Digestive Gland Complex Research Articles

Biomphalaria glabrata infected with Angiostrongylus cantonensis: Proteomic changes in the snail host

Angiostrongylus cantonensis is the main cause of human eosinophilic meningitis. Humans are accidental hosts, becoming infected due to ingestion of raw intermediate (snails and slugs) or paratenic hosts. Once ingested, the larvae migrate towards the brain where they die, causing the disease. To develop better mollusk control strategies, it is important to first understand what happens in the snail during infection, therefore our purpose was to characterize proteomic, metabolic and immunologic changes in Biomphalaria glabrata 24 h after infection with A. cantonensis. For this purpose, proteins were extracted from infected and uninfected snails and analyzed through mass spectrometry. Hemolymph was also collected, the number of hemocytes was counted and urea, nitric oxide, calcium, glycogen levels as well as alanine and aspartate aminotransferases activities were assessed. The cephalopodal region and gonad-digestive gland complex were dissected and their glycogen content was measured. After infection with A. cantonensis, we observed an increase of hemocytes and granulocytes as well as an increase in hemoglobin type 2 proteins. Temptin-like protein was also found up-regulated in infected snails. Several proteins with structural function (such as myosin heavy chain – striated muscle – like and protein LOC106059779 with ADAM/reprosolin domain) were also differentially expressed, suggesting loss/damage of internal tissues. Increase in phosphoglycerate mutase indicates an increase in glycolysis, possible to compensate the increase in energetic needs. Consequently, there is a decrease in glycogen reserves, particularly in the gonad – digestive gland complex.

Sex hormones in Strombus pugilis (Mollusca: Gastropoda) in different gonadal stages

Sex hormones play an essential role in sexual differentiation, maintenance of sexual characteristics, gamete maturation, and mating behavior. However, very little is known about their dynamics in molluscs. We conducted a study on sex hormone (17β-estradiol, testosterone, and progesterone) concentrations in male and female Strombus pugilis to identify their variations at different gonadal stages. A total of 90 organisms (30 per month) were collected in February, September, and November 2016. The gonadal digestive gland complex of each specimen was dissected and divided into two sections. One section was set in alcoholic Bouin's fluid and processed with classic histological techniques; the second was macerated with 80% ethanol to extract steroids and analyzed by enzyme immunoassays. Histological section analysis was used to classify gonadal development into three stages: gametogenesis, mature, and undifferentiated. Mature females were observed in September. Testosterone and 17β-estradiol concentrations in both sexes were highest in the mature stage. In S. pugilis, 17β-estradiol, progesterone, and testosterone were all present, with higher concentrations associated with reproductive activity.

Evaluation of changes in the carbohydrate metabolism of Biomphalaria glabrata Say, 1818 exposed to experimental coinfection by Angiostrongylus cantonensis (Nematoda) and Echinostoma paraensei (Trematoda)

The interaction between intermediate snail hosts and helminths can cause metabolic changes in the former. The snails use their reserves for maintenance of their vital processes, by activating the internal defense system and repairing tissue damage, while also supplying necessary energy for the parasites’ development. Our aims were to evaluate the lactate dehydrogenase activity and the glucose concentration in the hemolymph of Biomphalaria glabrata experimentally coinfected by Angiostrongylus cantonensis and Echinostoma paraensei. Besides these aspects, the glycogen content in the digestive gland complex and cephalopedal mass along with histochemical changes in parasitized snails were analyzed. The snails were divided in group A (infected by 1200 L1 of A. cantonensis), group E (infected by 20 E. paraensei miracidia), group A + E (co-infected with A. cantonensis first and after a week by E. paraensei), group E + A (co-infected with E. paraensei first and then by A. cantonensis) and control group (not infected). During four weeks after exposure, samples were collected for biochemical and histochemical analyses. In the infected snails, glucose levels and glycogen content in the digestive gland complex and cephalopedal mass were significantly lower, in contrast with an increase of lactate dehydrogenase activity. These results indicate that the intense energy demand resulting from the presence of parasites causes the host snail to accelerate the anaerobic degradation of carbohydrates to obtain energy, in an attempt to maintain homeostasis. Both parasites were observed in histochemical analysis to cause tissue damages in the snails. So, although the snails were able to sustain the coinfection, several metabolic and tissue changes occurred, mainly in those infected with E. paraensei and then with A. cantonensis.

Effect of Basudin, Selecron and the phytoalkaloid Colchicine (pesticides) on biological and molecular parameters of Biomphalaria alexandrina snails

The results showed that survival rates of Biomphalaria alexandrina snails, reproductive potential and hatchability of eggs were evaluated post exposure to Basudin, Selecron and Colchicine. As well, DNA and RNA changes in the cells of ovotestis–digestive gland complex of treated snails were estimated. The current molluscicide Bayluscide was used as a reference compound. The pesticide Selecron proved to be more toxic to B. alexandrina snails than Basudin and Colchicine. Juvenile snails were dead post 3 weeks of exposure to the sublethal concentration LC 0 of either Selecron or Basudin, while 26.75% of snails still alive at Bayluscide treatment. In addition, exposure of adult snails to LC 0 of Selecron for 24 h/week for 4 weeks markedly reduced their reproductive rate ( R 0) by 89.9%. Moreover, snails’ eggs failed to hatch post 24 h of exposure to LC 90 of either Selecron, Basudin or Bayluscide. Electrophoretic analysis indicated a decrease in the molecular weight of intact DNA in the ovotestis–digestive gland complex of snails treated with 250 ppm of Colchicine and LC 25 of Selecron, as it scored 1.2 and 76 bp, respectively, compared to 166.46 bp for control group, while the vice versa was recorded for RNA intensity. It was concluded that the tested pesticides have deleterious effects on snails’ reproductive rate, their eggs and the intensities of DNA and RNA in their ovotestis–digestive gland complex. Therefore, it is expected that reaching of such pesticides to snails’ habitats in water courses during plant pests control could minimize the population density of the snails intermediate hosts of schistosomiasis, hence probably interrupt and reduce the transmission of this parasite.

