Search

The review contains data on functional shifts in fishes, amphibians and birds caused by changes in the otolith system operation after stay under weightlessness conditions. These data are of theoretical and practical significance and are important to resolve some fundamental problems of vestibulogy. The analysis of the results of space experiments has shown that weightlessness conditions do not exert a substantial impact on formation and functional state of the otolith system in embryonic fishes, amphibians and birds developed during space flight. Weightlessness conditions do pot inhibit embryonic development of lower vertebrates but even have rather beneficial effect on it. This is consistent with conclusions concerning development of mammalian fetuses. The experimental results show that weightlessness can cause similar functional and behavioral vestibular shifts both in lower vertebrates and in mammals. For example, immediately after an orbital flight the vestibuloocular reflex in fish larvae and tadpoles (without lordosis) was stronger than in control individuals. A similar shift of the otolith reflex was observed in the majority of cosmonauts after short-term orbital flights. Immediately after landing adult terrestrial vertebrates, as well as human beings, exhibit lower activity levels, worse equilibrium and coordination of movements. Another interesting finding observed after landing of the cosmic apparatus was an unusual looping character of tadpole swimming. It is supposed that the unusual motor activity of animals as well as appearance of illusions in cosmonauts and astronauts after switching from 1 to 0 g have the same nature and are related to the change in character of otolith organs stimulation. Considering this similarity of vestibular reactions, using animals seems rather perspective. Besides it allows applying in experiments various invasive techniques.

Rhythmical contractile activity of amnion accompanies development reptiles and birds in the course of the large part of embryogenesis. These rhythmical contractions are myogenic and spontaneous. The strength, frequency, and character of the amnion contractions change in embryogenesis in a regular way. This type of rhythmical activity is sensitive to many neurotransmitters and external factors. Features of similarity and difference of the amnion rhythmical contractile activity in the reptile and bird embryogenesis are considered. There are discussed a possible functional significance of this rhythmical activity and its participation in response of embryo to external actions, such as temperature fluctuations and acute hypoxia.

It was shown on the example of chick embryo that the number tau 0 (tau n/tau 0) can be recommended as a measure of biological time and, for this purpose, the duration of the minimal mitotic cycle during synchronous cleavage divisions should be determined (in minutes) in various avian species. Based on the preliminary data, one can propose the comparability and similarity of the temporal programs of gastrulation and somitogenesis in the chick embryo and embryos of some fish and amphibians.

A review of one of the key problems of experimental hematology: the origin of hemopoietic stem cells in the development of vertebrates (amphibians, birds, and mammals). The appearance and functioning of two independent sources of hemopoietic stem cells (extra- and intraembryonic) were considered in amphibians, birds, and mammals. The contribution of each source to the formation of definitive hemopoietic tissue was analyzed. It was shown for amphibians and birds that intraembryonic organs such as the dorsolateral plate and the mesenchyme of dorsal aorta are involved in the formation of adult hemopoietic tissue, while the extraembryonic organs such as ventral islets and the yolk sac are devoid of true stem cells and provide only for the primary, transient hemopoiesis. New data have been considered concerning the previously unknown intraembryonic hemopoietic organ in mammals, a region of aorta-gonad-mesonephros arising in embryogenesis simultaneously with the yolk sac. Two extreme views on the involvement of stem cells of all these organs in the formation of definitive hemopoiesis have been considered. The data are provided on the interaction of the embryonic hemopoietic stem cells and the hemopoietic microenvironment of adult recipients.

The author presents for the first time empirical allometrical equations corresponding the mass of dinosaurs with the mass of their eggs, clutch size and its total mass. Comparison of these equations with those that were proposed for modern taxa of reptiles and birds shows that dinosaurs can be characterized by intermediate value of allometry index.

Golgi preparations of the pied flycatcher Wulst region (the structure analogous to the mammalian visual cortex) were analyzed using the method of computerized morphometry, to study the influence of visual deprivation on the development of different types of neurons selected previously. Deprivation was accomplished by covering the young's eye with nontransparent caps. The experiments were carried out in 10-day-old nestlings (the onset of patterned vision) and 13-day-old nestlings (functioning patterned vision). In 10-day-old nestlings, the deprivation produced constructive changes in dendritic apparatus of projective stellate cells (among them, the most pronounced was more than three-fold increase in the number of foci of maximal branching) practically not affecting the small stellate-like cells. In 13-day-old nestlings, cells belonging to all selected cell types underwent destructive changes: their quantitative characteristics were decreased as compared to those in control nestlings. A large number of tree-like neurons were revealed in the Wulst in the deprived 10-day-old nestlings while in the control age-matched nestlings they were virtually never found. This phenomenon may be explained by the increased affinity to impregnation evoked by deprivation-induced biochemical changes in the tree-like neurons or to increase in their number. In the latter case, the phenomenon may be considered as compensatory, directed at the establishing of contacts with nonvisual afferents.

New information about functional properties and peculiarities of alpha-tocopherol and ascorbic acid interaction in birds embryos organism with providing of adequate antioxidant status in embryogenesis and early ontogeny are given. Some characteristics of these natural antioxidants action in different embryonal tissues on the inhibition of lipids peroxidation processes depending on their level in the organism are shown.

Development of auditory sensitivity was studied by recording microphonic component of cochlear potentials during the period of opening the eyes in 6 species of birds with different types of ontogeny (Anas plathyrynchos, Larus canus and L. argentatus, Sterna paradisaea, Coloeus monedula and Corvus frugeleus). The onset of opening the eyes is accompanied by a delay in development of auditory sensitivity and temporary decrease of upper frequency limit of the audible range. Before such a delay acoustic afferentation is leading in feeding behaviour or in response of following in nestlings or chicks. After the period of delay pure tones lose the efficacy in eliciting feeding and following reactions, and the correlation between the low-frequency range of increased sensitivity and the efficacy of pure tone signals disappears, while the new peak of sensitivity appears which fits the maximal energetic component of the parental acoustic signals. It seems possible that the delay may be the result of brain temperature decrease while eyes open the thermoregulation being unstable. Such a delay may facilitate also the substitution of acoustic afferentation for visual in the main behavioural responses in early ontogeny.

