Localization of muscarinic receptors on cultured myenteric neurons: a combined autoradiographic and immunocytochemical approach.

In order to localize the distribution of muscarinic receptors over the surface of cultured myenteric neurons, an autoradiographic procedure for detecting muscarinic receptors (using [3H]propylbenzilylcholine mustard; [3H]PrBCM) has been combined with an immunofluorescence procedure visualizing neuronal morphology (using an antibody raised against rat brain synaptosomes; anti-CTX). Using this technique, muscarinic receptors were localized over discrete areas of the neuronal cell surface. Receptors were seen to be widely distributed over the somata and neurites of 10-20% of cultured myenteric neurons. The greatest concentration of receptors occurred over the cell somata and proximal neurites. Receptors appeared evenly distributed over labeled cell somata, where their density was estimated to be between 30 and 100 receptors/micron2. Distal regions of neurites were labeled intermittently with some varicosities and intervaricosities being labeled while others were unlabeled. Growth cones and nerve endings of labeled neurites were consistently labeled. The ability to localize muscarinic receptors on a subpopulation of immunocytochemically identified neurons enhances our understanding of muscarinic neurotransmission in myenteric neurons and provides an experimental system for the investigation of regulatory influences on neuronal neurotransmitter receptor expression and distribution.