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At least 1,279 records · Page 71Linked to original sources
PubMed1990

Use of snail neurons in developing quantitative ultrastructural parameters for neurotoxic side effects of Vinca antitumor agents.

The central nervous system of the snail Lymnaea stagnalis was studied in order to develop a test system to predict the neurotoxic side effects of the three cytostatic Vinca alkaloids, vincristine (VCR), vindesine (VDS), and vinblastine (VLB). Vinca alkaloids appear to interfere with microtubule formation by the induction of paracrystalline inclusions. After in vitro incubation the numbers of these inclusions were counted in cross-sections of the cerebral commissure using electron microscopy. For each compound the number of paracrystalline profiles increases with increasing concentrations and incubation times. At equimolar concentrations (0.15 mM), VCR induces more paracrystals than VDS, and VDS induces more than VLB. These effects are clear after short periods of incubation (e.g., after 2 h, VCR:VDS:VLB = 5:2:1). Equitoxic concentrations of VCR, VDS, and VLB induce similar numbers of paracrystals. Furthermore, morphological changes in the cell bodies of identified neurons (light green cells) in the cerebral ganglia were observed. Quantitative analysis shows that at equimolar concentrations the surface area of nuclear chromatin of all Vinca alkaloid-treated cells is approximately 30% lower than that of the controls. The lamellae of the rough endoplasmic reticulum are swollen and have lost their regular arrangement. For VDS and VLB this swelling is accompanied by a strong increase (about 3-fold) in the total surface area of the rough endoplasmic reticulum. No increase was observed for VCR. The compounds do not affect the number of secretory granules. In contrast to the controls, all Vinca-treated cells show lipid droplets. After VCR treatment they are about 5-fold as numerous as after treatment with VDS or VLB. The total surface area of lysosomes increases about 1.3-fold by VDS and VLB treatment and about 3-fold by VCR treatment. From these quantitative data it is concluded that VCR is more neurotoxic than VDS and VLB. VDS appears to be more neurotoxic than VLB as judged from the data on paracrystal induction. On the basis of a comparison of these data with clinical data on Vinca-induced neurotoxicities, it is proposed that neurons of the snail L. stagnalis may be suitable for the development of a test system to predict the degree of clinical neurotoxicity induced by Vinca antitumor drugs.

Animals↗
PubMedDate not supplied

[The role of dopamine and serotonin in modulating the defensive behavior of the edible snail].

Dopamine application in concentration of 10(-5)-10(-6) M into saline around the snail CNS leads to decrease of excitability of LPa7 neurone which is presynaptic in relation to defensive behaviour command neurones, and to decrease of amplitude of monosynaptic excitatory postsynaptic potential (EPSP) in the command neurones elicited by intracellular stimulation of LPa7 neurone. Besides, the dopamine causes a decrease of summated EPSP amplitude in the studied neurones in response to intestinal nerve stimulation (70% in average), a change of rest potential towards hyperpolarization for 6-8 mV, a reduction of the command neurones input resistance (20% in average). The described influences can lead to a general increase of the threshold of defensive system reaction to stimulation. Dopamine action on the defensive behaviour command neurones is significantly weakened in serotonine presence. Against the dopamine background, the efficiency of serotonine influence on the value of EPSP in command neurones in response to testing stimulus is reduced. According to the obtained data, a conclusion is made that interrelation of dopamine and serotonine concentrations can be a base for formation of behaviour choice in snail.

Animals↗
PubMed1989

Isolation of microcercous cercariae from snails caught in an endemic focus of Paragonimus uterobilateralis in Liberia, West Africa.

Microcercous cercariae have been recovered from the snail Homorus (Striosubulina) striatella RANG. which were collected in a focus of human lung fluke disease in Liberia, West Africa, and are here described. Metacercariae of Paragonimus uterobilateralis were isolated from freshwater crabs (Liberonautes latidactylus) captured at the same location, and at the same time, as the infected snails. The dimensions of the Liberian cercariae have been found to differ markedly from those of a cercaria from Cameroon previously described as that of Paragonimus africanus. The structure and dimensions of the Liberian cercariae clearly resemble those of the cercariae of other species of Paragonimus from Asia and America.

Animals↗
PubMed1989

[Various principles of the organization of preterminal and terminal branches of afferent conductors in neuropil of the snail dorsal ganglia].

