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PubMed2000

Mitochondrial phylogeny of extant Hawaiian tree snails (Achatinellinae).

Hawaiian tree snails in the endemic subfamily Achatinellinae display a staggering variety of shell colors and banding patterns. Despite numerous attempts to classify this morphological variation, a conclusive phylogeny has not been proposed. To improve conservation efforts, we sought to better understand the species identities and phylogenetic relationships among the extant species of Achatinella and Partulina using partial mitochondrial 16S ribosomal DNA sequences. The reconstructed phylogeny showed a high degree of support for more recent branches, but gave little support to deeper nodes. The most confident branches challenge previous systematic arrangements of these snails, grouping species that previously had been placed into different subgenera. High levels of sequence divergence within some species may reflect the long-term isolation of subpopulations. Rapid rates of sequence divergence may have saturated base substitutions and contributed to the lack of resolution of higher-order relationships. We did not find support for the monophyly of the Achatinella species, nor thus for a single colonization of Oahu from Maui Nui.

Animals↗
PubMed1976

Water regulation in aestivating snails. Ultrastructural and analytical evidence for an unusual cellular phenomenon.

Aestivating snails form abundant lamellate vesicles in the cells of the mantle collar, an epithelium known to regulate the rate at which water is lost from its surface. Since lamellate vesicles are much reduced in hydrated mantle tissue of recently stimulated animals it is tentatively concluded that the vesicles, and their contents, form a barrier to water movement within these cells. X-ray microanalysis of unfixed thin sections shows that there is a concentration gradient of ions within these cells in aestivating animals which is not present in stimulated snails.

Adaptation, Physiological↗
PubMed1992

Albumen gland of the snail Achatina fulica is the site for synthesis of AchatininH, a sialic acid binding lectin.

A sialic acid binding lectin, AchatininH was purified from the hemolymph of Achatina fulica snail. To identify the site of synthesis of AchatininH, in vitro incubation studies in presence of labelled amino acid precursor were performed. Different organs from the snail were sliced and incubated in methionine-deficient Eagle's minimum essential medium containing [35S]-methionine at 25 degrees C for 5 h. After termination of incubation, tissues were homogenized, centrifuged and the de novo synthesized protein was immunoprecipitated with specific AchatininH antibody, followed by protein-A. The precipitated antigen-antibody complex was analysed by SDS-PAGE. Data obtained from native gel electrophoresis and SDS-PAGE radioautographic analysis indicates that AchatininH is synthesized in the albumen gland.

Animals↗
PubMed1991

DARPP-32 like protein in specific snail (Helix aspersa) neurones.

Monoclonal antibodies to DARPP-32 recognise an antigen which is present in specific neurones in the snail (Helix aspersa). Consecutive sections 10-microns-thick processed for the localisation of DARPP-32 and tyrosine-hydroxylase immunoreactivity did not show a coexistence in any neuronal structures. DARPP-32 positive cells were, however, often morphologically closely associated with tyrosine-hydroxylase positive cells, implying a functional relationship consistent with the proposed role of DARPP-32. Immunochemical analysis of the DARPP-32 immunoreactive material in the snail nervous system shows that the substance has a molecular weight of 28 kDa and therefore different from the DARPP-32 protein found in the rat brain.

Animals↗
PubMed1994

Functional morphology of the neuropeptidergic light-yellow-cell system in pulmonate snails.

The light yellow neuropeptidergic cell system of the basommatophoran snail Lymnaea stagnalis is homologous to the R3-R14 system of the opisthobranch Aplysia californica, and produces three different neuropeptides. Systems homologous to the light yellow cells of Lymnaea stagnalis have been investigated morphologically in two Basommatophora (Lymnaea ovata, Bulinus truncatus) and three Stylommatophora (Helix aspersa, Cepaea nemoralis, Deroceras reticulatum). To this end, an antibody to synthetic light-yellow-cell peptide-II and oligonucleotides to mRNAs encoding parts of peptide-I and peptide-III, were used. The in situ hybridization probes gave negative results. On the other hand, neuronal cell clusters were observed in the central nervous system of all species studied by immunocytochemistry. These clusters were located in the ganglia of the visceral complex. The neurons project axons into all nerves of these ganglia, especially into the pallial nerves, into the connective tissue of the central nervous system, and into the neuropile of various ganglia. The morphology of the systems is similar to that of the light-yellow-cell system of Lymnaea stagnalis. In all species, the wall of the aorta was innervated by immunoreactive axons. Peripheral innervation by the light-yellow-cell system was investigated in Helix aspersa and Deroceras reticulatum. Serial and alternate sections of whole snails were studied. Reconstructions were made of the heart-kidney-lung complex of these animals. In both species, the muscular vessels of the pulmonary system at the right side of the body were strongly innervated by immunoreactive axons.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1977

The penetration of Fasciola hepatica miracidia into the snail host Fossaria bulimoides. A scanning electron microscope study.

