bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice storm effects on the canopy structure of a northern hardwood forest after 8 years
Authors: Weeks Brian C. , Hamburg Steven P. , Vadeboncoeur Matthew A.
Published: August 2009

Ice storms can cause severe damage to forest canopies, resulting in differential mortality among tree species and size classes and leading to long-lasting changes in the vertical structure and composition of the forest. An intense ice storm in 1998 damaged large areas of the northern hardwood forest, including much of the Hubbard Brook Experimental Forest, New Hampshire (USA). Following up on detailed poststorm assessments, we measured changes in the vertical structure of the forest canopy 8 years poststorm. We focused on how the presence of disease-induced advance regeneration of American beech ( Fagus grandifolia Ehrh.) has affected canopy structure in the recovering forest. We measured foliage-height profiles using a point-quadrat approach and a pole-mounted leaf area index (LAI) sensor. Although the total LAIs of damaged and undamaged areas were similar, areas damaged in 1998 showed an increased proportion of total leaf area between 6 and 10 m above the ground. The foliage at this height is largely (54%) beech. To the extent that this heavily beech-dominated understory layer suppresses regeneration of other species, these findings suggest that rare disturbances of mature northern hardwood forests affected by beech bark disease will increase the importance of damage-prone and economically marginal beech.
Seed germination and seedling vigor of weevil-damaged acorns of red oak
Authors: Lombardo Jeffrey A. , McCarthy Brian C.
Published: August 2009

Acorn weevils (Coleoptera: Curculionidae) are well-known predators of oak acorns in the eastern hardwood forest region of the United States. We examined the germination percentage of seeds, as well as the physical characteristics of seedlings, originating from both weevil-damaged and sound acorns of red oak ( Quercus rubra L.) to determine if weevil depredation impacts seedling vigor. Seeds were grown under greenhouse conditions for a period of 8 weeks. X-ray imaging was used as a nondestructive method for determining seed condition prior to germination. The combined data set showed a reduction in germination percentage from 86% for sound acorns to 26% for those damaged by weevils. Seven seedling metrics were evaluated for differences between seedlings originating from sound and those from weevil-damaged acorns. Of these metrics, the number of leaf flushes, total number of leaves, root collar diameter, shoot length, and dry mass were significantly (P < 0.05) different. Two variables, root length and shoot diameter, were not significantly different. Early allocation of resources to root establishment likely explains these findings. Because of reduced stem height and leaf number, seedlings from weevil-damaged acorns are likely to be less competitive in the forest understory than those from sound acorns.
Fuel treatment effects on stand-level carbon pools, treatment-related emissions, and fire risk in a Sierra Nevada mixed-conifer forestPublication No. 143 of the National Fire and Fire Surrogate Project.
Authors: Stephens Scott L. , Moghaddas Jason J. , Hartsough Bruce R. , Moghaddas Emily E.Y. , Clinton Nicholas E.
Published: August 2009

Policies have been enacted to encourage carbon (C) sequestration through afforestation, reforestation, and other silvicultural practices; however, the effects of wildfires on forest C stocks are poorly understood. We present information from Sierran mixed-conifer forests regarding how control, mechanical, prescribed-fire, and mechanical followed by prescribed-fire treatments affected C pools. Secondly, we report CO2 emissions from machinery and burning associated with the treatments. Lastly, the effects of treatments on the potential for C loss to wildfire are presented. The amount of aboveground C in live trees was significantly reduced in mechanical-only and mechanical plus fire treatments; C contained in dead trees was not significantly different. There was no significant difference in aboveground live and dead tree C between the fire-only and control treatments. Fire-only and mechanical plus fire treatments emitted significantly more CO2 than the mechanical treatment and control. Modeling results for the control demonstrated 90% of the live tree C had a high (>75%) chance of being killed in a wildfire; in contrast, all three active treatments had low vulnerabilities to C loss. With wildfire severity increasing in most Sierran forests, management actions designed to increase fire resistance are justified for long-term C sequestration.
Improving initiation, genotype capture, and family representation in somatic embryogenesis of Pinus radiata by a combination of zygotic embryo maturity, media, and explant preparation
Authors: Hargreaves Cathy L. , Reeves Cathie B. , Find Jens I. , Gough Keiko , Josekutty Puthiyaparambil , Skudder Dolina B. , van der Maas Susan A. , Sigley Margaret R. , Menzies Mike I. , Low Charlie B. , Mullin Tim J.
Published: August 2009

The principal aim of this investigation was to improve somatic embryogenesis initiation and to enhance representation of families and genotypes within those families of Pinus radiata D. Don. A total of 19 open-pollinated seed families, many with unrelated and weakly related parents, were tested. Optimum stage of cone maturity for initiation success was tested by five collections made at 1 week intervals, spanning the developmental period from pro-embryo to cotyledonary embryos. Two media were compared; embryo-development media (EDM6) and a modified Litvay medium (Glitz). Two zygotic embryo explant-preparation techniques were tested; embryos with retained megagametophytes and excised embryos. Proliferating embryogenic tissues were obtained from all four treatments (2850 explants per treatment, 570 per collection time) for the 19 families. The best initiation rates were achieved with a combination of Glitz medium with excised zygotic embryos, with 55% of explants from all collections and all families combined giving rise to proliferating embryogenic tissue. At the optimal collection time for each of the families, this treatment gave a range of 47%–97% initiation success with an average of 70% per family.
DESIGN OF WRAPPER FOR SELF-MANAGEMENT OF COTS COMPONENTS
Authors: SHIN MICHAEL E. , PANIAGUA FERNANDO
Published: August 2009

