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PubMed2004

Spatial distributions of observables in systems under thermal gradients.

Departures of observables from their thermal equilibrium expectation values are studied under heat flow in steady-state nonequilibrium environments. The relation between the spatial and temperature dependence of these nonequilibrium behaviors and the underlying statistical properties are clarified from general considerations. The predictions are then confirmed in direct numerical simulations within the Fermi-Pasta-Ulam beta model. Nonequilibrium momentum distribution functions are also examined and characterized through their cumulants and the properties of higher order cumulants are discussed.

Journal Article↗
PubMed1988

In situ hybridization reveals differential spatial distribution of mRNAs for type I and type II collagen in the chick limb bud.

During limb development, type I collagen disappears from the region where cartilage develops and synthesis of type II collagen, which is characteristic of cartilage, begins. In situ hybridization using antisense RNA probes was used to investigate the spatial localization of type I and type II collagen mRNAs. The distribution of the mRNA for type II collagen corresponded well with the pattern of type II collagen synthesis, suggesting control at the level of transcription and mRNA accumulation. In contrast, the pattern of mRNA for type I collagen remained more or less uniform and did not correspond with the synthesis of the protein, suggesting control primarily at the level of translation or of RNA processing.

Animals↗
PubMed2006

Differences in the spatial distribution of airborne pollen concentrations at different urban locations within a city.

BACKGROUND: The objective of the present work was to compare pollen counts at three different urban locations within a city to each other and to the counts from a fixed trap. This information could be useful to delimit zones in the urbanized part of the city according to the risk of allergic affections. METHODS: Aerobiological sampling using portable traps was carried out at three points in urban zones of the city of Badajoz (SW Spain) over one year at the same time as continuous sampling using a fixed trap at a point in the nonurban outskirts of the city. The sources of airborne pollen were studied by counting the trees in the streets and squares of the selected zones. A statistical analysis was performed of the differences between the portable and fixed traps and of the temporal and spatial variation in the city as a function of the distribution of the most important pollen sources. RESULTS: Forty-eight pollen types were identified with the fixed trap, and 28 with the portable traps. The grass, olive, and oak pollens come from almost exclusively external sources, there being no spatial differences in their concentrations in the city. Cypress pollen concentrations were much higher at the urban locations than at the fixed trap site. Plane tree pollen levels could be locally very high, reflecting the proximity of the source. Except for ornamental plants, pollen levels were lower at the urban locations than at the site on the outskirts of the city. CONCLUSIONS: (1) Using portable traps at different urban zones in a city could provide information about the spatial variation of atmospheric pollen levels. (2) A knowledge of the often widely variable distribution of ornamental plants with potentially allergenic pollen could be useful in indicating city zones with a greater or lesser incidence of potential pollinosis.

Air Pollutants↗
PubMed2003

Spatial distribution of Ca(2+) signals during repetitive depolarizing stimuli in adrenal chromaffin cells.

Exocytosis in adrenal chromaffin cells is strongly influenced by the pattern of stimulation. To understand the dynamic and spatial properties of the underlying Ca(2+) signal, we used pulsed laser Ca(2+) imaging to capture Ca(2+) gradients during stimulation by single and repetitive depolarizing stimuli. Short single pulses (10-100 ms) lead to the development of submembrane Ca(2+) gradients, as previously described (F. D. Marengo and J. R. Monck, 2000, Biophysical Journal, 79:1800-1820). Repetitive stimulation with trains of multiple pulses (50 ms each, 2Hz) produce a pattern of intracellular Ca(2+) increase that progressively changes from the typical Ca(2+) gradient seen after a single pulse to a Ca(2+) increase throughout the cell that peaks at values 3-4 times higher than the maximum values obtained at the end of single pulses. After seven or more pulses, the fluorescence increase was typically larger in the interior of the cell than in the submembrane region. The pattern of Ca(2+) gradient was not modified by inhibitors of Ca(2+)-induced Ca(2+) release (ryanodine), inhibitors of IP(3)-induced Ca(2+) release (xestospongin), or treatments designed to deplete intracellular Ca(2+) stores (thapsigargin). However, we found that the large fluorescence increase in the cell interior spatially colocalized with the nucleus. These results can be simulated using mathematical models of Ca(2+) redistribution in which the nucleus takes up Ca(2+) by active or passive transport mechanisms. These results show that chromaffin cells can respond to depolarizing stimuli with different dynamic Ca(2+) signals in the submembrane space, the cytosol, and the nucleus.

