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At least 1,189 records · Page 66Linked to original sources
PubMed2002

Vasculogenesis and angiogenesis in the subcardinal venous plexus of quail mesonephros: spatial and temporal morphological analysis.

Vasculogenesis and angiogenesis are involved in a coordinated program for the development of the mesonephric subcardinal venous plexus of quail embryo. Vasculogenesis occurs between days 3 and 4 of incubation, while angiogenesis takes place from day 5 to day 7. Examination of vascular corrosion casts and whole mounts, and tissue sections labelled with specific markers to hemangioblast lineage (QH1, LEP100 and AcPase activity), allowed us to distinguish six phases in the formation of subcardinal plexus. (1) Appearance of isolated angioblast-like cells where the subcardinal plexus will form. (2) Alignment of angioblast-like cells into cellular strands. (3) Formation of compact vascular cords by association of angioblast-like strands. (4) Polygonal interconnection of vascular cords to constitute the primary subcardinal plexus. In this stage, isolated angioblast-like cells were present inside inter-vascular spaces. (5) The splitting of primary inter-vascular spaces by angiogenic sprouts to form secondary subcardinal plexus (outward angiogenesis). Isolated angioblast-like cells were not present in this stage. (6) Expansion of the secondary subcardinal plexus by insertion of slender transcapillary tissue pillars (inward angiogenesis) and angiogenic sprouts. We also describe three morphogenetic gradients during the development of the subcardinal plexus: ventral-to-dorsal, cranial-to-caudal and lateral-to-medial.

Animals↗
PubMedDate not supplied

Microdensitometer-computer correlation analysis of two distinct, spatially segregated classes of microtubule bridges in Allogromia pseudopodia.

Previous video-light microscopic studies have shown that the microtubule bundles in the pseudopodia of foraminiferan protists display several types of movements in vivo, including active bending, zipping/splaying, and axial translocations. To gain insight into the types and arrangement of microtubule-associated proteins (e.g., mechanoenzymes, crosslinkers) in such a highly dynamic system, we employed microdensitometric-computer correlation methods to analyze, quantitatively, intermicrotubule bridges in thin-section electron micrographs of Allogromia laticollaris and Allogromia sp. (strain NF). Two distinct bridges occupying mutually exclusive zones between adjacent microtubules were identified. Type I bridges displayed a single axial repeat (34 nm for A. laticollaris and 28 nm for Allogromia sp.) and Type II bridges showed a typical 12-dimer helical superlattice pattern. In A. laticollaris, the two types of bridges were morphologically distinct: Type I bridges were aligned perpendicular to the microtubule wall and were 23-nm wide with an electron-lucent core; Type II bridges were irregular filaments projecting from the microtubules at various angles. When compared with the known distribution of microtubule-associated proteins in other systems, our findings indicate that, in vivo, Allogromia pseudopodial microtubules are decorated with MAP2-like bridges interrupted by discrete clusters of a dynein-like component.

Animals↗
PubMed2006

Spatially-correlated mass spectrometric analysis of microbe--mineral interactions.

A new methodology for examining the interactions of microbes with heterogeneous minerals is presented. Imaging laser desorption Fourier transform mass spectrometry was used to examine the colonization patterns of Burkholderia vietnamiensis G4 (previously Burkholderia cepacia G4) on a heterogeneous basalt sample. Depth-profile imaging found that the bacterium preferentially colonized the plagioclase mineral phase within the basalt.

Burkholderia cepacia↗
PubMed2005

Asymptotically exact analysis of stochastic metapopulation dynamics with explicit spatial structure.

We describe a mathematically exact method for the analysis of spatially structured Markov processes. The method is based on a systematic perturbation expansion around the deterministic, non-spatial mean-field theory, using the theory of distributions to account for space and the underlying stochastic differential equations to account for stochasticity. As an example, we consider a spatial version of the Levins metapopulation model, in which the habitat patches are distributed in the d-dimensional landscape Rd in a random (but possibly correlated) manner. Assuming that the dispersal kernel is characterized by a length scale L, we examine how the behavior of the metapopulation deviates from the mean-field model for a finite but large L. For example, we show that the equilibrium fraction of occupied patches is given by p(0)+c/L(d)+O(L(-3d/2)), where p(0) is the equilibrium state of the Levins model and the constant c depends on p(0), the dispersal kernel, and the structure of the landscape. We show that patch occupancy can be increased or decreased by spatial structure, but is always decreased by stochasticity. Comparison with simulations show that the analytical results are not only asymptotically exact (as L-->infinity), but a good approximation also when L is relatively small.

