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At least 1,207 records · Page 67Linked to original sources
PubMed1994

Defense reaction in the pond snail Planorbis corneus. II. Central pattern generator.

1. In the isolated CNS of the pond snail Planorbis corneus, spontaneous bursts of activity in the motor neurons (MNs) supplying the columellar muscle were occasionally observed. The biphasic pattern of this activity, with a shorter (3-5 s) initial burst and longer (20-40 s) subsequent burst, was similar to that of the motor output during the general ("whole-body") defense reaction. In preparations consisting of the CNS isolated with the columellar muscle or with the lung, spontaneous biphasic contractions of the muscle as well as openings of the pneumostome with a temporal pattern characteristic of the defense reaction were observed. These findings demonstrated that the efferent pattern of the defense reaction in the snail is, to a large extent, produced by a special neuronal mechanism (the central pattern generator, CPG) triggered by the sensory input, rather than generated by ongoing processing of sensory input. The CPG consists of two components responsible for generation of two phases of the defense reaction. A characteristic feature of the CPG is that the magnitude of its response depends in a graded fashion on the strength of the initial stimulus. 2. In the pleural ganglia there are at least two electrically connected interneurons (DRN1s) that play an important role in generation of the first phase of the defense reaction. Processes of the DRN1s form a ring passing through all (except pedal and buccal) ganglia. The DRN1s received an excitatory input when a peripheral nerve was stimulated. They generated action potentials of long (0.2-2 s) duration. The DRN1 from the right ganglion was studied in more detail.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed2006

Repression of prostaglandin dehydrogenase by epidermal growth factor and snail increases prostaglandin E2 and promotes cancer progression.

Prostaglandin E(2) (PGE(2)), a proinflammatory bioactive lipid, promotes cancer progression by modulating proliferation, apoptosis, and angiogenesis. PGE(2) is a downstream product of cyclooxygenase (COX) and is biochemically inactivated by prostaglandin dehydrogenase (PGDH). In the present study, we investigated the mechanisms by which PGDH is down-regulated in cancer. We show that epidermal growth factor (EGF) represses PGDH expression in colorectal cancer cells. EGF receptor (EGFR) signaling induces Snail, which binds conserved E-box elements in the PGDH promoter to repress transcription. Induction of PGE(2) catabolism through inhibition of EGFR signaling blocks cancer growth in vivo. In human colon cancers, elevated Snail expression correlates well with down-regulation of PGDH. These data indicate that PGDH may serve a tumor suppressor function in colorectal cancer and provide a possible COX-2-independent way to target PGE(2) to inhibit cancer progression.

Animals↗
PubMed2005

Effects of a new isoquinolinone derivative on induction of action potential bursts in central snail neuron.

The effects of 7-bromo-1,4-dihydro-2-phenyl-4,4-bis(4-pyridinylmethyl)2H-isoquinolin-3-one dihydrochloride (BDPBI) on induction of action potential bursts were studied pharmacologically on the RP4 central neuron of the giant African snail (Achatina fulica Ferussac). The effects of m-3M3FBS, a phospholipase activator and HTMT, a histamine (H1) receptor agonist, on the neuron were also tested. The RP4 neuron showed spontaneous firing of action potential. Extracellular application of BDPBI (150 micromol/l) reversibly elicited bursts of potential (BoP) on the neuron. m-3M3FBS and HTMT also elicited BoP on the RP4 neuron. The BoP elicited by BDPBI were blocked by U73122 (6 micromol/l), a compound commonly used as a phospholipase C (PLC) inhibitor. Neomycin (3.5 mmol/l), a high-magnesium solution (30 mmol/l), replacing the physiological sodium ion with lithium ion or adding diphenhydramine, chloropheniramine decreased the BoP elicited by BDPBI. The BoP elicited by BDPBI were not inhibited after administration with (1) prazosin, propranolol, atropine, d-tubocurarine, hexamethonium, haloperidol, cimetidine, (2) calcium-free solution, (3) high-potassium (12 mmol/l) solution, and (4) pretreatment with KT-5720. The BoP elicited by HTMT was not inhibited after administration of diphenhydramine or chloropheniramine. Voltage-clamped studies revealed that BDPBI decreased the amplitudes of calcium and steady-state outward currents while it did not alter the amplitude of the fast inward current. No negative slope relationship of the steady-state current voltage relationship was found in BDPBI-treated neurons. It is concluded that BDPBI reversibly elicited BoP in the central snail neuron. The effect was not due to (1) the extracellular calcium ion fluxes, or (2) the activation of cholinergic, adrenergic or histamine receptors. The BDPBI-elicited BoP were dependent on the phospholipase activity in the neuron.

