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Results for “Spatial Distribution”

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PubMed1990

Spatial distribution of intracellular, free Ca2+ in isolated rat parotid acini.

The spatial distribution of intracellular, free Ca2+ ([Ca2+]i) in rat parotid acini was measured by imaging fura-2 fluorescence from individual acinar cells by means of a digital imaging microscope. Upon cholinergic stimulation in a Krebs-Ringer bicarbonate buffer at (37 degrees C), [Ca2+]i increased synchronously at both the basolateral and luminal membranes as well as in all cells of the secretory endpiece, reaching peak [Ca2+]i levels 1 s after stimulation. Atropine addition caused a rapid down-regulation of [Ca2+]i, which, however, never reached prestimulatory levels. When acini were stimulated in a medium containing 5 nM Ca2+, the Ca2+ mobilization arising from internal pools caused an increase in [Ca2+]i predominantly near the basolateral area, where the endoplasmic reticulum is located, and standing Ca2+ gradients were observed for up to 10 s. A mathematical model is developed to simulate the time courses of the Ca2+ profiles through the cytoplasm using estimated values of the Ca2+ diffusion coefficients and the cytosolic Ca2+ buffering capacity. It is concluded that under physiological conditions, the Ca2+ release from the endoplasmic reticulum is responsible for the activation of the basolaterally located K+ channels. Furthermore, Ca2+ influx from the interstitium is responsible for much of the rise in [Ca2+]i near the luminal membranes, where the Cl- channels are supposed to be located.

Animals↗

PubMedDate not supplied

Comparison of electrophysiological and histochemical methods for assessing the spatial distribution of muscle fibres of a motor unit within muscle.

The spatial distribution of muscle fibres of a motor unit has been examined in patients with a variety of neuromuscular disorders using the fibre density (FD) technique of single fibre EMG and the enclosed fibre count (EFC) method, and the results of the two approaches compared. Agreement between the findings occurred in 64% of cases; an increase in both parameters was seen only in neurogenic conditions. FD was found to be more sensitive to minor disturbances of motor unit architecture as seen in myopathies and mild neurogenic states, and this factor together with sampling differences accounted for most of the discrepancies between the two methods. The finding of normal FD and EFC values in the presence of fibre type disproportion helped to exclude reinnervation as the cause by confirming the predominantly diffuse distribution of muscle fibres.

Adenosine Triphosphatases↗

PubMed1992

An application of a spatially distributed queuing model to an ambulance system.

An application of a spatially distributed queuing model to an ambulance system is presented. The purpose of this research was to assess the usefulness of a variation of the "hypercube" queuing model developed specifically for modeling an ambulance system. The model was applied to the emergency medical system of Greenville County, South Carolina using historical data. Results indicate that the model provides reasonably accurate estimates of system performance measures when the input parameters can be accurately specified.

Ambulances↗

PubMed2003

Spatial distribution of Rhodopseudomonas palustris ecotypes on a local scale.

The number, spatial distribution, and significance of genetically distinguishable ecotypes of prokaryotes in the environment are poorly understood. Oda et al. (Y. Oda, B. Star, L. A. Huisman, J. C. Gottschal, and L. J. Forney, Appl. Environ. Microbiol. 69:xxx-xxx, 2003) have shown that Rhodopseudomonas palustris ecotypes were lognormally distributed along a 10-m transect and that multiple strains of the species could coexist in 0.5-g sediment samples. To extend these observations, we investigated the clonal diversity of R. palustris in 0.5-g samples taken from the corners and center of a 1-m square. A total of 35 or 36 clones were recovered by direct plating from each sample and were characterized by BOX A1R repetitive element-PCR genomic DNA fingerprinting. Isolates with fingerprint images that were >/=80% similar to each other were defined as the same genotype. Among the 178 isolates studied, 32 genotypes were identified, and each genotype contained between 1 and 40 isolates. These clusters were consistent with minor variations found in 16S rRNA gene sequences. The Shannon indices of the genotypic diversity within each location ranged from 1.08 (5 genotypes) to 2.18 (13 genotypes). Comparison of the rank abundance of genotypes found in pairs of locations showed that strains from three locations were similar to each other, with Morisita-Horn similarity coefficients ranging from 0.59 to 0.71. All comparisons involving the remaining two locations resulted in coefficients between 0 and 0.12. From these results we inferred that the patterns of ecotype diversity at the sampling site are patchy at a 1-m scale and postulated that factors such as mixing, competitive interactions, and microhabitat variability are likely to be responsible for the maintenance of the similarities between some locations and the differences between others.

DNA Fingerprinting↗

PubMed1978

Spatial distribution of pulmonary blood flow in dogs in increased force environments.