Animals↗
PubMedDate not supplied

Spatial, temporal and numeric analysis of Alzheimer changes in the nucleus coeruleus.

The distribution of neurofibrillary tangles in the nucleus coeruleus was topographically and quantitatively analyzed. The topographical analysis showed statistically significant differences with regard to the distribution of neurofibrillary tangles in the dorsal-ventral and medial-lateral axes. More neurofibrillary tangles were found to be located in the dorsal and medial regions than in ventral and lateral areas. No significant difference in neurofibrillary tangle content was found between the rostral and the caudal areas of the nucleus coeruleus. Neurofibrillary tangle formation begins in the central parts of the nucleus coeruleus. The total number of neuromelanized neurons in the nucleus coeruleus was determined using a modern, unbiased sampling scheme and related to the cortical stage of Alzheimer's disease-related neurofibrillary changes present. A statistically significant reduction (50%) in nucleus coeruleus neurons was evident only in cases meeting the histopathological criteria for Alzheimer's disease. The extent of reduction in the total number of neurons in the nucleus coeruleus did not correlate with the number of neurofibrillary tangles observed. Our data suggest that despite the relatively early susceptibility of the nucleus coeruleus to neurofibrillary tangle formation, significant neuronal loss appears to occur much later, with an estimated average delay time of at least 25 years. Nonetheless, comparison of the topographical pattern of neurofibrillary tangle formation and cell loss indicates that neuronal loss is tangle-related.

Age Factors↗
PubMed2003

A comparative analysis of structure and spatial distribution of decorin in human leiomyoma and normal myometrium.

Leiomyoma is a benign smooth muscle tumor of the uterus that affects many women in active reproductive life. It is composed by bundles of smooth muscle cells surrounded by extracellular matrix. We have recently shown that the glycosylation of extracellular matrix proteoglycans is modified in leiomyoma: increased amounts of galactosaminoglycans with structural modifications are present. The data here presented show that decorin is present in both normal myometrium and leiomyoma but tumoral decorin is glycosylated with longer galactosaminoglycan side chains. Furthermore, these chains contain a higher ratio D-glucuronate/L-iduronate, as compared to normal tissue. To determine if these changes in proteoglycan glycosylation correlates with modifications in the extracellular matrix organization, we compared the general structural architecture of leiomyoma to normal myometrium. By histochemical and immunofluorescence methods, we found a reorganization of muscle fibers and extracellular matrix, with changes in the distribution of glycoproteins, proteoglycans, and collagen. Thin reticular fibers, possibly composed by types I and III collagen, were replaced by thick fibers, possibly richer in type I collagen. Type I collagen colocalized with decorin both in leiomyoma and normal myometrium, in contrast to type IV collagen that did not. The relative amount of decorin was increased and the distribution of decorin and collagen was totally modified in the tumor, as compared to the normal myometrium. These findings reveal that not only decorin structure is modified in leiomyoma but also the tissue architecture changed, especially concerning extracellular matrix.

Adult↗
PubMed2002

Production, analysis, and application of spatially resolved shells in solid-phase polymer spheres.

Two-photon fluorescence microscopy has been used to interrogate the interior functionality of polymer resin beads. By employing this technique, the spatial distribution of the initial functionality contained within the polymer matrix has been determined. Spatially resolved, concentric shells were then produced synthetically in these polymer spheres via a series of protection/deprotection reactions in which two-photon fluorescence microscopy was employed to monitor each successive step. To demonstrate the potential utility of these techniques in combinatorial screening, a set of beads was prepared containing a unique tripeptide sequence in each of the three concentric shells within each individual bead. The set was then screened for the binding affinity of each tripeptide toward a fluorescent ligand.