Adaptation, Physiological↗
PubMed2001

A review of the contamination of soil with lead II. Spatial distribution and risk assessment of soil lead.

Contamination of soil with lead has occurred on a global scale. Exposure to lead may cause adverse effects to human health and the environment. It is therefore desirable to obtain a quantitative estimate of the potential risk of lead contamination. Numerous studies have been conducted collecting lead concentration data from both natural and contaminated soil on a range of scales. Very few of these studies have made serious attempts to spatially describe the data. In order to identify contaminated land and to enable development of appropriate environmental guidelines, it is essential to have an understanding of the universal range of lead concentrations. Such data also assists in assessing any potential risk to the environment or human health. This paper reviews the multitude of data collected on soil Pb concentrations. Lead surveys are discussed on the basis of land use, with Australian data presented separately. Data from lead surveys of agricultural, urban and industrial areas, as well as nationwide surveys are summarised. A small but increasing number of studies have employed spatial prediction techniques such as kriging to map the distribution of lead concentrations in soil. These studies are also summarised and a brief description of the basis for their use presented. Finally, environmental and health risk assessment is discussed and some methodologies in use around the world reviewed.

Agriculture↗
PubMed1996

Temporal and spatial distribution of ferredoxin isoproteins in tomato fruit.

Five ferredoxin (Fd) isoproteins (FdA, FdB, FdC, FdD, and FdE) were isolated from tomato (Lycopersicon esculentum cv Momotaro) fruit. These isoproteins showed differential temporal and spatial accumulation patterns. FdA and FdC were present in leaves. FdE was present in roots, and FdB and FdD were fruit-specific. During fruit growth, the relative abundance of FdA decreased and that of FdE increased. The FdE/FdA ratio was higher in the inner tissues of the fruit than in the outer tissue, and it was correlated with starch accumulation. In darkgrown fruit the contents of FdA, FdB, and FdC, as well as chlorophyll, decreased remarkably relative to their light-grown counterparts; however, the contents of FdE and starch did not change significantly. Under in vitro conditions FdE showed higher cytochrome c reduction activity than FdA and FdB. These results, together with their N-terminal sequences, indicate that both photosynthetic- and heterotrophic-type Fd isoproteins are present in tomato fruit.

Amino Acid Sequence↗
PubMed2000

Temporal and spatial distribution of the variants of merozoite surface protein-1 (MSP-1) in Plasmodium falciparum populations in Brazil.

The polymorphic, merozoite surface protein-1 (MSP-1) of Plasmodium falciparum, an antigen of the parasite's asexual blood-stages, is a major malaria-vaccine candidate. Nucleotide sequences of each variable domain or block of this antigen may be grouped into one of three possible allelic types (K1, MAD20 and RO33), and 24 major types of the msp-1 gene may be defined, as unique combinations of allelic types in these variable blocks. Isolates collected from the Brazilian Amazon, over a period of 14 years, have now been investigated, by PCR-based typing of the msp-1 gene. Thirteen of the 24 possible gene-types were identified, and 336 P. falciparum clones were fully typed among 239 isolates. Most parasites (87%) belonged to one of the seven most frequent gene-types. Marked temporal variation in the distribution of msp-1 variants was found when comparing parasites sampled in the same sites at intervals of at least 5 years. Spatial variations were also found when comparing parasites from both neighbouring and distant sites within the Amazon Basin. The between-population variance in the frequencies of msp-1 allelic types found in Brazil, as estimated by Wright's FST statistic, is of similar magnitude to that found in previous world-wide comparisons. The potential implications of these findings for the development of an MSP-1-based, multivalent malaria vaccine are discussed.