Spatial distribution of pulmonary blood flow (SDPBF) during 2- to 3-min exposures to 6-8 Gy acceleration was studied, using radioactive microspheres in dogs, and compared to previously reported 1 Gy control distributions. Isotope distributions were measured by scintiscanning individual 1-cm-thick cross sections of excised, fixed lungs. Results indicate: 1) the fraction of cardiac output traversing left and right lungs did not change systematically with the duration and magnitude of acceleration; but 2) the fraction is strongly affected by the occurrence or absence of fast deep breaths, which cause an increase or decrease, respectively, in blood flow through the dependent lung; and 3) Gy acceleration caused a significant increase in relative pulmonary vascular resistance (PVR) in nondependent and dependent regions of the lung concurrent with a decrease in PVR in the midsagittal region of the thorax. Result 3 may be mediated primarily by changes in regional alveolar volume and geometry in the nondependent hemithorax conbined with hydrostatic effects of extravascular fluid and active hypoxic response in the dependent region and is superimposed on, and may override, hydrostatic effects of perfusion pressures on SDPBF during acceleration.

Adaptation, Physiological↗

PubMed1990

Components of field potentials evoked by white matter stimulation in isolated slices of primary visual cortex: spatial distributions and synaptic order.

1. We have recorded profiles of the spatial distributions of extracellular field potentials in transverse slices of rat primary visual cortex. Responses were evoked by electrical stimulation near the white matter/layer VI border and sampled from layers I to V along the radial axis orthogonal to the laminae and intersecting the stimulation site ("on-beam" recording). To assess the activity of "horizontal" connections, we also recorded profiles along axes parallel to the cortical lamination ("off-beam" recording), usually in layer III. Overall, our goal was to extend understanding of the physiology and organization of neocortical circuitry and to provide a basis for comparisons of data from different experiments and experimenters when neocortical field potentials are used in studies of plasticity and pharmacology. 2. Responses were highly specific with respect to the cortical layers. We distinguish four major components: two kinds of population spike ("S1" and "S2") and two slower waveforms ("W1" and "W2"). The latter appear to represent flow of current in apical dendrites of the supragranular layers. Component W1, the earliest slow component, is a synaptically driven field potential dipole that is positive in layer I and negative in layer II. Based on estimates of current source densities (CSDs), we attribute this to entry of depolarizing current into dendrites and/or cell somata in layer II, ascending intradendritic current, and passive depolarization of inactive dendritic membrane in layer I. Component W1 rises during the 20 ms after stimulation and falls during the 50-100 ms thereafter. Component W2 is also positive in layer I but maximally negative in layer III. It rises for approximately 100 ms after stimulation and decays during the following 400-800 ms. 3. Component S1 does not depend on synaptic transmission because it persists during the application of glutamate receptor antagonists or medium that is low in Ca2+. This component is largest in layer III, radial to the site of stimulation. There, it is a negative deflection, typically 1-2 mV in amplitude and lasting roughly 2 ms, with a latency to peak between 2 and 4.5 ms. Component S1 is most likely a population spike due to synchronized firing of cell somata activated antidromically via unmyelinated efferent axons. 4. Component S2 is a short (less than 20 ms) burst of population spikes specifically in layer III. Individual S2 spikes closely resemble S1 spikes, and we propose that the same neuronal population generates both. However, S2 spikes require glutamatergic synaptic transmission.(ABSTRACT TRUNCATED AT 400 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2001

Spatial distribution of prostate cancers undetected on initial needle biopsies.

OBJECTIVES: The spatial distribution of cancer foci of prostate carcinomas with negative initial biopsies was compared to that of prostate carcinomas with positive initial biopsies to detect areas in which carcinomas were more frequently located when the initial biopsy was negative. METHODS: Twenty patients with prostate cancer and a negative initial biopsy trial were detected among 218 patients with preceding systematic biopsies (9.2%) in our hospital. Analysis of the prostatectomy specimens regarding cancer distribution, multifocality, tumour size, Gleason score, and stage was performed using pathohistological techniques and three-dimensional computer reconstruction. RESULTS: Prostatectomy specimens with negative initial biopsies showed more frequently cancer foci in apical (p<0.0001) and dorsal (p<0.02) prostatic compartments, higher incidence of multifocality (p<0.01), and smaller size of carcinoma foci (p<0.00003) compared to carcinomas in 81 stage-matched prostatectomy specimens with positive initial biopsies. Comparing both groups, no significant differences were noted in Gleason score of preoperative biopsies and prostatectomies, prostate weight, prostate-specific antigen (PSA) level, digital rectal examination, and patients age. CONCLUSIONS: Missing the cancer in clinically significant prostate carcinomas by current systematic biopsy techniques may also be due to an apico-dorsal cancer location, particularly in combination with multifocality and small size of carcinoma foci in large prostates. In case of reasonable clinical suspicion of prostate cancer and negative initial biopsy, an early repeat biopsy with special emphasis on the apico-dorsal peripheral zone should be envisaged.

