Changes in intra-abdominal pressure, trunk muscle activation and force during isokinetic lifting and lowering

Intra-abdominal pressure (IAP), force and electromyographic (EMG) activity from the abdominal (intra-muscular) and trunk extensor (surface) muscles were measured in seven male subjects during maximal and sub-maximal sagittal lifting and lowering with straight arms and legs. An isokinetic dynamometer was used to provide five constant velocities (0.12–0.96 m·s^–1) of lifting (pulling against the resistance of the motor) and lowering (resisting the downward pull of the motor). For the maximal efforts, position-specific lowering force was greater than lifting force at each respective velocity. In contrast, corresponding IAPs during lowering were less than those during lifting. Highest mean force occurred during slow lowering (1547 N at 0.24 m·s^–1) while highest IAP occurred during the fastest lifts (17.8 kPa at 0.48–0.96 m·s^–1). Among the abdominal muscles, the highest level of activity and the best correlation to variations in IAP (r=0.970 over velocities) was demonstrated by the transversus abdominis muscle. At each velocity the EMG activity of the primary trunk and hip extensors was less during lowering (eccentric muscle action) than lifting (concentric muscle action) despite higher levels of force (r between –0.896 and –0.851). Sub-maximal efforts resulted in IAP increasing linearly with increasing lifting or lowering force (r=0.918 and 0.882, respectively). However, at any given force IAP was less during lowering than lifting. This difference was negated if force and IAP were expressed relative to their respective lifting and lowering maxima. It appears that the IAP increase primarily accomplished by the activation of the transversus abdominis muscle can have the dual function of stabilising the trunk and reducing compression forces in the lumbar spine via its extensor moment. The neural mechanisms involved in sensing and regulating both IAP and trunk extensor activity in relation to the type of muscle action, velocity and effort during the maximal and sub-maximal loading tasks are unknown.     

Post- stocking movements and recapture of hatchery-reared trout released into flowing waters—effect of prior acclimation to flow

Hatchery-reared brown trout, Salmo trutta , (f.l., 16–27 cm) were stocked into the Afon Clettwr, Afon Western Cleddau and Afon Dysynni, Wales. The effects of (a) retaining fish caged in the river for 24 h before release, and (b) a period of acclimation to flowing water (up to 0.24 m s⁻¹) in tanks prior to stocking were investigated. Data on percentage recapture and post-stocking movements were obtained from trapping, electrofishing and tag returns. In-stream acclimation resulted in a higher percentage recapture and a more limited dispersion of the fish stocked under low river flow conditions, but had no effect on trout stocked into a river where higher water velocities were experienced. Acclimation, in tanks, to a flow of 0.1 ms⁻¹ for 14 days led to higher percentage recaptures, whereas acclimation for only 2 days resulted in fewer returns than for unacclimated fish. No differences in fish distribution within the rivers could be attributed to these acclimation procedures.     

The physiology and biochemistry of cultivar-strain interactions in the white clover-Rhizobium symbiosis

Two white clover cultivars were inoculated with two Rhizobium leguminosarum bv. trifolii strains in a factorial series of experiments. Plants were grown in axenic conditions in nitrogen free nutrient solution in a controlled environment room. Variations in nitrogen fixation were dependent partly upon general strain effects, partly upon general cultivar effects but there were also substantial differences attributable to precise interactions between specific combinations. The physiological and biochemical basis of these differences was examined. There were variations in the onset of nodulation and nitrogenase (acetylene reduction) activity. The rate at which nitrogenase activity developed also differed between associations as did the average size and number of nodules but none of these effects correlated well with differences in plant dry matter accumulation. Studies on nodule biochemistry revealed that the major nitrogen fixation enzymes were present in all four associations. Nodule protein content and enzyme activity (on a g nodule fresh weight basis) were substantially greater in associations formed by the more effective strain but cannot explain the interactive effect on dry matter accumulation. The relevance of these data to our understanding of factors regulating variations in nitrogen fixation is discussed.     

