Biogeochemical Characteristics of Earth's Volcanic Permafrost: An Analog of Extraterrestrial Environments

This article describes a study of frozen volcanic deposits collected from volcanoes Tolbachik and Bezymianny on the Kamchatka Peninsula, Russia, and Deception Island volcano, Antarctica. In addition, we studied suprasnow ash layers deposited after the 2007 eruptions of volcanoes Shiveluch and Bezymianny on Kamchatka. The main objectives were to characterize the presence and survivability of thermophilic microorganisms in perennially frozen volcanic deposits. As opposed to permafrost from the polar regions, viable thermophiles were detected in volcanic permafrost by cultivation, microscopy, and sequencing. In the permafrost of Tolbachik volcano, we observed methane formation by both psychrophilic and thermophilic methanogenic archaea, while at 37°C, methane production was noticeably lower. Thermophilic bacteria isolated from volcanic permafrost from the Deception Island were 99.93% related to Geobacillus stearothermophilus. Our data showed biological sulfur reduction to sulfide at 85°C and even at 130°C, where hyperthermophilic archaea of the genus Thermoproteus were registered. Sequences of hyperthermophilic bacteria of the genus Caldicellulosiruptor were discovered in clone libraries from fresh volcanic ash deposited on snow. Microorganisms found in volcanic terrestrial permafrost may serve as a model for the alien inhabitants of Mars, a cryogenic planet with numerous volcanoes. Thermophiles and hyperthermophiles and their metabolic processes represent a guideline for the future exploration missions on Mars.

Increased Synthesis of a Magnesium Transporter MgtA During Recombinant Autotransporter Expression in Escherichia coli

Overproduction of the membrane proteins in Escherichia coli cells is a common approach to obtain sufficient material for their functional and structural studies. However, the efficiency of this process can be limited by toxic effects which decrease the viability of the host and lead to low yield of the product. During the expression of the esterase autotransporter AT877 from Psychrobacter cryohalolentis K5^T, we observed significant growth inhibition of the C41(DE3) cells in comparison with the same cells producing other recombinant proteins. Induction of AT877 synthesis also resulted in the elevated expression of a magnesium transporter MgtA and decreased ATP content of the cells. To characterize the response to overexpression of the autotransporter in bacterial cells, we performed a comparative analysis of their proteomic profile by mass spectrometry. According to the obtained data, E. coli cells which synthesize AT877 experience complex stress condition presumably associated with secretion apparatus overloading and improper localization of the recombinant protein. Several response pathways were shown to be activated by AT877 overproduction including Cpx, PhoP/PhoQ, Psp, and σ^E The obtained results open new opportunities for optimization of the recombinant membrane protein expression in E. coli for structural studies and biotechnological applications.

A definition of bioinks and their distinction from biomaterial inks

Biofabrication aims to fabricate biologically functional products through bioprinting or bioassembly (Groll et al 2016 Biofabrication 8 013001). In biofabrication processes, cells are positioned at defined coordinates in three-dimensional space using automated and computer controlled techniques (Moroni et al 2018 Trends Biotechnol. 36 384-402), usually with the aid of biomaterials that are either (i) directly processed with the cells as suspensions/dispersions, (ii) deposited simultaneously in a separate printing process, or (iii) used as a transient support material. Materials that are suited for biofabrication are often referred to as bioinks and have become an important area of research within the field. In view of this special issue on bioinks, we aim herein to briefly summarize the historic evolution of this term within the field of biofabrication. Furthermore, we propose a simple but general definition of bioinks, and clarify its distinction from biomaterial inks.