Journal Article↗
PubMed1994

Spatial-dynamic population systems: analysis and projection.

"In this paper a set of more-detailed multiregional population accounts is proposed to specify more realistically the exposure time of populations at risk for various components of population change. The concepts of population-time at risk and forward demographic rates based on the initial population are discussed. The relations of the forward demographic rates defined in this paper with the occurrence-exposure demographic rates are discussed. A more precise and straightforward multiregional population model is developed on the basis of forward demographic rates. The model is also expressed in the familiar matrix form of multiregional, cohort-survival models." Some applications of the model are made to data for China.

Asia↗
PubMed1999

SOFIA: spatially optimal fast initial analysis of biomagnetic signals.

A method of analysing biomagnetic signals is presented which focuses attention on activity in a specific region of interest. The method is based on the construction of virtual sensors, corresponding to linear combinations of lead fields that are optimally localized within the region of interest. This method is fast and stable. It is tested against physiologically plausible computer generated signals and also against more elaborate analysis of real data. The results show that the method can be very effective as a fast scanning tool identifying activity from pre-defined regions of interest.

Algorithms↗
PubMed2006

Perturbative analysis of generally nonlocal spatial optical solitons.

In analogy to a perturbed harmonic oscillator, we calculate the fundamental and some other higher order soliton solutions of the nonlocal nonlinear Schödinger equation (NNLSE) in the second approximation in the generally nonlocal case. Comparing with numerical simulations we show that soliton solutions in the second approximation can describe the generally nonlocal soliton states of the NNLSE more exactly than that in the zeroth approximation. We show that for the nonlocal case of an exponential-decay type nonlocal response the Gaussian-function-like soliton solutions cannot describe the nonlocal soliton states exactly even in the strongly nonlocal case. The properties of such nonlocal solitons are investigated. In the strongly nonlocal limit, the soliton's power and phase constant are both in inverse proportion to the fourth power of its beam width for the nonlocal case of a Gaussian function type nonlocal response, and are both in inverse proportion to the third power of its beam width for the nonlocal case of an exponential-decay type nonlocal response.

Journal Article↗
PubMed2001

A case study comparing static and spatially explicit ecological exposure analysis methods.

Exposure to chemical contaminants must be estimated when performing ecological risk assessments. A previous article proposed a habitat area and quality conditioned population exposure estimator, E[HQ]P, and described an individual-based, random walk, Monte Carlo model (SE3M) to facilitate calculation of E[HQ]P. In this article, E[HQ]P was compared with exposure estimates from a baseline risk assessment that evaluated mink and great blue heron exposure to fluoride at a federal Superfund site. Calculation of E[HQ]P took into consideration a receptor's forage area, movement behavior, population size, and the areal extent and quality of suitable habitat. The baseline assessment used four methods that did (total and unit Tier 2) and did not (total and unit Tier 1) consider habitat area or quality; where "total" included all exposure units on site and "unit" only a given exposure unit. Total Tier 1 estimates were consistently higher than E[HQ]P (e.g., 169.1 mg/kg x d versus 21.6 mg/kg x d). Risk managers using total Tier 1 results for decision making would be unlikely to underestimate exposure; however, implementability of correspondingly lower remedial objectives could be challenging. Unit Tier 1 estimates were higher (e.g., 96.5 mg/kg x d versus 61.6 mg/kg x d) or lower (e.g., 3.5 mg/kg x d versus 51.1 mg/kg x d) than E[HQ]P depending on variations in landscape features. Total Tier 2 and E[HQ]P estimates were similar (e.g., 20.7 mg/kg x d versus 21.6 mg/kg x d) when an ecologically questionable average exposure was assumed. Unit Tier 2 estimates were consistently well below E[HQ]P (e.g., 17.8 mg/kg x d versus 61.6 mg/kg x d) when an average exposure was not assumed. Risk managers using unit Tier 1 or 2 results could be basing their decisions on potentially large underestimates of exposure. By forgoing average exposure assumptions, and explicitly addressing landscape heterogeneity, SE3M appears capable of yielding exposure estimates that are not as potentially misleading to risk managers as those produced with traditional averaging methods.

