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At least 721 records · Page 40Linked to original sources

PubMed1997

Effect of the plant Azolla pinnata on survival, growth rate, fecundity and hatchability of egg-masses of Biomphalaria alexandrina snails.

Data indicated that Azolla pinnata plants variously reduce the growth rate of Biomphalaria alexandrina snails expressed as net increase in shell diameter (direct or indirect exposure). The plant density played an important role in this respect. The higher the plant density was the lower the growth rate and vice versa. Too, indirect exposure of newly hatched B. alexandrina resulted from exposed treated eggs reduced the growth rate of these snails. Data revealed that direct and/or indirect exposure to the abnormal high density (50,000 plants/L) resulted in complete kill of B. alexandrina snails after two weeks from continuous exposure. Snails exposed directly to Azolla at 50,000 and 25,000 plants/L failed to lay eggs. On the other hand, sanils exposed to 10,000 plants/L laid few eggs, resulted in low reproductive rate (57.94) compared with unexposed ones (110.6). The same trend of results was recorded with hatchability of Biomphalaria eggs.

Animals↗

PubMed2003

Slime-trail tracking in the predatory snail, Euglandina rosea.

Euglandina rosea, a predatory land snail, tracks prey and mates by following slime trails. Euglandina follow slime trails more than 80% of the time, following trails of their own species, but not those of prey snails, in the direction that they were laid. The attractive elements of prey slime are small, water-soluble compounds detected by specialized lip extensions. Although olfaction plays no role in trail following, strong odors disrupt tracking. Inhibition of nitric oxide synthase also disrupts slime trail following, suggesting a role for nitric oxide in neural processing of slime trail stimuli. Euglandina can be conditioned to follow novel trails of glutamate or arginine paired with feeding on prey snails. These experiments demonstrate that slime-trail tracking in Euglandina is a robust, easily measured behavior that makes a good model system for studying sensory processing and learning in a novel modality.

Animals↗

PubMed1958

The ecology of vector snail habitants and mosquito breeding-places: the experimental approach to basic problems.

The ecology of freshwater snails-in particular those which act as intermediate hosts of bilharziasis-is reviewed in the light of the much more extensive knowledge available on the breeding-places of anopheline mosquitos. Experimental ecological methods are recommended for the field and laboratory investigation of a number of common problems involved in the study of snail habitats and mosquito breeding-places. Among the environmental factors discussed are temperature, oxygen concentration, water movement, pollution and salinity. Sampling methods for estimating populations of both snails and mosquito larvae are also described. An attempt is made to show how malacologists and entomologists alike would benefit from improved facilities for keeping abreast of general developments in the wider field of freshwater ecology.

Animals↗

PubMed1962

A mud-sampling technique for the study of the ecology of aquatic snails, and its use in the evaluation of the efficacy of molluscicides in field trials.

The author describes a sampling technique suitable for estimating the population densities of African aquatic snails in the field by the removal of a plug of mud and its subsequent detailed examination. This device has been used in field trials with the molluscicides ICI 24223 and Bayer 73. Estimates of percentage kills were based on counts of live and dead snails in each mud sample before and after molluscicide treatment. Statistical analysis of these counts suggests that most snails killed by the molluscicides were subsequently recovered, thus providing some confirmatory evidence of the validity of these estimates.

Animals↗

PubMed1962

Key to the identification of east and central African freshwater snails of medical and veterinary importance.

This identification key has been prepared to enable field workers in eastern and centra Africa to identify the species and subspecies of snails acting as intermediate hosts of various flukes causing bilharziasis and related diseases in man and his domestic stock.The area covered by the key is eastern Africa from the Sudan and Somalia in the north to Southern Rhodesia in the south. The key includes all species and subspecies of the three medically and veterinarily important genera, Lymnaea, Bulinus and Biomphalaria. All other freshwater pulmonates of the area can be identified as to genus only.Those features of the shells and soft parts of snails which are used in identification are discussed in some detail, and indications are given as to methods of collection, preservation and dissection of snails.