The influence of trematodes on the macroalgae consumption by the common periwinkleLittorina littorea

Trematodes are ubiquitous elements of coastal ecosystems that commonly modify the phenotype of their invertebrate hosts, often with ramifications to higher levels of ecological organization. In this context, trematode infections have been suggested to reduce the consumption of the herbivorous gastropodLittorina littorea(L.) (Mollusca: Gastropoda), in turn affecting the composition of the macroalgal community on which the snail grazes. Here, we examine the effect of two species of trematodes,Renicola roscovitaandHimasthla elongata, onL. littorea's consumption in two outdoor microcosm experiments offering the snails two different ephemeral green algae species as a food source. Our results show that, irrespective of the species of parasite and food source, infection decreases consumption: uninfected snails consumed up to 65% more macroalgal biomass than infected snails. Aside from infection status, gender and size also influenced the snails' consumption rate significantly. The differing histopathological impacts of the two species of trematodes on the hosts' gonad–digestive gland complex (in which the parasites reside), suggests that parasitic castration is a likely mechanism for the reduced energy demand of infected periwinkles. Together with existing evidence, our investigation suggests that trematodes in general depress the grazing activity ofL. littorea, and that the resulting community regulation occurs throughout the snails' distributional range.

Inhibition of Esterases in the Marine GastropodLittorina littoreaExposed to Cadmium

Electrophoretic analysis ofLittorina littoreaesterases indicated the presence of a cathodal migration isoenzyme (EST-C), which was identified in extracts obtained from the gonad–digestive gland complex. A loss of EST-C enzyme activity was observed in individuals exposed to Cd2+. This loss of activity was complete in 86% of individuals dead by the action of Cd2+and in 68% of those individuals that survived Cd2+exposure. This difference was statistically significant.In vitroinhibition of esterases by different concentrations of Cd2+and Cu2+was studied in individuals not experimentally exposed to heavy metals, to determine whether EST-C inhibition was caused by direct binding of Cd2+to the esterase molecule or by Cd2+displacement of a metal ion from essential Cu2+- or Zn2+-containing proteins, which may then be responsible for the inhibition of esterase. Contrary to what happened when individuals were exposed to Cd2+, in thein vitroexperiment with Cd2+, inhibition of anodal but not cathodal systems was observed. At the same time, when Cu2+was used in thein vitroexperiment, both anodal and cathodal systems were inhibited. These results suggest that the inhibition of EST-C activity by Cd2+takes placein vivoand seems not to be due to the direct action of Cd2+on the molecule, but rather is a process in which transcriptional, posttranscriptional, and other inhibitory processes may be involved.

Seasonal changes in the level and content of different biochemical constituents in tropical cerithiidsCerithidea (Cerithideopsilla) cingulata (Gmelin 1790) andCerithium coralium Kiener 1841

The level and content of different biochemical constituents were investigated over a period of one year (January–December 1982) in foot, gonad digestive gland complex and viscera of two tropical cerithiids, inhabiting two different regions of backwaters. Their seasonal indices exhibited bimodal pattern of cycling and this trend was more predominant in gonad digestive gland complex and foot. In all the body components of both species, the biochemical content was found to show considerable changes when compared to their levels. In both the cerithiids, the gonad digestive gland depicted remarkable variations with the season, followed by foot. The viscera did not show much variation when compared to other body components. The carbohydrates and glycogen of both the species showed a primary peak in March and a secondary peak in September indicating maturity of gonads. This was followed by a decline in their constituents which might be due to spawning. Lipid utilisation was also observed in both the animals next to carbohydrates and glycogen. Proteins were least utilised in the process of reproduction. Thus a carbohydrate-oriented metabolism was recorded in both the species. The results were compared with the other molluscs.

Starvation as a stress factor influencing the metabolism of a tropical intertidal gastropodMorula granulata (Duclos)

The snailMorula granulata (Duclos) survived the starvation stress over a period of 30 days but 50% mortality occurred on the 70th day. The changes in the level and content of different biochemical constituents viz carbohydrates, glycogen, free sugars, protein, total ninhydrin positive substances and lipids were investigated in foot, gonad digestive gland complex and viscera of the animal at intervals of 10 days up to 70 days. All these biochemical constituents (both level and content) were found to decrease with the period of starvation showing their utilisation except total ninhydrin positive substances which exhibited an increase. Of all the 3 tissues, the gonad digestive gland complex was affected most during starvation. ‘Lipid-oriented’ metabolism was observed in this animal showing maximum utilisation of lipids during starvation. Respiratory studies revealed a decreased pattern of oxygen consumption with increasing period of starvation when calculated per snail or per tissue weight. The recalculated intercept values (a) also showed a decreasing trend when exposed to starvation.