The Distribution of Muscarinic Receptor Sites in the Nervous System of the Dog

The concentration of muscarinic receptors has been measured in 22 areas of the dog nervous system by measuring the atropine‐sensitive uptake of tritium‐labelled propylbenzilylcholine mustard. The highest concentration of receptor was found in the caudate nucleus, intermediate concentrations were found in five areas of cerebral cortex, the other basal ganglia and the superior colliculus. Significant concentrations were found in the corpus callosum and subcortical white matter, and are believed to be on axons derived from cholinoceptive neurons. The results are discussed in relation to other evidence concerning cholinergic transmission in the nervous system.