Snails of the species Fossaria bullimoides were exposed to miracidia of Fasciola hepatica for given periods of time. The course of penetration was followed by means of scanning electron microscopy. Topographical features of miracidial morphology were studied with emphasis on epidermal plates and body shape. Comparisons are made on the rate of penetration into this snail host.

Animals↗
PubMed1988

Kinetic analysis of acetylcholine-induced chloride current in isolated snail neurons.

1. Kinetics of activation and desensitization phases of the acetylcholine (ACh)-induced chloride current (ICI) were studied using isolated single neurons of Japanese land snail and the "concentration clamp" technique. 2. The dose-response curve for the peak ICI gave a dissociation constant of 7.1 x 10(-6) M and a Hill coefficient of 1.8. 3. The current-voltage relationship was linear in the voltage range examined (-60 to +10 mV) and the reversal potential (EACh) was -7.2 +/- 1.5 mV (N = 10). The value was close to the calculated equilibrium potential for chloride ions (ECI). 4. Both activation and desensitization phases of the ACh-induced ICI consisted of a single exponential at concentrations less than 3 x 10(-6) M and a double exponential at higher concentrations. The time constants of both phases decreased with increasing ACh concentrations but showed no potential dependency. 5. The recovery from desensitization of the ICI induced by 5 x 10(-6) M ACh proceeded double exponentially, with time constants of 11 and 114 sec at a holding potential of -30 mV. 6. Noise analysis was performed on a steady-state current induced by 3 x 10(-7) to 2 x 10(-6) M ACh. The mean open time was about 60 msec at 10(-6) M ACh and the single-channel conductance was 14 PS. 7. These results suggest that the ACh receptor-Cl channel complex in snail neurons has two binding sites with the dissociation constant of 7.1 x 10(-6) M and is rapidly activated and desensitized to a steady level in the presence of the agonist.

Acetylcholine↗
PubMed1992

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

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

Animals↗
PubMed1989

Specific insulin binding sites in snail (Helix aspersa) ganglia.

1. Insulin binding sites were characterized and quantified in snail (Helix aspersa) ganglia by incubation of tissue sections with 125I-porcine insulin, autoradiography with [3H]Ultrofilm, image analysis coupled to computer-assisted microdensitometry, and comparison with 125I-standards. Cellular localization was performed in the same sections by emulsion autoradiography. 2. Specific insulin binding sites were demonstrated in discretely localized groups of neurons of the cerebral, pleural, parietal, visceral, and pedal ganglia and in nerves. Scatchard analysis performed with consecutive sections from single animals revealed a single class of high-affinity insulin binding sites (Kd, 0.13 +/- 0.01 nM; Bmax, 157 +/- 10 fmol/mg protein). 3. Our results suggest that insulin may play a role as a neurotransmitter or neuromodulator in snail ganglia.

Animals↗
PubMedDate not supplied

Interrelationships of the emotionally positive and negative regions of the brain of the edible snail.

The changes in the behavior of the garden snail during self-stimulation through electrodes chronically implanted in specific regions of the brain are described in this study. The stimulation of the mesocerebral region led to an increase in the frequency of reinforced behavior, whereas stimulation of the rostral portion of the parietal ganglia led to a decrease in the frequency of reinforced behavior. An inference is reached regarding the emotional coloration of the effects of the stimulation of these regions. The interrelationships of the neurons located in the mesocerebrum and the parietal ganglia were studied in neurophysiologic experiments. It was found that the activation of the cells of the mesocerebrum inhibits the spontaneous activity of the serotoninergic cells of the pedal ganglia which sensitize the defensive reactions of the snail, and simultaneosly attenuate the sensory input of the command neurons of defensive behavior, which leads to the effective inhibition of the defensive reactions that is necessary during the activation of sexual behavior.

Animals↗
PubMedDate not supplied

Arachidonic acid and its acyclic derivatives regulate short-term plasticity of the cholinoreceptors of neurons of the edible snail.

The influence of eicosanoids on the dynamics of the extinction of the inward current, induced by repeated iontophoretic applications of acetylcholine to the soma has been demonstrated in identified RPa3 and LPa3 neurons of the edible snail by means of bielectrode recording of the membrane potential. The extracellular action of arachidonic acid (50-100 mumole/l) intensifies the extinction. Quinacrine (100-600 mumole/l), an inhibitor of phospholipase A2, which decreases the content of arachidonic acid in the cells, acts ambiguously. Nordihydroguaiaretic acid (3-10 mumole/l), which is an inhibitor of the lipoxygenase oxidation of arachidonic acid, attenuates the extinction. Indomethacin (10-50 mumole/l), a blocker of cyclooxygenase oxidation of arachidonic acid, does not influence extinction. All of the compounds investigated decrease the amplitude of the inward current induced by acetylcholine. The results obtained make it possible to hypothesize that arachidonic acid and its acyclic metabolites, which are formed as a result of lipoxygenase oxidation, regulate short-term plasticity of the cholinoreceptors of neurons of the edible snail. The cyclic eicosanoids which are formed during the cyclooxygenase oxidation of arachidonic acid do not exert a regulatory effect on the plasticity of the cholinoreceptors.