Africa↗

PubMed1999

Gonadotropin-releasing hormone neuronal system of the freshwater snails Helisoma trivolvis and Lymnaea stagnalis: possible involvement in reproduction.

Peptides of the gonadotropin-releasing hormone (GnRH) family are present in neural and nonneural tissues throughout the chordate phylum. Although GnRH peptides have been implicated in nonreproductive functions, their primary function is to control reproduction by regulating sexual behaviors and inducing gonadotropin hormone release from the pituitary. Evidence suggesting the presence of a similar peptide in the central nervous system (CNS) of the gastropod mollusc Helisoma trivolvis has recently been provided. In the present study, we examined the tissue distribution of the peptide and found that it is likely restricted to the nervous system. The neuronal system containing the endogenous GnRH-like peptide is described further and is shown, in part, to innervate the male reproductive tract. Immunostaining in the closely related snail, Lymnaea stagnalis, showed a conservation in the locations of some immunoreactive neurons. Notably, staining occurred in and adjacent to the lateral lobes of both snails. Because these lobes contain neurons involved in the stimulation of egg laying and GnRH staining occurred in additional areas in the Helisoma CNS that are involved in reproduction, we suggest that the endogenous GnRH-like peptide plays a role in regulating reproduction in freshwater snails.

Animals↗

PubMed1997

Light-dependent and -independent behavioral effects of extremely low frequency magnetic fields in a land snail are consistent with a parametric resonance mechanism.

Exposure to extremely low frequency (ELF) magnetic fields has been shown to attenuate endogenous opioid peptide mediated antinociception or "analgaesia" in the terrestrial pulmonate snail, Cepaea nemoralis. Here we examine the roles of light in determining this effect and address the mechanisms associated with mediating the effects of the ELF magnetic fields in both the presence and absence of light. Specifically, we consider whether the magnetic field effects involve an indirect induced electric current mechanism or a direct effect such as a parametric resonance mechanism (PRM). We exposed snails in both the presence and absence of light at three different frequencies (30, 60, and 120 Hz) with static field values (BDC) and ELF magnetic field amplitude (peak) and direction (BAC) set according to the predictions of the PRM for Ca2+. Analgaesia was induced in snails by injecting them with an enkephalinase inhibitor, which augments endogenous opioid (enkephalin) activity. We found that the magnetic field exposure reduced this opioid-induced analgaesia significantly more if the exposure occurred in the presence rather than the absence of light. However, the percentage reduction in analgaesia in both the presence and absence of light was not dependent on the ELF frequency. This finding suggests that in both the presence and the absence of light the effect of the ELF magnetic field was mediated by a direct magnetic field detection mechanism such as the PRM rather than an induced current mechanism.

Animals↗

PubMed2004

Worniu, a Snail family zinc-finger protein, is required for brain development in Drosophila.

The Snail family of zinc-finger transcriptional repressors is essential for morphogenetic cell movements, mesoderm formation, and neurogenesis during embryonic development. These proteins also control cell cycle, cell death, and cancer progression. In Drosophila, three members of this protein family, Snail, Escargot, and Worniu, have essential but redundant functions in asymmetric cell division of neuroblasts. In addition, Snail is critical for early mesoderm formation and Escargot is required for maintaining diploidy in wing imaginal disc cells. In this report, we demonstrate that Worniu plays a role in brain development. We show that alleles of the l(2)35Da complementation group are mutants of worniu. The developing larvae of these mutant alleles fail to shorten their brainstems. The brain phenotype, as well as the lethality, of these mutants can be rescued by worniu transgenes. Moreover, RNAi experiments targeting the worniu transcript show the same nonshortening phenotype in larval brains. worniu is expressed in the neuroblasts of brain hemispheres and ventral ganglions. The results suggest that the loss of Worniu function within the neuroblasts ultimately causes the larval brainstem to fail to go through shortening during development.

Animals↗

PubMedDate not supplied

Histopathological effects of Thiodan on the freshwater snail, Galba truncatula (gastropoda, pulmonata).

