Cross-phylum extrapolation of the Daphnia magna chronic biotic ligand model for zinc to the snail Lymnaea stagnalis and the rotifer Brachionus calyciflorus

We investigated if the chronic zinc biotic ligand model (BLM) developed earlier for the arthropod Daphnia magna could be extrapolated to predict chronic ecotoxicity of zinc as a function of water chemistry to two species from other phyla, i.e. the mollusc Lymnaea stagnalis and the rotifer Brachionus calyciflorus. We chronically exposed these two species to zinc in six natural surface waters. These water covered a wide range of pH (6.8-8.3), dissolved organic carbon (1.2-12.7mg/L) and Ca (8.8-118mg/L). Across all waters tested, the 28d-EC10s (200-1629μg Zn/L) and EC50s (382-2026μg Zn/L) for L. stagnalis spanned a 8.1-fold and 5.3-fold range, respectively. The 2d-EC10s (142-550μg Zn/L) and 2d-EC50s (195-1104μg Zn/L) for B. calyciflorus spanned a 3.9-fold and 5.7-fold range, respectively. The data indicated that higher pH and higher concentrations of Ca and DOC were generally associated with lower toxicity (higher ECx values). Furthermore, the chronic Zn BLM for D. magna, when calibrated only to reflect the intrinsic sensitivity of L. stagnalis and B. calyciflorus, was able to predict all ECx values with a less than 1.6-fold error, which demonstrates that the chronic D. magna Zn BLM can be extrapolated to other invertebrate phyla. This lends further support to the use of the chronic Zn BLM to account for bioavailability of zinc in aquatic risk assessment and the derivation of environmental quality standards.

Development of partial life-cycle experiments to assess the effects of endocrine disruptors on the freshwater gastropod Lymnaea stagnalis: a case-study with vinclozolin

Long-term effects of endocrine disruptors (EDs) on aquatic invertebrates remain difficult to assess, mainly due to the lack of appropriate sensitive toxicity test methods and relevant data analysis procedures. This study aimed at identifying windows of sensitivity to EDs along the life-cycle of the freshwater snail Lymnaea stagnalis, a candidate species for the development of forthcoming test guidelines. Juveniles, sub-adults, young adults and adults were exposed for 21 days to the fungicide vinclozolin (VZ). Survival, growth, onset of reproduction, fertility and fecundity were monitored weekly. Data were analyzed using standard statistical analysis procedures and mixed-effect models. No deleterious effect on survival and growth occurred in snails exposed to VZ at environmentally relevant concentrations. A significant impairment of the male function occurred in young adults, leading to infertility at concentrations exceeding 0.025 μg/L. Furthermore, fecundity was impaired in adults exposed to concentrations exceeding 25 μg/L. Biological responses depended on VZ concentration, exposure duration and on their interaction, leading to complex response patterns. The use of a standard statistical approach to analyze those data led to underestimation of VZ effects on reproduction, whereas effects could reliably be analyzed by mixed-effect models. L. stagnalis may be among the most sensitive invertebrate species to VZ, a 21-day reproduction test allowing the detection of deleterious effects at environmentally relevant concentrations of the fungicide. These results thus reinforce the relevance of L. stagnalis as a good candidate species for the development of guidelines devoted to the risk assessment of EDs.

