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PubMed2004

Hydrocarbon pollution fixed to combined sewer sediment: a case study in Paris.

Over a period of two years (2000-2001), sediment samples were extracted from 40 silt traps (STs) spread through the combined sewer system of Paris. All sediment samples were analysed for physico-chemical parameters (pH, organic matter content, grain size distribution), with total hydrocarbons (THs) and 16 polycyclic aromatic hydrocarbons (PAHs) selected from the priority list of the US-EPA. The two main objectives of the study were (1) to determine the hydrocarbon contamination levels in the sediments of the Paris combined sewer system and (2) to investigate the PAH fingerprints in order to assess their spatial variability and to elucidate the PAH origins. The results show that there is some important inter-site and intra-site variations in hydrocarbon contents. Despite this variability, TH and PAH contamination levels (50th percentile) in the Parisian sewer sediment are estimated at 530 and 18 microg g(-1), respectively. The investigation of the aromatic compound distributions in all of the 40 STs has underlined that there is, at the Paris sewer system scale, a homogeneous PAH background pollution. Moreover, the study of the PAH fingerprints, using specific ratios, suggests the predominance of a pyrolytic origin for those PAHs fixed to the sewer sediment.

Cities↗
PubMed2003

[Streptococcus pneumoniae transmission in a nursing home: analysis of an epidemic outbreak].

BACKGROUND AND OBJECTIVE: On the basis of an outbreak of pneumococcal pneumonia in a nursing home, we analyze causes and patterns of transmission and discuss preventive interventions carried out on the target population. PATIENTS AND METHOD: A retrospective cohort study was designed on 232 residents to identify risk factors associated with the outbreak. A descriptive study of those nasopharyngeal carriers of pneumococcus among nursing home workers was also carried out. RESULTS: Twenty cases of pneumococcal pneumonia were detected with 4 deaths; 13 cases were confirmed. Cases occurred on a close temporal aggregation form but they were quite disseminated spatially. Among the factors investigated, an older age was the only factor significantly associated (p = 0.02) with the risk of disease. In 4 workers, strains of Streptococcus pneumoniae were isolated from nasopharyngeal swabs; two of them corresponded to the serotype 3, as it was the strain isolated from the blood of a nursing home case. The number of new cases decreased dramatically after vaccination and/or chemoprophylaxis. CONCLUSIONS: Vaccination and chemoprophylaxis administered to nursing home residents seemed effective measures to halt the spread of this outbreak. Detection of the S. pneumoniae antigen by immunochromatographic tests in urine samples is a valuable tool for detecting an outbreak.

Aged↗
PubMed2002

Toward automated quality assurance for intensity- modulated radiation therapy.

PURPOSE: To investigate whether high-quality, relatively inexpensive, document and transparency scanners used as densitometers are sufficiently quantitative for routine quality assurance (QA). METHODS AND MATERIALS: The scanner we investigated used a linear amplifier, digitizing gray-scale images to 12-bit resolution with a user-selected spatial resolution of 0.170 mm(2) pixels. To reduce Newton's rings artifacts, the standard glass platen was replaced by glass with an antireflective coating. Conversion of reading to transmission was conducted by permanently placing a calibrated photographic step tablet on the scanner platen. After conversion to light transmission, a zero-phase two-dimensional Wiener filter was used to reduce pixel-to-pixel signal variation. Light-scatter artifacts were removed by deconvolution of a measured light-spread kernel. The light-spread kernel artifacts were significant along the scanner's detector axis, but were insignificant along the scanning axis. RESULTS: Pixel-to-pixel noise was better than 2% for optical densities, ranging from 0.4 to 2.0 and 0 to 2.7 for the unfiltered and filtered images, respectively. The document scanning system response was compared against a confocal scanning laser densitometer. A series of IMRT dose distribution and dose calibration film sets were scanned using the two scanners, and the measured dose was compared. The maximum mean and standard deviation of the measured dose difference between the document scanner and confocal scanner was 1.48% and 1.06%, respectively. CONCLUSION: While the document scanners are not as flexible as dedicated film densitometers, these results indicate that, using the intensity and scatter corrections, the system provides accurate and precise measurements up to an optical density of 2.0, sufficient for routine IMRT film QA. For some film types, this requires the reduction in monitor units to limit the dose delivered to the film. The user must be cautious that the delivered IMRT dose is scaled appropriately. This inexpensive and accurate system is being integrated into an automated QA program.

