Differences in shell shape of naturally infected Lymnaea stagnalis (L.) individuals as the effect of the activity of digenetic trematode larvae

The shells of Lymnaea stagnalis show great morphological variability. This phenomenon has been described as the result of an environmental influence. The main object of the present study was to compare some biometric data from shells of naturally infected and uninfected snails from 25 different lakes in the central part of Poland. The height of the shell, the height of the spiral, and the width of the shell were measured. Some inter- and intrapopulation differences among individuals were found. Greater variability of shell shape was observed among snails parasitized with digenean larvae than in nonparasitized ones. Snails infected with Echinoparyphium aconiatum, Echinostoma revolutum, Diplostomum pseudospathaceum, and Opisthioglyphe ranae differed in shell shape compared with uninfected individuals. Snails infected with Plagiorchis elegans did not differ from uninfected individuals. The same was true of snails in which the commensal oligochaete, Chaetogaster limnei, was found. The results of the present study support the assumption that the deformation of shells of the snails under study was in some way influenced by the presence of certain species of digenetic trematodes.     

Shell attachment in the pond snail Lymnaea stagnalis (L.)

The attachment of the body of the snail Lymnaea stagnalis to the shell was studied by histochemistry and light and electron microscopy. Muscles of the body wall insert into the connective tissue by way of long thin projections of sarcolemma. The muscle cells end under the basement membrane of a specialised area of the epidermis, the adhesive epithelium. The cells of this epithelium are filled with microfilaments and possess characteristic knob-like microvilli. The epithelium is attached to the shell by way of an adhesive substance containing proteins and mucopolysaccharides.This research was made possible by a grant from the Netherlands Organization for Pure Research (Z.W.O.)     

The GABA-ergic regulation of the Lymnaea stagnalis (L.) dorsal longitudinal muscle contractions

Presence of GABA-immunoreactive fibres in the nerve cervicalis inferior was shown as well as their regulatory effects upon contractions of the dorsal longitudinal muscle in Lymnaea stagnalis. The exogenous GABA affected the amplitude of evoked muscle contractions diminishing them at concentrations from 10(-8) M and augmenting them from above 10(-5) M. Picrotoxin produced opposite effects on the muscle contractions in the same concentration range. Bicucullin did not affect the contractions. The findings are discussed from the standpoint of the supposed functional heterogeneity of the GABA receptors in the mollusc nerve-muscle junction.     

Serotonergic innervation of the foot of the pond snail Lymnaea stagnalis (L.)

The aminergic innervation of the foot of Lymnaea stagnalis was investigated using electron microscopy, immunocytochemistry, and HPLC. The foot was found to contain large amounts of serotonin and dopamine, though at lower concentrations than are found in nervous tissue. Serotonin containing tissue was concentrated in the ventral surface of the foot, under ciliated areas of the epidermis where it occurred in varicosities, with fine tracts joining these varicosities. Varicosities also occurred in deeper tissues, probably adjacent to mucus cells. Positive fluorescence for serotonin in axons was found in nerves innervating the foot, but few neuronal cell bodies containing serotonin were detected, indicating that most of the innervation was coming from the central ganglia. Axon varicosities were found using TEM on ciliated cells, mucus cells, and muscle cells as well as interaxonal junctions (possibly non-synaptic) within nerves. The neuronal varicosities contacting the ciliated cells and mucus cells contained mostly dense-cored vesicles of between 60 and 100 nm in diameter. Smaller, lucent vesicles also occurred in these terminals. The origin and significance of this innervation is discussed. It is suggested that both serotonin and dopamine may play a large role in controlling ciliary gliding by the foot.     

Eicosanoids: their biosynthesis in accessory sex organs of Lymnaea stagnalis (L.)

Summary

High performance liquid chromatography has been used to identify the eicosanoids produced from radiolabelled arachidonic acid by accessory sex organs of Lymnaea stagnalis. Radiolabelled compounds co-eluting with the primary prostaglandins normally associated with invertebrates were present, together with two eicosanoids known to occur in vertebrates. These results lend support to the suggestion of van Duivenboden (Int. J. Invertebr. Reprod., 6 (1983) 249–257) that prostaglandins (PGs) are involved in accelerating the onset of egg laying in female copulants of this species. The inability of indomethacin and aspirin to completely inhibit PG biosynthesis in L. stagnalis suggests that the PG synthetase of this snail differs from that of mammals and most other invertebrates.     

