The Stomatogastric and Enteric Nervous System of the Pulmonate SnailMegalobulimus abbreviatus: A Neurochemical Analysis

Abstract

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.

Evolution of nitric oxide regulation of gut function

“…The correlation of nNOS/NO function involved in pylorus regulation between sea urchins and vertebrates is intriguing. In protostomes, digestive tracts are also partitioned with sphincters and there are enteric neurons (32)(33)(34). However, we know of no reports of nNOS/NO regulation of gut function in most protostomes.…”

The first brain: Species comparisons and evolutionary implications for the enteric and central nervous systems

“…In snails 2 layers of ganglia, identified as myenteric and submucosal ganglia, as is observed in other invertebrates and in mammals (Figure ), have been described. Nerve tracing studies indicate that ganglionic clusters of molluscs, including the stomatogastric ganglia, project axons to the digestive tube, perhaps making connections with enteric neurons …”

Occurrence of Cruzia tentaculata Larvae in the Land Snail Megalobulimus abbreviatus—Influence of Natural Parasite Load on Snail Physiology

“…To answer these questions, the present study analyzes snails of the species Megalobulimus abbreviatus Bequaert, 1948, collected from southern Brazil, naturally infected by nematode larvae. Concerning the possible effects of this interaction on the health of the host, which has been used as an experimental model in neurophysiological studies (Achaval et al, 2005; De Fraga et al, 2010; Martinez-Pereira et al, 2017), this study aimed to identify the species of nematode found in M. abbreviatus and to evaluate the general health conditions of the snails in relation to parasite load. The relationships between parasite load and intermediary metabolism, ovotestis and albumen gland measurements and structural changes to the intestinal tract resulting from the presence of encapsulated larvae, were analyzed.…”