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PubMed1992

Development of serotoninlike immunoreactivity in the embryonic nervous system of the snail Lymnaea stagnalis.

In our initial effort to study the ontogeny of the gastropod nervous system, we used histological techniques to examine the post-embryonic development of cells which exhibit serotoninlike immunoreactivity in Lymnaea (Croll and Chiasson, J. Comp. Neurol. 230:122-142, '89). The present study complements that report by examining the embryonic development of these neurons. The first serotoninlike immunoreactive (SLIR) cells to be detected in the embryos are the paired C4 neurons of the cerebral ganglia. These cells are faintly visible at about 37-38% of embryonic development and have already produced axons which traverse the cerebral commissure. By about 2-3% later the axon tips reach the pedal ganglia and appose the next SLIR cells to appear, the EPe1 neurons. Over the next 30% of development four more pairs of cerebral neurons are added adjacent to the C4 neurons and over ten cells are added to each of the pedal ganglia. At about 70% of development SLIR fibers are first detected in the parietal and visceral ganglia forming the abdominal ring. Around this time the somata of the C1 neurons also first appear in the cerebral ganglia together with their prominent axons projecting to the buccal ganglia. The last 30% of development is marked by a massive addition of SLIR cells (up to 60) in each pedal ganglion. The early appearance of the first SLIR cells suggests that they may be among the first nerve cells to differentiate and that they may play central roles in the formation of the CNS. We hypothesize that most of the animal's neural circuitry is laid down during embryogenesis by a stereotypic ontogenetic program with post-embryonic neurogenesis subserving mostly compensatory and modulatory purposes.

Animals↗
PubMed1992

Distribution of the peptide Ala-Pro-Gly-Trp-NH2 (APGWamide) in the nervous system and periphery of the snail Lymnaea stagnalis as revealed by immunocytochemistry and in situ hybridization.

Immunocytochemistry and in situ hybridization were used to identify 200-250 central neurons that synthesize and contain the peptide APGWamide in the central nervous system of Lymnaea. The majority of these cells reside within the right anterior lobe of the cerebral ganglion and most appear to have projections to the ventral lobe of the ganglion. The neurites then branch to innervate the lobe and to send further projections into the penial nerve and to the PeIb cluster of the right pedal ganglion. The right ventral lobe also contains a cluster of about 30-40 somata, which apparently synthesize and contain APGWamide. Other populations of cells found in both the right and left anterior lobes project ipsilaterally to the pleural, parietal, and visceral ganglia. Prominent somata are also located in clusters in the visceral and right parietal ganglia. These cells project ipsilaterally into caudal neuropilar regions of the cerebral ganglia. Peripheral projections of central neurons form a dense plexus of varicose, APGWamide-containing fibres in superficial layers of the penis and preputium. Other peripheral projections were noted in the prostate and vas deferens. No peripherally located cell bodies appeared to contain or synthesize the peptide. The results show that APGWamide is widely present in the central nervous system and male reproductive organs and suggest that it plays a major role in control of reproduction.

Animals↗
PubMed1993

Ultrastructural evidence for the axonal localization of caudodorsal cell hormone mRNA in the central nervous system of the mollusc Lymnaea stagnalis.

The technique of in situ hybridization has been used to evaluate the expression of an ovulation hormone mRNA (caudodorsal cell hormone; CDCH) in the central nervous system (CNS) of the mollusc Lymnaea stagnalis. Hybridization with radioactive as well as with nonradioactive labeled oligonucleotide and plasmid probes revealed a specific labeling on cell bodies of caudodorsal cells (CDCs), which are known to produce CDCH, on the light microscopical level. In addition, specific labeling was observed outside the cell bodies, as far as the cerebral commissure, where CDCH is released in the haemolymph. To investigate whether these signals represent an axonal localization of the CDCH mRNA, we performed in situ hybridization at the electron microscopical (EM) level. The results showed an intraaxonal localization of CDCH mRNA with digoxigenin labeled oligonucleotide and plasmid probes. Gold labeling was observed in secretion granules, and double labeling experiments showed that these granules also contain CDCH. This specific intragranular localization suggest that CDCH mRNA is transported through the axon and released by exocytosis in the haemolymph.

Animals↗
PubMed1979

Effect of thyrotropin releasing factor on body weight of the pond snail Lymnaea stagnalis.