Animals↗
PubMedDate not supplied

Eicosapolyynoic acids, inhibitors of lipoxygenases, weaken the short-term plasticity of cholinoreceptors of neurons of the edible snail.

The influence of three polyacetylenic analogs of natural polyenoic acids which are inhibitors of their lipoxygenase oxidation on the dynamics of the extinction of the inward current induced by repeated iontophoretic applications of acetylcholine to the soma was investigated in identified RPa3 and LPa3 of the edible snail using the method of bielectrode recording of the potential on the membrane. It was found that eicosa-5,8,11,14-tetraynoic acid (30-60 mumole/liter) and eicosa-5,8,11,14,17-pentaynoic acid (4-50 mumole/liter) decrease the amplitude of the inward current induced by application of acetylcholine, and attenuate its extinction during repeated applications. The third analog, eicosa-8,11,14-triaynoic acid, does not exert a modulating influence on the magnitude of the current and its extinction. It was hypothesized that the lipoxygenase metabolites of the polyenoic acids regulate the plasticity of the cholinoreceptors of the neurons of the edible snail. Taking the nonidentical inhibition by the compounds used of the various lipoxygenases into account, the participation in the plasticity of the cholinoreceptors of those eicosanoids which are formed from arachidonic acid under the influence of 5-lipoxygenases is most probable. At the same time, a regulatory role of the eicosanoids formed under the influence of other lipoxygenases is not excluded.

5,8,11,14-Eicosatetraynoic Acid↗
PubMedDate not supplied

Role of dopamine and serotonin in modulation of snail defensive behavior.

The application of 10(-5)-10(-6) M dopamine to physiologic saline surrounding snail CNS leads to decreased excitability of the LPa7 neuron (presynaptic in relation to the defensive behavior command neurons) and decreased amplitude of the monosynaptic excitatory postsynaptic potential (EPSP) in the command neurons brought about by intracellular stimulation of the LPa7 neuron. In addition, dopamine causes an average 70% decrease in the amplitude of the summation EPSP in command neurons in response to intestinal nerve stimulation, a 6-8 mV change in the resting potential towards hyperpolarization, and an average 20% decrease in the command neurons' input resistance. These actions can lead to an overall increase in the threshold of the defensive system's reaction to stimulation. The effect of dopamine on command neurons is significantly reduced in the presence of serotonin. In the presence of dopamine, the efficacy of serotonin action on the size of the response elicited in command neurons is reduced. Based on the data obtained, it was concluded that the interrelation of dopamine and serotonin concentrations could be the basis for the formation of behavioral choice in snails.

Aggression↗
PubMedDate not supplied

Reinforcing effect of stimulation of the mesocerebral region of the brain of the edible snail.

Two regions of the brain of the edible snail were stimulated. The spontaneous movements, either opening or closing, of the opening of the mantle cavity served as the signal for the stimulation. The stimulation of the region of the mesocerebrum of the edible snail in a semi-intact preparation may serve as a positive reinforcement of intercurrent behavior, while stimulation of the rostral portion of the parietal ganglia may serve as a negative reinforcement. Depending upon whether the movement itself or its absence is reinforced, the change in the intercurrent behavior may change sign.

Animals↗
PubMed1979

Zinc-dependent action potentials in giant neurons of the snail, Euhadra quaestia.

In giant neurons of subesophageal ganglion of the Japanese land snail, Euhadra quaestia Deshayes, permeation of Zn ions through Ca channels were investigated with a conventional current clamp method. All-or-none action potentials of long duration (90 to 120 sec) were evoked in 24 mM Zn containing salines. The overshoots were about +10 mV and the maximum rate of rises (MRRs) was about 2.9 V/sec. The amplitudes and the MRRs of the action potentials depended on external Zn ion concentrations. The action potentials were suppressed by specific Ca-channel inhibitors such as Co2+, La3+ and Verapamil, but they were resistant to Na-channel inhibitor, tetrodotoxin, even at 30 microM. It is concluded that these action potentials are generated by Zn ions permeating Ca channels in snail neuronal membrane. On the basis of Hagiwara and Takahashi's (S. Hagiwara & K. Takahashi, 1967, J. Gen. Physiol. 50:583) model of Ca channels, it is inferred that Zn ions are 5 to 10 times stronger in affinity to Ca channels than Ca ions, but 10 to 20 times less permeable.

