Fine Structure of the Tentacles of Phoronis australis Haswell (Phoronida,Lophophorata)

The epidermis of the tentacles of Phoronis australis consists of six cell types: supporting cells, choanocyte-like sensory cells, both types monociliated, secretory A-cells with a mucous secretion, and three kinds of B-cells with mucoprotein secretions. On cross-sections of the tentacle, one can distinguish four faces: the frontal one, heavily ciliated and located between the two frontolateral rows of sensory cells, the lateral and the abfrontal ones. The orientation of the basal structures of the cilia is related to the direction of their beat. The basiepidermal nervous system is grouped mainly at the frontal and abfrontal faces. The basement membrane is thickest on the frontal face and consists of circular collagen fibrils near the epidermis and longitudinal ones near the peritoneum. All peritoneal cells surrounding the mesocoel are provided with smooth longitudinal myofibrils, and isolated axons are situated between these cells and the basement membrane. The wall of the single blood capillary in each tentacle consists of epitheliomuscular cells with circular myofilaments, lying on a thin internal basal lamina; there is no endothelium.     

Characteristics of the action of the influenza virus on the microcirculatory vessels in an experiment

The dynamic light-optic and electron microscopic examination of the organs of experimental animals with the influenza infection have revealed the most pronounced pathology in vessels of the lung and brain microcirculation. The early developing perivascular edema around capillaries which is induced by an increase in the transcellular transport without a disturbance of the dense contact integrity is observed in the brain tissue. Variations in the lung microvessels manifested in a rise of the pinocytosis activity of endothelial cells, in a change of the luminal surface profile and damage of the supermembrane layer. A reversible aggregation of plate and erythrocytes was observed in the lung and brain microvessel lumen at early periods. The revealed changes, including the main of them--microvessel permeability disturbance, are associated with the dynamics of the concentration of the influenza virus and its complexes with antibodies in the organs under study.     

Effect of cadmium intoxication on glucose utilization in energy metabolism of muscles

The influence of cadmium intoxication on carbohydrate metabolism in skeletal muscles and liver of the male Wistar rats has been studied. Cadmium was administered as cadmium acetate in a dose of 0.3 mg Cd2+/kg body weight for three months. At the same time the control rats were injected with 0.9% NaCl. The animals were decapitated and samples of their skeletal muscles: the soleus muscle (composed mainly of red slow twitch fibers; ST) the gastrocnemius muscle containing two types of fibers (white fast twitch fibers FTb and red fast twitch fibers, FTa) and the liver were dissected out. In the samples of muscles, liver and serum contents of glycogen, glucose, pyruvate and lactate, as well as activities of hexokinase, pyruvate kinase and lactate dehydrogenase were measured. Intoxication of rats with cadmium for three months resulted in a reduction of glycolytic enzymes in the serum, ST and FTa muscle fibers and in the liver but did not change the activities of glycolytic enzymes in the FTb muscle fibers. The data obtained for the concentrations of glycogen in the liver and skeletal muscles suggest different mechanisms of cadmium influence on glycogen utilization in these organs.     

Zoosporogenesis in Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew

During sporulation of Pseudoperonospora cubensis on cucumber leaves ( Cucumis saliva ) zoosporangia are formed on the dichotomously branched sporangiophore. The mature zoosporangium has a preformed discharge papilla and the cytoplasm is uncleaved. The zoosporangium wall is decorated and the outer layer of the wall is electron opaque in ultrathin sections. As the zoosporangium is able to survive freezing (- 18°C) for prolonged periods of time (3–4 months) the zoosporangium may serve as the "resting" structure which survives overwintering in Northern latitudes in the absence of oospore formation.
Zoospore cleavage can be synchronized by placing freshly harvested zoosporangia in distilled water. Cleavage of the zoosporangial cytoplasm is by means of the fusion of small vesicles apparently derived from dictyosomes which become highly active after zoosporogenesis is induced.
Vesicles with an osmiophilic electron opaque content are the dominant type of vesicle found in the zoosporangia. The content of these vesicles undergoes dynamic changes during zoosporogenesis and during the late stages of sporogenesis the content becomes finely striated as is typical of these vesicles when observed in the zoospore. On the basis of the results presented here it is suggested that zoosporangium formation and zoosporogenesis in P. cubensis could serve as a model system for assays with obligate oomycetous plant pathogens, also in relation to fungicide mode of action studies.     

Synthesis and AT2 receptor-binding properties of angiotensin II analogues.

The present study investigates the importance of the amino acid side chains in the octapeptide angiotensin II (Ang II) for binding to the AT2 receptor. A Gly scan was performed where each amino acid in Ang II was substituted one-by-one with glycine. The resulting set of peptides was tested for affinity to the AT2 receptor (porcine myometrial membranes). For a comparison, the peptides were also tested for affinity to the AT1 receptor (rat liver membranes). Only the substitution of Arg2 reduced affinity to the AT2 receptor considerably (92-fold when compared with Ang II). For the other Gly-substituted analogues the affinity to the AT2 receptor was only moderately affected. To further investigate the role of the Arg2 side chain for receptor binding, we synthesized some N-terminally modified Ang II analogues. According to these studies a positive charge in the N-terminal end of angiotensin III [Ang II (2-8)] is not required for high AT2 receptor affinity but seems to be more important in Ang II. With respect to the AT1 receptor, [Gly2]Ang II and [Gly8]Ang II lacked binding affinity (Ki > 10 microM). Replacement of the Val3 or Ile5 residues with Gly produced only a slight decrease in affinity. Interestingly, substitution of Tyr4 or His6, which are known to be very important for AT1 receptor binding, resulted in only 48 and 14 times reduction in affinity, respectively.     

