Morphofunctional changes in the small intestine epithelium of the frog <Emphasis Type="Italic">Rana temporaria</Emphasis> in the course of hibernation

The structure and function of small intestine epithelium have been studied in overwintering frogs at various stages of hibernation. Experiments on the in vitro absorption of arginine vasotocin (AVT) have shown that the epithelium ability for absorption of this nonapeptide without hydrolysis persists during hibernation. However, there is a decline in AVT absorption observed in January–February and later on (as compared with that in October–December) which is most pronounced in March–April. Changes in the epithelial structure appear by midwinter and are growing towards spring. In April–May, enterocyte height decreased by 33%, microvilli length by 40%, and number of mitochondria by 57% relative to the values at the beginning of hibernation. The absence of signs of breakdown attests to the adaptive nature of the observed changes. The dynamics of the studied parameters reveals morphological and functional plasticity of small intestinal epithelium in Rana temporaria over the hibernation period.     

Probing the role of copper in the biosynthesis of the molybdenum cofactor in <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

The crystal structure of Cnx1G, an enzyme involved in the biosynthesis of the molybdenum cofactor (Moco) in Arabidopsis thaliana, revealed the remarkable feature of a copper ion bound to the dithiolene unit of a molybdopterin intermediate (Kuper et al. Nature 430:803-806, 2004). To characterize further the role of copper in Moco biosynthesis, we examined the in vivo and/or in vitro activity of two Moco-dependent enzymes, dimethyl sulfoxide reductase (DMSOR) and nitrate reductase (NR), from cells grown under a variety of copper conditions. We found the activities of DMSOR and NR were not affected when copper was depleted from the media of either Escherichia coli or Rhodobacter sphaeroides. These data suggest that while copper may be utilized during Moco biosynthesis when it is available, copper does not appear to be strictly required for Moco biosynthesis in these two organisms.     

Changes in the diet of the coastal cod <Emphasis Type="Italic">Gadus morhua marisalbi</Emphasis> in the Kandalaksha Gulf of the White Sea under conditions of increased abundance of three-spined stickleback <Emphasis Type="Italic">Gasterosteus aculeatus</Emphasis>

The data on feeding of coastal cod Gadus morhua marisalbi in the area of the Chupa Bay (Kandalaksha Gulf of the White Sea) are presented. In the food spectrum of cod, over 25 cm long fish and their eggs dominated (77.5% by frequency of occurrence and 91.7% by weight). Other groups of food organisms occupied a secondary place. Among fish, three-spined stickleback Gasterosteus aculeatus was the most prominent food item in the diet of cod (48.3% by weight). The published data on long-term changes of the diet of cod are considered, which are mostly related to considerable fluctuations of the abundance of three-spined stickleback in the White Sea. It is shown that, at present, three-spined stickleback again plays an important role in the diet of the White Sea cod     

Estimation of the biological age in females of the Taiga tick <Emphasis Type="Italic">Ixodes persulcatus</Emphasis> by changes in the body shape and the surface of the integument

A method of visual estimation of the biological age of living hungry tick females by visible changes in the depth of the marginal groove and the structure of the alloscutum cuticle during natural ageing is developed. In recently activated individuals, the body is convex and the marginal groove is exposed, demonstrating distinctly visible cuticular microfolds. In attenuated ticks, the body is flattened and the marginal fold overlays the marginal groove, concealing cuticular microfolds.     

Vegetation of the aquatic and marshland habitats in the Orava region,including the first records of <Emphasis Type="Italic">Potametum alpini,Potametum zizii</Emphasis> and <Emphasis Type="Italic">Ranunculo-Juncetum bulbosi</Emphasis> in the territory of Slovakia

