bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of a Novel Chromogenic Agar Medium for Isolation and Differentiation of Vancomycin-Resistant
Enterococcus faecium
and
Enterococcus faecalis
Isolates
Authors: Ledeboer Nathan A. , Das Kingshuk , Eveland Michael , Roger-Dalbert Céline , Mailler Sandrine , Chatellier Sonia , Dunne William Michael
Published: March 2007

The development of reliable and rapid methods for the identification of patients colonized with vancomycin-resistant enterococci (VRE) is central to the containment of this agent within a hospital environment. To this end, we evaluated a prototype chromogenic agar medium (VRE-BMX; bioMérieux, Marcy l'Etoile, France) used to recover VRE from clinical specimens. This medium can also identify isolated colonies as either vancomycin-resistant
Enterococcus faecium
or
Enterococcus faecalis
, based on distinct colony colors. We compared the performance of VRE-BMX with bile esculin azide agar supplemented with vancomycin (BEAV). For this study, 147 stool samples were plated on each test medium and examined after 24 and 48 h of incubation. At 24 h, the sensitivity and specificity of each medium were as follows: BEAV, 90.9% and 89.9%, respectively; VRE-BMX, 96.4% and 96.6%, respectively. The positive predictive values (PPV) of VRE-BMX and BEAV at 24 h were 89.8% and 80.7%, respectively. VRE-BMX provided the identification of 10 isolates of vancomycin-resistant
E. faecalis
and 4 isolates of vancomycin-resistant
E. faecium
that were not recovered by BEAV. Further, VRE-BMX was capable of identifying patients colonized with both
E. faecium
and
E. faecalis
, a feature useful for infection control purposes that is not a function of BEAV. In terms of the recovery of vancomycin-resistant
E. faecium
and
E. faecalis
, the sensitivity and PPV were as follows: BEAV, 75.7% and 74.6%, respectively; VRE-BMX, 95.5% and 91.3%, respectively. In this initial evaluation, we found that VRE-BMX provided improved recovery of VRE from stool specimens, with the added advantage of being able to differentiate between vancomycin-resistant
E. faecalis
and
E. faecium
. Extending the incubation period beyond 24 h did not significantly improve the recovery of VRE and resulted in decreased specificity.
Impact of Competitive Inhibition and Sequence Variation upon the Sensitivity of Malaria PCR
Authors: Bialasiewicz Seweryn , Whiley David M. , Nissen Michael D. , Sloots Theo P.
Published: March 2007

Real-time PCR assays for
Plasmodium
species utilizing universal and species-specific primers were compared to investigate variables influencing decreased assay sensitivity. Sequence variation in oligomer targets and competitive inhibition of dual-species templates in universal-primer mixes were found to decrease assay sensitivity.
Association between Methicillin Susceptibility and Biofilm Regulation in
Staphylococcus aureus
Isolates from Device-Related Infections
Authors: O'Neill Eoghan , Pozzi Clarissa , Houston Patrick , Smyth Davida , Humphreys Hilary , Robinson D. Ashley , O'Gara James P.
Published: March 2007

Production of
icaADBC
-encoded polysaccharide intercellular adhesin, or poly-
N
-acetylglucosamine (PIA/PNAG), represents an important biofilm mechanism in staphylococci. We previously described a glucose-induced,
ica
-independent biofilm mechanism in four methicillin-resistant
Staphylococcus aureus
(MRSA) isolates. Here, biofilm regulation by NaCl and glucose was characterized in 114 MRSA and 98 methicillin-sensitive
S. aureus
(MSSA) isolates from diagnosed device-related infections. NaCl-induced biofilm development was significantly more prevalent among MSSA than MRSA isolates, and this association was independent of the isolate's genetic background as assessed by
spa
sequence typing. Among MSSA isolates, PIA/PNAG production correlated with biofilm development in NaCl, whereas in MRSA isolates grown in NaCl or glucose, PIA/PNAG production was not detected even though
icaADBC
was transcribed and regulated. Glucose-induced biofilm in MRSA was
ica
independent and apparently mediated by a protein adhesin(s). Experiments performed with strains that were amenable to genetic manipulation revealed that deletion of
icaADBC
had no effect on biofilm in a further six MRSA isolates but abolished biofilm in four MSSA isolates. Mutation of
sarA
abolished biofilm in seven MRSA and eight MSSA isolates. In contrast, mutation of
agr
in 13 MRSA and 8 MSSA isolates substantially increased biofilm (more than twofold) in only 5 of 21 (23%) isolates and had no significant impact on biofilm in the remaining 16 isolates. We conclude that biofilm development in MRSA is
ica
independent and involves a protein adhesin(s) regulated by SarA and Agr, whereas SarA-regulated PIA/PNAG plays a more important role in MSSA biofilm development.
High-Resolution Genotyping of
Chlamydia trachomatis
Strains by Multilocus Sequence Analysis
Authors: Klint Markus , Fuxelius Hans-Henrik , Goldkuhl Renée Röstlinger , Skarin Hanna , Rutemark Christian , Andersson Siv G. E. , Persson Kenneth , Herrmann Björn
Published: March 2007

