bluuebunny/crossref_metadata_2025 huggingface dataset:
In Vivo Acquisition of High-Level Resistance to Imipenem inEscherichia coli
Authors: Poirel Laurent , Héritier Claire , Spicq Colette , Nordmann Patrice
Published: August 2004

Four clonally relatedEscherichia colistrains were isolated successively from bile duct of a girl suffering from sclerosing cholangitis. One of them, selected after an imipenem-containing regimen, was resistant to carbapenems and to broad-spectrum cephalosporins due to a plasmid-mediated cephalosporinase, CMY-2, and the lack of outer membrane proteins OmpF and OmpC.
Persistence of Human Immunodeficiency Virus Type 1 Subtype B DNA in Dried-Blood Samples on FTA Filter Paper
Authors: Li Chung-Chen , Beck Ingrid A. , Seidel Kristy D. , Frenkel Lisa M.
Published: August 2004

The stability of human immunodeficiency virus type 1 (HIV-1) DNA in whole blood collected on filter paper (FTA Card) was evaluated. After >4 years of storage at room temperature in the dark our qualitative assay detected virus at a rate similar to that of our initial test (58 of 60, 97%;
P
= 0.16), suggesting long-term HIV-1 DNA stability.
Modified Multiplex PCR Method for Detection of Pyrogenic Exotoxin Genes in Staphylococcal Isolates
Authors: Løvseth Astrid , Loncarevic Semir , Berdal Knut G.
Published: August 2004

A modified multiplex PCR method for detection of nine
Staphylococcus aureus
enterotoxin genes (
sea
,
seb
,
sec
,
sed
,
see
,
seg
,
seh
,
sei
, and
sej
) and one form of immunoreactive toxic shock syndrome toxin based on a previously published method (S. R. Monday and G. A. Bohach, J. Clin. Microbiol.
37:
3411-3414, 1999) has been developed. The modified PCR protocol seems robust and gives reliable results.
Reemerging Threat of Epidemic Typhus in Algeria
Authors: Mokrani K. , Fournier P. E. , Dalichaouche M. , Tebbal S. , Aouati A. , Raoult D.
Published: August 2004

We report a case of epidemic typhus in a patient from the Batna region of Algeria, who presented with generalized febrile exanthema. The clinical diagnosis was confirmed by serological cross-adsorption followed by Western blotting. Our report emphasizes the threat of epidemic typhus in the highlands of Algeria.
Two Novel Clinical Presentations of
Burkholderia cepacia
Infection
Authors: Mukhopadhyay Chiranjoy , Bhargava Anudita , Ayyagari Archana
Published: August 2004

We report two cases of multidrug-resistant
Burkholderia cepacia
(
B. cepacia
genomovar I) and
Burkholderia multivorans
causing multiple liver abscesses in a patient with bronchial asthma (case 1) and peritonitis in a patient with cirrhosis and hepatitis C virus disease (case 2), respectively. Both patients were treated successfully.
Electron Binding to Nucleic Acid Bases. Experimental and Theoretical Studies. A Review
Authors: Svozil Daniel , Jungwirth Pavel , Havlas Zdeněk
Published: July 2004

An in-depth knowledge of an excess electron binding mechanism to DNA and RNA nucleobases is important for our understanding of radiation damage influence on the biological functions of nucleic acids, as well as for the possible use of DNA molecules as wires in molecular electronic circuits. The of anions created by electron attachment to individual nucleic acid bases is discussed in detail. The principles of the experimental and theoretical approaches to the description of these anions are outlined, and the available results concerning valence- and dipole-bound anions of nucleic acid bases are reviewed. A review with 167 references.
Polarographic and Voltammetric Behavior of the Antibiotic Cefetamet; Reduction of the Methoxyimino Group
Authors: Aleksić Mara , Kapetanović Vera , Zuman Petr
Published: July 2004

Evaluation of DC polarographic i-E curves and analogous curves obtained by cyclic voltammetry in aqueous buffers as well as in buffers containing 30% v/v ethanol indicated that the methoxyimino group of cefetamet is reduced on DME and HDME in the following way: the methoxyimino group can be at the electrode surface rapidly protonated up to pH about 9. In the protonated form of the grouping (>C=NH-OCH3)+, the OCH3 is cleaved off in the first two-electron step. The resulting imine is in equilibrium with its protonated form, which is reduced in a second two-electron step. At pH higher than about 10, the unprotonated form of the methoxyimino group is reduced in a single four-electron step to amine. Studies using cyclic voltammetry were complicated by adsorption phenomena.
Second and Third Derivatives of UV Spectra as a Tool for Identification of Major Anthocyanins from Aronia melanocarpa Extract, Separated Using Reversed-Phase High-Performance Liquid Chromatography
Authors: Minkiewicz Piotr , Pliszka Barbara , Dziuba Jerzy , Oszmiański Jan
Published: July 2004

The aim of the study was to propose a method for identification of major anthocyanins in black chokeberry: cyanidin 3-O-β-D-galactopyranoside and cyanidin 3-O-α-L-arabinopyranoside, using reversed-phase high-performance liquid chromatography on line with UV spectroscopy. The similarity indexes between standard spectra and spectra of major components of black chokeberry extract were calculated. The calculations were performed for zero-order spectra and first-fifth derivatives. Only the second and third derivatives of UV spectra provided correct identification of the compounds investigated. Third derivatives of spectra gave higher values of the parameters (calculated using Student's test) indicating statistical significance between similarity indexes to the derivatives of spectra of anthocyanin standards. Third derivative UV spectroscopy may be thus recommended as a tool to identify anthocyanins.
Generator of Fine Polydisperse Aerosol
Authors: Mikuška Pavel
Published: July 2004