Terahertz radiation from bismuth surface induced by femtosecond laser pulses

We report on the first experimental observation of terahertz (THz) wave generation from bismuth mono- and polycrystalline samples irradiated by femtosecond laser pulses. Dependencies of the THz signal on the crystal orientation, optical pulse energy, incidence angle, and polarization are presented and discussed together with features of the sample surfaces. The optical-to-THz conversion efficiency was up to two orders of magnitude higher than for metal at a moderate fluence of ∼1  mJ/cm². We also found nonlinear effects not previously observed using other metal and semiconductor materials: (a) asymmetry of THz response with respect to a half-turn of a sample around its normal, (b) THz polarization control by orientation of the sample surface, and

[SPREADING OF TISSUE SPHEROIDS FROM PRIMARY HUMAN FIBROBLASTS ON THE SURFACE OF MICROFIBROUS ELECTROSPUN POLYURETHANE MATRIX (A scanning electron microscopic study)]

Tissue spheroids biofabricated from primary human fibroblasts using non-adhesive agarose forms, were placed by 3D bioprinter on the surface of microfibrous electrospun matrix. It was demonstrated that tissue spheroids attached to the surface of matrix during several hours and then gradually spread for several days which indicates high level of biocompatibiity of electrospun microfibrous polyurethane matrix. During this activity, human fibroblasts used processes of leading cell borders for initial step of attachment to matrix filaments. Tissue constructions formed during spreading of tissue spheroids on the surface of electrospun microfibrous polyurethane matrix seem to be a perspective technology platform for development of new methods of biofabrication and 3D bioprinting.

[PERIPHERAL AUTONOMOUS REGULATION OF SINUS (SINOATRIAL) NODE IN TYPE 1 AND 2 DIABETES MELLITUS]

The aim of this work was to study peripheral vegetative regulation of pacemaker activity of the sinus (sinoatrial) node (SN) by high resolution analysis of cardiac rhythm variability (CRV) in patients with type 1 and 2 diabetes mellitus (DM). All CRV waves in the temporal and spectral regions were shown to be reduced. Regulatory effects of SN were pathologically distributed as appears from the increase of inefficient sympatho-metabolic influence due to the decrease of sympatho-parasympathetic one. Such change and redistribution of effects of regulatory SN factors are the predictors of cardiovascular disorders associated with DM1 and DM2. The low-amplitude CRV fluctuations of certain period and frequency suggest their pathogenetic relationship with DM decompensation. They differed from normal parasympathetic lengthening of a single RR-interval due to the high speed of pulse passage along parasympathetic fibers. It is supposed that these waves with periods 2.33. ± 2.35 and 2.3 ± 2.1 s and spectral density peaks 0.23 ± 0.045 and 0.24 ± 0.16 Hz showing average and moderate correlation with clinical and laboratory data (r = 0.543 ± 0.028 in DM1 and 0.388 ± 0.034 in DM2) are markers of diabetic endotoxicosis.

Terahertz emission from a metallic surface induced by a femtosecond optic pulse

Results of experimental and theoretical investigations on generation of terahertz radiation at the interaction of femtosecond laser pulses with a metal surface are presented. Investigations are performed with the laser pulse intensities higher compared with that used in papers [Opt. Lett.29, 2674 (2004); Opt. Lett.30, 1402 (2005)]. The most effective generation is observed for p-polarized optical pulses with incidence angles in the range 5°-10° (from the surface), depending on the kind of metal. For the copper, the exponential growth of terahertz pulse energy with the increase of optical pulse energy was registered. Theoretical interpretation for some of the experimental results is proposed based on the model of free electrons in metal.

[Dysregulation of the sinoatrial node of the heart in patients with coronary heart disease during coronary artery bypass surgery]

Results of estimation of variability of cardiac rhythms in patients with coronary heart disease during coronary artery bypass surgery are presented. The aim of the study was to search for innovative methods for the assessment of the patients' conditions as a criterion for their rational choice for cardiosurgical intervention to enable adequate anesthesiological support and postoperative follow-up. We revealed additional characteristics of cardiac rhythm variability facilitating such choice and predictors of the risk of life-threatening heart arrhythmias. It is shown that high-resolution analysis of cardiac rhythms allows such peculiarities of dynamics of patient's conditions to be revealed that can not be exposed by the existing standard methods.