Genotyping of
Chlamydia trachomatis
is limited by the low sequence variation in the genome, and no adequate method is available for analysis of the spread of chlamydial infections in the community. We have developed a multilocus sequence typing (MLST) system based on five target regions and compared it with analysis of
ompA
, the single gene most extensively used for genotyping. Sequence determination of 16 reference strains, comprising all major serotypes, serotypes A to L3, showed that the number of genetic variants in the five separate target regions ranged from 8 to 16. The genetic variation in 47 clinical
C. trachomatis
isolates of representative serotypes (14 serotype D, 12 serotype E, 11 serotype G, and 10 serotype K strains) was analyzed; and the MLST system detected 32 variants, whereas 12 variants were detected by using
ompA
analysis. Specimens of the predominant serotype, serotype E, were differentiated into seven genotypes by MLST but into only two by
ompA
analysis. The MLST system was applied to
C. trachomatis
specimens from a population of men who have sex with men and was able to differentiate 10 specimens of one predominant
ompA
genotype G variant into four distinct MLST variants. To conclude, our MLST system can be used to discriminate
C. trachomatis
strains and can be applied to high-resolution molecular epidemiology.
Importance of the Penultimate Positive Charge in Mouse Hepatitis Coronavirus A59 Membrane Protein
Authors: Verma Sandhya , Lopez Lisa A. , Bednar Valerie , Hogue Brenda G.
Published: March 2007

The coronavirus membrane (M) protein carboxy tail interacts with the nucleocapsid during virus assembly. Previous studies demonstrated that the two terminal residues are important, and the charged residue (R227) in the penultimate position in the mouse hepatitis coronavirus (MHV) A59 M protein was suggested to participate in intermolecular interactions with negative charges in the nucleocapsid (N) protein. To determine the significance of the positive charge at position 227, we substituted the arginine with lysine (K), aspartic acid (D), glutamic acid (E), or alanine (A) and studied these by reverse genetics in the context of a MHV full-length infectious clone. Viruses with wild-type phenotype were readily recovered with the K or A substitutions. In contrast, negative-charge substitutions were not tolerated as well. In all recovered R227D viruses the negative charge was replaced with heterologous residues resulting from apparent template switching during negative-strand synthesis of subgenomic RNA 7. An additional second-site compensatory V202I substitution was present in some viruses. Recovered R227E viruses had second-site changes within the M protein carboxy tail that were partially compensatory. Significantly, most of the second site changes in the R227E mutant viruses were previously shown to compensate for the removal of negative charges in the N protein. Our results strongly indicate that a positive charge is not absolutely required. It is clear that other regions within the tail must also be involved in helping mediate interactions between the M protein and the nucleocapsid.
Antiviral Antibodies Are Necessary for Control of Simian Immunodeficiency Virus Replication
Authors: Miller Christopher J. , Genescà Meritxell , Abel Kristina , Montefiori David , Forthal Donald , Bost Kristen , Li Jun , Favre David , McCune Joseph M.
Published: March 2007

To better define the role of B cells in the control of pathogenic simian immunodeficiency virus (SIV) replication, six rhesus monkeys were depleted of B cells by intravenous infusion of rituximab (anti-CD20) 28 days and 7 days before intravaginal SIVmac239 inoculation and every 21 days thereafter until AIDS developed. Although the blood and tissues were similarly depleted of B cells, anti-SIV immunoglobulin G (IgG) antibody responses were completely blocked in only three of the six animals. In all six animals, levels of viral RNA (vRNA) in plasma peaked at 2 weeks and declined by 4 weeks postinoculation (PI). However, the three animals prevented from making an anti-SIV antibody response had significantly higher plasma vRNA levels through 12 weeks PI (P= 0.012). The remaining three B-cell-depleted animals made moderate anti-SIV IgG antibody responses, maintained moderate plasma SIV loads, and showed an expected rate of disease progression, surviving to 24 weeks PI without developing AIDS. In contrast, all three of the B-cell-depleted animals prevented from making anti-SIV IgG responses developed AIDS by 16 weeks PI (P= 0.0001). These observations indicate that antiviral antibody responses are critical in maintaining effective control of SIV replication at early time points postinfection.
Human Serum Amyloid A Protein Inhibits Hepatitis C Virus Entry into Cells
Authors: Cai Zhaohui , Cai Lei , Jiang Jieyun , Chang Kyung-Soo , van der Westhuyzen Deneys R. , Luo Guangxiang
Published: March 2007

Serum amyloid A (SAA) is an acute-phase protein induced by a variety of inflammatory stimuli, including bacterial and viral infections. SAA was recently found to function as an opsonin for gram-negative bacteria. We report here that SAA inhibited hepatitis C virus (HCV) infection in cultured cells. SAA reduced HCV infectivity in a dose-dependent manner when added during HCV infection but not after virus entry. SAA bound HCV virions and specifically blocked HCV entry but did not affect virus attachment. These findings suggest that SAA functions as part of the host innate immune defense mechanisms against HCV infection in humans.
Intracellular Kaposi's Sarcoma-Associated Herpesvirus Load Determines Early Loss of Immune Synapse Components
Authors: Adang Laura A. , Tomescu Costin , Law Wai K. , Kedes Dean H.
Published: March 2007

