Striatal muscarinic receptors are associated with substance P and somatostatin containing neurons.

The cellular localization of muscarinic acetylcholine binding sites (mAChr) in relation to immunohistochemically characterized cell populations within the rat caudate nucleus has been determined using in vitro autoradiography of the reversible antagonist ligand, quinuclidinyl benzilate [( 3H]QNB). The pattern of autoradiographic silver grain deposition in the striatum was contrasted with the localization of two peptide-containing neuronal populations in the striatum. Substance P-immunoreactive somata demonstrated prevalent association of mAChr binding sites, as did somatostatin-immunoreactive cells. Substantially more striatal muscarinic binding sites were aggregated over the somatostatin interneuron population of the caudate nucleus than were associated with the substance P somata in concurrently performed experiments. This data further substantiates the heterogeneity in organization of the caudate nucleus, and the results are discussed in relation to the processing of information within this basal ganglia region.