Trophic transfer of aluminium through an aquatic grazer-omnivore food chain

The potential for trophic transfer of aluminium (Al) was investigated using a grazing detritivore, the freshwater snail Lymnaea stagnalis, and a predator, the signal crayfish Pacifastacus leniusculus. Snails were exposed to either aqueous Al (500 microg l(-1)) in the presence or absence of an inorganic ligand (phosphate (+P); 500 microg l(-1)) for 30 days, or kept as unexposed controls. Subcellular partitioning of Al in the snail tissues was characterised using ultracentrifugation. Al content in the soft tissues and the subcellular fractions was measured using inductively coupled plasma atomic emission spectroscopy. Exposed and control snails were fed to individually housed crayfish (n=6 per group) over 40 days. Water samples, uneaten snail tissue and faeces were collected throughout the experiment in order to assess the fate of Al. Behavioural toxicity to the crayfish was assessed at four time points, and tissue accumulation of Al in soft tissues was measured following a 2-day depuration period. Snails exposed to Al+P accumulated more Al per snail than those exposed to Al only (291 microg vs 206 microg), and also contained a higher proportion of detoxified Al (in inorganic granules and associated with heat stable proteins) (39% vs 26%). There were no significant differences in behavioural activity between the different groups of crayfish at any time point. Crayfish fed snails exposed to only Al accumulated significant levels of Al in their total soft tissues, compared to controls; crayfish fed Al+P-exposed snails did not, even though concentrations of Al in these snails were higher. The highest concentrations of Al were found in the green gland in both crayfish feeding groups, and the gut and hepatopancreas in crayfish fed Al only exposed snails; all of these were significantly higher than in crayfish fed control snails. There was no significant accumulation of Al in the gills or flexor muscle in any group. At least 17% of trophically available Al in the snail tissues was accumulated by the crayfish. This proportion was similar in both feeding groups but, as the proportion of trophically available Al in the snails exposed to Al+P was lower, this led to lower accumulation in the Al+P crayfish feeding group. This study indicates that in comparison to vertebrates, aquatic invertebrates accumulate a higher proportion of Al via oral ingestion but it does not accumulate in tissues that may pose a threat to human consumers.

Impact of toxic cyanobacteria on gastropods and microcystin accumulation in a eutrophic lake (Grand-Lieu, France) with special reference to Physa (= Physella) acuta

Hepatotoxic microcystins (MCs) produced by cyanobacteria are known to accumulate in gastropods following grazing of toxic cyanobacteria and/or absorption of MCs dissolved in water, with adverse effects on life history traits demonstrated in the laboratory. In the field, such effects may vary depending on species, according to their relative sensitivity and ecology. The aims of this study were to i) establish how various intensities of MC-producing cyanobacteria proliferations alter the structure of gastropod community and ii) compare MC tissue concentration in gastropods in the field with those obtained in our previous laboratory experiments on the prosobranch Potamopyrgus antipodarum and the pulmonate Lymnaea stagnalis. We explored these questions through a one-year field study at three stations at Grand-Lieu Lake (France) affected by different intensities of cyanobacteria proliferations. A survey of the community structure and MC content of both cyanobacteria and gastropods was associated with a caging experiment involving P. antipodarum and L. stagnalis. In total, 2592 gastropods belonging to 7 prosobranch and 16 pulmonate species were collected. However, distribution among the stations was unequal with 62% vs 2% of gastropods sampled respectively at the stations with the lowest vs highest concentrations of MC. Irrespective of the station, pulmonates were always more diverse, more abundant and occurred at higher frequencies than prosobranchs. Only the pulmonate Physa acuta occurred at all stations, with abundance and MC tissue concentration (< or = 4.32 microg g DW(-1)) depending on the degrees of MC-producing cyanobacteria proliferations in the stations; therefore, P. acuta is proposed as a potential sentinel species. The caging experiment demonstrated a higher MC accumulation in L. stagnalis (< or = 0.36 microg g DW(-1) for 71% of individuals) than in P. antipodarum (< or = 0.02 microg g DW(-1) for 12%), corroborating previous laboratory observations. Results are discussed in terms of differential gastropod sensitivity and MC transfer through the food web.

Histopathology and microcystin distribution in Lymnaea stagnalis (Gastropoda) following toxic cyanobacterial or dissolved microcystin-LR exposure

The accumulation of hepatotoxic microcystins (MCs) in gastropods has been demonstrated to be higher following grazing of toxic cyanobacteria than from MCs dissolved in ambient water. Previous studies, however, did not adequately consider MCs covalently bound to protein phosphatases, which may represent a considerably part of the MC body burden. Thus, using an immunohistochemical method, we examined and compared the histopathology and organ distribution of covalently bound MCs in Lymnaea stagnalis following a 5-week exposure to (i) dmMC-LR, dmMC-RR, and MC-YR-producing Planktothrix agardhii (5 microg MC-LReqL(-1)) and (ii) dissolved MC-LR (33 and 100 microgL(-1)). A subsequent 3-week depuration investigated potential MC elimination and tissue regeneration. Following both exposures, bound MCs were primarily observed in the digestive gland and tract of L. stagnalis. Snails exposed to toxic cyanobacteria showed severe and widespread necrotic changes in the digestive gland co-occurring with a pronounced cytoplasmic presence of MCs in digestive cells and in the lumen of digestive lobules. Snails exposed to dissolved MC-LR showed moderate and negligible pathological changes of the digestive gland co-occurring with a restrained presence of MCs in the apical membrane of digestive cells and in the lumen of digestive lobules. These results confirm lower uptake of dissolved MC-LR and correspondingly lower cytotoxicity in the digestive gland of L. stagnalis. In contrast, after ingestion of MC-containing cyanobacterial filaments, the most likely longer residual time within the digestive gland and/or the MC variant involved (e.g., MC-YR) allowed for increased MC uptake, consequently a higher MC burden in situ and thus a more pronounced ensuing pathology. While no pathological changes were observed in kidney, foot and the genital gland, MCs were detected in spermatozoids and oocytes of all exposed snails, most likely involving a hemolymph transport from the digestive system to the genital gland. The latter results indicate the potential for adverse impact of MCs on gastropod health and reproduction as well as the possible transfer of MCs to higher trophic levels of the food web.