The actions of three volatile general anaesthetics on withdrawal responses of the pond-snail Lymnaea stagnalis (L.)

1. The gastropod mollusc Lymnaea stagnalis (L.) is an ideal model system for studies on anaesthesia. It is reversibly anaesthetized by the general anaesthetics halothane, enflurane and isoflurane. 2. Criteria for "anaesthesia" in Lymnaea were established. The reflex used in ED50 trials was the whole animal withdrawal reflex. 3. ED50 values for halothane, enflurane and isoflurane were, 0.83% v.v. (volume for volume), 1.01% v.v. and 1.09% v.v. respectively. 4. Relationships between anaesthetic concentrations, weights of animals and mortality rates are reported.     

The morphology and electrophysiology of the neurones of the paired pedal ganglia of Lymnaea stagnalis (L.)

1. A morphological and electrophysiological map of the identifiable neurones and neuronal clusters of the paired pedal ganglia has been prepared. 2. Neuronal morphology was investigated using the fluorescent dye, Lucifer Yellow CH, whilst electrophysiological properties were studied using conventional intracellular recording techniques and the phase plane technique. 3. The paired pedal ganglia are largely symmetrical and giant neurones usually have contralateral homologues. 4. Neuronal clusters are also paired, but minor asymmetries, both of identifiable neurones and neuronal clusters have been found to exist. 5. These asymmetries are thought to be related to asymmetries of body form. 6. Most of the individually identifiable neurones possess obligatory axon branches which are invariant from one preparation to the next, but variant branches also occur. 7. Within the neuronal clusters, morphology appears to be more variable. 8. Individually identifiable neurones and neuronal clusters were characterized electrophysiologically according to the criteria of action potential shape, spontaneous activity pattern, electrical coupling and common synaptic inputs. 9. Homologous pairs of neurones usually have similar electrophysiological properties, as do those within clusters. 10. A number of wide-acting synaptic inputs have been identified on neurones of the pedal, buccal, visceral and parietal ganglia.     

Electrotonic coupling within a cluster of neurosecretory endogenous oscillators in Lymnaea stagnalis (L.)

• 1.1. Double intracellular and extracellular recordings from cell bodies and axons were made to study the interactions between the neurosecretory “Light Yellow” bursting pacemaker cells (LYC) in the right parietal ganglion of Lymnaea stagnalis.
• 2.2. The LYC are interconnected by low efficiency, non-rectifying electrotonic junctions, transmitting low frequencies only.
• 3.3. Often bursts in different cells coincide; apparently the junctions are responsible for this coherence.
• 4.4. It is inferred that the coupling serves to bring about a pulse-wise release of the cluster's secretory product.

     

Regulation of secretory activity in the albumen gland of the pulmonate snail Lymnaea stagnalis (L.)

The secretory activity of the albumen gland of the freshwater snail Lymnaea stagnalis was studied morphometrically (both at the light- and at the electron-microscope level) and biochemically under the following experimental conditions: (1) glandular tissue was implanted into acceptor snails and the glandular activity of the implants was compared to that of the glands of the donors and acceptors; (2) glandular activity was measured at various periods after oviposition; and (3) the activity was measured during a 24 h cycle (diurnal activity). The results indicate that cellular release of secretion material is regulated by a nervous mechanism, whereas synthetic activity is under hormonal control.     

Lead toxicity,locomotion and feeding in the freshwater snail,Lymnaea stagnalis (L.)

The effects of lead (5 or 10 ppm) on the survival of the freshwater snail Lymnaea stagnalis (L.) collected from lead contaminated or uncontaminated environments were evaluated under controlled laboratory conditions. The animals from the contaminated environment had significantly greater survivability than those from the unpolluted environment to subsequent acute (up to 24 days) exposure to lead. Acute (72 h) exposure to lead inhibited several behavioural activities including locomotion, feeding, tentacle extension and emergence from the shell. Lead bioaccumulated in the snail tissues, especially the buccal mass and stomach. The freshwater snail provides a valuable system for studying the bioaccumulation and development of tolerance to environmental lead. Electronic Publication     

The anatomy of neurosecretory neurones in the pond snail Lymnaea stagnalis (L.).

