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PubMed1989

The distribution of intracellular acetylcholine receptors and nuclei in developing avian fast-twitch muscle fibres during synapse elimination.

The spatial distribution of intracellular acetylcholine receptors along the length of fibres from the avian posterior latissimus dorsi muscle has been investigated during embryonic development, when distributed synaptic sites are eliminated from the muscle fibres. Cell surface AChR were irreversibly blocked with unlabelled alpha-bungarotoxin (alpha-BGT). Muscles were then fixed and ultrasonically dissociated into fibre fragments, treated with 0.5% saponin and stained with 125I-alpha-BGT. This revealed an intracellular pool of curare sensitive binding sites equivalent to about 10% of total cell AChR. The spatial distribution of this pool was studied by autoradiography. Large (longer than 2 microns) AChR-clusters (AChR-C) characteristic of neuromuscular contacts were localized on the same fibres by immunofluorescence with an anti-AChR antibody. At E11, relatively high levels of intracellular AChR were observed throughout the length of fibres. Between E11 and E18 intracellular AChR declined (19 fold) in extrajunctional parts of fibres but remained high in segments of fibre corresponding to AChR-clusters. Treatment of E14 embryos with an inhibitor of protein synthesis (cycloheximide) reduced intracellular AChR to 22 +/- 6% (mean +/- SE) of control levels, suggesting that most of the intracellular binding represented newly-synthesized AChR. Between E11 and E18 cell nuclei were found to accumulate beneath AChR-C. The mean density of nuclei in segments of fibre corresponding to AChR-C increased 5 fold between E11 and E18, but remained unchanged in extrajunctional segments. It is suggested that the elimination of excess distributed AChR-C may be due to the preferential accumulation of nuclei at a single AChR-C on each fibre accompanied by the down regulation of AChR synthesis associated with nuclei at the remaining AChR-C.

Animals↗
PubMed1994

Mean-field calculations of chain packing and conformational statistics in lipid bilayers: comparison with experiments and molecular dynamics studies.

A molecular, mean-field theory of chain packing statistics in aggregates of amphiphilic molecules is applied to calculate the conformational properties of the lipid chains comprising the hydrophobic cores of dipalmitoyl-phosphatidylcholine (DPPC), dioleoyl-phosphatidylcholine (DOPC), and palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayers in their fluid state. The central quantity in this theory, the probability distribution of chain conformations, is evaluated by minimizing the free energy of the bilayer assuming only that the segment density within the hydrophobic region is uniform (liquidlike). Using this distribution we calculate chain conformational properties such as bond orientational order parameters and spatial distributions of the various chain segments. The lipid chains, both the saturated palmitoyl (-(CH2)14-CH3) and the unsaturated oleoyl (-(CH2)7-CH = CH-(CH2)7-CH3) chains are modeled using rotational isomeric state schemes. All possible chain conformations are enumerated and their statistical weights are determined by the self-consistency equations expressing the condition of uniform density. The hydrophobic core of the DPPC bilayer is treated as composed of single (palmitoyl) chain amphiphiles, i.e., the interactions between chains originating from the same lipid headgroup are assumed to be the same as those between chains belonging to different molecules. Similarly, the DOPC system is treated as a bilayer of oleoyl chains. The POPC bilayer is modeled as an equimolar mixture of palmitoyl and oleoyl chains. Bond orientational order parameter profiles, and segment spatial distributions are calculated for the three systems above, for several values of the bilayer thickness (or, equivalently, average area/headgroup) chosen, where possible, so as to allow for comparisons with available experimental data and/or molecular dynamics simulations. In most cases the agreement between the mean-field calculations, which are relatively easy to perform, and the experimental and simulation data is very good, supporting their use as an efficient tool for analyzing a variety of systems subject to varying conditions (e.g., bilayers of different compositions or thicknesses at different temperatures).

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

Evolution of distributions and spatial correlations of single-particle forces and stresses during compression of ductile granular materials.

