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At least 649 records · Page 36Linked to original sources
PubMed2005

Spatial extent of degraded sediment quality in Puget Sound (Washington State, U.S.A.) based upon measures of the sediment quality triad.

A survey was designed and conducted to determine the severity, spatial patterns, and spatial extent of degraded sediment quality in Puget Sound (Washington State, USA). A weight of evidence compiled from results of chemical analyses, toxicity tests, and benthic infaunal analyses was used to classify the quality of sediments. Sediment samples were collected from 300 locations within a 2363 km(2) area extending from the US/Canada border to the inlets of southern Puget Sound and Hood Canal. Degraded conditions, as indicated with a combination of high chemical concentrations, significant toxicity, and adversely altered benthos, occurred in samples that represented about 1% of the total area. These conditions invariably occurred in samples collected within urbanized bays and industrial waterways, especially near the urban centers of Everett, Seattle, Tacoma, and Bremerton. Sediments with high quality (as indicated by no toxicity, no contamination, and the presence of a relatively abundant and diverse infauna) occurred in samples that represented a majority (68%) of the total study area. Sediments in which results of the three kinds of analyses were not in agreement were classified as intermediate in quality and represented about 31% of the total area. Relative to many other estuaries and marine bays of the USA, Puget Sound sediments ranked among those with minimal evidence of toxicant-induced degradation.

Aliivibrio fischeri↗
PubMed2000

Evaluating environmental contamination in Ria Formosa (Portugal) using stress indexes of Spartina maritima.

Species of Spartina are potentially useful for biomonitoring coastal systems because they are abundant in the intertidal and have a wide geographic distribution in temperate zones. In this study, three indexes of physiological stress, thiolic protein concentration, adenylic energy charge (AEC) index [AEC = ATP + 0.5ADP/(ATP + ADP + AMP)] and photosynthetic efficiency (Fv/Fm), are measured in Spartina maritima plants collected at four sites and compared with metal concentrations in the sediments and Spartina tissues. Two sites were close to urban centers and two were located further away, in less contaminated areas. Concentrations of copper, cadmium, lead and zinc were determined by atomic absorption spectrophotometry, thiolic proteins were determined by polarography and adenilic nucleotides were determined by high performance liquid chromatography. Photosynthetic efficiencies were measured with a fluorometer. The sediments of sites closer to urban centers had higher concentrations of metals than the sites located further away. Metal concentration within plants did not follow this spatial pattern, probably due to spatial differences in metal bioavailability, uptake rates, internal transport and excretion processes. Concentrations of all metals studied were higher in underground plant structures than aerial, except cadmium whose levels were not significantly different. On the other hand, the stress indexes followed the spatial pattern of metals in the sediment. Thiolic protein concentrations were higher in plants from polluted sites, and were three to four times higher in aerial than in underground plant structures. Leaf AEC ratios and photosynthetic efficiencies were lower in plants from polluted sites indicating that they were growing under stressful conditions. We conclude that the use of these indexes in S. maritima represent a useful tool to monitor contamination in Ria Formosa lagoon as they provide an integrated measure of the toxicological burden of contamination.

Environmental Monitoring↗
PubMed1996

Expression of S9 and actin CyIIa mRNAs reveals dorso-ventral polarity and mesodermal sublineages in the vegetal plate of the sea urchin embryo.