A simple and inexpensive laboratory generator of test aerosol is described. The generator is based on the principle of pneumatic atomization of a solution of a soluble compound by high-velocity air stream. After evaporation of solvent from produced droplets, solid particles are formed. The generator provides continuous unattended long-term operation with constant aerosol output. The performance characteristics of the generator were evaluated by spraying solutions of NaNO3 and (NH4)2SO4. The generator produced polydisperse aerosol in a fine region of particle sizes with a geometric mean diameter of 52.1 nm and a geometric standard deviation of 1.90 for the NaNO3 concentration in the sprayed solution 30 g/l. The total number concentration of the produced aerosol was 3.14 × 107 cm-3 at a nominal air flow rate 78 l/min. The number concentration of particles increased with increasing flow rate of solution, solute concentration and pressure of compressed air through the atomizer or with decreasing total air flow rate through the generator. The change in any of these variables can be used to adjust the particle number concentration. NaNO3 aerosol generation rate was 0.172 mg/min for the NaNO3 concentration in the sprayed solution 30 g/l.
Preparation of Organometallic and Silyl Complexes of Palladium(II) via [PdCl(SnCl3)L2], where L = PPh3, P(p-Tol)3
Authors: Noskowska Małgorzata , Duczmal Wojciech
Published: July 2004

A new method for preparing organometallic and monosilyl complexes of Pd(II), based on the interaction between [PdCl(SnCl3)L2] (L = PPh3 or P(p-Tol)3) and appropriate organohalogen compound or chlorosilane has been developed. The products without tin have been obtained with good yield (85-97%). The reaction mechanism has been proposed on the basis of kinetic and chemometric investigations of the reaction between [PdCl(SnCl3)(PPh3)2] and Me2SiCl2.
Structure of Disilylated Acetoacetohydroxamic Acid
Authors: Schraml Jan , Hetflejš Jiří , Šabata Stanislav , Blechta Vratislav , Sýkora Jan , Roithová Jana
Published: July 2004

As proved by 29Si and 15N NMR spectra, the reaction of N,O-bis(trimethylsilyl)hydroxylamine with diketene yields a mixture of E and Z isomers of O,O'-bis(trimethylsilyl)acetoacetohydroximic acid ((E)-3 and (Z)-3), and not the conformers of N,O-bis(trimethylsilyl)acetoacetohydroxamic acid (1), as believed up to now. In contrast, the acetylation of N,O-dimethylhydroxylamine leads to methyl N-methylacetohydroxamate (5), analogous to the structure 1.
Effect of para Substitution on Dissociation of N-Phenylbenzenesulfonamides
Authors: Mansfeld Martin , Pařík Patrik , Ludwig Miroslav
Published: July 2004

The reaction of substituted anilines and benzenesulfonyl chlorides has been used to prepare 49 substituted N-phenylbenzenesulfonamides of general formula 4-X-C6H4SO2NHC6H4-Y-4'. Their purity was checked by elemental analysis. The substituents X and Y include H, CH3, CH3O, Cl, Br, CN, and NO2. The dissociation constants of all compounds were determined by potentiometric titration in methanol, acetonitrile, N,N-dimethylformamide, and pyridine. The obtained dissociation constants, pKHA, were correlated with various sets of substituent constants. It was found that the effects of substituents X and Y on the dissociation are best described by using the Hammett equation with σp constants and the Yukawa-Tsuno equation with σp- and σp constants, respectively. This result confirms the direct conjugation of Y substituent with the reaction centre. The explained variability using the additive model was above 96% in all the solvents used. The data also provided information about the transmission effect of the SO2 group. The average dissociation constants were further processed by the latent variables methods, principal components and conjugated deviations analyses.
Synthesis and Leukemia Cell Growth Inhibition of a Series of 1,3-Dithiazolylbenzene Derivatives
Authors: Lagoja Irene M. , Nauwelaerts Koen , Bal-Mahieu Christine , Pasqualini Michela , Bailly Christian , Herdewijn Piet
Published: July 2004

By a slightly modified Hantzsch thiazole synthesis either 1,3-bis[(thiazol-2-yl)amino]benzene derivatives 2 or 1,3-bis[2-iminothiazol-3(2H)-yl]benzene derivatives 3 were exclusively obtained. The compounds can be distinguished by NMR spectroscopy. Compounds 2a-2d and 3a-3d were evaluated for their potential antitumor activity, DNA interaction, and for their activity against DNA and RNA viruses and against HIV-1 and HIV-2.
A Simple Synthesis of Highly Functionalized Ketenimines Derived from N-Aryl-2,2,2-trichloroacetamides, Alkyl Isocyanides and Dialkyl Acetylenedicarboxylates
Authors: Yavari Issa , Djahaniani Hoorieh , Nasiri Farough
Published: July 2004

The 1:1 reactive intermediates produced in the reaction between alkyl isocyanides and dialkyl acetylenedicarboxylates were trapped with N-aryl-2,2,2-trichloroacetamides. When the aryl group was 1-naphthyl, two products were obtained in nearly 2:1 ratio.
Effects of 3α-Amino-5α-pregnan-20-one on GABAA Receptor: Synthesis, Activity and Cytotoxicity
Authors: Matyáš Libor , Kasal Alexander , Babot Riera Zoila , Sunol Cristina E.
Published: July 2004