The anatomy of three neurosecretory cell types in the central nervous system (c.n.s.) of the gastropod mollusc Lymnaea stagnalis (L.)- the Dark Green Cells, Yellow Cells and Yellow-green Cells-has been studied by using bright and dark field illumination of material stained for neurosecretion by the Alcian Blue-Alcian Yellow technique. The neuronal geometry of single and groups of neurosecretory cells of the various types has been reconstructed from serial sections, and the likely destination of most of their processes has been determined. Dark Green Cells are monopolar, occur exclusively within the central nervous system (c.n.s.), have few or no branches terminating in neuropile, and send axons to the surface of the pleuro-parietal and pleuro-cerebral connectives. The majority of Dark Green Cell axons however (80-85%), project down nerves which innervate ventral and anterior parts of the head-foot, the neck and the mantle. Dark Green Cell axons can be found in small nerves throughout these areas, and may terminate in a find plexus of axons on the surfaces of the nerves. Since previous experimental work has shown that the Dark Green Cells are involved in osmotic or ionic regulation, these results suggest that the target organ of the Dark Green Cells may be the skin. Yellow Cells occur both within and outside the c.n.s. They are usually monopolar, but can be bipolar. They have several axons which normally arise separately from a single pole of the cell body, or close to it. One or more processes leave the cell proximal to the point where separate axons arise, and may run unbranched for some distance through neuropile before terminating in fine brances and blobs of various sizes. These branches may release hormone inside the c.n.s. Yellow-green Cells are mono-, bi- or multi-polar, and like the Yellow Cells are found both within and outside the c.n.s. Some Yellow-green Cells, though not all, have projections which terminate in neuropile in fine branches and blobs. Yellow-green Cell bodies which occur in nerves can project back along the nerve into the c.n.s. The axons of Yellow Cells and Yellow-green Cells project to release sites in various ways. Some project into the connective tissue shealth of the c.n.s., which serves as a neurohaemal organ, either directly through the surface of a ganglion, or from the pleuro-cerebral or pleuro-parietal connectives. Other axons leave the c.n.s. via nerves leaving the left and right parietal and visceral ganglia; projections into the intestinal, anal, and internal right parietal nerves being most numerous. Axons which may be from either, or both Yellow Cells and Yellow-green Cells, can be found along the entire unbranched lengths of these nerves, and in subsequent branches which innervate organs lying in the anterior turn of the shell. All of these orgnas are closely associated with the lung cavity...     

Environmental osmolarity and neurosecretory neurones in Lymnaea stagnalis (L.).

Cell body volume and Alcian blue-Alcian Yellow staining properties of neurosecretory neurones in the brain of Lymnaea stagnalis were compared for snails kept in de-ionised water and standard tapwater. In the same experiment, the ionic content of the blood, blood volume and body weight and environmental ionic composition were measured. Five days of immersion in de-ionised water resulted in significant decreases in body weight, blood volume and blood, Na+ and Cl- concentrations but no change in blood Ca2+, K+,and HCO3- concentrations, compared with controls. No consistently significant differences across the 5 day period were found in cell body volumes for Dark Green Cells, Yellow Cells or Light Green Cells (used as a control) when these volumes were compared for large numbers of cells from snails kept in de-ionised water and standard tapwater. However, the number of Yellow Cells which could be counted in snails kept in de-ionised water was lower than the number from standard tapwater by day 2 of the experiment and lower for Yellow-green Cells by day 5. We interpret this lower number to be the result of depletion of Alcian blue-Alcian Yellow stained neurosecretory material in these cells which made them impossible to distinguish. This was confirmed by examination of visceral Yellow Cells which could be identified on the basis of known location close to the visceral-right parietal connective.     

Neuronal and non-neuronal control of the neurosecretory Caudo-Dorsal cells of the freshwater snail Lymnaea stagnalis (L.)

The cerebral ganglia of the freshwater snail Lymnaea stagnalis contain two clusters of neurosecretory Caudo-Dorsal Cells (CDC). These cells produce a neurohormone which stimulates ovulation. Ganglion transplantation and quantitative electron microscopy show that neuronal isolation of the cerebral ganglia complex (CCC) results in an activation of the CDC. It was, therefore, concluded that the CDC are controlled by an inhibitory neuronal input originating outside the cerebral ganglia. Ultrastructural studies on synaptic degeneration in the CCC suggest that this input reaches the CDC via a special type of synapse-like structure, the type C-SLS.Furthermore, transplantation of CCC into acceptor snails leads to a reduced release and an increased intracellular breakdown of neurohormone in the CDC of the nervous system of the acceptors. It is supposed that these phenomena are caused by the release of an (unknown) factor from the transplanted CCC. Special attention was given to the formation and degradation of a peculiar type of neurohormone granule, the large electron dense granule.