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Results for “Spatial Distribution”

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At least 145 records · Page 8Linked to original sources

PubMed1984

The macular pigment. II. Spatial distribution in primate retinas.

The spatial density distribution of macular pigment in primate retinas was described by two-wavelength microdensitometry of retinal sections. The macular pigment is most dense along the path of the receptor axons in the center of the fovea. Another band of high density is present in the inner plexiform layer in many retinas. The density in both fiber layers declines to low, relatively constant levels within 1 mm eccentricity. Both the total retinal density of macular pigment and the contributions of subsets of the retinal layers were estimated by integrating along the path of light traversing the retina from the vitreal surface to the outer segments. The integrated densities were measured at several eccentricities to establish the profile of macular pigment density along a diameter through the fovea. The macular pigment profile was unimodal in some cases and trimodal in others. The main central peak always occurred in the center of the fovea. The total retinal density of the central peak ranged from 0.42-1.0 absorbance. Most of the pigment is interposed between the outer segments and the stimulating light and is effective as a visual filter. The macular pigment is dichroic, with the major axis of absorption oriented tangential to a circle centered on the fovea. This is consistent with commonly accepted explanations of Haidinger 's brushes.

Animals↗

PubMed2006

[Three-dimensional spatial distribution patterns of Monochamus alternatus and its natural enemy Dastarcus helophoroides].

In 2003 to approximately 2005, the Monochamus alternatus-infected Pinus thunbergii, P. massoniana and P. elliotii in pure and mixed forests were selected as attractants and dissected with one meter section manner, and five aggregation indices were used to analyze the spatial distribution patterns of M. alternatus and its natural enemy Dastarcus helophoroides. The results showed that M. alternatus and D. helophoroides had the horizontal distribution indices of diffused coefficient C > 1, diffused index I delta > 1, Kuno index C(A) > 0, clump intensity index I > 1, and swarm index Iw > 1 in the two stands, suggesting their aggregated horizontal distribution patterns, and except D. helophoroides on the P. massoniana in mixed forest appeared assemble vertical distribution, these two insects all had an even vertical distribution, with their C < 1, I delta < 1, C(A) < 0, Iw < 1, and I < 0. The spatial distribution patterns of M. alternatus and D. helophoroides were consistent, and the latter was spatially following the former.

Animals↗

PubMed1991

Automated cytometry of muscle fibre sections: size and spatial distribution of the four fibre types in young and adult rats.

An automated cytometry program was applied to the extensor digitorum longus muscle of young and adult rats. Lesser diameter and spatial distribution of about 4000 fibres were measured in digital images from ATPase-stained muscle sections. All fibre types grow thicker with age, but the coefficient of variation of the diameter is age-independent. At both ages, 2B fibres have the largest mean diameter and are most frequent. 2A fibres in young rats present a diameter smaller or equal to type 1 but then show a faster increase in size; their relative number increases from 20 to 28%. Consequently type 2A displays the most important change with age. The spatial distribution of fibres is mathematically expressed; most images show a random distribution of type 1 and type 2 fibres. Taking into account the variation of fibre size of each type, the number of fibres which should be measured in order to reach a specified precision was calculated.

Analysis of Variance↗

PubMed2001

Life history and spatial distribution of the enchytraeid worm Cognettia sphagnetorum (Oligochaeta) in metal-polluted soil: below-ground sink-source population dynamics?

We studied the life history, metal-avoidance behavior, spatial distribution, and population growth of enchytraeid worms (Cognettia sphagnetorum [Oligochaeta]) originating from two sites: one uncontaminated, and another patchily polluted by heavy metals. Effects of patchy soil contamination on populations were studied in microcosms. In uncontaminated soil, worms from the polluted site had lower viability and reduced growth rate as juveniles but higher growth rate as adults compared to worms from the unpolluted site. They were also smaller in size at fragmentation (reproduction). Worms from the polluted site reached a larger population size than worms from the unpolluted site. Hence, worms from the polluted site seemed to allocate more energy to reproduction, because such a strategy can be highly adaptive when living in a less-polluted patch (the source) in, on average, a highly polluted environment. The C. sphagnetorum actively avoided Cu-contaminated soil, with the response being stronger in individuals from the contaminated site. When an unpolluted patch (the source) was surrounded by a toxic environment (the sink), worms were found in the sink, either because intraspecific competition overrode the avoidance behavior or because of random walk migration. As a result, total population size in these microcosms were as high as those in totally uncontaminated microcosms. Our results indicate that avoidance behavior and increased allocation to reproduction, together with the observed dispersal pattern, can be an adaptive strategy for C. sphagnetorum in the presence of small, less-polluted patches in, on average, a hostile environment. Hence, sink-source population regulation can explain spatial distribution and survival of C. sphagnetorum in patchily polluted field soils. When such population dynamics occur, this pattern should be taken into account when population densities in the field are monitored for ecological risk-assessment procedures concerning toxicants.