The 3α-hydroxy function has been considered essential for the biological activity of neurosteroids at the GABAA receptor. It was found that 3α-amino-5α-pregnan-20-one (3) increased the binding of [3H]flunitrazepam at the GABAA receptor in the primary culture of cortical neurons. This derivative did not display cytotoxicity at relevant neuroactive concentrations, and its structure enabled us to gain further insight into possible functional group modifications in position 3α. Various synthetic methods were investigated in search for the most suitable synthetic approach.
Novel Route to Enantiopure 2,2'-Diaryl-1,1'-binaphthalenes by Stereoconservative Suzuki Arylation at Positions 2 and 2'
Authors: Brath Henrich , Dubovská Margaréta , Juríček Michal , Kasák Peter , Putala Martin
Published: July 2004

The Suzuki arylation of enantiopure 2,2'-diiodo-1,1'-binaphthalene affords the 2,2'-diarylated products in considerable yields (up to 52%), however, significantly racemized. The reversed-polarity approach, using novel enantiopure 1,1'-binaphthalene-2,2'-diyldiboronic acid, prepared either by resolution or by stereoconservative boronation, allowed, after optimization of coupling conditions, to obtain the model 2,2'-ditolylated product in good yield (56%) as well, but in addition, without impairing of enantiomeric purity (i.e. stereoconservatively). The developed synthetic approach was found to be an expedient method for the synthesis of enantiopure 2,2'-diaryl-1,1'-binaphthalenes, especially for those with electron-neutral and electron-deficient poor aryl groups. Observing that the diboronic acid decomposes by hydrodeboronation under the reaction conditions, 2-aryl-1,1'-binaphthalenes were isolated as the main products from the reaction with less reactive electron-rich aryl iodides.
Forest floor microbial community response to tree species and fertilization of regenerating coniferous forests
Authors: Leckie S E , Prescott C E , Grayston S J
Published: August 2004

We studied the effect of tree species and fertilization on the forest floor microbial community of 15-year-old regenerating forests. We sampled F and H forest floor layers of plots planted to Thuja plicata (Donn ex D. Don.) or Tsuga heterophylla (Raf.) Sarg. on N-poor and N-rich sites, with and without fertilizer treatments. Microbial community composition was assessed using phospholipid fatty acid analysis and by enumerating populations of culturable bacteria and fungi. Potential microbial functioning was assessed using community-level physiological profiling. There was little differentiation of community-level physiological profiles of F and H layers and few differences among the treatments. Total microbial biomass was greater in the F than H layer, and the two layers had distinct phospholipid fatty acid profiles. Site effects were detected mainly in the residual H layer, and tree species effects were seen mainly in the F layer, which has developed since harvesting. The effect of fertilization depended on site and tree species, with very little response in cedar plots, and the greatest effects in hemlock plots, coinciding with the greater growth response of hemlock. These results indicate that differences in plant growth rates, rather than direct effects of fertilization, influenced the microbial communities.
Soil carbon sequestration with forest expansion in an arctic foresttundra landscape
Authors: Steltzer Heidi
Published: August 2004

Soil carbon (C) and nitrogen (N) pools were measured under the canopy of 29 white spruce (Picea glauca (Moench) Voss) trees and in the surrounding tundra 3 and 6 m away from each tree at three sites of recent forest expansion along the Agashashok River in northwestern Alaska. The aim was to characterize the potential for forest expansion to lead to increased soil C pools across diverse tundra types. Soil C beneath the trees correlated positively with tree age, suggesting that tree establishment has led to C storage in the soils under their canopy at a rate of 18.5 ± 4.6 g C·m2·year1. Soil C in the surrounding tundra did not differ from those under the trees and showed no relationship to tree age. This characterization of the soil C pools at the 3-m scale strengthens the assertion that the pattern associated with the trees is an effect of the trees, because tree age cannot explain variation among tundra sampling locations at this scale. Potential mechanisms by which these white spruce trees could increase soil C pools include greater production and lower litter quality.
Intensive short rotation forestry in boreal climates: present and future perspectives
Authors: Weih Martin
Published: August 2004

Short rotation forestry (SRF) is regarded as a silvicultural practice employing high-density plantations of fast-growing tree species on fertile land with a rotation period of fewer than 1012 years. I address the challenges and possibilities of SRF applications under the circumstances of a boreal climate, today as well as after anticipated climate change. The implications of a pronounced winter season for the performance of biomass crops are discussed. Poplars, aspens, and willows are superior in boreal SRF because of their fast growth rate in combination with good cold hardiness. These trees can enrich the coniferous forests of boreal regions and increase biodiversity in open agricultural landscapes of the boreal zone. Further, SRF plantations can serve as tools for the amelioration of environmental problems at local (e.g., phytoremediation) and global (e.g., increased greenhouse effect) scales. The biomass yields achieved in boreal SRF and the appropriate production systems appear do not appear to be principally different from warmer regions, but there are some differences with respect to the importance of fertilization, appropriate spacing, and rotation length. The major barriers for a rapid development of SRF appear not to be climatic, technical, or environmental constraints in many boreal regions.
THE THERMODYNAMIC LIMIT FOR FINITE DIMENSIONAL CLASSICAL AND QUANTUM DISORDERED SYSTEMS
Authors: CONTUCCI PIERLUIGI , GIARDINÀ CRISTIAN , PULÉ JOSEPH
Published: August 2004

