Patterns of muscarinic cholinergic binding in the striatum and their relation to dopamine islands and striosomes

Abstract

The distribution of muscarinic cholinergic binding sites in the striatum was studied in relation to the locations of other neurochemical markers in the developing rat, cat, ferret, and human. In addition, patterns of striatal muscarinic binding were studied in the adult cat. Receptor binding autoradiography was carried out with tritiated propylbenzilylcholine mustard ([³H]‐PrBCM), an irreversible muscarinic antagonist, and subsequent serial section analyses involved comparisons among patterns of muscarinic binding, catecholamine histofluorescence, acetylcholinesterase (AChE) staining, Nissl staining, and cell labeling with [³H]‐thymidine.Muscarinic binding in the immature striatum was characterized by local patchiness as well as regional density gradients in all species, with the most complex patterns appearing in the human. Patches of dense muscarinic binding were shown to lie in register with fluorescent dopamine islands (rat, cat, ferret), with AChE‐positive patches (all species), and with clusters of neurons pulse‐labeled by exposure to [³H]‐thymidine on embryonic day 27 (ferret). At the developmental stages examined, the [³H]‐PrBCM‐positive patches were roughly aligned with regions of weak Nissl staining (cat, human).Striatal [³H]‐PrBCM binding in the adult cat was dense, and though it usually appeared nearly homogeneous, in some sections patches of elevated binding were present. These had as counterparts, in neighboring sections, AChE‐poor striosomes. We conclude that during development muscarinic cholinergic function is compartmentalized in the striatum in association with dopamine‐containing afferents, and that this compartmentalization may persist to some degree in the adult.