A 5-HT1A-like receptor is involved in the regulation of the embryonic rotation of Lymnaea stagnalis L

Cilia driven rotation of the pond snail Lymnaea stagnalis embryos is regulated by serotonin (5-HT). In the present study, physiological and biochemical assays were used to identify the 5-HT receptor type involved in rotation. The 5-HTergic agonists applied stimulated the rotation by 180-400% and their rank order potency was as follows: LSD>5-HT>8-OH-DPAT>WB4101>>5-CT. The applied antagonists, spiperone, propranalol and mianserin inhibited the 5-HT or 8-OH-DPAT stimulated rotation of the embryos by 50-70%. (3)H-5-HT was bound specifically to the washed pellet of the embryo homogenates. The specific binding of (3)H-5-HT was saturable and showed a single, high affinity binding site with K(d) 7.36 nM and B(max) 221 fmol/mg pellet values. This is the first report demonstrating the high affinity binding of (3)H-5-HT to the native receptor in molluscs. All of the pharmacons that stimulated the rotation or inhibited the 5-HT or 8-OH-DPAT evoked stimulation displaced effectively the binding of (3)H-5-HT. 5-HT resulted in the inhibition of forskolin stimulated cAMP accumulation, showing that 5-HT is negatively coupled to adenylate cyclase. Our results suggest that in the 5-HTergic regulation of the embryonic rotation in L. stagnalis a 5-HT(1A)-like receptor of the vertebrate type is involved.

Contrary effects of octopamine receptor ligands on behavioral and neuronal changes in locomotion of lymnaea

The pond snail Lymnaea stagnalis moves along the sides and bottom of an aquarium, but it can also glide upside down on its back below the water's surface. We have termed these two forms of locomotion "standard locomotion" and "upside-down gliding," respectively. Previous studies showed that standard locomotion is produced by both cilia activity on the foot and peristaltic contraction of the foot muscles, whereas upside-down gliding is mainly caused by cilia activity. The pedal A neurons are thought to receive excitatory octopaminergic input, which ultimately results in increased cilia beating. However, the relationship between locomotory speed and the responses of these neurons to octopamine is not known. We thus examined the effects of both an agonist and an antagonist of octopamine receptors on locomotory speed and the firing rate of the pedal A neurons. We also examined, at the electron and light-microscopic levels, whether structural changes occur in cilia following the application of either an agonist or an antagonist of octopamine receptors to the central nervous system (CNS). We found that the application of an octopamine antagonist to the CNS increased the speed of both forms of locomotion, whereas application of octopamine increased only the firing rate of the pedal A neurons. Microscopic examination of the cilia proved that there were no changes in their morphology after application of octopamine ligands. These data suggest that there is an unidentified octopaminergic neuronal network in the CNS whose activation reduces cilia movement and thus locomotory speed.

Haemocyte lysosomal fragility facing an environmental reality: a toxicological perspective with atrazine and Lymnaea stagnalis (Gastropoda, Pulmonata) as a test case

The present study investigates the potential use of haemocyte lysosomal fragility as a reliable indicator of toxic injury in snails subjected to herbicide atrazine. Two cytochemical assays were used. The first one was based on microscopic observations of neutral red dye, and the second one on a fluorescence spectroscopy approach using acridine orange, which had the advantage of being more reliable in assessing minor cell damage. Two sets of experiments were carried out in controlled laboratory conditions (temperature, photoperiod) and in outdoor microcosms, which produce more realistic ecological conditions. An unequivocal relationship was shown, linking atrazine exposure to Lymnaea stagnalis haemocytes lysosomal permeability. High temperatures also had a negative effect on the lysosomal membrane. In the microcosms, the response was affected by seasonal factors, and led to an integrated cell response. It was concluded that lysosomal sensitivity reflects environmental changes. Moreover, the technique using acridine orange was shown to be sufficiently sensitive and reliable to serve as a lysosomal marker in a controlled environment.