We provide a very simple proof for the existence of the thermodynamic limit for the quenched specific pressure for classical and quantum disordered systems on a d-dimensional lattice, including spin glasses. We develop a method which relies simply on Jensen's inequality and which works for any disorder distribution with the only condition (stability) that the quenched specific pressure is bounded.
A COUPLED SPHERICAL HARMONICS EXPANSION MODEL FOR CONFINED PARTICLES
Authors: BOURGADE JEAN-PIERRE
Published: August 2004

Our goal in this paper is to derive from a kinetic setting a diffusion model for the transport of charged particles trapped in a surface potential. The so-obtained model is derived through a diffusion approximation, as we assume the thermalization to be governed by particle-wall collisions. In order to take into account the possible inelasticity of such collisions, we introduce a nonlocal (in energy) collision operator on the boundary. At the macroscopic scale, this results in a coupled (in energy) Spherical Harmonics Expansion (SHE) model. The model is both formally and rigorously derived from the kinetic equation, and existence is obtained as a by-product of the derivation.
ATTITUDE TOWARDS ENTREPRENEURSHIP EDUCATION AND NEW VENTURE CREATION
Authors: LEE LENA , WONG POH-KAM
Published: July 2004

Does an individual's positive attitude towards entrepreneurship education promote the growth of new ventures? It appears that it does. The empirical results presented in this paper support a prima facie claim that a relationship exists between attitude towards entrepreneurial education and business start-up. The aim of this paper is to investigate the hypothesised positive relationship between new venture founding and attitude towards entrepreneurial education (AEE). Limited if any research on new venture founding in the past has explored the contribution of AEE in business start-ups. A survey is carried out on a large sample (more than 15,000) of tertiary students residing in Singapore. In analysing the dataset, we have controlled for various factors in the regression analysis. Due to the limitations of our study, we are cautious not to assert any causal link between these 2 variables. The implications of the results to policy makers and educators are discussed along with suggestions for future research in order to refine our present understanding of these relationships.
e-EXTINCTION: AN ILLUSION OF KNOWLEDGE, THE PRESENCE OF IGNORANCE, OR EVOLUTIONARY FATE?
Authors: JONES COLIN , HECKER ROB
Published: July 2004

At present, the rate of small firm adoption of the Internet's ubiquitous World Wide Web (the web) far exceeds the actual exploitation its commercial potential. An inability to strategically acquire, comprehend and use external knowledge is proposed as a major barrier to optimal exploitation of the Internet. This paper discusses the limitations of applying market orientation theory to explain and guide small firm exploitation of the web. Absorptive capacity is introduced as an alternative theory that when viewed from an evolutionary perspective provides potentially more insightful discussion. An inability to detect emerging business model dominant designs is suggested to be a mixture of the nature of the technology that supports the Internet and underdeveloped small firm knowledge processing capabilities. We conclude with consideration of the practical and theoretical implications that arise from the paper.
BUSINESS FAMILY AND FAMILY BUSINESS: COMPLEMENTARY AND CONFLICTING VALUES
Authors: DEGADT JAN
Published: July 2004

A family business can be defined as a business where a family exercises a significant influence over ownership and/or management. The objectives and the values of the family business and the business family can be complementary but they can also be conflicting. The entrepreneur has to take account of the wishes and objectives of his extended family and of his small family or household.

An empirical research – made possible by the support of Cera Foundation - has been conducted with 1032 Belgian entrepreneurs, 501 in agriculture and 531 outside agriculture. Areas of conflict can be related to the allocation of profits and the position of individual family members in the family business. The survey shows that most entrepreneurs work very hard and spend a lot of time in the business. Only a minority of the respondents consider family values 'important', but when they do, the family gets a very high place in the hierarchy of values. Satisfaction on the job and autonomy (being one's own boss) are the most important values.

Most entrepreneurs get considerable support from their husband or wife. They want to have a day of rest each week and want to leave business when their age is between 60 and 70. If a succession is possible, most prefer to have one of their children to succeed them. The succession is a process that has to be planned carefully.

The interaction between the business family and the family business can have positive and negative effects, but in a market economy the competitiveness of the business must be preserved in all circumstances.
Unraveling the genetics of chronic kidney disease using animal models
Authors: Korstanje Ron , DiPetrillo Keith
Published: August 2004

Identifying genes underlying common forms of kidney disease in humans has proven difficult, expensive, and time consuming. Quantitative trait loci (QTL) for several complex traits are concordant among mice, rats, and humans, suggesting that genetic findings from these animal models are relevant to human disease. Therefore, we reviewed the literature on genetic studies of kidney disease in rat and mouse and examined the concordance between kidney disease QTL across species. Fifteen genomic regions contribute to kidney disease in the rat, with 12 replicated either in a separate rat cross or in another species. Five loci found in humans were concordant to QTL found in the rat. Two of these were found by homology to a previously identified rat QTL on chromosome 1, demonstrating that kidney disease loci in animal models can predict the location of kidney disease loci in humans. In contrast to the rat, the mouse has been underutilized in the genetic analysis of polygenic kidney disease, although mutagenesis and QTL analysis in the mouse are likely to contribute new findings in the near future. Knowledge of kidney disease loci conserved between the mouse and rat will identify prime candidate loci to test for association with chronic kidney disease in humans.
Phasic Stimuli Evoke Precisely Timed Spikes in Intermittently Discharging Mitral Cells
Authors: Balu Ramani , Larimer Phillip , Strowbridge Ben W.
Published: July 2004