Earlier studies had demonstrated that in Lymnaea stagnalis thyrotropin releasing factor (TRF) may be the secretory product of the so-called dark green neurosecretory cells. The dark green cells are believed to serve an osmoregulatory function. If TRF is the secretory product of the dark green cells, it should be capable of controlling the salt and water balance in L. stagnalis. In this study, the effect and fate of synthetic TRF injected in vivo into L. stagnalis was assessed. It was found that TRF caused an increase in the rate of loss of body water which normally occurs after anaesthesia. TRF also increased the loss of body water when it was administered to unanaesthetized animals. The peptide was accumulated and degraded by the tissues of the foot, mantle, and head regions, tissues which are believed to be the targets of the hormone of the dark green cells. Our results support the hypothesis that TRF may be the secretory product of the dark green cells and may be involved in osmoregulation in L. stagnalis.

Animals↗
PubMed2003

Nitric oxide mediates metabolism as well as respiratory and cardiac responses to hypoxia in the snail lymnaea stagnalis.

Lymnaea stagnalis were exposed to hypoxic and chemical challenges while ventilation, heart rate and metabolism were monitored. Hypoxia increased ventilatory behavior, but this response was eliminated by immersion in 0.75 mM nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7 NI). 7 NI also suppressed ventilatory behavior under normoxia. 10.0 mM L-arginine (ARG, the NOS substrate) increased ventilatory behavior under normoxia, but dampened the hypoxic response. The heart-rate response to NOS inhibition exhibited dose-dependent contradictory characteristics. Under both normoxia and hypoxia 0.25 mM 7 NI increased heart rate, while 0.75 mM 7 NI suppressed it. The effect of 0.50 mM 7 NI depended on whether normoxia or hypoxia was coincident; under normoxia 0.50 mM 7 NI increased heart rate, while under hypoxia this concentration suppressed heart rate. Exposure to ARG did not elicit dose-dependent contradictory responses. Heart rate increased when treated with 10.0 mM ARG under normoxia and hypoxia, while 1.0 mM ARG increased heart rate only under hypoxia. Metabolic responses to NOS inhibition also exhibited dose-dependent contradictory changes. V.O2 decreased over 60% in response to 0.75 mM 7 NI, and baseline V.O2 was restored when exposure ceased. In contrast, 0.25 mM 7 NI increased V.O2 10%, and the increase continued after exposure ceased. 0.50 mM 7 NI decreased V.O2 40%, but V.O2 increased when exposure ceased. ARG had only the effect of increasing V.O2, and only at 10.0 mM concentration. Based on these results and on NO's known role as a neuromodulator, we conclude that the cardio-respiratory responses to hypoxia are, in part, mediated by NO.

Animals↗
PubMed1993

NADPH-oxidase activity: the probable source of reactive oxygen intermediate generation in hemocytes of the gastropod Lymnaea stagnalis.

Macrophage-like defense cells (hemocytes) of the pond snail Lymnaea stagnalis generate reactive oxygen intermediates (ROIs) upon contact with non-self, following kinetics similar to those of ROI production by mammalian leukocytes during respiratory burst. In this study, several inhibitors of NADPH-oxidase, the key enzyme of the respiratory burst in mammalian phagocytes, were tested for their effect on oxidative activities [as demonstrated by nitroblue tetrazolium (NBT) reduction and luminol-dependent chemiluminescence (LDCL)] of phagocytosing snail hemocytes. In the presence of diphenylene iodonium, zymosan-stimulated hemocytes of L. stagnalis failed to reduce NBT and showed a markedly reduced LDCL response. Also, compounds that prevent assembly of functional NADPH-oxidase complexes in activated mammalian cells were effective; preincubation of hemocytes with 1,4-naphthoquinone inhibited the LDCL response and NBT reduction upon phagocytic stimulation. Furthermore, coincubation but not preincubation with five different catechol-like phenols inhibited oxidative activities of zymosan-stimulated hemocytes. These results imply similarities in composition and regulation of the ROI-generating mechanisms of both mammalian and snail defense cells. It is postulated that in L. stagnalis hemocytes, (1) NADPH-oxidase activity is responsible for ROI production, (2) an active NADPH-oxidase enzyme complex has to be assembled from putative cytosolic and membrane-associated components, and (3) continuous replacement of active NADPH-oxidase enzyme complexes is necessary to sustain respiratory burst-like oxidative activities during interactions with non-self.

Animals↗
PubMed2001

Optical detection of neuromodulatory effects of conditioned taste aversion in the pond snail Lymnaea stagnalis.

