bluuebunny/crossref_metadata_2025 huggingface dataset:
NONLINEAR PHENOMENA IN THE SINGLE-MODE DYNAMICS OF A CABLE-SUPPORTED BEAM
Authors: LENCI STEFANO , RUZZICONI LAURA
Published: May 2009

In this paper we discuss the practical usefulness of nonlinear dynamical analysis for the design of a planar cable-supported beam: we refer to a feasible case, assuming the value of the parameters corresponding to a realistic pedestrian footbridge. We consider a one degree of freedom model, obtained by the classical Galerkin reduction technique: the ensuing ordinary differential equation has both quadratic and cubic terms, due to geometric nonlinearities. Extensive numerical simulations are performed: they point out that this model, in spite of its apparent simplicity, is able to highlight the complex dynamics of the cable-supported beam, describing several common and uncommon nonlinear phenomena. Each of them is interpreted in terms of oscillations of the considered mechanical system; we explain the relevance of all the obtained results in the design of the examined structure under steady loads as wind and pedestrians, but also under transient phenomena as earthquake and gust; the ensuing issues, the most dangerous ranges and also the sensibility to perturbations are discussed in detail. In particular we deal with the importance, for an engineering design, of a careful interpretation of: isola bifurcation, transition to chaos both by period doubling cascade and reverse boundary crisis, multistability with coexistence of chaotic and periodic attractors, fractal basins boundaries, erosion of immediate basins, interrupted sequence of period doubling bifurcations. Also the effects of secondary attractors are analyzed, and it is shown that in general they cannot be neglected even if their range of existence is very small. We underline that all these investigations are performed choosing the excitation frequency far from resonances in order to alert the designer that the system dynamics may be complex independently of the activation mechanism due to resonance.
INTEGRATION-FREE ANALYSIS OF NONSMOOTH LOCAL DYNAMICS IN PLANAR FILIPPOV SYSTEMS
Authors: ARANGO IVÁN , TABORDA JOHN ALEXANDER
Published: May 2009

In this paper, we present a novel method to analyze the behavior of discontinuous piecewise-smooth autonomous systems (denominated Filippov systems) in the planar neighborhood of the discontinuity boundary (DB). The method uses the evaluation of the vector fields on DB to analyze the nonsmooth local dynamics of the Filippov system without the integration of the ODE sets. The method is useful in the detection of nonsmooth bifurcations in Filippov systems. We propose a classification of the points, events and events combinations on DB. This classification is more complete in comparison with the others previously reported. Additional characteristics as flow direction and sliding stability are included explicitly. The lines and the points are characterized with didactic symbols and the exclusive conditions for their existence are based on geometric criterions. Boolean-valued functions are used to formulate the conditions of existence. Different problems are analyzed with the proposed methodology.
ANALYSIS AND MODELING OF AN EXPERIMENTAL DEVICE BY FINITE-TIME LYAPUNOV EXPONENT METHOD
Authors: SANTITISSADEEKORN N. , BOHL D. , BOLLT E. M.
Published: May 2009

In this paper, we investigate the transport and mixing process of the batch mixers with two different configurations, the centered-blade and offset-blade mixers, by using a dynamical system approach. The 2-D velocity fields of the mixers measured using Particle Image Velocimetry (PIV) are used to identify the Lagrangian coherent structures (LCSs). The results show that the LCSs separate the physical space into two portions. In the case of the center-blade mixer the portion bounded inside the LCS experiences a relatively slow mixing relative to the portion outside of the LCS boundary. However, when the blade position is located near the wall, the LCS becomes more complicated but it still separates regions of fast mixing from a slower one. We develop a heuristic dynamical system model of our mixers to understand how the vorticity strength at the blade tips influences the variation of the LCSs. Finally, we define an appropriate notion of mixing to study the mixing rate of our mixing devices.
THE BASIN OF ATTRACTION OF LOZI MAPPINGS
Authors: BAPTISTA DIOGO , SEVERINO RICARDO , VINAGRE SANDRA
Published: May 2009

For parameter values which assure its existence, we characterize the basin of attraction for the Lozi map strange attractor.
STOCHASTIC DRIVING AND COUPLING CONTROL METHOD TO SUPPRESS SPIRAL WAVES AND SPATIOTEMPORAL CHAOS AND ANALYSIS OF CORRELATION
Authors: HUANHUAN TIAN , YU XUE , YUJUAN LIANG , SANJUN KANG
Published: May 2009

In this paper, the stochastic driving and coupling method to effectively suppress the turbulence and spiral waves is proposed. It is confirmed that the drive system ensures the response achieves complete synchronization via the computation of the Pearson's coefficient γ. The minimum time units of achieving complete synchronization N versus the coupling proportion P takes on the power-law N ~ P-k.
BIFURCATIONS IN AN ITERATIVE OPTIMIZATION PROCESS FOR INTENSITY MODULATED RADIATION THERAPY
Authors: FUJIMOTO KEN'ICHI , YOSHINAGA TETSUYA
Published: May 2009

We investigate bifurcations in an iterative method for optimizing an objective function derived from the intensity modulated radiation therapy (IMRT). Through the bifurcation analysis of discrete dynamical systems for small IMRT plans, we obtained bifurcation diagrams showing suitable parameter values for the convergence of fixed points corresponding to global or local minima of the objectives, and we found that rich nonlinear phenomena including a chaotic state can occur. We also illustrate that a similar bifurcation phenomenon occurs in a large IMRT system. The results on bifurcation structure are useful for suggesting the parameter design of IMRT plans with normal operation.
BIFURCATIONS IN THE TOPOLOGY OF ZERO-VELOCITY SURFACES IN THE PHOTO-GRAVITATIONAL COPENHAGEN PROBLEM
Authors: KALVOURIDIS T. J.
Published: May 2009