Biopsy, Needle↗

PubMed1994

Spatial distribution of negative health indices in ecological hazard areas in Poland.

Spatial distribution of negative health indices (relative risk, synthetic measure) was demonstrated in 27 ecological hazard areas (EHAs) in Poland. For comparison reference areas were selected. The health indices were used for developing a general index of harmfulness characteristic for individual EHA. The health status ranking in EHAs is useful in setting priorities for remediation.

Environmental Monitoring↗

PubMed2000

Spatial distribution of allozyme polymorphisms following clonal and sexual reproduction in populations of Rhus javanica (Anacardiaceae).

Rhus javanica L. (Anacardiaceae), a dioecious tree with both sexual reproduction and clonal growth, is widely distributed in warm temperate, subtropical, and tropical regions in east Asia. We used allozyme loci and spatial autocorrelation statistics to examine clonal structure and the spatial distribution of allozyme polymorphisms in two Korean populations. Populations of the species maintain moderate levels of allozyme variability (mean He=0.175, GST=0.060), and high levels of multilocus genotypic diversity (mean DG=0.971). Clone-pair distances ranged from 1.4 m to 57.4 m, and had high mean values of 24.0 m and 25.6 m in the two study populations. Approximate genetic patch widths were inferred to be 23-25 m. The results indicated that within populations there is moderate (one study population) or no (other study population) spatial genetic structure among sexually reproduced individuals, and vegetatively reproduced genotypes also are almost randomly distributed. The spatial genetic structure among sexually reproduced trees in the one case is probably caused by limited pollen dispersal in that population, and the lack of structure in the other probably results from the short time elapsed since founding. It appears that clonal reproduction also does not contribute substantially to genetic isolation by distance neither among the sexually reproduced individuals nor the total population. Ramets often establish long distances from their progenitors and thus do not substantially increase the degree of local consanguineous matings.

Genetic Markers↗

PubMed2005

Spatial distribution of ectomycorrhizal Basidiomycete Russula subsect. Foetentinae populations in a primary dipterocarp rainforest.

The spatial distribution of basidiocarps of the ectomycorrhizal Basidiomycete Russula subsect. Foetentinae was assessed in a primary forest in the Western Ghâts (India) dominated by the ectomycorrhizal tree species Vateria indica and Dipterocarpus indicus. Over a 7,700-m(2) sampling area, both trees and basidiocarps of Russula subsect. Foetentinae were mapped during the first month of the 2002 rainy season. First-order spatial analysis revealed that the distribution of the 45 collected carpophores was highly aggregated, with 60% of all basidiocarps located at a distance lower than 1 m from the nearest one. The genetic structure of the Russula subsect. Foetentinae population was studied by inter-simple sequence repeat polymorphism analysis using three primers. Eighteen of the 45 genotypes were represented by single basidiocarps. Twenty-seven basidiocarps were identified as belonging to 11 genets or separated ramets. Five genets were small, with diameters ranging from 0.5 to 5 m. The six others were large, with a diameter ranging from 31 m to a maximum measured distance of 70 m. In spite of the lack of data concerning the reproductive biology of this species, the presence of large genets suggests that mature stands may shelter well-spread underground mycelium, crucial for durable interaction with plant partner.

Basidiomycota↗

PubMed2000

A mark-release-recapture study on the spatial distribution of host-seeking anophelines in northern Thailand.

A mark-release-recapture experiment was conducted at Mae Taeng, Chiangmai, Thailand, in November 1990 to examine the movement of released host-seeking mosquitoes in a heterogeneous environment. A total of 1,848 mosquitoes of nine anopheline species was field-collected, marked with fluorescent dye, and released. Adult collections were made for four nights after the release at five collection sites surrounding the release site. Three different attractants, dry ice (5 kg/site/night), human, and cow bait were used to collect a large number and a wide variety of adult mosquitoes. The recapture rate of released mosquitoes differed among species, ranging from 0 to 7.5%. The species composition was significantly different among collection sites and collection methods, and samples from dry ice collection showed intermediate species composition between those from human and cow bait collections. The spatial distribution of released mosquitoes was not significantly different from that of unmarked mosquitoes. Different behavioral responses to heterogeneous environments by different species of host-seeking mosquitoes was suggested as the underlying mechanism of species-specific spatial distribution of mosquitoes in the study area.