Mitral cells, the principal cells of the olfactory bulb, respond to sensory stimulation with precisely timed patterns of action potentials. By contrast, the same neurons generate intermittent spike clusters with variable timing in response to simple step depolarizations. We made whole cell recordings from mitral cells in rat olfactory bulb slices to examine the mechanisms by which normal sensory stimuli could generate precisely timed spike clusters. We found that individual mitral cells fired clusters of action potentials at 20-40 Hz, interspersed with periods of subthreshold membrane potential oscillations in response to depolarizing current steps. TTX (1 μM) blocked a sustained depolarizing current and fast subthreshold oscillations in mitral cells. Phasic stimuli that mimic trains of slow excitatory postsynaptic potentials (EPSPs) that occur during sniffing evoked precisely timed spike clusters in repeated trials. The amplitude of the first simulated EPSP in a train gated the generation of spikes on subsequent EPSPs. 4-aminopyridine (4-AP)–sensitive K+ channels are critical to the generation of spike clusters and reproducible spike timing in response to phasic stimuli. Based on these results, we propose that spike clustering is a process that depends on the interaction between a 4-AP–sensitive K+ current and a subthreshold TTX-sensitive Na+ current; interactions between these currents may allow mitral cells to respond selectively to stimuli in the theta frequency range. These intrinsic properties of mitral cells may be important for precisely timing spikes evoked by phasic stimuli that occur in response to odor presentation in vivo.
Respiratory-Like Rhythmic Activity Can Be Produced by an Excitatory Network of Non-Pacemaker Neuron Models
Authors: Kosmidis Efstratios K. , Pierrefiche Olivier , Vibert Jean-François
Published: July 2004

It is still unclear whether the respiratory-like rhythm observed in slice preparations containing the pre-Bötzinger complex is of pacemaker or network origin. The rhythm persists in the absence of inhibition, but blocking pacemaker activity did not always result in rhythm abolition. We developed a computational model of the slice to show that respiratory-like rhythm can emerge as a network property without pacemakers or synaptic inhibition. The key currents of our model cell are the low- and high-threshold calcium currents and the calcium-dependent potassium current. Depolarization of a single unit by current steps or by raising the external potassium concentration can induce periodic bursting activity. Gaussian stimulation increased the excitability of the model without evoking oscillatory activity, as indicated by autocorrelation analysis. In response to hyperpolarizing pulses, the model produces prolonged relative refractory periods. At the network level, an increase of external potassium concentration triggers rhythmic activity that can be attributed to cellular periodic bursting, network properties, or both, depending on different parameters. Gaussian stimulation also induces rhythmic activity that depends solely on network properties. In all cases, the calcium-dependent potassium current has a central role in burst termination and interburst duration. However, when periodic inhibition is considered, the activation of this current is responsible for the characteristic amplification ramp of the emerged rhythm. Our results may explain controversial results from studies blocking pacemakers in vitro and show a shift in the role of the calcium-dependent potassium current in the presence of network inhibition.
Perceptual Illusion of “Paradoxical Heat” Engages the Insular Cortex
Authors: Davis K. D. , Pope G. E. , Crawley A. P. , Mikulis D. J.
Published: July 2004

Paradoxical heat (PH), the illusion of skin heat, accompanies many neurological disorders. Using the technique of percept-related functional MRI, we found a region of the right insular cortex specifically activated when subjects perceive a heat sensation in their right hand even though their skin temperature is cool or at neutral. This region was suppressed during mild skin cooling. We propose that this differential response is a manifestation of the role of the insula in signaling temperature perceptions regardless of the actual temperature of the skin. These findings suggest that a region within the insula has a complex role in heat perception, perhaps contributing to a specific, rather than general, thermosensory perception. These data provide insight to our basic understanding of normal and pathological thermosensory perceptions.
Light-Evoked Oscillatory Discharges in Retinal Ganglion Cells Are Generated by Rhythmic Synaptic Inputs
Authors: Arai Itaru , Yamada Yoshiyuki , Asaka Tomomitsu , Tachibana Masao
Published: July 2004

In the visual system, optimal light stimulation sometimes generates γ-range (ca. 20 ∼ 80 Hz) synchronous oscillatory spike discharges. This phenomenon is assumed to be related to perceptual integration. Applying a planar multi-electrode array to the isolated frog retina, Ishikane et al. demonstrated that dimming detectors, off-sustained type ganglion cells, generate synchronous oscillatory spike discharges in response to diffuse dimming illumination. In the present study, applying the whole cell current-clamp technique to the isolated frog retina, we examined how light-evoked oscillatory spike discharges were generated in dimming detectors. Light-evoked oscillatory (∼30 Hz) spike discharges were triggered by rhythmic (∼30 Hz) fluctuations superimposed on a depolarizing plateau potential. When a suprathreshold steady depolarizing current was injected into a dimming detector, only a few spikes were evoked at the stimulus onset. However, repetitive spikes were triggered by a γ-range sinusoidal current superimposed on the steady depolarizing current. Thus the light-evoked rhythmic fluctuations are likely to be generated presynaptically. The light-evoked rhythmic fluctuations were suppressed not by intracellular application of N-(2,6-dimethyl-phenylcarbamoylmethyl)triethylammonium bromide (QX-314), a Na+ channel blocker, to the whole cell clamped dimming detector but by bath-application of tetrodotoxin to the retina. The light-evoked rhythmic fluctuations were suppressed by a GABAA receptor antagonist but potentiated by a GABAC receptor antagonist, whereas these fluctuations were little affected by a glycine receptor antagonist. Because amacrine cells are spiking neurons and because GABA is one of the main transmitters released from amacrine cells, amacrine cells may participate in generating rhythmically fluctuated synaptic input to dimming detectors.
Generalized Integrate-and-Fire Models of Neuronal Activity Approximate Spike Trains of a Detailed Model to a High Degree of Accuracy
Authors: Jolivet Renaud , Lewis Timothy J. , Gerstner Wulfram
Published: July 2004