Tissue accumulation of aluminium is not a predictor of toxicity in the freshwater snail, Lymnaea stagnalis

The amount of toxic metal accumulated by an organism is often taken as an indicator of potential toxicity. We investigated this relationship in the freshwater snail, Lymnaea stagnalis, exposed to 500 microg l(-1) Al over 30 days, either alone or in the presence of phosphate (500 microg l(-1) P) or a fulvic acid surrogate (FAS; 10 mg l(-1) C). Behavioural activity was assessed and tissue accumulation of Al quantified. Lability of Al within the water column was a good predictor of toxicity. FAS increased both Al lability and behavioural dysfunction, whereas phosphate reduced Al lability, and completely abolished Al-induced behavioural toxicity. Tissue accumulation of Al was not linked to toxicity. Higher levels of Al were accumulated in snails exposed to Al + P, compared to those exposed to Al alone, whereas FAS reduced Al accumulation. These findings demonstrate that the degree of tissue accumulation of a metal can be independent of toxicity.

High net calcium uptake explains the hypersensitivity of the freshwater pulmonate snail, Lymnaea stagnalis, to chronic lead exposure

Previous studies have shown that freshwater pulmonate snails of the genus Lymnaea are exceedingly sensitive to chronic Pb exposure. An EC20 of <4microgl(-1)Pb for juvenile snail growth has recently been determined for Lymnaea stagnalis, which is at or below the current USEPA water quality criterion for Pb. We characterized ionoregulation and acid-base balance in Pb-exposed L. stagnalis (young adults approximately 1g) to investigate the mechanisms underlying this hypersensitivity. After 21-day exposure to 18.9microgl(-1)Pb, Ca(2+) influx was significantly inhibited (39%) and corresponding net Ca(2+) flux was significantly reduced from 224 to -23nmolg(-1)h(-1). An 85% increase in Cl(-) influx was also observed, while Na(+) ion transport appeared unaffected. Finally, a marked alkalosis of extracellular fluid was observed with pH increasing from 8.35 in the control to 8.65 in the 18.9microgl(-1) Pb-exposed group. Results based on direct measurement of Ca(2+) influx in 1g snails gave an influx nearly an order of magnitude higher (750nmolg(-1)h(-1)) than in comparably sized fish in similar water chemistry. Under control conditions, specific growth rate in newly hatched snails was estimated at 16.7% per day over the first 38-day post-hatch and whole body Ca(2+) concentrations were relatively constant at approximately 1100nmolg(-1) over this period. Based on these data, it is estimated that newly hatched snails have net Ca(2+) uptake rates on the order of 7600nmolg(-1)h(-1). A model was developed integrating these data and measured inhibition of Ca(2+) influx rates of 13.4% and 38.7% in snails exposed to 2.7 and 18.9microgl(-1)Pb, respectively. The model estimates 45% and 83% reductions in newly hatched snail growth after 30-day exposure in these two Pb-exposed groups. These results compare well with previous direct measurements of 47% and 90% reductions in growth at similar Pb concentrations, indicating the high net Ca(2+) uptake is the controlling factor in observed Pb hypersensitivity.

In vitro effects of fipronil on neuronal excitability in mammalian and molluscan nervous systems

The effect of the insecticide fipronil on non-target organisms was studied on rat brain slices and identified giant neurons of the pond snail Lymnaea stagnalis. This compound acts as an antagonist on GABA(A) receptors. Although fipronil has moderate mammalian toxicity, our experiments confirmed that it modifies neuronal excitability in the rat somatosensory cortex. The amplitudes of evoked field potentials increased significantly after 30 min fipronil treatment. Short-term plasticity was examined with paired-pulse stimulation, this phenomenon was not affected by fipronil. On the other hand, the efficacy of LTP-induction was enhanced in the treated slices. Fipronil is highly toxic to freshwater invertebrates, especially molluscs. In Lymnaea stagnalis, the firing pattern of a GABA receptor- containing neuron (RPeD1) was studied. On this neuron, GABA has an excitatory, hypopolarizing effect. Fipronil treatment decreased the action potential frequency in a concentration-dependent manner. On the membrane potential of the cell, it had a slightly hyperpolarizing effect. These experiments confirmed that fipronil toxicity is mediated by GABA receptors in the nervous system of invertebrates as well as vertebrates. These types of experiments may help in establishing tolerance levels of pesticide residues and in finding proper treatment in case of eventual poisonings.