Branching responses of a plagiotropic clonal herb to localised incidence of light simulating that reflected from vegetation

Plants sense the presence of neighbouring vegetation through phytochrome photoreceptors perceiving a lowered red to far-red ratio (R:FR) of light reflected from such vegetation. We hypothesised that it would be advantageous for the grassland clonal herb, Trifolium repens, to have an inhibitory branching response to perception by leaves of light reflected from neighbouring vegetation (i.e. light with lowered R:FR ratio) but have no response to interception of such light by the plagiotropic stem. We tested whether photoreception of reflected light by plagiotropic stems resulted in a different branching response to photoreception by leaves and whether leaf ontogeny influenced the response. To simulate light reflected from vegetation, FR light-emitting-diodes were used to supplement controlled environment room light so that the R:FR ratio, but not the photosynthetic photon fluence rate, of light incident at the stem or leaf of a phytomer of T. repens was lowered from 1.20 to 0.25. The plagiotropic stems were unresponsive to light simulating that reflected from vegetation. This response differs from that of stems of orthotropic species, indicating that plagiotropic stems have evolved an organ-specific photobiology. Treatment of the mature leaf with light of lowered FR ratio reduced phytomer production only of the branch in the axil of the treated leaf. Similar treatment of the immature leaf retarded, in addition, branching at basal phytomers on the same side of the primary stem axis. Thus the response to light simulating that reflected from neighbouring vegetation depended upon whether the light was incident at the stem or the leaf and on the stage of leaf development. We argue that such responses improve the performance and fitness of T. repens within grassland habitats by allowing axillary buds on plagiotropic stems to branch freely when stems are in receipt of light reflected from vegetation while leaves are in full light.     

The interferon-inducible protein viperin inhibits influenza virus release by perturbing lipid rafts

Interferons initiate the host antiviral response by inducing a number of genes, most with no defined antiviral function. Here we show that the interferon-induced protein viperin inhibits influenza A virus release from the plasma membrane of infected cells. Viperin expression altered plasma membrane fluidity by affecting the formation of lipid rafts, which are detergent-resistant membrane microdomains known to be the sites of influenza virus budding. Intracellular interaction of viperin with farnesyl diphosphate synthase (FPPS), an enzyme essential for isoprenoid biosynthesis, decreased the activity of the enzyme. Overexpression of FPPS reversed viperin-mediated inhibition of virus production and restored normal membrane fluidity, and reduction of FPPS levels by siRNA inhibited virus release and replication, indicating that the FPPS interaction underlies viperin's effects. These findings suggest that targeting the release stage of the life cycle may affect the replication of many enveloped viruses. Furthermore, FPPS may be an attractive target for antiviral therapy.     

Endoproteolytic cleavage of TUG protein regulates GLUT4 glucose transporter translocation

To promote glucose uptake into fat and muscle cells, insulin causes the translocation of GLUT4 glucose transporters from intracellular vesicles to the cell surface. Previous data support a model in which TUG traps GLUT4-containing vesicles and tethers them intracellularly in unstimulated cells and in which insulin mobilizes this pool of vesicles by releasing this tether. Here we show that TUG undergoes site-specific endoproteolytic cleavage, which separates a GLUT4-binding, N-terminal region of TUG from a C-terminal region previously suggested to bind an intracellular anchor. Cleavage is accelerated by insulin stimulation in 3T3-L1 adipocytes and is highly dependent upon adipocyte differentiation. The N-terminal TUG cleavage product has properties of a novel 18-kDa ubiquitin-like modifier, which we call TUGUL. The C-terminal product is observed at the expected size of 42 kDa and also as a 54-kDa form that is released from membranes into the cytosol. In transfected cells, intact TUG links GLUT4 to PIST and also binds Golgin-160 through its C-terminal region. PIST is an effector of TC10α, a GTPase previously shown to transmit an insulin signal required for GLUT4 translocation, and we show using RNAi that TC10α is required for TUG proteolytic processing. Finally, we demonstrate that a cleavage-resistant form of TUG does not support highly insulin-responsive GLUT4 translocation or glucose uptake in 3T3-L1 adipocytes. Together with previous results, these data support a model whereby insulin stimulates TUG cleavage to liberate GLUT4 storage vesicles from the Golgi matrix, which promotes GLUT4 translocation to the cell surface and enhances glucose uptake.     

