Distribution of muscarinic cholinergic high and low affinity agonist binding sites: a light microscopic autoradiographic study.

The distribution of high vs. low affinity muscarinic agonist binding sites has been determined using quantitative techniques of receptor autoradiography. The low affinity agonist sites predominate in many regions of the forebrain including the cerebral cortex, striatum, hippocampus, amygdala and thalamus. The high affinity agonist sites predominate in the brainstem and represent exclusively the type of muscarinic cholinergic receptor normally present in the principal nucleus of the trigeminal nerve, facial nerve nucleus, hypoglossal nerve nucleus, and in the ventral horn of the spinal cord. The regional localization of these subpopulations provides valuable information for future studies which seek to determine the functional importance of subtypes of muscarinic agonist binding sites.