This paper describes an approach to the design of a wrapper for self-managing COTS (commercial off-the-shelf) components. Each wrapper for COTS components encapsulates the properties of self-management — detection, reconfiguration, and repair. A COTS component deals with the application perspectives, whereas the wrapper handles the self-management perspectives, separately from the application perspectives. Each wrapper for self-managing COTS components is structured into several objects in support of detection, reconfiguration, and repair of the anomalous COTS components. The approach suggested in this paper is applied to the distributed elevator system consisting of multiple COTS components.
TRAP.NET: A REALIZATION OF TRANSPARENT SHAPING IN .NET
Authors: SADJADI S. MASOUD , TRIGOSO FERNANDO
Published: August 2009

We define adaptability as the capacity of software in adjusting its behavior in response to changing conditions. To list just a few examples, adaptability is important in pervasive computing, where software in mobile devices need to adapt to dynamic changes in wireless networks; autonomic computing, where software in critical systems are required to be self-manageable; and grid computing, where software for long running scientific applications need to be resilient to hardware crashes and network outages. In this paper, we provide a realization of the transparent shaping programming model, called TRAP.NET, which enables transparent adaptation in existing .NET applications as a response to the changes in the application requirements and/or to the changes in their execution environment. Using TRAP.NET, we can adapt an application dynamically, at run time, or statically, at load time, without the need to manually modify the application original functionality-hence transparent.
A SEGMENT BASED APPROACH FOR THE REDUCTION OF THE NUMBER OF TEST CASES FOR PERFORMANCE EVALUATION OF COMPONENTS
Authors: CANGUSSU JOÃO W. , COOPER KENDRA , WONG W. ERIC
Published: August 2009

Component-based software development techniques are being adopted to rapidly deploy complex, high quality systems. One of its aspects is the selection of components that realize the specified requirements. In addition to the functional requirements, the selection must be done taking into account some non-functional requirements such as performance, reliability, and usability. Hence, data that characterize the non-functional behavior of the components is needed; a test set is needed to collect this data for each component under consideration. This set may be large, which results in a considerable increase in the cost of the development process. Here, a process is proposed to considerably reduce the number of test cases used in the performance evaluation of components. The process is based on sequential curve fittings from an incremental number of test cases until a minimal pre-specified residual error is achieved. The incremental selection of test cases is done in two different ways: randomly and adaptively. The accuracy and performance of the proposed approach are dependent on the values of the desired residual error. The smaller the residual error, the higher the accuracy. However, performance has an opposite behavior. The smaller the error, the larger the number of test cases needed. The results from experiments with image compression components are a clear indication that a reduction in the number of test cases can be achieved while maintaining reasonable accuracy when using the proposed approach.
AN APPROACH TO CONSTRUCTING HIGH-AVAILABLE DECENTRALIZED SYSTEMS VIA SELF-ADAPTIVE COMPONENTS
Authors: SUN XI , ZHOU LI , ZHUANG LEI , JIAO WEN PIN , MEI HONG
Published: August 2009

In decentralized computing environments, systems are built mainly from components that are developed and maintained independently by different third-party providers. The executions and evolutions of components located on distributed sites are beyond the control of the system developers, and the availabilities of those components are, to some extent, unpredictable because of their own tendencies and the unstable network. As a result, it is still a great challenge to construct high-available decentralized systems. In this paper, a self-adaptive component model is proposed to model those components distributed on the Internet and a running framework is described for constructing systems composed of self-adaptive components. Self-adaptive components can adjust their knowledge about the availabilities of the required services via learning from the feedback of historical invocations. Based on the knowledge, components can find the most appropriate service providers effectively and automatically. Experiments show that systems can always gain high availabilities under dynamic decentralized environments by using the approach.
AUTOMATED TEST CODE GENERATION FROM CLASS STATE MODELS
Authors: XU DIANXIANG , XU WEIFENG , WONG W. ERIC
Published: August 2009

This paper presents an approach to automated generation of executable test code from class models represented by the UML protocol state machines. It supports several coverage criteria for state models, including state coverage, transition coverage, and basic and extended round-trip coverage. It allows the tester to add and modify detailed test parameters (e.g., actual arguments for method invocations and implementation-specific environments) if necessary. When the state model is modified due to requirements change, the hand-crafted test parameters, if still valid, are automatically reused. This reduces the working load for regeneration of tests for modified models. In addition to test code, we also automatically generate state wrapper aspects in AspectJ, which facilitates comparing actual object states to expected states during test execution. This enables the automated verdict of pass/failure for test cases without the need to modify the source code of the class under test. We present two examples for which the executable test code is generated. They demonstrate the reuse of test parameters and testing of object interactions, respectively.
EXPONENTIAL SUMS ON 𝔸n. IV
Authors: ADOLPHSON ALAN , SPERBER STEVEN
Published: August 2009

