Muscarinic acetylcholine receptors are localized on striatal cyclic GMP-containing neurons

The localization of muscarinic acetylcholine receptors has been determined using in vitro binding of radiolabeled quinuclidinyl benzilate ([3H]QNB), a specific reversible muscarinic receptor antagonist. All cyclic GMP-immunoreactive neurons in the rat striatum show clustering of [3H]QNB silver grains overlying their somata following autoradiographic analysis. The autoradiography of total binding of silver grains over the cyclic GMP-containing neurons was approximately 800 times as dense as the surrounding neuropil localization of radioligand binding sites. Incubation of striatal tissue slices in the presence of micromolar atropine, to determine non-specific binding of [3H]QNB, decreased the autoradiographic silver grain density of the neuropil about 2.5 times, and lessened the number of receptor sites detectable on cyclic GMP-positive neurons at least 5-fold. Biochemical examination of [3H]QNB binding on tissue sections demonstrated that the ligand binding is saturable and dependent on section thickness for the muscarine receptor subtype of acetylcholine.