Role of aminergic (serotonin and dopamine) systems in the embryogenesis and different embryonic behaviors of the pond snail, Lymnaea stagnalis

A detailed biochemical and pharmacological analysis of the dopaminergic (DAergic) and serotonergic (5-HTergic) systems was performed during the embryogenesis of Lymnaea stagnalis, to monitor their role in development and different behaviors. The dopamine (DA) level and the synthesizing decarboxylase enzyme activity showed a continuous increase, whereas the serotonin (5-HT) concentration remained low until late postmetamorphic development, when they all showed a rapid and significant increase. Application of monoamine precursors increased, whereas enzyme inhibitors and neurotoxins reduced monoamine levels; all treatments resulting in a prolongation of embryogenesis. Following, p-chlorphenylalanine (pCPA) and 3-hydroxybenzylhydrazine (Nsd-1015) treatments, no 5-HT immunoreactivity could be detected in the embryonic nervous system. These findings suggest that changes of monoamine levels in either (negative or positive) direction cause slowing of embryogenesis. Embryonic rotation and radula protrusion rate was enhanced following both serotonin and dopamine application, whereas frequency of gliding was increased by serotonin treatment. These results clearly indicate the involvement of 5-HT and DA in the regulation of a broad range of embryonic behaviors. Pharmacological characterization of a 5-HT receptor associated with the L. stagnalis embryonic behaviors studied revealed that a mammalian 5-HT(1)-like receptor type is involved in the 5-HTergic regulation of locomotion activity.

Effect of binary combination of deltamethrin+MGK-264 on the levels of phospholipid and lipid peroxidation in the snail Lymnaea acuminata

Effect of sublethal treatment of (40% and 60% of 48 h LC50) of deltamethrin+MGK on phospholipid level and rate of lipid peroxidation in nervous and foot tissue of Lymnaea acuminata were studied. Maximum reduction in phospholipid (24.10%) level and increase in rate of lipid peroxidation (586.8%) were observed in foot tissue of snail exposed to 60% of 48 h LC50 of deltamethrin+MGK 264 for 96 h. Alterations in the levels of phospholipids and rate of lipid peroxidation were time and concentration dependent. Use of MGK-264 with deltamethrin increases the toxicity of deltamethrin and their action on membrane phospholipids and rate of lipid peroxidation.

Reduction of growth and haemolymph Ca levels in the freshwater snail Lymnaea stagnalis chronically exposed to cobalt

The ecological risk assessment and the development of water-quality criteria for Co are currently still hampered by insufficient knowledge about the toxicity of Co to freshwater organisms. A relevant group of organisms, for which no toxicity data with Co are available, is the class of the herbivorous pulmonate freshwater snails, which fulfil a pivotal role in the consumption and decomposition of aquatic plants and epihyton. We measured the growth rate of the pond snail Lymnaea stagnalis chronically exposed for 28 days to a series of Co concentrations. The no observed effect concentration (NOEC) and the lowest observed effect concentration (LOEC) for growth rate were 26 and 79 microg Co/L, respectively. Growth rate of snails exposed to 79 microg Co/L and higher concentrations was more impaired in the final 2 weeks of exposure than in the first 2 weeks of exposure. The reduced growth rate at 79 microg Co/L was accompanied by a reduced concentration of Ca in the haemolymph at the end of the exposure. Possible mechanisms of toxicity of Co to snail growth were suggested to be an impairment of Ca uptake and homeostasis and/or feeding inhibition. Although additional research is needed to investigate the relative importance of these mechanisms, as well as the interrelatedness between them, the toxicity data currently presented can assist in risk assessment and water-quality criteria development.