We find new conditions on a polynomial over a finite field that guarantee that the exponential sum defined by the polynomial has only one nonvanishing p-adic cohomology group, hence the L-function associated to the exponential sum is a polynomial or the reciprocal of a polynomial.
MILD PRO-p-GROUPS AS GALOIS GROUPS OVER GLOBAL FIELDS
Authors: SALLE LANDRY
Published: August 2009

This paper is devoted to finding new examples of mild pro-p-groups as Galois groups over global fields, following the work of Labute ([6]). We focus on the Galois group [Formula: see text] of the maximal T-split S-ramified pro-p-extension of a global field k. We first retrieve some facts on presentations of such a group, including a study of the local-global principle for the cohomology group [Formula: see text], then we show separately in the case of function fields and in the case of number fields how it can be used to find some mild pro-p-groups.
TENTH POWER QUALIFIED RESIDUE DIFFERENCE SETS
Authors: BYARD KEVIN
Published: August 2009

Qualified residue difference sets of power n are known to exist for n = 2, 4, 6, as do similar sets that include the zero element, while both classes of set are known to be nonexistent for n = 8. Both classes of set are proved nonexistent for n = 10.
PARABOLIC GENERALIZED MODULAR FORMS AND THEIR CHARACTERS
Authors: KNOPP MARVIN , MASON GEOFFREY
Published: August 2009

We make a detailed study of the generalized modular forms of weight zero and their associated multiplier systems (characters) on an arbitrary subgroup Γ of finite index in the modular group. Among other things, we show that every generalized divisor on the compact Riemann surface associated to Γ is the divisor of a modular form (with unitary character) which is unique up to scalars. This extends a result of Petersson, and has applications to the Eichler cohomology.
SELF-POINTS ON ELLIPTIC CURVES OF PRIME CONDUCTOR
Authors: DELAUNAY CHRISTOPHE , WUTHRICH CHRISTIAN
Published: August 2009

Let E be an elliptic curve of conductor p. Given a cyclic subgroup C of order p in E[p], we construct a modular point PC on E, called self-point, as the image of (E,C) on X0(p) under the modular parametrization X0(p) → E. We prove that the point is of infinite order in the Mordell–Weil group of E over the field of definition of C. One can deduce a lower bound on the growth of the rank of the Mordell–Weil group in its PGL 2(ℤp)-tower inside ℚ(E[p∞]).
Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group
Authors: Tolstoy Eline , Hill Vanessa , Tosi Monica
Published: August 2009

Within the Local Universe galaxies can be studied in great detail star by star, and here we review the results of quantitative studies in nearby dwarf galaxies. The color-magnitude diagram synthesis method is well established as the most accurate way to determine star-formation histories of galaxies back to the earliest times. This approach received a large boost from the exceptional data sets that wide-field CCD imagers on the ground and the Hubble Space Telescope could provide. Spectroscopic studies using large ground-based telescopes such as VLT, Magellan, Keck, and HET have allowed the determination of abundances and kinematics for significant samples of stars in nearby dwarf galaxies. These studies have shown how the properties of stellar populations can vary spatially and temporally. This leads to important constraints to theories of galaxy formation and evolution. The combination of spectroscopy and imaging and what they have taught us about dwarf galaxy formation and evolution is the aim of this review.
Gravitational Waves from Merging Compact Binaries
Authors: Hughes Scott A.
Published: August 2009

Largely motivated by the development of highly sensitive gravitational-wave detectors, our understanding of merging compact binaries and the gravitational waves they generate has improved dramatically in recent years. Breakthroughs in numerical relativity now allow us to model the coalescence of two black holes with no approximations or simplifications. There has also been outstanding progress in our analytical understanding of binaries. We review these developments, examining merging binaries using black hole perturbation theory, post-Newtonian expansions, and direct numerical integration of the field equations. We summarize these approaches and what they have taught us about gravitational waves from compact binaries. We place these results in the context of gravitational-wave generating systems, analyzing the impact gravitational-wave emission has on their sources, as well as what we can learn about them from direct gravitational-wave measurements.
High-Contrast Observations in Optical and Infrared Astronomy
Authors: Oppenheimer Ben R. , Hinkley Sasha
Published: August 2009

High-contrast observations in optical and infrared astronomy are defined as any observation requiring a technique to reveal a celestial object of interest that is in such close angular proximity to another source brighter by a factor of at least 105that optical effects hinder or prevent the collection of photons directly from the target of observation. This is a relatively new type of observation that enables research on previously obscured parts of the Universe. In particular, it is most applicable to comparative planetary science, a field that directly attacks such questions as “how common are planetary systems? What types of planets exist, and are there planets other than Earth that are capable of supporting life as we know it?” We survey the scientific motivations for high-contrast observations, provide an overview of the techniques currently being used or developed, and discuss some ideas and studies for future prospects.
Physical Properties and Environments of Nearby Galaxies
Authors: Blanton Michael R. , Moustakas John
Published: August 2009

