NEURAL MODULATION OF GUT MOTILITY BY MYOMODULIN PEPTIDES AND ACETYLCHOLINE IN THE SNAIL LYMNAEA

Families of peptide neuromodulators are believed to play important rol es in neural networks that control behaviors. Here, we investigate the expression and role of one such group of modulators, the myomodulins, in the feeding system of Lymnaea stagnalis. Using a combination of in situ hybridization and antibody staining, expression of the myomoduli n gene was confirmed in a number of identified behaviorally significan t neuronal types, including the paired B2 motor neurons. The B2 cells were shown to project axons to the proesophagus, where they modulate f oregut contractile activity. The presence of the five myomodulin pepti de structures was confirmed in the B2 cells, the proesophagus, and the intervening nerve by mass spectrometry. Using a sensitive cell cultur e assay, evidence that the B2 cells are cholinergic also is presented. Application of four of the five myomodulin peptides to the isolated f oregut increased both contraction frequency and tonus, whereas the mai n effect of acetylcholine (ACh) application was a large tonal contract ion. The fifth myomodulin peptide (pQIPMLRLamide) appeared to have lit tle or no effect on gut motility. Coapplication of all five myomodulin peptides gave a greater increase in tonus than that produced by the p eptides applied individually, suggesting that corelease of the peptide s onto the gut would produce an enhanced response. The combined effect s that the myomodulin peptides and ACh have on foregut motility can mi mic the main actions of B2 cell stimulation.