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PubMed1998

Postembryonic neurogenesis in the procerebrum of the terrestrial snail, Helix lucorum L.

Neuronogenesis during posthatching development of the procerebrum of the terrestrial snail Helix lucorum was analyzed using bromodeoxyuridine immunohistochemistry to label proliferating cells. Comparison of the distribution of labeled cells in a series of animals which differed in age at the time of incubation with bromodeoxyuridine, in survival time after incubation, and in age at sacrifice reveals a clear pattern and developmental sequence in neuron origin. First, the proliferating cells are located only at the apical portion of the procerebrum. Second, cells which are produced at any particular age remain, for the most part, confined to a single layer in the procerebrum. Third, as development proceeds, each layer of previously produced neurons is displaced toward the basal part of the procerebrum by the production of additional neurons. Our results suggest that the vast majority of the neurons (probably about 70-80%) of the snail procerebrum are produced during the first 1-2 months of posthatching development.

Animals↗
PubMed1996

Behavioural evidence that magnetic field effects in the land snail, Cepaea nemoralis, might not depend on magnetite or induced electric currents.

Although extremely low frequency (ELF) magnetic fields (<300 Hz) appear to exert a variety of biological effects, the magnetic field sensing/transduction mechanism(s) remains to be established. Here, using the inhibitory effects of magnetic fields on endogenous opioid peptide-mediated "analgaesic" response of the land snail, Cepaea nemoralis, we addressed the mechanism(s) of action of ELF magnetic fields. Indirect mechanisms involving both induced electric fields and direct magnetic field detection mechanisms (e.g., magnetite, parametric resonance) were evaluated. Snails were exposed to a static magnetic field (B(DC) = 78 +/- 1 mu T) and to a 60 Hz magnetic field (B(AC) = 299 +/- 1 mu T peak) with the angle between the static and 60 Hz magnetic fields varied in eight steps between 0 degrees and 90 degrees. At 0 degrees and 90 degrees, the magnetic field reduced opioid-induced analgaesia by approximately 20 percent, and this inhibition was increased to a maximum of 50 percent when the angle was between 50 degrees and 70 degrees. Because B(AC) was fixed in amplitude, direction, and frequency, any induced electric currents would be constant independent of the B(AC)/B(DC) angle. Also, an energy transduction mechanism involving magnetite should show greatest sensitivity at 90 degrees. Therefore, the energy transduction mechanism probably does not involve induced electric currents or magnetite. Rather, our results suggest a direct magnetic field detection mechanism consistent with the parametric resonance model proposed by Lednev.

Animals↗
PubMedDate not supplied

Dyakia bioluminescence--1. Bioluminescence and fluorescence spectra of the land snail, D. striata.

The luminescent land snail Dyakia striata displayed a bioluminescence spectrum with a maximum wavelength of 515 nm. A green fluorescent substance extracted from the photogenic organ of an adult snail had a similar wavelength maximum but its fluorescence spectrum differed from that of flavin chromophore substances involved in light emission in some other luminescent organisms.

Animals↗
PubMed1989

Interganglionic dendrites constitute an output pathway from the procerebrum of the snail Achatina fulica.

The procerebrum is an olfactory processing region that occupies approximately one-third of the total brain area in pulmonate gastropod molluscs. It has many unusual features, including a development separate from the rest of the brain and the absence of axons belonging to its intrinsic neurons. We have investigated the input and output pathways of the procerebrum in the terrestrial snail Achatina fulica by using hexamminecobalt chloride as a selective label. Both the tentacle nerve and the cerebropedal connective nerve contribute to a fine neural plexus that is distributed throughout the neuropile region of the procerebrum. The fibers from the tentacle nerve are predominantly presynaptic, whereas those from the cerebropedal connective are predominantly postsynaptic. The postsynaptic fibers (dendrites) were traced to two groups of nerve cells (total number, 20-25) near the ventral surface of the ipsilateral pedal ganglion. No evidence was obtained for any other numerically significant output pathway from the procerebrum. Since locomotion is known to be controlled by the pedal ganglion, these results provide an anatomical substrate for the strong influence of olfaction on locomotor behavior in snails. The pathway is unusual in that the dendrites are interganglionic and can be as long as 5 mm.

Animals↗
PubMed2002

Synthesis, distribution, and levels of an egg lipoprotein from the apple snail Pomacea canaliculata (Mollusca: Gastropoda).