Uniaxial compression of disordered packings of millimeter-sized ductile particles formed from microcrystalline cellulose is investigated experimentally, at compression pressures in the vicinity of the minimum pressure required to form a coherent compact. Distributions of normal forces and stresses exerted by individual particles on a confining wall are determined. Spatial force and stress correlations are investigated. The distribution of normal forces is found to narrow with increasing pressure, but no indication of a crossover to a Gaussian decay at high forces is observed. The distribution of normal stresses is found to be considerably more Gaussian in shape for all pressures investigated. This finding may be interpreted as resulting from a positive correlation between the area corresponding to each particle and the force it experienced during compression. Spatial force and stress correlations are observed for distances smaller than three particle diameters. The spatial stress correlations indicate that the mode of stress transmission changes when the compression pressure exceeds the minimum pressure required to form a coherent compact.

Journal Article↗
PubMed1993

Monitoring trypanosomiasis in space and time.

The paper examines the possible contributions to be made by Geographic Information Systems (GIS) to studies on human and animal trypanosomiasis in Africa. The epidemiological characteristics of trypanosomiasis are reviewed in the light of the formula for the basic reproductive rate or number of vector-borne diseases. The paper then describes how important biological characteristics of the vectors of trypanosomiasis in West Africa may be monitored using data from the NOAA series of meteorological satellites. This will lead to an understanding of the spatial distribution of both vectors and disease. An alternative, statistical approach to understanding the spatial distribution of tsetse, based on linear discriminant analysis, is illustrated with the example of Glossina morsitans in Zimbabwe, Kenya and Tanzania. In the case of Zimbabwe, a single climatic variable, the maximum of the mean monthly temperature, correctly predicts the pre-rinderpest distribution of tsetse over 82% of the country; additional climatic and vegetation variables do not improve considerably on this figure. In the cases of Kenya and Tanzania, however, another variable, the maximum of the mean monthly Normalized Difference Vegetation Index, is the single most important variable, giving correct predictions over 69% of the area; the other climatic and vegetation variables improve this to 82% overall. Such statistical analyses can guide field work towards the correct biological interpretation of the distributional limits of vectors and may also be used to make predictions about the impact of global change on vector ranges. Examples are given of the areas of Zimbabwe which would become climatically suitable for tsetse given mean temperature increases of 1, 2 and 3 degrees Centigrade. Five possible causes for sleeping sickness outbreaks are given, illustrated by the analysis of field data or from the output of mathematical models. One cause is abiotic (variation in rainfall), three are biotic (variation in vectorial potential, host immunity, or parasite virulence) and one is historical (the impact of explorers, colonizers and dictators). The implications for disease monitoring, in order to anticipate sleeping sickness outbreaks, are briefly discussed. It is concluded that present data are inadequate to distinguish between these hypotheses. The idea that sleeping sickness outbreaks are periodic (i.e. cyclical) is only barely supported by hard data. Hence it is even difficult to conclude whether the major cause of sleeping sickness outbreaks is biotic (which, in model situations, tends to produce cyclical epidemics) or abiotic.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

Formation of multifractal population patterns from reproductive growth and local resettlement.

We consider the general character of the spatial distribution of a population that grows through reproduction and subsequent local resettlement of new population members. We present several simple one- and two-dimensional point placement models to illustrate possible generic behavior of these distributions. We show, numerically and analytically, that these models all lead to multifractal spatial distributions of population. Additionally, we make qualitative links between our models and the example of the Earth at Night image, showing the Earth's nighttime man-made light as seen from space. The Earth at Night data suffer from saturation of the sensing photodetectors at high brightness ("clipping"), and we account for how this influences the determined dimension spectrum of the light intensity distribution.

Animals↗
PubMed2001

A random walk through models of nonlinear clustering.

A few simple models of the mass function of collapsed objects are presented. The emphasis is on apparently unrelated models which end up giving the same answer for the number density and merger histories of virialized clumps. Models of the spatial distribution of the clumps and how they can be used to model the spatial distribution of the mass are briefly discussed.

