Interactive effects of grazing and shrubs on the annual plant community in semi‐arid Mediterranean shrublands

Question: We studied the interactive effects of grazing and dwarf shrub cover on the structure of a highly diverse annual plant community. Location: Mediterranean, semi‐arid shrubland in the Northern Negev desert, Israel. Methods: Variation in the biomass and plant density of annual species in the shrub and open patches was monitored during four years, inside and outside exclosures protected from sheep grazing, in two contrasting topographic sites: north and south‐facing slopes that differed in their dominant dwarf shrubs species: Sarcopoterium spinosus and Corydothymus capitatus, respectively. Results: Above‐ground biomass, density and richness of annual species were lower under the canopy of both shrub species compared to the adjacent open patches in the absence of grazing. Grazing reduced the biomass of annuals in open patches of both topographic sites, but not in the shrub patches. On the north‐facing slope, grazing also reduced plant density and richness in the open patches, but increased plant density in the shrub patches. At the species level, various response patterns to the combined effects of grazing and patch type were exhibited by different annuals. Protection against the direct impacts of grazing by shrub cover as well as species‐specific interactions between shrubs and annuals were observed. A conceptual mechanistic model explaining these interactions is proposed. Conclusion: In semi‐arid Mediterranean shrublands grazing and dwarf shrub cover interact in shaping the structure of the annual plant community through (1) direct impacts of grazing restricted to the open patches, (2) species‐specific facilitation/ interference occurring in the shrub patches and (3) subsequent further processes occurring among the interconnected shrub and open patches mediated through variation in seed flows between patches.     

Transcytosis of Streptococcus iniae through skin epithelial barriers: an in vitro study

By constructing a biological model based on in vitro culture of polarized rainbow trout primary skin epithelial cell monolayers, the series of early events that precede Streptococcus iniae infection, particularly colonization and translocation through external barriers, were analyzed. Streptococcus iniae promptly invades skin epithelial cells, but the rapid decline of viable intracellular bacteria points out the limited capability of intracellular survival for this bacterium. Translocation assays, supported by electron microscopy microphotographs, demonstrate that following successful in vitro invasion of skin epithelial cell, the bacterium exists free in the cytoplasm after release from the endosome, and translocates through the skin barrier. Bacterial invasion and transcytosis is not accompanied by apparent cell-line damages or disruption of host cells' tight junctions. It is hypothesized that the phenomenon of epithelial invasion coupled to the rapid translocation through the barrier plays a crucial role in Streptococcus iniae infection.     

α4β2 nicotinic acetylcholine receptors in the early postnatal mouse superior cervical ganglion

Heteropentameric nicotinic acetylcholine receptors (nAChR) mediate fast synaptic transmission in ganglia of the autonomic nervous system. It is undisputed that α3 and β4 are the predominant subunits in the superior cervical ganglion (SCG); however, reports on the presence of receptors that contain α4 have been controversial. Here, we have searched for the presence of α4-containing nAChRs in the postnatal rat and mouse SCG. We now show by immunoprecipitation combined with radioligand binding that α4-containing receptors constitute about 20% of hetero-oligomeric nAChRs in postnatal Day 3 (P3) mice. However, already by P9, the level of α4 approaches zero. In contrast, the number of α4-containing receptors is close to zero in the rat SCG at all times investigated. Deletion of the β2 subunit by using α5β2-double knockout (KO) mice removes all α4-containing receptors, suggesting that in the postnatal mouse SCG, α4 co-assembles only with β2 but not with β4. α4β2 receptors are, on the other hand, up-regulated in the SCG of P3 α5β4-double KO mice, where they make up about 50% of receptors that bind [(3) H]-epibatidine. Nonetheless, receptors on the surface of SCG neurons from α5β4-double KO mice maintained for one to two days in culture comprise <10% of α4β2 and >90% of α3β2, as determined by patch clamp recordings with α4β2- and α3β2-specific ligands. We propose that in the P3 SCG of wild type mice, α3β4 (±α5) represent about 62% of receptors, whereas 17% are α3β2β4, and 21% are α4β2 (±α5) receptors.     