We review the physical properties of nearby, relatively luminous galaxies, using results from newly available massive data sets together with more detailed observations. First, we present the global distribution of properties, including the optical and ultraviolet (UV) luminosity, stellar mass, and atomic gas mass functions. Second, we describe the shift of the galaxy population from late galaxy types in underdense regions to early galaxy types in overdense regions. We emphasize that the scaling relations followed by each galaxy type change very little with environment, with the exception of some minor but detectable effects. The shift in the population is apparent even at the densities of small groups and therefore cannot be exclusively due to physical processes operating in rich clusters. Third, we divide galaxies into four crude types—spiral, lenticular, elliptical, and merging systems—and describe some of their more detailed properties. We attempt to put these detailed properties into the global context provided by large surveys.
Hot Subdwarf Stars
Authors: Heber Ulrich
Published: August 2009

Hot subdwarf stars (sdBs, sdOs) are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. They are found in all Galactic stellar populations and are sufficiently common to account for the UV-upturn of early-type galaxies. About half of the sdBs reside in close binaries; companions are white dwarfs or low-mass main-sequence stars. Binary population-synthesis models explain naturally the actual sdB binary fractions of field and globular cluster stars as well as of He-sdOs if white-dwarf mergers are considered. Hot helium flashes explain the chemical composition of He-sdOs. Asteroseismology of a dozen pulsating sdB stars allowed determination of their masses and detection of a planet to V391 Peg. The discoveries of an sdO star unbound to the Galaxy, potential SN Ia progenitors and probably a hidden population of neutron stars or black hole companions have great impact on astrophysics at large.
Regulation of Tissue Growth through Nutrient Sensing
Authors: Hietakangas Ville , Cohen Stephen M.
Published: August 2009

Nutrition is a key regulator of tissue growth. In animals, nutritional status is monitored and signaled at both the cellular and systemic levels. The main mediator of cellular nutrient sensing is the protein kinase TOR (target of rapamycin). TOR receives information from levels of cellular amino acids and energy, and it regulates the activity of processes involved in cell growth, such as protein synthesis and autophagy. Insulin-like signaling is the main mechanism of systemic nutrient sensing and mediates its growth-regulatory functions largely through the phosphatidylinositol 3-kinase (PI3K)/AKT protein kinase pathway. Other nutrition-regulated hormonal mechanisms contribute to growth control by modulating the activity of insulin-like signaling. The pathways mediating signals from systemic and cellular levels converge, allowing cells to combine information from both sources. Here we give an overview of the mechanisms that adjust animal tissue growth in response to nutrition and highlight some general features of the signaling pathways involved.
Negative modulation of inositol 1,4,5-trisphosphate type 1 receptor expression prevents dystrophin-deficient muscle cells death
Authors: Mondin Ludivine , Balghi Haouaria , Constantin Bruno , Cognard Christian , Sebille Stéphane
Published: August 2009

Evidence for a modulatory effect of cyclosporin A (CsA) on calcium signaling and cell survival in dystrophin-deficient cells is presented. Our previous works strongly supported the hypothesis of an overactivation of Ca2+ release via inositol 1,4,5-trisphosphate (IP3) receptors (IP3R) in dystrophin-deficient cells, both during membrane depolarization and at rest, through spontaneous Ca2+ release events. Forced expression of mini-dystrophin in these cells contributed, during stimulation and in resting condition, to the recovery of a controlled calcium homeostasis. In the present work, we demonstrate that CsA exposure displayed a dual-modulator effect on calcium signaling in dystrophin-deficient cells. Short-time incubation induced a decrease of IP3-dependent calcium release, leading to patterns of release similar to those observed in myotubes expressing mini-dystrophin, whereas long-time incubation reduced the expression of the type I of IP3 receptors (IP3R-1) RNA levels. Moreover, both IP3R-1 knockdown and blockade through 2-aminoethoxydiphenyle borate or CsA induced improved survival of dystrophin-deficient myotubes, demonstrating the cell death dependence on the IP3-dependent calcium signaling as well as the protective effect of CsA. Inhibition of the IP3 pathway could be a very interesting approach for reducing the natural cell death of dystrophin-deficient cells in development.
Angiotensin II induces RhoA activation through SHP2-dependent dephosphorylation of the RhoGAP p190A in vascular smooth muscle cells
Authors: Bregeon Jeremy , Loirand Gervaise , Pacaud Pierre , Rolli-Derkinderen Malvyne
Published: August 2009

Angiotensin II (ANG II) is a major regulator of blood pressure that essentially acts through activation of ANG II type 1 receptor (AT1R) of vascular smooth muscle cells (VSMC). AT1R activates numerous intracellular signaling pathways, including the small G protein RhoA known to control several VSMC functions. Nevertheless, the mechanisms leading to RhoA activation by AT1R are unknown. RhoA activation can result from activation of RhoA exchange factor and/or inhibition of Rho GTPase-activating protein (GAP). Here we hypothesize that a RhoGAP could participate to RhoA activation induced by ANG II in rat aortic VSMC. The knockdown of the RhoGAP p190A by small interfering RNA (siRNA) abolishes the activation of RhoA-Rho kinase pathway induced after 5 min of ANG II (0.1 μM) stimulation in rat aortic VSMC. We then show that AT1R activation induces p190A dephosphorylation and inactivation. In addition, expression of catalytically inactive or phosphoresistant p190A mutants increases the basal activity of RhoA-Rho kinase pathway, whereas phosphomimetic mutant inhibits early RhoA activation by ANG II. Using siRNA and mutant overexpression, we then demonstrate that the tyrosine phosphatase SHP2 is necessary for 1) maintaining p190A basally phosphorylated and activated by the tyrosine kinase c-Abl, and 2) inducing p190A dephosphorylation and RhoA activation in response to AT1R activation. Our work then defines p190A as a new mediator of RhoA activation by ANG II in VSMC.
MEK, p38, and PI-3K mediate cross talk between EGFR and TNFR in enhancing hepatocyte growth factor production from human mesenchymal stem cells
Authors: Wang Yue , Weil Brent R. , Herrmann Jeremy L. , Abarbanell Aaron M. , Tan Jiangning , Markel Troy A. , Kelly Megan L. , Meldrum Daniel R.
Published: August 2009

