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PubMed2005

Changes in the properties of the modulatory cerebral giant cells contribute to aging in the feeding system of Lymnaea.

This study examined whether electrophysiological changes in the endogenous properties and connectivity of the modulatory serotonergic cerebral giant cells (CGCs) contributed to the age-related changes in feeding behavior of the pond snail, Lymnaea. With increasing age there was a decrease in spontaneous CGC firing rates and decreased excitability of the CGCs to both chemosensory stimulation (0.05M sucrose applied to the lips) and direct intracellular current injection. These changes could be accounted for by a decrease in the input resistance of the neuron and an increase in the amplitude and the duration of the after-hyperpolarization. Decreases were also seen in the % of CGC pairs that were electrically coupled causing asynchronous firing. Together these changes would tend to reduce the ability of the CGCs to gate and control the frequency of the feeding behavior. Part of the ability of the CGCs to gate and frequency control the feeding network is to provide a background level of excitation to the feeding motor neurons. Recordings from B1 and B4 motor neurons showed an age-related hyperpolarization of the resting membrane potential consistent with a deficit in CGC function. Increases were seen in the strength of the evoked CGC-->B1 connection, however, this increase failed to compensate for the deficits in CGC excitability. In summary, age-related changes in the properties of the CGCs were consistent with them contributing to the age-related changes in feeding behavior seen in Lymnaea.

Aging↗
PubMed2005

Operant conditioning of an in vitro CNS-pneumostome preparation of Lymnaea.

Operant conditioning of aerial respiratory behaviour and its consolidation into long-term memory in Lymnaea has been previously studied in both intact, freely moving snails and in in vitro preparations made from previously trained snails. Here, we show in previously untrained semi-intact in vitro Lymnaea preparations that aerial respiratory behaviour can also be operantly conditioned. Neither yoked control nor 'run-down' control procedures in these in vitro preparations result in an alteration of aerial respiratory behaviour. Memory in the operantly trained semi-intact preparations persists for at least 1h after training. Intracellular recordings made from RPeD1, one of the 3-CPG neurons and the neuron that initiates CPG activity; show that there are specific changes in central excitatory input to this neuron concurrent with learning and its consolidation into memory. In addition following the acquisition of learning and its consolidation into memory the ability of RPeD1 and VI/J neurons when depolarized to cause a pneumostome opening is significantly decreased. Thus, previously untrained in vitro semi-intact preparations can be used to study changes in neuronal activity in a neuron known to be both necessary for the behaviour and for memory formation.

Activity Cycles↗
PubMed2000

Polycyclic neuromodulation of the feeding rhythm of the pond snail Lymnaea stagnalis by the intrinsic octopaminergic interneuron, OC.

We have examined the role of the octopamine-containing buccal OC interneuron in the fictive feeding rhythm generated by depolarizing a modulatory interneuron, SO, in the isolated central nervous system (CNS) of Lymnaea stagnalis. Before stimulating the SO, the initial fictive feeding rate was 2.0+/-0.37 bites/min (mean+/-S.E.). When the SO was stimulated, the fictive feeding rate more than doubled, increasing by 5.4+/-2.6 bites/min. Prestimulation of OC facilitates the ability of the modulatory neuron SO to drive fictive feeding 4 s later. Following OC stimulation, the increase in SO-driven feeding rate was 10.8+/-1.6 bites/min, significantly more than when only the SO was stimulated (P<0.02, paired t-test on five preparations). OC activity is not required during the SO stimulation for this enhancement. The maximum of the SO driven rhythm occurs between 6 and 12 s after the end of the OC stimulation at 20 bites/min. This is the maximum feeding rate of intact Lymnaea in sucrose. Facilitation is mimicked by bath applied octopamine at 5 microM. Facilitation is specific to OC interneurons, as the same prestimulation of the electrically coupled neuron N3P (central pattern generator) interneurons does not affect the feeding rhythm. The OC interneuron acts as a long term, polycyclic modulator, which peaks several feeding cycles after the OC activity.

Adrenergic alpha-Agonists↗
PubMed2000

The respiratory central pattern generator of Lymnaea: a model, measured and malleable.

