Electron microscopic study of rapid morphogenetic processes in embryonic tissue explants of amphibia]

Submicroscopic rearrangements are described. They serve as the bases of rapid (up to 20 min) changes in the form of the common frog neurula explants: formation of filamentous layer under "naked" surface, appearance of lobopodia on "naked" surface, their "flow", cell polarization and submersion. In all these processes an active part appears to be played by microtubules and microfilaments the bundles of which are always oriented along the long axes of active cells or the directions of passive mechanical tensions. In the cells which are not yet polarized the microtubules form under the surface adjacent to the already polarized cell. This may be considered as one of the chains of cooperative cell polarization.     

A quantitative study of regional and stage specific reaction of African clawed frog embryonic tissues on mechanical stress

Residual deformation of fragments of the embryonic tissues preserved after relaxation of the stretching force serve as a criterion of active redistribution of their cells caused by this stretching. We measured residual deformations of the Xenopus laevis ventral and dorsal ectoderm at the early gastrula and lateral ectoderm at the late gastrula-early neurula after stretching of varying time and force. While the samples responded to moderate (up to 40%) short-term stretching as elastic bodies (residual deformations were absent), residual deformation appeared in the early gastrula tissues after 30-60-min stretching, which were more pronounced in the ventral tissues than in the dorsal ones. On the contrary, a contractile reaction developed in the late gastrula-early neurula tissues in response to 60-min stretching, which almost relaxed residual deformation within 20 min after unloading. A conclusion was drawn that gastrulation and neurulation proceed under the conditions of relaxing and nonrelaxing mechanical tensions, respectively. Mechanical bases and morphogenetic role of the described reactions is discussed.     

The antidepressant-like effect of Ocimum basilicum in an animal model of depression

We investigated the efficacy of Ocimum basilicum (OB) essential oils for treating depression related behavioral, biochemical and histopathological changes caused by exposure to chronic unpredictable mild stress (CUMS) in mice and to explore the mechanism underlying the pathology. Male albino mice were divided into four groups: controls; CUMS; CUMS plus fluoxetine, the antidepressant administered for pharmacological validation of OB; and CUMS plus OB. Behavioral tests included the forced swim test (FST), elevated plus-maze (EPM) and the open ?eld test (OFT); these tests were performed at the end of the experiment. We assessed serum corticosterone level, protein, gene and immunoexpression of brain-derived neurotropic factor (BDNF) and glucocorticoid receptors (GRs) as well as immunoexpression of glial fibrillary acidic protein (GFAP), Ki67, caspase-3 in the hippocampus. CUMS caused depression in the mice as evidenced by prolonged immobility in the FST, prolonged time spent in the open arms during the EPM test and reduction of open field activity in the OFT. OB ameliorated the CUMS induced depressive status. OB significantly reduced the corticosterone level and up-regulated protein and gene expressions of BDNF and GR. OB reduced CUMS induced hippocampal neuron atrophy and apoptosis, and increased the number of the astrocytes and new nerve cells. OB significantly increased GFAP-positive cells as well as BDNF and GR immunoexpression in the hippocampus.     

Involvement of guanine nucleotide exchange factor xLARG in epiboly of cells of the animal pole of Xenopus laevis embryos

The development of multicellular organisms is a complicated coordinated process of the movement of groups of embryonic cells, which is controlled by many regulatory systems. At present little is known about the regulation of the earliest manifestations of the movement in the embryogenesis: epiboly and radial intercalation. The coordinators of these processes may be small GTPases of the Rho family and their activators, the factors of exchange of guanylic nucleotides. It has been shown in this work that the overexpression of the factor of exchange of guanylic nucleotides xLARG in Xenopus laevis embryos leads to an increase in the amount of the active form of xLARG. In addition, an increase in the expression of xLARG disturbs the process of radial intercalation. The data obtained suggest that xLARG is involved in maintaining the xLARG activation level necessary for the occurrence of epiboly.     

Statistical and frequency-amplitude characteristics of ultra-weak emissions of loach eggs and embryos under normal conditions and on their optic interactions. II. Changes in characteristics of ultra-weak emissions upon optic interaction of groups of embryos of different ages.

We compared the characteristics of ultraweak emissions from groups of loach embryos of different ages in the presence or absence of optic interaction. The percentage of zero values of emission gradually increased during the first hour of optic interaction. The number and height of rare big pulses estimated by the value of kurtosis increased in parallel. In addition, the correlation between the Fourier spectra of optically interacting samples decreased at a higher rate than in the absence of optical contact. Just after the 1-hour optic interaction was terminated, the number of high pulses decreased in a younger interacting group and increased in the older one and the farther away the partner groups were in developmental stages, the more pronounced these differences were. Measurements of the Fourier spectra after long-term (12-22-hour) optic interactions have shown that an "exchange" of autocorrelation characteristics of the spectra took place among the samples: the sums of autocorrelation coefficients were inverted in the vast majority of cases, often with an "overshoot" or, at least, were smoothed over with reference to the control samples. We conclude that the previously described effects of optic interactions between groups of loach embryos of different ages could be due to changes in the frequency spectra of their ultraweak emissions.     