Alleles↗
PubMed1997

Spatial distribution of dihydropyridine receptors in the plasma membrane of guinea pig cardiac myocytes investigated by correlative confocal microscopy and label-fracture electron microscopy.

Excitation-contraction coupling in cardiac muscle is thought to depend fundamentally on the spatial organization of sarcolemmal dihydropyridine receptors (L-type calcium channels) in relation to ryanodine receptors (calcium-release channels of the sarcoplasmic reticulum). In the present study, we have investigated the distribution of dihydropyridine receptors in the guinea pig myocyte plasma membrane by correlative immunoconfocal microscopy and label-fracture electron microscopy. Label-fracture, a method in freeze-fracture cytochemistry, permits immunogold localization of cell surface proteins in en face membrane views. Taken together, results from confocal microscopy and label-fracture replicas suggest that, in the peripheral plasma membrane, calcium channels are organized predominantly in the form of clusters. Confocal microscopy also suggests a similar organization in the transverse tubules. It is hypothesized that these clusters may lie adjacent to junctional sarcoplasmic reticulum, permitting the close coupling of influx of calcium through plasma membrane calcium channels to trigger release of calcium from the intracellular stores, as part of the mechanism of calcium-induced calcium release.

Animals↗
PubMed1991

Distributed spatial coding in the superior colliculus: a review.

This paper reviews evidence that the superior colliculus (SC) of the midbrain represents visual direction and certain aspects of saccadic eye movements in the distribution of activity across a population of cells. Accurate and precise eye movements appear to be mediated, in part at least, by cells of the SC that have large sensory receptive fields and/or discharge in association with a range of saccades. This implies that visual points or saccade targets are represented by patches rather than points of activity in the SC. Perturbation of the pattern of collicular discharge by focal inactivation modifies saccade amplitude and direction in a way consistent with distributed coding. Several models have been advanced to explain how such a code might be implemented in the colliculus. Evidence related to these hypotheses is examined and continuing uncertainties are identified.

Animals↗
PubMed1997

Age-related changes in the temporal and spatial distributions of fibrillin and elastin mRNAs and proteins in acute cutaneous wounds of healthy humans.

Elasticity and resilience of the skin are determined largely by the elastin framework, whose microfibrillar scaffold is composed of fibrillin. To date, the spatial and temporal patterns of expression of human elastin and fibrillin during would healing have not been described. Ninety healthy human subjects underwent 4 mm cutaneous punch biopsy wounds from the upper inner arm, which were re-excised from day 3 to 3 months post-wounding. There were marked changes in the patterns of distribution and the amounts of elastin and fibrillin in sun-protected skin with ageing. However, there were no major age-related differences in the mRNA levels for elastin, fibrillin-1 and fibrillin-2 using in situ hybridization. Elastin and fibrillin appeared in greatest amounts in the wounds of the elderly, particularly in females. A regenerative pattern of elastin and fibrillin arcades at the dermo-epidermal junction was observed in the wounds of aged subjects. mRNA expression of elastin was greatest in the wounds of the aged (from day 3 to day 14 post-wounding) with a similar spatial and temporal pattern to fibrillin-1 expression; this suggests that fibrillin-1 is the major contributor to dermal elastic fibre construction during wound repair. Fibrillin-2 was expressed only in the wounds of the aged and expression was confined to areas proximal to dermal blood vessels. The clear-cut differences in the localization of the two members of the fibrillin family suggest that these have well-defined roles in normal skin and wound tissue. In summary, these data indicate that ageing is associated with increased expression of fibrillin and elastin during acute wound healing and concomitant restoration of the papillary dermal architecture with an improved quality of scarring.

Acute Disease↗
PubMed2000

Spatial distribution of semicircular canal nerve evoked monosynaptic response components in frog vestibular nuclei.

