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Search Results: 1 - 10 of 557063 matches for " Gary A. B. Armstrong "
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Natural Variation in the Thermotolerance of Neural Function and Behavior due to a cGMP-Dependent Protein Kinase
Ken Dawson-Scully, Gary A. B. Armstrong, Clement Kent, R. Meldrum Robertson, Marla B. Sokolowski
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000773
Abstract: Although it is acknowledged that genetic variation contributes to individual differences in thermotolerance, the specific genes and pathways involved and how they are modulated by the environment remain poorly understood. We link natural variation in the thermotolerance of neural function and behavior in Drosophila melanogaster to the foraging gene (for, which encodes a cGMP-dependent protein kinase (PKG)) as well as to its downstream target, protein phosphatase 2A (PP2A). Genetic and pharmacological manipulations revealed that reduced PKG (or PP2A) activity caused increased thermotolerance of synaptic transmission at the larval neuromuscular junction. Like synaptic transmission, feeding movements were preserved at higher temperatures in larvae with lower PKG levels. In a comparative assay, pharmacological manipulations altering thermotolerance in a central circuit of Locusta migratoria demonstrated conservation of this neuroprotective pathway. In this circuit, either the inhibition of PKG or PP2A induced robust thermotolerance of neural function. We suggest that PKG and therefore the polymorphism associated with the allelic variation in for may provide populations with natural variation in heat stress tolerance. for's function in behavior is conserved across most organisms, including ants, bees, nematodes, and mammals. PKG's role in thermotolerance may also apply to these and other species. Natural variation in thermotolerance arising from genes involved in the PKG pathway could impact the evolution of thermotolerance in natural populations.
Glial Hsp70 Protects K+ Homeostasis in the Drosophila Brain during Repetitive Anoxic Depolarization
Gary A. B. Armstrong, Chengfeng Xiao, Jennifer L. Krill, Laurent Seroude, Ken Dawson-Scully, R. Meldrum Robertson
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0028994
Abstract: Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the effects of energetic compromise in Drosophila by targeting the Na+/K+-ATPase. Acute ouabain treatment of intact flies resulted in subsequent repetitive comas that led to death and were associated with transient loss of K+ homeostasis in the brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion homeostasis we subjected flies to repetitive anoxia while recording extracellular [K+] in the brain. We show that targeted expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.
Stress Preconditioning of Spreading Depression in the Locust CNS
Corinne I. Rodgers, Gary A. B. Armstrong, Kelly L. Shoemaker, John D. LaBrie, Christopher D. Moyes, R. Meldrum Robertson
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0001366
Abstract: Cortical spreading depression (CSD) is closely associated with important pathologies including stroke, seizures and migraine. The mechanisms underlying SD in its various forms are still incompletely understood. Here we describe SD-like events in an invertebrate model, the ventilatory central pattern generator (CPG) of locusts. Using K+ -sensitive microelectrodes, we measured extracellular K+ concentration ([K+]o) in the metathoracic neuropile of the CPG while monitoring CPG output electromyographically from muscle 161 in the second abdominal segment to investigate the role K+ in failure of neural circuit operation induced by various stressors. Failure of ventilation in response to different stressors (hyperthermia, anoxia, ATP depletion, Na+/K+ ATPase impairment, K+ injection) was associated with a disturbance of CNS ion homeostasis that shares the characteristics of CSD and SD-like events in vertebrates. Hyperthermic failure was preconditioned by prior heat shock (3 h, 45°C) and induced-thermotolerance was associated with an increase in the rate of clearance of extracellular K+ that was not linked to changes in ATP levels or total Na+/K+ ATPase activity. Our findings suggest that SD-like events in locusts are adaptive to terminate neural network operation and conserve energy during stress and that they can be preconditioned by experience. We propose that they share mechanisms with CSD in mammals suggesting a common evolutionary origin.
