbic-related processes in the ventral striatum. Along the ventral edge of the nucleus accumbens and putamen, specific domains with extremely high [³H]BRM binding values were identified.