Character of ramifications in the preterminal and terminal axonal parts in the neuropil of the dorsal ganglia have been studied in 16 edible snails (Halix pomatia). The nervous tissue is impregnated with silver nitrate after Golgifast method. Serial sections are made in two projections: horizontal and vertical. The analysis of peculiarities of the spatial distribution of the afferent fibers (AF) demonstrates their several forms that are united into the following types: dominant, probable and transitional. Comparison of the edible snail AF with those in the higher vertebrata makes it possible to conclude that the character of ramification of their preterminal and terminal parts and principle of organizational connections of the AF with the postsynaptical structures are principally similar.

Afferent Pathways↗
PubMed1986

Histological and pharmacological investigations of the two symmetrically situated giant neurons, RPeNLN and LPeNLN, identified on the anterior surface of the pedal ganglia of an African giant snail (Achatina fulica Férussac).

Morphological and pharmacological investigations were made of two giant neurons, RPeNLN (right pedal nerve large neuron) and LPeNLN (left pedal nerve large neuron), situated symmetrically on the anterior surface of the pedal ganglia of an African giant snail (Achatina fulica Férussac). The two neurons (about 250-300 microns in diameter) were the largest ones identified in the ganglia of the snail species. The axonal pathways of the two neurons were symmetrical; of their four main axonal branches, the three main branches innervated the ipsilateral pedal nerves, whereas the last main branch projected to the contralateral pedal nerves. The pharmacological features of the two neurons were very similar. Both were inhibited markedly by dopamine [minimum effective concentrations (MECs): 3 X 10(-6)-10(-5) M], DL-octopamine (MECs: 2 X 10(-6)-2 X 10(-5) M), 5-hydroxytryptamine (MEC: 3 X 10(-6) M), GABA (MEC: 3 X 10(-4) M), L-homocysteic acid (MECs: 3 X 10(-5)-10(-4) M) and erythro-beta-hydroxy-L-glutamic acid (MEC: 3 X 10(-5) M). Acetylcholine showed varied effects, either excitatory or inhibitory, on the two neurons examined. No substances were found to have any marked excitatory effects on the neurons.

Animals↗
PubMedDate not supplied

[Specific and nonspecific components in the neurohumoral link of the conditioned food-refusal reflex in the edible snail].

On snails, the action was studied of hemolymph of donors with conditioned food refusal reflex on acquisition of the same habit by intact snails-recipients in case of coincidence or of difference of conditioned stimuli in donors and recipients. Specific component of the facilitating effect was distinctly manifest at selection of optimal doze of hemolymph and depended on the season. At non-optimal parameters of the experiment the specific component of the facilitating effect was masked by the non-specific one, or an inhibitory effect took place. The data obtained testify to multicomponent composition of the neurohumoral link in the mechanism of conditioned reflex formation.

Animals↗
PubMed1987

[The role of cAMP in generating excitatory serotonin responses of neurons in the edible snail].

The neurons of the dorsal surface of snail Helix subesophageal ganglia respond similarly to the application of serotonin and the intracellular cAMP injection. These responses represent membrane depolarization. They increase in amplitude with membrane hyperpolarization and have a reverse potential between +10 and -30 mV. Presumably, these responses are associated with increased conductance for several ions. The values of the reverse potentials of serotonin and cAMP responses coincide in 7 out of 17 cells. Phosphodiesterase inhibitor theophylline caused a reversible increase in the amplitude and duration of both serotonin and cAMP responses and, used at a concentration of 1 mM, simulated them. The results obtained meet 2 out of 4 criteria demonstrating that cyclic nucleotides mediate a neurotransmitter response. It is suggested that cAMP may act as a second messenger in excitatory serotonin responses of snail Helix neurons.

Animals↗
PubMed1988

[Electrophysiological and neurochemical study of long-term sensitization in the snail].

The long-term sensitization of avoidance reflex was produced in snail Helix pomatia, which led to the remarkable increase in the pneumostome closures period. The formation of long-term sensitization is also accompanied by increase in excitability of command neurons of this reflex. One of the possible mechanisms of this phenomenon is the depolarization of these cells. The quantitative redistribution of water-soluble proteins with relative mobility 0.54 0.42 0.40 was also observed in the identified neurons, both included in the avoidance reflex (command neurons) and non-included (bursting neurons, nerve cells of pool D). The protein with the relative mobility of 0.75 was unique for the nerve cells of neurosecretory pool D in sensitized snails, and was never found in control animals.

