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At least 271 records · Page 15Linked to original sources
PubMed2000

Membrane transduction pathway in the neuronal control of protein secretion by the albumen gland in Helisoma (Mollusca).

The albumen gland in Helisoma secretes a perivitelline fluid which surrounds each egg and is made up of several 66 kDa protein subunits and polysaccharide complexes. Forskolin, an adenylate cyclase activator, stimulated the secretion and release of the perivitelline fluid. An acidic extract of the central nervous system increased the intracellular concentration of cAMP in the albumen gland and this results in the release of the 66 kDa molecule and other proteins. Digestion of the brain extract with proteases abolished this activity, suggesting that the factor is a peptide. Cyclic AMP analogues and [BMX also stimulated the protein secretion in dose-dependent manner. Forskolin when added with the brain factor had an additive response. SQ22536, a non-competitive inhibitor of adenylate cyclase, inhibited brain extract dependent adenylate cyclase activity whereas aluminum fluoride, a G protein activator, was found to stimulate adenylate cyclase. Dopamine also stimulates protein secretion by the albumen gland and through the application of various agonists and antagonists of dopamine, it was established that the neurotransmitter acts via D1-like receptors by stimulating adenylate cyclase.

Animals↗
PubMed2000

[Genetic and morphological variability of the gastropod mollusk Nucella heyseana (Mollusca, Gastropoda) in the environmental optimum and pessimum].

Genotypic variability at six allozyme loci and six morphological shell characters was examined in 450 individuals (four samples) of mollusk Nucella heysana from the Vrangel' Bight (Nakhodka Bay) and the Vostok Bay (Peter the Great Gulf, Sea of Japan). An analysis of variation in allele frequencies showed that each of the two localities (Vostok and Nakhodka bays) in the analyzed region is inhabited by a single, albeit genetically heterogeneous, population. A canonical analysis and an analysis of variance of individual heterozygosity (Ho) and morphological variation indicate an association between Ho and morphological variation depending on habitat (interaction) in settlements in the Vrangel' Bight and, to a lesser extent, in the Vostok Bay. These results indicate that, in extreme environmental conditions, allozyme phenotypes may be selected either themselves or as markers of genes linked with them.

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PubMedDate not supplied

[The role of the natural selection in supporting genotypical constancy of natural populations of Bradybaena fruticum (Muller), Mollusca, Gastropoda, as a result of ecological monitoring].

Prolonged 16-year's monitoring has revealed dynamics of genotypical structure in two generations of mollusks from eight natural populations of Bradybaena fruticum in four areas of Moscow region and two Moscow parks. The selection effect was determined through the analysis of shifts of allele frequencies, different age groups of the same generation and adults of different generations were compared. The selection effect on two polymorphous locuses--conchological and allozymic is revealed. It is shown, that the natural selection supports constancy of indicated polymorphous characters in populations in time. Two aspects of action of selection are revealed: the selection during life of one generation changes alleles' value; the direction of selection revealed among generations shows the advantage of geterozygotes. Vectors of selection in generations can differ. The mechanism of maintaining populational gomeostas in time is revealed. The supposition about primary importance of one of estherases alleles is confirmed.

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PubMed2001

[Secondary production and condition index in Arca zebra (Mollusca: Vivaldia) in the Gulf of Cariaco, Venezuela].

Production and condition index of a turkeywing (Arca zebra) population were studied from August 1984 to August 1985 in Pariche, Cariaco Gulf, Venezuela. Production was studied through bimonthly collections using a method designed for populations with continuous reproduction and indistinguishable age classes. The population distribution was stable with a mean density of 37 ind.m-2. A production of 131.61 g dry weight m-2 year-1 was calculated from data on density, biomass and weight increase along the year. Highest production was between February 1985 and August 1985 (65%) and concentrated in individuals 60.00-79.95 mm long (45.73%). There was large seasonal variation in the mean monthly condition index (IC = (Ps/Ph) x 100) in the two size classes examined: it reached a maximum in July 1985 (26.84%) and a minimum in January 1985 (16.31%).

Animals↗
PubMedDate not supplied

[Effect of different concentrations of heavy metal ions on the normal physical and chemical characteristics of the hemolymph of Palanorbarius purpura (Mollusca: Bulinidae) in the norm and during a trematode infection].