Action Potentials↗
PubMed2004

Schistosomes in the Xe Kong river of Cambodia: the detection of Schistosoma mekongi in a natural population of snails and observations on the intermediate host's distribution.

A natural population of Neotricula aperta (Gastropoda: Pomatiopsidae) in the Xe Kong river of Cambodia was found to be infected with Schistosoma mekongi--apparently the first time this parasite has been found in snails outside the Mekong river. Only 0.14% of the N. aperta collected were found infected. Potential habitats for N. aperta were examined in selected rivers of central and southern Laos and Cambodia, so that the density of N. aperta at each site could be estimated. At survey sites where sufficient snails were collected, the population was also screened for infection with S. mekongi. The geographical distribution of N. aperta outside the Mekong river is shown to be much greater than previously documented; this is in agreement with predictions based on palaeo-geographical models and the evolutionary history and historical biogeography (phylogeography) of the species. The Xe Kong river is identified as a potential source of N. aperta colonists entering Cambodia from Laos. The findings, which indicate that there is a risk of human infection with S. mekongi in areas distant from the Mekong river, have important implications for schistosomiasis-control strategies in the region.

Animals↗
PubMed2005

Shooting darts: co-evolution and counter-adaptation in hermaphroditic snails.

BACKGROUND: Evolutionary conflicts of interest between the sexes often lead to co-evolutionary arms races consisting of repeated arisal of traits advantageous for one sex but harmful to the other sex, and counter-adaptations by the latter. In hermaphrodites, these antagonistic interactions are at least an equally important driving force. Here, we investigate the evolution of one of the most striking examples of sexual conflict in hermaphrodites, the so-called shooting of love-darts in land snails. Stabbing this calcareous dart through the partner's skin ultimately increases paternity. This trait is obviously beneficial for the shooter, but it manipulates sperm storage in the receiver. Hence, an arms race between the love-dart and the spermatophore receiving organs may be expected. RESULTS: We performed a detailed phylogenetic analysis of 28S ribosomal RNA gene sequences from dart-possessing land snail species. Both the Shimodaira-Hasegawa test and Bayesian posterior probabilities rejected a monophyletic origin of most reproductive structures, including the love-dart, indicating that most traits arose repeatedly. Based on the inferred phylogenetic trees, we calculated phylogenetically independent contrasts for the different reproductive traits. Subsequent principal component and correlation analyses demonstrated that these contrasts covary, meaning that correlated evolution of these traits occurred. CONCLUSION: Our study represents the first comprehensive comparative analysis of reproductive organ characteristics in simultaneous hermaphrodites. Moreover, it strongly suggests that co-evolutionary arms races can result from sexual conflict in these organisms and play a key role in the evolution of hermaphroditic mating systems.

Adaptation, Biological↗
PubMed2005

Why do snails have hairs? A Bayesian inference of character evolution.

