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D V Lychakov

Publications and source records attributed to D V Lychakov.

29 records · Page 2Linked to original sources
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[Surface structure of the otolithic organs of the tadpole of the clawed toad Xenopus laevis].

Beginning from the blastula and tail bud stages, 15 larvae of the clawed toad were kept in three EMKON containers at temperature 15 degrees for 8-9 days. Structure of the hair cells and otolith membrane of the larval otolithic organs was examined with a light microscope, TEM and SEM. In contrast to previous studies, it was found that at the stages mentioned larval otolithic organs are presented not by two, but by three maculae, i.e. the utricular, saccular and lagenar ones with two otoliths. Saccular and lagenar maculae are covered by a common otolith membrane. Separate otoconia may loose from the otolith membrane, this process being enhanced by fixation. Within the maculae, receptor cells differ with respect to the structure of hair bundles. Basing on the morphology of ciliary tufts, 4 types of the hair cells were identified. However, TEM examination did not reveal significant differences in the ultrastructure of these types of cells. Maculae of the three otolithic organs varied in the cell type patterns and cell polarization. No continuous row of the immature hair cells was found along the perimeter of the maculae.

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[Scanning electron microscope study of the labyrinth of Macaca mulatta under hypokinetic conditions].

Rhesus monkeys have been kept in horizontal position under klinostatic or antiorthostatic hypokinetic conditions for 7 and 19 days. Using scanning electron microscope, studies were made of the otolithic membrane of the utricle, the receptor surface of the utricle, crista ampullaris of the lateral semicircular canals, the organ of Corti, the stria vascularis and spiral ligament. No significant differences were found between control and experimental animals.

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[Receptor surface of Corti's organ in guinea pig embryos].

Using scanning electron microscope, studies have been made of the structure of the receptive surface of the organ of Corti in 48- and 57-day old embryos of the guinea pig. It was found that some structural modifications take place in this period: the size and the number of microvilli in the supporting cells decrease, the width of the organ of Corti increases, the number of ball-like cytoplasmic protrusions from the cellular surface decreases, the number of kinocilia in the receptor cells is reduced. These processes are associated presumably with the development of Nuel's space, Corti's tunnel, the origin of flexible connection between the tectorial membrane and the receptive surface, as well as with maturation of the ionic composition of the inner ear fluid.

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[Vestibular apparatus study of the toad, Xenopus laevis, and rats under prolonged weightlessness].

Fertilized eggs of the clawed toad Xenopus laevis were placed aboard of orbital laboratory of "Salut-6" spacecraft where they developed for 20 days at temperature 15 degrees C. The larvae were fixed in weightlessness. Light and electronmicroscopic studies revealed undisturbed structure on the saccular and utricular maculae and otolith membranes. Some ultrastructural abnormalities were found in the inner ear of adult rats after 20 days of weightlessness ("Kosmos-936").

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[The utricular otolith membrane in the guinea pig].

Several types of otoconia are present in the otolithic membrane of the utricle of fetal, young and adult guinea pigs. These include smooth, transitional and rough otoconia, and a few rhombohedrons. The smooth otoconia are nearly the same numeric fraction in all the specimens. The mean size of otoconia increases only during the course of gestation. Our measurements indicate that the diameter (d) and the length (l) of otoconia are related linearly as: d = 0.4l + 0.4. The smooth otoconia seem to be independent morphological form which is not derived from more "primitive", rough or transitional ones. The otoconia consist mainly of CaCO3 and contain Na, Mg and trace amount of K. The chemical composition of otoconia is similar in fetal, young and adult guinea pigs.

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[The content of electrolytes (Na, K, Ca, Mg) in vertebrate otoliths and otoconia].

Na, K, Ca and Mg concentrations have been determined in the otoliths and otoconia of the lamprey, skate, guppy and hen. Lamprey otoliths sharply differ from the otoliths and otoconia of other animals with respect to their K and Ca content. In all the animals investigated excluding lamprey, only traces of K were found. Na concentration in the otilithic apparatus of the investigated animals varies within 0.475-1.04 mM/g. Na presumably is bound to proteins of the organic matrix and plays an important role in the growth of otoliths and otoconia. Concentration of Ca in the otoliths and otoconia of all animals excluding the lamprey was equal to 9.09-9.63 mM/g: organic substances constitute 4-10 per cent of their mass. In the lamprey, Ca concentration in the otoliths was found to be 5.33 mM/g, the content of organic matter amounting to more than 40 per cent. In constantly growing otoliths of fish, concentration of Mg was significantly lower than in otoconia of fish and other animals. This is presumably due to the fact that Mg inhibits crystalline growth of calcium salts.

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[The vestibular apparatus of quail embryos in an experiment on the Kosmos-1129 biosatellite].

The light microscope was used to study serial sections of labyrinths of quail embryos incubated and reared during 12 d orbiting of Cosmos 1129. On recovery the embryos were aged 9, 11.5 and 12 days. No significant deviations in the development of the vestibular apparatus in flight species were noted as compared to the controls. Given this and our experimental data about in-space development of fish and amphibians we may deduce that hypo-g does not exert a noticeable altering effect on the vestibular embryogenesis. Nevertheless, it should be pointed out that in all otolith organs and semicircular channel ampules of the flight embryos cup-form neural endings innervating type I sensory cells were markedly swollen in contrast to the control. Earlier swollen cup-form nerve endings have been found in one adult rat after 7 days of space flight aboard Cosmos 1667. However, exposure in space does not bring about a substantial swelling of bud-like nerve endings which contact type II sensory cells. Thus, a conclusion may be drawn that spaceflight factors are liable to produce shifts in the type I sensory cell--cup-form nerve ending unit but they do not affect type II sensory cell--bud-like nerve ending unit to the extent when effects can be identified by light microscopy.

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[Light and electron microscopic study of the photoreceptors of the lamprey Lampetra fluviatilis].

Photoreceptors of the retina have been investigated by electron microscopic and light microscopic techniques using differential staining. The observed differences between short and long photoreceptors suggest that the former act as the receptors of scotopic system and contain rhodopsin, whereas the latter contain presumably cone pigment and may be classified as receptors of photopic system.

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