We have used whole amount in situ hybridization to analyze the patterns of expression of two genes, S9 and actin CyIIa, during the development of the sea urchin, Strongylocentrotus purpuratus. We demonstrate that at the late blastula stage, these two mRNAs are expressed specifically by cells of the vegetal plate. Their domains of expression, however, are different. S9 mRNA is broadly distributed within most of the vegetal plate except for the central region, while CyIIa expression is restricted to a population of 10-15 cells in the ventral region of the plate. S9-expressing secondary mesenchyme cells (SMCs) migrate from the vegetal plate into the blastocoel early in gastrulation and later populate the dorsal ectoderm. The numbers, morphology, and migratory behavior of these cells strongly suggest that they are pigment cells. Throughout gastrulation, CyIIa mRNA is expressed by a population of presumptive SMCs at the ventral aspect of the archenteron tip. The pattern of expression of this mRNA is dynamic, however, and by the early pluteus stage, CyIIa mRNA accumulates in primary mesenchyme cells (PMCs), SMCs, and endodermal cells of the gut. When embryos are treated with NiCl2, a compound that has been shown to ventralize other embryonic tissues, CyIIa mRNA is expressed by an increased number of cells in the vegetal plate in a radially symmetrical pattern. The spatial pattern of CyIIa expression provides the first direct molecular evidence that the vegetal plate is polarized along the dorso-ventral (D-V) axis of the embryo. This gene product should be a valuable marker in future studies of D-V axis specification, as it can be detected at earlier developmental stages than existing molecular markers of this axis. Our observations show that the vegetal plate consists of subterritories of gene expression, and provide further support for the view that diversification of the presumptive, non-skeletogenic mesoderm begins prior to the onset of invagination.

Actins↗
PubMed2000

Geostatistical analysis of the distribution of NH(4)(+) and NO(2)(-)-oxidizing bacteria and serotypes at the millimeter scale along a soil transect.

Soil is known to be heterogeneous for different activities at several spatial scales. Most studies have focused on macro- and meso-scales but micro-scales are rarely addressed. Hence, the spatial structure of NH(4)(+)- and NO(2)(-)-oxidizers and of various serotypes of the latter was studied along two transects of approximately 10 cm, with two micro-samples taken from each millimeter. The presence of NH(4)(+)- and NO(2)(-)-oxidizers in a micro-sample was detected using colorimetric tests for the presence or absence of NO(2)(-) in cultures of the micro-samples. Geostatistics was used to determine the range of spatial influence of the bacterial types. For both types, semi-variograms indicated a non-random spatial pattern. The spatial dependence ranged from 2 to 4 mm for NO(2)(-)- and NH(4)(+)-oxidizers respectively, and the two bacterial types were not independently spatially located. Among the six serotypes of NO(2)(-)-oxidizers, only one exhibited a spatial dependence. The existence of a spatial structure at the millimeter scale suggests that micro-scale sampling should be employed for soil studies. Therby, data on bacterial populations and activities can be referred to a spatial scale which is meaningful to these organisms.

Journal Article↗
PubMed2004

Selective ablation of a class of amacrine cells alters spatial processing in the retina.

Several recent studies have suggested that the spatial tuning of retinal ganglion cells may be a more complex process than previously thought. The working hypothesis for many years was that the tuning was shaped by operations performed in the first synaptic layer of the retina, but recent work shows that operations in the second synaptic layer, involving amacrine cells, also play a significant role (Cook and McReynolds, 1998; Taylor, 1999; Flores-Herr et al., 2001). Although it is clear that amacrine cells are involved, the precise roles of the different amacrine subtypes in the many aspects of spatial tuning have not yet been established. Here we used a cell class ablation method to remove one subtype, the neuropeptide Y-expressing cells (NPY cells), and tapped into a part of the circuitry that tunes ganglion cells toward large spatial patterns (low spatial frequencies). When the subtype was ablated, ganglion cells tuned toward low spatial frequencies, both ON- and OFF-type cells, lost this preferential tuning. The effect was specific because ablation of another amacrine subtype did not produce it. Further analysis showed that the change in tuning was attributable to a decrease in the receptive field surround size of the ganglion cell. Other parameters, such as the size, strength, and asymmetry of the center and the strength of the surround, were not statistically significantly affected. These results thus show a mechanism for tuning cells to low spatial frequencies; an operation in the second synaptic layer, mediated by NPY cells, extends the surround of the ganglion cell.

Amacrine Cells↗
PubMedDate not supplied

ABH antigen secretion in Basques and the spatial variation pattern of the secretor locus in Spain.