Adaptation, Physiological↗

PubMed1997

Spatial distribution of cytoskeleton intermediate filaments during fetal rat hepatocyte differentiation.

The construction of the liver parenchyma throughout fetal development depends on the elaboration of intercellular contacts between epithelial cells and between epithelial and mesenchymal cells. During this time, the spatial distribution of cytokeratins in hepatocytes shows a striking evolution as demonstrated by confocal microscopy and image analysis. In the early stages of fetal rat development, the liver is mainly a hematopoietic organ and hepatocytes represent fewer than 40% of all liver cells. At this time, cytokeratin filaments are scarce and are randomly distributed inside the cytoplasm. A coexpression of desmin and cytokeratin is found in some cells. Intercellular contacts between epithelial and mesenchymal cells are more numerous than between epithelial cells. Later in development, hepatocytes are arranged in a "muralium duplex" architecture (two-cell-thick sheets). Contacts between hepatocytes become more numerous and bile canaliculi become well developed. The density of cytokeratin filaments increases and appears to be very high near the bile canaliculi. In adult liver, hepatocytes are arranged in a "muralium simplex" architecture. Cytokeratin filaments show a symmetrical distribution in relation to the nuclear region. The highest density of filaments is found near the cytoplasmic membrane. Variations of the spatial distribution of intermediate filaments throughout hepatocyte differentiation were investigated in a pilot study using computerized image analysis. We found significant differences between the filament networks in fetal and adult hepatocytes.

Animals↗

PubMed2005

Femoral neck shape and the spatial distribution of its mineral mass varies with its size: Clinical and biomechanical implications.

The femoral neck (FN) is a cantilever with external and internal dimensions determining its size, shape, the spatial distribution of the mineralized cortical and trabecular bone tissue mass, and its strength. Geometric indices of FN strength are often derived using FN dimensions estimated in vivo from dual X-ray absorptiometry (DXA) assuming that the FN cross section approximates a circle or a square. As DXA does not measure FN depth, we examined whether circular, square, or elliptical models of FN cross sections predict FN depth, and so its external volume, shape, volumetric bone mineral density (vBMD), and geometric indices of strength. We studied paired FN specimens from 13 Caucasian female cadavers (mean age 69 years, range 29 to 85) using DXA, micro-computed tomography (mu-CT), and direct calliper measurements. DXA accurately measured FN width (supero-inferior diameter) but models assuming a circular and a square cross section overestimated FN depth (antero-posterior diameter) and volume, and so underestimated vBMD by 15.0 +/- 5.8% (circular cross section) and by 33.2 +/- 4.6% (square cross section) (both P < 0.05). As depth was less than the width, an elliptical model with a constant depth/width ratio of 0.75 reduced the accuracy error in vBMD to 14.0 +/- 8.5% (P = 0.10). However, as FN width increased, FN depth increased relatively less. An elliptical model using a quadratic equation to mimic this changing in shape with increasing size reduced the error in vBMD to 4.4 +/- 7.7% (NS). Circular cross-section models overestimated section modulus at the mid-FN by about 51%. The elliptical models reduced the error two- to three fold. Images from micro-CT scanning show that the FN cross-sectional shape resembles an ellipse with the long axis and the maximum moment of inertia (I(max)) oriented in the supero-inferior direction, and the cortical mass concentrated inferiorly. The larger the cross section, the more elliptical the shape, and the greater the I(max) supero-inferiorly, while I(min) (in the antero-posterior direction) remains relatively constant. The shape, spatial distribution of bone, and moments of inertia are likely to be adaptations to bending moments during bipedalism. Assuming the FN cross section approximates a circle or square produces errors in FN depth, volume, vBMD, and geometric indices of bone strength. Studies are needed to determine the effects of age, sex, and race on FN size and shape in health and disease.