We demonstrate that single-variable integrate-and-fire models can quantitatively capture the dynamics of a physiologically detailed model for fast-spiking cortical neurons. Through a systematic set of approximations, we reduce the conductance-based model to 2 variants of integrate-and-fire models. In the first variant (nonlinear integrate-and-fire model), parameters depend on the instantaneous membrane potential, whereas in the second variant, they depend on the time elapsed since the last spike [Spike Response Model (SRM)]. The direct reduction links features of the simple models to biophysical features of the full conductance-based model. To quantitatively test the predictive power of the SRM and of the nonlinear integrate-and-fire model, we compare spike trains in the simple models to those in the full conductance-based model when the models are subjected to identical randomly fluctuating input. For random current input, the simple models reproduce 70–80 percent of the spikes in the full model (with temporal precision of ±2 ms) over a wide range of firing frequencies. For random conductance injection, up to 73 percent of spikes are coincident. We also present a technique for numerically optimizing parameters in the SRM and the nonlinear integrate-and-fire model based on spike trains in the full conductance-based model. This technique can be used to tune simple models to reproduce spike trains of real neurons.
Context Contingent Signal Processing in the Cerebellar Flocculus and Ventral Paraflocculus During Gaze Saccades
Authors: Belton T. , McCrea R. A.
Published: July 2004

The vestibuloocular reflex (VOR) functions to stabilize gaze when the head moves. The flocculus region (FLR) of the cerebellar cortex, which includes the flocculus and ventral paraflocculus, plays an essential role in modifying signal processing in VOR pathways so that images of interest remain stable on the retina. In squirrel monkeys, the firing rate of most FLR Pk cells is modulated during VOR eye movements evoked by passive movement of the head. In this study, the responses of 48 FLR Purkinje cells, the firing rates of which were strongly modulated during VOR evoked by passive whole body rotation or passive head-on-trunk rotation, were compared to the responses generated during compensatory VOR eye movements evoked by the active head movements of eye-head saccades. Most (42/48) of the Purkinje cells were insensitive to eye-head saccade-related VOR eye movements. A few (6/48) generated bursts of spikes during saccade-related VOR but only during on-direction eye movements. Considered as a population FLR Pk cells were <5% as responsive to the saccade-related VOR as they were to the VOR evoked by passive head movements. The observations suggest that the FLR has little influence on signal processing in VOR pathways during eye-head saccade-related VOR eye movements. We conclude that the image-stabilizing signals generated by the FLR are highly dependent on the behavioral context and are called on primarily when external forces unrelated to self-generated eye and head movements are the cause of image instability.
Contribution of Intrinsic Neuronal Factors in the Generation of Cortically Driven Electrographic Seizures
Authors: Timofeev Igor , Grenier François , Steriade Mircea
Published: July 2004

Some electrographic seizures are generated intracortically. The cellular and ionic bases of cortically generated spontaneous seizures are not fully understood. Here we investigated spontaneously occurring seizures consisting of spike-wave complexes intermingled with fast runs in ketamine-xylazine anesthetized cats, using dual intracellular recordings in which one pipette contained a control solution and another pipette contained blockers of K+, Na+, or Ca2+ currents. We show that closely located neocortical neurons display virtually identical fluctuations of the membrane potential during electrographic seizures, thus directly demonstrating a high degree of focal synchrony during paroxysmal activity. In addition to synaptic drives, the persistent Na+ current [ INa(p)] and probably the high-threshold Ca2+ current contributed to the generation of paroxysmal depolarizing shifts (PDSs) during cortically driven seizures. Ca2+-activated K+ current [ IK(Ca)] took also part in the control of the amplitude and duration of PDSs. The hyperpolarizing components of seizures largely depended on Cs+-sensitive K+ currents. IK(Ca) played a significant, while not exclusive, role in the mediation of hyperpolarizing potentials related to EEG “waves” during spike-wave seizures. We conclude that intrinsic cellular factors have significant role in the generation of depolarizing and hyperpolarizing components of seizures.
Presynaptic Activity and Ca2+ Entry Are Required for the Maintenance of NMDA Receptor–Independent LTP at Visual Cortical Excitatory Synapses
Authors: Liu Hong Nian , Kurotani Tohru , Ren Ming , Yamada Kazumasa , Yoshimura Yumiko , Komatsu Yukio
Published: July 2004