[Antioxidative protection in the central nervous ganglia of a mollusc Lymnaea stagnalis at modulation of activity of the NO-ergic system]

In experiments on molluscs Lymnnaea stagnalis the state of antioxidative protection is studied in central nervous ganglia during a long-term activation (inhibition) of synthesis of nitric monoxide (NO) in the body. Effect of the blocker of NO-synthase N(G)-nitro-L-arginine (L-NNA) at the background of enhancement of pulmonary respiration has been established to be associated with a rise of levels of reduced glutathione and TBK-active products in the nervous tissue at preservation of a relatively high superoxide dismutase activity and a low glutathione peroxidase activity as compared with control group and the animals treated with the metabolic precursor of NO synthesis L-arginine. In spite of the revealed disturbances of balance of the body pro- and antioxidative system, DNA electrophoresis detected no products of its degradation, which can indicate the absence of massive programmed death of the nervous tissue cells in Lymnaea stagnalis during modulation of activity of the NO-ergic system.

Molluscicidal saponins from leaves of Hedera canariensis

Activity-guided fractionation of the methanol extract of Hedera canariensis (var. Gloire de Maringo) Wild leaves afforded five saponins 1-5. Chemical and spectral methods (MS, 1HNMR, 13CNMR) showed that they are glycosides of hederagenin and oleanolic acid. The results showed that 4,5 exhibited molluscicidal properties, compound 1 was inactive. Mortality rate of exposed snails increased by increasing plant extract concentration. Lymnaea cailliaudi was more sensitive to plant extract than Biomphalaria alexandrina. The histopathological study revealed distinct damage in the structure of the stomach and ovotestis of treated L. cailliaudi snails. Saponin content was determined in term of haemolytic index.

Avoidance of aluminum toxicity in freshwater snails involves intracellular silicon-aluminum biointeraction

Silicon (Si) ameliorates aluminum (Al) toxicity to a range of organisms, but in almost all cases this is due to ex vivo Si-Al interactions forming inert hydroxyaluminosilicates (HAS). We hypothesized a Si-specific intracellular mechanism for Al detoxification in aquatic snails, involving regulation of orthosilicic acid [Si(OH)4]. However, the possibility of ex vivo formation and uptake of soluble HAS could not be ruled out Here we provide unequivocal evidence for Si-Al interaction in vivo, including their intracellular colocalization. In snails preloaded with Si(0H)4, behavioral toxicity in response to subsequent exposure to Al was abolished. Similarly, recovery from Al-induced toxicity was faster when Si(OH)4 was provided, together with rapid loss of Al from the major detoxificatory organ (digestive gland). Temporal separation of Al and Si exposure excluded the possibility of their interaction ex vivo. Elemental mapping using analytical transmission electron microscopy revealed nanometre-scale colocalization of Si and Al within excretory granules in the digestive gland, consistent with recruitment of Si(OH)4, followed by high-affinity Al binding to form particles similarto allophane, an amorphous HAS. Given the environmental abundance of both elements, we anticipate this to be a widespread phenomenon, providing a cellular defense against the profoundly toxic Al(III) ion.

Histoenzymological study on the toxicity of copper sulphate in the digestive glands of Lymnaea luteola

During 24 and 48 hr of exposure, the digestive glands of Lymnaea treated with a lethal concentration of 0.038 mgl(-1) CuSO4 revealed intense activity of acid phosphatase in perilobular margin. On the other hand, same area of the gland showed moderate activity of ATPase during 24 and 48 hr of exposure. However, alkaline phosphatase showed average activity in perialveolar region and perilobular margin during 24 and 48, and 72 hr of exposure respectively The changes in the activity of these enzymes were nonsignificant in alveolar margin and perialveolar region of the gland. It is interesting to note moderate activity of acid phosphatase in perialveolar region during 24 hr of exposure.

[Strophanthin induced changes in the ion currents of Lymnaea stagnalis and Planorbis corneus neurons]

Experiments on isolated neurons of Lymnaea stagnalis and Planorbis corneus using the intracellular dialysis and fixed membrane potential techniques showed that strophanthin G in a concentration range from 10(-11) to 10(-6) M produce dolse-dependent reversible suppression of the ion currents in potassium, calcium, and sodium channels. At the maximum concentration (10(-6) M), the maximum suppression (up to 55% of that in the control) was observed for the calcium ion current. At the minimum concentration (10(-12) M), the drug did not influence the sodium ion current, but slightly (approximately by 5%) increased the calcium and potassium ion currents. In addition, strophanthin accelerated the inactivation of slow potassium ion currents.

