Quantitative autoradiography of M₂ muscarinic receptors in the rat brain identified by using a selective radioligand [³H]AF-DX 116

Muscarinic receptors of the M₂ type have been studied in the rat brain using quantitative autoradiography with the selective ligand, [³H]AF-DX 116. High specific binding of [³H]AF-DX 116 was found in areas such as laminae IV and V of the parietal cerebral cortex, thalamus and hypothalamus and dentate gyrus. Intermediate [³H]AF-DX 116 binding was found in the frontal cortex, hippocampus, caudate-putamen, nucleus accumbens, and claustrum as well as in certain brainstem nuclei such as the nucleus of the solitary tract and the dorsal motor nuclei of the vagus. In contrast, the accessory olfactory nucleus, globus pallidus and cerebellum contained very low concentrations of M₂ receptors. The present study demonstrates a unique regional distribution of M₂ receptors in the rat brain.