Lifelong infection is a hallmark of all herpesviruses, and their survival depends on countering host immune defenses. The human gammaherpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) encodes an array of proteins that contribute to immune evasion, including modulator of immune recognition 2 (MIR2), an E3 ubiquitin ligase. Exogenously expressed MIR2 downregulates the surface expression of several immune synapse proteins, including major histocompatibility complex (MHC) class 1, ICAM-1 (CD54), and PECAM (CD31). Although immunofluorescence assays detect this lytic gene in only 1 to 5% of cells within infected cultures, we have found that de novo infection of naive cells leads to the downregulation of these immune synapse components in a major proportion of the population. Investigating the possibility that low levels of MIR2 are responsible for this downregulation in the context of viral infection, we found that MIR2 transduction recapitulated the patterns of surface downregulation following de novo infection and that both MIR2 promoter activation, MIR2 expression level, and immune synapse component downregulation were proportional to the concentration of KSHV added to the culture. Additionally, MIR2-specific small interfering RNA reversed the downregulation effects. Finally, using a sensitive, high-throughput assay to detect levels of the virus in individual cells, we also observed that downregulation of MHC class I and ICAM-1 correlated with intracellular viral load. Together, these results suggest that the effects of MIR2 are gene dosage dependent and that low levels of this viral protein contribute to the widespread downregulation of immune-modulating cell surface proteins during the initial stages of KSHV infection.
Structure-Dependent Modulation of Alpha Interferon Production by Porcine Circovirus 2 Oligodeoxyribonucleotide and CpG DNAs in Porcine Peripheral Blood Mononuclear Cells
Authors: Wikström Frida Hasslung , Meehan Brian M. , Berg Mikael , Timmusk Sirje , Elving Josefine , Fuxler Lisbeth , Magnusson Mattias , Allan Gordon M. , McNeilly Francis , Fossum Caroline
Published: March 2007

DNA sequences containing CpG motifs are recognized as immunomodulators in several species. Phosphodiester oligodeoxyribonucleotides (ODNs) representing sequences from the genome of porcine circovirus type 2 (PCV2) have been identified as potent inducers (ODN PCV2/5) or inhibitors (ODN PCV2/1) of alpha interferon (IFN-α) production by porcine peripheral blood mononuclear cells (poPBMCs) in vitro. In this study, the IFN-α-inducing or -inhibitory activities of specific phosphodiester ODNs were demonstrated to be dependent on their ability to form secondary structures. When a poly(G) sequence was added to a stimulatory self-complementary ODN, high levels of IFN-α were elicited, and the induction was not dependent on pretreatment with the transfecting agent Lipofectin. In addition, the IFN-α-inducing ODN required the presence of an intact CpG dinucleotide, whereas the inhibitory activity of ODN PCV2/1 was not affected by methylation or removal of the central CpG dinucleotide. Of particular significance, the IFN-α inhibition elicited by ODN PCV2/1 was only effective against induction stimulated by DNA control inducers and not RNA control inducers, indicating activity directed to TLR9 signaling. The PCV2 genome as a whole was demonstrated to induce IFN-α in cultures of poPBMCs, and the presence of immune modulatory sequences within the genome of PCV2 may, therefore, have implications with regard to the immune evasion mechanisms utilized by PCV2.
SOME SMALL CANCELLATION PROPERTIES OF RANDOM GROUPS
Authors: OLLIVIER YANN
Published: March 2007

We work in the density model of random groups. We prove that they satisfy an isoperimetric inequality with sharp constant 1-2d depending upon the density parameter d. This implies in particular a property generalizing the ordinary C′ small cancellation condition, which could be termed "macroscopic cancellation". This also sharpens the evaluation of the hyperbolicity constant δ.

As a consequence we get that the standard presentation of a random group at density d < 1/5 satisfies the Dehn algorithm and Greendlinger's lemma, and that it does not for d > 1/5.

For this we establish a version of the local-global principle for hyperbolic spaces (Cartan–Hadamard–Gromov theorem) involving arbitrarily small loss in the isoperimetric constant.
LAZARD'S ELIMINATION (IN TRACES) IS FINITE-STATE RECOGNIZABLE
Authors: DUCHAMP GÉRARD , LUQUE JEAN-GABRIEL
Published: March 2007

We prove that the codes issued from the elimination of any sub-alphabet in a trace monoid are finite-state recognizable. This implies in particular that the transitive factorizations of the trace monoids are recognizable by (boolean) finite-state automata.
AN AMENABLE ASCENDING UNION OF NON-AMENABLE SEMIGROUPS
Authors: DONNELLY JOHN
Published: March 2007

We construct an example of a right amenable semigroup which is the ascending union of semigroups, none of which are right amenable.
ON THE KROHN–RHODES COMPLEXITY OF SEMIGROUPS OF UPPER TRIANGULAR MATRICES
Authors: KAMBITES MARK
Published: March 2007

We consider the Krohn–Rhodes complexity of certain semigroups of upper triangular matrices over finite fields. We show that for any n > 1 and finite field k, the semigroups of all n × n upper triangular matrices over k and of all n × n unitriangular matrices over k have complexity n - 1. A consequence is that the complexity c > 1 of a finite semigroup places a lower bound of c + 1 on the dimension of any faithful triangular representation of that semigroup over a finite field.
THE MANIFESTATION OF GROUP ENDS IN THE TODD–COXETER COSET ENUMERATION PROCEDURE
Authors: PIGGOTT ADAM
Published: March 2007

The issue of recognizing group properties, such as the cardinality of the group, directly from the dynamics of an incomplete coset enumeration is discussed. In particular, it is shown that the property of having two ends is recognizable in such a way. Further, sufficient conditions are given for termination of a coset enumeration with the declaration that the group under consideration has infinitely-many ends.
POSITIVE DARWINIAN SELECTION: DOES THE COMPARATIVE METHOD RULE?
Authors: FORSDYKE DONALD R.
Published: March 2007