Histopathological alterations in three tissues, namely, digestive gland, foot and mantle of the freshwater snail Galba truncatula induced by Thiodan 35 EC, a commercial preparation of endosulfan, were studied in the laboratory. The snails were exposed to five sublethal concentrations of Thiodan, two of them higher concentrations at 0.33% and 0.65% in glass jars for short-term exposure (96 h) and three of them lower concentrations at 0.08%, 0.16% and 0.27% for long-term exposure (10, 20 and 30 days). Thiodan caused significant histopathological changes in the tissues of the snail, irrespective of the concentration of the pesticide and its exposure period. The histopathological changes included accumulation of amoebocytes in the hemolymphatic spaces between the tubules of the digestive gland, exudation in the lumen of tubules, expansion of hemolymphatic spaces between the tubules and increase of vacuolation and necrotic changes in the digestive cells. Disruption of columnar muscle fibers and alteration of epithelial layers were detected in the foot and mantle of the treated specimens. The number and size of mucous and protein cells in the foot and mantle also changed.

Animals↗

PubMed2006

Snail controls differentiation of hepatocytes by repressing HNF4alpha expression.

Epithelial-to-mesenchymal transition (EMT) is a coordinated process, occurring both during morphogenesis and tumor progression, that allows epithelial cells to dissociate from initial contacts and migrate to secondary sites. The transcriptional repressors of the Snail family induce EMT in different epithelial cell lines and their expression is strictly correlated with EMT during the development and progression of carcinomas. We have previously shown that EMT in hepatocytes correlates with the downregulation of hepatic differentiation key factors HNFs (hepatocyte nuclear factors), and in particular of HNF4alpha. Here, we demonstrate that Snail overexpression is sufficient (i) to induce EMT in hepatocytes with conversion of morphology, downregulation of several epithelial adhesion molecules, reduction of proliferation and induction of matrix metalloproteinase 2 expression and, (ii) most relevantly, to repress the transcription of the HNF4alpha gene through a direct binding to its promoter. These finding demonstrate that Snail is at the crossroads of the regulation of EMT in hepatocytes by a dual control of epithelial morphogenesis and differentiation.

Animals↗

PubMed1993

Tracing neural pathways in snail olfaction: from the tip of the tentacles to the brain and beyond.

The anatomical organization of the olfactory system of terrestrial snails and slugs is described in this paper, primarily on the basis of experiments using the African snail Achatina fulica. Behavioral studies demonstrate the functional competence of olfaction in mediating food finding, conspecific attraction, and homing. The neural substrate for olfaction is characterized by an extraordinarily large number of neurons relative to the rest of the nervous system, and by the fact that many of them are unusually small. There exist multiple serial and parallel pathways connecting the olfactory organ, located at the tip of the tentacle, with integrative centers in the central nervous system. Our methods of studying these pathways have relied on the selective neural labels horseradish peroxidase and hexamminecobaltous chloride. One afferent pathway contains synaptic glomeruli whose ultrastructure is similar to that of the glomeruli seen in the mammalian olfactory bulb and the insect olfactory lobe. All of the olfactory neuropils, but especially the tentacle ganglion, contain large numbers of morphologically symmetrical chemical synapses. The procerebrum is a unique region of the snail brain that possesses further features analogous with olfactory areas in other animal groups. Olfactory axons from the tentacle terminate in the procerebrum, but the intrinsic neurons do not project outside of it. An output pathway from the procerebrum to the pedal ganglion has been identified and found to consist of inter-ganglionic dendrites. The major challenge for future studies is to elucidate the pattern of connectivity within, rather than between, the various olfactory neuropils.

Animals↗

PubMed1988

Electrical responses to amputation of the eye in the mystery snail.