Commiphora molmol extracts as plant molluscicide against Lymnaea natalensis

Two extracts from the herbal plant, Commiphora molmol showed a high molluscicidal effect against Lymnaea natalensis. The oil extract was more potent than the oleo-resin. A concentration of 10 ppm of the oil extract killed 100% of L. natalensis after 5th day, but the oleo-resin extract killed 100% of them at a concentration 20 ppm after 5th day.

Behavioural and neural deficits induced by rotenone in the pond snailLymnaea stagnalis. A possible model for Parkinson's disease in an invertebrate

Parkinson's disease is a neurodegenerative disorder, related to the loss of dopamine (DA)-containing neurons in the substantia nigra. In experimental animals, both vertebrates and invertebrates, rotenone, a commercially available organic pesticide, induces symptoms of Parkinson's disease. We found that that rotenone is toxic to the pond snail Lymnaea stagnalis (4-day LC50 0.8 microM). Rotenone, at concentrations from 0.1 to 5 microM, caused progressive and irreversible behavioural deficits in both acute and chronic exposure. Chronic exposure to 0.5 microM rotenone led to a progressive decrease in spontaneous locomotion and in feeding, reaching almost 100% inhibition of both behaviours by the 7th day of rotenone treatment. In the central nervous system preparation made on the 7th day of treatment the postsynaptic potentials evoked by the identified dopaminergic RPeD1 neuron disappeared whereas the synaptic inputs received by the RPeD1 from a peptidergic neuron (VD4) were still functional. Immunostaining revealed that the tyrosine hydroxylase immunoreactivity decreased below the detectable level in both the RPeD1 cell body and its axonal processes. Finally, HPLC assay showed a significant (25%) decrease in DA level in the CNS by the 7th day of rotenone treatment. We conclude that, as in vertebrates, rotenone disrupts feeding and locomotion of the model mollusc Lymnaea stagnalis. One possible target of rotenone is the dopaminergic neurons in the CNS. We therefore suggest that Lymnaea stagnalis is a suitable invertebrate model for the study of Parkinson's disease, allowing direct analysis of the response of dopaminergic systems to rotenone at behavioural, cellular and neuronal levels.

Repeated cocaine effects on learning, memory and extinction in the pond snail Lymnaea stagnalis

The persistence of drug addiction suggests that drugs of abuse enhance learning and/or impair extinction of the drug memory. We studied the effects of repeated cocaine on learning, memory and reinstatement in the pond snail, Lymnaea stagnalis. Respiratory behavior can be operantly conditioned and extinguished in Lymnaea, and this behavior is dependent on a critical dopamine neuron. We tested the hypothesis that repeated cocaine exposure promotes learning and memory or attenuates the ability to extinguish the memory of respiratory behavior that relies on this dopaminergic neuron. Rotating disk electrode voltammetry revealed a K(m) and V(max) of dopamine uptake in snail brain of 0.9 micromol l(-1) and 558 pmol s(-1) g(-1) respectively, and the IC(50) of cocaine for dopamine was approximately 0.03 micromol l(-1). For operant conditioning, snails were given 5 days of 1 h day(-1) immersion in water (control) or 0.1 micromol l(-1) cocaine, which was the lowest dose that maximally inhibited dopamine uptake, and snails were trained 3 days later. No changes were found between the two groups for learning or memory of the operant behavior. However, snails treated with 0.1 micromol l(-1) cocaine demonstrated impairment of extinction memory during reinstatement of the behavior compared with controls. Our findings suggest that repeated exposure to cocaine modifies the interaction between the original memory trace and active inhibition of this trace through extinction training. An understanding of these basic processes in a simple model system may have important implications for treatment strategies in cocaine addiction.