Animals↗

PubMed2003

Spatial distribution of liposome encapsulated tin etiopurpurin dichloride (SnET2) in the canine prostate: implications for computer simulation of photodynamic therapy.

Photodynamic therapy (PDT) is a minimally invasive treatment that can be employed in many human diseases including prostate cancer. PDT for prostate cancer depends on the sequestration of a photosensitizing drug within the glandular tissue. The photosensitizer is subsequently activated by light (usually from a laser) and the active drug destroys tissue. Since prostate cancer is a multifocal disease, PDT must ablate the glandular prostate completely. This will depend on the precise placement of light sources in the prostate and delivery of a therapeutic light dose to the entire gland. Also, sources of light and their spatial distribution must be tailored to each individual patient. The uniform, therapeutic light distribution can be achieved by interstitial light irradiation. In this case, the light is delivered by diffusers placed within the substance of the prostate parallel to the urethra at a distance optimized to deliver adequate levels of light and to create the desired photodynamic effect. To help achieve the uniform light distribution throughout the prostate we have developed a computer program that can determine treatment effects. The program predicts the best set of parameters and the position of light diffusers in space, and displays them in graphical or in numerical form assuming a fixed attenuation coefficient. The two parameters of greatest importance in the computer simulation are attenuation coefficient and critical fluence. Both depend on the concentration of active drug within the prostate gland. It is necessary to know the nature of the spatial distribution of photosensitizer within the prostate to execute computer modeling of PDT with high precision. We found that the concentration of SnET2 is heterogeneous in nature, and is higher in the proximity of the glandular capsule. It is clear therefore that any future attempts of computerized modeling of this procedure must take into consideration the uneven sequestration of photosensitizer and the consequential asymmetrical necrosis of the prostate.

Algorithms↗

PubMed2000

The spatial distribution of visual attention in developmental dyslexia.

The present study investigated the spatial distribution of visual attention in dyslexic and normally reading children. The performances of the two groups were investigated using two different paradigms. In experiment 1 we analyzed the distribution of processing resources both inside and outside the focus of visual attention by simply recording reaction times to the detection of a white dot target projected at different eccentricities from the fovea. The distribution of attentional resources differed significantly between the two groups of children. The eccentricity of the stimulus was significant only for normally reading children - who showed a normal gradient - as it influenced their detection speed, whereas it had no effect on dyslexic children, who exhibited a diffused distribution of visual processing resources inside the visual field. In experiment 2 we studied the distributed (unfocused) mode of attention in a visual search task by measuring reaction times to a target stimulus inside a large configuration with a variable number of distractors. Results show that as compared to normal children dyslexics are better able to distribute their attentional resources diffusely. Our conclusion is that reading disability may be characterized by a diffused distribution of visual processing resources. These data might be interpreted in the framework of studies on magnocellular deficits in dyslexia, whereby the anomalous distribution of visual attention might explain how transient pathway functioning influences the reading process.

Adolescent↗

PubMed1999

[Analysis for spatial distribution of Oncomelania snail in mainland China by geographic information system(GIS) database].

OBJECTIVE: To analyze spatial distribution of Oncomelania snail populations in mainland China by geographic information system (GIS) database. METHODS: Genetic variation experiment data and experimental data of susceptibility of 34 snail populations were collected from nine provinces in China, to set up a database. A world digital map was linked with the database in a software ArcView Release 3.0 a to be used to divide zones with ArcView spatial analyze function and GIS overlaying function. AVHRR NDVI satellite images were collected to form a new one for prevalent season, which were overlaid with distribution maps of heterozygous indices of snail populations, polymorphic locus percentage and infection rates of snail population with schistosome for classifying the images. RESULTS: Spatial analysis showed that distribution maps of genetic heterozygous indices of snail, percentage of polymophic loci and infection rate of snail can be divided into two large zones, i.e., east zone and west zone, both with varied pictures. Analysis for overlaying three-stratum distribution map with AVHRR NDVI satellite image showed four distinctly different spatial zones, including west Sichuan zone, west Yunnan zone, middle zone of river, lake and marshland, and southeast coastal zone. CONCLUSION: It is the first time using GIS to analyze data of Oncomelania population genetics and confirmed the population structure of Oncomelania snails presented discrete sub-population model, which supports the theory of sub-species of Oncomelania spp. Exited in mainland China.

Animals↗

PubMed2005

Applying spatial distribution analysis techniques to classification of 3D medical images.