Absorptiometry, Photon↗

PubMed1997

Imaging of axonal damage in multiple sclerosis: spatial distribution of magnetic resonance imaging lesions.

We performed magnetic resonance imaging and magnetic resonance spectroscopic imaging on 28 patients with multiple sclerosis stratified for disability and clinical course (relapsing with at least partial remissions or secondary progressive disease). Lesions were segmented on the conventional proton density and T2-weighted magnetic resonance images, and lesion distribution images were generated for, each patient. The conventional magnetic resonance and spectroscopic images were transformed into a standard brain-based stereotaxic coordinate space, allowing comparison of images from different patients on a voxel-by-voxel basis. The spatial distribution of lesions in the transformed magnetic resonance images did not differ significantly between the relapsing and the progressive disease groups. We then generated from the individual data sets, group lesion probability distribution images for the relapsing and the progressive disease groups. The spatial distribution of metabolites was characterized with respect to lesion distribution using the magnetic resonance spectroscopic images transformed into stereotaxic space and averaged. The neuronal marker N-acetylaspartate was diffusely lower in the multiple sclerosis patients than in normal control subjects. Comparison of the averaged metabolite and T2-weighted lesion probability images confirmed loss of N-acetylaspartate in regions of both high and low lesion probability. This suggests that diffuse axonal volume loss or dysfunction extends beyond the inflammatory lesions of multiple sclerosis, perhaps due to microscopic disease or wallerian degeneration along projection pathways of axons traversing the lesions.

Adult↗

PubMed1993

The spatial distribution of spindle microtubules in anaphase 3Y1 cells.

The spatial distribution of the microtubules (MT) in the rat 3Y1 cells in mitosis was investigated by immunoelectron microscopy and computer-graphic reconstruction of serial thin sections. In anaphase the interzone-MT increased in number gradually with advancing phase, while the kinetochore-MT in half-spindles decreased. The interzone-MT overlapped with each other at the equatorial region of the cell, and they formed a specific structure called the 'stem bodies'. The ends of the interzone-MT opposite to the stem bodies often attached to chromosomes but not to the poles. The stem bodies were not labeled with immunogold particles of anti-alpha tubulin. Some of the stem bodies or MT which originate from stem bodies were found just beneath the plasma membrane in the equatorial region where abundant actin filaments appear showing the formation of the contractile ring and subsequently the cleavage furrow begins. On the basis of these observations it is assumed that the interzone-MT is involved both in the separation of chromosomes in anaphase and in the formation of the cleavage furrow in telophase.

Anaphase↗

PubMed2001

Modelling the spatial distribution of SO2 and NOx emissions in Ireland.

The spatial distributions of sulphur dioxide (SO2) and nitrogen oxides (NOx) emissions are essential inputs to models of atmospheric transport and deposition. Information of this type is required for international negotiations on emission reduction through the critical load approach. High-resolution emission maps for the Republic of Ireland have been created using emission totals and a geographical information system, supported by surrogate statistics and landcover information. Data have been subsequently allocated to the EMEP 50 x 50-km grid, used in long-range transport models for the investigation of transboundary air pollution. Approximately two-thirds of SO2 emissions in Ireland emanate from two grid-squares. Over 50% of total SO2 emissions originate from one grid-square in the west of Ireland, where the largest point sources of SO2 are located. Approximately 15% of the total SO2 emissions originate from the grid-square containing Dublin. SO2 emission densities for the remaining areas are very low, < 1 t km-2 year-1 for most grid-squares. NOx emissions show a very similar distribution pattern. However, NOx emissions are more evenly spread over the country, as about 40% of total NOx emissions originate from road transport.

Air Movements↗

PubMed2005

Simulation of dendritic CaV1.3 channels in cat lumbar motoneurons: spatial distribution.