We study the evolution of the regions where three-dimensional motions of a small body are allowed in the Copenhagen case of the restricted three-body problem where one or both primaries, are radiation sources. We discuss the bifurcations in the topology of the zero-velocity surfaces, as well as in the trapping regions of the particle motion for various cases.
TUTTE POLYNOMIALS OF TENSOR PRODUCTS OF SIGNED GRAPHS AND THEIR APPLICATIONS IN KNOT THEORY
Authors: DIAO Y. , HETYEI G. , HINSON K.
Published: May 2009

It is well-known that the Jones polynomial of an alternating knot is closely related to the Tutte polynomial of a special graph obtained from a regular projection of the knot. Relying on the results of Bollobás and Riordan, we introduce a generalization of Kauffman's Tutte polynomial of signed graphs for which describing the effect of taking a signed tensor product of signed graphs is very simple. We show that this Tutte polynomial of a signed tensor product of signed graphs may be expressed in terms of the Tutte polynomials of the original signed graphs by using a simple substitution rule. Our result enables us to compute the Jones polynomials of some large non-alternating knots. The combinatorics used to prove our main result is similar to Tutte's original way of counting "activities" and specializes to a new, perhaps simpler proof of the known formulas for the ordinary Tutte polynomial of the tensor product of unsigned graphs or matroids.
BOUNDARY SLOPES OF IMMERSED SURFACES IN HAKEN MANIFOLDS
Authors: ZHANG QIANG
Published: May 2009

In this paper, we give a bound for the number of boundary slopes of orientable immersed proper π1-injective surfaces of given genus g in an orientable Haken 3-manifold M with a torus boundary, where the bound is independent of M, and a function of g and m, the number of the Jaco–Shalen–Johannson decomposition tori of M.
THE LOWER CENTRAL AND DERIVED SERIES OF THE BRAID GROUPS OF THE FINITELY-PUNCTURED SPHERE
Authors: GONÇALVES DACIBERG LIMA , GUASCHI JOHN
Published: May 2009

Motivated in part by the study of Fadell–Neuwirth short exact sequences, we determine the lower central and derived series for the braid groups of the finitely-punctured sphere. For n ≥ 1, the class of m-string braid groups Bm(𝕊2\{x1,…,xn}) of the n-punctured sphere includes the usual Artin braid groups Bm(for n = 1), those of the annulus, which are Artin groups of type B (for n = 2), and affine Artin groups of type [Formula: see text] (for n = 3).

We first consider the case n = 1. Motivated by the study of almost periodic solutions of algebraic equations with almost periodic coefficients, Gorin and Lin calculated the commutator subgroup of the Artin braid groups. We extend their results, and show that the lower central series (respectively, derived series) of Bmis completely determined for all m ∈ ℕ (respectively, for all m ≠ 4). In the exceptional case m = 4, we obtain some higher elements of the derived series and its quotients.

When n ≥ 2, we prove that the lower central series (respectively, derived series) of Bm(𝕊2\{x1,…,xn}) is constant from the commutator subgroup onwards for all m ≥ 3 (respectively, m ≥ 5). The case m = 1 is that of the free group of rank n - 1. The case n = 2 is of particular interest notably when m = 2 also. In this case, the commutator subgroup is a free group of infinite rank. We then go on to show that B2(𝕊2\{x1,x2}) admits various interpretations, as the Baumslag–Solitar group BS(2,2), or as a one-relator group with non-trivial centre for example. We conclude from this latter fact that B2(𝕊2\{x1,x2}) is residually nilpotent, and that from the commutator subgroup onwards, its lower central series coincides with that of the free product ℤ2* ℤ. Further, its lower central series quotients Γi/Γi + 1are direct sums of copies of ℤ2, the number of summands being determined explicitly. In the case m ≥ 3 and n = 2, we obtain a presentation of the derived subgroup, from which we deduce its Abelianization. Finally, in the case n = 3, we obtain partial results for the derived series, and we prove that the lower central series quotients Γi/Γi + 1are 2-elementary finitely-generated groups.
ESCAPE TRAJECTORIES VERSUS MAGNETIC ENTRAPMENT: CHARGED PARTICLE DYNAMICS IN POLOIDAL MAGNETIC FIELDS AROUND SCHWARZSCHILD BLACK HOLES
Authors: PRETI GIOVANNI
Published: May 2009

We examine the nonequatorial orbits of charged particles under the combined influence of Schwarzschild curvature and external purely poloidal magnetic fields — the uniform and dipole ones — corresponding to analytical solutions to the Maxwell equations in the given space–time. Particle confinement in bound cross-equatorial orbits can occur, due to a magnetic bottle effect, but also natural escape trajectories can be obtained, without the need for additional devices — like electric or toroidal magnetic fields — previously invoked to this end. The conditions leading to either of these outcomes, entrapment or escape, are examined, and a comparison with the flat space–time case is made, evaluating the role played by gravity in the overall charged particle dynamics.
DOES THE HETEROTIC SUPERSTRING THEORY CONTAIN CLOSED TIME-LIKE LINES?
Authors: POLLOCK M. D.
Published: May 2009

