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At least 1,279 records · Page 71Linked to original sources
PubMed2005

Serca isoform expression in the mammalian retina.

The sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA) is a key intracellular calcium transporter, which regulates cellular calcium concentration [Ca2+] by transporting Ca2+ ions from the cytosol into the endoplasmic reticulum. SERCA-mediated Ca2+ sequestration controls proper folding of newly synthesized proteins within the ER as well as the timing and spatial patterning of depolarization-evoked Ca2+ responses in the cytoplasm. To understand the spatial and temporal properties of Ca2+ homeostasis in retinal neurons better, I studied expression and distribution of all three SERCA isoforms in the mouse retina using isoform-specific antibodies. No immunostaining was observed with the SERCA1 antibody. SERCA2 was expressed in photoreceptor inner segments, amacrine and ganglion cells of the mouse retina. Similar SERCA2 localization was observed in adult rat, macaque and ground squirrel retinas. Analysis of distribution of SERCA2 immunofluorescence in the developing mouse retina revealed prominent SERCA2 signals throughout postnatal development. The N89 antibodys used to identify the SERCA3 isoforms labelled cone outer segments, inner segments of photoreceptors and cell processes in the inner nuclear layer of the mouse retina. These results imply that the SERCA2 isoform controls Ca2+ sequestration into the endoplasmic reticulum in most classes of retinal neuron. A potential role for SERCA3 in cone function is suggested.

Animals↗
PubMed2003

Multiplatform optical monitoring of eutrophication in temporally and spatially variable lakes.

Representative spatial patterns of eutrophication variables cannot be produced using traditional in situ sampling techniques. Spatial heterogeneity complicates the study of seasonal and long-term trends and the evaluation of water management policies. Remote sensing, however, with its broad view has the potential to deliver the relevant information. This paper will address the added value of synoptic eutrophication maps to the standard monitoring program of two large, spatially and temporally variable lakes in the Netherlands, Lakes IJssel and Marken. Remote sensing images were obtained from SeaWiFS; and combined with hyperspectral reflectance data from the airborne EPS-a sensor and the shipboard PR-650 spectroradiometer. The PR-650 data were used in selecting the most appropriate algorithms for SeaWiFS and EPS-a. A special algorithm for case II waters with high chlorophyll content was applied to SeaWiFS data to obtain chlorophyll concentrations. Synoptic maps of suspended matter were retrieved using inversion of a model for irradiance reflectance. For the airborne sensor inversion of reflectance was used for both suspended matter and chlorophyll. Satellite and airborne sensors clearly are complementary to each other. Comparison of satellite data with the airborne data and the (scarcely available) in situ data reveal underlying problems with: (i) validation of remote sensing images; and (ii) comparing data at different spatial and temporal scales. In our study, we found a reasonable agreement between different data sources at seasonal time scales, but at shorter time scales the differences can be (much) larger. In situ data suffer from poor reproducibility, related to the natural variability at small spatial scales (patchiness), combined with a significant temporal variability. The standard in situ monitoring program in Lakes IJssel and Marken lacks both the necessary spatial coverage as well as an appropriate sampling frequency. This indicates that for reliable monitoring, a synoptic data set, sampled at a high frequency is required. Remote sensing can partially fulfil this demand but still lacks the demanded frequency, mainly due to regular cloud cover. The answer may be in a multiplatform monitoring approach, as used in our study (combining in situ data with shipboard, airborne and satellite optical data) and in combining monitoring data with models. Satellite remote sensing is most powerful in determining properties that are inherent to the whole lake system, like the overall mean chlorophyll-a concentration. Computational models may meet the demand for a sufficiently high sampling frequency by deterministic interpolation of the data in time.

Chlorophyll↗
PubMed2003

Development of the human cerebral cortex: a histochemical study.