BACKGROUND: Costly structures need to represent an adaptive advantage in order to be maintained over evolutionary times. Contrary to many other conspicuous shell ornamentations of gastropods, the haired shells of several Stylommatophoran land snails still lack a convincing adaptive explanation. In the present study, we analysed the correlation between the presence/absence of hairs and habitat conditions in the genus Trochulus in a Bayesian framework of character evolution. RESULTS: Haired shells appeared to be the ancestral character state, a feature most probably lost three times independently. These losses were correlated with a shift from humid to dry habitats, indicating an adaptive function of hairs in moist environments. It had been previously hypothesised that these costly protein structures of the outer shell layer facilitate the locomotion in moist habitats. Our experiments, on the contrary, showed an increased adherence of haired shells to wet surfaces. CONCLUSION: We propose the hypothesis that the possession of hairs facilitates the adherence of the snails to their herbaceous food plants during foraging when humidity levels are high. The absence of hairs in some Trochulus species could thus be explained as a loss of the potential adaptive function linked to habitat shifts.

Adaptation, Biological↗
PubMed2004

Apical sensory neurones mediate developmental retardation induced by conspecific environmental stimuli in freshwater pulmonate snails.

Freshwater pond snails Helisoma trivolvis and Lymnaea stagnalis undergo larval development and metamorphosis inside egg capsules. We report that their development is permanently under slight tonic inhibitory influence of the anterior sensory monoaminergic neurones, which are the remnants of the apical sensory organ. Conspecific juvenile snails, when reared under conditions of starvation and crowding, release chemical signals that are detected by these neurones in encapsulated larvae and reversibly suppress larval development, thus providing a link between environmental signals and developmental regulation. Induced retardation starts from the trochophore stage and results in up to twofold prolongation of the larval lifespan. Upon stimulation with the signal, the neurones increase synthesis and release of monoamines [serotonin (5-HT) in Helisoma and dopamine in Lymnaea] that inhibit larval development acting via ergometrine-sensitive internal receptors. Thus, the novel regulatory mechanism in larval development of molluscs is suggested and compared with the phenomenon of dauer larvae formation in the nematode Caenorhabditis elegans.

5-Hydroxytryptophan↗
PubMed1976

A special pattern of the smooth endoplasmic reticulum in the kidney of the snail Cryptomphalus aspersa.

A special structural pattern of the smooth endoplasmic reticulum (SER) has been observed in the kidney of the snail Cryptomphalus aspersa. Two types of cells (clear and dark) cover the foldings of the renal sac; the dark cells are by far the most numerous. A cisterna of SER enveloping the nucleus appears invariably in both types of cells, with no disruptions, or small ones (from 50 to 90 nm) along its profile. The layer of cytoplasm lodged between the external nuclear membrane and this cisterna is found invariably to be from 0-20 to 0-25 mum in width. Glycogen is abundant in the cytoplasm as alpha particles, and also in the nucleus, but as beta particles. It is noteworthy that absolutely no glycogen is present in the layer of cytoplasm lodged between the nuclear membrane and the surrounding SER envelope. Long profiles of SER are also observed closely approaching and parallel to the plasma membrane of the dark cells. Considering the role of SER in glycogen metabolism in the kidney of the snail, the possible function of these cisternae as a support system ofr enzymes involved in the metabolism of glucides is discussed.

Animals↗
PubMed2000

Processes contributing to metabolic depression in hepatopancreas cells from the snail Helix aspersa.

Cells isolated from the hepatopancreas of the land snail Helix aspersa strongly depress respiration both immediately in response to lowered P(O2) (oxygen conformation) and, in the longer term, during aestivation. These phenomena were analysed by dividing cellular respiration into non-mitochondrial and mitochondrial respiration using the mitochondrial poisons myxothiazol, antimycin and azide. Non-mitochondrial respiration accounted for a surprisingly large proportion, 65+/-5 %, of cellular respiration in control cells at 70 % air saturation. Non-mitochondrial respiration decreased substantially as oxygen tension was lowered, but mitochondrial respiration did not, and the oxygen-conforming behaviour of the cells was due entirely to the oxygen-dependence of non-mitochondrial oxygen consumption. Non-mitochondrial respiration was still responsible for 45+/-2 % of cellular respiration at physiological oxygen tension. Mitochondrial respiration was further subdivided into respiration used to drive ATP turnover and respiration used to drive futile proton cycling across the mitochondrial inner membrane using the ATP synthase inhibitor oligomycin. At physiological oxygen tensions, 34+/-5 % of cellular respiration was used to drive ATP turnover and 22+/-4 % was used to drive proton cycling, echoing the metabolic inefficiency previously observed in liver cells from mammals, reptiles and amphibians. The respiration rate of hepatopancreas cells from aestivating snails was only 37 % of the control value. This was caused by proportional decreases in non-mitochondrial and mitochondrial respiration and in respiration to drive ATP turnover and to drive proton cycling. Thus, the fraction of cellular respiration devoted to different processes remained constant and the cellular energy balance was preserved in the hypometabolic state.