Great progress has been made, and continues to be made in our understanding of the neuronal mechanisms underlying respiration in a wide variety of model systems. The central pattern generator (CPG) controlling aerial respiration in the pond-snail Lymnaea is a particularly well-studied model. Using in vitro and semi-intact preparations, the neural circuitry that controls aerial respiration has been characterized as consisting of three identified interneurons. Furthermore, insight has been gained into the behavioural, cellular and synaptic mechanisms by which this circuit controls respiratory rhythmogenesis. It has also been demonstrated that aerial respiratory behaviour can be modified both by experience and by environmental factors. Studies have shown that, in a behavioural hierarchy, respiration is subservient to the whole-body withdrawal response that respiratory behaviour can be modified through operant conditioning, and that respiratory behaviour is altered by hypoxia. Through research on the Lymnaea respiratory CPG we are coming to a better understanding of the construction and malleability of a CPG network. The malleability of this CPG is of particular interest. No longer can neuronal networks underlying respiratory behaviour be considered hard-wired; they have inherent plasticity.

Animals↗
PubMed1989

Goal-tracking behavior in the pond snail, Lymnaea stagnalis.

The occurrence of goal-tracking, an unconditioned stimulus (US)-directed autoshaping behavior, was studied in open-field tests with control and classically conditioned pond snails, Lymnaea stagnalis. In an appetitive classical conditioning paradigm with a tactile stimulus as conditioned stimulus (CS) and a localized food stimulus as US a conditioned feeding response built up in the experimental but not in the control animals. In the post-training open-field tests the experimental group alone showed an enhanced attraction toward the source of water current in the environment which previously signalled the arrival of the US but did not act as CS in the classical conditioning procedure. We suggest that this stimulus-directed goal-tracking behavior in Lymnaea is the result of a classical-operant interaction, described so far only in vertebrate animals, and that neurophysiological analysis of this behavior is possible in this snail.

Animals↗
PubMed2001

Effects of endocrine modulating substances on reproduction in the hermaphroditic snail Lymnaea stagnalis L.

Various man-made agents like pesticides, industrial chemicals and some natural substances have the potential to alter hormonal pathways that regulate reproductive processes in certain species of wildlife. Until now, only a few investigations have been undertaken to determine the effects of these substances on reproductive capacities (fecundity and fertility) in exposed invertebrate aquatic species. In this study one of the most abundant mollusc of European limnic systems, the hermaphroditic gastropod Lymnaea stagnalis was investigated to determine the effects of endocrine modulating substances on reproductive parameters. Known endocrine modulating substances were tested using the following nominal concentrations; Tributyltin (TBT in ng Sn/l) and beta-sitosterol at 1, 10 and 100 ng/l, respectively, and 4-nonylphenol (4-NP) at 1, 10 and 100 microg/l. In addition, experiments were carried out with 1, 10 and 100 ng/l of t-methyltestosterone. All the testing was carried out on recently matured adults of Lymnaea. Fifteen to twenty snails per treatment were exposed for between 7 and 12 weeks in a semi-static test with a weekly exchange of testwater. Shell height and weight and mortality of the adults, egg production, hatching rate of the eggs, and histopathology of the adult snails were analysed. The same parameters were investigated on F(1) generation snails from exposed parents at two dates (1 week after exposure and at the end of the exposure duration). Treatments with TBT and 4-NP had only slight effects on the egg production of the adults and hatching rate of the eggs. However, increased histopathological changes were observed in epithelial tissues of the adult snails, e.g. lung and foot also characterised by extreme inflammatory processes. While beta-sitosterol and t-methyltestosterone had no effect on the shell height and weight or the mortality of adult snails nor on the egg production or ensuing egg hatching rate, beta-sitosterol treated snails presented a distinct atrophy of the albumen gland and so did t-methyltestosterone, albeit with a lower degree of atrophy. The observed histopathological effects due to exposure to tributyltin or 4-NP are suggested to lead to long-term adverse reproductive effects mediated by an impairment of the fitness of the snails. In the experiments the steroid-dependant (beta-sitosterol and t-methyltestosterone) degeneration of the albumen gland caused no obvious adverse effects on the fecundity nor fertility of the adults or on F(1)-generation. However, the impact on fertility following a prolonged exposure to high concentrations of the phytoestrogen cannot be predicted.

Animals↗
PubMed2001

Nicotinic receptors in Lymnaea stagnalis neurons are blocked by alpha-neurotoxins from cobra venoms.