In recent years, improvement in diagnostic techniques has led to better recognition of "disorders of cortical development". These disorders constitute a significant cause of epilepsy, mental retardation, developmental delay and neurological deficits in childhood, and may also contribute to the pathogenesis of psychological and neurodegenerative diseases in adults. Hitherto, however, few systematic studies of the human fetal cortex have been performed, and little is known about the ontogenetic processes of the neocortex in man. The aim of the study is to establish an understanding of the developmental events that occur in the second and third trimesters of gestation, by investigating the biochemical patterns of development of the human neocortex during this period. The temporal and spatial patterns of expression of the neuronal markers gamma-aminobutyric acid (GABA), choline acetyltransferase (ChAT), dopamine beta hydroxylase (DBH), dopamine receptor DR1 and synaptophysin, as well as the glial cell markers glial fibrillary acidic protein (GFAP), S100B and excitatory amino acid transporter protein GLT-1 are delineated in the fetal cortex using immunohistochemistry. Results of this study showed that different neuronal and glial cell proteins follow different developmental patterns and many show inter- or intra-regional variations in expression. Details of these patterns are described and discussed. The early expression of these proteins suggests that they play important roles in the developmental processes of cell proliferation, migration and differentiation. Both neurotransmitters and glial cell proteins probably function outside the confines of synapses in the fetal brain, as paracrine/autocrine factors. Early developmental events seem to be dictated by an innate programme, whereas late events may be more susceptible to extrinsic influences. It is hoped that knowledge of the normal developmental process can lead to better understanding of the causes and mechanisms of "disorders of cortical development", and to better treatments.

Acetylcholine↗
PubMed2004

Using reporter genes to study cis-regulatory elements.

This chapter summarizes four powerful assays for analyzing gene expression in cis-regulatory studies. The enzymatic assays (CAT, luciferase, lacZ) are currently limited by their application to embryo homogenates or fixed samples, but offer more robust analysis of gene activity than GFP. Assays based on CAT enzymatic activity or on CAT mRNA detection by WMISH are laborious but are well established for accurately quantifying gene expression and to determine spatial patterns at defined timepoints during development. LacZ assays are the current standard for spatially visualizing gene products in whole-mount fixed embryos. They are very sensitive but they provide limited temporal or quantitative information due to the perdurance of beta-galactosidase and the subtleties of the staining technique. Recently developed luciferase assays promise to be even more sensitive and accurate than the CAT and lacZ assays, and applicable to living cells and embryos. But, they have not yet been well established in invertebrate deuterostome research. GFP allows visualization of gene expression within living embryos. But because this is not an enzymatic assay, sensitivity can be a problem, particularly for weak promoters. Furthermore, imaging live embryos and quantifying gene expression in space and time (due to scattering of light by tissue, the perdurance of GFP, and other experimental details) is currently fraught with challenges. Ongoing improvements in imaging technology and the advent of multiple fluorescent proteins, as well as fluorescent and luminescent assays for vital imaging, will dramatically facilitate studies of gene expression in the coming decade.

Animals↗
PubMed2002

Pattern-motion responses in human visual cortex.

Physiological models of visual motion processing posit that 'pattern-motion cells' represent the direction of moving objects independent of their particular spatial pattern. We performed fMRI experiments to identify neuronal activity in the human brain selective for pattern motion. A protocol using adaptation to moving 'plaid' stimuli allowed us to separate pattern-motion responses from other types of motion-related activity within the same brain structures, and revealed strong pattern-motion selectivity in human visual area MT+. Reducing the perceptual coherence of the plaids yielded a corresponding decrease in pattern-motion responsivity, providing evidence that percepts of coherent motion are closely linked to the activity of pattern-motion cells in human MT+.

Adult↗
PubMed2001

Additive noise in noise-induced nonequilibrium transitions.

We study different nonlinear systems which possess noise-induced nonequlibrium transitions and shed light on the role of additive noise in these effects. We find that the influence of additive noise can be very nontrivial: it can induce first- and second-order phase transitions, can change properties of on-off intermittency, or stabilize oscillations. For the Swift-Hohenberg coupling, that is a paradigm in the study of pattern formation, we show that additive noise can cause the formation of ordered spatial patterns in distributed systems. We show also the effect of doubly stochastic resonance, which differs from stochastic resonance, because the influence of noise is twofold: multiplicative noise and coupling induce a bistability of a system, and additive noise changes a response of this noise-induced structure to the periodic driving. Despite the close similarity, we point out several important distinctions between conventional stochastic resonance and doubly stochastic resonance. Finally, we discuss open questions and possible experimental implementations. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed1994

The role of intervening patterns in the storage of the movement aftereffect.