To detect positive Darwinian selection it is thought essential to compare two sequences. Despite its defects, "the comparative method rules." However, genes evolving rapidly under positive selection conflict more with internal forces (the genome phenotype) than genes evolving slowly under negative selection. In particular, there is conflict with stem-loop potential. The conflict between protein-encoding potential (primary information) and stem-loop potential (secondary information) permits detection of positive selection in a single sequence. The degree to which secondary information is compromised provides a measure of the speed of transmission of primary information. Thus, the sovereignty of the comparative method is challenged not only by its own defects, but also by the availability of a single-sequence method. However, while of limited utility for positive selection, the comparative method casts new light on Darwin's great question — the origin of species. Comparison of rates of synonymous and non-synonymous mutation suggests that branching into new species begins with synonymous mutations.
ROLE OF CYTOTOXIC T-LYMPHOCYTES IN TUMOR STABILITY: A PREY-PREDATOR MODELING APPROACH
Authors: MUKHOPADHYAY B. , BHATTACHARYYA R.
Published: March 2007

We present and analyze a three-species mathematical model of tumor progression and regression using prey-predator dynamics. The tumor cell population is supposed to be the prey species and the cytotoxic T-lymphocytes (CTL) and macrophages (which are killer cells of the immune system) as their predator. Using a ratio-dependent predation functional form, the ODE model is analyzed for stability criteria. A discrete time delay required for destruction of tumor cells is then incorporated into the basic model and the resulting delayed model is studied to explore the significance of various system parameters controlling the stability of the system. The active killer cells are shown to be the key population species controlling the system dynamics. A range of the delay parameter is estimated that ensures stability of different system components. Numerical simulations are performed to support analytical findings.
TOXIN-ALLELOPATHY AMONG PHYTOPLANKTON SPECIES PREVENTS COMPETITIVE EXCLUSION
Authors: ROY SHOVONLAL , CHATTOPADHYAY JOYDEV
Published: March 2007

Toxic or allelopathic compounds liberated by toxin-producing phytoplankton (TPP) acts as a strong mediator in plankton dynamics. On an analysis of a set of phytoplankton biomass data that have been collected by our group in the northwest part of the Bay of Bengal, and by analysis of a three-component mathematical model under a constant as well as a stochastic environment, we explore the role of toxin-allelopathy in determining the dynamic behavior of the competing phytoplankton species. The overall results, based on analytical and numerical wings, demonstrate that toxin-allelopathy due to the TPP promotes a stable co-existence of those competitive phytoplankton that would otherwise exhibit competitive exclusion of the weak species. Our study suggests that TPP might be a potential candidate for maintaining the co-existence and diversity of competing phytoplankton species.
DEVELOPMENT OF HYDROXYAPATITE COATING PREPARED BY SOL–GEL TECHNIQUE
Authors: WANG HUI , CHEN CHUANZHONG , WANG DIANGANG
Published: March 2007

Metallic biomaterial, as a kind of composite materials, has been applied extensively in medical field due to its mechanical advantages and biological affinity. The sol–gel technique, as a new method to prepare the hydroxyapatite (HA) coating, has a lot of advantages. Therefore, the principle, characteristic and the researchment status of sol–gel technique are introduced. And the structure, characteristic and bioactivity of the HA coatings prepared by this method, as well as the influence of various parameters are discussed. Finally, the applied prospects of sol–gel technique in medical field are discussed.
ELECTROCHEMICALLY SYNTHESIZED COPPER NANOTUBES AND NANOROD ARRAYS IN POLYCARBONATE MEMBRANES
Authors: XUE SHOUHONG , WANG ZHENGDE
Published: March 2007

The large area, highly uniform copper nanorod arrays with cylindrical morphology in polycarbonate membranes (PC) have been successfully prepared by electrochemical deposition. The copper nanorod arrays have the length of 3 μm, the diameter of 400 nm, approximately, which correspond closely to the pore diameter and thickness of membranes. The copper nanotubes were also obtained by controlling initial voltage and polycarbonate membranes treatment process. The possible growing mechanisms of copper nanostructures in membrane pores were discussed.
GROWTH MECHANISM OF IRON FILMS ON SILICONE OIL SURFACES PREPARED BY SPUTTERING METHOD
Authors: YU SEN-JIANG , ZHANG YONG-JU , CHEN JIANG-XING , GE HONG-LIANG
Published: March 2007

The growth mechanism and characteristic ordered patterns of iron ( Fe ) films deposited on the silicone oil surfaces by a DC-magnetron sputtering method are presented in this paper. It is found that as the film thickness increases, the iron atoms deposited on the oil surface first form compact clusters, then transfer to ramified aggregates and web-shaped structures, and finally form a continuous iron film. The average branch width of the ramified aggregates is about 0.34 μm, which is almost independent of the sputtering power, i.e., the deposition rate. In the continuous iron films, large spatially disk-shaped patterns are observed, which result from spontaneous ordered organization of the iron atoms and atomic clusters driven by the internal stress in this nearly free sustained film system.
SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION (SI-ATRP) OF ACRYLAMIDE FROM POLY(VINYL CHLORIDE) FILM AND ITS SORPTION PROPERTY TOWARD MERCURY ION
Authors: LIU PENG
Published: March 2007

The polyacrylamide surface grafted poly(vinyl chloride) (PAM-PVC) film was successfully prepared via a facile copper-mediated surface-initiated atom transfer radical polymerization (SI-ATRP) of acrylamide (AM) from the surfaces of the PVC thin film with their surface labile chlorines as initiation sites. Graft reaction was first-order kinetic with respect to the polymerizing time in the low monomer conversion stage, this being typical for ATRP. A percentage of grafting (PG) of 32.1% was achieved in 6 h, calculated from the elemental analysis results. The surface morphology of the product was characterized with scanning electron microscopy (SEM). The sorption property of the grafted film toward Hg (II) ion was also preliminarily investigated.
NANO-PARTICLES AND FILMS OF CARBON NITRIDE PREPARED BY USING THE SIMPLE PLASMA SPUTTERING DEPOSITION TECHNIQUES
Authors: YANG B. Q. , LI H. Y. , SHI Y. C. , FENG P. X.
Published: March 2007

