Autoradiographic localization of muscarinic agonist binding sites in the rat central nervous system with (+)-cis-[³H]methyldioxolane

(+)-cis-[³H]Methyldioxolane ((+)-[³H]CD), a potent muscarinic agonist, was used to label high-affinity agonist states of muscarinic receptors in thin tissue sections of the rat central nervous system. Light microscopic autoradiography of atropine-sensitive (+)-[³H]CD binding sites revealed regions of dense labeling (superior colliculus, inferior colliculus, lateral geniculate body, hypoglossal (XII) nucleus, facial (VII) nucleus, tractus diagonalis) and regions of sparse labeling (hippocampus, dentate gyrus). The inverse regional correlation between high-affinity (+)-[³H]CD states and binding sites for the muscarinic antagonists [³H]pirenzepine (r = -0.79) and (-)-[³H]quinuclidinyl benzilate (r = -0.30) underscores potentially important differences between agonist and antagonist binding to CNS tissue slices.