Wohlgemuth, having measured the duration of the motion aftereffect (MAE), instructed subjects to close their eyes immediately after adaptation for a period of time longer than the MAE. Upon opening their eyes the subjects reported a residual effect, albeit somewhat shorter than the original effect. Thus the decay of the aftereffect appeared to have been retarded by the period of darkness. This effect is known as 'storage' and poses a problem for any model of the MAE based on the fatiguing of direction-selective units in the visual pathway. A reexamination is made of storage of the MAE, again concentrating on the intervening stimulation between movement adaptation and aftereffect test. The results suggest that the nature of the intervening pattern between adaptation and test conditions is remarkably unimportant. A total of 11 different storage patterns were examined after adaptation to high-contrast drifting horizontal sinewave gratings. For 10 of these patterns large and robust storage effects were found. The exception occurred when the spatial pattern of the storage stimulus was identical to the adaptation and test stimuli. It is proposed that storage cannot be understood in terms of a simple fatigue model of the MAE and that one component of the effect may share similarities with contingent aftereffects.

Contrast Sensitivity↗
PubMed2003

Proper multivariate conditional autoregressive models for spatial data analysis.

In the past decade conditional autoregressive modelling specifications have found considerable application for the analysis of spatial data. Nearly all of this work is done in the univariate case and employs an improper specification. Our contribution here is to move to multivariate conditional autoregressive models and to provide rich, flexible classes which yield proper distributions. Our approach is to introduce spatial autoregression parameters. We first clarify what classes can be developed from the family of Mardia (1988) and contrast with recent work of Kim et al. (2000). We then present a novel parametric linear transformation which provides an extension with attractive interpretation. We propose to employ these models as specifications for second-stage spatial effects in hierarchical models. Two applications are discussed; one for the two-dimensional case modelling spatial patterns of child growth, the other for a four-dimensional situation modelling spatial variation in HLA-B allele frequencies. In each case, full Bayesian inference is carried out using Markov chain Monte Carlo simulation.

Alleles↗
PubMed2001

Different cost of reproduction for the males and females of the rare dioecious shrub Corema conradii (Empetraceae).

Males and females of dioecious plant species often differ in their reproductive investment. Such differences frequently result in differential demographic costs represented by lower growth, survival, and/or frequency of reproduction, and/or by more variable reproductive effort through time for females. We present the results of a study on Corema conradii, a rare dioecious shrub of the coastal dune heathlands of northeastern North America. We estimated the reproductive investment of both males and females, determined their age structure, and compared their spatial patterns in a population at Îles-de-la-Madeleine, Quebec. We also determined the sex ratio of the four populations known to occur on the islands. Males invested more in reproduction at flowering, but when fruit production was considered, female reproductive investment was higher in terms of biomass, Mg, and Ca, but not in terms of N, P, and K. The age frequency distribution of males and females did not differ significantly from one another. The population dispersion pattern was contagious, with patches of similar-age individuals. There was no spatial segregation between males and females, although the sex ratio varied somewhat spatially. Females did not start reproducing at a later age than males and did not appear to have a shorter longevity. However, the crown and radial growth rates of females were lower than those of males. When estimated by the crown intercept method, the sex ratio of all four populations was male biased. However, because males had a higher crown growth rate, genet sex ratio was in fact balanced. Higher investment in reproduction was associated with a lower growth rate, which represents a differential cost of reproduction according to sex in this species.

Journal Article↗
PubMed1986

The genetic structure of a tribal population, the Yanomama Indians. XV. Patterns inferred by autocorrelation analysis.

Fifteen allele frequencies have previously been determined for 50 villages of the Yanomama, an Amerindian tribe from southern Venezuela and northern Brazil. These frequencies were subjected to spatial autocorrelation analysis to investigate their population structure. There are significant spatial patterns for most allele frequencies. Clinical patterns, investigated by one-dimensional and directional spatial correlograms, were relatively few in number and were moderate in strength. Overall, however, there is a marked decline in genetic similarity with geographic distance. The results are compatible with a hierarchic population structure superimposed on the geography, and generated by a stochastic fission-fusion model of village propagation, followed by localized gene flow. Strong temporal autocorrelations of allele frequencies based on linguistic-historical distances representing time since divergence were also found. There appears to be a stronger relation between geography and linguistic-historical hierarchic subdivisions than between either feature and genetic distances. These findings confirm by different approaches the results of earlier analyses concerning the important roles of both stochastic and social factors in determining village allele frequencies and the occurrence within this tribe of some allele frequency clines most likely due to the operation of chance historical processes.

Alleles↗
PubMed2006

Mislocalization of perceived saccade target position induced by perisaccadic visual stimulation.