Nanoscale particles and films of carbon nitride (CN) were synthesized on Si (100) substrates at room temperature by using simple plasma sputtering deposition techniques based on DC Glow Discharge with Hollow Cathode electrodes. The bonding structures of the films were investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. G and D bands in Raman spectra of the samples were identified. Following an increase of the precursor nitrogen pressure, the intensity of the D band in Raman spectra of the sample became strong. Similar phenomenon was also observed with an increase of the bias voltage. Scanning electron microscope images of the samples indicated that smooth and uniform CN x films were obtained at low bias voltages. Whereas, setting a pulsed bias voltage up to 5 kV, several groups of nanoparticles were observed. Each group of nanoparticles showed "sunflower" type of distribution.
VALUATION OF GUARANTEED ANNUITY OPTIONS IN AFFINE TERM STRUCTURE MODELS
Authors: CHU CHI CHIU , KWOK YUE KUEN
Published: March 2007

We propose three analytic approximation methods for numerical valuation of the guaranteed annuity options in deferred annuity pension policies. The approximation methods include the stochastic duration approach, Edgeworth expansion, and analytic approximation in affine diffusions. The payoff structure in the annuity policies is similar to a quanto call option written on a coupon-bearing bond. To circumvent the limitations of the one-factor interest rate model, we model the interest rate dynamics by a two-factor affine interest rate term structure model. The numerical accuracy and the computational efficiency of these approximation methods are analyzed. We also investigate the value sensitivity of the guaranteed annuity option with respect to different parameters in the pricing model.
STOCHASTIC MODEL PREDICTIVE CONTROL AND PORTFOLIO OPTIMIZATION
Authors: HERZOG FLORIAN , DONDI GABRIEL , GEERING HANS P.
Published: March 2007

This paper proposes a solution method for the discrete-time long-term dynamic portfolio optimization problem with state and asset allocation constraints. We use the ideas of Model Predictive Control (MPC) to solve the constrained stochastic control problem. MPC is a solution technique which was developed to solve constrained optimal control problems for deterministic control applications. MPC solves the optimal control problem with a receding horizon where a series of consecutive open-loop optimal control problems is solved.

The aim of this paper is to develop an MPC approach to the problem of long-term portfolio optimization when the expected returns of the risky assets are modeled using a factor model based on stochastic Gaussian processes. We prove that MPC is a suboptimal control strategy for stochastic systems which uses the new information advantageously and thus is better than the pure optimal open-loop control. For the open-loop optimal control optimization, we derive the conditional portfolio distribution and the corresponding conditional portfolio mean and variance. The mean and the variance depend on future decision about the asset allocation.

For the dynamic portfolio optimization problem, we consider constraints on the asset allocation as well as probabilistic constraints on the attainable values of the portfolio wealth. We discuss two different objectives, a classical mean–variance objective and the objective to maximize the probability of exceeding a predetermined value of the portfolio. The dynamic portfolio optimization problem is stated, and the solution via MPC is explained in detail. The results are then illustrated in a case study.
THE MARKET REACTION TO STOCK SPLITS — EVIDENCE FROM INDIA
Authors: MISHRA A. K.
Published: March 2007

Stock splits are a relatively new phenomenon in the Indian context. This paper examines the market effect of stock splits on stock price, return, volatility, and trading volume around the split ex-dates for a sample of stock splits undertaken in the Indian stock market over the period 1999–2005.

The traditional view of stock splits as cosmetic transactions that simply divide the same pie into more slices is inconsistent with the significant wealth effect associated with the announcement of a stock split. However, the empirical evidence confirms a negative effect on price and return of stock splits. The overall cumulative abnormal returns after the split are negative. These results suggest that stock splits have induced the market to revise its optimistic valuation about future firm performance, rejecting signaling hypothesis to which splits convey positive information to markets. Hence, stock splits have reduced the wealth of the shareholders. The results also show that presence of a positive effect on volatility and trading volume following the split events, thus suggesting that split events enhance liquidity.
Activation of classical protein kinase C decreases transport via systems y+ and y+L
Authors: Rotmann Alexander , Simon Alexandra , Martiné Ursula , Habermeier Alice , Closs Ellen I.
Published: March 2007