OBJECTIVE: The objective of this paper is to classify 3D medical images by analyzing spatial distributions to model and characterize the arrangement of the regions of interest (ROIs) in 3D space. METHODS AND MATERIAL: Two methods are proposed for facilitating such classification. The first method uses measures of similarity, such as the Mahalanobis distance and the Kullback-Leibler (KL) divergence, to compute the difference between spatial probability distributions of ROIs in an image of a new subject and each of the considered classes represented by historical data (e.g., normal versus disease class). A new subject is predicted to belong to the class corresponding to the most similar dataset. The second method employs the maximum likelihood (ML) principle to predict the class that most likely produced the dataset of the new subject. RESULTS: The proposed methods have been experimentally evaluated on three datasets: synthetic data (mixtures of Gaussian distributions), realistic lesion-deficit data (generated by a simulator conforming to a clinical study), and functional MRI activation data obtained from a study designed to explore neuroanatomical correlates of semantic processing in Alzheimer's disease (AD). CONCLUSION: Performed experiments demonstrated that the approaches based on the KL divergence and the ML method provide superior accuracy compared to the Mahalanobis distance. The later technique could still be a method of choice when the distributions differ significantly, since it is faster and less complex. The obtained classification accuracy with errors smaller than 1% supports that useful diagnosis assistance could be achieved assuming sufficiently informative historic data and sufficient information on the new subject.

Algorithms↗

PubMed1998

Influence of spatial distribution with blur on fluctuations in accommodation.

PURPOSE: We investigated the influence of spatial distribution of retinal image with blur on the waveform of microfluctuations in accommodation. METHODS: We studied changes in accommodation in 8 young emmetropic subjects (21.88 +/- 2.36 years old), who viewed monocularly a target with the natural pupil. The spatial frequency of the target was varied from 0.85 to 15 cpd in 7 steps, and the blur intensity was increased in 7 steps to obtain a Gaussian distribution of retinal image. Continuous accommodation signals were recorded using an eye-tracking infrared optometer with a sampling frequency of 40.98 Hz, and analyzed with a fast Fourier transform (FFT) analyzer. The power spectra of the low frequency component (LFC, < 0.6 Hz) and the high frequency component (HFC) at approximately 1.9 Hz were calculated for each target with a frequency resolution of 0.02 Hz. RESULTS: Microfluctuations in accommodation increased as the blur was increased and decreased at further increases in blur intensity level. Microfluctuations peaked at a lower blur level as the spatial frequency was increased. Power spectral analysis revealed that these changes in the microfluctuations could be attributed mainly to increases of power in the LFC. CONCLUSIONS: Blurring of the edge and reduction in contrast provided accommodative cues, inducing microfluctuations in accommodation, and the LFC increased as the target sharpness was reduced, possibly in an attempt by the accommodation system to maintain the sharpness of the retinal image under poor stimulus conditions. However, when the blur level was increased, the amount of blur was indistinguishable and microfluctuations in accommodation decreased.

Accommodation, Ocular↗

PubMed1993

Spatial distribution of muscle fibers in a lumbrical muscle of the rat.

The spatial distributions of two different populations of muscle fibers were measured in cross-sections taken from the mid-belly of adult 4DL muscles. Muscle fibers belonging to a single motor unit (identified by glycogen depletion) were distributed randomly in most muscles. Muscle fibers which contained slow myosin (identified immunohistochemically) were distributed nonrandomly, being evenly distributed throughout most of the muscle cross-section, but excluded from the edge of the muscle. Interpreted from a developmental perspective, the results are consistent with the proposals that slow myosin-containing fibers in the adult represent the original population of primary myotubes, and that the adult pattern of motor unit fiber type is achieved by synapse elimination from mismatched fibers rather than by conversion of fiber type.

Animals↗

PubMed2002

Oviducal sperm storage in turkeys: spatial distribution of sperm within the uterovaginal junction sperm-storage tubules.

The spatial distribution of sperm within the sperm storage tubules (SST) found in the uterovaginal junction (UVJ) of the turkey is not known. In this study, we inseminated sperm stained with a fluorescent dye (Hoechst 33342) to determine their distribution in SST in the ventral, dorsal, and lateral regions of the proximal, middle, and distal regions of the UVJ. There was no preferential filling in the ventral-dorsal axis of the UVJ. In contrast, preferential filling of the SST was observed in the middle section of the UVJ. Here the individual SST were clearly longer and more pleomorphic than the SST in the more proximal and distal aspects of the UVJ. While no information on the temporal aspect of SST filling by sperm could be gleaned, it is evident that the more morphologically developed SST either accept sperm more readily or store sperm more efficiently than SST elsewhere in the UVJ.

Animals↗