Adenosine Triphosphate↗
PubMed2002

Analysis of monoamines, adenosine and GABA in tissues of the land snail Helix lucorum and lizard Agama stellio stellio during hibernation.

The aim of the present study was to determine the levels of monoamines, GABA and adenosine in the brain, heart and haemolymph of the land snail Helix lucorum and in the brain, heart and blood of lizard Agama stellio stellio during long-term hibernation. We measured levels of the monoamines serotonin (5-HT) and its main metabolite 5-hydroxyindole-3-acetic acid (5-HIAA), dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA), norepinephrine (NE) and epinephrine (E). The most abundant amines detected in the brain and heart of active H. lucorum were 5-HT and DA. Of the metabolites examined only 5-HIAA was found in the brain. NE was found at very low levels but only in the brain, while E was not detected in the brain and heart. The levels of 5-HT and 5-HIAA increased in the brain and heart of H. lucorum within the first months of hibernation, showing a significant decrease thereafter. The levels of DA did not change during hibernation. The results indicated that 5-HT might be involved in preparing snails for entry into hibernation. GABA was only found in the brain of H. lucorum, and the levels were low; these levels remained during hibernation. Adenosine was present in brain and heart of H. lucorum, and during hibernation, the level of adenosine decreased significantly in the brain but remained steady in the heart. The monoamines 5-HT, DA and NE were present in the brain of active lizards A. stellio stellio, whereas E was found only at very low levels. Moreover, the metabolites 5-HIAA, DOPAC and HVA were detected in the brain of active lizards. The monoamines 5-HT, DA, NE and E were also detected in the heart and blood of active lizards. During hibernation the levels of these four monoamines were decreased significantly in the brain and heart of A. stellio stellio. In contrast, the levels of E increased in the heart and blood of hibernating lizards. Adenosine was detected in both heart and brain of active lizards, but hibernation caused a marked decrease in its levels at both tissues. GABA was found at higher levels than monoamines and adenosine in the brain of active lizards, and hibernation caused a significant increase in its levels, indicating an important role of GABA in inhibition of neuronal activity in hibernating lizards.

Adenosine↗
PubMed2005

Evaluation of snail mucin motifs as rectal absorption enhancer for insulin in non-diabetic rat models.

The use of snail mucin motifs as rectal absorption enhancer for insulin has been evaluated. The mucin motifs were extracted from the giant African snail Archachatina marginata by differential precipitation with acetone. The mucin motifs were found to have a molecular weight of 5780 Da and an isoelectric point of 3.4. At the concentrations evaluated, the mucin exhibited rectal absorption enhancing property for the administration of insulin in rats. The % basal blood glucose level of the rats that received the batch of suppositories containing no mucin were consistently above 100% except at the ninetieth minute when it came down slightly to 97.2%. Rats dosed with the batch containing 7%w/w suppositories showed the greatest blood glucose reduction with mean % basal blood glucose concentration of 61.2%. Batches of the suppository containing 5% and 7% mucin showed more marked and consistent lowering in blood glucose concentration than the other batches containing lower amounts of the rectal absorption enhancer. The batch with 7% mucin reduced the basal glucose level to 44% within 2 h of administration of the glycero-gelatin suppository loaded mucin.