Anisotropic effects of terahertz emission from laser sparks in air

Strong terahertz (THz) radiation can be generated by intense femtosecond laser pulses propagating in air. The excitation of transient current induced in the wake just behind the laser pulse is studied in detail using numerical simulations on the basis of Maxwell's equations for THz-band fields and hydrodynamic model for the plasma motion. It is shown that the thermal effects, anisotropic in character in the case of linear polarized laser field, can explain observed quadrupole-type THz radiation pattern in the experiment performed by Akhmedzhanov [Radiophys. Quantum Electron. 52, 482 (2009)]. Taking into account the transverse structure of the plasma filament, our numerical code enables us to calculate the spatial distribution and temporal evolution of terahertz electron current, its spectrum, and angular emission pattern. It is shown that an expansion of full fields in terms of azimuthal modes is a useful tool for research of THz generation in many situations of practical interest.

[Analysis of cardiac rhythm variability in patients with sinoatrial node dysfunction]

The study was designed to elucidate the wave structure of heart rhythm variability (HRV) for the assessment of vegetative regulation of pacemaker activity of the sinoatrial node in 362 patients with coronary heart disease. The results were compared with the data of routine cardiologic examination. Sinus node dysfunction and weakness were shown to be accompanied by differential autonomous dysregulations that may be used as additional symptoms for the diagnosis of arrhythmias. Precision analysis of HRV permits to evaluate the arrhythmogenic events behind vegetative regulation of the sinus node, hemodynamic significance of arrhythmic episodes, and dependence of sinoatrial blockade on the degree of autonomous dysregulation. Autonomous cardioneuropathy syndrome is distinguished, its association with necrobiotic changes in the sinus node is demonstrated by electron microscopy.

[Sinus rhythm variability in bronchial asthma]

The subjects, 265 patients with bronchial asthma (BA) patients (mean age: 41.92 +/- 1.36 yr), were examined using spirometry, peak-flowmetry, body plethysmography, EchoCG, and bronchoscopy with biopsy and histologic study. A high-resolution method--rhythmocardiography with temporal statistical and spectral analysis of sinus rhythm variability at rest and at directed testing using hardware and software complex KAP-RK-01-Micor (Chelyabinsk)--was applied. The patients with BA displayed sinus node dysregulation, insufficient vegetative providence, significant depression of peripheral sympathico-parasympathetic regulation in general, intensification of humoral-and-metabolic influence on pacemaker cells in the sinus node, and the forming of a pathophysiological pattern of response to stimuli during tests.

[Calcium as a regulator of intracellular processes in actinomycetes: a review]

Data on the effects of calcium ions (Ca2+) on processes of morphological and physiological differentiation in cultures of actinomycetes have been reviewed, with emphasis on representatives of the genus Streptomyces. Evidence accumulated thus far, of the regulatory role of serine-threonine protein kinases in the differentiation and of the possible involvement of Ca2+-dependent protein kinases in secondary metabolism (including antibiotic biosynthesis) are analyzed. The possibility that regulatory elements of apoptosis (including Ca2+-dependent) function in actinomycetes is discussed. A hypothesis is advanced, according to which determinants of antibiotic resistance play a key role in the network of signal transduction systems of actinomycetes.

[Antioxidant effect on the growth of Saccharopolyspora erythraea and biosynthesis of erythromycins]

Oxidative stress in the mycelium of submerged culture of S. erythraea, an organism producing erythromycins, was observed. The stress could be eliminated by addition of antioxidants, such as butyloxyanisole, alpha-tocopherol, cytochrome C to the culture. In the presence of the antioxidants the mycelium lysis decreased, the level of the decrease being higher in the medium preferably containing carbohydrates vs. the medium mainly containing lipids (soybean oil). The antioxidants had no specific effect on the biosynthesis of erythromycins.