The influence of cobra neurotoxins on the Cl-dependent responses to acetylcholine (ACh) of Lymnaea neurons was studied by the voltage-clamp technique. It was found that a short chain neurotoxin II (NT II), a long chain cobratoxin (CTX) and weak neurotoxin (WTX) diminished the ACh-induced currents, the block being concentration-dependent and competitive. The IC(50) values of 130 nM for CTX, 11 microM for NT II, and 67 microM for WTX were determined. The block induced by NT II was quickly reversible upon toxin washout, whereas the action of CTX and WTX was only partially reversible even after an hour of intensive washing. The data obtained suggest that acetylcholine receptors (AChRs) in Lymnaea neurons have common features with cation-selective alpha 7 AChRs of vertebrates and one type of Aplysia Cl-conducting AChRs.

Acetylcholine↗
PubMed1997

Enhancement of an inhibitory input to the feeding central pattern generator in Lymnaea stagnalis during conditioned taste-aversion learning.

To study the neuronal mechanism of a conditioned taste-aversion (CTA) learning in the pond snail Lymnaea stagnalis, we examined the synaptic connection between the neuron 1 medial (N1M) cell and the cerebral giant cell (CGC), the former is an interneuron in central pattern generator for the feeding response and the latter is a regulatory neuron to the central pattern generator. Inhibitory postsynaptic potential (IPSP) which was evoked in the N1M cell by activation of the CGC was larger and lasted longer in the conditioned animal than that in the control animal. The electrical properties of the cell body of CGC and the responses of the CGC to the chemosensory inputs were not changed during the CTA learning. These results, together with the previous report indicating the existence of excitatory projection from the N1M cell to the feeding motoneuron, suggest that enhanced IPSP in the N1M cell may underlie the suppression of feeding responses in the Lymnaea CTA learning.

Animals↗
PubMed1996

Met-enkephalin and morphiceptin modulate a GABA-induced inward current in the CNS of Lymnaea stagnalis L.

1. The interaction between GABA and opioid peptides (met-enkephalin and morphiceptin) was studied on the identified, isolated and internally perfused neurons of Lymnaea stagnalis L. (Gastropoda, Basommatophora). 2. GABA (10(-7)-10(-5)M) activated a Cl-dependent inward current with about -20 mV equilibrium potential. Slow and fast GABA-induced inward currents were recorded with different kinetic parameters in distinct identified neurons. 3. Both types of GABA-induced inward currents were reduced or blocked by met-enkephalin (10(-7)-10(-5)M) and morphiceptin (10(-7)-10(-5)M) in a dose-dependent manner. GABA-activated fast inward current was modulated in a biphasic way in some neurons. Opioid reduction of the GABA-activated slow inward current was reversible, whereas the fast current was not. 4. The reversible inhibition of the GABA-induced slow inward current produced by met-enkephalin or morphiceptin was naloxone (10(-5)-10(-4)M)-sensitive, whereas the irreversible block of the fast GABA response was not antagonised by naloxone. Some additive effects between GABA and the peptides were also noted. 5. The modulatory effect of the opioid peptides on the GABA response altered the peak current, the time-to-peak and inactivation time-course of the GABA-induced current. 6. Thus, the identified, isolated and internally perfused neurons of Lymnaea stagnalis L. provide a useful model for studying postsynaptic mechanisms of interaction between GABA and opioid peptides. This interaction is a phenomenon of evolutionary significance because of it is also found in mammals.

Animals↗
PubMed2002

Heterosynaptic modulation by the octopaminergic OC interneurons increases the synaptic outputs of protraction phase interneurons (SO, N1L) in the feeding system of Lymnaea stagnalis.

We examined the cholinergic synapses between protraction phase interneurons (SO or N1L) and their targets (N1M interneuron, B1 motoneuron) in the buccal ganglia of the pond snail Lymnaea stagnalis. We have tested the hypothesis that the OC (octopamine-containing) interneuron, an intrinsic modulator of the feeding network, can increase the synaptic efficacy from the SO or N1L to their targets. Prestimulation of the OC interneuron, 4 s before the activation of the SO or N1L increases the strength of their output synapses by 75% (SO)-110% (N1L). The individual excitatory postsynaptic potentials evoked by SO or N1L stimulation increase in size. OC prestimulation also produces an increase in the firing rate of these presynaptic interneurons: SO 40%; N1L 33%. The facilitation lasts up to 6 s after the end of the OC burst. The enhancement of PSPs is seen at all the output synapses (both excitatory and inhibitory) of the SO and N1L interneurons. The output synapses of the non-cholinergic swallowing phase N3p interneuron are not affected, even when the same postsynaptic target is selected. The SO-->N1M, SO-->B1 and N1L-->N1M synapses are also strengthened by bath application of 1-5 microM octopamine (average increase 60%). The major effect is an increased excitability of the SO; the B1 motoneuron response to the main transmitter of the SO, acetylcholine, is unaffected. Increased synaptic outputs of the protraction phase SO and N1L interneurons is functionally significant for generation of feeding pattern in the Lymnaea CNS. Strengthening the connections of SO and N1L to the central pattern generator (N1M) interneurons enhances their ability to drive fictive feeding. Thus heterosynaptic facilitation by the octopaminergic OC interneurons in the central pattern generator network may contribute to the behavioral plasticity of feeding in the intact animal.