Causal solutions of the Gödel type, for which the line element is ds2 = dt2 - 2b e mxdtdv - c e 2mxdv2 - dx2 - dz2 with c = 0, are known to exist for gravitational theories containing a cosmological constant Λ and quadratic higher-derivative terms defined by the Lagrangian L = -(1/2)κ-2(R + 2Λ) + A1R2 + A2RijRij. Here, we show that acausal solutions, for which c < 0, containing closed time-like lines, can be constructed only if A2 = 0. Extension of this analysis to the heterotic superstring theory, including a generic massless scalar field ϕ plus quadratic and quartic gravitational terms [Formula: see text] and [Formula: see text], again yields a causal solution with c = 0, and also Λ = 0, as required for anomaly freedom, while solutions with c < 0 are ruled out. More general rotational space–times appear to be intractable analytically, and therefore it remains a matter of conjecture that the heterotic superstring admits only classical Lorentzian solutions which respect causality. For the energy density ρ(ϕ) of the scalar field is positive semi-definite only when g00 ≥ 0, which is equivalent to the causality condition g11 ≤ 0 or c ≥ 0 in a Lorentzian space–time for which det gij < 0; while ρ(ϕ) is unbounded from below in the presence of closed time-like lines, when g11 > 0, implying instability of ϕ, which will react back on the metric until it becomes causal.
A FIVE-DIMENSIONAL SPHERICALLY SYMMETRIC SOLUTION IN EINSTEIN–YANG–MILLS THEORY WITH THE GAUSS–BONNET TERM
Authors: SLAGTER R. J.
Published: May 2009

We present a numerical solution on a five-dimensional spherically symmetric space–time, in Einstein–Yang–Mills — Gauss–Bonnet theory, using a two-point boundary value routine. It turns out that the Gauss–Bonnet contribution has a profound influence on the behavior of the particle-like solution: it increases the number of nodes of the YM field. When a negative cosmological constant is incorporated in the model, it turns out that there is no horizon and no singular behavior of the model. For a positive cosmological constant the model has singular behavior.
A CONCEPTUAL MODEL FOR THE STRATEGIC ORIENTATION OF SMALL FIRMS
Authors: FULFORD HEATHER , RIZZO ALEX
Published: May 2009

The study of patterns of small firm strategic behavior, or strategic orientation, is gradually gaining prominence in the literature. Strategic behavior is a consequence of various antecedents, such as the prevalent management philosophy and environmental dynamism. It, in turn, determines the particular engineering stance adopted, structures and processes deployed, and ultimately, organizational performance.

The purpose of this paper is to critique, enhance and extend a model proposed by Aloulou and Fayolle (2005) that is focused particularly on the entrepreneurial orientation of small firms. A model is proposed for small firm strategic orientation that is based on a configurational approach, and applies the concepts of the adaptive cycle and the firm's lifecycle. The rationale for, and the various dimensions of the proposed model are described, and recommendations made for future research on small firm strategic behavior.
COGNITIVE MAPS AND PERCEPTIONS OF ENTREPRENEURIAL GROWTH: A QUASI-EXPERIMENTAL STUDY IN THE DIFFERENCES BETWEEN TECHNOLOGY ENTREPRENEURS, CORPORATE MANAGERS, AND STUDENTS
Authors: CARSRUD ALAN , BRÄNNBACK MALIN , NORDBERG LEIF , RENKO MAIJA
Published: May 2009

This paper reports on a comparative quasi-experiment of how perceptions of entrepreneurial growth strategies differ between students, managers and technology entrepreneurs. The differences in perceptions as to what critical factors drive three strategies: no growth, market share growth and annual profit growth across to stages: start-up and take-off are measured. The ranks of the critical success factors are the dependent measures and the strategies and the phases the independent variables. Results show that experience impacts the ability to distinguish between strategies. Results also show that the perceptions of the critical success factors significantly differ between the groups. Hence even experience will yield quite different cognitive maps.
DEVELOPMENT CORPORATIONS IN ABORIGINAL COMMUNITIES: THE CANADIAN EXPERIENCE
Authors: CURRY JOHN , DONKER HAN , KREHBIEL RICHARD
Published: May 2009

This study examines the historical development of corporate governance structures in First Nations communities in British Columbia, where development corporations are employed to assist privately-owned and community-owned entrepreneurial enterprises. First Nations entrepreneurial activity functions in an environment where business must market to a global economy while preserving traditional values, beliefs and other cultural elements. A brief history of First Nations and their enterprise development efforts is presented. Empirical research findings describe the close relationship between local community and corporate goals and identify conflicts of interest between political leaders and management of development corporations. The evidence demonstrates entrepreneurial success and economic development of First Nations communities rely on an independent decision-making process within business development corporations. An alternative business model is developed utilizing the empirical research, social enterprise literature and the unique regional cooperative model of the Mondragon region of Spain. The new model respects the land base and other environmental and social values while providing a framework for economic success. Exploration of this unique enterprise-to-region development model, which incorporates consideration for the natural environment and social and cultural values, offers lessons to other societies and regions that will assist in the movement toward an economic system based on concepts of sustainability.
CULTURAL VALUES, MARKET INSTITUTIONS, AND ENTREPRENEURSHIP POTENTIAL: A COMPARATIVE STUDY OF THE UNITED STATES, TAIWAN, AND VIETNAM
Authors: NGUYEN THANG V. , BRYANT SCOTT E. , ROSE JERMAN , TSENG CHIUNG-HUI , KAPASUWAN SUPARA
Published: May 2009