[Biogenesis and regulation of biosynthesis of erythromycins in Saccharopolyspora erythraea: a review]

Data on the structure and stages of biosynthesis of erythromycins, relating to (1) successive addition of L-mycarose and D-desosamine to the lactones erythronolide B and mycarosyl-erythronolide B, respectively, and (2) biotransformation of erythromycin D to erythromycin A, are presented. Pathways of biosynthesis of L-mycarose, D-desosamine, and methylmalonyl-CoA and methylpropionyl-CoA precursors of erythronolide B are reviewed, along with the properties of genes coding the enzymes involved. Possible mechanisms of biochemical and gene regulation of erythromycin biosynthesis in Saccharopolyspora erythraea are discussed, including the role of factors ensuring predominant formation of the target product, erythromycin A.

[Dependence of the composition of the avermectin complex of Streptomyces avermitilis on glucose content of the growth medium]

The effects of glucose concentration in the medium and O-methyl-L-threonine resistance on the ratio of components of the avermectin complex produced by Streptomyces avermitilis have been studied. Glucose deficiency increases the ratio of components A and a, while decreasing that of components 1 in the complex. A mutation that renders the microorganisms resistant to O-methyl-L-threonine (an analog of isoleucine) increases the ratio of components a, while decreasing that of components 1 in the complex. The distribution of a and b in fractions 1 and 2 remains constant: the values of the ratio a/b in the fractions amount, respectively, to 1:1 and 2:1. The relation of the variations in the composition of the avermectin complex to changes in the carbohydrate metabolism of the producer stain, underlain by availability of the source of carbon, is discussed.

Regaining chondrocyte phenotype in thermosensitive gel culture

Chondrocyte tissue engineering continues to be a challenging problem. When chondrocytes are duplicated in vitro, it is imperative to obtain an adequate number of cells of optimal phenotype. A temperature-sensitive polymer gel, a copolymer of poly(N-isopropylacrylamide) and acrylic acid (PNiPAAm-co-Aac), has the ability of gelling at 37 degrees C (the lower critical solution temperature, LCST) or above and liquefying below that temperature (Vernon and Gutowska, Macromol. Symp. 1996;109:155-167). The hypothesis of this study was that chondrocytes could (1) duplicate in the copolymer gel; (2) regain their chondrocyte phenotype; and (3) be easily recovered from the gel by simply lowering the temperature below 37 degrees C. Chondrocytes from adult rabbit scapular cartilage were harvested and cultured in a monolayer culture until confluency (approximately 2 weeks). Next, the cells were harvested and seeded into the copolymer gel and cultured for 2-4 weeks. The phenotype of the cultured cells was then characterized. Two groups of control cultures, monolayer and agarose gel, were used to compare their ability to maintain chondrocyte phenotype. The results showed that chondrocytes isolated from rabbit scapula can re-express chondrocyte phenotype in agarose culture and polymer gel culture but not in monolayer culture. Also, cultured chondrocytes can be easily recovered from polymer gel culture by simply lowering the temperature. This new in vitro method of chondrocyte culture is recommended for chondrocyte propagation and regaining chondrocyte phenotype before cell seeding or transplantation.

Calcium-induced alterations in the functioning of protein serine/threonine and tyrosine kinases in Streptomyces fradiae cells

In Streptomyces fradiae, calcium ions induce alterations in intensity and specificity of the secondary metabolism and stimulate sporulation. Using in vivo labeling, we demonstrate that in S. fradiae phosphorylation of some proteins are also influenced by Ca2+ added exogenously. Calcium ions at physiological concentration increase phosphorylation of multiple proteins on serine/threonine residues and suppress modification of a 140-kDa protein on tyrosine residues. Assay of protein kinases in situ demonstrated that Ca2+-induced differences in the pattern of protein phosphorylation in vivo are accompanied by Ca2+-dependent cessation of autophosphorylation of 140-kDa tyrosine kinase and by increased autophosphorylation of three serine/threonine kinases with molecular masses of 127, 65, and 31.5 kDa.