Activation of protein kinase C (PKC) downregulates the human cationic amino acid transporters hCAT-1 (SLC7A1) and hCAT-3 (SLC7A3) (Rotmann A, Strand D, Martiné U, Closs EI. J Biol Chem 279: 54185–54192, 2004; Rotmann A, Vekony N, Gassner D, Niegisch G, Strand D, Martine U, Closs EI. Biochem J 395: 117–123, 2006). However, others found that PKC increased arginine transport in various mammalian cell types, suggesting that the expression of different arginine transporters might be responsible for the opposite PKC effects. We thus investigated the consequence of PKC activation by phorbol-12-myristate-13-acetate (PMA) in various human cell lines expressing leucine-insensitive system y+ [hCAT-1, hCAT-2B (SLC7A2), or hCAT-3] as well as leucine-sensitive system y+L [y+LAT1 (SLC7A7) or y+LAT2 (SLC7A6)] arginine transporters. PMA reduced system y+ activity in all cell lines tested, independent of the hCAT isoform expressed, while mRNAs encoding the individual hCAT isoforms were either unchanged or increased. System y+L activity was also inhibited by PMA. The extent and onset of inhibition varied between cell lines; however, a PMA-induced increase in arginine transport was never observed. In addition, when expressed in Xenopus laevis oocytes, y+LAT1 and y+LAT2 activity was reduced by PMA, and this inhibition could be prevented by the PKC inhibitor bisindolylmaleimide I. In ECV304 cells, PMA-induced inhibition of systems y+ and y+L could be prevented by Gö6976, a specific inhibitor of conventional PKCs. Thymelea toxin, which activates preferentially classical PKC, had a similar inhibitory effect as PMA. In contrast, phosphatidylinositol-3,4,5-triphosphate-dipalmitoyl, an activator of atypical PKC, had no effect. These data demonstrate that systems y+ and y+L are both downregulated by classical PKC.
Large-conductance calcium-activated potassium channel activity is absent in human and mouse neutrophils and is not required for innate immunity
Authors: Essin Kirill , Salanova Birgit , Kettritz Ralph , Sausbier Matthias , Luft Friedrich C. , Kraus Dirk , Bohn Erwin , Autenrieth Ingo B. , Peschel Andreas , Ruth Peter , Gollasch Maik
Published: March 2007

Large-conductance Ca2+-activated K+ (BK) channels are reported to be essential for NADPH oxidase-dependent microbial killing and innate immunity in leukocytes. Using human peripheral blood and mouse bone marrow neutrophils, pharmacological targeting, and BK channel gene-deficient (BK−/−) mice, we stimulated NADPH oxidase activity with 12- O-tetradecanoylphorbol-13-acetate (PMA) and performed patch-clamp recordings on isolated neutrophils. Although PMA stimulated NADPH oxidase activity as assessed by O2− and H2O2 production, our patch-clamp experiments failed to show PMA-activated BK channel currents in neutrophils. In our studies, PMA induced slowly activating currents, which were insensitive to the BK channel inhibitor iberiotoxin. Instead, the currents were blocked by Zn2+, which indicates activation of proton channel currents. BK channels are gated by elevated intracellular Ca2+ and membrane depolarization. We did not observe BK channel currents, even during extreme depolarization to +140 mV and after elevation of intracellular Ca2+ by N-formyl-l-methionyl-l-leucyl-phenylalanine. As a control, we examined BK channel currents in cerebral and tibial artery smooth muscle cells, which showed characteristic BK channel current pharmacology. Iberiotoxin did not block killing of Staphylococcus aureus or Candida albicans. Moreover, we addressed the role of BK channels in a systemic S. aureus and Yersinia enterocolitica mouse infection model. After 3 and 5 days of infection, we found no differences in the number of bacteria in spleen and kidney between BK−/− and BK+/+ mice. In conclusion, our experiments failed to identify functional BK channels in neutrophils. We therefore conclude that BK channels are not essential for innate immunity.
l-Glutamine in vitro regulates rat aortic glutamate content and modulates nitric oxide formation and contractility responses
Authors: Schachter David
Published: March 2007

These studies test the hypothesis that l-glutamine at its physiological plasma concentration, ∼0.5 mM, can increase tissue content and net synthesis of glutamate in rat aortic segments in vitro, thereby mediating relaxation of the underlying smooth muscle in the elastic reservoir region of the thoracic aorta. Aortic segments were incubated in an isotonic medium with and without 21 amino acids at their normal plasma concentrations. Of these amino acids only l-glutamine and l-leucine at their plasma concentrations increased glutamate synthesis and content. Tissue glutamate content resulting from increasing concentrations of each precursor reached an upper level of ∼1.3–1.6 μmol/g wet wt. Regulation of the tissue glutamate content involves an interaction of the synthetic pathways in which l-glutamine inhibits the endothelial leucine-to-glutamate pathway. l-Glutamine increases nitric oxide (NO) formation, and NO inhibits the controlling enzyme of the endothelial leucine-to-glutamate pathway, the branched-chain α-ketoacid dehydrogenase complex. Treatment of precontracted aortic rings with 0.5 mM l-glutamine elicits smooth muscle relaxation, a response that requires endothelial nitric oxide synthase activity and an intact endothelium. The results demonstrate that in vitro l-glutamine at its normal concentration in plasma can regulate rat aortic glutamate content and modulate NO formation and contractility responses of the thoracic aortic wall.
Enhancement of intragastric acid stability of a fat emulsion meal delays gastric emptying and increases cholecystokinin release and gallbladder contraction
Authors: Marciani Luca , Wickham Martin , Singh Gulzar , Bush Debbie , Pick Barbara , Cox Eleanor , Fillery-Travis Annette , Faulks Richard , Marsden Charles , Gowland Penny A. , Spiller Robin C.
Published: March 2007