This study examines the impact of national cultural values and the development of market institutions on three aspects of entrepreneurship (desire, intention, and confidence in creating new ventures). We ask: What different kinds of effects do cultural and institutional factors have on different aspects of entrepreneurship? Our samples come from Vietnam, Taiwan, and the United States (US). The use of three countries allows us to distinguish the separate influences of culture and market institutions on entrepreneurship. Our results suggest that only culture has a significant impact on individuals' desires to create new ventures. However, we found mixed results on whether culture or institution affects individuals' intentions and confidence in creating new ventures. Contrary to our hypotheses, the Vietnam sample had higher scores on intention to create new ventures than both the US and Taiwan samples. The Vietnam sample was also higher than Taiwan on the confidence in creating new ventures. This may suggest an interaction effect of cultural and institutional factors on entrepreneurship. This interaction deserves more attention in future research.
NICHE AGRICULTURAL PRODUCERS' ACQUISITION OF CAPITAL
Authors: VAN AUKEN HOWARD , ZHANG JIN
Published: May 2009

Capital acquisition is one of the most challenging and important issues facing small firms. This paper examines issues related to the acquisition of capital by niche agricultural producers. Niche agricultural producers face greater capital acquisition challenges than traditional small firms because their business models are not well understood and, thus, often considered high risk. Few studies have examined the capital acquisition of niche agricultural producers despite the importance of the overall agricultural industry and niche producers. The findings show firms that are more familiar with sources of capital are more likely to acquire capital. Commercial banks have a pivotal role in providing financial advice and are an important source of capital.
Editorial: "ACTIVE BIOMIMETIC SYSTEMS: FORCE GENERATION AND CARGO TRANSPORT BY MOLECULAR MACHINES"
Authors: LIPOWSKY REINHARD , VALLERIANI ANGELO
Published: May 2009

This special issue of Biophysical Reviews and Letters describes recent advances in the area of active biomimetic systems, which are inspired by the cytoskeletal architecture found in all eukaryotic cells. The main building blocks of these systems are provided by two types of cytoskeletal filaments, F-actin and microtubules, as well as molecular stepping motors such as kinesins and myosins. All of these building blocks represent molecular machines: They are coupled to nucleotide hydrolysis and are able to convert the chemical energy released from this process into mechanical work. Bundles of filaments and teams of stepping motors generate strong pushing forces and perform long-ranged cargo transport.
KINESIN BYPASSING BLOCKAGES ON MICROTUBULE RAILS
Authors: DREBLOW KERSTIN , KALCHISHKOVA NIKOLINA , BÖHM KONRAD J.
Published: May 2009

Kinesins are motor proteins which convert the chemical energy of ATP into mechanical energy to move along proteinaceous microtubule rails and to transport different cargoes to defined intracellular destinations. It is well documented that following the track of a single protofilament is the thermodynamically most effective mechanism of kinesin movement along microtubules. However, the question arises what happens when a kinesin molecule encounters a hindrance along the protofilament. The present study describes a simple, cell-free approach which enables to study the effects of structural blockages on kinesin-based transport. This experimental approach uses dimeric conventional kinesin moving nanometre-sized gold beads along immobilized microtubules whose surface has been irreversibly decorated by blocking proteins. We demonstrated that the continuous bead transport temporarily stopped at sites of blockages, but usually continued after a certain resting time. Our results suggest that single dimeric kinesin molecules are able to change to another protofilament if the next tubulin dimer where the second head should bind is blocked. A bypassing mechanism is discussed which is considered to be one fundamental prerequisite to realize a kinesin-mediated cargo-transport along microtubules over long distances, required for e.g., the fast axonal transport in motor neurons.
COLLECTIVE OSCILLATIONS OF PROCESSIVE MOLECULAR MOTORS
Authors: CAMPÀS O. , LEDUC C. , BASSEREAU P. , JOANNY J.-F. , PROST J.
Published: May 2009

We present both a theoretical and an experimental study of the long time behavior of membrane nanotubes pulled from giant unilamellar vesicles by molecular motors. Experimentally, two types of behaviors are observed, either tubes stall at a finite length or they undergo periodic oscillations. Theoretically we write the equations for the tube dynamics as a two-dimensional dynamical system where the variables are the tube length (or the force required to pull the tube at a given length) and the number of motors at the tip pulling the tube. We construct stability diagrams showing the stalling and oscillating states and present an example of oscillations in a non-linear regime. These results can explain the membrane tube retractions and oscillations observed in living cells.
BIOMIMETIC MODELS OF THE ACTIN CORTEX
Authors: HARASZTI TAMÁS , SCHULZ SIMON , UHRIG KAI , KURRE RAINER , ROOS WOUTER , SCHMITZ CHRISTIAN H. J. , CURTIS JENNIFER E. , MAIER TIMO , CLEMEN ANABEL E.-M. , SPATZ JOACHIM P.
Published: May 2009

The cytoskeleton is an actively regulated complex network in the cell. One of the most researched components is actin. In our work we developed and tested two microfluidic systems both being applicable to construct quasi 2-dimensional biomimetic actin networks. The first system uses polydimethylsiloxane micropillars, the other polystyrene microparticles held by holographic optical tweezers as anchoring points. Our devices provide actin networks with mesh sizes from a few micrometers up to the order of 10 micrometers. Qualitative analysis shows similar network formation in both systems. Crosslinking was tested using filamin, α-actinin, Ca and Mg ions. The crosslinking process is characterized by a zipping like event, which is limited only by the high stretching modulus of the actin filaments.
DDR1/E-cadherin complex regulates the activation of DDR1 and cell spreading
Authors: Wang Chau-Zen , Yeh Yi-Chun , Tang Ming-Jer
Published: May 2009