Journal Article↗
PubMed2005

Control of the pulse width in a diode-pumped passively Q-switched Nd:GdVO4/KTP green laser with a Cr4+:YAG saturable absorber.

Different techniques to control the pulse width of a diode-pumped passively Q-switched Nd:GdVO4/KTP green laser have been theoretically and experimentally studied. It is shown that, when we vary the positidns of the saturable absorber in the laser axis and the pump beam waist in the gain medium, we obtain an efficient means to control the pulse width. The experiments performed on a diode-pumped Nd:GdVO4/KTP green laser passively Q-switched by a Cr4+:YAG saturable absorber are consistent with the theoretical calculations obtained from the rate equation model, in which the intracavity photon density that is assumed to be the Gaussian spatial distribution, the longitudinal variation of the intracavity photon density, and the pump beam spatial distribution are also considered.

Journal Article↗
PubMed2005

[Spatial variability of soil phosphorus in field scale].

In this paper, the spatial variability of soil total P and Olsen-P at the depths of 0 approximately 10 and 10 approximately 20 cm in a field-scale was examined by using traditional statistics combined with geostatistics methods. A sampling grid of 30 m x 42 m including 49 pairs of soil sampling points was established in the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences. The results showed that the variance coefficients were much higher for Olsen-P (46.56% approximately 56.42%) than for total P (11.68% approximately 13.33%). Both total P and Olsen-P in the two soil depths had strongly spatial structures and similar spatial correlation ranges. The parameters derived from best-fitted models showed that the spatial variability of both total P and Olsen-P was mainly affected by structural factors, with C/(C0 + C) being higher than 66% for all the variables. The kriging contour maps showed that both total P and Olsen-P in the two soil depths had similar spatial distribution patterns. A more precise sampling scheme could be made based on the spatial distribution pattern of test soil properties combined with traditional variance coefficients. To recognize the strong variability of soil Olsen-P in field-scale is of significance for better understanding the P cycling in farm ecosystems and for precise agriculture.

Crops, Agricultural↗
PubMed2000

Epistatic repression of PHANTASTICA and class 1 KNOTTED genes is uncoupled in tomato.

Class 1 KNOTTED genes (KNOX) and PHANTASTICA (PHAN) are both central to meristem establishment and maintenance and, in maize and Antirrhinum, it has been proposed that PHAN acts as an epigenetic repressor of KNOX. In tomato, a distinct spatial distribution of Tkn2 KNOX transcripts compared to Antirrhinum and maize suggests either a different spatial distribution of tomato PHAN (Le-phan) transcripts, or that PHAN alone is insufficient for KNOX repression in tomato. We established the pattern of Le-phan expression, including a first demonstration of PHAN expression in healthy roots, and found Le-phan and Tkn2 transcripts to be temporally and spatially coincidental, with PHAN exhibiting an expression pattern in tomato distinct from that in plants with simple leaves. Our results imply that the expression of Le-phan is insufficient for the repression of Tkn2 in tomato and suggest an expanded role for either gene in the establishment of cell identity in plant development.

Base Sequence↗
PubMed1998

Raised object on a planar surface stroked across the fingerpad: responses of cutaneous mechanoreceptors to shape and orientation.