The vegetation of the aquatic and marshland habitats of the Orava region (north of Slovakia) was studied in 2009, using traditional phytosociological methods. Sixteen aquatic and eighteen marsh plant communities were described within 96 phytosociological relevés by using TWINSPAN with the application of the dominance principle. Three associations, Potametum alpini, Potametum zizii and Ranunculo-Juncetum bulbosi, were found as new communities for Slovakia. Myriophylletum verticillati, Potametum nodosi, Potametum graminei and Alisma gramineum community were recorded in the northernmost localities in Slovakia. Among marsh communities, Calletum palustris is very rare, both in the Orava region and in Slovakia as a whole. According to Ellenberg’s indicator values (EIV), moisture was evaluated as the main ecological gradient. Plant communities are ordered along the first Detrended Correspodence Analysis (DCA) axis in a typical hydroseries (Potametea → Lemnetea → Phragmition communis → Phalaridion arundinaceae, Oenanthion aquaticae and Sparganio-Glycerion → Magnocaricion elatae). The second DCA axis was most correlated with EIV for nutrients. Among the five directly measured ecological characteristics (temperature, pH and conductivity of water, water depth, and substrate type), conductivity of water (0.44, P < 0.01) and substrate type (0.32, P < 0.05) were the statistically significant variables explaining the variability along the first DCA axis.     

Developmental changes in the effects of prostaglandin E<Subscript>2</Subscript> in the chicken ductus arteriosus

Prostaglandin E₂ (PGE₂) is the major vasodilator prostanoid of the mammalian ductus arteriosus (DA). In the present study we analyzed the response of isolated DA rings from 15-, 19- and 21-day-old chicken embryos to PGE₂ and other vascular smooth muscle relaxing agents acting through the cyclic AMP signaling pathway. PGE₂ exhibited a relaxant response in the 15-day DA, but not in the 19- and 21-day DA. Moreover, high concentrations of PGE₂ (≥3 μM in 15-day and ≥1 μM in 19-day and 21-day DA) induced contraction of the chicken DA. The presence of the TP receptor antagonist SQ29,548, unmasked a relaxant effect of PGE₂ in the 19- and 21-day DA and increased the relaxation induced by PGE₂ in the 15-day DA. The presence of the EP receptor antagonist AH6809 abolished PGE₂-mediated relaxation. The relaxant responses induced by PGE₂ and the β-adrenoceptor agonist isoproterenol, but not those elicited by the adenylate cyclase activator forskolin or the phosphodiesterase 3 inhibitor milrinone, decreased with maturation. High oxygen concentrations (95%) decreased the relaxation to PGE₂. The relaxing potency and efficacy of isoproterenol and milrinone were higher in the pulmonary than in the aortic side of the DA, whereas no regional differences were found in the response to PGE₂. We conclude that, in contrast to the mammalian situation, PGE₂ is a weak relaxant agent of the chicken DA and, with advancing incubation, it even stimulates TP vasoconstrictive receptors.     

On the occurrence of the thumbnail crab <Emphasis Type="Italic">Thia scutellata</Emphasis> in the inner German Bight

The thumbnail crab Thia scutellata occurs in the German Bight in at least two stable populations: at Borkum Riff and Loreley Bank. The western (Borkum Riff) population is larger than the eastern (Loreley Bank) one, probably because of the more frequent ingression of south-western warmer water along the Dutch coast. The sediments of these two localities are well-sorted middle sands with a very low amount of finer fractions.     

On the Onset of Cracks in Arteries¹

We present a theoretical approach to study the onset of failure localization into cracks in arterial wall. The arterial wall is a soft composite comprising hydrated ground matrix of proteoglycans reinforced by spatially dispersed elastin and collagen fibers. As any material, the arterial tissue cannot accumulate and dissipate strain energy beyond a critical value. This critical value is enforced in the constitutive theory via energy limiters. The limiters automatically bound reachable stresses and allow examining the mathematical condition of strong ellipticity. Loss of the strong ellipticity physically means inability of material to propagate superimposed waves. The waves cannot propagate because material failure localizes into cracks perpendicular to a possible wave direction. Thus, not only the onset of a crack can be analyzed but also its direction. We use the recently developed constitutive theories of the arterial wall including 8 and 16 structure tensors to account for the fiber dispersion. We enhance these theories with energy limiters. We examine the loss of strong ellipticity in uniaxial tension and pure shear in circumferential and axial directions of the arterial wall. We find that the vanishing longitudinal wave speed predicts the appearance of cracks in the direction perpendicular to tension. We also find that the vanishing transverse wave speed predicts the appearance of cracks in the the direction inclined (non-perpendicular) to tension. The latter result is counter-intuitive yet it is supported by recent experimental observations.