The perceptual localization of objects flashed at the time of a saccade often shows large spatial distortions. These perisaccadic mislocalizations exhibit different spatial patterns depending on the experimental condition. In darkness, when only extraretinal information is available, mislocalization is spatially uniform. In light and when visual references are available, mislocalization is directed toward the saccade target, resembling a compression of visual space. These patterns are derived from measurements of the absolute perceived position of the flashed object in egocentric space. Here, we report that also the perceived location of the saccade target is altered when an object is flashed perisaccadically. The mislocalization of the target depends on the presentation time of the flashed object and is directed toward the position of the flash. The resulting compression of the relative distance between target and flash is similar in darkness and in light and can also be found during fixation. When the localization of the flashed object is described relative to the perceived location of the saccade target, spatial compression becomes similar in many experimental conditions. We therefore suggest that perisaccadic compression relies on an encoding of relative spatial locations of objects rather than on localizations in egocentric space.

Adult↗
PubMed1978

Visual detection of spatial contrast; influence of location in the visual field, target extent and illuminance level.

A model is proposed that permits the prediction of contrast detection thresholds for arbitrary spatial patterns. The influence of the inhomogeneous structure of the visual field and a form of spatial integration are incorporated in the model. A hypothetical density function for the spatial sampling units, which specifies the distribution of these units with respect to both size and location, is described. The density function is compared with anatomical and electrophysiological knowledge of the density of retinal and cortical receptive fields. This density function permits a particularly lucid interpretation in terms of pattern processing. It can be considered as a system that permits simultaneous global and focal views of the surroundings. Thedensity function, together with a schematized adaptation behaviour of single units, and an incoherent summation rule permit us to calculate a measure of the mass response, and consequently the threshold function. Predictions of the model are compared with recently obtained psychophysical data. In particular an explanation is offered for certain invariance properties of spatial contrast detection that seems to possess promising generality.

Animals↗
PubMed2003

Adaptation at specific loci. VII. Natural selection, dispersal and the diversity of molecular-functional variation patterns among butterfly species complexes (Colias: Lepidoptera, Pieridae).

Natural genetic variants at the phosphoglucose isomerase, PGI, gene differ in spatial patterning of their polymorphism among species complexes of Colias butterflies in North America. In both lowland and alpine complexes, molecular-functional properties of the polymorphic genotypes can be used to predict genotype-specific adult flight performances and resulting large genotypic differences in adult fitness components. In the lowland species complex, there is striking uniformity of PGI polymorph frequencies at a number of sites across the American West; this fits with earlier findings of strong, similar differences in fitness components over this range. In an alpine complex, Colias meadii shows similar uniformity of PGI frequencies within habitat types, either montane steppe or alpine tundra, over several hundred kilometres in the absence of dispersal. At the same time, large shifts (10-20%) in frequency of the most common alleles occur between steppe and tundra populations, whether these are isolated or, as in some cases, are in contact and exchange many dispersing adults each generation. Data on male mating success of common C. meadii PGI genotypes in steppe and tundra show heterozygote advantage in both habitat types, with shifts in relative homozygote disadvantage between habitats which are consistent with observed frequency differences. Nonadaptive explanations for this situation are rejected, and alternative, thermal-ecology-based adaptive hypotheses are proposed for later experimental test. These findings show that strong local selection may dominate dispersal as an evolutionary agent, whether or not dispersal is present, and that selection may often be the major force promoting 'cohesion' of species over long distances. This case offers new opportunities for integrating studies of molecular structure and function with ecological aspects of natural selection in the wild, both within and among species.

Adaptation, Biological↗
PubMed2005

Dancing waves in reaction-diffusion systems.

The mechanism of pattern formation in reaction-diffusion systems is treated as an interesting subject, generally for understanding self-organization observed in living systems and natural phenomena. Several spatial patterns appear in the reaction-diffusion systems where an activator and an inhibitor coexist as an intermediate, as represented by a traveling wave, a stationary wave called a Turing structure, etc. Here, we show new kinds of waves in reaction-diffusion systems, which exhibit reciprocating motion without colliding into each other or blinking periodically. These patterns have never been observed in the conventional numerical models, although experimentally oscillating spots have been often observed. Our model demonstrates that other than the ratio of diffusion coefficients for both intermediates, the thickness of reaction media acts to generate inhibitory effect. The spatial factor of the medium contributes to new pattern formation in reaction-diffusion systems. For the design of new functional materials, the concept might be useful as a simple controlling method for pattern dynamics.

Journal Article↗
PubMed2005

Clonal and spatial genetic structures of aspen (Populus tremuloides Michx.).