Multiple site optical recording was used to analyze the neural activity changes caused by conditioned taste aversion (CTA) training in the pond snail Lymnaea stagnalis. In response to electrical stimulation of the median lip nerve, which transmits chemosensory signals of appetitive taste to the central nervous system, we optically detected large numbers of spikes in several parts of the buccal ganglion. The effects of CTA training on the spike responses were examined in two areas of the ganglion where the most active neural responses occurred. In one area (termed Area I) that included the N1 medial (N1M) cells, a class of central pattern generator interneurons involved in feeding behavior, the number of spikes in a period 1500-2000 ms after median lip nerve stimulation was significantly reduced in conditioned animals compared to control animals. In another area (termed Area II) positioned between buccal motoneurons, the B3 and B4CL (cluster) cells, the evoked spike responses were unaffected by CTA training. These results, taken together with our previous results indicating an enhancement of an inhibitory input to the N1M cells during CTA, suggest that an appetitive taste signal transmitted to the N1M cells through the median lip nerves is suppressed during CTA, resulting in a decrease of the feeding response.

Action Potentials↗
PubMed1980

States of excitability in ovulation hormone producing neuroendocrine cells of Lymnaea stagnalis (gastropoda) and their relation to the egg-laying cycle.

The electrotonically coupled network of about 100 neuroendocrine caudodorsal cells (CDC) of the freshwater snail Lymnaea stagnalis exhibits three states of excitability with distinct electrophysiological characteristics. Transitions between these states occur spontaneously or can be induced experimentally. The CDC produce an ovulation hormone, and the excitability states are clearly related to the egg-laying cycle of the snail. Two hours before egg laying, the cells enter an active state, which lasts one hour. This phase is characterized by a spontaneous firing pattern, which in preparations can be evoked as an afterdischarge, and during which the hormone is thought to be released. After this, the cells enter an inhibited state in which no other activity than directly stimulus-dependent ortho- and antidromic action potentials can be evoked. This phase lasts till about four hours after egg laying. The subsequent resting state is characterized by facilitation of the responses upon repetitive stimulation of the cells, leading to depolarization of the network and additional action potentials. In this phase, an afterdischarge can be evoked, which brings the cells into the active state again.

Action Potentials↗
PubMed1981

Axonal branching pattern and coupling mechanisms of the cerebral giant neurones in the snail, Lymnaea stagnalis.

The axonal branching pattern of the two cerebral giant neurones (CGCs) of Lymnaea stagnalis was studied with intrasomatically applied horseradish peroxidase. The cells are symmetrical. Each CGC projects to the ipsilateral n. labialis medius and n. arteriae labialis, the subcerebral commissure, and to all ipsi- and contralateral buccal nerves. The contralateral buccal nerves are reached via the ipsilateral cerebro-buccal connective and the buccal commissure. The CGC fire action potentials 1:1 in a driver-follower relationship. Each cell is capable of both driving and following. The relationship depends on the membrane potentials of the somata. In driving CGC spikes are initiated in a cerebral spike trigger zone located near the soma. In following cells spikes are initiated in a distal zone located in the buccal ganglia. The buccal zone is only affected by the partner CGC. CGC are synchronized by three coupling mechanisms: mutual excitatory chemical synapses, electrotonic coupling, and common input. The chemical and electrotonic connections are located in the buccal ganglia. All spikes are relayed to the partner cell via the chemical synapses. The electrotonic coupling improves the efficiency of the chemical synapses. The dual connection selectively synchronizes the CGC-axonal spikes from each side of the buccal mass. Common excitatory input affects the cerebral spike trigger zones and can initiate simultaneously spikes in both cells. This results in bilateral synchrony of spikes in the CGC-axons in both the buccal and the lip nerves.

Action Potentials↗
PubMed1981

Pacemaking mechanism of the afterdischarge of the ovulation hormone-producing caudo-dorsal cells in the gastropod mollusc Lymnaea stagnalis.

The ovulation hormone-producing caudo-dorsal cells (CDC) of Lymnaea stagnalis have three states of excitability (active, inhibited, and resting), which are related to the egg-laying cycle. Active state CDC produce a firing pattern of prolonged spiking activity (1 spike/2 s), which in the animal occurs shortly before egg laying. In preparations it is evoked as an afterdischarge upon repetitive stimulation of CDC. The afterdischarge is not synaptically driven, but rests on a pacemaking mechanism. CDC are silent in the inhibited and resting states, which follow egg laying. In these states the membrane potential is mainly dependent on [K+]0. In the active state the ratio of the K+, Na+, and Ca2+ permeabilities has changed considerably, probably resulting from an increased permeability to Na+ and Ca2+. The firing rate in the afterdischarge is dependent on the membrane potential, which is confirmed experimentally by varying [K+]0. [Na+]0 and [Ca2+]0 directly influence the firing rate. Firing stops in Na+-free saline, but is enhanced by Ca2+-free or high-Mg2+ saline. TTX does not affect firing. Relatively high concentrations of Co2+ and La3+ (2 x 10(-3) M) strongly inhibit CDC. Regular firing can be changed into bursting by various means, such as high K+ or addition of 1 mM Ba2+. Bursting normally occurs at the beginning of the afterdischarge. Postburst hyperpolarizations are reduced in Ca2+-free saline and by low Co2+ (10(-4)--5 X 10(-4) M). Active CDC are driven by a pacemaking mechanism constituted by a voltage-dependent Na+/Ca2+ channel and a Ca2+-dependent K+ channel, thus resembling that of bursting pacemakers. The pacemaking mechanism is inactive in the resting and inhibited state.

