MUSCARINIC RECEPTORS IN THE PRENATAL MOUSE EMBRYO - COMPARISON OF M35-IMMUNOHISTOCHEMISTRY WITH [H-3] QUINUCLIDINYL BENZYLATE AUTORADIOGRAPHY

Muscarinic cholinergic receptors are widespread in nervous tissue and smooth muscle or paracrine epithelial cells of various organs. In the embryo, muscarinic receptors are transitorily expressed in the early b lastoderm. and later on in blastemic tissues during morphogenesis. Rec ently, a monoclonal antibody (M35) against muscarinic receptor from ca lf brain became available. In the present study the use of M35-immunoh istochemistry is compared to autoradiographic localization of muscarin ic binding sites in the mouse embryo. The aim of the study is to test the suitability of the antibody for localization of muscrinic receptor s in embryonic tissues. For autoradiography whole-body sagittal cryost at sections of the 17- and 18-day mouse embryo were covered with LKB-U ltrofilm after incubation with the radioactive ligand [H-3] quinuclidi nyl benzylate (QNB). For immunohistochemistry cryostat sections of for malin fixed tissues were used. In general, all tissues exhibiting liga nd binding were also recognized by the antibody. M35-immunohistochemis try resulted in higher spatial resolution of receptor localization tha n [H-3]QNB autoradiography. Definitive muscarinic receptors were obser ved in smooth muscle and the epithelial lining of the vascular, intest inal, respiratory and urinary system, in the brain, spinal cord and pe ripheral nerves. The embryonic type of the muscarinic receptor was det ected in the mesothelium of lung and liver, in the nephrogenic blastem a of the metanephros, and in lung mesenchyme. A large amount of embryo nic muscarinic receptors was found in the remnants of the notochord an d in the nucleus pulposus of the developing vertebral column. A functi on in morphogenesis is discussed of the embryonic muscarinic receptor.