Administration, Rectal↗
PubMed1994

Bleeding of pulmonate snails.

A technique for removing blood (haemolymph) by syringe from African land snails (Achatina spp.) is described. The method avoids the need for shell perforation or incision of soft tissues and appears to have few adverse effects on the snail.

Animals↗
PubMed2004

A signaling pathway involving TGF-beta2 and snail in hair follicle morphogenesis.

In a common theme of organogenesis, certain cells within a multipotent epithelial sheet exchange signals with their neighbors and develop into a bud structure. Using hair bud morphogenesis as a paradigm, we employed mutant mouse models and cultured keratinocytes to dissect the contributions of multiple extracellular cues in orchestrating adhesion dynamics and proliferation to shape the cluster of cells involved. We found that transforming growth factor beta2 signaling is necessary to transiently induce the transcription factor Snail and activate the Ras-mitogen-activated protein kinase (MAPK) pathway in the bud. In the epidermis, Snail misexpression leads to hyperproliferation and a reduction in intercellular adhesion. When E-cadherin is transcriptionally down-regulated, associated adhesion proteins with dual functions in signaling are released from cell-cell contacts, a process which we demonstrate leads to Ras-MAPK activation. These studies provide insights into how multipotent cells within a sheet are stimulated to undergo transcriptional changes that result in proliferation, junctional remodeling, and bud formation. This novel signaling pathway further weaves together the web of different morphogens and downstream transcriptional events that guide hair bud formation within the developing skin.

Animals↗
PubMed2025

Complexity of schistosome vector bulinine snails in Kenya: Insights from nuclear genome size variation, complete mitochondrial genome sequence, and morphometric analysis.

Investigations of nuclear genome size, complete mitochondrial genome (mitogenome) sequence, and morphometrics were conducted on specimens of Bulinus snails (Gastropoda: Planorbidae) collected from 14 locations across the east coast, central Kenya, and western Kenya around the Lake Victoria region (November 2013 and January 2024). Flow cytometry measurements of DNA content (C-value) revealed unexpected variation in nuclear genome size, with diploid Bulinus africanus and B. forskalii species groups showing C-values ranging from 0.76 to 1.98 pg, while tetraploid B. truncatus had a C-value of 1.82 pg. Additionally, C-values for six B. globosus specimens from different localities ranged from 1.43 to 1.98 pg. These findings suggest that bulinine snails, particularly the B. africanus species group, have undergone genome expansion, whole genome duplication (polyploidization), or both, which have not been previously recognized. Next-generation sequencing was performed to determine and annotate 14 complete mitogenome sequences. Despite the well-conserved arrangement of protein-coding genes, two versions of mtDNA genome structure, distinguished by the tRNA-D (Asp) location, were found, designated as DCF (Asp-Cys-Phe) type (in the B. forskalii group and the B. truncatus/tropicus complex) and CF (Cys-Phe) type (in the B. africanus group). Phylogenetic analyses based on complete mtDNA sequences of bulinines from Kenya, along with cytochrome c oxidase subunit I (COX1) sequences from various localities across Africa, contributed to resolving species identities and provided further support for the presence of multiple or cryptic species in the taxon B. globosus. A landmark-based morphometric analysis was ineffective in distinguishing these species. This study reveals unexpected nuclear genome size variation, provides new mitogenome sequences, and highlights the limitations of morphological analysis. It offers valuable insights into the cytogenetics, polyploidy, genomics, taxonomy, and evolution of bulinines, which serve as intermediate hosts for schistosomes responsible for human urogenital schistosomiasis and intestinal schistosomiasis in domestic and wild mammals.

Animals↗
PubMed2004

Evidence for genetic control of adult weight plasticity in the snail Helix aspersa.

