Toxic effects of cadmium on reproduction, development, and hatching in the freshwater snail Lymnaea stagnalis for water quality monitoring.

The freshwater snail Lymnaea stagnalis was exposed to cadmium concentrations of 0, 25, 50, 100, 200, and 400 microgram liter-1. The influence of this highly toxic metal on various stages of reproduction (number of egg masses, number of eggs, embryo development, and hatching) was studied. Egg production ceased at 400 microgram Cd2+ liter-1 and hatching was reduced to 0.4% with 200 microgram liter-1 at 20 degreesC. The study revealed that embryo development was the most sensitive stage, the main anomalies observed depending on the Cd2+ concentration. At the highest concentration studied (400 microgram liter-1) the eggs were blocked in the first cleavage stage. At 100 and 200 microgram Cd2+ liter-1, development of the eggs was halted at various stages of embryogenesis (cleavage, gastrula, veliger, and prehatching) depending on their position in the egg masses. At concentrations of 25 to 100 microgram Cd2+ liter-1, development was slowed down and hatching occurred 5 to 15 days later than in the controls (controls hatched 12 to 13 days after laying). The results obtained demonstrate the effects of Cd2+ on reproduction and development in L. stagnalis and provide information on the targets affected (neuroendocrine control of laying or cell multiplication and organogenesis of the embryos). It is thus possible to predict the probability of survival of the species in an environment polluted with cadmium and to compare it with the effects of other pollutants in the same or other species.

Cross-reactivity between terrestrial snails (Helix species) and house-dust mite (Dermatophagoides pteronyssinus). I. In vivo study.

Clinical reports have suggested an unusual frequency in the number of patients with food allergy to snails who are also allergic to the house-dust mite (HDM). As allergy to HDM is one of the most frequent sensitizations in atopic patients of Western countries, evaluation of the relevance of the concomitant sensitization to Dermatophagoides pteronyssinus and to snails is an important consideration. To evaluate the responsibility of different snail components and of snail mites for inducing in vivo hypersensitivity in patients allergic to HDM, the in vivo reactivity of patients with clinical symptoms after ingestion of snails was assessed by skin prick tests with extracts and hemolymph from four different Helix species snails, and extracts from the snail parasitic mite, Riccardoella limacum. In addition, to obtain epidemiologic data on cosensitization to HDM and snails in allergic patients, the frequency of snail sensitization and its relationship to HDM sensitization were determined in a population of 169 allergic children. All patients allergic to snails had positive skin prick tests to the snail extracts and none to R. limacum extract. The number of positive skin reactions did not significantly differ whatever the species, snail part, or heating procedure used. The strongest reactions were obtained with Helix pomatia (Burgundy snail). Among the 169 prospectively tested children, 38 had a positive prick test to snail extracts; 79% of the snail-sensitized children had sensitization to HDM; and 31% of the children allergic to HDM were found to be sensitized to snails. These results show that snail components, and not the mite R. limacum, were responsible for the in vivo hypersensitivity. These snail components reacting in vivo are present in different parts of snails, including the hemolymph. One-third of the children allergic to HDM were sensitized to snails without any previous ingestion of snails: this observation suggests that HDM was the sensitizing agent and that the cross-reaction could be clinically relevant in countries where eating snails is common.

Dose-dependent effects of cadmium on the growth of snails in toxicity bioassays.

The effects on survival and growth of exposure to cadmium (Cd) in the food were analyzed in juvenile snails (age one month, mean weight 1 g) of the two subspecies Helix aspersa aspersa (H.a.a.) and H. aspersa maxima (H.a.m.). The experiments lasted for four weeks and the animals were fed with special snail food containing 0-, 50-, 100-, 200-, 400-, and 800 microg Cd/g of dry food. No significant adverse effect (NOEC) was noted at 50 microg/g for three weeks. A negative effect of Cd on growth was noted from 100 to 800 microg/g and plotting the growth coefficient variation against the Cd concentration led to an estimate of the EC75 at day 14 of 370 microg/g in H.a.a. and 470 microg/g in H.a.m. and at day 28 of 290 microg/g in H.a.a. and 330 microg/g in H.a.m. Juvenile snails are thus a suitable material for use as bioindicators in the assay of contamination of food.