Discoidin domain receptors (DDRs) 1 and 2, collagen receptors, regulate cell adhesion and a broad range of cell behavior. Their adhesion-dependent regulation of signaling associated with adhesion proteins has not been elucidated. We report a novel mechanism: the cross talk of DDR1 and E-cadherin negatively and adhesion dependently regulated both DDR1 activity and DDR1-suppressed cell spreading. E-cadherin forms complexes with both DDR1 isoforms (a and b). E-cadherin regulates DDR1 activity associated with the cell-junction complexes formed between DDR1 and E-cadherin. These complexes are formed independently of DDR1 activation and of β-catenin and p120-catenin binding to E-cadherin; they are ubiquitous in epithelial cells. Small interfering RNA-mediated gene silencing of E-cadherin restores both DDR1 activity and DDR1-suppressed cell spreading and increases the apically and basally located DDR1 in E-cadherin-null cells. We conclude that E-cadherin-mediated adhesions decrease DDR1 activity, which subsequently eliminates DDR1-suppressed cell spreading, by sequestering DDR1 to cell junctions, which prevents its contact with collagen ligand.
Novel bUT-B2 urea transporter isoform is constitutively activated
Authors: Tickle P. , Thistlethwaite A. , Smith C. P. , Stewart G. S.
Published: May 2009

Our previous studies have detailed a novel facilitative UT-B urea transporter isoform, bUT-B2. Despite the existence of mouse and human orthologs, the functional characteristics of UT-B2 remain undefined. In this report, we produced a stable MDCK cell line that expressed bUT-B2 protein and investigated the transepithelial urea flux across cultured cell monolayers. We observed a large basal urea flux that was significantly reduced by known inhibitors of facilitative urea transporters; 1,3 dimethylurea ( P < 0.001, n = 17), thionicotinamide ( P < 0.05, n = 11), and phloretin ( P < 0.05, n = 9). Pre-exposure for 1 h to the antidiuretic hormone vasopressin had no effect on bUT-B2-mediated urea transport (NS, n = 3). Acute vasopressin exposure for up to 30 min also failed to elicit any transient response (NS, n = 9). Further investigation confirmed that bUT-B2 function was not affected by alteration of intracellular cAMP (NS, n = 4), intracellular calcium (NS, n = 3), or protein kinase activity (NS, n = 4). Finally, immunoblot data suggested a possible role for glycosylation in regulating bUT-B2 function. In conclusion, this study showed that bUT-B2-mediated transepithelial urea transport was constitutively activated and unaffected by known regulators of renal UT-A urea transporters.
A role of the (pro)renin receptor in neuronal cell differentiation
Authors: Contrepas Aurelie , Walker Joy , Koulakoff Annette , Franek Karl J. , Qadri Fatimunnisa , Giaume Christian , Corvol Pierre , Schwartz Charles E. , Nguyen Genevieve
Published: May 2009

The (pro)renin receptor [(P)RR] plays a pivotal role in the renin-angiotensin system. Experimental models emphasize the role of (P)RR in organ damage associated with hypertension and diabetes. However, a mutation of the (P)RR gene, resulting in frame deletion of exon 4 [Δ4-(P)RR] is associated with X-linked mental retardation (XLMR) and epilepsy pointing to a novel role of (P)RR in brain development and cognitive function. We have studied (P)RR expression in mouse brain, as well as the effect of transfection of Δ4-(P)RR on neuronal differentiation of rat neuroendocrine PC-12 cells induced by nerve growth factor (NGF). In situ hybridization showed a wide distribution of (P)RR, including in key regions involved in the regulation of blood pressure and body fluid homeostasis. In mouse neurons, the receptor is on the plasma membrane and in synaptic vesicles, and stimulation by renin provokes ERK1/2 phosphorylation. In PC-12 cells, (P)RR localized mainly in the Golgi and in endoplasmic reticulum and redistributed to neurite projections during NGF-induced differentiation. In contrast, Δ4-(P)RR remained cytosolic and inhibited NGF-induced neuronal differentiation and ERK1/2 activation. Cotransfection of PC-12 cells with (P)RR and Δ4-(P)RR cDNA resulted in altered localization of (P)RR and inhibited (P)RR redistribution to neurite projections upon NGF stimulation. Furthermore, (P)RR dimerized with itself and with Δ4-(P)RR, suggesting that the XLMR and epilepsy phenotype resulted from a dominant-negative effect of Δ4-(P)RR, which coexists with normal transcript in affected males. In conclusion, our results show that (P)RR is expressed in mouse brain and suggest that the XLMR and epilepsy phenotype might result from a dominant-negative effect of the Δ4-(P)RR protein.
Nesfatin-1 exerts cardiovascular actions in brain: possible interaction with the central melanocortin system
Authors: Yosten Gina L. C. , Samson Willis K.
Published: May 2009