Artifacts↗
PubMed2006

Interactions between environment, species traits, and human uses describe patterns of plant invasions.

Although invasive alien species (IAS) are a major threat to biodiversity, human health, and economy, our understanding of the factors controlling their distribution and abundance is limited. Here, we determine how environmental factors, land use, life-history traits of the invaders, residence time, origin, and human usage interact to shape the spatial pattern of invasive alien plant species in South Africa. Relationships between the environmental factors and the extrinsic and intrinsic attributes of species were investigated using RLQ analysis, a multivariate method for relating a species-attribute table to an environmental table by way of a species presence/absence table. We then clustered species according to their position on the RLQ axes, and tested these groups for phylogenetic independence. The first three axes of the RLQ explained 99% of the variation and were strongly related to the species attributes. The clustering showed that, after accounting for environmental factors, the spatial pattern of IAS in South Africa was driven by human uses, life forms, and reproductive traits. The seven clusters of species strongly reflected geographical distribution, but also intrinsic species attributes and patterns of human use. Two of the clusters, centered on the genera Acacia and Opuntia, were phylogenetically non-independent. The remaining clusters comprised species of diverse taxonomic affinities, but sharing traits facilitating invasion in particular habitats. This information is useful for assessing the extent to which the potential spread of recent introductions can be predicted by considering the interaction of their biological attributes, region of origin, and human use.

Agriculture↗
PubMed1997

Termination of epileptic afterdischarge in the hippocampus.

The mechanism of afterdischarge termination in the various hippocampal regions was examined in the rat. Stimulation of the perforant path or the commissural system was used to elicit afterdischarges. Combination of multiple site recordings with silicon probes, current source density analysis, and unit recordings in the awake animal allowed for a high spatial resolution of the field events. Interpretation of the field observations was aided by intracellular recordings from anesthetized rats. Irrespective of the evoking conditions, afterdischarges always terminated first in the CA1 region. Termination of the afterdischarge was heralded by a large DC shift initiated in dendritic layers associated with a low amplitude "afterdischarge termination oscillation" (ATO) at 40 to 80 Hz in the cell body layer. ATOs were also observed in the CA3 region and the dentate gyrus. The DC shift spread at the same velocity (0. 1-0.2 mm/sec) in all directions and could cross the hippocampal fissure. All but 1 of the 25 putative interneurons in the CA1 and dentate regions ceased to fire before the onset of ATO. Intracellularly, ATO and the emerging DC potential were associated with fast depolarizing potentials and firing of pyramidal cells and depolarization block of spike initiation, respectively. Both field ATO and the intracellular depolarization shift were replicated by focal microinjection of potassium. We hypothesize that [K+]o lost by the intensely discharging neurons during the afterdischarge triggers propagating waves of depolarization in the astrocytic network. In turn, astrocytes release potassium, which induces a depolarization block of spike generation in neurons, resulting in "postictal depression" of the EEG.

Animals↗
PubMed2006

Physiological studies of cortical spreading depression.

Cortical spreading depression (CSD) produces propagating waves of transient neuronal hyperexcitability followed by depression. CSD is initiated by K+ release following neuronal firing or electrical, mechanical or chemical stimuli. A triphasic (30-50 s) cortical potential transient accompanies localized transmembrane redistributions of K+, glutamate, Ca2+, Na+, Cl- and H+. Accumulated K+ in the restricted interstitial space can cause both further neuronal depolarisation and inward movement of K+ into astrocytes that buffers this increased extracellular K+ concentration ([K+])o. However, astrocyte interconnections may then propagate the CSD wave by K+ liberation through an opening of remote K+ channels by volume, Ca2+ or N-methyl-D-aspartate receptor activation. Changes in cerebral blood volume and in apparent water diffusion co-efficient (ADC) accompanying CSD were first studied using magnetic resonance imaging (MRI) in whole lissencephalic brains. Diffusion-weighted echoplanar imaging in gyrencephalic brains went on to demonstrate CSD features that paralleled classical migraine aura. The ADC activity persisted minutes/hours post KCl stimulus. Pixelwise analyses distinguished single primary events and multiple, spatially restricted, slower propagating, secondary events whose detailed features varied with the nature of the originating stimulus. These ADC changes varied reciprocally with T2*-weighted (i.e. referring to spin-spin relaxation times) waveforms reflecting local blood flow. There followed prolonged decreases in cerebral blood flow culminating in late cerebrovascular changes blocked by the antimigraine agent sumatriptan. CSD phenomena have possible translational significance for human migraine aura and other cerebral pathologies such as the peri-infarct depolarisation events that follow ischaemia and brain injury.

