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

The nematode Cruzia tentaculata is reported here for the first time in the land snail Megalobulimus abbreviatus in southern Brazil. The snails were infected with a high prevalence of larvae up to the L3 stage (68.6%). Cysts were located mainly in the mantle (pulmonary cavity) and the nerve ring. No other helminths were identified in the collected snails. Some physiological aspects were compared between snails infected with L3 larvae and non-infected snails and among infected animals with different parasite loads. No differences were found in hemolymph protein, glucose, or urea content between L3-infected and non-infected snails, nor among animals with different parasite loads. Discontinuous lesions in the rectum associated with the presence of encapsulated larvae were visible in animals with high parasite loads and were more frequent in adult animals. All analyses were carried out during the breeding season; however, the albumen glands of mature snails had a smaller volume in those with higher parasite loads. Ovotestis weight was also significantly negatively correlated with parasite load. Snail reproductive capacity could, therefore, be partially impaired but only for individuals with higher parasite loads. Considering only the measured parameters, natural infection by C. tentaculata does not appear to affect intermediary metabolism of M. abbreviatus. A greater number of larvae and greater severity of tissue injuries are more frequently observed in older snails.

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.

General morphology and innervation of the midgut and hindgut of Megalobulimus abbreviatus (Gastropoda, Pulmonata).

We describe the morphology and innervation of the midgut and hindgut of the giant land snail Megalobulimus abbreviatus for the first time. The midgut (stomach and intestine) and hindgut (rectum and anus) are innervated by the subesophageal ganglia, through the gastrointestinal branch (originated from the visceral nerve) and the rectum-anal nerve, respectively. Backfilling through these nerves revealed neuronal bodies, mainly in the right parietal and visceral ganglia. The enteric plexuses of the midgut and hindgut are formed by extensive axonal networks and several neuronal somata arranged in clusters or as isolated cells. The gastrointestinal branch and the rectum-anal nerve directly innervate the enteric plexuses of the intestine and the hindgut, respectively. However, the outer wall of the stomach has a stomatogastric nervous system, which consists of four ganglia: stomatogastric, gastric, cardic, and pyloric. Fibers of the gastrointestinal branch project to these ganglia. Anterograde tracing from stomatogastric system ganglia revealed that the enteric plexus of the stomach is innervated only by these peripheral ganglia. Anterograde tracing of the gastrointestinal branch did not result in labeling in the enteric plexus of the stomach. Therefore, the midgut and hindgut of M. abbreviatus is controlled by an intrinsic innervation, constituted by the submucous and myenteric plexuses, which are innervated directly by neurons from the subesophageal ganglia or indirectly via the stomatogastric nervous system (for the stomach).

Carbohydrate metabolism in the central nervous system of the megalobulimus oblongus snail during anoxia exposure and post-anoxia recovery.

The effects of anoxic exposure and the post-anoxia aerobic recovery period on carbohydrate metabolism in the central nervous system (CNS) of the land snail Megalobulimus oblongus, an anoxia-tolerant land gastropod, were studied. The snails were exposed to anoxia for periods of 1.5, 3, 6, 12, 18, or 24 hr. In order to study the post-anoxia recovery phase, snails exposed to a 3-hr period of anoxia were returned to aerobic conditions for 1.5, 3, 6, or 15 hr. Glycogen and glucose concentrations in the CNS, hemolymph glucose concentration, and glycogen phosphorylase (active form, GPa) activity in the CNS were analyzed. Anoxia does not significantly affect the concentration of CNS glucose but induces hyperglycemia and a reduction of CNS GPa activity. The glycogen concentration was decreased at 12 hr of anoxia; however, by 18 and 24 hr in anoxia, the glycogen content was not significantly different from basal control values. During the post-anoxia period, the reduction in GPa activity and the increased hemolymph glucose concentration induced by anoxia returned to control values. These results suggest that the CNS of M. oblongus may use hemolymph glucose to fulfill the metabolic demands during anoxia. However, the hypothesis of tissue metabolic arrest cannot be excluded.