Nesfatin-1 is a recently discovered hypothalamic peptide that was shown to suppress food intake through a melanocortin-3/4 receptor-dependent mechanism. Since nesfatin-1 mRNA is detected in the paraventricular nucleus of the hypothalamus, and because many peptides that alter food intake also influence cardiovascular function, we tested the ability of centrally administered nesfatin-1 to affect mean arterial pressure (MAP) in conscious, freely moving rats. Significant increases in MAP were observed following intracerebroventricular administration of nesfatin-1. Pretreatment with either the melanocortin-3/4 receptor antagonist, SHU9119 (intracerebroventricular), or the α-adrenergic antagonist, phentolamine (intra-arterial), abrogated the rise in MAP induced by nesfatin-1, indicating that nesfatin-1 may interact with the central melanocortin system to increase sympathetic nerve activity and lead to an increase in MAP. Thus we have identified a novel action of nesfatin-1, in addition to its anorexigenic effects, to stimulate autonomic nervous system activity.
Postprandial changes in plasma growth hormone, insulin, insulin-like growth factor (IGF)-I, and IGF-binding proteins in coho salmon fasted for varying periods
Authors: Shimizu Munetaka , Cooper Kathleen A. , Dickhoff Walton W. , Beckman Brian R.
Published: May 2009

We examined postprandial changes in circulating growth hormone (GH), insulin, insulin-like growth factor (IGF)-I, and IGF-binding proteins (IGFBPs) in yearling coho salmon under different feeding regimes. Fish were initially fasted for 1 day, 1 wk, or 3 wk. Fasted fish were then fed, and blood was collected at 4-h intervals over 26 h. After the various periods of fasting, basal levels of insulin were relatively constant, whereas those of IGF-I, IGFBPs and GH changed in proportion to the duration of the fast. A single meal caused a rapid, large increase in the circulating insulin levels, but the degree of the increase was influenced by the fasting period. IGF-I showed a moderate increase 2 h after the meal but only in the regularly fed fish. Plasma levels of 41-kDa IGFBP were increased in all groups within 6 h after the single meal. The fasting period did not influence the response of 41-kDa IGFBP to the meal. IGFBP-1 and GH decreased after the meal to the same extent among groups regardless of the fasting period. The present study shows that insulin and IGF-I respond differently to long (weeks)- and short (hours)-term nutritional changes in salmon; insulin maintains its basal level but changes acutely in response to food intake, whereas IGF-I adjusts its basal levels to the long-term nutritional status and is less responsive to acute nutritional input. IGFBPs maintain their sensitivity to food intake, even after prolonged fasting, suggesting their critical role in the nutritional regulation of salmon growth.
Dietary sodium modulates the interaction between efferent renal sympathetic nerve activity and afferent renal nerve activity: role of endothelin
Authors: Kopp Ulla C. , Grisk Olaf , Cicha Michael Z. , Smith Lori A. , Steinbach Antje , Schlüter Torsten , Mähler Nicole , Hökfelt Tomas
Published: May 2009

Increasing efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA), which in turn decreases ERSNA via activation of the renorenal reflexes in the overall goal of maintaining low ERSNA. We now examined whether the ERSNA-induced increases in ARNA are modulated by dietary sodium and the role of endothelin (ET). The ARNA response to reflex increases in ERSNA was enhanced in high (HNa)- vs. low-sodium (LNa) diet rats, 7,560 ± 1,470 vs. 900 ± 390%·s. The norepinephrine (NE) concentration required to increase PGE2 and substance P release from isolated renal pelvises was 10 pM in HNa and 6,250 pM in LNa diet rats. In HNa diet pelvises 10 pM NE increased PGE2 release from 67 ± 6 to 150 ± 13 pg/min and substance P release from 6.7 ± 0.8 to 12.3 ± 1.8 pg/min. In LNa diet pelvises 6,250 pM NE increased PGE2 release from 64 ± 5 to 129 ± 22 pg/min and substance P release from 4.5 ± 0.4 to 6.6 ± 0.7 pg/min. In the renal pelvic wall, ETB-R are present on unmyelinated Schwann cells close to the afferent nerves and ETA-R on smooth muscle cells. ETA-receptor (R) protein expression in the renal pelvic wall is increased in LNa diet. In HNa diet, renal pelvic administration of the ETB-R antagonist BQ788 reduced ERSNA-induced increases in ARNA and NE-induced release of PGE2 and substance P. In LNa diet, the ETA-R antagonist BQ123 enhanced ERSNA-induced increases in ARNA and NE-induced release of substance P without altering PGE2 release. In conclusion, activation of ETB-R and ETA-R contributes to the enhanced and suppressed interaction between ERSNA and ARNA in conditions of HNa and LNa diet, respectively, suggesting a role for ET in the renal control of ERSNA that is dependent on dietary sodium.
The full-length calcium-sensing receptor dampens the calcemic response to 1α,25(OH)2 vitamin D3 in vivo independently of parathyroid hormone
Authors: Egbuna Ogo , Quinn Steven , Kantham Lakshmi , Butters Robert , Pang Jiang , Pollak Martin , Goltzman David , Brown Edward
Published: May 2009

