MONOAMINE RECEPTORS IN THE AMYGDALOID COMPLEX OF THE TREE SHREW (TUPAIA-BELANGERI)

Although it is well known that the mammalian amygdala comprises a hete rogeneous complex of cytoarchitectonically and histochemically distinc t nuclei, the association of these nuclei with different monoamine sys tems has not been described in detail. We therefore investigated the p attern of receptors for monoamines in the amygdala of the tree shrew ( Tupaia belangeri). Binding sites for the alpha(2)-adrenoceptor ligand (H-3)rauwolscine, the alpha(1)-adrenoceptor ligand (H-3)prazosin, the beta-adrenoceptor ligand (I-125)iodocyanopindolol, and the serotonin(1 A)-receptor ligand (H-3)8-hydroxy-2(di-n-propylamino)tetralin were vis ualized by in vitro autoradiography, and anatomically localized by com paring the autoradiograms to Nissl- and acetylcholinesterase-stained s ections. To characterize binding of the radioligands pharmacologically , displacement experiments with different specific competitors were pe rformed. Whereas the highest number of alpha(2)-adrenergic binding sit es was detected in the medial and the central nucleus as well as in th e intercalated nuclei, the majority of serotonin(1A) binding sites was found in the magnocellular basal nucleus and the accessory basal nucl eus, demonstrating a clear difference in the anatomy of the alpha(2)-a drenergic and the serotonin(1A) receptor systems. In contrast, the pat tern of alpha(1)-adrenoceptor binding partially overlaps with that of both former receptor types. While the number of alpha-adrenergic and s erotonin(1A) binding sites is relatively high in the tree shrew amygda la, there is only a low number of beta-adrenergic binding sites in mos t nuclei. However, in the cortical nuclei, moderate to high numbers of binding sites for all radioligands are present. Therefore, according to our data on the tree shrew amygdala, which is anatomically similar to the amygdala of cats and primates, alpha(2)-adrenoceptors cover pri marily the medial part of the amygdaloid formation and serotonin(1A)-r eceptors predominantly occupy the basal nuclei, whereas alpha(1)-adren oceptors are present in both parts of the formation. (C) 1994 Wiley-Li ss, Inc.