The representations of orientation and shape were studied in the responses of cutaneous mechanoreceptors to an isolated, raised object on a planar surface stroked across the fingerpad. The objects were the top portions of a sphere with a 5-mm radius, and two toroids each with a radius of 5 mm along one axis and differing radii of 1 or 3 mm along the orthogonal axis. The velocity and direction of stroking were fixed while the orientation of the object in the horizontal plane was varied. Each object was stroked along a series of laterally shifted, parallel, linear trajectories over the receptive fields of slowly adapting, type I (SA), and rapidly adapting, type I (RA) mechanoreceptive afferents innervating the fingerpad of the monkey. "Spatial event plots" (SEPs) of the occurrence of action potentials, as a function of the location of each object on the receptive field, were interpreted as the responses of a spatially distributed population of fibers. That portion of the plot evoked by the curved object (the SEPc) provided a representation of the shape and orientation of the two-dimensional outline of the object in the horizontal plane in contact with the skin. For both SAs and RAs, the major vector of the SEPc, obtained by a principal components analysis, was linearly related to the physical orientation of the major axis of each toroid. The spatial distribution of discharge rates [spatial rate surface profiles (SRSs), after plotting mean instantaneous frequency versus spatial locus within the SEPc] represented object shape in a third dimension, normal to the skin surface. The shape of the SA SRSs, well fitted by Gaussian equations, better represented object shape than that of the RA SRSs. A cross-sectional profile along the minor axis [spatial rate profile (SRP)] was approximately triangular for SAs. After normalization for differences in peak height, the falling slopes of the SA SRPs increased, and the base widths decreased with curvature of the object's minor axis. These curvature-related differences in slopes and widths were invariant with changes in object orientation. It is hypothesized that circularity in object shape is coded by the constancy of slopes of SA SRPs between peak and base and that the constancy of differences in the widths and falling slopes evoked by different raised objects encodes, respectively, the differences in their sizes and shapes regardless of differences in their orientation on the skin.

Action Potentials↗
PubMed1999

Spatial organization of four hnRNP proteins in relation to sites of transcription, to nuclear speckles, and to each other in interphase nuclei and nuclear matrices of HeLa cells.

RNA polymerase II transcripts are complexed with heterogeneous nuclear ribonucleoprotein (hnRNP) proteins. These proteins are involved in several aspects of the maturation and transport of hnRNA. We performed a detailed study of the spatial distribution of four hnRNP proteins (hnRNP C, I, L, and U) in HeLa nuclei, using immunofluorescent labeling and confocal microscopy. Despite the fact that hnRNP proteins have been shown to coimmunoprecipitate, a hallmark of hnRNP proteins, we find that hnRNP C, I, and L have a spatial nuclear distribution that is not related to that of hnRNP U. We also examined the distribution of hnRNP proteins in relation to that of nascent transcripts. The four hnRNP proteins that we examined are not enriched at sites of RNA synthesis. Using antibodies against the nuclear poly(A)-binding protein (PAB II) we investigated the relationship between the distribution of hnRNP proteins and that of nuclear domains (nuclear speckles) that are enriched in splicing factors, poly(A)+RNA, and PAB II. We found that the four hnRNP proteins are not enriched in these domains. This indicates that the poly(A)+RNA, present in high concentration in speckles, is not complexed with these hnRNP proteins. This is in agreement with the notion that poly(A)+RNA in speckles is different from ordinary hnRNA. Previously, we have shown that hnRNP proteins are the major protein components of the fibrogranular internal nuclear matrix (K. A. Mattern et al. (1996) J. Cell. Biochem. 62, 275-289; K. A. Mattern et al. (1997) J. Cell. Biochem. 65, 42-52). We observed that in nuclear matrices the spatial distributions of the four hnRNP proteins, like that of nascent RNA and PAB II, are essentially the same as observed in intact nuclei. Moreover, also in nuclear matrix preparations, like in intact nuclei, nascent RNA and PAB II have spatial distributions that differ from those of hnRNP proteins. Our results are compatible with the notion that hnRNP proteins are able to form complexes of many different, probably overlapping, compositions.

Cell Nucleus↗
PubMed2002

Characterization of gastric myoelectrical rhythms in patients with systemic sclerosis using multichannel surface electrogastrography.

The aim of this study was to characterize multichannel surface electrogastrography (EGG) recordings in patients with systemic sclerosis (scleroderma, SSc) compared to normal controls. Ten SSc patients and 13 healthy age-matched controls were enrolled in this study. Gastric myoelectrical activity was recorded using a four-channel electrogastrograph with abdominal surface electrodes. The EGG was recorded in the morning for 1 hr in the fasting state, and 1 hr after a standardized (500 kcal) test meal. It was found that: (1) The regularity of the gastric slow wave was significantly lower in the SSc patients when compared with the normal controls in both fasting and fed states. (2) There was a significantly higher incidence of bradygastria in the SSc patients. (3) The SSc patients showed a significantly lower percentage of slow wave coupling among the four-channel EGGs than the controls. (4) In comparison with the controls, the patients showed an impaired spatial distribution of gastric slow wave power in both fasting and fed states and an impaired spatial distribution of slow wave frequency in the fasting state. It was concluded that SSc patients have an abnormal gastric slow wave as shown in the multichannel EGG as a decreased percentage of normal slow waves and impaired spatial coordination of gastric slow waves. The multichannel EGG may serve as a simple, noninvasive, and cost-effective method to assess gastric motility disorders and their relevance in patients with SSc.

