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D V Lychakov

Publications and source records attributed to D V Lychakov.

At least 19 recordsLinked to original sources
PubMed2006

Fish otolith asymmetry: morphometry and modeling.

Mathematical modeling suggests that relatively large values of otolith mass asymmetry in fishes can alter acoustic functionality and may be responsible for abnormal fish behavior when subjected to weightlessness during parabolic or space flight [D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17-34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55-69]. The results of morphometric studies of otolith mass asymmetry suppose that the absolute value and the sign of the otolith mass asymmetry can change many times during the growth of individual fish within the range +/-20% [D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17-34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55-69]. This implies that the adverse effects of otolith asymmetry on acoustic and vestibular functionality could change during the lifetime of an individual fish. The aims of the present article were to examine the nature of otolith mass asymmetry fluctuation and to quantify otolith mass asymmetry in a large number of teleost fishes to verify our previous measurements. A dimensionless measure of otolith mass asymmetry, chi, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass asymmetry was studied in 59 Mediterranean teleost species (395 otolith pairs), 14 Black Sea teleost species (42 otolith pairs), red drum (196 otolith pairs) and guppy (30 otolith pairs). Utricular otolith mass asymmetry was studied in carp (103 otolith pairs) and goldfish (45 otolith pairs). In accordance with our previous results the value of chi did not depend on fish size (length or mass), systematic or ecological position of the fish, or otolith growth rate. In the great majority of the fishes studied, the saccular otolith chi was small /chi/ <0.05 (or <5%). Mathematical modeling indicates that values of chi vary among individual fish, but that the value is probably stable during a fish's lifetime.

Animals↗
PubMed2005

Fish otolith mass asymmetry: morphometry and influence on acoustic functionality.

The role of the fish otolith mass asymmetry in acoustic functionality is studied. The saccular, lagenar and utricular otoliths are weighted in two species of the Black Sea rays, 15 species of the Black Sea teleost fish and guppy fish. The dimensionless otolith mass asymmetry chi is calculated as ratio of the difference between masses of the right and left paired otoliths to average otolith mass. In the most fish studied the otolith mass asymmetry is within the range of -0.2 < chi < +0.2 (< 20%). We do not find specific fish species with extremely large or extremely small otolith asymmetry. The large otoliths do not belong solely to any particular side, left or right. The heavier otoliths of different otolithic organs can be located in different labyrinths. No relationship has been found between the magnitude of the otolith mass asymmetry and the length (mass, age) of the animal. The suggested fluctuation model of the otolith growth can interpret these results. The model supposes that the otolith growth rate varies slightly hither and thither during lifetime of the individual fish. Therefore, the sign of the relative otolith mass asymmetry can change several times in the process of the individual fish growth but within the range outlined above. Mathematical modeling shows that acoustic functionality (sensitivity, temporal processing, sound localization) of the fish can be disturbed by the otolith mass asymmetry. But this is valid only for the fish with largest otolith masses, characteristic of the bottom and littoral fish, and with highest otolith asymmetry. For most fish the values of otolith mass asymmetry is well below critical values. Thus, the most fish get around the troubles related to the otolith mass asymmetry. We suggest that a specific physicochemical mechanism of the paired otolith growth that maintains the otolith mass asymmetry at the lowest possible level should exist. However, the principle and details of this mechanism are still far from being understood.

Animals↗
PubMed2000

Otolith regularities.

The masses and the area sizes of the otoliths for the utriculus, sacculus and lagena of 15 species of the Black Sea fish are analyzed. Morphometrical otolith regularities are derived and their functional and ecomorphological explanations are suggested. The otolith regularities are summarized in four otolith rules: (1) the masses of the otoliths gradually increase with the fish growth. (2) The mass ratio of the sacculus and utriculus or the sacculus and lagena otoliths does not change with the fish growth. (3) The ratio between the otolith area s and the otolith mass m is described by the exponential equation s=alpham(2/3). (4) The ratio between the otolith and macula sizes does not change with fish growth. Mathematical modeling of the otolith displacement responses to the acoustic and the instant force stimuli is performed. Based on the modeling the functional and ecomorphological explanations of the otolith regularities are suggested: (1) the greater the otolith mass, the higher the acoustic sensitivity at low frequencies and the sharper the frequency-response curve at its maximum. (2) The separation between maxima of the frequency-response curves for the saccular and lagenar otoliths remains virtually constant with the fish growth. (3) The bottom and littoral fish have better auditory capabilities than the pelagic fish. (4) The sensitivity to vestibular stimuli for greater otoliths is higher but the response is slower. The corresponding acceleration resolution for greater otoliths is higher and the range of accelerations in which the otolith organ can operate is narrower. (5) The relative vestibular sensitivities of the utriculus, sacculus and lagena otolith organs remain constant with fish growth. (6) The otolith organs of the bottom and littoral fish are tuned to different accelerations and possess different functional properties. The otolith organs of pelagic fish are adapted to a limited range of accelerations and are less sensitive to low accelerations as compared to the bottom and littoral fish.

Acoustic Stimulation↗
PubMed1984

Microspectrophotometric study of visual pigments in five species of geckos.

Photoreceptors and visual pigments were studied by light microscopy and microspectrophotometry in geckos Teratoscincus scincus, Gymnodactylus russovi, G. caspius, G. fedchenkovi and G. kotschui. Type A single, type B double and the thicker members of type C double cells were found to contain a green-sensitive visual pigment with the maximum absorption at 534-537 nm. Blue-absorbing pigment (lambda m = 446-460 nm) was only found in the thinner members of type C doubles.

Animals↗
PubMed1975

[Some quantitative characteristics of the frog retinal rod outer segments].