1α,25(OH)2 vitamin D3 [1,25(OH)2D3] increases serum Ca2+ concentration in vivo, an action counteracted by activation of the Ca2+-sensing receptor (CaSR), which decreases parathyroid hormone (PTH) secretion and increases renal Ca2+ excretion. Relatively little is known of the role the CaSR plays in this response through its potentially direct actions in kidney, gut, and bone independently of PTH. We report PTH-independent roles of the CaSR in modulating the response to exogenous 1,25(OH)2D3 in mice with targeted disruption of both the CaSR and PTH genes (C−P−) compared with that in mice with disruption of the PTH gene alone (C+P−) or wild-type mice (C+P+). After intraperitoneal injection of 0.5 ng/g body wt 1,25(OH)2D3, peak calcemic responses were observed at 24 h in all three genotypes in association with 1) a greater increase in serum Ca2+ in C−P− mice than in the other genotypes on a Ca2+-replete diet that was attenuated by a Ca2+-deficient diet and pamidronate, 2) increased urinary Ca2+-to-creatinine ratios (UCa/Cr) in the C+P− and C+P+ mice but a lowered ratio in the C−P− mice on a Ca2+-replete diet, and 3) no increase in calcitonin (CT) secretion in the C+P+ and C+P− mice and a small increase in the C−P− mice. PTH deficiency had the anticipated effects on the expression of key genes involved in Ca2+ transport at baseline in the duodenum and kidney, and injection of 1,25(OH)2D3 increased gene expression 8 h later. However, the changes in the genes evaluated did not fully explain the differences in serum Ca2+ seen among the genotypes. In conclusion, mice lacking the full-length CaSR have increased sensitivity to the calcemic action of 1,25(OH)2D3 in the setting of PTH deficiency. This is principally from enhanced 1,25(OH)2D3-mediated gut Ca2+ absorption and decreased renal Ca2+ excretion, without any differences in bone-related release of Ca2+ or CT secretion among the three genotypes that could explain the differences in their calcemic responses.
Replacement of connexin 40 by connexin 45 causes ectopic localization of renin-producing cells in the kidney but maintains in vivo control of renin gene expression
Authors: Kurtz Lisa , Gerl Melanie , Kriz Wilhelm , Wagner Charlotte , Kurtz Armin
Published: May 2009

Deletion of connexin 40 (Cx40) leads to ectopic hyperplasia of renin-producing cells in the kidney, which is associated with dysregulated hyperreninemia and hypertension. The aim of this study was to determine whether Cx45 is able to substitute the function of Cx40 with regard to the localization of renin-producing cells. For this purpose, we have studied the distribution of renin-expressing cells under both normal conditions and during a stimulatory challenge of the renin system by inducing salt deprivation in mice, achieved by replacing the coding sequence of the Cx40 gene with that of Cx45 (Cx40ki45). In both wild-type (WT) mice and Cx40ki45 mice under normal conditions, renin-expressing cells were located at the juxtaglomerular position, whereas in Cx40-deficient mice they were located in the periglomerular interstitium. Upon challenge of the renin system, renin mRNA and the number of renin-expressing cells increased in WT mice in the media layer of afferent arterioles, while neither parameter changed significantly in Cx40-deficient mice. In Cx40ki45 mice, challenge of the renin system markedly increased both renin mRNA and the number of renin-expressing cells. However, the newly recruited renin-expressing cells were localized mainly outside the afferent vessels in the periglomerular interstitium. We found no evidence of cell divisions in renin-expressing cells in any of the genotypes investigated in this study, suggesting that the ectopically localized, renin-expressing cells in Cx40ki45 mice were already preexisting but were not renin-expressing under normal conditions. In summary, we infer from our findings that the function of Cx40 for the localization of potential renin-producing cells cannot be substituted by that of Cx45, although the regulability of renin gene expression can.
Optical Imaging of Postsynaptic Odor Representation in the Glomerular Layer of the Mouse Olfactory Bulb
Authors: Fletcher Max L. , Masurkar Arjun V. , Xing Junling , Imamura Fumiaki , Xiong Wenhui , Nagayama Shin , Mutoh Hiroki , Greer Charles A. , Knöpfel Thomas , Chen Wei R.
Published: May 2009

Olfactory glomeruli are the loci where the first odor-representation map emerges. The glomerular layer comprises exquisite local synaptic circuits for the processing of olfactory coding patterns immediately after their emergence. To understand how an odor map is transferred from afferent terminals to postsynaptic dendrites, it is essential to directly monitor the odor-evoked glomerular postsynaptic activity patterns. Here we report the use of a transgenic mouse expressing a Ca2+-sensitive green fluorescence protein (GCaMP2) under a Kv3.1 potassium-channel promoter. Immunostaining revealed that GCaMP2 was specifically expressed in mitral and tufted cells and a subpopulation of juxtaglomerular cells but not in olfactory nerve terminals. Both in vitro and in vivo imaging combined with glutamate receptor pharmacology confirmed that odor maps reported by GCaMP2 were of a postsynaptic origin. These mice thus provided an unprecedented opportunity to analyze the spatial activity pattern reflecting purely postsynaptic olfactory codes. The odor-evoked GCaMP2 signal had both focal and diffuse spatial components. The focalized hot spots corresponded to individually activated glomeruli. In GCaMP2-reported postsynaptic odor maps, different odorants activated distinct but overlapping sets of glomeruli. Increasing odor concentration increased both individual glomerular response amplitude and the total number of activated glomeruli. Furthermore, the GCaMP2 response displayed a fast time course that enabled us to analyze the temporal dynamics of odor maps over consecutive sniff cycles. In summary, with cell-specific targeting of a genetically encoded Ca2+indicator, we have successfully isolated and characterized an intermediate level of odor representation between olfactory nerve input and principal mitral/tufted cell output.
A Novel Neuronal Pathway for Visually Guided Escape inDrosophila melanogaster
Authors: Fotowat Haleh , Fayyazuddin Amir , Bellen Hugo J. , Gabbiani Fabrizio
Published: May 2009