Functional requirements for the lysosomal thiol reductase GILT in MHC class II-restricted antigen processing

Ag processing and presentation via MHC class II is essential for activation of CD4(+) T lymphocytes. gamma-IFN-inducible lysosomal thiol reductase (GILT) is present in the MHC class II loading compartment and has been shown to facilitate class II Ag processing and recall responses to Ags containing disulfide bonds such as hen egg lysozyme (HEL). Reduction of proteins within the MHC class II loading compartment is hypothesized to expose residues for class II binding and protease trimming. In vitro analysis has shown that the active site of GILT involves Cys(46) and Cys(49), present in a CXXC motif that shares similarity with the thioredoxin family. To define the functional requirements for GILT in MHC class II Ag processing, a GILT-deficient murine B cell lymphoma line was generated and stably transduced with wild-type and cysteine mutants of GILT. Intracellular flow cytometric, immunoblotting, and immunofluorescence analyses demonstrated that wild-type and mutant GILT were expressed and maintained lysosomal localization. Transduction with wild-type GILT reconstituted MHC class II processing of a GILT-dependent HEL epitope. Mutation of either Cys(46) or Cys(49) abrogated MHC class II processing of a GILT-dependent HEL epitope. In addition, biochemical analysis of these mutants suggested that the active site facilitates processing of precursor GILT to the mature form. Precursor forms of GILT-bearing mutations in Cys(200) or Cys(211), previously found to display thiol reductase activity in vitro, could not mediate Ag processing. These studies demonstrate that the thiol reductase activity of GILT is its essential function in MHC class II-restricted Ag processing.     

Mass-dependent predation risk as a mechanism for house sparrow declines?

House sparrow (Passer domesticus) numbers have declined rapidly in both rural and urban habitats across Western Europe over the last 30 years, leading to their inclusion on the UK conservation red list. The decline in farmland has been linked to a reduction in winter survival caused by reduced food supply. This reduction in food supply is associated with agricultural intensification that has led to the loss of seed-rich winter stubble and access to spilt grain. However, urban house sparrows have also declined, suggesting that reduced food supply in farmland is not the sole reason for the decline. Here, we show that changes in house sparrow mass and thus fat reserves are not regulated to minimize starvation risk, as would be expected if limited winter food were the only cause of population decline. Instead, the species appears to be responding to mass-dependent predation risk, with starvation risk and predation risk traded-off such that house sparrows may be particularly vulnerable to environmental change that reduces the predictability of the food supply.     

Weak breeding seasonality of a songbird in a seasonally arid tropical environment arises from individual flexibility and strongly seasonal moult

In some tropical birds, breeding seasonality is weak at the population level, even where there are predictable seasonal peaks in environmental conditions. It therefore remains unclear whether individuals are adapted to breeding at specific times of the year or flexible to variable environmental conditions. We tested whether the relative year‐round breeding activity of the Common Bulbul Pycnonotus barbatus arises due to within‐individual variability in breeding dates. We collected data from 827 birds via mist‐netting over 2 years with corresponding local weather data. We used a combination of climate envelope and generalized linear mixed models to explore how the timing of breeding is influenced by time of year, individual variation, rainfall and temperature in a West African savannah where seasonal precipitation determines annual variation in environmental conditions. We also pooled 65 breeding records from 19 individuals recorded between 2006 and 2017 based on brood patch occurrence and behavioural observation to compare within‐individual and population variability in breeding dates. We show that the breeding dates of individuals may be as variable as for the population as a whole. However, we observed a seasonal peak in juvenile occurrence that varies significantly between years. Models suggest no relationship between nesting and moult, and within‐year variation in rainfall and temperature, and birds were unlikely to breed during moult but may do so afterwards. Moult was very seasonal, correlating strongly with day length. We suggest that because environmental conditions permit year‐round breeding, and because reproductive output is subject to high predation risk, there is probably a weak selection for individuals to match breeding with variable peak conditions in the environment. Instead, moult, which always occurs annually and successfully, is probably under strong selection to match variable peak conditions in the environment so that long‐term survival ensures future reproduction.