Human bone marrow mesenchymal stem cells (MSCs) are a potent source of growth factors, which are partly responsible for their beneficial paracrine effects. We reported previously that transforming growth factor-α (TGF-α), a putative mediator of wound healing and the injury response, increases the release of vascular endothelial growth factor (VEGF), augments tumor necrosis factor-α (TNF-α)-stimulated VEGF production, and activates mitogen-activated protein kinases and phosphatidylinositol 3-kinase (PI-3K) pathway in human MSCs. The experiments described in this report indicate that TGF-α increases MSC-derived hepatocyte growth factor (HGF) production. TGF-α-stimulated HGF production was abolished by inhibition of MEK, p38, PI-3K, or by small interfering RNA (siRNA) targeting TNF receptor 2 (TNFR2), but was not attenuated by siRNA targeting TNF receptor 1 (TNFR1). Ablation of TNFR1 significantly increased basal and stimulated HGF. A potent synergy between TGF-α and TNF-α was noted in MSC HGF production. This synergistic effect was abolished by MEK, P38, PI-3K inhibition, or by ablation of both TNF receptors using siRNA. We conclude that 1) novel cross talk occurs between tumor necrosis factor receptor and TGF-α/epidermal growth factor receptor in stimulating MSC HGF production; 2) this cross talk is mediated, at least partially, via activation of MEK, p38, and PI-3K; 3) TGF-α stimulates MSCs to produce HGF by MEK, p38, PI-3K, and TNFR2-dependent mechanisms; and 4) TNFR1 acts to decrease basal TGF-α and TNF-α-stimulated HGF.
Alterations in mechanical properties of mesenteric resistance arteries in experimental portal hypertension
Authors: Resch Markus , Wiest Reiner , Moleda Lukas , Fredersdorf Sabine , Stoelcker Benjamin , Schroeder Josef A. , Schölmerich Juergen , Endemann Dierk H.
Published: August 2009

Splanchnic vasodilation is the pathophysiological hallmark in the development of the hyperdynamic circulatory syndrome in liver cirrhosis and portal hypertension. This has been attributed so far mainly to a marked vascular hyporeactivity to endogenous vasoconstrictors. However, myogenic tone and vessel stiffness have not been addressed in mesenteric arteries in liver cirrhosis. CCl4−-induced ascitic cirrhotic (LC) and age-matched control rats, portal vein-ligated (PVL) rats, and sham-operated rats were investigated. Third-order mesenteric resistance arteries were studied under no-flow conditions using a pressure myograph measuring media thickness and lumen diameter in response to incremental increases in intramural pressure, from which wall mechanics were calculated. Electron microscopy was used for investigation of wall ultrastructure, especially the fenestrae in internal elastic lamina (IEL). In PVL animals, no significant change in passive vessel strain, stress, media-to-lumen ratio, or cross-sectional area was noted. In contrast, in LC rats, vessel strain was markedly elevated compared with healthy control rats, indicating a marked reduction in vessel stiffness. In addition, the strain-stress curve was shifted to the right, and the elastic modulus in dependency on vessel stress decreased, demonstrating predominantly structure-dependent factors to be involved. The media-to-lumen quotient was not significantly altered, but cross-sectional area was highly increased in LC rats, indicating hypertrophic outward remodeling. These findings were paralleled by enlarged fenestrae in the IEL but no change in thickness of IEL or proportion of extracellular matrix or vascular smooth muscle in LC rats. We concluded that, in long-standing severe portal hypertension such as ascitic LC but not in short-term conditions such as PVL, mesenteric resistance arteries exhibit vascular remodeling and markedly less resistant mechanical properties, leading to decreased vessel stiffness accompanied by structural changes in the IEL. This may well contribute to the maintenance and severity of splanchnic arterial vasodilation in LC.
Localization of acyl ghrelin- and des-acyl ghrelin-immunoreactive cells in the rat stomach and their responses to intragastric pH
Authors: Mizutani Makoto , Atsuchi Kaori , Asakawa Akihiro , Matsuda Norifumi , Fujimura Masaki , Inui Akio , Kato Ikuo , Fujimiya Mineko
Published: August 2009