The effect of interleukin-8 on the viability of injected adipose tissue in nude mice

Adipose tissue injection as a free graft for the correction of soft-tissue defects is a widespread procedure in plastic surgery. The main problem in achieving long-term soft-tissue augmentation is partial absorption of the injected fat and hence the need for overcorrection and re-injection. The purpose of this study was to improve the viability of the injected fat by the use of interleukin-8. The rationale for the use of interleukin-8 was its abilities to accelerate angiogenesis and attract inflammatory cells and fibroblasts, providing the injected adipocytes more feeding vessels and a well-established graft bed to enhance their viability. Human adipose tissue, obtained by suction-assisted lipectomy, was re-injected into the subcutis in the scalp of nude mice. Interleukin-8 (0.25 ng) was injected subcutaneously to the scalp as a preparation of the recipient site 24 hours before the fat injection and was added to the fat graft itself (25 ng per 1 cc of injected fat). In the control group, pure fat without interleukin-8 was injected and no interleukin-8 was added for the preparation of the recipient site. One cubic centimeter of fat was injected in each animal in both the study and control groups. There were 10 animals in each group. The animals were euthanized 15 weeks after the procedure. Graft weight and volume were measured and histologic evaluation was performed. In addition, triglyceride content and adipose cell sizes were measured as parameters for fat cells viability. Histologic analysis demonstrated significantly less cyst formation in the group treated with interleukin-8. No significant differences were found between the groups with regard to graft weight and volume or the other histologic parameters investigated. No significant differences were demonstrated in adipose cell sizes and their triglyceride content. In conclusion, less cyst formation, indicating improved quality of the injected fat, can be obtained by the addition of interleukin-8. Further studies of various dosages of interleukin-8 and their long-term effect are required before these encouraging results could be applied clinically.     

Density and intercohort priority effects on larval <Emphasis Type="Italic">Salamandra salamandra</Emphasis> in temporary pools

Priority effects, i.e., effects of an early cohort on the performance of a later cohort, are generally studied between, and not within, species. The paucity of intraspecific assessments does not reflect a lack of ecological importance, but the technical problem associated with differentiating between conspecific cohorts. Here, we examine priority and density-dependent effects on larval Salamandra salamandra infraimmaculata. Larvae deposited by their mother early in the season have increased risk of desiccation, as rains at the beginning of the season are less frequent and unpredictable. However, breeding later may incur a high cost through conspecific priority effects, including cannibalism and competition. In an outdoor artificial pool experiment, we established densities of 0, 1, 2, 4 or 6 newly born larvae per pool (∼30 l), and 40 days later, added a second cohort of three newly born larvae to each pool. We differentiated between cohorts using natural individual-specific markings. For the early cohort, increasing density decreased survival and size at metamorphosis, and increased time to metamorphosis. For the late cohort, survival was 100% in pools without early-cohort larvae, but ranged between 13 and 33% in the presence of early-cohort larvae. Time to metamorphosis was significantly longer in the presence of low vs high densities of early-cohort larvae. Results suggest that early-cohort larvae are mainly subjected to exploitative competition and cannibalism mediated by food limitation, and that late-cohort larvae are subjected to cannibalism and interference due to size asymmetry between cohorts. The strong priority effects suggest that Salamandra females could increase their fitness by adjusting the number of larvae they deposit in specific pools to avoid cannibalism and intraspecific competition.     

Role of xanthine oxidase, lactoperoxidase, and NO in the innate immune system of mammary secretion during active involution in dairy cows: manipulation with casein hydrolyzates

The aims of this study were to test whether xanthine oxidase, lactoperoxidase, and NO are components of the innate immune system of mammary secretion during active involution in dairy cows, and whether the innate immune system is activated by casein hydrolysates. Our laboratory has shown recently that infusion of CNH into mammary glands induced involution and was associated with earlier increases in the concentrations of components of the innate immune system. Intact casein is inactive and served as control. Half of the glands of 8 Holstein cows scheduled for dry off (approximately 60 days before parturition) were injected for 3 days with a single dose of casein hydrolyzates and the contralateral glands with a single dose of intact casein with the same concentration. Involution elicited marked increases in xanthine oxidase and lactoperoxidase activities, and accumulation of urate and nitrate. NO and H(2)O(2) were constantly produced in the mammary gland secretion. Nitrite formed either by autooxidation of NO or by conversion of nitrate to nitrite by xanthine oxidase was converted into the powerful nitric dioxide radical by lactoperoxidase and H(2)O(2) that is derived from the metabolism of xanthine oxidase. Nitric dioxide is most likely responsible for the formation of nitrosothiols on thiol-bearing groups, which allows an extended NO presence in mammary secretion. Nitrite is effectively converted to nitrate, which accumulated in the range of approximately 25 microM -1 mM from the start of the experiment to the complete involution of glands. The mammary secretion in all glands was bactericidal and bacteriostatic during established involution, and this appeared sooner and more acutely in glands treated with casein hydrolyzates, within 8 to 24 h. It is concluded that xanthine oxidase, lactoperoxidase, and NO are components of the mammary innate immune system that form bactericidal and bacteriostatic activities in mammary secretions. The innate immune system play a major role in preventing intramammary infection during milk stasis and its activation may increase its effectiveness.     