We have shown that some neural activity is required for the maintenance of long-term potentiation (LTP) at visual cortical inhibitory synapses. We tested whether this was also the case in N-methyl-d-aspartate (NMDA) receptor–independent LTP of excitatory connections in layer 2/3 cells of developing rat visual cortex. This LTP occurred after 2-Hz stimulation was applied for 15 min and always persisted for several hours while test stimulation was continued at 0.1 Hz. When test stimulation was stopped for 1 h after LTP induction, only one-third of the LTP instances disappeared, but most did disappear under a pharmacological suppression of spontaneous firing, indicating that LTP maintenance requires either evoked or spontaneous activities. LTP was totally abolished by a temporary blockade of action potentials with lidocaine or the removal of extracellular Ca2+ after LTP induction, but it persisted under a voltage clamp of postsynaptic cells or after a temporary blockade of postsynaptic activity with the glutamate receptor antagonist kynurenate, suggesting that LTP maintenance requires presynaptic, but not postsynaptic, firing and Ca2+ entry. More than one-half of the LTP instances were abolished after a pharmacological blockade of P-type Ca2+ channels, whereas it persisted after either L-type or Ni2+-sensitive Ca2+ channel blockades. These results show that the maintenance of NMDA receptor–independent excitatory LTP requires presynaptic firing and Ca2+ channel activation as inhibitory LTP, although the necessary level of firing and Ca2+ entry seems lower for the former than the latter and the Ca2+ channel types involved are only partly the same.
Activation of a Calcium-Activated Cation Current During Epileptiform Discharges and Its Possible Role in Sustaining Seizure-Like Events in Neocortical Slices
Authors: Schiller Yitzhak
Published: July 2004

Epileptic seizures are composed of recurrent bursts of intense firing separated by periods of electrical quiescence. The mechanisms responsible for sustaining seizures and generating recurrent bursts are yet unclear. Using whole cell voltage recordings combined with intracellular calcium fluorescence imaging from bicuculline (BCC)-treated neocortical brain slices, I showed isolated paroxysmal depolarization shift (PDS) discharges were followed by a sustained afterdepolarization waveform (SADW) with an average peak amplitude of 3.3 ± 0.9 mV and average half-width of 6.2 ± 0.6 s. The SADW was mediated by the calcium-activated nonspecific cation current ( Ican) as it had a reversal potential of –33.1 ± 6.8 mV, was unaffected by changing the intracellular chloride concentrations, was markedly diminished by buffering [Ca2+]iwith intracellular bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid (BAPTA), and was reversibly abolished by the Icanblocker flufenamic acid (FFA). The Ca2+influx responsible for activation of Icanwas mediated by both N-methyl-d-aspartate-receptor channels, voltage-gated calcium channels and, to a lesser extent, internal calcium stores. In addition to isolated PDS discharges, BCC-treated brain slices also produced seizure-like events, which were accompanied by a prolonged depolarizing waveform underlying individual ictal bursts. The similarities between the initial part of this waveform and the SADW and the fact it was markedly reduced by buffering [Ca2+]iwith BAPTA strongly suggested it was mediated, at least in part, by Ican. Addition of FFA reversibly eliminated recurrent bursting, and transformed seizure-like events into isolated PDS responses. These results indicated Icanwas activated during epileptiform discharges and probably participated in sustaining seizure-like events.
Influence of Age on Adaptability of Human Mastication
Authors: Peyron Marie-Agnès , Blanc Olivier , Lund James P. , Woda Alain
Published: July 2004

The objective of this work was to study the influence of age on the ability of subjects to adapt mastication to changes in the hardness of foods. The study was carried out on 67 volunteers aged from 25 to 75 yr (29 males, 38 females) who had complete healthy dentitions. Surface electromyograms of the left and right masseter and temporalis muscles were recorded simultaneously with jaw movements using an electromagnetic transducer. Each volunteer was asked to chew and swallow four visco-elastic model foods of different hardness, each presented three times in random order. The number of masticatory cycles, their frequency, and the sum of all electromyographic (EMG) activity in all four muscles were calculated for each masticatory sequence. Multiple linear regression analyses were used to assess the effects of hardness, age, and gender. Hardness was associated to an increase in the mean number of cycles and mean summed EMG activity per sequence. It also increased mean vertical amplitude. Mean vertical amplitude and mean summed EMG activity per sequence were higher in males. These adaptations were present at all ages. Age was associated with an increase of 0.3 cycles per sequence per year of life and with a progressive increase in mean summed EMG activity per sequence. Cycle and opening duration early in the sequence also fell with age. We concluded that although the number of cycles needed to chew a standard piece of food increases progressively with age, the capacity to adapt to changes in the hardness of food is maintained.
Precision of Spike Trains in Primate Retinal Ganglion Cells
Authors: Uzzell V. J. , Chichilnisky E. J.
Published: July 2004

Recent studies have revealed striking precision in the spike trains of retinal ganglion cells in several species and suggested that this precision could be an important aspect of visual signaling. However, the precision of spike trains has not yet been described in primate retina. The spike time and count variability of parasol (magnocellular-projecting) retinal ganglion cells was examined in isolated macaque monkey retinas stimulated with repeated presentations of high contrast, spatially uniform intensity modulation. At the onset of clearly delineated periods of firing, retinal ganglion cells fired spikes time-locked to the stimulus with a variability across trials as low as 1 ms. Spike count variance across trials was much lower than the mean and sometimes approached the minimum variance possible with discrete counts, inconsistent with Poisson statistics expected from independently generated spikes. Spike time and count variability decreased systematically with stimulus strength. These findings were consistent with a model in which firing probability was determined by a stimulus-driven free firing rate modulated by a recovery function representing the action potential absolute and relative refractory period.
Decoding Continuous and Discrete Motor Behaviors Using Motor and Premotor Cortical Ensembles
Authors: Hatsopoulos Nicholas , Joshi Jignesh , O'Leary John G.
Published: July 2004