Secretion of the ABH blood group antigen was analyzed in 305 saliva samples of students in the Basque Country University. The frequency of ABH non-secretor was 26.23%, a result very close to that obtained in autoctonous Basques (22-23%) and in other populations from the West (Galicia) and Centre (Castille) of Spain. With certain exceptions, the frequencies of non-secretor se allele present a fairly homogeneous variability pattern and no significant spatial orientation or tendencies of se gene distribution are observed in the Iberian Peninsula.

ABO Blood-Group System↗
PubMed1987

Developmentally regulated rat brain mRNAs: molecular and anatomical characterization.

In order to identify markers for developing neural cell populations and gain molecular insights into the processes of neural development and differentiation, we have selected cDNA clones of rat brain mRNAs that are expressed in brain at embryonic day 16 (E16) with at least 10-fold greater abundance than they are in adult brain. Eleven such clones were obtained from a cDNA library of E16 brain poly(A)+ RNA using a combination of differential and subtractive hybridization screens. The temporal and spatial patterns of expression of the mRNAs corresponding to these clones were characterized by Northern (RNA) blotting and by in situ hybridization. Although all the mRNAs were enriched in embryonic brain, different mRNAs demonstrated maximum abundance at different times in late embryogenesis. The mRNAs can be grouped into 3 classes on the basis of their patterns of spatial expression in the embryo: one cDNA clone from each class and its corresponding mRNAs have been characterized in more detail. Class C represents mRNAs that are highly enriched in the nervous system and may be expressed in newly differentiating neurons; the example chosen was shown by nucleotide sequence analysis to encode the brain alpha 1 isotype of tubulin. Class B mRNAs have a broader distribution in the developing embryo but are expressed predominantly in the ventricular germinal zones of the developing nervous system and may represent molecules involved with neurogenesis. A third class (Class A) includes mRNAs with a more homogeneous distribution within the embryo and developing nervous system, which may encode "housekeeping" molecules. These clones and their encoded products will provide markers for cell populations at particular stages of neural development.

Animals↗
PubMed1991

Symbol dynamic maps of spatial-temporal chaotic vibrations in a string of impact oscillators.

Spatially complex, temporally chaotic dynamics of N-coupled impact oscillators connected by a string are studied experimentally using a discrete measure of the motion for each of the masses. For N=8, a binary assignment of symbols, corresponding to whether or not the masses impact an amplitude constraint, is used to code the spatial pattern as a binary number and to store its change in time in a computer. A spatial pattern return map is then used to observe the change in spatial patterns with time. Bifurcations in spatial impact patterns are observed in this experiment. An entropy measure is also used to characterize the dynamics. Numerical simulation shows behavior similar to the experimental system.

Journal Article↗
PubMed1995

A survey of spinal dorsal horn neurones encoding the spatial organization of withdrawal reflexes in the rat.

The withdrawal reflex pathways to hindlimb muscles have an elaborate spatial organization in the rat. In short, the distribution of sensitivity within the cutaneous receptive field of a single muscle has a spatial pattern that is a mirror image of the spatial pattern of the withdrawal of the skin surface ensuing on contraction in the respective muscle. In the present study, a search for neurones encoding the specific spatial input-output relationship of withdrawal reflexes to single muscles was made in the lumbosacral spinal cord in halothane/nitrous oxide-anaesthetized rats. The cutaneous receptive fields of 147 dorsal horn neurones in the L4-5 segments receiving a nociceptive input and a convergent input from A and C fibres from the hindpaw were studied. The spatial pattern of the response amplitude within the receptive fields of 118 neurones was quantitatively compared with those of withdrawal reflexes to single muscles. Response patterns exhibiting a high similarity to those of withdrawal reflexes to single muscles were found in 27 neurones located in the deep dorsal horn. Twenty-six of these belonged to class 2 (responding to tactile and nociceptive input) and one belonged to class 3 (responding only to nociceptive input). None of the neurones tested (n = 20) with reflex-like response patterns could be antidromically driven from the upper cervical cord, suggesting that they were spinal interneurones. With some overlap, putative interneurones of the withdrawal reflexes to the plantar flexors of the digits, the plantar flexors of the ankle, the pronators, the dorsiflexors of the ankle, and a flexor of the knee, were found in succession in a mediolateral direction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Optimal movement between patches under incomplete information about the spatial distribution of food items.