The site of synthesis of mollusc lipoproteins is hitherto unknown and was investigated for perivitellin 2 (PV2), an egg lipoprotein found in the freshwater snail Pomacea canaliculata. Tissues (albumen gland, gonad-digestive gland complex, and muscle) from vitellogenic females were incubated in vitro with 14C-leucine at 25 degrees C for 12 hr. At the end of incubation, soluble proteins from tissue homogenates and medium were analyzed for de novo protein synthesis by electrophoresis and HPLC, and radiolabeled proteins were quantified by liquid scintillation. Two albumen gland radiolabeled proteins (67 and 31 kDa) co-migrated with the subunits of PV2, and they represented 6.0% of the total labeled protein in that tissue. Western blot analysis confirmed the presence of PV2 only in the albumen gland. In vivo experiments where adult females were injected with 3H-leucine revealed that PV2 was not present in hemolymph. ELISA analysis in all tissues of the snail confirmed the PV2 presence only in the albumen gland and developing eggs with levels of 26 and 98 mg/g protein, respectively. Therefore, the albumen gland is the only site for PV2 synthesis, and no extra-gland synthesis, circulation, or accumulation could be found. PV2 subunits were further characterized analyzing N-terminal sequences which showed no homology with other proteins.

Animals↗
PubMed1979

Enzyme changes accompanying thermal acclimation in two species of pleurocerid snails.

Goniobasis cahawbensis is a stream snail that experiences an annual temperature cycle. G. cochliaris is limited in distribution to springs, and their immediate vicinities, which are characterized by nearly constant annual temperatures. The present study sought to determine whether temperature dependent biochemical differences exist that might account for the differential distribution of these congeneric pleurocerid snails. Eight enzymes were examined following acclimation to 10 degrees, 17 degrees and 24 degrees C. No significant temperature dependent qualitative differences in enzyme phenotypes were demonstrable in either species by starch-gel electrophoresis for malate dehydrogenase, glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase, phosphoglucomutase, superoxide dismutase and acetyl and butyryl esterases. Significant quantitative differences were observed in three of these enzymes. G. cahawbensis cytosol malate dehydrogenase activity increased significantly with increasing acclimation temperature, while G. cochliaris malate dehydrogenase activity remained unchanged. The activities of glucose-6-phosphate dehydrogenase did not differ significantly between acclimation temperatures for either species; however, the overall activity of both enzymes was significantly higher for G. cochliaris. Appreciable levels of LDH activity were not demonstrable by electrophoresis or enzymatic assay.

Adaptation, Physiological↗
PubMed1988

Eye regeneration in the mystery snail.

Mystery snails (Family Ampullariidae) are aquatic prosobranchs which possess structurally complex eyes at the tip of a cephalic eyestalk. No other sensory organs are found in association with this stalk. These snails possess the ability to regenerate the eye completely after amputation through the mid-eyestalk. Amputation induces gross changes in the cellular character of the entire eyestalk; in particular, an invagination of integumentary epithelium at the apex of the eyestalk stump produces a shallow cleft or "eyecup." Differentiation of all components of the eye apparently occurs by transdetermination of these epithelial cells. Retinal differentiation and the appearance of a new lens is observed as soon as 14 days postamputation. Complete eyes (by external observation), although smaller than the originals, have regenerated by 25 days postamputation. We compare this regeneration to the reconstruction of other animal tissues, in particular the regeneration of amphibian limbs.

Animals↗
PubMed2004

Characterization of the major egg glycolipoproteins from the perivitellin fluid of the apple snail Pomacea canaliculata.

Ovorubin and PV2 are the major lipoglycocarotenoproteins present in the perivitellus of the freshwater snail eggs of Pomacea canaliculata, a rapidly expanding rice field pest. We have previously characterized these two particles regarding their lipid and protein compositions, their synthesis and tissular distribution, and their contributions of energy and structural precursors for the developing embryo. In the present study, we have characterized the glycosidic moieties associated to these perivitellines. Both proteins were isolated from egg homogenates by ultracentrifugation, and high performance liquid chromatography (HPLC) using anionic exchange and size exclusion columns. Total carbohydrates accounted for 17.8% and 2.5% (w/w) of the apparent molecular mass of ovorubin and PV2, respectively. Analysis by size exclusion chromatography showed that the amount of O-linked oligosaccharides is higher than that of the N-linked species (59% and 67% w/w of total carbohydrates of ovorubin and PV2, respectively). Glycosylation patterns were determined by a set of biotinilated lectins onto blotted purified proteins. Lectin affinities confirmed the presence of aspargine-linked carbohydrates, probably of hybrid and high mannose types. Jacaline affinity suggested the presence of O-linked residues derived from the T-antigen. Total carbohydrate composition determined by gas liquid chromatography (GLC) showed that mannose was the major monosaccharide in both perivitellins followed by GlcNAc and Gal in ovorubin, and Gal and GlcNAc in PV2. Only one fatty acid (22:1 n-9) accounted for 46% and 56% of the fatty acids present in ovorubin and PV2, respectively. Carbohydrate role on these reserve proteins during embryogenesis of the apple snail is discussed.