Animals↗
PubMed1995

Saccade-related activity in monkey superior colliculus. II. Spread of activity during saccades.

1. In the companion paper we described two classes of cells in the monkey superior colliculus (SC) that were related to saccade generation, buildup cells and burst cells, which fell into two functional sublayers within the intermediate layers of the SC. Fixation cells in the rostral SC were deemed to be part of the buildup cell layer. The buildup cells had several characteristics in common with cells in the cat described as having a "hill of activity" moving across the SC, but the burst cells had no such characteristics. In this paper we further investigate whether there is evidence for such a moving hill of activity in the monkey by analyzing the spatial and temporal activity of cells across the SC during the generation of visually guided saccades. 2. We recorded the activity of single cells while the monkey made saccades of different amplitudes (0.5-60 degrees). We recorded cells from locations extending from the rostral to caudal SC in order to sample cells whose optimal amplitudes ranged from small to large saccades. This allowed us to see any shift of activity across the SC before, during, and after saccades. It also allowed us to determine the fraction of the SC that was active during the successive phases of saccade generation. 3. During active visual fixation, the fixation cells in the rostral pole of the buildup layer showed an increased discharge rate. From the population reconstruction, we estimate that the zone of active cells spanned the most rostral 0.72 mm in each SC. Assuming the SC is 5 mm in length, approximately 15% of the cells lying along the horizontal meridian in the buildup layer would be active during fixation. 4. At least 100 ms before the initiation of a saccade, long-lead activity began to appear in the buildup layer at the site on the SC motor map related to the next saccade. Fixation activity in the rostral poles simultaneously began to diminish, but the cells in the burst layer remained relatively silent. 5. Approximately 25 ms before saccade onset, the fixation cells ceased firing and both burst and buildup cells began to burst. The active zone in the burst layer was estimated to be approximately 1.4 mm diam, occupying roughly 28% of the SC along a line running from the rostral pole through the center of the initially active zone. The size of this active area among the burst cells was independent of saccade amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Development of the visual system of the chick. II. Mechanisms of axonal guidance.

The quest to understand axonal guidance mechanisms requires exact and multidisciplinary analyses of axon navigation. This review is the second part of an attempt to synthesise experimental data with theoretical models of the development of the topographic connection of the chick retina with the tectum. The first part included classic ideas from developmental biology and recent achievements on the molecular level in understanding cytodifferentiation and histogenesis [J. Mey, S. Thanos, Development of the visual system of the chick. (I) Cell differentiation and histogenesis, Brain Res. Rev. 32 (2000) 343-379]. The present part deals with the question of how millions of fibres exit from the eye, traverse over several millimetres and spread over the optic tectum to assemble a topographic map, whose precision accounts for the sensory performance of the visual system. The following topics gained special attention in this review. (i) A remarkable conceptual continuity between classic embryology and recent molecular biology has revealed that positional cellular specification precedes and determines the formation of the retinotectal map. (ii) Graded expression of asymmetric genes, transcriptional factors and receptors for signal transduction during early development seem to play a crucial role in determining the spatial identity of neurons within surface areas of retina and optic tectum. (iii) The chemoaffinity hypothesis constitutes the conceptual framework for development of the retinotopic organisation of the primary visual pathway. Studies of repulsive factors in vitro developed the original hypothesis from a theoretical postulate of chemoattraction to an empirically supported concept based on chemorepulsion. (iv) The independent but synchronous development of retina and optic tectum in topo-chronologically corresponding patterns ensures that ingrowing retinal axons encounter receptive target tissue at appropriate locations, and at the time when connections are due to be formed. (v) The growth cones of the retino-fugal axons seem to be guided both by local cues on glial endfeet and within the extracellular matrix. On the molecular level, the ephrins and their receptors have emerged as the most likely candidates for the material substrate of a topographic projection along the anterior-posterior axis of the optic tectum. Yet, since a number of alternative molecules have been proposed for the same function, it remains the challenge for the near future to define the proportional contribution of each one of the individual mechanisms proposed by matching theoretical predictions with the experimental evidence.