Short-term simultaneous effect of high concentrations (LC25, LC50, LC75) of heavy metal ions. (Cu2+, Zn2+, Cd2+ and Pb2+) and infection with trematode partenites Echinoparyphium aconiatum onto haemolymph of mollusk has been investigated. It was noted that low doses of toxicant (2.5 and 10 maximum admitted concentrations) have variable effect. In infected molluscs the concentration of haemoglobin decreases, while in intact ones it increases. In relation to this index, it was found, that the ion Cu2+ is highly toxic, Zn2+ and Cd(2+)--toxic, Pb(2+)--moderately toxic.

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PubMedDate not supplied

[The effect of trematode invasion and chromium sulphate on the crude protein content in the haemolymph of Viviparus viviparus (Mollusca: Gastropoda: Pectinibranchia)].

The combined effect of the trematode infection (Echinoparyphium sp.) and various concentrations of chromium sulphate (0.01, 1, 100 mg/l) onto the crude protein content in the haemolymph of the mollusc Viviparus viviparus was investigated. The normal contents of the crude protein is 0.7-1.22%. In adult specimens its concentration is 20-80% higher than in molluscs of junior age group. Sex difference by this index, which is higher in females, begins to manifest in four year old individuals only. The contents of crude protein in the haemolymph of pregnant females is 1.5 times higher than in latent ones. Under the low intensity of the trematode infection, the contents of crude protein in the haemolymph remains normal, while in the case of heavy infection, it decrease 100 times or lower. In the cases of 0.01-1 mg/l concentrations of chromium sulphate, the content of protein in the haemolymph of V. viviparus decreases, while in the case of 100 mg/l it increases abruptly, in comparison to the norm. The trematode infection intensifies these processes.

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PubMed2002

[Somatic polyploidy in neurons of the gastropod mollusca. III. Mitosis and endomitosis in the postnatal development of neurons in the Succinea snail central nervous system].

General morphology of chromatin, the number of chromosomes and chromocenters in normal condition and at the increase of bivalent cation (Ca2+, Mg2+) concentration were studied with the purpose to reveal mechanisms of polyploidization of neuron nuclei in the snail Succinea lauta (Gastropoda, Pulmonata). The morphology of nuclei was studied on squashed preparations. Normal diploid mitoses are described in the cerebral ganglia. A possibility is supposed that part of neurons or neuroblasts in the central nervous system (CNS) of succineid snail may divide mitotically. It has been shown that the basic mechanism of neuron postnatal growth is endomitotic polyploidization of nuclei. The transition from ordinary mitosis to polyploid cycles occurs via restitutional (polyploidizing) mitosis (4c2n-->4c4n). The next endocycles are carried out by means of classic endomitosis up to reaching the highest ploidy levels--4096n--16,384n. The study of general morphology of chromatin and chromocenters at normal condition and at artificial compactization enabled us to exclude any probability of polyteny in the CNS of lauta.

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PubMed1992

Amplification of GC-rich DNAs in neuronal nuclei of Planorbarius corneus (L.) (Mollusca, pulmonata).

Quantitative microfluorometric evaluation of DNA content in nerve cells of the Pulmonate Gastropod Planorbarius corneus has indicated that the increase in nuclear volume is due to DNA amplification. Indeed, it has been observed that the DNA contents are scattered at random between 2C and 1,000C values. This is not in agreement with the occurrence of repeated duplications of the whole genome. Furthermore, chromatin photo-oxidation, a technique useful in discriminating GC-rich from AT-rich DNAs, suggests that DNA amplification involves GC-rich sequences.

Animals↗
PubMed1992

Patterns of neural and behavioral activity in freely-moving Navanax inermis (Mollusca; Opisthobranchia).

As part of an ongoing neuroethological study of complex behavior in the opisthobranch mollusc, Navanax inermis, I have extended the available gross anatomical descriptions and used cuff electrodes to obtain chronic recordings from whole nerves or connectives. The major anatomical findings concern a) finer branches of the pedal nerves, particularly P3C P4 and P5; b) the distribution of nerves from the abdominal and subintestinal ganglia; and c) a possible neurohaemal area of the supraintestinal ganglion. With cuff electrodes it has been possible to get good quality recordings (often with spikes in the mv range) during the full repertoire of sexual, predatory and cannibalistic behaviors. The high degree of cryptic neural activity and the fact that in Navanax behaviors are not mutually exclusive, make it difficult to identify one-to-one correspondences between behaviors and neural patterns, However, there is an apparent correlation between the activity of a very large unit(s) on P5 and an exploratory behavior, the Face-Down head posture when it is directed at the substrate rather than prey, or a conspecific.

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