Animals↗
PubMed1980

Investigation of burst generation by the electrically coupled cyberchron network in the snail Helisoma using a single-electrode voltage clamp.

This paper describes the results of investigating burst generation by the cyberchron network in the snail Helisoma. The cyberchron network is composed of aproximately 20 electrically coupled neurons and controls the feeding behavior of the snail. The electrical coupling between network members has made it particularly difficult to distinguish between the importance and involvement of single-cell and network properties in burst generation by this system. The present investigations utilized the new single-electrode voltage clamp to examine the membrane properties and network interactions of the cyberchron neurons: (1) A slow outward current is activated by moderately large depolarizing commands (-40 to 0 mV) and does not undergo inactivation decay (i.e., decline in magnitude) during a command potential step maintained for 10 sec or more. The lack of inactivation of the outward current in cyberchron neurons appears to be due to the dominating role of a Ca-dependent K current. (2) There are two functionally distinct classes of cyberchrons--current generator cyberchrons and follower cyberchrons. (3) Primary current generator cyberchrons have membrane properties similar to endogenous bursting neurons (e.g., persistent inward Ca current and negative resistance region in I-V plot) and appear to provide the main driving and timing current for the rest of the network. (4) The vast majority of cyberchrons are secondary current generator cyberchrons with membrane properties which exhibit inward-going rectification and appear to burst as a result of regenerative excitation with one another and the primary current generator cyberchrons. (5) The second class of cyberchrons are driven by the electrical synaptic input from the current generator cyberchrons, do not exhibit inward-going rectification, and are called follower cyberchrons. (6) Burst termination is due to activation of a slow outward tail current in most cyberchrons during the burst (probably Ca-activated K current) which causes a hyperpolarization in individual cyberchrons, terminating the burst. (7) Decay of the outward tail current causes the cyberchrons to depolarize, which activates the persistent inward Ca current in the primary current generator cyberchrons, starting the burst cycle anew.

Action Potentials↗
PubMed1983

Neuronal elements in snail tentacles as revealed by horseradish peroxidase backfilling.

The snail tentacle ganglion is a prominent structure that innervates an epithelial pad sensitive to wind and odors. Its neural composition, and that of the sensory pad, was studied in the terrestrial snail Achatina fulica by applying horseradish peroxidase to the distal end of the cut tentactle nerve. Five types of neurons were labelled by the procedure: receptors, located in the subepithelial region; three kinds of interneurons, located in the ganglion and its digitlike extensions; and a bipolar neuron, located in the dermo-muscular wall of the tentacle. In contrast to earlier descriptions based on silver stains, the present results demonstrate the presence of neurons of large size (soma diameters up to 46 microns). Also, contrary to earlier interpretations, the results indicate that all five identified cell types send axons directly to the CNS.

Animals↗
PubMed1985

Behavioral recovery associated with central nervous system regeneration in the snail Melampus.

The pulmonate snail Melampus bidentatus regenerates central nervous tracts following commissurotomy, connective transection, and cerebral ganglion ablation. Our goal was to determine whether or not neural regrowth within the central nervous system restored behaviors disrupted by lesions. One behavior that is disrupted by commissurotomy is retraction of facial structures that are contralateral to a stimulated facial region, a response that normally accompanies the ipsilateral retraction. Tentacle withdrawal on the side contralateral to stimulation reappeared on a timescale that was correlated with growth of a commissural link (8-19 days post-lesion). Electrophysiological recordings from a labial nerve pathway that has a contralateral component similar to the contralateral tentacle response showed that development or strengthening of an alternative pathway could also mediate contralateral responses. Thus, a major conclusion of this study was that both tract regeneration and changes in existing CNS pathways can underlie recovery. The percentage (approx. 75%) of snails that regenerate the cerebral commissure and show behavioral recovery is established early in the period following commissure transection. Behavioral recovery and anatomical evidence of regeneration were also correlated in the other two operations: single cerebral ganglion removal and unilateral cerebropleural and cerebropedal connective transection. We conclude that Melampus is able to regenerate neuronal connectivity that can restore normal behavior.

Animals↗
PubMed2004

Molluscicidal effects of neem (Azadirachta indica) extracts on edible tropical land snails.