Acyl ghrelin has a 28-amino acid sequence with O-n-octanoyl acid modification at the serine 3 position, whereas des-acyl ghrelin has no octanoyl acid modification. Although these peptides exert different physiological functions, no previous studies have shown the different localization of acyl ghrelin and des-acyl ghrelin in the stomach. Here we have developed an antibody specific for des-acyl ghrelin that does not crossreact with acyl ghrelin. Both acyl ghrelin- and des-acyl ghrelin-immunoreactive cells were distributed in the oxyntic and antral mucosa of the rat stomach, with higher density in the antral mucosa than oxyntic mucosa. Immunofluorescence double staining showed that acyl ghrelin- and des-acyl ghrelin-positive reactions overlapped in closed-type round cells, whereas des-acyl ghrelin-positive reaction was found in open-type cells in which acyl ghrelin was negative. Acyl ghrelin-/des-acyl ghrelin-positive closed-type cells contain obestatin; on the other hand, des-acyl ghrelin-positive open-type cells contain somatostatin. We measured the release of acyl ghrelin and des-acyl ghrelin in vascularly perfused rat stomach by ELISA, and the effects of different intragastric pH levels on the release of each peptide were examined. The release of des-acyl ghrelin from the perfused stomach was greater at pH 2 than at pH 4; however, the release of acyl ghrelin was not affected by intragastric pH. The present study demonstrated the differential localization of acyl ghrelin and des-acyl ghrelin in the rat stomach and their different responses to the intragastric pH.
Comparison of sarcoplasmic reticulum calcium content in atrial and ventricular myocytes of three fish species
Authors: Haverinen Jaakko , Vornanen Matti
Published: August 2009

Ryanodine (Ry) sensitivity of cardiac contraction differs between teleost species, between atrium and ventricle, and according to the thermal history of the fish. The hypothesis that variability in Ry sensitivity of contraction is due to species-specific, chamber-specific, and temperature-related differences in the sarcoplasmic reticulum (SR) Ca2+content, was tested by comparing steady-state (SS) and maximal (Max) Ca2+loads of the SR in three teleost fish, rainbow trout ( Oncorhynchus mykiss), burbot ( Lota lota), and crucian carp ( Carassius carassius), which differ in the extent of SR contribution to excitation-contraction coupling. Fish were acclimated at 4°C (cold-acclimation, CA) or 18°C (warm-acclimation, WA), and SR Ca2+content was released by a rapid application of 10 mM caffeine to single cardiac myocytes; its amount was determined from the Na+-Ca2+exchange current at 18°C. SS Ca2+load was larger in atrial (304–915 μmol/l) than ventricular (224–540 μmol/l) myocytes in all fish species ( P < 0.05), and the same was true for Max SR Ca2+content: 550–1,522 μmol/l and 438–840 μmol/l for atrial and ventricular myocytes, respectively ( P < 0.05). Consistent with the hypothesis, acclimation to cold increased Ca2+load of the cardiac SR in the burbot heart, but contrary to the hypothesis, temperature acclimation did not affect SR Ca2+content in rainbow trout and crucian carp hearts. Furthermore, there was an inverse relation between SR Ca2+content and Ry sensitivity of contraction force: the species with the smallest SR Ca2+content (burbot) is most sensitive to Ry. Collectively, these findings show that SR Ca2+content of fish cardiac myocytes is several times larger than that in mammalian cardiac SR.
Saliva and other taste stimuli are important for gustatory processing of linoleic acid
Authors: Stratford Jennifer M. , Contreras Robert J.
Published: August 2009

Paradoxically, bilateral transection of the chorda tympani nerve (CTX) raises the taste discrimination threshold for the free fatty acid, linoleic acid (LA), yet the chorda tympani nerve (CT) is unresponsive to lingual application of LA alone. LA may require a background of saliva to activate taste cells, since CTX decreases saliva production through denervation of the submaxillary and sublingual salivary glands. To assess the role of saliva, we measured LA taste discrimination thresholds for animals whose submaxillary and sublingual salivary glands were removed and also recorded CT responses to LA mixed in artificial saliva. Partial desalivation shifted LA discrimination thresholds from between 5.5 and 11 μM to between 11 and 22 μM. However, this effect was not as pronounced as previously seen with CTX animals. Surprisingly, the CT was unresponsive to LA mixed with artificial saliva, suggesting that artificial saliva may lack components necessary for LA taste. Additionally, fats may primarily enhance other tastes. We previously reported that LA increases CT responses to monosodium glutamate (MSG). Thus we also recorded CT whole nerve responses to taste mixtures of LA and sodium chloride (NaCl), sucrose (SUC), citric acid (CA), or quinine hydrochloride (QHCl) in anesthetized rats. We found that LA increased CT responses to NaCl but did not alter CT responses to SUC, CA, and QHCl. Thus CT recordings either lack the sensitivity to detect small changes to SUC, CA, and QHCl or LA may affect CT responses to MSG and NaCl only, perhaps by specifically modulating gustatory processing of Na+.
Developmental delays consistent with cochlear hypothyroidism contribute to failure to develop hearing in mice lacking Slc26a4/pendrin expression
Authors: Wangemann Philine , Kim Hyoung-Mi , Billings Sara , Nakaya Kazuhiro , Li Xiangming , Singh Ruchira , Sharlin David S. , Forrest Douglas , Marcus Daniel C. , Fong Peying
Published: August 2009