Phenotypic plasticity and canalization are important topics in quantitative genetics and evolution. Both concepts are related to environmental sensitivity. The latter can be modeled using a model with genetically structured environmental variance. This work reports the results of a genetic analysis of adult weight in the snail Helix aspersa. Several models of heterogeneous variance are fitted using a Bayesian, MCMC approach. Exploratory analyses using posterior predictive model checking and model comparisons based on the deviance information criterion favor a model postulating a genetically structured heterogeneous environmental variance. Our analysis provides a strong indication of a positive genetic correlation between additive genetic values affecting the mean and those affecting environmental variation of adult body weight. The possibility of manipulating environmental variance by selection is illustrated numerically using estimates of parameters derived from the snail data set.

Animals↗
PubMed2005

Mutations in snail family genes enhance craniosynostosis of Twist1 haplo-insufficient mice: implications for Saethre-Chotzen Syndrome.

In Drosophila, mutations in the Twist gene interact with mutations in the Snail gene. We show that the mouse Twist1 mutation interacts with Snai1 and Snai2 mutations to enhance aberrant cranial suture fusion, demonstrating that genetic interactions between genes of the Twist and Snail families have been conserved during evolution.

Acrocephalosyndactylia↗
PubMed2004

Functional morphology of the salivary gland of the snail, Helix pomatia: a histochemical and immunocytochemical study.

Functional morphology of Helix pomatia salivary gland cells was studied at light microscopic level by using different histochemical methods. Three cell types could be demonstrated in the salivary gland: mucocytes, granular and vacuolated cells. The distribution and the number of the different cell types were different in active and inactive snails. In active feeding animals, dilatated interlobular salivary ducts were observed, which were never present in inactive ones. In active animals an additional cell type, the cystic cell could also be observed. Periodic acid Schiff staining revealed both mucuos and serous elements in the salivary gland. Furthermore, hematoxyline-eosin staining indicated the occurrence of a cell layer with high mitotic activity in the acini. Applying immunohistochemical methods with monoclonal mouse anti-human Ki-67 clone, B56 and polyclonal rabbit anti-human Ki-67 antibodies, we also were able to demonstrate the occurrence of dividing cells in the salivary gland. Analysis of 1-2 microm semi-thin Araldite sections stained with toluidine-blue showed that the saliva can be released, in addition to possible exocytosis, by the lysis of cystic cells. Using an apoptosis kit, we could also establish that this process was due to rather an apoptotic than a necrotic mechanism. In the salivary gland of active snails, where an intensive salivation takes place, significantly more apoptotic cells occurred, if compared to that of inactive animals. It is suggested that programmed cell death may also be involved in the saliva release.

Animals↗
PubMedDate not supplied

[Molluscacide activity of piquerol A isolated from Piqueria trinervia (Compositae) on 8 species of pulmonate snails].

In laboratory trials an aqueous solution of Piquerol A from Piqueria trinervia, collected in several regions of Mexico, showed a molluscicide action on the adults of eight different pulmonates snails species: Fossaria (Fossaria) humilis, F. (Bakerilymnaea) sp., Pseudosuccinea columella and Stagnicola attenuata from Mexico; F. (B.) cubensis and Physa cubensis from Cuba; P. columella and Biomphalaria glabrata from Brazil; B. glabrata from Puerto Rico; and S. elodes from U.S.A. The solution was tested at 50, 25 and 5 ppm concentration, for two periods of 6 and 24 hours, at room temperature (20-22 degrees C). A 100% mortality was obtained for all species at 50 ppm concentration after 6 hours of exposure; the same percentage at 25 ppm after 24 hours; and 60 to 100% mortality at 5 ppm concentration during 24 hours of exposure. No recovery was observed among any of the treated snails. Piquerol A is a sesquiterpene with low stability in nature and has previously only been tested as an insecticide and as an inhibitor of metabolism in cell cultures: no field trails have been made on its toxicity to other aquatic fauna as yet, but it is believed Piquerol A could be an excellent molluscicide for use in areas where focal transmission of schistosomiasis and fascioliasis are taking place. This is the first time experiments on molluscicides have been carried out in Mexico.

Animals↗