The avian primitive (Hensen's) knot is the main center of invagination and final determination of endodermal and mesodermal cells at gastrulation. At stages when the primitive streak is lengthening, cells in the primitive knot have the widest morphogenetic potencies and an outstanding ability for neural induction among other parts of the blastoderm. This labile state of the cells is characterized cytologically by an increased catabolism, expressed as an intensified decomposition of the intracellular yolk and increased autophagocytosis. In some places, the partly digested yolk is excreted from the cells and the marker-enzyme of lysosomes--acidic phosphotase--appears in the intercellular space. Some cells perish, and their debris are absorbed by neighbouring cells. The length of the intercellular contact is decreasing. Thus, the period of cell determination is characterized cytologically as a critical period, after P.G. Svetlov, with high injury and decreased regulatory activity. Individualization of the germ layers proves to be the beginning of a new developmental phase and at the cellular level it possesses some signs of transdifferentiation.

The comparative histological study of processes of embryonic histogenesis of the oesophagus epithelium in certain representatives of vertebrate animals (fishes, amphibia, reptiles, birds, mammals) and man was carried out in the light of the academician A. N. Severtsov's theory of phylembryogenesis. It has been shown that phylogenetic changes of the oesophagus lining of vertebrates related with its evolutionary transformations are regularly reflected in the stages or steps of the oesophagus epithelium histogenesis in ontogenesis of each systematic unit of the subtype. The first step is the phylembryogenesis of the oesophagus lining in all vertebrates is the monolayer epithelium of the endodermal origin; the secone step is the striated muco-ciliated (in low vertebrates and most reptiles) and pseudostratified (embryos of higher vertebrates) epithelium; the third step is the pseudostratified mucous epithelium (bony fishes) and stratified lining (prefetuses of higher vertebrates). The forth step is the stratified mucous (steppe turtle) and stratified muco-ciliated epithelium (fetuses of birds, many mammals and man). The fifth step--stratified squamous epithelium (birds, mammals, man). The academician A. N. Severtsov's theory of phylembryogenesis clearly points to the origins (the entoderm), routs and mechanisms of the transformation of the oesophagus lining in its evolutionary development.

A review of the origin of stem blood cells in ontogeny of vertebrates is presented. The comparative analysis of the data on laying, determination and migration of the hemopoietic precursor cells during embryogenesis in various taxonomic groups (teleosteans, urodeleans, anurans, avians and mammals) is performed. The change of the hemopoietic site and erythroid cells populations has been described. The data on sources of blood cell precursors and the origin of hemopoietic cells in the primordiums of hemopoietic organs were classified. A conclusion has been reached that in the course of evolution the hemopoietic anlage is gradually divided into two parts: one part migrates to the extraembryonic (ventral) mesoderm and another one remains intraembryonically and gives rice to the predecessors of definitive hemopoietic stem cells.

By means of the method for formation of quail-hen transplantation chimeras , contribution of the neural crest cells in the eye development has been studied in early avian embryos. In 6-9 day-old chimeras the neural crest cells participate in formation of the eye sclera and ciliary body, and they also form corneal endothelium and stroma.

Characteristics of auditory evoked potentials (EP) were studied in 1.5 to 7.5 days old Pied Flycatchers nestlings (Ficedula hypoleuca) with chronically implanted electrodes in the field L (analogue of the mammal's auditory cortex). EPs simultaneously with behaviour were recorded in nestlings under conditions similar to natural, in response to "feeding" calls and pure tones of different frequency and intensity. It was found that EP generation thresholds do not depend on the sum total of factors which influence the organization of feeding behaviour. The EP generation threshold is by 13-36 dB (for different frequencies) below that of the appearance of feeding responses in nestling with a maximum high motivation. It is suggested that the realization of inborn behaviour with a signal basis needs not only an integration (formed in the process of embryogenesis) of a definite sensory input with a complex of structures of the "feeding centre", but also the presence of a massive modality-specific inflow.

Temporal hemopoietic organs in the quail embryo are the yolk sac, heart, mesonephros, metanephros, liver, pancreas, small intestine and its mesentrey. In some organs either only erythroid cells (the heart, small intestine and its mesentery), or only granulocytes (the pancreas) are formed. In other temporal organs cell differentiation of both erythrocytic and granulocytic series takes place; as a rule, the erythrocytic series predominate. Maximum of erythro- and granulocytopoiesis in all the temporal hemopoietic organs occur on the 9th--11th incubation days. By the end of the second week of incubation the hemopoietic activity either essentially decreases or stops. The definitive hemopoietic organs are the bone marrow, spleen and organs of the lymphoid system--the thymus and the bursa Fabricii. Differentiation of erythrocytes is especially active in the spleen; granulocytes are predominantly formed in the bone marrow. In the thymus and bursa Fabricii the phase of temporal granulocytohemopoietic activity precedes lymphocytopoiesis. A complete change of erythrocytic population takes 5--6 days of incubation. The definite erythrocytes, even before they appear in blood islets of the yolk sac, are identified in the cardiac hemopoietic focus and in the kidneys of the embryo extremities on the 3d--4th day of incubation. A comparative investigation on development of the hemopoietic tissue in embryogenesis of the quail, hen and starling has been performed.