Most second-order vestibular neurons receive a canal-specific monosynaptic excitation, although the central projections of semicircular canal afferents overlap extensively. This remarkable canal specificity prompted us to study the spatial organization of evoked field potentials following selective stimulation of individual canal nerves. Electrically evoked responses in the vestibular nuclei were mapped systematically in vitro. Constructed activation maps were superimposed on a cytoarchitectonically defined anatomical map. The spatial activation maps for pre- and postsynaptic response components evoked by stimulation of a given canal nerve were similar. Activation maps for monosynaptic inputs from different canals tended to show a differential distribution of their peak amplitudes, although the overlap was considerable. Anterior vertical canal signals peaked in the superior vestibular nucleus, posterior vertical canal signals peaked in the descending and in the dorsal part of the lateral vestibular nucleus, whereas horizontal canal signals peaked in the descending and in the ventral part of the lateral vestibular nucleus. A similar, differential but overlapping, spatial organization of the canal inputs was described also for other vertebrates, suggesting a crude but rather conservative topographical organization of semicircular canal nerve projections within the vestibular nuclei. Differences in the precision of topological representations between vestibular and other sensory modalities are discussed.

Animals↗
PubMed1979

The dynamics of infection of Tribolium confusum by Hymenolepis diminuta: the influence of infective-stage density and spatial distribution.

The mean parasite burden of a population of Tribolium confusum is shown to rise to a plateau as the exposure density of infective eggs of Hymenolepis diminuta increases. The level of this plateau is shown to be dependent on the nutritional status of the host population, being depressed from approximately 18 cysticeroids/beetle in hosts which have been starved prior to experimentation, to approximately 2 cysticercoids/beetle in satiated hosts. A simple model is used to describe the shape of this infection functional response in terms of the predator-prey interaction between hosts (T. confusum) and parasite infective stages (H. diminuta eggs). The distribution of successful infections/host is shown to be over-dispersed, even when hosts are exposed to infective stages arranged in a uniform spatial pattern. The over-dispersion of parasite numbers/host is shown to become more severe as the spatial pattern of infective stages changes from under-dispersed, through random, to over-dispersed. Experimental results are discussed in relation to the dynamics of parasite-host interactions, in which infection takes place by host ingestion of a free-living infective stage.

Feeding Behavior↗
PubMed1993

Detection and spatial distribution of the beta 2 integrin (Mac-1) and L-selectin (LECAM-1) adherence receptors on human neutrophils by high-resolution field emission SEM.

We have developed a method utilizing high-resolution field emission SEM and backscatter electron imaging of immunogold for detection of cell adhesion receptors on the surface of unfixed human neutrophils, using indirect immunogold localization of specific murine monoclonal antibodies (MAb) to the cell adhesion receptors L-selectin (LECAM-1) and the beta 2 integrin (Mac-1). We have observed that these two receptor populations occupy different membrane domains on the surface of unactivated human neutrophils. LECAM-1 was observed to occur in clusters on the tips of microvilli or membrane ruffles and was seldom detected on the membrane of the cell body. On the other hand, Mac-1 was found mainly on the membrane of the cell body in unactivated neutrophils, either singly or in small clusters, and was only rarely encountered on microvilli or ruffles. In contrast, the distribution of Mac-1 on activated, spreading neutrophils was markedly increased (up-regulated) and occurred in clusters on both the membrane of the cell body and also of surface projections, i.e., microvilli and ruffles. The unique distributions of LECAM-1 and Mac-1 on the surface of unactivated human neutrophils, as observed by high-resolution LVSEM, confirm the spatial relationships of these receptor types as predicted by models for the attachment of circulating neutrophils to vascular endothelium and their emigration to sites of inflammation.

Cell Adhesion Molecules↗
PubMedDate not supplied

The spatial distribution of the antagonistic surround of MT/V5 neurons.