If the food distribution contains spatial pattern, the food density in a particular patch provides a forager with information about nearby patches. Foragers might use this information to exploit patchily distributed resources profitably. We model the decision on how far to move to the next patch in linear environments with different spatial patterns in the food distribution (clumped, random, and regular) for foragers that differ in their degree of information. An ignorant forager is uninformed and therefore always moves to the nearest patch (be it empty or filled). In contrast, a prescient forager is fully informed and only exploits filled patches, skipping all empty patches. A Bayesian assessor has prior knowledge about the content of patches (i.e. it knows the characteristics of the spatial pattern) and may skip neighbouring patches accordingly by moving to the patch where the highest gain rate is expected. In most clumped and regular distributions there is a benefit of assessment, i.e. Bayesian assessors achieve substantially higher long-term gain rates than ignorant foragers. However, this is not the case in distributions with less strong spatial pattern, despite the fact that there is a large potential benefit from a sophisticated movement rule (i.e. a large penalty of ignorance). Bayesian assessors do also not achieve substantially higher gain rates in environments that are relatively rich or poor in food. These results underline that an incompletely informed forager that is sensitive to spatial pattern should not always respond to existing pattern. Furthermore, we show that an assessing forager can enhance its long-term gain rate in highly clumped and some specific near-regular food distributions, by sampling the environment in slightly larger spatial units.

Animals↗
PubMed2004

Origin, structure, and role of background EEG activity. Part 1. Analytic amplitude.

OBJECTIVE: To explain the neural mechanisms of spontaneous EEG by measuring the spatiotemporal patterns of synchrony among beta-gamma oscillations during perception. METHODS: EEGs were measured from 8 x 8 (5.6 x 5.6 mm2) arrays fixed on the surfaces of primary sensory areas in rabbits that were trained to discriminate visual, auditory or tactile conditioned stimuli (CSs) eliciting conditioned responses (CRs). EEG preprocessing was by (i) bandpass filtering to extract the beta-gamma range (deleting theta-alpha); (ii) low-pass spatial filtering (not high-pass Laplacians used for localization), (iii) spatial averaging (not time averaging used for evoked potentials), and (iv) close spacing of 64 electrodes for simultaneous recording in each area (not sampling single signals from several areas); (v) novel algorithms were devised to measure synchrony and spatial pattern stability by calculating variances among patterns in 64-space derived from the 8 x 8 arrays (not by fitting equivalent dipoles). These methodological differences are crucial for the proposed new perspective on EEG. RESULTS: Spatial patterns of beta-gamma EEG emerged following sudden jumps in cortical activity called 'state transitions'. Each transition began with an abrupt phase re-setting to a new value on every channel, followed sequentially by re-synchronization, spatial pattern stabilization, and a dramatic increase in pattern amplitude. State transitions recurred at varying intervals in the theta range. A novel parameter was devised to estimate the perceptual information in the beta-gamma EEG, which disclosed 2-4 patterns with high information content in the CS-CR interval on each trial; each began with a state transition and lasted approximately 0.1 s. CONCLUSIONS: The function of each primary sensory neocortex was discontinuous; discrete spatial patterns occurred in frames like those in cinema. The frames before and after the CS-CR interval had low content. SIGNIFICANCE: Derivation and interpretation of unit data in studies of perception might benefit from using multichannel EEG recordings to define distinctive epochs that are demarcated by state transitions of neocortical dynamics in the CS-CR intervals, particularly in consideration of the possibility that EEG may reveal recurring episodes of exchange and sharing of perceptual information among multiple sensory cortices. Simultaneously recorded, multichannel beta-gamma EEG might assist in the interpretation of images derived by fMRI, since high beta-gamma EEG amplitudes imply high rates of energy utilization. The spatial pattern intermittency provides a tag to distinguish gamma bursts from contaminating EMG activity in scalp recording in order to establish beta-gamma recording as a standard clinical tool. Finally, EEG cannot fail to have a major impact on brain theory.