We used computer simulations to study the dendritic spatial distribution of low voltage-activated L-type calcium (Ca(V)1.3 type) channels, which mediate hysteretic persistent inward current (PIC) in spinal motoneurons. This study was prompted by the growing experimental evidence of the functional interactions between synaptic inputs and active conductances over the motoneuron dendritic tree. A compartmental cable model of an adult cat alpha-motoneuron was developed in NEURON simulation environment constituting the detailed morphology of type-identified triceps surae alpha-motoneuron and realistic distribution of group Ia afferent-to-motoneuron contacts. Simulations of different distributions of Ca(V)1.3 channels were conducted and the resultant behavior was compared to experimental data. Our results suggest that Ca(V)1.3 channels do not uniformly cover the whole motoneuron dendritic tree. Instead, their distribution is similar to that of synaptic contacts. We found that Ca(V)1.3 channels are primarily localized to a wide intermediate band overlapping with the dendritic Ia-synaptic territory at dendritic distances of 300 to 850 microm (0.62 +/- 0.21lambda) from the soma in triceps surae alpha-motoneurons. These findings explain the functional interaction between synaptic inputs and the Ca(V)1.3 channels over the motoneuron dendritic tree.

Animals↗

PubMed2002

[Sensitivity and parameters of the otolith as a spatially distributed system].

Comparison of the de Vries pendulum and spatially distributed otolith models allowed physical interpretation of the pendulum model parameters and determination of the influence of otolith structure on its mechanical sensitivity when otolith dynamics is represented by a parallel displacement relative to the receptor surface. Proof was obtained that in this case otolith dynamics is independent of total mass, and mechanic sensitivity is not proportional to size of the organ. Possible explanations of the effects of changed dynamics conditions on otolith parameters in the fish are discussed.

Animals↗

PubMed2003

[Influence of external electric current on the spatial distributions of porosity and fractional dimension of biofilms].

The spatial distributions of porosity and fractional dimension of autotrophic and heterotrophic/autotrophic biofilms applied by direct current in the range of 0-25 A/m2 were investigated by using the micro-slicing technique and image analysis. The results showed that the porosities of the autotrophic and heterotrophic/autotrophic biofilms respectively decreased from ca. 92% and 96% in the top layer to ca. 54% in the bottom layer while the fractional dimensions increased from 1.1 and 1.05 in the top layer to 1.4 in the bottom layer in the absence of current. The increase in the current density decreased the porosities and increased the fractional dimensions in the top layers. In the deeper layers, the current had insignificant influence on the porosity and fractional dimension.

Biofilms↗

PubMed2004

Determining drug spatial distribution within controlled delivery tablets using MFX imaging.

In this study, the potential of micro-focus X-ray (MFX) imaging as a tool in the design and quality control of drug delivery systems has been demonstrated. MFX imaging has been used to map the spatial distribution of a drug down to length-scales of approximately 10-100 microm and has shown that the spatial distribution of the drug amiodarone within a hydroxypropylmethylcellulose (HPMC) controlled release tablet (diameter 10 mm) is not homogeneous. MFX imaging allows an assessment to be made of the degree of mixing of the original powders. Despite vigorous mixing during the manufacture of the tablets, the drug particles, originally of size 180-420 microm, were found to be concentrated within isolated but spatially extended patches of sizes up to 1 mm that were scattered across the tablet.

Chemistry, Pharmaceutical↗

PubMed1977

Spatial distribution of the EOG in the rat; a variation with odour quality.

The spatial distribution of olfactory receptors in the rat has been studied by simultaneous recordings of the electroolfactograms (EOGs) from areas of the olfactory mucosa. The potentials were recorded from the dorsal surface of the cribriform plate, leaving the mucosa and the nasal cavities intact. The ratio between the peak amplitude of the EOG potentials served as a measure of the relative sensitivity of one area against the other. The results obtained by stimulating with 31 substances at 38 positions demonstrate a non-homogeneous distribution of different receptors. Each substance gives a spatial pattern of response efficiency. The response distributions are mapped on the cribriform plate for the different odours.

Animals↗

PubMed2006

Spatial distribution of stabilizer-derived nitroxide radicals during thermal degradation of poly(acrylonitrile-butadiene-styrene) copolymers: a unified picture from pulsed ELDOR and ESR imaging.