Attenuation of liver ischemia-reperfusion-induced atrial dysfunction by external pacing but not by isoproterenol

Remote ischemia-reperfusion detrimentally affects myocardial function by initially interfering with the rate of contraction. We investigated the usefulness of isoproterenol versus external electrical pacing in attenuating secondary functional damage of isolated Wistar rat atria. Atrial strips (n = 10/group) were bathed within oxygenated Krebs-Henseleit solution that exited from isolated livers that had been either perfused normally (controls) or underwent no flow (ischemia) for 2 h. In addition to one noninterventional ischemia-exposed strip group, a second group was externally paced at a fixed rate (55 pulses.min-1, 6 V) and a third "ischemia" group was treated with isoproterenol (0.1 mM), both interventions commencing upon the strips' exposure to the hepatic effluents. Control strips displayed unaltered contraction rate and systolic-generated tension during the 2-h exposure. Nontreated strips exposed to ischemic reperfusate experienced bradycardia compared with baseline values (7 +/- 2 vs. 50 +/- 12 beats.min-1, p < 0.05), followed <1-min later by a fall in the generated tension (11 +/- 4 vs. 20 +/- 6 mmHg, p < 0.05). The paced-ischemic strips displayed unaltered rate and force of contraction, whereas the addition of isoproterenol did not prevent deterioration in the rate and force of contraction (8 +/- 3 beats.min-1, 12 +/- 4 mmHg, respectively; p < 0.05 vs. baseline control ischemia-paced strips). Thus, external electrical pacing prevented liver ischemia-reperfusion-induced atrial strips' bradycardia and loss of contractility, while isoproterenol did not.     

Toxicity of propylene oxide at low pressure against life stages of four species of stored product insects

The relative toxicity of propylene oxide (PPO) at a low pressure of 100 mm Hg to four species of stored product insect at 30 degrees C over a 4-h exposure period was investigated. PPO at 100 mm Hg was toxic to all four species tested: Tribolium castaneum (Herbst), Plodia interpunctella (Hübner), Ephestia cautella (Wlk.), and Oryzaephilus surinamensis (L.). There were differences in susceptibility between the life stages of the tested insect species. Mortality tests on all life stages of the insects resulted in LD99 values ranging from 4.7 to 26.1 mg/liter. The pupal stage of E. cautella, O. surinamensis, and T. castaneum was the most tolerant stage with LD99 values of 14.4, 26.1, and 25.7 mg/liter, respectively. For P. interpunctella, the egg stage was most tolerant, with a LD99 value of 15.3 mg/liter. Generally, PPO at 100 mm Hg was more toxic to P. interpunctella and E. cautella than to O. surinamensis and T. castaneum. A 99% mortality of all life stages of the tested species was achieved at a concentrations x time product of 104.4 mg h/liter. These findings indicate that a combination of PPO with low pressure can render the fumigant a potential alternative to methyl bromide for rapid disinfestation of commodities.     

From components to regulatory motifs in signalling networks.

The developments in biochemistry and molecular biology over the past 30 years have produced an impressive parts list of cellular components. It has become increasingly clear that we need to understand how components come together to form systems. One area where this approach has been growing is cell signalling research. Here, instead of focusing on individual or small groups of signalling proteins, researchers are now using a more holistic perspective. This approach attempts to view how many components are working together in concert to process information and to orchestrate cellular phenotypic changes. Additionally, the advancements in experimental techniques to measure and visualize many cellular components at once gradually grow in diversity and accuracy. The multivariate data, produced by experiments, introduce new and exciting challenges for computational biologists, who develop models of cellular systems made up of interacting cellular components. The integration of high-throughput experimental results and information from legacy literature is expected to produce computational models that would rapidly enhance our understanding of the detail workings of mammalian cells.