Animals↗
PubMed1980

Design of a high resolution positron emission tomograph: the Neuro-PET.

The design of a high resolution positron emission tomograph is described. The scanner has four rings of detectors with an inside diameter of 38 cm and produces seven simultaneous slices, including three cross-slices. Each ring contains 128 bismuth germanate scintillation detectors with dimensions of 8.25 x 20 x 35 mm; adjacent crystals are separated by tapered tungsten septa that extend to within 7.5 mm of the front faces. The anticipated geometrical spatial resolution of the scanner is 4.5 mm full width at half maximum (FWHM) at the center of the image, and the sensitivity is 44,000 true counts/sec/ring (390,000 counts/sec total) for a uniform phantom 20 cm in diameter containing 1 muCi/cc activity. There are interchangeable collimators for use in high count rate studies, for narrowing the slice width from 1 cm FWHM to 5 mm FWHM, and for ultra-high resolution studies with a 2.5 mm FWHM geometrical point spread function. The electronic circuitry has separate timing and energy verification channels and can detect 95% of the coincidences with a timing window (twice the maximum time between two coincident pulses) of 14 nsec. The count rate capability of the electronics is 150,000 counts/sec/ring and 1.5 million counts/sec total.

Bismuth↗
PubMed2006

The neural site of attention matches the spatial scale of perception.

What is the neural locus of visual attention? Here we show that the locus is not fixed but instead changes rapidly to match the spatial scale of task-relevant information in the current scene. To accomplish this, we obtained electrical, magnetic, and hemodynamic measures of attention from human subjects while they detected large-scale or small-scale targets within multiscale stimulus patterns. Subjects did not know the scale of the target before stimulus onset, and yet the neural locus of attention-related activity between 250 and 300 ms varied according to the scale of the target. Specifically, maximal attention-related activity spread from a high-level, relatively anterior visual area (the lateral occipital complex) for large-scale targets to include a lower-level, more posterior area (visual area V4) for small-scale targets. This rapid change indicates that the neural locus of attention in visual cortex is not static but is instead determined rapidly and dynamically by means of an interaction between top-down task information and local information about the current visual input.

Adult↗
PubMed1993

Is filaggrin really a filament-aggregating protein in vivo?

Filaggrin, a basic protein of the stratum corneum, was named as such because of its capability to aggregate keratin intermediate filaments in vitro. To investigate its filament-aggregating capability in vivo, we performed immunoelectron microscopy in three autosomal dominant genodermatoses serving as in vivo models of abnormalities of keratin filament aggregation. In bullous congenital ichthyosiform erythroderma Brocq and epidermolytic palmoplantar keratoderma Voerner suprabasal clumping of keratin filaments prevents the normal spreading of keratohyalin between keratin filaments. Keratohyalin granules, either isolated or attached to clumped keratins, were specifically labelled by the anti-filaggrin antibody, whereas tonofilament clumps did not show any reaction. In epidermolysis bullosa herpetiformis Dowling-Meara the abnormal filament aggregation occurred in basal cell keratins where no reaction of the anti-filaggrin antibody was detected. In high level keratinocytes with normal distribution of tonofilaments, normal stellate keratohyalin reacted specifically. In all instances keratin filament clumping occurred independently of, and spatially separated from, the first signs of profilaggrin synthesis and keratohyalin granule formation. Thus, in these disorders, filaggrin is not involved in filament aggregation.

Adult↗
PubMed2003

Modelling pathogen transmission: the interrelationship between local and global approaches.