Double Electron-Electron Resonance (DEER) provides information on the spatial distribution of radicals on the length scale of a few nanometres, while Electron Spin Resonance Imaging (ESRI) provides information on a length scale of millimetres with a resolution of about 100 micrometres. Despite the gap between these length scales, results from the two techniques are found to complement and support each other in the characterization of the identity and distribution of nitroxide radicals derived from the Hindered Amine Stabilizer (HAS) Tinuvin 770 in poly(acrylonitrile-butadiene-styrene) (ABS) copolymers. DEER measurements demonstrate that there is no significant formation of biradicals from the bifunctional HAS, and provide the distributions of local radical concentrations. These distributions are poorly resolved for model-free analysis of the DEER data by the Tikhonov regularization; the resolution was significantly improved by utilizing information obtained by ESRI. DEER data can be fitted with only one adjustable parameter, namely the average radical concentration, if 1D and 2D spectral--spatial ESRI results on both the spatial distribution of nitroxides and their distribution between the acrylonitrile--styrene-rich (SAN) and butadiene-rich (B) microphases are considered.

Journal Article↗

PubMed2001

Lacustrine spatial distribution of landlocked Atlantic salmon populations assessed across generations by multilocus individual assignment and mixed-stock analyses.

The objective of this study was to assess the spatiotemporal distribution of four landlocked Atlantic salmon (Salmo salar) populations during their sympatric feeding phase in lake St-Jean (Québec, Canada). A total of 1100 fish captured over a period of 25 years was genotyped at six microsatellite loci in order to assess the temporal stability of the relative proportion of each population in different lake sectors using both individual-based assignment and mixed-stock analysis. Estimates of relative proportions obtained from both methods were highly correlated. A nonrandom spatial distribution of populations was observed for each period and, despite the fact that the overall proportion of each population varied over time, the pattern of differential distribution remained generally stable over time. Furthermore, there were indications that the extent of horizontal spatial overlap among populations was negatively correlated with that of their genetic differentiation at both microsatellites and a major histocompatibility complex locus, and independent of the geographical distance between the rivers of origin. We discuss the hypothesis that the temporal stability of spatial distribution, the lack of an association between spatial partitioning and geographical distance between rivers of origin, and the apparent negative correlation between spatial overlap and genetic differentiation, reflect the outcome of selective pressures driving behavioural differences for spatial niche partitioning among populations.

Animals↗

PubMed2003

Characterization and spatial distribution of ectomycorrhizas colonizing aspen clones released in an experimental field.

Ectomycorrhizas (EM) from aspen clones released on an experimental field were characterized by morphotyping, restriction analysis and internal transcribed spacer (ITS) sequencing. In addition, their community structure and spatial distribution was analyzed. Among the 23 observed morphotypes, six mycobionts dominated, forming roughly 90% of all ectomycorrhizas: Cenococcum geophilum, Laccaria sp., Phialocephala fortinii, two different Thelephoraceae, and one member of the Pezizales. The three most common morphotypes had an even spatial distribution, reflecting the high degree of homogeneity of the experimental field. The distribution of three other morphotypes was correlated with the distances to the spruce forest and deciduous trees bordering the experimental field. These two patterns allowed two invasion strategies of ectomycorrhizal fungi (EMF) to be recognized, the success of which depends on adaptation of the EMF to local ecological conditions.

Agaricales↗

PubMed1999

Is the spatial distribution of brain lesions associated with closed-head injury predictive of subsequent development of attention-deficit/hyperactivity disorder? Analysis with brain-image database.

PURPOSE: To determine whether there is an association between the spatial distribution of lesions detected at magnetic resonance (MR) imaging of the brain in children after closed-head injury and the development of secondary attention-deficit/hyperactivity disorder (ADHD). MATERIALS AND METHODS: Data obtained from 76 children without prior history of ADHD were analyzed. MR images were obtained 3 months after closed-head injury. After manual delineation of lesions, images were registered to the Talairach coordinate system. For each subject, registered images and secondary ADHD status were integrated into a brain-image database, which contains depiction (visualization) and statistical analysis software. Using this database, we assessed visually the spatial distributions of lesions and performed statistical analysis of image and clinical variables. RESULTS: Of the 76 children, 15 developed secondary ADHD. Depiction of the data suggested that children who developed secondary ADHD had more lesions in the right putamen than children who did not develop secondary ADHD; this impression was confirmed statistically. After Bonferroni correction, we could not demonstrate significant differences between secondary ADHD status and lesion burdens for the right caudate nucleus or the right globus pallidus. CONCLUSION: Closed-head injury-induced lesions in the right putamen in children are associated with subsequent development of secondary ADHD. Depiction software is useful in guiding statistical analysis of image data.

Adolescent↗