Drosophila melanogaster exhibits a robust escape response to objects approaching on a collision course. Although a pair of large command interneurons called the giant fibers (GFs) have been postulated to trigger such behaviors, their role has not been directly demonstrated. Here, we show that escape from visual stimuli like those generated by approaching predators does not rely on the activation of the GFs and consists of a more complex and less stereotyped motor sequence than that evoked by the GFs. Instead, the timing of escape is tightly correlated with the activity of previously undescribed descending interneurons that signal a threshold angular size of the approaching object. The activity pattern of these interneurons shares features with those of visual escape circuits of several species, including pigeons, frogs, and locusts, and may therefore have evolved under similar constraints. These results show that visually evoked escapes in Drosophila can rely on at least two descending neuronal pathways: the GFs and the novel pathway we characterize electrophysiologically. These pathways exhibit very different patterns of sensory activity and are associated with two distinct motor programs.
Enhanced Tonic GABA Current in Normotopic and Hilar Ectopic Dentate Granule Cells After Pilocarpine-Induced Status Epilepticus
Authors: Zhan Ren-Zhi , Nadler J. Victor
Published: May 2009

In temporal lobe epilepsy, loss of inhibitory neurons and circuit changes in the dentate gyrus promote hyperexcitability. This hyperexcitability is compensated to the point that dentate granule cells exhibit normal or even subnormal excitability under some conditions. This study explored the possibility that compensation involves enhanced tonic GABA inhibition. Whole cell patch-clamp recordings were made from normotopic granule cells in hippocampal slices from control rats and from both normotopic and hilar ectopic granule cells in slices from rats subjected to pilocarpine-induced status epilepticus. After status epilepticus, tonic GABA current was an order of magnitude greater than control in normotopic granule cells and was significantly greater in hilar ectopic than in normotopic granule cells. These differences could be observed whether or not the extracellular GABA concentration was increased by adding GABA to the superfusion medium or blocking plasma membrane transport. The enhanced tonic GABA current had both action potential–dependent and action potential–independent components. Pharmacological studies suggested that the small tonic GABA current of granule cells in control rats was mediated largely by high-affinity α4βxδ GABAAreceptors but that the much larger current recorded after status epilepticus was mediated largely by the lower-affinity α5βxγ2GABAAreceptors. A large α5βxγ2-mediated tonic current could be recorded from controls only when the extracellular GABA concentration was increased. Status epilepticus seemed not to impair the control of extracellular GABA concentration by plasma membrane transport substantially. Upregulated tonic GABA inhibition may account for the unexpectedly modest excitability of the dentate gyrus in epileptic brain.
Role of ATP-Dependent Calcium Regulation in Modulation of Drosophila Synaptic Thermotolerance
Authors: Klose M. K. , Boulianne G. L. , Robertson R. M. , Atwood H. L.
Published: May 2009

Maintenance of synaptic transmission requires regulation of intracellular Ca2+ in presynaptic nerve terminals; loss of this regulation at elevated temperatures may cause synaptic failure. Accordingly, we examined the thermosensitivity of presynaptic calcium regulation in Drosophila larval neuromuscular junctions, testing for effects of disrupting calcium clearance. Motor neurons were loaded with the ratiometric Ca2+ indicator Fura-dextran to monitor calcium regulation as temperature increased. Block of the Na+/Ca2+ exchanger or removal of extracellular Ca2+ prevented the normal temperature-induced increase in resting calcium. Conversely, two treatments that interfered with Ca2+ clearance—inactivation of the endoplasmic reticulum Ca2+-ATPase with thapsigargin and inhibition of the plasma membrane Ca2+-ATPase with high pH—significantly accelerated the temperature-induced rise in resting Ca2+ concentration and reduced the thermotolerance of synaptic transmission. Disrupting Ca2+-ATPase function by interfering with energy production also facilitated the temperature-induced rise in resting [Ca2+] and reduced thermotolerance of synaptic transmission. Conversely, fortifying energy levels with extra intracellular ATP extended the operating temperature range of both synaptic transmission and Ca2+ regulation. In each of these cases, Ca2+ elevations evoked by an electrical stimulation of the nerve (evoked Ca2+ responses) failed when resting Ca2+ remained >e 200 nM for several minutes. Failure of synaptic function was correlated with the release of intracellular calcium stores, and we provide evidence suggesting that release from the mitochondria disrupts evoked calcium responses and synaptic transmission. Thus the thermal limit of synaptic transmission may be directly linked to the stability of ATP-dependent mechanisms that regulate intracellular ion concentrations in the nerve terminal.
Integration of Predictive Feedforward and Sensory Feedback Signals for Online Control of Visually Guided Movement
Authors: Gritsenko V. , Yakovenko S. , Kalaska J. F.
Published: May 2009

Online control of movement requires complex integration of predictive central feedforward and peripheral sensory feedback signals. We studied the hand trajectories of human subjects pointing to visual targets that abruptly changed locations by different amounts and modeled the mechanism of rapid online correction using a dynamic model of a two-joint limb. Small unperceived and large detected target displacements could be attributed to different origins (motor execution errors vs. environmental changes, respectively) and compensated differently. However, the behavioral findings indicate that the rapid feedback pathway is recruited regardless of the amplitude or subjective awareness of target displacement and that the size of the earliest correction is always proportional to the amplitude of the target displacement over the tested range of perturbations. The modeling findings suggest that the rapid online corrections can be accomplished by superimposing a dynamically appropriate error correction signal onto the outgoing feedforward motor command to the original target. Furthermore, the modeling shows that the online correction mechanism must include compensation for the dynamic mechanical properties of the limb and for sensory delays in its error-correction pathway.