Retinal rod outer segments in frogs were studied by means of light microscopy, refractometry, microspectrophotometry, and electron microscopy. Analysis of the data obtained shows that an unidentified substance, which makes up about 50% of outer segment dry weight, is lost during routine biochemical investigations. The protein parts of the rhodopsin molecules make up 85% of the outer segments proteins and 25% of outer segment dry weight. Rhodopsin molecules can be arranged in a square array with a unit cell side of about 7 nm on one side of each disk membrane. Lipids in a single membrane occupy only 2 nm, and disk membranes are strongly hydrated.

Animals↗
PubMedDate not supplied

[The turning reflex, static endurance and structure of the vestibular apparatus receptors in rats exposed to whole-body low-frequency vibration].

Wistar rats were for 2 weeks exposed to vibrations of 18 Hz (acceleration of 2.3 G applied for 5.8 hrs a day for as long as 58 hrs) and 30 Hz (acceleration of 9.6 G applied for 5.1 hrs a day for as long as 56 hrs). The weight gain of experimental animals was less than that of control rats. Static endurance measured in terms of the time, during which the rats stayed on the vertical pole, decreased in the controls as their weight grew. Static endurance of the experimental rats remained essentially unchanged in spite of their growth. This may be associated with the stimulating effect of vibration on the muscle tone. The turning reflex was investigated using a specially designed unit, which allowed stroboscopic photography that was synchronized with the moment, when the animal began to fall down. The angles between the head and torso as related to the horizontal line were calculated and found to be unaltered in both experimental and control animals during 2 weeks. However, after exposure to vibration of both magnitudes the rats began to position the body off the horizontal line. Morphological examinations revealed no distinct structural changes in the utriculus, sacculus or posterior ampulla of the experimental rats when compared with the controls. At the same time it was demonstrated that the exposure produced swelling of cupulate nerve endings in the central compartment of the receptor epithelium of the posterior ampulla. The time course of morphofunctional changes of the vestibular apparatus in response to vibration of different frequencies (from 6 to 50 Hz) was also examined.

Animals↗
PubMedDate not supplied

[Study of the structure of receptor organs of the vestibular apparatus of rats after space flight on "Kosmos-1667"].

The receptor organs of the vestibular apparatus of rats flown for 7 days on Cosmos-1667 were examined. Serial sections were examined by light microscopy, some utriculus sections by electron microscopy, and otolith membranes by scanning electron microscopy. The fixation method used revealed a distinct structural heterogeneity of the receptor epithelium. In the striola area of the utriculus and sacculus as well as in the central apical area of cristae there are receptor cells surrounded by enlarged cup-like nerve endings. The nerve endings occupy over 70% of the cup-receptor cell complex. The area incorporating the enlarged nerve endings differs in size from animal to animal and from left to right ear in the same animal. The flown rat that was the first to be killed after recovery showed a very well pronounced asymmetry: in the right ear enlarged cups were seen all over the epithelium while in the left ear they were located in distinct spots. Since such changes were not identified in the remaining flown and control rats, it is concluded that they were produced by space flight effects but remained reversible and disappeared after recovery. This paper describes the causes responsible of the changes and their structural and functional relevances as well as other structural modifications that should be considered during vestibular studies.

Aerospace Medicine↗
PubMedDate not supplied

[Structural resistance of receptor organs of the vestibular apparatus to the factors of space flight].

Observations made in ground-based simulation studies and in real orbital flights on fish and amphibian larvae as well as on adult rats show that exposure to different space flight factors, particularly microgravity, for as long as 20 days produces no pathological changes in the structural organization of vestibular receptors. However the possibility of functional or adaptive rearrangements in maculae and crystae as well as in the otolith organ cannot be excluded. It appears that bony fish (Teleostei) are most suitable for the study of adaptive changes in the otolith apparatus. When examining ultrastructural changes in maculae and crystae, it is important to take into consideration spatial and structural nonhomogeneity of the receptor epithelium of vestibular organs.

Acceleration↗
PubMedDate not supplied

[Changes in the otolithic apparatus of rats and fish after long-term rotation with increased acceleration].

Otolith membranes of the utriculus and sacculus of rats exposed to 2 g during a month showed a typical size-related distribution of otoconia, which had optic activity. The length (L) and diameter (D) of utricular otoconia were linearly correlated as follows: D = 0.4 + + 0.4 L (microns). During chronic acceleration the mean size of utricular otoconia tended to diminish. Guppy fish were rotated at 1.8-2.2 g for 4 months and showed an absolute and a relative increase of the saccular mass when compared to the mass of the utricular or lagenar otolith. During chronic centrifugation the microrelief of the auditory sulcus of the saccular otolith changed. It can be concluded that prolonged centrifugation causes structural changes in the otolith apparatus of terrestrial and water animals which are probably of adaptive character.

Acceleration↗
PubMedDate not supplied

[Structure of the vestibular apparatus and ionic composition of the body of Xenopus laevis larvae as affected by weightlessness].

Clawed frog larvae (stages 45-46) that developed for 9 and 8 days beginning with the blastula and tail bud stages, respectively, in the weightless state were investigated. Scanning microscopy of the larval labyrinths did not reveal significant qualitative changes in the receptor and supporting cells of the maculae and in the otolith membrane. Determination of the electrolyte composition (Na, K, Ca, Mg) of the larval body showed no significant changes in the relative content of these elements. The morphometric examinations indicated an increase of the size of the utricular otoliths by 1.3 times as a result of exposure to weightlessness. There was a tendency for a greater asymmetry between the left and right otoliths in the same larva.

Animals↗