An improved, high-quality draft genome sequence of the Germination-Arrest Factor-producing Pseudomonas fluorescens WH6
Jeffrey A Kimbrel, Scott A Givan, Anne B Halgren, Allison L Creason, Dallice I Mills, Gary M Banowetz, Donald J Armstrong, Jeff H Chang
BMC Genomics , 2010, DOI: 10.1186/1471-2164-11-522
Abstract: We used a hybrid next-generation sequencing approach to develop a high-quality draft genome sequence for P. fluorescens WH6. We employed automated, manual, and experimental methods to further improve the draft genome sequence. From this assembly of 6.27 megabases, we predicted 5876 genes, of which 3115 were core to P. fluorescens and 1567 were unique to WH6. Comparative genomic studies of WH6 revealed high similarity in synteny and orthology of genes with P. fluorescens SBW25. A phylogenomic study also placed WH6 in the same lineage as SBW25. In a previous non-saturating mutagenesis screen we identified two genes necessary for GAF activity in WH6. Mapping of their flanking sequences revealed genes that encode a candidate anti-sigma factor and an aminotransferase. Finally, we discovered several candidate virulence and host-association mechanisms, one of which appears to be a complete type III secretion system.The improved high-quality draft genome sequence of WH6 contributes towards resolving the P. fluorescens species, providing additional impetus for establishing two separate lineages in P. fluorescens. Despite the high levels of orthology and synteny to SBW25, WH6 still had a substantial number of unique genes and represents another source for the discovery of genes with implications in affecting plant growth and health. Two genes are demonstrably necessary for GAF and further characterization of their proteins is important for developing natural products as control measure against grassy weeds. Finally, WH6 is the first isolate of P. fluorescens reported to encode a complete T3SS. This gives us the opportunity to explore the role of what has traditionally been thought of as a virulence mechanism for non-pathogenic interactions with plants.Pseudomonas fluorescens is a diverse species of bacteria that is found throughout natural habitats and associated with plants. Contributing to their diverse lifestyles is their ability to produce an equally diverse array of seco
Bayesian Lensing Shear Measurement
Gary M. Bernstein,Robert Armstrong
Physics , 2013, DOI: 10.1093/mnras/stt2326
Abstract: We derive an estimator of weak gravitational lensing shear from background galaxy images that avoids noise-induced biases through a rigorous Bayesian treatment of the measurement. The derived shear estimator disposes with the assignment of ellipticities to individual galaxies that is typical of previous approaches to galaxy lensing. Shear estimates from the mean of the Bayesian posterior are unbiased in the limit of large number of background galaxies, regardless of the noise level on individual galaxies. The Bayesian formalism requires a prior describing the (noiseless) distribution of the target galaxy population over some parameter space; this prior can be constructed from low-noise images of a subsample of the target population, attainable from long integrations of a fraction of the survey field. We find two ways to combine this exact treatment of noise with rigorous treatment of the effects of the instrumental point-spread function and sampling. The Bayesian model fitting (BMF) method assigns a likelihood of the pixel data to galaxy models (e.g. Sersic ellipses). The Bayesian Fourier domain (BFD) method compresses the pixel data to a small set of weighted moments calculated after PSF correction in Fourier space. A numerical test using a simplified model of a biased galaxy measurement process demonstrates that the Bayesian formalism recovers applied shears to $<1$ part in $10^3$ accuracy and provides accurate uncertainty estimates. BFD is the first shear measurement algorithm that is model-free and requires no approximations or ad hoc assumptions in correcting for the effects of PSF, noise, or sampling on the galaxy images. These algorithms are good candidates for attaining the part-per-thousand shear inference required for hemisphere-scale weak gravitational lensing surveys. (abridged)
On the pararneterisation of drainflow response functions
A. Armstrong
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2000,
Abstract: A procedure for the parameterisation of drain flow hydrographs is proposed. This involves the derivation of empirical linear response functions, which are themselves parameterised. The parameters are the time and height of the peak, and the recession characteristics. The recession limb of the hydrograph can be approximated best by the Youngs (1985) analysis, which requires two parameters. The merit of this method is illustrated by an analysis of data from a drainage experiment at North Wyke, Devon, UK; this shows that the model fits the data very well. Keywords: Drainflow hydrographs; response functions
Elevated Carbon Dioxide Level Suppresses Nutritional Quality of Lettuce and Spinach  [PDF]
Anju Giri, Brenden Armstrong, Channa B. Rajashekar
American Journal of Plant Sciences (AJPS) , 2016, DOI: 10.4236/ajps.2016.71024
Abstract: Rising global CO2 levels are a major factor that impacts not only the environment but also many plant functions including growth, productivity and nutritional quality. The study examined the impact of elevated [CO2] on nutritional quality and growth characteristics of lettuce (Lactuca sativa) and spinach (Spinacia oleracea). Elevated [CO2] decreased the concentration of many important nutrients including nitrogen (protein), potassium and phosphorus in the edible parts of both lettuce and spinach. The nitrogen concentration in lettuce shoots was reduced by more than 30% at elevated [CO2] compared to the plants grown at ambient level of CO2. Similarly the concentration of a number of micronutrients including sulfur, zinc, copper and magnesium, was depressed in lettuce shoots. Although the total phenolic content and antioxidant capacity were higher in lettuce at elevated CO2, they were not affected in spinach. The photosynthetic activity was variable among the plant species while there was no increase in the carbon accumulation in these plants at elevated [CO2]. However, there was significant reduction in the leaf stomatal conductance in both lettuce and spinach in response to higher [CO2], which is likely affect both water loss from the leaves and their photosynthetic activity. The results indicate a broad adverse impact of rising [CO2] on the nutritional quality of commonly consumed leafy vegetables namely, lettuce and spinach.