Immediately following amputation through the eyestalk of the mystery snail (Pomacea), a persistent ionic current enters the apical amputation surface of the eyestalk stump. The circuit is completed by current driven from undamaged integument of the eyestalk stump and other body regions. The current is relatively steady during the first 10 hours following amputation. Currents subsequently begin a slow decline to base line levels by 60 hours postamputation--a time coincident with wound healing processes. The "battery" driving this ionic current is the internally negative transepidermal potential existing across the snail integument--perhaps the result of a net inward pumping of chloride across the skin. This system is compared to other regeneration models such as the amphibian limb, bone fracture repair, and skin wound healing. We suggest that ionic current may be a control of eye regeneration in the snail.

Animals↗

PubMed2004

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.

Adaptation, Physiological↗

PubMed2006

Bursa tract diverticulum in the hermaphroditic land snail Arianta arbustorum (Stylommatophora: Helicidae): morphology, function, and evolutionary implications.

A bursa tract diverticulum is widespread in the female part of the hermaphroditic reproductive system of stylommatophoran pulmonates. However, the ultrastructure of the diverticulum is unknown and there is only anecdotal evidence for a spermatophore-dissolving function for this organ. In the present study, we examined the ultrastructure of the diverticulum and investigated histological, histochemical, and morphometric changes at different time intervals after mating in the simultaneously hermaphroditic land snail Arianta arbustorum. The diverticulum in this species of snail is a prominent organ, consisting of a luminal columnar epithelium surrounded by a thick layer of connective tissue. During mating, the diverticulum functions as the site of spermatophore uptake. Within the lumen of the diverticulum the spermatophore wall is dissolved or at least partly broken down. The digested material is taken up by epithelial cells and accumulated in molluscan-specific cells of the connective tissue, the so-called rhogocytes. Subsequent to copulation, the total diameter of the diverticulum increases markedly, reaching a maximum size 12 h after mating, while at the same time the thicknesses of the diverticulum wall and diverticulum epithelium decrease. The length of the diverticulum shows a positive allometry and a high phenotypic variation compared to snail size, which suggests that the diverticulum is under directional sexual selection. We propose that the diverticulum in A. arbustorum has evolved in response to selection pressures imposed by divergent evolutionary interests between male and female function.

Animals↗

PubMed2001

Photoperiod is the main cue that triggers supercooling ability in the land snail, Helix aspersa (Gastropoda: Helicidae).

Helix aspersa hibernates in Brittany (western France), where it may experience subzero temperatures. Studies on cold hardiness, although scarce in land snails, have shown a seasonal variation in supercooling ability, associated with high temperatures of crystallization (Tc). In the present work, two key environmental factors, temperature and photoperiod, were studied to elucidate, how they may affect the enhancement of supercooling ability in the snails from the end of summer to winter. Nine groups of adult snails were acclimated to different combinations of photoperiod (LD-16:8, LD-12:12, and LD-8:16 h) and temperature (15, 10, and 5 degrees C). Temperature of crystallization, hemolymph osmolality, and water content were measured. The results demonstrate a significant effect of the photoperiod on Tc, i.e., shorter photoperiods induce lower Tc (LD-16:8 h, mean Tc = -3.0 degrees C, SD = 2.0; LD-12:12 h, mean Tc = -4.3 degrees C, SD = 1.9; LD-8:16 h, mean Tc = -5.2 degrees C, SD = 1.9; n = 90), whereas the acclimation temperature had no effect. Measurements of hemolymph osmolality and water content showed that osmolality is negatively correlated with water content. Mechanisms such as dehydration are involved in the decrease of Tc. A declining photoperiod triggers a lower Tc, long before the onset of winter conditions. This response may have an adaptive component, allowing individuals to cope with the mild winters typically observed in oceanic regions.

Acclimatization↗

PubMed2001

Biotransformation and disposition of testosterone in the eastern mud snail Ilyanassa obsoleta.