[Effects of heavy metals on snail development. Use of snails as bio-indicators of heavy metal pollution for the preservation of human health]. / Effets des métaux lourds sur le développement des escargots. Utilisation des escargots comme bio-indicateurs de pollution par les métaux lourds pour la préservation de la santé de l'homme.

The use of snails as biological indicators is particularly appropriate for metals, which they accumulate in their organs. The aim of the present experiment was to carry out a rigorous experimentation in the laboratory and in the wild in order to develop a methodology for the use of snails at a known stage of growth that would give precise information on the toxicity of heavy metals for different concentrations and durations of exposure. We have developed a test of toxicity based on the effects of a noxious and carcinogenic element, cadmium, on the land-snail Helix aspersa aspersa (H.a.a) of one month of age. Five concentrations (50 to 800 micrograms/g), were selected to estimate the concentrations causing 50% inhibition of growth (EC 50) at 14 days: 190 micrograms/g and at 28 days: 180 micrograms/g. A soil matrix contaminated with metals (soil including 800 micrograms/g Cr, 20 micrograms/g Cd, 800 micrograms/g Pb and 2000 micrograms/g Zn) was incorporated into the food at 50 and 75%, it too inhibited the growth of juvenile snails compared to incorporation of control soil. An accurate and rapid (2 to 4 weeks) method is therefore available for the evaluation of the toxicity of pollutants by ingestion. The first trials of this method in the wild consisted of placing batches of 2-month-old snails, identical to those used in the first lab tests, in locations that were either polluted or not. Differences in growth were observed depending on the locations; analysis of the levels of metal in the organs of the snails should enable us to check if there is a correlation between these levels and the growth rates. The results obtained with cadmium compared to those of other authors working with earthworms and soil arthropods show that snails give responses to concentrations comparable to those of earthworms and much more rapidly and with more sensitivity than those of collembolla for example. The ease of handling snails and the perfect control of their breeding are essential factors in carrying out reliable bioassays in toxicology and in ecotoxicology.

Comparison of the bioaccumulation capacities of copper and zinc in two snail subspecies (Helix).

Bioaccumulation analyses of copper and zinc were carried out in two snail subspecies (Helix aspersa aspersa and Helix aspersa maxima) after 3 months of controlled farming (out of ground) with foods of different formulations. The results reveal some clear interspecific differences in affinity toward copper and zinc. For the two metals considered, H. aspersa aspersa has a bioaccumulation capacity much greater than that of H. aspersa maxima, mainly in the foot for copper and in the viscera for zinc. After 3 months, the concentrations of copper in feet and viscera are much higher than those presented in the literature on field animals. The farming and the analysis methodologies permitted obtaining snails under standard condition and open the way to the development of rational protocols for ecotoxicological studies in a laboratory as well as in the field.

Allogeneic and xenogeneic grafts in pulmonate gastropod molluscs: fates of neural transplants.

Neural intracerebral allo- and xenografts in pulmonate gastropods demonstrated a variation in the tolerance of neural xenogeneic grafts that was dependent on the phylogenetic distance between the donor and the host. Like allografts, neural congeneric xenografts (Hp/Haa and H1/Haa) of cerebral ganglia (CG) were tolerated and restored growth in juvenile mesocerebrum-deprived (Haa) snails. However, CG neural xenografts between different genera of stylommatophorans (Achatina fulica/Haa) or between genera of different orders (Lymnaea stagnalis: Basommatophora/Haa: Stylommatophora) revealed an interspecific histoincompatibility. These results, compared with those described by other authors, suggest that gastropods possess mechanisms for the recognition of non-self that depend on the organ considered and the phylogenetic distance separating host and donor. Research should now attempt to identify the factors responsible for graft destruction.