Animals↗
PubMed1982

Na+- and Ca2+-dependent components in action potentials of the ovulation hormone producing caudo-dorsal cells in Lymnaea stagnalis (Gastropoda).

Action potentials in the afterdischarge of the ovulation hormone producing caudo-dorsal cells (CDC) of Lymnaea stagnalis are strikingly different from electrically evoked spikes in the silent resting and inhibited states of these cells. Spikes evoked in the silent states consist of one fast peak (80-100 mV; 10-15 ms). The overshoot in Na+- and Ca2+-dependent. Spikes are blocked in Na+-free saline and by TTX. Repolarization is retarded by TEA. Co2+ increases the overshoot. Active state action potentials (60-80 mV) last up to 125 ms, due to activation of a slow component following the TTX-sensitive spike. The slow component is Na+- and Ca2+-dependent. In normal saline it is blocked by Co2+ and La3+. In Ca2+-free saline the remaining part of the slow component is blocked by La3+ only. The slow component is voltage-dependent in a graded fashion. Activation is bound to the active state in which the CDC are depolarized by 20 mV. TEA and Ca2+-free saline greatly increase spike duration in the active state. This suggests that, in addition to the classical TEA-sensitive channel, a Ca2+-dependent K+ channel is involved in repolarization of active state action potentials. The underlying membrane properties and the functional significance are discussed in relation to the pacemaking mechanism of the CDC.

Action Potentials↗
PubMed1982

Variability and frequent failure of lucifer yellow to pass between two electrically coupled neurons in Lymnaea stagnalis.

The electrically coupled giant neurosecretory neurons VD1 and RPD2 of Lymnaea stagnalis were found to have coupling coefficients ranging from ca. 0.1-0.6. When the fluoroescent dye Lucifer Yellow was injected intracellularly into one of the neurons, in most preparations no dye was observed to pass through into the coupled cell body or the process leading to it. There was no apparent correlation between the amount of dye coupling and the length of time allowed for diffusion of the dye in the cells. In eight preparations, the electrical coupling coefficient was measured before dye was injected. There was no correlation between dye coupling and the electrical coupling coefficient.

Animals↗
PubMed1985

Membrane mechanism of neuroendocrine caudo-dorsal cell inhibition by the ring neuron in the pond snail Lymnaea stagnalis.

Ovulation in the pond snail Lymnaea stagnalis is controlled by the neuroendocrine caudo-dorsal cells (CDCs) in the cerebral ganglia, which release an ovulation hormone during a period of impulse activity. Firing of the single RN in the right cerebral ganglion hyperpolarizes the CDCs. This hyperpolarization is caused by the opening of potassium channels in the axons that connect both the CDC clusters. By this action, that presumably is mediated by axonal branches of the RN in the intercerebral commissure closely associated with these CDC axons, the RN decouples both the CDC clusters. Although the RN has negative feedback on the CDC, it does not control afterdischarge characteristics. The authors suggest that the RN, next to the egg-laying behavior, is involved in another behavior, not compatible with ovulation. Male reproductive activity is presented as a possible candidate for such behavior.

Animals↗
PubMed1989

Effect of putative neuromodulators on rhythmic buccal motor output in Lymnaea stagnalis.

The effects of a variety of neuromodulator substances on rhythmic motor output and activity in neurons in the feeding circuitry of Lymnaea stagnalis were examined. Each neuromodulator produced a unique combination of effects at different levels in the network: i.e., pattern-generating interneurons (N1, N2, and N3), an identified higher-order interneuron (cerebral giant cell, CGC), and buccal motoneurons. 5-Hydroxytryptamine, acetylcholine, and FMRFamide all inhibited rhythmic motor activity. However, this was achieved in different ways. Dopamine changed the nature of rhythmic activity from one in which N2 interneuronal activity was predominant ("N2 rhythm") to a feeding rhythm. Dopamine was the only substance capable of activating the feeding rhythm. Activity in the CGC was increased by 5-hydroxytryptamine, dopamine, and acetylcholine and reduced by FMRFamide. Differential responses in buccal motoneurons were also observed. The results are discussed in relation to previous work on other species and also in terms of the selection of different patterns of motor output by neuromodulators.