Acoustic Stimulation↗
PubMed2001

A comparison of tactile spatial sensitivity on the palm and fingerpad.

Studies of tactile spatial pattern perception have, for the most part, been carried out using the fingerpad. On the basis of these studies, models have been developed linking spatial pattern identification and resolution with underlying neural structures. It has been suggested that with appropriate scaling, these models would apply to the processing of spatial patterns presented to other sites on the body. Spatial sensitivity was examined on another site on the body, the palm, using two measures, letter identification and grating orientation. The results from these measures were compared with results from similar studies conducted on the fingerpad and with estimates of the density of innervation of the fingerpad and palm. To produce levels of performance similar to those on the fingerpad required letters on the palm 50 mm in height, seven to nine times larger than those used on the fingerpad. Gratings had to be six to more than seven times larger on the palm to produce the same levels of performance achieved on the fingerpad. For the two types of receptor systems sensitive to spatial information, the ratio of density of innervation between the fingerpad and the palm is estimated to be 5.7:1 and 8.8:1. Performance of spatial tasks on the palm can be predicted quantitatively from fingerpad data with a moderate degree of accuracy. Qualitative comparisons between the palm and fingerpad data indicate that spatial patterns are processed similarly at the two sites.

Adult↗
PubMed1996

Temporal and spatial expression patterns of two G-protein coupled receptors in Drosophila melanogaster.

Temporal and spatial expression patterns of a muscarinic acetylcholine receptor (Acr60C) and an octopamine/tyramine receptor (Octyr) were determined in Drosophila melanogaster using quantitative Northern analysis and in situ hybridization to tissue sections. Expression of mRNA encoding both of these G-protein coupled receptors peaks initially in 18 to 21 hour embryos following the formation of the mature larval nervous system. Levels of mRNA then decline during larval stages, rising to a second peak in 3 to 4-day-old pupae after a period of major nervous system reorganization. The muscarinic acetylcholine receptor mRNA is expressed throughout the cortical regions of the central nervous system in adults and embryos. Particularly high levels of expression of Acr60C are observed in cell bodies adjacent to the antennal lobes, suggesting a major role for this muscarinic receptor in the processing of olfactory information. In contrast, the octopamine/tyramine receptor mRNA is distributed diffusely throughout the adult brain, with patches of signal concentrated in the cortex of the dorsal protocerebrum near the mushroom bodies. These patches may represent individual cells expressing Octyr receptors.

Animals↗
PubMed1990

Optical assessment of spatially ordered patterns of neural response to vagal stimulation in the early embryonic chick brainstem.

Spatial dynamic patternings of electrical responses to vagal nerve stimulations in the embryonic chick brainstem preparation were assessed by means of simultaneous multiple-site optical recordings of electrical activity. The vagus/brainstem preparations were dissected from early 7-day-old chick embryos (165-172 h after incubation), and they were stained with a voltage-sensitive merocyanine-rhodanine dye (NK2761). Application of depolarizing square current pulses to the vagus nerve fibers using a suction electrode evoked voltage-related optical (absorbance) signals that were recorded simultaneously from 127 contiguous sites in the whole brainstem preparation using a 12 x 12-element photodiode array. The optical signals evoked by the vagus nerve stimulation appeared to be concentrated longitudinally in the central region and in the lateral region ipsilateral to the site of brainstem stimulation. These response areas were orderly changed according to changes in the strength and in the duration of the stimulating current: the response area expanded as the strength or the duration of the stimulating current was increased. The size of the evoked optical signals also depended on the strength and on the duration of the stimulating current. We also measured critical (threshold) values of the strength and duration of the stimulating current to produce the optical responses, and we found that there was a regionally ordered distribution in the brainstem. In the experiments on transverse slices of the brainstem, the evoked optical responses were detected from limited areas near the dorsal surface of the stimulated side, and the response pattern depended on the strength and duration of the stimulating current in a manner similar to that in the whole brainstem preparations. On the basis of the data obtained from these experiments, we have constructed 3 kinds of response maps for the embryonic brainstem, and the results suggest the functionally ordered arrangement of the neurons in the vagus-related area in the embryonic brainstem.