Preprocessed fatty foods often contain calories added as a fat emulsion stabilized by emulsifiers. Emulsion stability in the acidic gastric environment can readily be manipulated by altering emulsifier chemistry. We tested the hypothesis that it would be possible to control gastric emptying, CCK release, and satiety by varying intragastric fat emulsion stability. Nine healthy volunteers received a test meal on two occasions, comprising a 500-ml 15% oil emulsion with 2.5% of one of two emulsifiers that produced emulsions that were either stable ( meal A) or unstable ( meal B) in the acid gastric environment. Gastric emptying and gallbladder volume changes were assessed by MRI. CCK plasma levels were measured and satiety scores were recorded. Meal B layered rapidly owing to fat emulsion breakdown. The gastric half-emptying time of the aqueous phase was faster for meal B (72 ± 13 min) than for meal A (171 ± 35 min, P < 0.008). Meal A released more CCK than meal B (integrated areas, respectively 1,095 ± 244 and 531 ± 111 pmol·min·l−1, P < 0.02), induced a greater gallbladder contraction ( P < 0.02), and decreased postprandial appetite ( P < 0.05), although no significant differences were observed in fullness and hunger. We conclude that acid-stable emulsions delayed gastric emptying and increased postprandial CCK levels and gallbladder contraction, whereas acid-instability led to rapid layering of fat in the gastric lumen with accelerated gastric emptying, lower CCK levels, and reduced gallbladder contraction. Manipulation of the acid stability of fat emulsion added to preprocessed foods could maximize satiety signaling and, in turn, help to reduce overconsumption of calories.
Taste and acceptance of pyrophosphates by rats and mice
Authors: McCaughey Stuart A. , Giza Barbara K. , Tordoff Michael G.
Published: March 2007

The palatability and taste quality of pyrophosphates were evaluated in a series of behavioral and electrophysiological experiments. In two-bottle choice tests with water, rats strongly preferred some concentrations of Na3HP2O7 and Na4P2O7, moderately preferred some concentrations of K4P2O7 and Fe4(P2O7)3, and were indifferent to or avoided all concentrations of Ca2P2O7 and Na2H2P2O7. The contribution of sodium to the preference for sodium pyrophosphates was ascertained: 1) Rats with a choice between Na4P2O7 and NaCl preferred 1 mM Na4P2O7 to 4 mM NaCl but preferred 40 or 150 mM NaCl to 10 mM Na4P2O7, 2) blocking salt taste transduction by mixing Na4P2O7 with amiloride reduced preferences but did not eliminate them, and 3) three mouse strains (FVB/J, C57BL/6J, and CBA/J) known to differ in sodium preference had the same rank order of preferences for Na3HP2O7 and NaCl, but peak preferences were higher for Na3HP2O7 than for NaCl. The taste qualities of pyrophosphates were determined by measuring taste-evoked responses of neurons in the nucleus of the solitary tract of rats. Across-neuron patterns of activity for sodium pyrophosphates were similar to that of NaCl but the pattern of Na3HP2O7 plus amiloride was unique from those of sweet, salty, sour, bitter, and umami stimuli. Taken together, the results indicate that the high palatability of some concentrations of Na3HP2O7 and Na4P2O7 is due partially to their salty taste, but there must also be another cause, which may include a novel orosensory component distinct from the five major taste qualities.
Combination of Neuronal Signals Representing Object-Centered Location and Saccade Direction in Macaque Supplementary Eye Field
Authors: Moorman David E. , Olson Carl R.
Published: March 2007

Neurons in the macaque supplementary eye field (SEF) fire at different rates in conjunction with planning saccades in different directions. They also exhibit object-centered spatial selectivity, firing at different rates when the target of the saccade is at the left or right end of a horizontal bar. To compare the rate of incidence of the two kinds of signal, and to determine how they combine, we recorded from SEF neurons while monkeys performed a task in which the target (a dot or the left or right end of a horizontal bar) could appear in any visual field quadrant. During the period when the target was visible on the screen and the monkey was preparing to make a saccade, many neurons exhibited selectivity for saccade direction, firing at a rate determined by the direction of the impending saccade irrespective of whether the target was a dot or the end of a bar. On bar trials, many of the same neurons exhibited object-centered selectivity, firing more strongly when the target was at the preferred end of the bar regardless of saccade direction. The rate of incidence of object-centered selectivity (33%) was lower overall than that of saccade-direction selectivity (56%). Signals related to saccade direction and the object-centered location of the target tended to combine additively. The results suggest that the SEF is at a transitional stage between representing the object-centered command and specifying the parameters of the saccade.
Oscillations of Local Field Potentials in the Rat Dorsal Striatum During Spontaneous and Instructed Behaviors
Authors: DeCoteau William E. , Thorn Catherine , Gibson Daniel J. , Courtemanche Richard , Mitra Partha , Kubota Yasuo , Graybiel Ann M.
Published: March 2007

Oscillatory activity is a candidate mechanism for providing frequency coding for the generation, storage and replay of sequential representations of events and episodes. We recorded local field potentials (LFPs) and spike activity in the striatum, a basal ganglia structure implicated in behavioral action-sequence learning and performance, as rats engaged in spontaneous and instructed behaviors in a T-maze task. We found that during voluntary behaviors, striatal LFPs exhibit prominent theta-band oscillations together with rhythms at higher and lower frequencies. Analysis of the theta-band activity demonstrated that these oscillations are strongly modulated during task performance and increase as the animals choose and execute their turning responses in the cue-instructed T-maze task. These theta rhythms are locally generated and are coherent across large parts of the striatum. We suggest that modulation of oscillatory activity in the striatum may be a key feature of neural processing related to the control of voluntary behavior.
Characterization of Na+-Activated K+ Currents in Larval Lamprey Spinal Cord Neurons
Authors: Hess Dietmar , Nanou Evanthia , El Manira Abdeljabbar
Published: March 2007

