The Stomatogastric and Enteric Nervous System of the Pulmonate Snail Megalobulimus abbreviatus: A Neurochemical Analysis.

Chemical coding of stomatogastric nervous system (STNS) and enteric nervous system (ENS) of midgut and hindgut in the snail Megalobulimus abbreviatus was investigated using histochemistry, histofluorescence, and immunohistochemistry. The gastrointestinal plexuses, constituted by intrinsic neurons and fibers originating from the subesophageal ganglia and/or STNS, showed intense acetylcholinesterase (AChE) and nicotinamide adenine dinucleotide diaphorase (NADPHd) activity. The enteric neurons and fibers with AChE activity are scattered in the submucosa and between both muscular layers of gastrointestinal tract, whereas NADPHd neurons and fibers are more abundant between muscular layers than in the submucosa. Catecholaminergic nerve fibers and varicosities are found mainly within the submucosa across the mid- and hindgut. Serotoninand FMRFamide-immunoreactive neurons and fibers originating from the STNS are distributed in the submucosa of the intestine and rectum. FMRFamide-immunoreactive neurons and fibers are present in the mucosa, submucosa, and muscular layers of mid- and hindgut. The neuron-like intraepithelial cells exhibited AChE activity, a few NADPHd activity, and immunoreactivity for serotonin and FMRFamide. Intense glial fibrillary acidic protein (GFAP) immunoreaction is found throughout the intestine plexuses and in the STNS ganglia. The GFAP immunoreaction in intramural plexuses suggests the presence of glial cells as an important component of ENS in this pulmonate snail.