[Alteration of serine/threonine protein kinase activity during growth of the wild type Streptomyces avermitilis strain and its chloramphenicol-resistant mutant]

The dynamics of serine/threonine protein kinase activity during the growth of the wild-type Streptomyces avermitilis strain and its chloramphenicol-resistant (Cmlr) pleiotropic mutant with an enhanced production of avermectins was studied by measuring the transfer of radiolabeled phosphate from [gamma-32P]ATP to the serine and threonine residues of proteins in cell-free extracts. In both of the strains studied, radiolabeled phosphate was found to incorporate into polypeptides with molecular masses of 32, 35, 41, 68, 75, 79, 83, and 137 kDa; however, the degree and the dynamics of phosphorylation of particular peptides were different in these strains. The differences revealed could not be accounted for by the interference of ATPases or phosphoprotein phosphatases. The data obtained may be interpreted as evidence that Cmlr mutation activates the protein kinase signalling system of S. avermitilis cells in the early stationary growth phase and thus enhances the production of avermectins and leads to some other physiological changes in the mutant strain.

Regime of wave-packet self-action in a medium with normal dispersion of the group velocity

Peculiar features of the self-action of non-one-dimensional wave packets described by the nonlinear Schrodinger equation with a hyperbolic spatial operator were studied analytically and numerically. It was shown that the self-action dynamics is determined by the consequence of the processes of transverse self-focusing filamentation and longitudinal splitting. Splitting scenarios were classified. It is shown that the strongest inhomogeneities are excited along "hyperbolas" in the self-similar collapse process.

[Effect of Ca2+ ions on biosynthesis and component composition of tylosin in Streptomyces fradiae]

The influence of Ca2+ ions on biosynthesis of tylosin complex by Streptomyces fradiae in an enriched medium under submerged conditions was studied. It was shown that Ca2+ (at the concentration of 20 to 30 mM CaCl2) stimulated the tylosin biosynthesis by eliminating the limit of incorporation of the precursors such as macrocin and desmycosin to the process and by inhibiting catabolism of tylosin to relomycin. No potentiation of the Ca2+ influence by effectors of cAMP metabolism i.e. sodium fluoride and papaverin was observed.

[The valvular apparatus and tissue organization of the endothelium of the thoracic duct]

The structure of ostial valves and valves located along the thoracic duct and of its branches ostial valves and right lymphatic duct ostial valves were studied in 30 experimental outbred dogs and 46 cats. Cryodestruction of thoracic duct was performed in 28 outbred cats. 1, 3, 7 and 14 days later perfusive fixation with intercellular borders impregnation was carried out with simultaneous examination of intact regions of intravalvular segments, cisterna chyli and area of thoracic duct trunks connection with valvular surfaces. Tissue organization in ageing was studied using the intervalvular segment of old animals. Specimens were studied by means of scanning electron microscopy and film preparations of endothelium. Valves, located along the thoracic duct length are bicuspid formations, while ostial ones are falciform and cuneiform respectively in 80 and 20%. Endotheliocytes of cuspids are characterized with high content of microfilaments bundles in the cytoplasm and low content of microvesicles. Cells of the valvular free margin cross the cuspid edge and have adaptive changes preventing their desquamation: fusiform shape, long basal processes and bundles of microfilaments in the cytoplasm. Peculiar "pericyte-like" cells alike with myofibroblasts lie deep in the cuspid thickness close to the sinusal venous side. Fascicles of the duct smooth myocytes reach the base of the valve. Besides, in the ostial valve stroma there is elastic membrane, better displayed along the cuspid venous side. Increased polymorphism and changes of the endotheliocytes metric characteristics were demonstrated in the zones of turbulent lymph flow. Analysis of the newly formed endothelium tissue mosaics allows to reveal mechanisms of monolayer repair: spreading and migration of endotheliocytes on the first day, their proliferation within three days, desquamation of newly formed endotheliocytes and spreading of adjacent cells on later stages.