Acetylcholine↗
PubMed1976

Molluscs interfering with the capacity of Fasciola hepatica miracidia to infect Lymnaea truncatula.

Fasciola hepatica miracidia labelled with radioselenium were used to study aspects of their host-finding capacity by determining radioactivity subsequently taken up by exposed 'target' snails (Lymnaea truncatula). Possible interfering effects exercised by a number of non-host snails and bivalves were examined in linear test channels. The infection rate (radioactivity) among 'target' snails was markedly lowered when non-host Lymnaea species (L. pereger, L. palustris, L. stagnalis) were interposed as 'decoys'. The prosobranch Bithynia tentaculata and the bivalve Sphaerium corneum exhibited a slight decoy effect whereas pulmonate species like Anisus vortex, Gyraulus albus, Planorbis planorbis, Physa fontinalis did not interfere with miracidial host-finding. Other experiments showed that miracidia are more strongly attracted towards L. truncatula than L. pereger. Miracidia are not able to penetrate intact egg clusters of L. truncatula.

Animals↗
PubMed2005

An expressed sequence tag survey of gene expression in the pond snail Lymnaea stagnalis, an intermediate vector of trematodes [corrected].

The pond snail Lymnaea stagnalis is an intermediate vector for the liver fluke Fasciola hepatica, a common parasite of ruminants and humans. Yet, despite being a disease of medical and economic importance, as well as a potentially useful comparative tool, the genetics of the relationship between Lymnaea and Fasciola has barely been investigated. As a complement to forthcoming F. hepatica expressed sequence tags (ESTs), we generated 1320 ESTs from L. stagnalis central nervous system (CNS) libraries. We estimate that these sequences derive from 771 different genes, of which 374 showed significant similarity to proteins in public databases, and 169 were similar to ESTs from the snail vector Biomphalaria glabrata. These L. stagnalis ESTs will provide insight into the function of the snail CNS, as well as the molecular components of behaviour and response to parasitism. In the future, the comparative analysis of Lymnaea/Fasciola with Biomphalaria/Schistosoma will help to understand both conserved and divergent aspects of the host-parasite relationship. The L. stagnalis ESTs will also assist gene prediction in the forthcoming B. glabrata genome sequence. The dataset is available for searching on the world-wide web at http://zeldia.cap.ed.ac.uk/mollusca.html.

Amino Acid Sequence↗
PubMed2005

Direct molecular imaging of Lymnaea stagnalis nervous tissue at subcellular spatial resolution by mass spectrometry.

The imaging capabilities of time-of-flight secondary ion mass spectrometry (ToF-SIMS) and MALDI-MS sample preparation methods were combined. We used this method, named matrix-enhanced (ME) SIMS, for direct molecular imaging of nervous tissue at micrometer spatial resolution. Cryosections of the cerebral ganglia of the freshwater snail Lymnaea stagnalis were placed on indium-tin-oxide (ITO)-coated conductive glass slides and covered with a thin layer of 2,5-dihydroxybenzoic acid by electrospray deposition. High-resolution molecular ion maps of cholesterol and the neuropeptide APGWamide were constructed. APGWamide was predominantly localized in the cluster of neurons that regulate male copulation behavior of Lymnaea. ME-SIMS imaging allows direct molecule-specific imaging from tissue sections without labeling and opens a complementary mass window (<2500 Da) to MALDI imaging mass spectrometry at an order of magnitude higher spatial resolution (<3 microm).

Animals↗
PubMed1991

Primary structure and origin of schistosomin, an anti-gonadotropic neuropeptide of the pond snail Lymnaea stagnalis.