Animals↗
PubMed2001

Spatial expression patterns of genes involved in cyclic AMP responses in Dictyostelium discoideum development.

The spatial expression patterns of genes involved in cyclic adenosine monophosphate (cAMP) responses during morphogenesis in Dictyostelium discoideum were analyzed by in situ hybridization. Genes encoding adenylyl cyclase A (ACA), cAMP receptor 1, G-protein alpha2 and beta subunits, cytosolic activator of ACA (CRAC and Aimless), catalytic subunit of protein kinase A (PKA-C) and cAMP phosphodiesterases (PDE and REG-A) were preferentially expressed in the anterior prestalk (tip) region of slugs, which acts as an organizing center. MAP kinase ERK2 (extracellular signal-regulated kinase-2) mRNA, however, was enriched in the posterior prespore region. At the culmination stage, the expression of ACA, CRAC and PKA-C mRNA increased in prespore cells in contrast with the previous stage. However, no alteration in the site of expression was observed for the other mRNA analyzed. Based on these findings, two and four classes of expression patterns were catalogued for these genes during the slug and culmination stages, respectively. Promoter analyses of genes in particular classes should enhance understanding of the regulation of dynamic and coordinated gene expression during morphogenesis.

Animals↗
PubMed2004

Spatial contouring of risk: a tool for environmental epidemiology.

The possible elevation of disease rates in the proximity of site-specific environmental hazards is much investigated. Single-site studies are subject to problems of reporting bias and statistical power, and multisite studies to heterogeneity of exposure. Both types of studies usually use concentric circular regions centered on a site as a surrogate for defining the exposed and unexposed populations. This approach does not take into account the actual spatial pattern of toxicant dispersion or the spatial pattern associated with the population, and so much useful information is wasted. We report a kernel density technique to map risk contours for disease, which is not influenced by the coordinates of any putative environmental hazard and which could be married to actual spatial exposure patterns.

Cluster Analysis↗
PubMed1997

Tactile pattern perception by two fingers: temporal interference and response competition.

The identification of a spatial pattern (target) presented to one fingerpad may be interfered with by the presentation of a second pattern (nontarget) to either the same fingerpad or a second fingerpad. A portion of the interference appears to be due to masking and a portion to response competition. In the present study, vibrotactile spatial patterns were designed to extend over two fingerpads. Target and nontarget patterns were presented to the same two fingerpads with a temporal separation between the two patterns. The function relating target identification to the temporal separation between the target and nontarget was very similar to the functions obtained with one-finger patterns in temporal masking studies. Subsequent measurements showed that a substantial portion of the interference resulted from response competition. Pattern categorization was better when patterns were presented to two fingers on opposite hands than to two fingers on the same hand; however, there was more interference for patterns presented bilaterally than for patterns presented ipsilaterally. The results supported the conclusion that similar processes are involved in the perception of sequences of spatial patterns whether the patterns are presented to one or to two fingers.

Adult↗
PubMed2003

Landscape dynamitic change in Mu Us Desert derived from Landsat TM data.

Landscape ecology emphasizes large areas and ecological effects of the spatial patterning of ecosystem. Recent developments in landscape ecology have emphasized the important relationship between spatial patterns and many ecological processes. Quantitative methods in landscape ecology link spatial patterns and ecological processes at broad spatial and temporal scales. In turn the increased attention on temporal change of ecosystem has highlighted the need for quantitative methods that can analyze patterns. This research applies quantitative methods--change detection to assess the ecosystem temporal change in the arid and semiarid area. Remote sensing offers the temporal change of ecosystem on landscape characteristics.

China↗