Exercise in Children during Health and Sickness
Mutasim Abu-Hasan,Neil Armstrong,Lars B. Andersen,Miles Weinberger,Patricia A. Nixon
International Journal of Pediatrics , 2010, DOI: 10.1155/2010/842537
Abstract:
Data Combinations Accounting for LISA Spacecraft Motion
Daniel A. Shaddock,Massimo Tinto,Frank B. Estabrook,J. W. Armstrong
Physics , 2003, DOI: 10.1103/PhysRevD.68.061303
Abstract: LISA is an array of three spacecraft in an approximately equilateral triangle configuration which will be used as a low-frequency gravitational wave detector. We present here new generalizations of the Michelson- and Sagnac-type time-delay interferometry data combinations. These combinations cancel laser phase noise in the presence of different up and down propagation delays in each arm of the array, and slowly varying systematic motion of the spacecraft. The gravitational wave sensitivities of these generalized combinations are the same as previously computed for the stationary cases, although the combinations are now more complicated. We introduce a diagrammatic representation to illustrate that these combinations are actually synthesized equal-arm interferometers.
The effect of forearm posture on wrist flexion in computer workers with chronic upper extremity musculoskeletal disorders
Ronald A Burgess, R Terry Thompson, Gary B Rollman
BMC Musculoskeletal Disorders , 2008, DOI: 10.1186/1471-2474-9-47
Abstract: We measured maximum active wrist flexion using a goniometer with the forearm supported in the prone, neutral, and supine postures. Data was obtained from 5 subjects with UEMSDs attributed to computer use and from 13 control subjects.The UEMSD group exhibited significantly restricted wrist flexion compared to the control group in both wrists at all forearm postures with the exception of the non-dominant wrist with the forearm prone. In both groups, maximum active wrist flexion decreased at the supine forearm posture compared to the prone posture. No UEMSD subjects reported an increase in pain symptoms during testing.The UEMSD group exhibited reduced wrist flexion compared to controls that did not appear to be pain related. A supine forearm posture reduced wrist flexion in both groups, but the reduction was approximately 100% greater in the UEMSD group. The effect of a supine forearm posture on wrist flexion is consistent with known biomechanical changes in the distal extensor carpi ulnaris tendon that occur with forearm supination. We infer from these results that wrist extensor muscle passive tension may be elevated in UEMSD subjects compared to controls, particularly in the extensor carpi ulnaris muscle. Measuring wrist flexion at the supine forearm posture may highlight flexion restrictions that are not otherwise apparent.Occupational hand use has been associated with chronic upper limb pain and dysfunction, but the issue of causality remains controversial [1]. However, recent reviews of the epidemiological literature have concluded that there is a moderate, but consistent association between computer use and hand/arm symptoms [2,3]. Some symptoms may be consistent with specific clinical diagnoses (e.g., carpal tunnel syndrome (CTS), lateral epicondylitis), but frequently the symptoms are non-specific (e.g., myalgia) [4]. A prospective study of computer users found that 50% of hand/arm symptoms were non-specific [5]. This collection of specific and non-specific sy
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