IMMUNOHISTOCHEMICAL LOCALIZATION OF NICOTINIC ACETYLCHOLINE-RECEPTORSIN THE GUINEA-PIG BOWEL AND PANCREAS

Although nicotinic acetylcholine receptors (nAChRs) are known to be pr esent on neural elements in both the bowel and the pancreas, the preci se location of these receptors has not previously been determined. Imm unocytochemistry, by using a rat monoclonal antibody (mAb35), which re cognizes alpha-bungarotoxin (alpha-Bgt)-insensitive nAChRs, and a poly clonal antibody raised against the alpha-Bgt-sensitive receptor subuni t, alpha 7, was used to locate receptor protein in guinea pig gut and pancreas. mAb35-receptor (mAb35-R) immunoreactivity was abundant in bo th enteric plexuses, enterochromaffin cells, and pancreatic ganglia. I mmunostaining was associated with the cell membrane, and clusters of m Ab35-R were observed on cell somas and dendrites. Receptor immunoreact ivity was also observed on terminals and axons, suggesting that a subs et of nAChRs is presynaptic. Internal sites of mAb35-R were observed i n permeabilized ganglia. Cells expressing the receptors were closely a ssociated with ChAT-immunoreactive nerve fibers. In addition, the majo rity of ChAT-positive neurons expressed both cell surface and internal stores of mAb35-R. In the bowel, clusters of mAb35-R were present on the soma and dendrites of Dogiel type I motorneurons and secretomotor neurons. Receptors were detected at the plasma membrane of calbindin-i mmunoreactive myenteric neurons. In contrast, calbindin-immunoresctive submucosal neurons did not express cell surface mAb35-R, supporting t he idea that they are sensory neurons. A subset of enteric neurons exp ressed both mAb35-R and glutamate receptor (GluR1) immunoreactivity. I n the pancreas, mAb35-R immunoreactivity was only observed in ganglia. alpha 7-immunoreactivity was found on both enteric cell bodies and ne rve fibers. Based on these results, it appears that visceral nAChRs ar e composed of at least four subunits and that both pre-and postsynapti c nAChRs are present in the gut and pancreas. (C) 1998 Wiley-Liss, Inc .