Inhibition of pea ferredoxin-NADP(H) reductase by Zn-ferrocyanide.

Ferredoxin-NADP(H) reductases (FNRs) represent a prototype of enzymes involved in numerous metabolic pathways. We found that pea FNR ferricyanide diaphorase activity was inhibited by Zn2+ (Ki 1.57 microM). Dichlorophenolindophenol diaphorase activity was also inhibited by Zn2+ (Ki 1.80 microM), but the addition of ferrocyanide was required, indicating that the inhibitor is an arrangement of both ions. Escherichia coli FNR was also inhibited by Zn-ferrocyanide, suggesting that inhibition is a consequence of common structural features of these flavoenzymes. The inhibitor behaves in a noncompetitive manner for NADPH and for artificial electron acceptors. Analysis of the oxidation state of the flavin during catalysis in the presence of the inhibitor suggests that the electron-transfer process between NADPH and the flavin is not significantly altered, and that the transfer between the flavin and the second substrate is mainly affected. Zn-ferrocyanide interacts with the reductase, probably increasing the accessibility of the prosthetic group to the solvent. Ferredoxin reduction was also inhibited by Zn-ferrocyanide in a noncompetitive manner, but the observed Ki was about nine times higher than those for the diaphorase reactions. The electron transfer to Anabaena flavodoxin was not affected by Zn-ferrocyanide. Binding of the apoflavodoxin to the reductase was sufficient to overcome the inhibition by Zn-ferrocyanide, suggesting that the interaction of FNRs with their proteinaceous electron partners may induce a conformational change in the reductase that alters or completely prevents the inhibitory effect.     

Litter quality and nutrient cycling affected by grazing-induced species replacements along a precipitation gradient

One of the potential mechanisms for the impact of herbivores on nutrient cycling is the effect of selective grazing on litter quality through changes in species composition. However, the scarce evidence collected on this mechanism is controversial and seemingly influenced by site-specific variables. In this paper, we explored the consequences of grazing-induced changes in species composition on litter quality and nitrogen cycling with a regional perspective. Along a 900-mm of mean annual rainfall gradient, we selected species promoted and diminished by grazing from three natural rangelands of Argentina, analyzed their litter quality, and determined their decomposition and nutrient release kinetics under common greenhouse conditions. Litter quality and decomposition rates were strongly associated with plant response to grazing. However, the magnitude and direction of these differences depended on the ecosystem considered. In the wettest site, the species promoted by grazing (forbs) had higher nitrogen and phosphorus contents, faster decomposition rates, and higher release of nitrogen to the soil than species diminished by grazing (C₃ and C₄ grasses). In the intermediate and dry sites, species promoted by grazing had lower nitrogen and phosphorus contents, and slower decomposition rates than those diminished by grazing (C₃ grasses in both cases). Decomposition of the entire group of species was not correlated with mean annual rainfall, but when litter of the species diminished by grazing was analyzed, it was negatively correlated with precipitation. Nitrogen was immobilized more often than mineralized, even after one year of incubation. Immobilization was negatively correlated with precipitation. All these results indicate that grazing may significantly alter nutrient cycling by affecting litter quality through changes in species composition. These effects seem to be larger when species replacements induced by grazing either involve functional groups, as it was the case in our wettest site, or change root to shoot ratios. Therefore, the functional groups involved in the replacement of species as well as shifts between belowground and aboveground allocation should play a key role in grazing-induced changes on nitrogen cycling.     

Effects of vagal neuromodulation and vagotomy on control of food intake and body weight in rats.

Food induced neurohumoral signals are conduced to data processing brain centers mainly as vagal afferent discharge resulting in food intake regulation. The aim of this study was to evaluate effects of vagal nerve neuromodulation in control of food intake with fed-pattern microchip (MC) pacing. Experiments were performed on 60 rats divided on 5 groups: I group 0,05Hz left vagal pacing, II - pacing of both vagal nerves with MC 0,05Hz, III- left vagal MC 0,1Hz pacing, IV - pacing of both vagal nerves with MC 0,1 Hz was performed. In group V left vagal pacing was combined with right side abdominal vagotomy. Body weight and total food intake decreased by 12% and 14% (I), 26% and 30%(II), 8% and 21%(III), 14% and 30%(IV), 38% and 41%(IV), respectively (p<0.05). Effects of both vagal nerves stimulation on final body weight and food intake was significantly more effective than only single nerve MC pacing however most effective was stimulation with 0,1Hz combined with right vagotomy. We conclude that vagal stimulation reduce food intake and body weight by increasing vagal afferent signals. Our results suggest that information in vagal afferents can be modulated resulting in changes of feeding behaviour and body weight.