[Activity of threonine deaminase and biosynthesis of avermectins in the culture of Streptomyces avermitilis]

The influence of ammonium, threonine, isoleucine and valine on the activity of threonine deaminase and the biosynthesis of avermectins in the culture of two mutants of Streptomyces avermitilis, i.e. a sensitive one and a resistant one with respect to alpha-amino-beta-oxyvaleric acid, a threonine antimetabolite, was studied. It was shown that the synthesis of threonine deaminase was induced by threonine and valine in the mycelium of both the mutants. The level of threonine deaminase was higher in the mycelium of the antimetabolite resistant mutant. The antibiotic activity of the resistant mutant was lower while the relative content of the group B avermectins in the pool of the synthesized avermectins was higher than that in the culture of the sensitive mutant.

[Effect of nitrogen-containing compounds on the biosynthesis of avermectins]

The influence of complex nitrogen-containing substrates (Difko yeast extract, EKD nutrient yeast extract, soy bean flour and cotton seed meal), ammonium salts and some amino acids (alanine, methionine, valine, isoleucine and threonine) on the biosynthesis of avermectins in the cultures of two mutants of Streptomyces avermitilis was studied. It was shown that an excess of the nitrogen compounds in the fermentation medium induced a decrease in the antibiotic biosynthesis and the relative content of the group B avermectins.

[Possible role of threonine metabolism in tetracycline biosynthesis]

The review presents the data on the metabolism of threonine and branched amino acids in actinomycetes. The data substantiate the hypothesis on the catabolism of carbohydrates through oxaloacetate--aspartate--threonine--ketomethyl valerate as an alternative pathway in the formation of acetyl-coA in the cells of tetracycline-producing cultures.

Branching patterns of human placental villous trees: perspectives of topological analysis

Topological analysis was applied to investigate the branching pattern of three specimens obtained from early human placenta (6, 9, and 16 weeks p.m.) reconstructed on the basis of semi-thin sections. Centripetal Horton-Strahler and centrifugal branching order nomenclature was used for topological description of the analysed tree-like structures. Bifurcation ratio and vertex ratio were determined for all three cases and were found to be relatively constant. It was shown that branching pattern is closely related to the model of random segment branching that implicates a high level of asymmetry and a small level of space limitation for branching. The significance of this approach for the analysis of development of the villous tree, for the analysis of mesenchymal villous heterogeneity, and for the estimation of physiological parameters for fetoplacental exchange is discussed. We suggest that topological analysis can lead to a new quantitative classification of branching patterns of the human placental villous trees in normal and pathologic pregnancies.

[Metabolism of alpha-ketoacids in erythromycin biosynthesis in various strains of Saccharopolyspora erythraea]

The absence of pyruvate and insignificant levels of alpha-keto-glutarate in the mycelium during the fermentation cycle were characteristic of a highly active erythromycin-producing strain of Saccharopolyspora erythraea. Alpha-keto-glutarate partially excreted to the fermentoffon broth. The activity of pyruvate decarboxylase and alpha-keto-glutarate decarboxylase was detected in the cells during the entire period of the cultivation. The same regularities were observed in the chloramphenicol resistant mutant of the strain. The mycelium of a low productive strain of S.erythraea contained not only alpha-keto-glutarate but also pyruvate and excreted large amounts of keto-acids. By the activity levels of the decarboxylases the low productive strain did not differ from the highly productive one. Propanol did not influence the growth of the low productive strain and the synthesis of erythromycin by it. However, it stimulated accumulation of keto-acids and especially pyruvate in both the mycelium and fermentation broth. Relation between the intensity of keto-acid metabolism and erythromycin biosynthesis is discussed.

[Use of analogs of primary metabolites in the selection of the producer of polymyxin B]

A number of amino acids were found to have effects on the growth of the polymyxin B-producing culture and biosynthesis of the antibiotic by it. Of special importance was the stimulating effect by methionine. Four selection stages were carried out with using structural analogs of purines and amino acids as selective factors. There were no stable variants with increased antibiotic productivity among the mutants resistant to the analogs of purines and leucine. The levels of polymyxin B accumulation by the variants resistant to 4-fluorophenylalanine were 30 to 50 per cent higher than those in the controls and the variants were characterized by low morphological and antibiotic production variation in the subcultures. The mechanisms of the methionine physiological effect and the prospects of using analogs of the primary metabolites in improvement of the culture producing polymyxin B are discussed.