In the pond snail Lymnaea stagnalis infected with the schistosome parasite Trichobilharzia ocellata, a peptide called schistosomin is released from the central nervous system, which counteracts the bioactivity of a number of gonadotropic hormones. This leads to inhibition of the reproductive activities of the infected snail. In order to determine the structure of schistosomin, the neuropeptide was purified from the central nervous system using gel-permeation chromatography and reverse-phase h.p.l.c. The complete primary structure of the peptide was determined by N-terminal sequencing and peptide mapping. Schistosomin is a single-chain molecule of 79 amino acids with a molecular mass of 8738 Da. The peptide contains eight cysteine residues which may give rise to four intramolecular disulphide bridges that fold the peptide into a stable globular structure. A database search did not reveal any known peptides that show significant sequence similarity to schistosomin. By means of immunocytochemistry, the peptide was shown to be localized in the growth-controlling neurosecretory light green cells, which are located in the cerebral ganglia of the central nervous system of Lymnaea. In addition to schistosomin, these neurons are known to produce various insulin-related peptides.

Amino Acid Sequence↗
PubMed1996

Various isoforms of myomodulin identified from the male copulatory organ of Lymnaea show overlapping yet distinct modulatory effects on the penis muscle.

Male copulatory behavior in the snail Lymnaea stagnalis is controlled by several types of peptidergic neurons, including a cluster of neurons in the ventral lobe of the right cerebral ganglion that show immunoreactivity to myomodulin-A of Aplysia and innervate the penis complex. We identified structurally myomodulin-A and three related peptides from Lymnaea and showed that they are present in a characteristic ratio in both the penis nerve and penis complex, suggesting that they are processed from a single precursor and transported from the ventral lobe to the penis complex. All four peptides decreased the relaxation time of electrically evoked contractions of the penis retractor muscle. However, their effects on the amplitude of contraction were different, ranging from no effect to an increase or a decrease in the amplitude. A mixture of the peptides in a ratio as determined by direct mass spectrometry of the penis nerve decreased the contraction time, the relaxation time, and the amplitude. These effects resemble those of one particular peptide in the mixture. The direct mass spectrometry determinations of the peptide profile in the penis nerve suggest that many more, as yet unidentified, neuropeptides are involved in modulation of muscle activities of the penis complex.

Amino Acid Sequence↗
PubMed2003

Peptidergic modulation of male sexual behavior in Lymnaea stagnalis: structural and functional characterization of -FVamide neuropeptides.

In the simultaneous hermaphrodite snail Lymnaea stagnalis, copulation as a male is controlled by neurons that send axons to the male copulatory organs via a single penis nerve. Using direct mass spectrometry of a penis nerve sample, we show that one of the molecular ions has a mass corresponding to GAPRFVamide, previously identified from the buccal ganglia, and named Lymnaea inhibitory peptide (LIP). The identity of this peptide is confirmed by partial peptide purification from the penis nerve, followed by post source decay mass spectrometry. We cloned the LIP-encoding cDNA, which predicts a prohormone that gives rise to five copies of LIP (now re-named LIP A), two other -FVamide peptides (LIPs B and C), and five structurally unrelated peptides. The LIP gene is expressed in neurons of the right cerebral ventral lobe that send their axons into the penis nerve. We show that the LIP A peptide is present in these neurons and in the penis nerve, and confirmed the presence of LIP B and C in the penis nerve by post source decay mass spectrometry. Finally, we demonstrate that LIP A, B and C inhibit the contractions of the penis retractor muscle, thereby implicating their role in male copulation behavior.

Amino Acid Sequence↗
PubMedDate not supplied

[Arguments and proposals for a new developmental interpretation of Fasciola hepatica L. in Lymnaea (Galba) truncatula Müller (author's transl)].

The authors study the influence of several factors: temperature, drying up of ground, bodily volume of intermediary host on development of the redial generations of Fasciola hepatica in Lymnaea truncatula. Three redial generations are seen in Lymnaea truncatula, whatever environmental factors. The number of rediae of generations 2 and 3 is correlated with bodily volume of the snail host. The temperature affects synchronism of cercarial maturation in rediae of generations 1 and 2.

Animals↗
PubMed1983

[Infection of Lymnaea cubensis by Fasciola hepatica in a high altitude region in Venezuela].

Lymnaea cubensis is the vector in a region of distome infection in Trujillo State at more than 1000 m altitude where almost all bovines are infected. A quarter of the molluscs were infected with a mean number of 20 rediae per infected molluc each redia capable of producing 16 cercariae. Prevalence of infection increases with size of molluse and is highest in those 4 to 5 mm long. However, Lymnaea as small as 3 mm produce cercariae and molluscicide treatments should be begun as soon as forms of this size appear.

Animals↗