The majority (217/325, 66%) of the neurons in the middle temporal (MT) area/V5 show strong antagonistic surrounds, defined here by a decrease of at least 50% in the summation curve. We mapped the antagonistic surround in 145 such cells, using eight circularly distributed surround stimulus patches (Surround Asymmetry Test, SAT) and also mapped the surround in 51 of these 145 cells using a grid consisting of 25 square patches (Surround Mapping Test, SMT). Both tests showed that the angular surround distribution was non-uniform in the majority of these neurons. In half the neurons, the antagonistic surround was asymmetric, and arose from a single region on one side of the excitatory receptive field (ERF). In another quarter of the sample the surround was bilaterally symmetric, and arose from a pair of regions on opposite sides of the ERF. Only the remaining 20% showed a circularly symmetric surround distribution. These three groups differed in their laminar distribution. The SMT showed that, radially, the surround antagonism reached a maximum, on average, at 1.5 times the ERF radius. Detailed comparisons of the spatial relationships of excitatory and inhibitory regions of the RF components shows that non-homogeneity of the surround influence appears to be an intrinsic property of the surround. Such a property may underly the extraction of the surface orientation and curvature from speed patterns.

Animals↗
PubMed2003

Flexural stiffness in insect wings. II. Spatial distribution and dynamic wing bending.

The dynamic, three-dimensional shape of flapping insect wings may influence many aspects of flight performance. Insect wing deformations during flight are largely passive, and are controlled primarily by the architecture and material properties of the wing. Although many details of wing structure are well understood, the distribution of flexural stiffness in insect wings and its effects on wing bending are unknown. In this study, we developed a method of estimating spatial variation in flexural stiffness in both the spanwise and chordwise direction of insect wings. We measured displacement along the wing in response to a point force, and modeled flexural stiffness variation as a simple mathematical function capable of approximating this measured displacement. We used this method to estimate flexural stiffness variation in the hawkmoth Manduca sexta, and the dragonfly Aeshna multicolor. In both species, flexural stiffness declines sharply from the wing base to the tip, and from the leading edge to the trailing edge; this variation can be approximated by an exponential decline. The wings of M. sexta also display dorsal/ventral asymmetry in flexural stiffness and significant differences between males and females. Finite element models based on M. sexta forewings demonstrate that the measured spatial variation in flexural stiffness preserves rigidity in proximal regions of the wing, while transferring bending to the edges, where aerodynamic force production is most sensitive to subtle changes in shape.

Animals↗
PubMed2004

Spatial distribution of inhibitory synaptic connections during development of ferret primary visual cortex.

Intracortical inhibition in the primary visual cortex plays an important role in creating properties like orientation and direction selectivity. However, the development of the spatial pattern of inhibitory connections is largely unexplored. This was investigated in the present study. Tangential slices of layers 2/3 of ferret striate cortex were prepared for whole-cell patch clamp recordings, and presynaptic inhibitory inputs to pyramidal neurons were scanned by local photolysis of Nmoc-caged glutamate. Inhibitory synaptic currents (IPSCs) were first detected around postnatal day (P) 17. They originated locally around the recorded cells. Both the number and the total areas supplying the inhibitory inputs increased thereafter and peaked at the time around and shortly after eye opening (P29-37). A refinement period then followed in which the areas providing the majority of inhibitory inputs shrank from 600 microm around the recorded neurons to 200-300 microm in more mature animals (>/=P38). The amplitude of IPSCs increased progressively with increasing age. Long-range inhibitory inputs (>600 microm) were present around eye opening and they often developed into a clustered patchy pattern in more mature animals (>/=P38). In summary, our results show a refinement and clustering in the spatial pattern of inhibitory connections during postnatal development of ferret visual cortex.

Aging↗
PubMed1985

Spatial distribution of cell fluorescence determined with a diode-matrix (32 x 32 elements) and computer controlled epifluorescence microscopy.

A photodiode-matrix with 32 x 32 light-sensitive elements has been used to determine spatial fluorescence intensity of Rhodamine-labelled yeast cells (Saccharomyces cerevisiae). The matrix with electronics was built into one of the oculars of an epifluorescence microscope, and the fluorescence intensity scanned at intervals, determined from a desk-computer. The signals from one image were amplified and stored in a buffer-memory before being put into an auxiliary memory. The sensitivity of each element was calibrated, and linear regression used to determine true fluorescence intensity (256 levels). After background subtraction the spatial intensity was presented on a plotter either on a 0-9 scale, or on a three-dimensional plot (x-y-intensity). The effect of continuous UV-microphotolysis on the fluorescence of Rhodamine-labelled yeast was also determined.

Computers↗