We describe two spatial (cellular automaton) host-pathogen models with contrasting types of transmission, where the biologically realistic transmission mechanisms are based entirely on 'local' interactions. The two models, fixed contact area (FCA) and fixed contact number (FCN), may be viewed as local 'equivalents' of commonly used global density- (and frequency-) dependent models. Their outputs are compared with each other and with the patterns generated by these global terms. In the FCN model, unoccupied cells are bypassed, but in the FCA model these impede pathogen spread, extending the period of the epidemic and reducing the prevalence of infection when the pathogen persists. Crucially, generalized linear modelling reveals that the global transmission terms betaSI and beta'SI/N are equally good at describing transmission in both the FCA and FCN models when infected individuals are homogeneously distributed and N is approximately constant, as at the quasi-equilibrium. However, when N varies, the global frequency-dependent term beta'SI/N is better than the density-dependent one, betaSI, at describing transmission in both the FCA and FCN models. Our approach may be used more generally to compare different local contact structures and select the most appropriate global transmission term.

Animals↗
PubMedDate not supplied

Describing the signal-transfer characteristics of asymmetrical radiographic screen-film systems.

The measurement of modulation transfer function for radiographic screen-film systems depends critically upon a proper linearization of the measured line spread function. This is normally done by photographic photometry (i.e., using the measured density versus log exposure relationship to transform the density line spread function into an exposure line spread function). It has been long appreciated that this procedure may fail for asymmetrical dual screen systems that use film with emulsion coated on both sides of the support. The advent of asymmetrical and near-zero crossover films that can be used with highly asymmetric screen pairs has prompted a reinvestigation of these concerns about the definition and measurement of modulation transfer function. For such cases, it is useful to define the contrast transfer function, which is a function of exposure and spatial frequency. When normalized by its zero frequency value the contrast transfer function can serve as the "effective MTF" for low-contrast input signals in such systems. In the limit of symmetrical systems this quantity approaches the conventionally measured MTF. The utility of this approach is demonstrated by applying it to a commercially available asymmetrical screen-film combination.

Emulsions↗
PubMed2003

Properties of saccadic responses in monkey when multiple competing visual stimuli are present.

Important insights into the neural organization of the saccadic system have been gained when the usually stereotyped movement trajectories of saccades have been altered by experimental manipulation. In the present study we produced trajectory variability in monkeys by using a visual search task in which both the location and color of an odd-colored target were changed randomly trial by trial, and the number of distractors was varied on each trial. We wished to determine whether increasing the number of distractors also increased the movement trajectory variation, i.e., the amount of initial directional deviation, endpoint deviation (averaging), and curvature of saccades. Overall, saccade latencies and the proportion of saccades directed to distractors decreased as the number of homogenous distractors increased. We also found that saccades have much more dispersion in their initial direction when distractors are present in comparison to the case when only a single target without distractors appears. However, initial dispersion decreases systematically as the number of distractors increases. The percentage of averaging saccades produced in the search task was not consistently dependent on the number of distractors. A significant fraction of averaging saccades still occurred for much wider spatial separations of stimuli than in previous studies using two visual stimuli with no specified target. The curvature of saccade trajectories increased dramatically when distractors were present, but the amount of curvature was not systematically affected by the number of distractors. Errors present in saccade trajectory in the search task were only poorly compensated. We conclude that these variable saccade trajectories result from incomplete or inaccurate specification of the target when competing stimuli are present and that a smaller number of more widely spread distractors facilitate saccade variability, perhaps due to the greater difficulty of target selection.

Animals↗
PubMed1999

Spatiotemporal organization of fast (>200 Hz) electrical oscillations in rat Vibrissa/Barrel cortex.

A 64-channel electrode array was used to study the spatial and temporal characteristics of fast (>200 Hz) electrical oscillations recorded from the surface of rat cortex in both awake and anesthetized animals. Transient vibrissal displacements were effective in evoking oscillatory responses in the vibrissa/barrel field and were tightly time-locked to stimulus onset, coinciding with the earliest temporal components of the coincident slow-wave response. Vibrissa-evoked fast oscillations exhibited modality specificity and were earliest and of largest amplitude over the cortical barrel, which corresponded to the vibrissa stimulated, spreading to sequentially engage neighboring barrels over subsequent oscillatory cycles. The response was enhanced after paired-vibrissal stimulation and was sensitive to time delays between movement of separate vibrissae. These data suggest that spatiotemporal interactions between fast oscillatory bursts in the barrel field may play a role in rapidly integrating information from the vibrissal array during the earliest cortical response to somatosensory stimulation.

