Functional and anatomical localization of mu opioid receptors in the striatum, amygdala, and extended amygdala of the nonhuman primate

The subregional distribution of mu opioid receptors and corresponding G-pro tein activation were examined in the striatum, amygdala, and extended amygd ala of cynomolgus monkeys. The topography of mu binding sites was defined u sing autoradiography with [H-3]DAMGO, a selective mu ligand. In adjacent se ctions, the distribution of receptor-activated G proteins was identified wi th DAMGO-stimulated guanylyl 5 '(gamma-[S-35]thio)triphosphate( [S-35]GTP g ammaS) binding. Within the striatum, the distribution of [3H]DAMGO binding sites was characterized by a distinct dorsalventral gradient with a higher concentration of binding sites at more rostral levels of the striatum. [H-3 ]DAMGO binding was further distinguished by the presence of patch-like aggr egations within the caudate, as well as smaller areas of very dense recepto r binding sites, previously identified in human striatum as neurochemically unique domains of the accumbens and putamen (NUDAPs). The amygdala contain ed the highest concentration of [H-3]DAMGO binding sites measured in this s tudy, with the densest levels of binding noted within the basal, accessory basal, paralaminar, and medial nuclei. In the striatum and amygdala, the di stribution of DAMGO-stimulated G-protein activation largely corresponded wi th the distribution of mu binding sites. The central and medial nuclei of t he amygdala, however, were notable exceptions. Whereas the concentration of [H-3]DAMGO binding sites in the central nucleus of the amygdala was very l ow, the concentration of DAMGO-stimulated G-protein activation in this nucl eus, as measured with [S-35] GTP gammaS binding, was relatively high compar ed to other portions of the amygdala containing much higher concentrations of [H-3]DAMGO binding sites. The converse was true in the medial nucleus, w here high concentrations of binding sites were associated with lower levels of DAMGO-stimulated G-protein activation. Finally, [H-3]DAMGO and [S-35]GT P gammaS binding within the amygdala, particularly the medial nucleus, form ed a continuum with the substantia innominata and bed nucleus of the stria terminalis, supporting the concept of the extended amygdala in primates. (C ) 2001 Wiley-Liss, Inc.