Adult↗
PubMed1984

Periodic simple cells in cat area 17.

Quantitative, high-resolution static receptive-field plots (response planes) in cat area 17 revealed simple cells whose receptive fields were composed of four to six excitatory regions alternating in space with up to seven inhibitory regions. The size, shape, and spacing of the excitatory regions within these receptive fields were highly regular, giving the receptive field a periodic appearance in space. We call these periodic simple cells. A periodic simple cell's response to moving stimuli could, in general, be anticipated from the detailed spatiotemporal map of excitatory and inhibitory regions provided by response planes. This observation suggests that periodic simple cells, like the more common simple cells composed of one to three excitatory regions, sum spatially distributed inputs in a roughly linear manner. Based on a quantitative assessment of the spatial distribution and time course of response of single excitatory regions within periodic receptive fields, as described in the previous paper, we characterized periodic simple cells as either X-like or Y-like. Furthermore, we found that periodic simple cells classified as X-like gave a more sustained response to standing contrast and had significantly smaller excitatory regions than those cells classified as Y-like. Periodic simple cells were found in layer III and at the border between layers III and IVab. It is suggested that these cells, which reside outside the primary zone of geniculate termination and include both X-like and Y-like types, may be constructed hierarchically from the convergence of lower order simple cells. In the spatial-frequency domain, periodic simple receptive fields were predicted to have bandwidths at half-maximum ranging from 0.80 to 1.4 octaves. By comparison, the predicted bandwidths of cells composed of two or three excitatory regions ranged from 1.6 to 4.3 octaves. Thus as additional excitatory regions are added to the receptive fields of simple cells, their bandwidth narrows in the spatial-frequency domain.

Animals↗
PubMed1994

Temporal distribution, localization and metabolism of all-trans-retinol, didehydroretinol and all-trans-retinal during Xenopus development.

Recently, the temporal and spatial distribution patterns of the retinoid receptor ligands 9-cis-retinoic acid and all-trans-retinoic acid were described in Xenopus embryos during early development [Creech Kraft, Schuh, Juchau and Kimelman (1994) Proc. Natl. Acad. Sci. U.S.A., in the press]. The present study demonstrates the presence and distribution of their likely precursors, all-trans-retinol, didehydroretinol, didehydroretinal and all-trans-retinal, as well as the occurrence of 4-oxo metabolites, in Xenopus embryos. The temporal and spatial distribution patterns of all-trans-retinol, didehydroretinol and all-trans-retinal did not coincide with that observed for 9-cis-retinoic acid but, in certain regards, were similar to the patterns delineated for all-trans-retinoic acid and all-trans-retinoyl beta-glucuronide. Evidence is presented that 9-cis-retinoic acid can be synthesized from both all-trans-retinoic acid and all-trans-retinol in Xenopus embryos, suggesting that the difference between the distributions of 9-cis-retinoic acid and the other retinoids may be caused by selective synthesis and/or protein binding of the 9-cis isomer.

Animals↗
PubMed2005

A distributed parameter identification problem in neuronal cable theory models.