Decoding motor behavior from neuronal signals has important implications for the development of a brain–machine interface (BMI) but also provides insights into the nature of different movement representations within cortical ensembles. Motor control can be hierarchically characterized as the selection and planning of discrete movement classes and/or postures followed by the execution of continuous limb trajectories. Based on simultaneous recordings in primary motor (MI) and dorsal premotor (PMd) cortices in behaving monkeys, we demonstrate that an MI ensemble can reconstruct hand or joint trajectory more accurately than an equally sized PMd ensemble. In contrast, PMd can more precisely predict the future occurrence of one of several discrete targets to be reached. This double dissociation suggests that a general-purpose BMI could take advantage of multiple cortical areas to control a wider variety of motor actions. These results also support the hierarchical view that MI ensembles are involved in lower-level movement execution, whereas PMd populations represent the early intention to move to visually presented targets.
An Lp − Lq version of Hardy′s theorem for spherical Fourier transform on semisimple Lie groups
Authors: Ben Farah S. , Mokni K. , Trimèche K.
Published: July 2004

We consider a real semisimple Lie group G with finite center and K a maximal compact subgroup of G. We prove an Lp − Lq version of Hardy′s theorem for the spherical Fourier transform on G. More precisely, let a, b be positive real numbers, 1 ≤ p, q ≤ ∞, and f a K‐bi‐invariant measurable function on G such that and (ha is the heat kernel on G). We establish that if ab ≥ 1/4 and p or q is finite, then f = 0 almost everywhere. If ab < 1/4, we prove that for all p, q, there are infinitely many nonzero functions f and if ab = 1/4 with p = q = ∞, we have f = const ha.
Double‐dual n‐types over Banach spaces not containing ℓ1
Authors: Pomper Markus
Published: July 2004

Let E be a Banach space. The concept of n‐type overE is introduced here, generalizing the concept of type overE introduced by Krivine and Maurey. Let E″ be the second dual of E and fix . The function τ : E × ℝn → ℝ, defined by letting for all x ∈ E and all a1, …, an ∈ ℝ, defines an n‐type over E. Types that can be represented in this way are called double‐dual n‐types; we say that realizes τ. Let E be a (not necessarily separable) Banach space that does not contain ℓ1. We study the set of elements of that realize a given double‐dual n‐type over E. We show that the set of realizations of this n‐type is convex. This generalizes a result of Haydon and Maurey who showed that the set of realizations of a given 1‐type over a separable Banach space E is convex. The proof makes use of Henson′s language for normed space structures and uses ideas from mathematical logic, most notably the Löwenheim‐Skolem theorem.
On the extendibility of the Diophantine triple {1, 5, c}
Authors: Abu Muriefah Fadwa S. , Al-Rashed Amal
Published: July 2004

We study the problem of extendibility of the triples of the form {1, 5, c}. We prove that if , where (sk) is a binary recursive sequence, k is a positive integer, and the statement that all solutions of a system of simultaneous Pellian equations z2 − ckx2 = ck − 1, 5z2 − cky2 = ck − 5 are given by (x, y, z) = (0, ±2, ±sk), is valid for 2 ≤ k ≤ 31, then it is valid for all positive integer k.
Ishikawa iterative sequence with errors for strongly pseudocontractive operators in arbitrary Banach spaces
Authors: Li Yongjin
Published: July 2004

The Ishikawa iterative sequences with errors are studied for Lipschitzian strongly pseudocontractive operators in arbitrary real Banach spaces; some well‐known results of Chidume (1998) and Zeng (2001) are generalized.
Product partitions and recursion formulae
Authors: Subbarao M. V.
Published: July 2004

Utilizing a method briefly hinted in the author′s paper written in 1991 jointly with V. C. Harris, we derive here a number of unpublished recursion formulae for a variety of product partition functions which we believe have not been considered before in the literature. These include the functions p*(n; k, h) (which stands for the number of product partitions of n > 1 into k parts of which h are distinct), and (which stands for the number of product partitions of n into exactly m parts with at most d repetitions of any part). We also derive recursion formulae for certain product partition functions without the use of generating functions.
Role of Endoscopic Ultrasound in the Diagnosis of Patients with Solid Pancreatic Masses
Authors: Kahl Stefan , Malfertheiner Peter
Published: July 2004

Endoscopic ultrasound (EUS) is the most sensitive imaging procedure for the detection of small solid pancreatic masses and is accurate in determining vascular invasion of the portal venous system. Even compared to the new CT techniques, EUS provides excellent results in preoperative staging of solid pancreatic tumors. Compared to helical CT techniques, EUS is less accurate in detecting tumor involvement of the superior mesenteric artery. EUS staging and EUS-guided FNA can be performed in a single-step procedure, to establish the diagnosis of cancer. There is no known negative impact of tumor cell seeding due to EUS-guided fine needle aspiration (FNA). Without FNA, EUS and additional methods are not able to reliably distinguish between inflammatory and malignant masses.