The effects of 350, 500 and 700 mg kg(-1) of crude extracts of neem, Azadirachta indica A Juss, on edible tropical land snails Archachatina marginata and Limicolaria aurora (Jay) were determined and compared with control using pawpaw, Carica papaya L as bait. Responses were measured through normal feeding, cessation of food intake, cessation of crawling, mucus secretion, lack of response to mechanical stimuli (mortality) and decomposition. Results showed no effects on the controls or snails exposed to neem seed oil extract. Crude extracts of bark, root and leaf of neem at 500 and 700 mg kg(-1) produced mortality after exposure for 48 h for L aurora and 72 h for A marginata.

Animals↗
PubMed2006

Novel alpha-conotoxins identified by gene sequencing from cone snails native to Hainan, and their sequence diversity.

Conotoxins (CTX) from the venom of marine cone snails (genus Conus) represent large families of proteins, which show a similar precursor organization with surprisingly conserved signal sequence of the precursor peptides, but highly diverse pharmacological activities. By using the conserved sequences found within the genes that encode the alpha-conotoxin precursors, a technique based on RT-PCR was used to identify, respectively, two novel peptides (LiC22, LeD2) from the two worm-hunting Conus species Conus lividus, and Conus litteratus, and one novel peptide (TeA21) from the snail-hunting Conus species Conus textile, all native to Hainan in China. The three peptides share an alpha4/7 subfamily alpha-conotoxins common cysteine pattern (CCX(4)CX(7)C, two disulfide bonds), which are competitive antagonists of nicotinic acetylcholine receptor (nAChRs). The cDNA of LiC22N encodes a precursor of 40 residues, including a propeptide of 19 residues and a mature peptide of 21 residues. The cDNA of LeD2N encodes a precursor of 41 residues, including a propeptide of 21 residues and a mature peptide of 16 residues with three additional Gly residues. The cDNA of TeA21N encodes a precursor of 38 residues, including a propeptide of 20 residues and a mature peptide of 17 residues with an additional residue Gly. The additional residue Gly of LeD2N and TeA21N is a prerequisite for the amidation of the preceding C-terminal Cys. All three sequences are processed at the common signal site -X-Arg- immediately before the mature peptide sequences. The properties of the alpha4/7 conotoxins known so far were discussed in detail. Phylogenetic analysis of the new conotoxins in the present study and the published homologue of alpha4/7 conotoxins from the other Conus species were performed systematically. Patterns of sequence divergence for the three regions of signal, proregion, and mature peptides, both nucleotide acids and residue substitutions in DNA and peptide levels, as well as Cys codon usage were analyzed, which suggest how these separate branches originated. Percent identities of the DNA and amino acid sequences of the signal region exhibited high conservation, whereas the sequences of the mature peptides ranged from almost identical to highly divergent between inter- and intra-species. Notably, the diversity of the proregion was also high, with an intermediate percentage of divergence between that observed in the signal and in the toxin regions. The data presented are new and are of importance, and should attract the interest of researchers in this field. The elucidated cDNAs of these toxins will facilitate a better understanding of the relationship of their structure and function, as well as the process of their evolutionary relationships.

Amino Acid Sequence↗
PubMed1998

Lineage-specific regulation of the Ciona snail gene in the embryonic mesoderm and neuroectoderm.

The snail gene encodes a highly conserved, zinc-finger transcription factor that has been implicated in the specification of mesodermal and neuronal tissues in a variety of organisms. In the ascidian, Ciona intestinalis, snail (Ci-sna) is expressed at the 32-cell stage in derivatives of the B4.1 blastomere, including B6.2, B6.4, and B7.5, which give rise to the primary-lineage tail muscles of the tadpole. At later stages, Ci-sna is expressed in the lineages that will form the secondary tail muscle, the lateral ependymal cells of the spinal cord, and the dorsal cells of the cerebral vesicle. A minimal, 504-bp cis-regulatory sequence from the Ci-sna promoter region, the B4.1 enhancer, is shown to direct the expression of heterologous promoters in primary-lineage muscles. Furthermore, evidence is presented that cis-regulatory elements necessary for expression in both the secondary muscle and neuronal lineages are separate from the B4.1 enhancer. We discuss the possibility that the classical muscle determinant present in ascidian eggs may correspond to bHLH activators, which bind to specific E-box sequences contained in the B4.1 enhancer.

Animals↗
PubMed1996

Effect of Zn, Cu, Pb, and Cd on fitness in snails (Helix aspersa).