Animals↗
PubMed2004

Spatial mapping of collagen fibril organisation in primate cornea-an X-ray diffraction investigation.

New insights are presented into the collagenous structure of the primate cornea. Wide-angle X-ray diffraction was used to map the fibrillar arrangement and distribution of collagen over three common marmoset corneas. The maps provide a point of reference to help interpret data from pathological corneas or primate models of refractive surgery. The results herein disclose a circum-corneal annulus of highly aligned collagen, 0.5-1.5 mm wide, where the cornea and sclera fuse at the limbus; a feature similar to that observed in human tissue. As in humans, the annulus is not uniform, varying in width, fibril angular spread, and collagen density around its circumference. However, more centrally the marmoset cornea exhibits a preferred lamella orientation in which proportionally more fibrils are oriented along the superior-inferior corneal meridian. This observation is in striking contrast with the situation in human cornea, where there is an orthogonal arrangement of preferentially aligned fibrils. Investigation of a further 16 corneas confirmed that approximately 33% (+/-1%) (n = 76) of fibrils in the central marmoset cornea lie within a 45 degrees sector of the superior-inferior meridian. Implications for the mechanical and optical properties of the cornea are discussed.

Age Factors↗
PubMed2000

Spatiotemporal dynamics of fibrin formation and spreading of active thrombin entering non-recalcified plasma by diffusion.

The spatiotemporal dynamics of clot growth was studied in non-stirred non-recalcified plasma where thrombin entered by diffusion. Under these conditions, the clot rapidly grew for 30-45 min and then stopped growing on reaching 0.4-0.5 mm in size. The dynamics of clot growth and its size almost did not depend on the thrombin concentration in the range from 50 to 400 nM. FITC-thrombin was shown to permeate the growing clot. The clot size in antithrombin-deficient plasma increases with decreasing antithrombin concentration, being 1.5 mm in the plasma depleted of antithrombin to 5% of its initial level. The data on the spatial distribution of amidolytic activity in the growth zone of the clot suggested that thrombin was not the sole source of this activity. Analysis showed that this additional activity arising during thrombin diffusion into plasma was largely accounted for by thrombin-alpha(2)-macroglobulin complex.

Antithrombins↗
PubMed1998

Subcellular and subsynaptic distribution of the NR1 subunit of the NMDA receptor in the neostriatum and globus pallidus of the rat: co-localization at synapses with the GluR2/3 subunit of the AMPA receptor.

Glutamatergic neurotransmission in the neostriatum and the globus pallidus is mediated through NMDA-type as well as other glutamate receptors and is critical in the expression of basal ganglia function. In order to characterize the cellular, subcellular and subsynaptic localization of NMDA receptors in the neostriatum and globus pallidus, multiple immunocytochemical techniques were applied using antibodies that recognize the NR1 subunit of the NMDA receptor. In order to determine the spatial relationship between NMDA receptors and AMPA receptors, double labelling was performed with the NR1 antibodies and an antibody that recognizes the GluR2 and 3 subunits of the AMPA receptor. In the neostriatum all neurons with characteristics of spiny projection neurons, some interneurons and many dendrites and spines were immunoreactive for NR1. In the globus pallidus most perikarya and many dendritic processes were immunopositive. Immunogold methods revealed that most NR1 labelling is associated with asymmetrical synapses and, like the labelling for GluR2/3, is evenly spread across the synapse. Double immunolabelling revealed that in neostriatum, over 80% of NR1-positive axospinous synapses are also positive for GluR2/3. In the globus pallidus most NR1-positive synapses are positive for GluR2/3. In both regions many synapses labelled only for GluR2/3 were also detected. These results, together with previous data, suggest that NMDA and AMPA receptor subunits are expressed by the same neurons in the neostriatum and globus pallidus and that NMDA and AMPA receptors are, at least in part, colocalized at individual asymmetrical synapses. The synaptic responses to glutamate in these regions are thus likely be mediated by both AMPA and NMDA receptors at the level of individual synapses.

Animals↗