Mutations of SLC26A4 cause an enlarged vestibular aqueduct, nonsyndromic deafness, and deafness as part of Pendred syndrome. SLC26A4 encodes pendrin, an anion exchanger located in the cochlea, thyroid, and kidney. The goal of the present study was to determine whether developmental delays, possibly mediated by systemic or local hypothyroidism, contribute to the failure to develop hearing in mice lacking Slc26a4 ( Slc26a4−/−). We evaluated thyroid function by voltage and pH measurements, by array-assisted gene expression analysis, and by determination of plasma thyroxine levels. Cochlear development was evaluated for signs of hypothyroidism by microscopy, in situ hybridization, and quantitative RT-PCR. No differences in plasma thyroxine levels were found in Slc26a4−/− and sex-matched Slc26a4+/− littermates between postnatal day 5 ( P5) and P90. In adult Slc26a4−/− mice, the transepithelial potential and the pH of thyroid follicles were reduced. No differences in the expression of genes that participate in thyroid hormone synthesis or ion transport were observed at P15, when plasma thyroxine levels peaked. Scala media of the cochlea was 10-fold enlarged, bulging into and thereby displacing fibrocytes, which express Dio2 to generate a cochlear thyroid hormone peak at P7. Cochlear development, including tunnel opening, arrival of efferent innervation at outer hair cells, endochondral and intramembraneous ossification, and developmental changes in the expression of Dio2, Dio3, and Tectb were delayed by 1–4 days. These data suggest that pendrin functions as a HCO3− transporter in the thyroid, that Slc26a4−/− mice are systemically euthyroid, and that delays in cochlear development, possibly due to local hypothyroidism, lead to the failure to develop hearing.
Activation of the epithelial Na+ channel in the collecting duct by vasopressin contributes to water reabsorption
Authors: Bugaj Vladislav , Pochynyuk Oleh , Stockand James D.
Published: August 2009

We used patch-clamp electrophysiology on isolated, split-open murine collecting ducts (CD) to test the hypothesis that regulation of epithelial sodium channel (ENaC) activity is a physiologically important effect of vasopressin. Surprisingly, this has not been tested directly before. We ask whether vasopressin affects ENaC activity distinguishing between acute and chronic effects, as well as, parsing the cellular signaling pathway and molecular mechanism of regulation. In addition, we quantified possible synergistic regulation of ENaC by vasopressin and aldosterone associating this with a requirement for distal nephron Na+ reabsorption during water conservation vs. maintenance of Na+ balance. We find that vasopressin significantly increases ENaC activity within 2–3 min by increasing open probability ( Po). This activation was dependent on adenylyl cyclase (AC) and PKA. Water restriction (18–24 h) and pretreatment of isolated CD with vasopressin (∼30 min) resulted in a similar increase in Po. In addition, this also increased the number ( N) of active ENaC in the apical membrane. Similar to Po, increases in N were sensitive to inhibitors of AC. Stressing animals with water and salt restriction separately and jointly revealed an important effect of vasopressin: conservation of water and Na+ each independently increased ENaC activity and jointly had a synergistic effect on channel activity. These results demonstrate a quantitatively important action of vasopressin on ENaC suggesting that distal nephron Na+ reabsorption mediated by this channel contributes to maintenance of water reabsorption. In addition, our results support that the combined actions of vasopressin and aldosterone are required to achieve maximally activated ENaC.
Dendritic Spine Remodeling After Spinal Cord Injury Alters Neuronal Signal Processing
Authors: Tan Andrew M. , Choi Jin-Sung , Waxman Stephen G. , Hains Bryan C.
Published: August 2009

Central sensitization, a prolonged hyperexcitability of dorsal horn nociceptive neurons, is a major contributor to abnormal pain processing after spinal cord injury (SCI). Dendritic spines are micron-sized dendrite protrusions that can regulate the efficacy of synaptic transmission. Here we used a computational approach to study whether changes in dendritic spine shape, density, and distribution can individually, or in combination, adversely modify the input–output function of a postsynaptic neuron to create a hyperexcitable neuronal state. The results demonstrate that a conversion from thin-shaped to more mature, mushroom-shaped spine structures results in enhanced synaptic transmission and fidelity, improved frequency-following ability, and reduced inhibitory gating effectiveness. Increasing the density and redistributing spines toward the soma results in a greater probability of action potential activation. Our results demonstrate that changes in dendritic spine morphology, documented in previous studies on spinal cord injury, contribute to the generation of pain following SCI.
Neural Substrates of Practice Structure That Support Future Off-Line Learning
Authors: Wymbs Nicholas F. , Grafton Scott T.
Published: August 2009