Aluminum↗
PubMed1994

Analysis of the spatial-frequency-dependent DQE of optically coupled digital mammography detectors.

The effect of optical coupling efficiency on the spatial-frequency-dependent propagation of signal and noise is considered for x-ray image detectors for digital mammography in which a phosphor screen is optically coupled to a charge-coupled device (CCD) image array. For experimental purposes, optical coupling between a Gd2O2S:Tb phosphor screen and a CCD image array was provided by relay lenses. Neutral density filters were inserted between the lenses to vary the optical coupling efficiency without altering the inherent spatial resolution. The total coupling efficiency, defined as the number of electrons (e-) recorded in the CCD per x-ray interaction in the phosphor, was calculated in each case. The modulation transfer function, and the contributions to the total noise power spectrum (NPS) of x-ray quantum noise, secondary quantum noise, and inherent detector noise were measured as a function of coupling efficiency. These data were used to calculate the spatial-frequency-dependent detective quantum efficiency [DQE(f)]. The NPS due to x-ray quantum noise had a significant spatial-frequency dependence for coupling efficiencies of more than 9 e- per x-ray interaction, but little spatial-frequency dependence for coupling efficiencies of less than 2 e- per x-ray interaction. These results indicate that to preserve high spatial-frequency values of DQE(f), and to ensure that images are x-ray quantum-noise limited at high spatial frequencies, a coupling efficiency on the order of 10 e- per x-ray interaction is required.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrons↗
PubMed2005

Quantitative analysis of changes in spatial distribution and plus-end geometry of microtubules involved in plant-cell cytokinesis.

The cell plate of higher plants is formed within a ribosome-excluding cell plate assembly matrix. Phragmoplast microtubules facilitate cell-plate formation by forming a scaffold that directs Golgi-derived vesicles to the forming cell plate. Here, we analyse the effects of the cell-plate assembly matrix on phragmoplast microtubule plus-end geometry by electron tomography of cryogenically fixed Arabidopsis meristem cells. Five distinct microtubules plus-end geometries are seen--blunt, extended, horned, flared and hybrid extended/horned. We have quantified and mapped these types of plus-end morphology during the different stages of cell-plate formation and analysed the effects of cell-plate assembly matrix association on microtubule plus-end morphologies. Our results show that somatic-type phragmoplast microtubules do not interdigitate at the cell plate mid-line. The cell-plate assembly matrix is shown to stabilize microtubule plus ends, as evidenced by the fact that of these microtubules that do not terminate in such a matrix, 40-80% are horn-shaped (shrinking), whereas of those that end in such a matrix, 50-70% are blunt (metastable). Also, a third of the blunt-ended microtubules within the cell-plate assembly matrix end at a distance of approximately 30 nm from the cell plate.

Arabidopsis↗
PubMed1993

[Analysis of left unilateral spatial neglect with a non-visual sensory-motor task].

An experiment was conducted to analyze the space-movement processes which unilateral spatial neglect (USN) patients manifested. Three kinds of movement features were tested which were reported in previous studies; (a) general coarse response tendency, (b) hypokinesia in the disordered space-side, and (c) more frequent response toward the normal space-side. Five left USN patients with right brain damage were compared with five non-USN right brain damaged patients, and five normal controls. As an experimental movement task, a non-visual movement reproduction with regard to kinesthetic sensory modality was adopted. Subjects were blindfolded and asked to reproduce the criterion-movement (length of 10 cm) toward right hand side in space. Three different experimental spaces were used in relation to the subject's body positions; 'left space (range from left shoulder to median line)', 'right space (from median line to right shoulder)', and 'right-outside space (outside of right shoulder)'. The criterion-movement was presented to the subjects, and then they reproduced the movement in either one of these three spaces. Generally, the left USN patients reproduced movements with more errors and less accuracy when the execution side was in the 'left space'. The results confirmed the observation that left USN patients showed more frequent response toward the right hand side direction in the 'left space'. The left USN patients with lesions in frontal and/or basal ganglia regions showed larger errors in this task compared to the left USN patient whose lesion is localized in the parietal region in the right hemisphere.

Aged↗