To portray aspen clonal and spatial genetic structures, we mapped and genotyped trees in two 1-ha plots, each containing three aspen cohorts originating from fire or subsequent secondary disturbances. We used four microsatellite loci to identify aspen clones and increment core analysis to determine tree age. Clonal dimensions were measured by the maximum distance between two ramets and the number of ramets per genet. Standard normal deviate (SND) was used to assess the spatial distribution of aspen genets and cohorts, and multivariate spatial genetic autocorrelations to assess the spatial distribution of aspen genetic variation. Most aspen genets consisted of only one ramet (> 75%). Median clonal dimensions were 19 and 29 m (maxima: 104 and 72 m in the two plots). No segregation was observed between clones. Aspen cohorts were spatially segregated but trees were spatially aggregated within old and medium-aged cohorts. In contrast, trees were more randomly distributed within the youngest cohorts. This coincided with a spatial genetic autocorrelation at small scales (up to 30 m) in the older cohorts and a more random genetic distribution in the youngest ones. Our results suggest that aspen spatial genetic structuring reflects the spatial patterns produced by the regeneration of discrete cohorts at different stages of succession. Vegetative reproduction leads to aspen genetic spatial structuring at small scales (few metres) until midsuccession. However, as the stand gets older, the spatial distribution of aspen trees and genetic structure evolve from a structured pattern to a more random one under a gap disturbances regime.

Clone Cells↗
PubMed2005

[Spatial and temporal pattern of Castanopsis fargesii seed rain in evergreen broad-leaved forest in Tiantong National Forest Park of Zhejiang, China].

Five mature plants of Castanopsis fargesii population were randomly chosen to study the spatial and temporal pattern of its seed rain in Tiantong National Forest Park, Zhejiang Province in 2003. The duration of seed rain observed from the five samples was about 45 days, from November 3rd to December 16th, with a distinguishable dropping peak between November 18th and 27th. The average seed rain density estimated from the traps deployed under the crown was 112.8 seeds.m(-2), ranging from 70 to 239.5 seeds.m(-2). Of the total acorns collected by seed traps, the viable accounted for 27.3%, the immature 25.7%, the eaten by rodents 5.0%, and the infected by larvae 42.0%. The acorns on the ground mainly distributed under the parent tree crown within 8 m from the trunk, and the spatial pattern of seed density on the ground fitted the quadratic distribution.

China↗
PubMed2005

Toward the neurocomputer: image processing and pattern recognition with neuronal cultures.

Information processing in the nervous system is based on parallel computation, adaptation and learning. These features cannot be easily implemented on conventional silicon devices. In order to obtain a better insight of how neurons process information, we have explored the possibility of using biological neurons as parallel and adaptable computing elements for image processing and pattern recognition. Commercially available multielectrode arrays (MEAs) were used to record and stimulate the electrical activity from neuronal cultures. By mapping digital images, i.e., arrays of pixels, into the stimulation of neuronal cultures, a low and bandpass filtering of images could be quickly and easily obtained. Responses to specific spatial patterns of stimulation were potentiated by an appropriate training (tetanization). Learning allowed pattern recognition and extraction of spatial features in processed images. Therefore, neurocomputers, (i.e., hybrid devices containing man-made elements and natural neurons) seem feasible and may become a new generation of computing devices, to be developed by a synergy of Neuroscience and Material Science.

Animals↗
PubMed1998

Electron transfer kinetics at a biotin/avidin patterned glassy carbon electrode.

Photolithographic techniques using a laser interference pattern were used to attach photobiotin to micron-sized stripes on the surface of a carbon electrode. Fluorophore-tagged avidin was attached to this spatially-patterned biotin with essentially no loss in spatial resolution. The kinetics of the glassy carbon surface were examined to see if electron transfer sites could indeed be segregated from the attachment sites of photobiotin-immobilized avidin. The ECL of luminol and SECM were used to verify the segregation between underivatized sites (which exhibit normal electron transfer kinetics) and extensively derivatized biotin/avidin surfaces (which presumably exhibit slow electron transfer kinetics). Both techniques were found to be capable of differentiating the protein-covered surface from bare carbon with sufficient resolution to tell whether a significant portion of the carbon surface is still active and available to detect the product of an enzyme generated analyte. These results indicate that extensive biotin/avidin derivatization of the surface does decrease the electron transfer rate of a carbon electrode, and that the photolithographic approach was able to modify specific sections of the electrode surface, while leaving other regions untouched and available for facile electron transfer. This leads to a more general protocol for the construction of enzyme-based biosensors which utilize diffusable mediators.

Avidin↗