Off-line learning is facilitated when motor skills are acquired under a random practice schedule and retention suffers when a similar set of motor skills are practiced under a blocked schedule. The current study identified the neural correlates of a random training schedule while participants learned a set of four-element finger sequences using their nondominant hand during functional magnetic resonance imaging. A go/no go task was used to separately probe brain areas supporting sequence preparation and production. By the end of training, the random practice schedule, relative to the block schedule, recruited a broad premotor–parietal network as well as sensorimotor and subcortical regions during both preparation and production trials, despite equivalent motor performance. Longitudinal analysis demonstrated that preparation-related activity under a random schedule remained stable or increased over time. The blocked schedule showed the opposite pattern. Across individual subjects, successful skill retention was correlated with greater activity at the end of training in the ipsilateral left motor cortex, for both preparation and production. This is consistent with recent evidence that attributes off-line learning to training-related processing within primary motor cortex. These results reflect the importance of an overlooked aspect of motor skill learning. Specifically, how trials are organized during training—with a random schedule—provides an effective basis for the formation of enduring motor memories, through enhanced engagement of core regions involved in the active preparation and implementation of motor programs.
Social Context Rapidly Modulates the Influence of Auditory Feedback on Avian Vocal Motor Control
Authors: Sakata Jon T. , Brainard Michael S.
Published: August 2009

Sensory feedback is important for the learning and control of a variety of behaviors. Vocal motor production in songbirds is a powerful model system to study sensory influences on behavior because the learning, maintenance, and control of song are critically dependent on auditory feedback. Based on previous behavioral and neural experiments, it has been hypothesized that songs produced in isolation [undirected (UD) song] represent a form of vocal practice, whereas songs produced to females during courtship interactions [female-directed (FD) song] represent a form of vocal performance. According to this “practice versus performance” framework, auditory feedback should be more influential when birds engage in vocal practice than when they engage in vocal performance. To directly test this hypothesis, we used a computerized system to perturb auditory feedback at precise locations during the songs of Bengalese finches and compared the degree to which feedback perturbations caused song interruptions as well as changes to the sequencing and timing of syllables between interleaved renditions of UD and FD song. We found that feedback perturbation caused fewer song interruptions and smaller changes to syllable timing during FD song than during UD song. These data show that changes in the social context in which song is produced rapidly modulate the influence of auditory feedback on song control in a manner consistent with the practice versus performance framework. More generally, they indicate that, for song, as for other motor skills including human speech, the influence of sensory feedback on activity within vocal premotor circuitry can be dynamically modulated.
Acute Changes in Motor Cortical Excitability During Slow Oscillatory and Constant Anodal Transcranial Direct Current Stimulation
Authors: Bergmann Til Ole , Groppa Sergiu , Seeger Markus , Mölle Matthias , Marshall Lisa , Siebner Hartwig Roman
Published: August 2009

Transcranial oscillatory current stimulation has recently emerged as a noninvasive technique that can interact with ongoing endogenous rhythms of the human brain. Yet, there is still little knowledge on how time-varied exogenous currents acutely modulate cortical excitability. In ten healthy individuals we used on-line single-pulse transcranial magnetic stimulation (TMS) to search for systematic shifts in corticospinal excitability during anodal sleeplike 0.8-Hz slow oscillatory transcranial direct current stimulation (so-tDCS). In separate sessions, we repeatedly applied 30-s trials (two blocks at 20 min) of either anodal so-tDCS or constant tDCS (c-tDCS) to the primary motor hand area during quiet wakefulness. Simultaneously and time-locked to different phase angles of the slow oscillation, motor-evoked potentials (MEPs) as an index of corticospinal excitability were obtained in the contralateral hand muscles 10, 20, and 30 s after the onset of tDCS. MEPs were also measured off-line before, between, and after both stimulation blocks to detect any lasting excitability shifts. Both tDCS modes increased MEP amplitudes during stimulation with an attenuation of the facilitatory effect toward the end of a 30-s tDCS trial. No phase-locking of corticospinal excitability to the exogenous oscillation was observed during so-tDCS. Off-line TMS revealed that both c-tDCS and so-tDCS resulted in a lasting excitability increase. The individual magnitude of MEP facilitation during the first tDCS trials predicted the lasting MEP facilitation found after tDCS. We conclude that sleep slow oscillation-like excitability changes cannot be actively imposed on the awake cortex with so-tDCS, but phase-independent on-line as well as off-line facilitation can reliably be induced.
Zebrafish Motor Neuron Subtypes Differ Electrically Prior to Axonal Outgrowth
Authors: Moreno Rosa L. , Ribera Angeles B.
Published: August 2009

Different muscle targets and transcription factor expression patterns reveal the presence of motor neuron subtypes. However, it is not known whether these subtypes also differ with respect to electrical membrane properties. To address this question, we studied primary motor neurons (PMNs) in the spinal cord of zebrafish embryos. PMN genesis occurs during gastrulation and gives rise to a heterogeneous set of motor neurons that differ with respect to transcription factor expression, muscle targets, and soma location within each spinal cord segment. The unique subtype-specific soma locations and axonal trajectories of two PMNs—MiP (middle) and CaP (caudal)—allowed their identification in situ as early as 17 h postfertilization (hpf), prior to axon genesis. Between 17 and 48 hpf, CaPs and MiPs displayed subtype-specific electrical membrane properties. Voltage-dependent inward and outward currents differed significantly between MiPs and CaPs. Moreover, by 48 hpf, CaPs and MiPs displayed subtype-specific firing behaviors. Our results demonstrate that motor neurons that differ with respect to muscle targets and transcription factor expression acquire subtype-specific electrical membrane properties. Moreover, the differences are evident prior to axon genesis and persist to the latest stage studied, 2 days postfertilization.