Acetylcholine↗
PubMed2005

Effect of binary combination of some plant-derived molluscicides with MGK-264 or piperonyl butoxide on the reproduction of the snail Lymnaea acuminata.

The effects of sub-lethal treatments (20 and 60% of 24-h LC(50)) with plant-derived molluscicides Annona squamosa, acetogenins, Argemone mexicana seed and protopine, in combination (1 + 5) with MGK-264 (ENT 8184) or piperonyl butoxide on the reproduction of Lymnaea acuminata has been studied. The plant-derived molluscicides and their active molluscicidal components, protopine and acetogenins, in combination with ENT 8184 or piperonyl butoxide caused a significant reduction in the fecundity, hatchability and survival of young snails. Combination of A squamosa seed powder with piperonyl butoxide was very effective as it caused a complete arrest of snail fecundity within 24 h of treatment. Removal of the snails to fresh water after the 96-h treatments caused a significant recovery in the fecundity of L acuminata.

Acetogenins↗
PubMed2005

Variation in the response of juvenile and adult gastropods (Lymnaea stagnalis) to cyanobacterial toxin (microcystin-LR).

Owing to the increasing public health problem related to the proliferation of toxin-producing cyanobacteria in aquatic ecosystems, we have investigated the response of the pond snail Lymnaea stagnalis exposed to 33 microg/L microcystin-LR for 6 weeks, through its life traits (survival, growth, fecundity) and locomotion; uptake of microcystin-LR was also quantified in the snail body tissues. To study the potential plasticity of the response related to the development stage, snails were exposed to the toxin as sexually immature and mature. According to our results, microcystin-LR accumulated in snail tissues at a higher level in juveniles (7.96 ng/g fresh weight) versus adults (2.17 ng/g fresh weight). Whatever the age, survival, growth, and locomotion were not affected by the toxin, and fecundity of polluted adults was reduced by half. These results are discussed in terms of negative effects of aqueous microcystin-LR occurrence on the dynamics of natural populations of gastropods.

Age Factors↗
PubMed1993

Purification and characterization of a novel tetradecapeptide that modulates oesophagus motility in Lymnaea stagnalis.

The isolated oesophagus of Lymnaea stagnalis was used as a bioassay preparation to identify peptides that modulate the activity of the oesophagus. Several modulatory messengers were detected from the oesophageal extract. One of these, having an excitatory action, was further purified from both the oesophagus and the central nervous system through high performance gel permeation chromatography followed by serial reversed phase high performance liquid chromatography. The purified peptide was chemically characterized through amino acid sequencing and mass spectrometry as GFRANSASRVAHGY-NH2.

Amino Acid Sequence↗
PubMed1998

Toxic effects of cadmium on reproduction, development, and hatching in the freshwater snail Lymnaea stagnalis for water quality monitoring.

The freshwater snail Lymnaea stagnalis was exposed to cadmium concentrations of 0, 25, 50, 100, 200, and 400 microgram liter-1. The influence of this highly toxic metal on various stages of reproduction (number of egg masses, number of eggs, embryo development, and hatching) was studied. Egg production ceased at 400 microgram Cd2+ liter-1 and hatching was reduced to 0.4% with 200 microgram liter-1 at 20 degreesC. The study revealed that embryo development was the most sensitive stage, the main anomalies observed depending on the Cd2+ concentration. At the highest concentration studied (400 microgram liter-1) the eggs were blocked in the first cleavage stage. At 100 and 200 microgram Cd2+ liter-1, development of the eggs was halted at various stages of embryogenesis (cleavage, gastrula, veliger, and prehatching) depending on their position in the egg masses. At concentrations of 25 to 100 microgram Cd2+ liter-1, development was slowed down and hatching occurred 5 to 15 days later than in the controls (controls hatched 12 to 13 days after laying). The results obtained demonstrate the effects of Cd2+ on reproduction and development in L. stagnalis and provide information on the targets affected (neuroendocrine control of laying or cell multiplication and organogenesis of the embryos). It is thus possible to predict the probability of survival of the species in an environment polluted with cadmium and to compare it with the effects of other pollutants in the same or other species.

Animals↗