Elevated testosterone levels have been reported to be associated with imposex (pseudohermaphroditism), the superimposition of male characteristics such as a penis and vas deferens on female gonachoristic snails. Tributyltin (TBT), a marine biocide in anti-fouling paints, is a known causal agent of imposex. Evidence suggests that imposex is elicited by TBT-mediated changes in the biotransformation and disposition of testosterone. To identify potential targets of TBT in gastropod species susceptible to imposex, biotransformation and disposition of testosterone in normal individuals must first be characterized. Nonimposex mud snail, Ilyanassa obsoleta, readily extracted [(14)C]testosterone, added to aqueous media, and converted the testosterone to at least five apolar conjugates designated AP1 through AP5. All were retained by the organisms. No significant amount of [(14)C]testosterone was retained or eliminated as polar metabolites. Following enzymatic hydrolysis of the most abundant metabolite (AP1), free fatty acids and [(14)C]testosterone were liberated. Furthermore, AP1 was produced when homogenized snail tissue was incubated with [(14)C]testosterone and oleoyl coenzyme A or palmitoyl coenzyme A. These results indicate that AP1, which represents over 70% of the testosterone biotransformation products, is a fatty acid ester of testosterone. Apolar metabolites AP2-AP5 might represent testosterone derivatives that are multiply conjugated to fatty acid molecules. Fatty acid conjugates of testosterone have not been previously described in the gastropods. The esterification of testosterone to fatty acids might be a mechanism where by steroid titers are regulated and could represent a target of TBT toxicity.

Acyltransferases↗

PubMed2001

A single serotonergic modulatory cell can mediate reinforcement in the withdrawal network of the terrestrial snail.

A cluster of 40 serotonergic cells in the rostral part of pedal ganglia of the terrestrial snail Helix lucorum was shown previously to participate in the modulation of withdrawal behavior and to be necessary during the acquisition of aversive withdrawal conditioning in intact snails. Local extracellular stimulation of the serotonergic cells paired with a test stimulus elicited a pairing-specific increase (the difference between paired and explicitly unpaired sessions was significant, p <.01) of synaptic responses to test stimulation in the premotor interneurons involved in withdrawal. This result suggested participation of serotonergic cells in mediating the reinforcement in the withdrawal network. Intracellular stimulation of only one identified Pd4 cell from the pedal group of serotonergic neurons paired with a test stimulus also significantly increased (the difference between paired and explicitly unpaired sessions was significant, p <.05) synaptic responses to paired nerve stimulation in same premotor interneurons involved in withdrawal. Morphological investigation of a cluster of pedal serotonergic neurons showed that only the Pd4 cell had branches in the parietal ganglia neuropile where the synapses of premotor withdrawal interneurons and of presynaptic neurons are located. The data suggest that a single serotonergic cell can mediate the reinforcement in the withdrawal network of the terrestrial snail. Patterns of responses of the Pd4 cells to tactile and chemical stimuli conform to the suggestion.

Animals↗

PubMed1994

Calcium cells from snails: response to vitamin D metabolites.

Calcium is one of the most important substances affecting the life of molluscs, and vitamin D was shown to be an essential nutrient for land snails. In an attempt to elucidate the role that vitamin D plays in calcium metabolism of land snails, we have developed a procedure for the isolation of specialized calcium cells from digestive gland of land snails, and were able to culture these cells. The effect of vitamin D metabolites on the intracellular exchangeable calcium and alkaline phosphatase activity was studied. The metabolites tested were 25-hydroxycholecalciferol (25(OH)D3), 24,25-dihydroxycholecalciferol (24,25(OH)2D3), 1,25-dihydroxycholecalciferol (1,25(OH)2D3), and the molluscan metabolite E. 25(OH)D3 was found to be the most active sterol in elevating intracellular exchangeable calcium and the activity of alkaline phosphatase, and the molluscan metabolite E was found to be the most potent sterol in the suppression of alkaline phosphatase activity. 1,25(OH)2D3 was shown to suppress both activities at high concentrations, and 24,25(OH)2D3 increased the intracellular exchangeable calcium only at high concentrations. Thus, 25(OH)D3 which is regarded as a storage form of vitamin D and devoid of biological activity, seems to be biologically active in invertebrates.

24,25-Dihydroxyvitamin D 3↗