Action Potentials↗
PubMed1989

Identification of a locality in snake venom alpha-neurotoxins with a significant compositional similarity to marine snail alpha-conotoxins: implications for evolution and structure/activity.

alpha-neurotoxins from elapid snake venoms and alpha-conotoxins from marine snails bind specifically and with high affinity to nicotinic cholinoceptors. Although both types of toxin are polypeptides, there is more than a fourfold difference in size between the two and no clear sequence homology is evident. A systematic computer search of the three-dimensional structure of erabutoxin b (an alpha-neurotoxin from the false sea snake Laticauda semifasciata) was performed to identify the locality that most closely matched the amino acid compositions of the smaller alpha-conotoxins (from the marine snails Conus magus and Conus geographus). The area of greatest similarity centered on residue position 25 of erabutoxin b, a locale that is conserved throughout the snake alpha-neurotoxins and their homologues. Six proteins unrelated to erabutoxin b were compared to the alpha-conotoxins to show that the extent of the erabutoxin b/alpha-conotoxin match was too high to be coincidental. Homologues of erabutoxin b, namely alpha-cobratoxin from Naja naja siamensis and cytotoxin VII4 from Naja mossambica mossambica, were also analyzed. The extent of the matching with the alpha-conotoxins decreased in the series erabutoxin b greater than alpha-cobratoxin greater than cytotoxin VII4, and this also relates the order of similarity to the pharmacological properties of the alpha-conotoxins. The alpha-conotoxin-like area of the snake alpha-neurotoxins is peripheral to the site previously considered important for binding to the cholinoceptor, even though it seems to represent the focus of evolutionary convergence between the two types of neurotoxin. The area of resemblance does, however, have strong associations with the conformational behavior of the snake toxins. Hence, the outcome of this study has important consequences for the current ideas on snake alpha-neurotoxin structure/activity relationships and the evolutionary origins of neurotoxicity.

Amino Acid Sequence↗
PubMed1996

Tyrosine hydroxylase-negative, dopaminergic neurons are targets for transmitter-depleting action of haloperidol in the snail brain.

1. The effects of long term administration of micromolar concentrations of the D2 antagonist haloperidol upon monoaminergic neurons in the snail Lymnaea stagnalis was investigated. 2. Treatment by bath application with 0.5-2.0 micromolar haloperidol, caused a significant, continuous depletion of dopamine levels in the nervous system as revealed by high performance liquid chromatography. 3. A transient depletion of serotonin was also observed, but DOPA and norepinephrine levels were unaffected. Similar depletion of dopamine was observed after the land snail, Achatina fulica, was injected with haloperidol on each of 4 consecutive days. 4. The depletion of dopamine as revealed with glyoxylate-induced fluorescence in Lymnaea appears to be restricted to a subpopulation of catecholaminergic neurons which are immuno-negative for tyrosine hydroxylase, the synthetic enzyme responsible for the conversion of tyrosine to DOPA. 5. The results thus demonstrate a depleting action of low micromolar doses of chronic haloperidol on specific subsets of dopaminergic neurons and a novel preparation for studying catecholaminergic mechanisms operating across the animal kingdom.

Animals↗
PubMed1996

Modulation of in vivo neuronal sprouting by serotonin in the adult CNS of the snail.

1. During in situ recovery from a lesion to the cerebrobuccal connective (CBC) in the snail Achatina fulica, neurons of the buccal ganglia undergo extensive regeneration and sprouting as assessed by axonal dye-fillings of the CBC. 2. These changes are preceded by the distal degeneration of severed fibres from the serotonergic metacerebral giant neuron (MCG), which results in the depletion of serotonin (5-HT) in the ipsilateral buccal ganglion. We have investigated the potential role of this depletion in causing some of the ensuing neuroplastic events. 3. Pharmacological depletion of 5-HT using either 5,7-dihydroxtryptamine or p-chlorophenylalanine in normal, unlesioned animals was found to produce supernumerary neuronal labelling similar to that seen following a lesion. 4. Systemic daily injections of 5-HT were found to partly suppress the sprouting response following the CBC lesion. For example, the contralateral, uninjured MCG which is normally induced by the lesion to sprout novel projections into the denervated ganglion, is suppressed from doing so by the 5-HT treatment. 5. These growth inhibiting effects of 5-HT upon the contralateral MCG could be antagonized by the prior administration of the 5-HT receptor blocker cyproheptadine, suggesting a specific receptor mediated action. 6. We suggest that 5-HT may play a role in governing the state of neuronal outgrowth in vivo in the CNS of the adult snail, as has been suggested by early development and neuronal cultural studies.

Age Factors↗