Action Potentials↗
PubMedDate not supplied

[Differences in the responses of identified neurons to chemical stimuli in satiated and hungry edible snails].

Reactions of command neurones for avoidance behaviour to food were investigated in hungry and satiated snails in "CNS-chemoreceptor" preparations, in which hemolymph was washed out by saline. Neuronal responses in hungry animal preparations differed significantly from responses in satiated animals preparations. Perfusion of hungry animal preparations with hemolymph of satiated animals changed significantly the responses of command neurones for avoidance behaviour. These responses resembled the reactions of the same neurones to food after aversive conditioning to food of hungry snails. The role of humoral factor in learning is discussed.

Animals↗
PubMed1986

The effect of 2450 MHz microwave radiation on the ultrastructure of snail neurons.

An electron microscopical study of snail neurons was undertaken to verify whether any ultrastructural alterations accompany microwave-induced electrophysiological changes observed in these neurons. Subesophageal ganglia from Helix aspersa snails were exposed to 2450 MHz microwave radiation in vitro at SAR 12.9 mW/g for 60 minutes. It was found that exposure at 21 degrees C causes minor changes in Golgi complexes and slight swelling of the endoplasmic reticulum.

Animals↗
PubMedDate not supplied

[Role of the giant serotonin-containing cell of the cerebral ganglion in the edible snail in organizing its food-acquiring behavior].

By adding dopamine or serotonin to a bath with snail's isolated nervous system and by intracellular activation of giant cerebral serotonergic cells it was established in neurophysiological experiments that, in spite of activating effect of serotonin on buccal motorneurones, dopamine is the transmitter triggering feeding movements of the buccal mass and feeding pattern in buccal motorneurones. This conclusion is confirmed by behavioural experiments in which an experimental group was injected by neruotoxin 5,6-dihydroxytryptamine selectively impairing serotonergic neurones. The consumatory phase of feeding (triggered by dopamine) did not change in treated animals, while the appetitive phase was significantly impaired. It was noted that the giant metacerebral cell was activated during burst activity in buccal motoneurones. The conclusion is made that giant serotonergic cerebral cells only modulate but do not trigger the feeding behaviour in the snail Helix lucorum.

5,6-Dihydroxytryptamine↗
PubMed1986

Water snails as paratenic hosts of Hymenolepididae Fuhrmann, 1907 in Czechoslovakia.

The distribution of cysticercoids of Hymenolepididae Fuhrmann, 1907 parasitizing water birds (Anseriformes and Ralliformes) in Czechoslovakia was studied. A total of 2970 snail specimens (429 Lymnaea stagnalis (L.), 531 L. ovata (Drap.), 1, 462 L. peregra (O. F. Müll.), 158 L. auricularia (L.), 262 Planorbis planorbis (L.) and 65 Viviparus viviparus (L.)) were examined for this purpose. Among them, 122 snails were infected with cysticercoids of 13 cestode species (Dicranotaenia coronula (Dujardin, 1845), Diorchis inflata (Rudolphi, 1810), D. nyrocae Yamaguti, 1935, D. ransomi Schultz, 1940, Diploposthe laevis (Bloch, 1782), Echinocotyle rosetteri Blanchard, 1891, Fimbriaria fasciolaris (Pallas, 1781), Microsomacanthus compressa (Linton 1892), M. paracompressa (Czaplinski, 1956), M. paramicrosoma (Gasowska, 1931), M. spiralibursata (Czaplinski, 1956), Sobolevicanthus gracilis (Zeder, 1803), and S. octacantha (Krabbe, 1869).

Animals↗
PubMedDate not supplied

[Dynamics of elaboration of a conditioned reflex and differentiations in the snail].

It is shown that dynamics of percentage of conditioned food refusals by snails Helix pomatia and Helix lucorum is satisfactorily approximated by regression equation of exponential type with included coefficient reflecting the animals state before the beginning of learning. The ability is established of the snails to practically completely differentiate various alimentary conditioned stimuli. The introduction of differentiation always improved the reflex consolidation. Conditioned reactions to differentiation stimulus appeared at the elaboration stage and were absent at the stage of conditioned reflex consolidation.