Potassium channels play an important role in controlling neuronal firing and synaptic interactions. Na+-activated K+ ( KNa) channels have been shown to exist in neurons in different regions of the CNS, but their physiological function has been difficult to assess. In this study, we have examined if neurons in the spinal cord possess KNa currents. We used whole cell recordings from isolated spinal cord neurons in lamprey. These neurons display two different KNa currents. The first was transient and activated by the Na+ influx during the action potentials, and it was abolished when Na+ channels were blocked by tetrodotoxin. The second KNa current was sustained and persisted in tetrodotoxin. Both KNa currents were abolished when Na+ was substituted with choline or N-methyl-d-glucamine, indicating that they are indeed dependent on Na+ influx into neurons. When Na+ was substituted with Li+, the amplitude of the inward current was unchanged, whereas the transient KNa current was reduced but not abolished. This suggests that the transient KNa current is partially activated by Li+. These two KNa currents have different roles in controlling the action potential waveform. The transient KNa appears to act as a negative feedback mechanism sensing the Na+ influx underlying the action potential and may thus be critical for setting the amplitude and duration of the action potential. The sustained KNa current has a slow kinetic of activation and may underlie the slow Ca2+-independent afterhyperpolarization mediated by repetitive firing in lamprey spinal cord neurons.
Simultaneous Recording of Macaque Premotor and Primary Motor Cortex Neuronal Populations Reveals Different Functional Contributions to Visuomotor Grasp
Authors: Umilta M. A. , Brochier T. , Spinks R. L. , Lemon R. N.
Published: March 2007

To understand the relative contributions of primary motor cortex (M1) and area F5 of the ventral premotor cortex (PMv) to visually guided grasp, we made simultaneous multiple electrode recordings from the hand representations of these two areas in two adult macaque monkeys. The monkeys were trained to fixate, reach out and grasp one of six objects presented in a pseudorandom order. In M1 326 task-related neurons, 104 of which were identified as pyramidal tract neurons, and 138 F5 neurons were analyzed as separate populations. All three populations showed activity that distinguished the six objects grasped by the monkey. These three populations responded in a manner that generalized across different sets of objects. F5 neurons showed object/grasp related tuning earlier than M1 neurons in the visual presentation and premovement periods. Also F5 neurons generally showed a greater preference for particular objects/grasps than did M1 neurons. F5 neurons remained tuned to a particular grasp throughout both the premovement and reach-to-grasp phases of the task, whereas M1 neurons showed different selectivity during the different phases. We also found that different types of grasp appear to be represented by different overall levels of activity within the F5-M1 circuit. Altogether these properties are consistent with the notion that F5 grasping-related neurons play a role in translating visual information about the physical properties of an object into the motor commands that are appropriate for grasping, and which are elaborated within M1 for delivery to the appropriate spinal machinery controlling hand and digit muscles.
Electrically Evoked Responses in Onset Chopper Neurons in Guinea Pig Cochlear Nucleus
Authors: Mulders Wilhelmina H.A.M. , Harvey Alan R. , Robertson Donald
Published: March 2007

Extracellular recordings were obtained from single cochlear nucleus neurons in guinea pigs anesthetized with Nembutal and Hypnorm. Neurons were classified by their spontaneous firing rates and responses to acoustic stimuli. In addition, electrical shocks were applied to the midline at the level of the IVth ventricle and spike responses were recorded. Spikes were evoked by shocks only in neurons that were classified as onset choppers (Oc). The shock-evoked spikes could be extinguished by acoustically evoked action potentials in the same neurons. In roughly 30% of the sample of Oc neurons, quantitative aspects of the timing of this extinction were not compatible with the shock-evoked spike being antidromically conducted from Oc output axons. Together with the presence of temporal jitter at high shock rates, the data suggest the possibility that at least some of the shock-evoked spikes may be generated by excitatory synaptic input to the Oc neurons, most likely from the collaterals of the medial olivocochlear system (MOCS), whose axons pass close to the floor of the IVth ventricle. This excitatory synaptic input may operate to modulate the activity of Oc neurons in addition to MOCS actions in the auditory periphery.
P/Q-Type, But Not N-Type, Calcium Channels Mediate GABA Release From Fast-Spiking Interneurons to Pyramidal Cells in Rat Prefrontal Cortex
Authors: Zaitsev A. V. , Povysheva N. V. , Lewis D. A. , Krimer L. S.
Published: March 2007

The Cav2.1 (P/Q-) and Cav2.2 (N-type) voltage-gated calcium channels (VGCCs) play a predominant role in neurotransmitter release at central synapses, but their distribution is not uniform across different types of synapses. Although the functional significance of the differential distribution of N- and P/Q-type VGCCs is poorly understood, distinct types of VGCCs appear to differentially affect synaptic properties. For example, P/Q-type VGCCs are located closer to release sites and are less affected by G-protein-mediated inhibition than are N-type VGCCs. Thus P/Q-type VGCCs might be beneficial at synapses with high probability of release and precise timing of neurotransmission, such as the inhibitory inputs from parvalbumin-containing fast-spiking (FS) interneurons to pyramidal cells (PCs) in the neocortex. To determine whether VGCCs types predominate at synapses from FS interneurons to PCs in rat prefrontal cortex, whole cell paired recordings ( n = 14) combined with intracellular labeling and fluorescence immunohistochemistry for parvalbumin were performed in acute slices. Bath application of the specific N-type VGCC blocker ω-conotoxin-GVIa (1 μM) did not alter inhibitory postsynaptic potential amplitude, failure rate, or synaptic dynamics; in contrast, application of P/Q-type VGCC blocker ω-agatoxin-IVa (0.5 μM) completely and irreversibly blocked neurotransmission. These results indicate that P/Q-type VGCCs mediate the GABA release from parvalbumin-positive FS interneurons to PCs in the rat neocortex.