Brain grafts of cerebral ganglia have effectiveness in growth restoration of damaged Helix aspersa mesocerebrum.

The microsurgical extirpation of the mesocerebrum from the brain of fast-growing juvenile snails (Helix aspersa aspersa: H.a.a.) stops their growth. This suggests that neurosecretory cells of the mesocerebrum secrete a growth hormone. Neural grafting has been used as a tool to restore the impaired growth function after mesocerebrum removal in juvenile H.a.a snails. The transplantation of desheathed cerebral ganglia (CG) (i.e. CG with their glioconjunctive outer covering removed), into the place where the mesocerebrum had been re-established growth which depended on the age of the donors. For the grafts of H.a.a CG into H.a.a, it was CG from the youngest donors that restored growth best. However, the CG of adult snails still conserved a slight growth-stimulating activity. Transplantation of the CG from the large, fast-growing sub-species H. aspersa maxima (H.a.m), into the brain of H.a.a with mesocerebrum removed induced faster growth than the H.a.a CG probably because of a more abundant secretion of growth hormone. Our results show that intracerebral CG grafts are well tolerated in snails and that labeling of the neurones of the transplanted CG with a vital fluorescent stain (Fast blue), allowed the observation, over several months, of their integration into the lesion zone of the host brain.

[Influence of brain grafts on growth restoration of snail (Helix aspersa) deprived of the midbrain]. / Influence de greffes cérébrales dans la restauration de la croissance de l'escargot (Helix aspersa) privé de mesocerebrum.

Microsurgical removal of the mesocerebrum from the brain of juvenile snails stopped their growth whereas intracerebral implantation of desheathed cerebral ganglia (CG) re-established it. When the animals were grafted with CG from very young snails growth was much more stimulated than with CG from donors of the same age or from adults. Furthermore, young CG of juvenile fast growing specimens of the large species (Helix aspersa maxima) induced a higher growth rate than the CG of the ordinary small garden snails (Helix aspersa aspersa). Labelling of the neural grafts with the vital fluorescent dye fast blue enabled us to follow the repopulation of the lesioned area of the brain of the host during the functional integration of the implanted neurons into the circuits that control growth in snails.

Immunocytochemical localization of insulin-related peptide(s) in the central nervous system of the snail Helix aspersa Müller: involvement in growth control.

1. The presence of insulin-like substances has been demonstrated by immunocytochemistry in the central nervous system of the snail Helix aspersa. 2. The immunopositivity has been observed especially in the large perikarya of the mesocerebral green cells [the cerebral green cells (CeGC) stained in green by the alcian blue:alcian yellow technique]. 3. The removal of either the mesocerebrum or the CeGC stops the growth of the snail and induces the increase of the glycogen content in the mantle edge. 4. Our results show the existence of insulin-like material in the neurosecretory cells. Previous data having demonstrated the presence of specific binding sites to insulin in the cephalic ganglia of Helix aspersa, one may suggest that insulin could play a neuromodulatory or a neurotransmittory role in the central nervous system and might control the growth.

Photoperiod and temperature interaction in the determination of reproduction of the edible snail, Helix pomatia.

Snails were kept in self-cleaning housing chambers in an artificially controlled environment. Mating was frequent under long days (18 h light) and rare under short days (8 h light) regardless of whether the snails were kept at 15 degrees C or 20 degrees C. An interaction between photoperiod and temperature was observed for egg laying. The number of eggs laid (45-50/snail) and the frequency of egg laying (90-130%) were greater in long than in short days (16-35/snail and 27-77%) but a temperature of 20 degrees C redressed, to some extent, the inhibitory effect of short days. At both temperatures only long photoperiods brought about cyclic reproduction over a period of 16 weeks, confirming the synchronizing role of photoperiod on the neuroendocrine control of egg laying in this species of snail.