Animals↗
PubMed1987

[Water-soluble and membrane proteins of the central nervous system of the edible snail at different stages of long-term sensitization].

An increase in the amount of water-soluble proteins with the mobility of 0.56 in polyacrylamide gel was observed in the snail central nervous system at the early stages of long-term sensitization of the defensive reflex. Such an increase seems to be associated with the enhanced motor activity and a rise in the excitation level at this stage. 2 hours, 1 day and 3 days after long-term sensitization a dramatic decrease in the amount of water-soluble proteins with the mobility of 0.54, 0.42, 0.40 and membrane protein with the molecular weight of 24000 kD was observed. Such a decrease appears to reflect the stage nature of long-term sensitization and to be linked with shifts in the functional characteristics of some cellular elements of snail central nervous system.

Animals↗
PubMed1979

Microelectrode investigations of learning phenomena in snail (Helix pomatia) neurones.

We have examined changes of postsynaptic potentials and of pattern activity of the identified silent and oscillatory snail neurones in Helix pomatia during conditioning. Local changes of EPSP or IPSP have been recorded during association following the first stimulus in the silent cells, whereas spike discharges could be observed in response to the 2nd stimulus. In the oscillatory neurones changes of pattern activity have been recorded following the 2nd stimulus, while the first stimulus proved to be ineffective. The formation of temporary connections of snail neurones seemed to be a specific phenomenon, because it was necessary to pair stimuli of different inputs for the development of these modifications. These plastic changes seemed to depend on the interstimulus as well as on the intertrial intervals. Our experimental data underline the probable role of the stimulus parameters and of the electrical properties of neurones during the formation of learned neuronal responses.

Action Potentials↗
PubMed1976

Histochemical studies on mucosubstances in the prostate gland of the pulmonate snail Semperula maculata in the annual breeding-aestivation cycle.

Prostate gland of the pulmonate (terrestrial) snail Semperula maculata was studied histochemically for the presence of polysaccharides. PAS technique and differential staining methods employing Alcian blue, aldehyde fuchsin and Azure A at different pH values and combined with enzyme digestion test and lipid extraction were used. Two histochemically different cell types were found in the prostate gland: the type 1 cells which elaborate neutral mucosubstances and supposedly also phospholipoproteins, and type 2 cells producing glycogen. Both these cell types show seasonal fluctuations of the stores of materials secreted by them. Thus in type 1 cells the weakest histochemical reactivity indicating the lowest concentration of their secretion appears just after cessation of the snails' breeding activity (September) and persists throughout the post-breeding and early pre-breeding seasons which both together constitute the aestivation period. During the rest of the pre-breeding season a strong reactivity gradually develops and culminates in May i.e. immediately before the onset of the breeding activities which in turn initiate a decline of the reactivity. The type 2 cells become most reactive in the middle of the pre-breeding season (May) and decrease their reactivity after cessation of the breeding season. The number of both types of cells parallels the reactivity changes.

Adaptation, Physiological↗
PubMedDate not supplied

[Results and problems set by the introduction of Zonitidae snails in some biotopes of Lymnaea trancatula Müller in Indre and Haute-Vienne, France (author's transl)].

Systematic placing of Zonitidea snails: Zonitoides nitidus and Oxychilus draparnaudi alone or in groups, in different series of habitats of Lymnaea truncatula in Haute-Vienne, France (1974-1976) shows: --the elimination of Lymnaea truncatula is entire after two years in temporary habitats covered with grass just mowed at the beginning of summer drying. The presence of stones, which make shelters, increases numbers of surviving snails. --predators-placing without previous grass-mowing is effective only on banks of rivers.

Animals↗
PubMed1981

Biological control of the snail intermediate hosts of human Schistosoma spp.: a review of its present status and future prospects.

The biological control of freshwater snail hosts of schistosome parasites has attracted much attention in recent years, but the efficiency of such bio-control agents has rarely been tested outside laboratory conditions. The present paper attempts to summarize the present status of biological control of snails intermediate hosts, to indicate some major gaps in our knowledge of this subject, especially those of a practical kind and, not least, to identify studies and activities which apparently merit priority for further sponsorship and support.

Animals↗