Juveniles and adults of the Brown garden snail (Helix aspersa Müll.) were fed on an artificial diet contaminated with Zn (ca. 40-12,000 micrograms.g-1 dry wt), Cu (ca. 9-1600 micrograms.g-1 dry wt), pb (ca. 0.4-12,700 micrograms.g-1 dry wt), Cd (ca. 0.16-145 micrograms.g-1 dry wt), and all four metals mixed together for 120 days. Significant negative exponential regressions of food consumption and fecundity on concentrations were found for all treatments. Growth rate was affected significantly only by Zn and mixed treatments. The calculated EC20(consumption) values for juveniles were (in microgram.g1): Zn, 855; Cu, 248; Pb, 5290; Cd, 60; and for adults: Zn, 1240; Cu, 275; Pb, 3120; Cd, 147. In mixed treatment EC20(consumption) values were substantially lower indicating the additive effect of pollution with these four metals. EC20(consumption) for Zn in mixed treatment was 329 micrograms.g-1 for juveniles and 661 micrograms.g-1 for adults. The following EC20 values were estimated for fecundity (in micrograms.g-1): Zn, 1740; Cu, 533; Pb, 6140; Cd, 120; Zn in mixed treatment, 2210. The relative toxicities of the four metals were compared with their ratios in contaminated field sites. Comparing Zn and Cd, for example, even though Zn is ca. 13-24 times less toxic than Cd, it is usually present in plants and forest litter in concentrations ca. 100 times greater than those of Cd. Thus, of these two metals, Zn appeared to be potentially the most important pollutant in ecologically relevant situations. No effect of any treatment on mortality was found during the 4-month experiment. The calculated scenarios of population dynamics under the stress of chronic pollution with mixtures of the four metals revealed that the delayed reproduction due to estivation of snails may be the main cause of population decline at high metal concentrations in food. However, at concentrations at and below ca. 1000 micrograms Zn.g-1 in food, if the reproduction is not delayed the population may persist for a long time (0.25 control number after 50 years).

Aging↗
PubMed1997

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.

Animals↗
PubMed2000

Relationship between toxicokinetics of carbaryl and effect on acetylcholinesterase activity in Pomacea patula snail.

The 96-h LC(50) value of carbaryl was 14.6 microg/mL for the snail Pomacea patula. Organisms were exposed for 72 h to a low sublethal concentration (0.1 of LC(50)) using a semistatic contamination system; bioconcentration and elimination experiments were performed evaluating simultaneously acetylcholinesterase (ACHase) activity. The inhibition of the digestive gland ACHase reached 76% when the carbaryl concentration in tissue was 3.2 microg/g. The increased enzyme inhibition was observed concomitantly with the bioconcentration of carbaryl until 7 h. ACHase inhibition was linearly dependent on the uptake and bioconcentration of carbaryl (r(2)=0.87). The transfer of snails to carbaryl-free water after 72 h of exposure was followed by rapid monophasic elimination with a half-life of 1.0 h. However, ACHase activity levels never returned to control values. These results revealed that the bioconcentration might play a critical role in contributing to the toxicity of carbaryl.

Animals↗
PubMed1996

Deterministic chaos in mathematical model of pacemaker activity in bursting neurons of snail, Helix pomatia.

Chaotic regimes in a mathematical model of pacemaker activity in the bursting neurons of a snail Helix pomatia, have been investigated. The model includes a slow-wave generating mechanism, a spike-generating mechanism, an inward Ca current, intracellular Ca ions, [Ca2+]in, their fast buffering and uptake by intracellular Ca stores, and a [Ca2+]in-inhibited Ca current. Chemosensitive voltage-activated conductance, gB*, responsible for termination of the spike burst, and chemosensitive sodium conductance, gNa*, responsible for the depolarization phase of the slow-wave, were used as control parameters. These conductances in intact snail bursting neuron are regulated by neuropeptides. Time courses of the membrane potential and [Ca2+]in were employed to analyse different regimes in the model. Histograms of interspike intervals, autocorrelograms, spectral characteristics, one-dimensional return maps, phase plane trajectories, positive Lyapunov exponent and especially cascades of period-doubling bifurcations demonstrate that approaches to chaos were generated. The bifurcation diagram as a function of gB* and the ([Ca2+]in-V) phase diagram of initial conditions reveal fractal features. It has been observed that a short-lasting depolarizing current of elevation of [Ca2+]in may evoke transformation of chaotic activity into a regular bursting one. These kinds of transitions do not require any changes in the parameters of the model. The results demonstrate that chaotic regimes of neuronal activity modulated by neuropeptides may play a relevant role in information processing and storage at the level of a single neuron.

Animals↗