Dendritic and axonal processes of nerve cells, along with the soma itself, have membranes with spatially distributed densities of ionic channels of various kinds. These ionic channels play a major role in characterizing the types of excitable responses expected of the cell type. These densities are usually represented as constant parameters in neural models because of the difficulty in experimentally estimating them. However, through microelectrode measurements and selective ion staining techniques, it is known that ion channels are non-uniformly spatially distributed. This paper presents a non-optimization approach to recovering a single spatially non-uniform ion density through use of temporal data that can be gotten from recording microelectrode measurements at the ends of a neural fiber segment of interest. The numerical approach is first applied to a linear cable model and a transformed version of the linear model that has closed-form solutions. Then the numerical method is shown to be applicable to non-linear nerve models by showing it can recover the potassium conductance in the Morris-Lecar model for barnacle muscle, and recover the spine density in a continuous dendritic spine model by Baer and Rinzel.

Action Potentials↗
PubMed1998

Accumulation of tributyl- and triphenyltin compounds in Pacific oyster, Crassostrea gigas, from the Chinhae Bay System, Korea.

Butyl- and phenyltin residues were quantified in seawater and Pacific oyster (Crassostrea gigas) from the Chinhae Bay System, Korea. Butyltin compounds were detected in all the seawater and C. gigas samples, whereas phenyltin compounds were not detected in any seawater samples. Tributyltin (TBT) concentrations in seawater ranged <8-35 ng Sn L-1. TBT and triphenyltin (TPhT) concentrations in oysters ranged 95-885 and 155-678 ng Sn g-1, respectively. Spatial distribution of TBT was closely related to boating and dry-docking activities. However, spatial distribution of TPhT was not consistent with that of TBT. The estimated biological concentration factor (BCF) for TBT in C. gigas was about 25,000. Furthermore, 19 and 28% of total body burdens of TBT and TPhT were found in gonadal mass of C. gigas just prior to the spawning period, indicating that a proportional amount of TBT and TPhT would be released with a following reproductive process.

Animals↗
PubMed1992

Computer-aided two-dimensional high-resolution axon tracing: an application using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL).

A computer-aided method for mapping the spatial distribution of axons labeled with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL) has been devised. The method is based upon a histochemical charting system that controls a motorized microscope stage. The Computerized Charting System (CCS) does not require a camera lucida and can be installed on a common laboratory computer with minimal specialized hardware. The system provides features for storing, manipulating, and plotting the data, and recording the location of photographic images. The CCS has been used in our laboratory for: (1) the analysis of retrograde and anterograde neuroanatomical tract tracing using horseradish peroxidase, fluorescent dyes, PHAL, and 3H-labeled amino acids; (2) mapping the distribution of cells identified by immunohistochemistry; (3) mapping the distribution of silver grain-positive cells using in situ hybridization; (4) mapping the spatial distribution of neurofibrillary tangles and neuritic plaques in Alzheimer's disease; and (5) mapping the pattern of congophilic angiopathy in human brain. With the addition of high-resolution tracing features, the CCS provides a cost-effective and comprehensive alternative to the tedious and often inaccurate X-Y recording techniques used routinely in neuroanatomy and neuropathology.

Animals↗
PubMedDate not supplied

Rationale for, and recent progress in, 3D reconstruction of the heart and lungs.

Three-dimensional information of the structure and function of the heart and lungs is needed for several reasons including the following: (a) An apparent change in shape or location of the imaged ventricular wall may either be due to the heart moving through the imaged region, or because it truly represents that change in geometry, or a mixture of the two. In addition, as diseases of the heart and lungs are often heterogeneous in their spatial distribution, we expect the structural and functional consequences to also be heterogeneous in their spatial distribution; (b) Comparison of a selected anatomic feature (e.g., a coronary artery stenosis or pulmonary opacity) at long time intervals may make detection and/or quantitation of lesion progression questionable. The use of a 3D reconstruction to calculate a projection image with a reproducible angle of view is a particularly powerful consequence of 3D image reconstruction; (c) Use of image information from one imaging modality helps improve the quantitative characteristics of an image generated with another imaging modality; (d) Radiation treatment planning requires knowledge of the 3D distribution of radiation attenuation coefficients so that 3D distribution of the regional deposition of radiation energy can be quantitated; (e) Allows for indirect estimation of the physiological dimensions of one aspect of an organ so that the degree of disease of that part of the organ can be assessed.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Graphics↗