Cytomechanical control of morphogenesis

The role of mechanically strained state of cells and multicellular structures in morphogenesis regulating in vertebrate embryos is discussed. Regular changes in patterns of mechanical strain during embryonic development are described. Artificial relaxation of mechanical strain performed on definite developmental stages and retension of embryonic tissues in arbitrary directions considerably affects morphogenesis and cell differentiation patterns. Cytomechanical models of morphogenesis are reviewed and a concept of hyperrestoration of mechanical strain as a possible driving force of morphogeneiss is suggested.     

Productivity of forests in the Eurosiberian boreal region and their potential to act as a carbon sink –- a synthesis

Based on review and original data, this synthesis investigates carbon pools and fluxes of Siberian and European forests (600 and 300 million ha, respectively). We examine the productivity of ecosystems, expressed as positive rate when the amount of carbon in the ecosystem increases, while (following micrometeorological convention) downward fluxes from the atmosphere to the vegetation (NEE = Net Ecosystem Exchange) are expressed as negative numbers. Productivity parameters are Net Primary Productivity (NPP=whole plant growth), Net Ecosystem Productivity (NEP = CO₂ assimilation minus ecosystem respiration), and Net Biome Productivity (NBP = NEP minus carbon losses through disturbances bypassing respiration, e.g. by fire and logging). Based on chronosequence studies and national forestry statistics we estimate a low average NPP for boreal forests in Siberia: 123 gC m^–2 y^–1. This contrasts with a similar calculation for Europe which suggests a much higher average NPP of 460 gC m^–2 y^–1 for the forests there. Despite a smaller area, European forests have a higher total NPP than Siberia (1.2–1.6 vs. 0.6–0.9 × 10¹⁵ gC region^–1 y^–1). This arises as a consequence of differences in growing season length, climate and nutrition. For a chronosequence of Pinus sylvestris stands studied in central Siberia during summer, NEE was most negative in a 67-y old stand regenerating after fire (– 192 mmol m^–2 d^–1) which is close to NEE in a cultivated forest of Germany (– 210 mmol m^–2 d^–1). Considerable net ecosystem CO₂-uptake was also measured in Siberia in 200- and 215-y old stands (NEE:174 and – 63 mmol m^–2 d^–1) while NEP of 7- and 13-y old logging areas were close to the ecosystem compensation point. Two Siberian bogs and a bog in European Russia were also significant carbon sinks (– 102 to – 104 mmol m^–2 d^–1). Integrated over a growing season (June to September) we measured a total growing season NEE of – 14 mol m^–2 summer^–1 (– 168 gC m^–2 summer^–1) in a 200-y Siberian pine stand and – 5 mol m^–2 summer^–1 (– 60 gC m^–2 summer^–1) in Siberian and European Russian bogs. By contrast, over the same period, a spruce forest in European Russia was a carbon source to the atmosphere of (NEE: + 7 mol m^–2 summer^–1 = + 84 gC m^–2 summer^–1). Two years after a windthrow in European Russia, with all trees being uplifted and few successional species, lost 16 mol C m^–2 to the atmosphere over a 3-month in summer, compared to the cumulative NEE over a growing season in a German forest of – 15.5 mol m^–2 summer^–1 (– 186 gC m^–2 summer^–1; European flux network annual averaged – 205 gC m^–2 y^–1). Differences in CO₂-exchange rates coincided with differences in the Bowen ratio, with logging areas partitioning most incoming radiation into sensible heat whereas bogs partitioned most into evaporation (latent heat). Effects of these different surface energy exchanges on local climate (convective storms and fires) and comparisons with the Canadian BOREAS experiment are discussed. Following a classification of disturbances and their effects on ecosystem carbon balances, fire and logging are discussed as the main processes causing carbon losses that bypass heterotrophic respiration in Siberia. Following two approaches, NBP was estimated to be only about 13–16 mmol m^–2 y^–1 for Siberia. It may reach 67 mmol m^–2 y^–1 in North America, and about 140–400 mmol m^–2 y^–1 in Scandinavia. We conclude that fire speeds up the carbon cycle, but that it results also in long-term carbon sequestration by charcoal formation. For at least 14 years after logging, regrowth forests remain net sources of CO₂ to the atmosphere. This has important implications regarding the effects of Siberian forest management on atmospheric concentrations. For many years after logging has taken place, regrowth forests remain weaker sinks for atmospheric CO₂ than are nearby old-growth forests.     

Using wintergreen oil for mounting mosquito larvae: a safer alternative to xylene

Permanent mounting of fourth instar mosquito larvae is essential for identifying Aedes spp. This procedure requires extensive exposure to xylene, a clearing agent in the mounting process. We investigated wintergreen oil as a substitute for xylene. Five hundred larvae were mounted on slides to evaluate shrinkage or expansion of specimens after clearing using xylene or wintergreen oil. We examined the ventral brush and siphonal hair tufts for species identification and for preservation of morphological characteristics after clearing specimens in xylene or wintergreen oil. Shrinkage of the length of whole larvae and width of the head, thorax and abdomen after mounting was significantly greater after clearing with xylene than with wintergreen oil. The length of the comb scale nearest the ventral brush was similar for both clearing agents. The clarity of the specimens after mounting was improved by clearing with wintergreen oil, but the integrity of the ventral brush and siphonal hair tufts were similar for both clearing agents.