Haemocyte apoptosis as a general cellular immune response of the snail, Lymnaea stagnalis, to a toxicant

The effects of a xenobiotic on the circulating haemocytes of Lymnaea stagnalis were investigated after short-term (24 h, 96 h) and long-term (504 h) exposure of snails to environmental concentrations. Fomesafen, a pro-oxidant generator led to the activation of the haemocyte apoptotic program by promoting reactive oxygen species (ROS). Cells entering apoptosis underwent a series of events, both on the plasma membrane and in the mitochondria; these events were quantified by flow cytofluorometry. The data showed a loss of mitochondrial transmembrane potential (Deltapsim), which was dose-dependent and time-dependent and related to an increased release of superoxide anions. The phosphatidylserine that was exposed at the outer plasma membrane was not related to the disruption of either ROS or Deltapsim but was strongly correlated with the haemocyte concentration (total haemocyte count). This cascade of apoptotic processes occurred in a dose-independent manner and was not strengthened over time. The increase of circulating haemocytes depended upon the life span of the cells and might have reflected either facilitated cell turn-over or the accompanying presence of haemocytes phagocytosing apoptotic cells.

Chronic toxicity of tributyltin to development and reproduction of the European freshwater snail Lymnaea stagnalis (L.)

Chronic toxicity, growth and reproduction were measured in the freshwater gastropod Lymnaea stagnalis exposed to waterborne bis(tri-n-butyltin) oxide (TBTO) over a range of four nominal concentrations (0-10microg TBTl(-1)). Egg development was completely inhibited at 10microg TBTl(-1), whilst abnormal embryonic development was observed at 1microg TBTl(-1). For the solvent control and the 0.01microg TBTl(-1)treatment group, normal development of L. stagnalis was observed. Survivorship of hatchlings was significantly reduced by TBT at 1microgl(-1) while inhibition of shell growth of L. stagnalis was also observed at this concentration. The data were used to determine intrinsic growth rates (r) using two theoretical approaches (the Euler-Lotka equation and a Leslie Matrix). Both approaches showed that survival, fecundity and population growth rate were reduced at 1microg TBTl(-1). Interestingly, at 0.01microg TBTl(-1) snails showed a higher fecundity and growth rate than in the solvent control. The TBT concentration at which the r would equal zero (ECr(0)) and the population NOEC (No Observed Effect Concentration) were estimated. The population NOEC was defined as either the lower 95% confidence or lower 95% pointwise percentile limit of the ECr(0). Values obtained using the two different approaches were similar and thus a geometric mean was calculated to obtain a final representative population NOEC value for L. stagnalis of 2745ng TBTl(-1). The present data together with chronic toxicity TBT data for freshwater organisms, obtained from peer-reviewed literature, were used to construct a species sensitivity distribution (SSD). A predicted no effect concentration was then derived from the SSD (hazardous concentration at 5%, i.e., HC5 or 95% protection level). This SSD was compared with the SSD derived from saltwater species datasets. The HC5 value for saltwater species (3.55ng TBTl(-1); lower confidence limit: 1.93ng TBTl(-1)) was significantly lower than that for freshwater species (30.13ng TBTl(-1); lower confidence limit: 9.23ng TBTl(-1)), indicating that saltwater species are probably more susceptible to TBT than their freshwater counterparts.

Specific inhibitors of mitogen-activated protein kinase and PI3-K pathways impair immune responses by hemocytes of trematode intermediate host snails

To characterize molecular mechanisms regulating snail cellular immune responses, the contributions of mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase (PI3-K) were examined in hemocytes of the trematode intermediate host snails Biomphalaria glabrata and Lymnaea stagnalis. Simultaneous measurement of phagocytosis/encapsulation and H2O2 production by hemocytes in the presence or absence of specific signal transduction inhibitors was used to assess the role of extracellular-signal regulated kinases 1 and 2 (ERK1/2), p38, JNK and PI3-K. Hemocyte spreading was significantly reduced in a dose-dependent manner by the ERK inhibitor, PD098059, and by wortmannin, a potent PI3-K inhibitor. The JNK inhibitor, SP600125, and the p38 kinase inhibitor, SB203580, had no effect on hemocyte spreading. Sheep red blood cell phagocytosis was significantly impaired by PD098059, SP600125, and SB203580. Hydrogen peroxide production during phagocytosis was severely inhibited by PD098059. Additionally, PD098059, but not the other inhibitors, significantly impaired the cellular encapsulation of trematode larvae and H2O2 production during encapsulation. These results suggest that MAPK and PI3-K signal transduction pathways play a pivotal role in the immune responses of snail hemocytes. PI3-K and ERK appear to strongly regulate cell motility. ERK, JNK and p38 contribute to phagocytosis-mediated signal transduction. ERK also play a major role in oxidative burst activation and the encapsulation of trematode larvae by snail hemocytes.