["Circular bands" on the casts of the microcirculatory bed of the human heart in ontogenesis (data from scanning electron microscopy of corrosive casts)]

By means of scanning electron microscopy of corrosive casts, applied to the human cardiac hemomicrocirculatory bed vessels, beginning from 6-9-month-old fetuses up to persons of elderly and old age, peculiarities in form, dimensions and distribution have been revealed in the wall of the arterial part of the vessels of the hemomicrocirculatory bed of so called circular strips. They are inevitable structural components in the wall of the vessels mentioned and correspond to smooth myocytes, shifted at methylmetacrilate injection.

[The microcirculatory bed of the normal rat thyroid and during hypokinesia based on scanning electron microscopy data on corrosion preparations]

In 12 mature white rats with body mass of 180-230 g, that are kept in tight pencil-cases for 10, 30 and 90 days (3 rats make the control), by means of scanning electron microscopy of corrosive preparations reorganizations of three-dimensional spatial organization of the thyroid microcirculatory bed are studied. In intact animals single-layered network of the perifollicular capillaries consists of widely anastomotic blood microvessels and makes 68 +/- 7% of the follicular surface. At hypokinesia (Hk) lasting for 10 days, the perifollicular capillaries are sharply dilated, the capillary network area makes 74 +/- 4%. A large amount of processes appear on the capillary walls. On the 30th day of Hk unequal distribution of capillaries on the follicular surface is noted, that is heterogeneity in organization of the perifollicular capillary networks is manifested. In 90 days of Hk reduction of the capillaries is recorded, rarefied pericapillary network prevails, twistedness of the capillaries is clearly manifested, their complex branching decreases. The capillary network area makes 54 +/- 3% of the follicular area. A large amount of pin-shaped protrusions of the capillary wall appear.

[Microrelief of the internal surface of the thoracic duct in dogs (based on scanning electron microscopy data)]

The investigation has been performed on 17 mature dogs. With the aim to investigate the internal surface of the thoracic duct, the methods of scanning electron microscopy of native, impregnated and corrosive preparations have been used. The analysis of the scannograms obtained demonstrates that the valves of the thoracic ducts are mainly bicuspid, have a typical infundibular form, their cuspides are fused, forming a mesentery-like fold on the duct wall. It plays the main role in ensuring unilateral transport of lymph. The microrelief of the thoracic duct endothelium possesses a rather complex organization. The following relief formations are distinguished in endotheliocytes: 1. nuclei-containing eminence, 2. marginal processes, 3. separate microvilli. The dependence of the microrelief on arrangement of endothelial cells in the valvular area or intervalvular fragments is noted. This is also concerned orientation of endotheliocytes; therefore, predominance of stretched endotheliocytes of the postvalvular fragment can be connected with demonstration of viscous friction force in the lymph stream, that produces deforming and orienting influence on the endotheliocytes.

[Ultrastructure of the inner surface of the aorta of mature and old animals]

In the experiments, performed on 12 white rats and 8 rabbits, by means of scanning electron microscopy of the native preparations and in a number of cases with use of silver nitrate impregnation, the internal surface structure has been studied in the aortal membrane of mature and old animals. At ageing the integrity and continuity of the endothelial monolayer is preserved, on the surface local intimal pits, craters and microdefects appear, adhesiveness of endothelium to leucocytes increases. Orientation of the intimal folds is disturbed. The type of the senescent remodeling in the endothelial layer revealed predisposes to development of atherosclerosis.

[Architectonics of the vascular bed of the fetal portion of the mature human placenta (based on data of scanning electron microscopy)]

Peculiarities of the microangioarchitectonics in the trunks, intermediate and terminal villi of the placenta have been described at a noncomplicated pregnancy. Signs of neovasculogenesis are demonstrated in the microcirculatory bed of the terminal villi. Possible connection between reduction of the paravasal capillary network, as the intermediate villi become mature, and neovasculogenesis is discussed.