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At least 1,243 records · Page 69Linked to original sources
PubMed2004

Focused array transducer for two-dimensional optoacoustic tomography.

Optoacoustic (OA) imaging utilizes short laser pulses to create acoustic sources in tissue and time resolved detection of generated pressure profiles for image reconstruction. The ultrasonic transients provide information on the distribution of optical absorption coefficient that can be useful for early cancer diagnostics. In this work a new design of wide-band array transducer is developed and tested. The array consists of 32 focused piezo-elements made of PVDF slabs imposed on a cylindrical surface. A single array element response to an OA signal coming from arbitrarily located point source is investigated theoretically and experimentally. The measured signals correspond well to numerically calculated ones. Focal zone maps of the elements with aperture angles 30 degrees and 60 degrees are presented and discussed; the resolution in direction perpendicular to the imaging plane is determined. Point spread function of the whole array is calculated using experimentally obtained signals from the sources located at different distances from the array. Backprojection algorithm is employed for reconstruction of the optoacoustic images. It is shown that the spatial resolution of the images yielded by the proposed array increases significantly compared to previous transducer designs.

Equipment Design↗
PubMed1975

Localized desensitization of Limulus photoreceptors produced by light or intracellular calcium ion injection.

Spots of light were used to measure the light sensitivity of spatially separated regions of single Limulus photoreceptors. The desensitization caused by irradiating part of the cell was largest in the irradiated region. The desensitization caused by intracellular calcium ion injection was largest near the infection site. The spread of desensitization away from the injection site suggests that calcium ion can diffuse over neuronal dimensions, but that the effective rate of diffusion is not so high as to abolish calcium gradients. The results are compatible with the previously proposed hypothesis that a rise in the intracellular calcium ion concentration mediates light adaptation.

Animals↗
PubMed2005

Spatial variability of soil phosphorus in relation to the topographic index and critical source areas: sampling for assessing risk to water quality.

A measure of soil P status in agricultural soils is generally required for assisting with prediction of potential P loss from agricultural catchments and assessing risk for water quality. The objectives of this paper are twofold: (i) investigating the soil P status, distribution, and variability, both spatially and with soil depth, of two different first-order catchments; and (ii) determining variation in soil P concentration in relation to catchment topography (quantified as the "topographic index") and critical source areas (CSAs). The soil P measurements showed large spatial variability, not only between fields and land uses, but also within individual fields and in part was thought to be strongly influenced by areas where cattle tended to congregate and areas where manure was most commonly spread. Topographic index alone was not related to the distribution of soil P, and does not seem to provide an adequate indicator for CSAs in the study catchments. However, CSAs may be used in conjunction with soil P data for help in determining a more "effective" catchment soil P status. The difficulties in defining CSAs a priori, particularly for modeling and prediction purposes, however, suggest that other more "integrated" measures of catchment soil P status, such as baseflow P concentrations or streambed sediment P concentrations, might be more useful. Since observed soil P distribution is variable and is also difficult to relate to nationally available soil P data, any assessment of soil P status for determining risk of P loss is uncertain and problematic, given other catchment physicochemical characteristics and the sampling strategy employed.

Databases, Factual↗
PubMed1986

[Movement of temperature waves across the cerebral cortex of the white rat].

In acute experiments on immobilized or anesthetized white rats the spatial distribution and dynamics of temperature on the dorsal surface of the cerebral cortex were investigated by the thermovision technique and digital image processing through the intact skull. Under certain conditions the appearance of moving thermowaves that spread over the cortex for 8-30 mm during 2-9 s with a rate of 2-10 mm/s was found. Among the trajectories of these waves the circular one was more common: it began in one hemisphere, spread in one or another direction, then went over to the second hemisphere, moved in the opposite direction and came back to the initial zone. Linear and semicircular trajectories were found as well with or without crossing from one hemisphere to the other. The mechanisms and possible functional significance of the effect are discussed.

Animals↗
PubMed2006

Effects of heterogeneity on spread and persistence in rivers.

The question how aquatic populations persist in rivers when individuals are constantly lost due to downstream drift has been termed the "drift paradox." Recent modeling approaches have revealed diffusion-mediated persistence as a solution. We study logistically growing populations with and without a benthic stage and consider spatially varying growth rates. We use idealized hydrodynamic equations to link river cross-sectional area to flow speed and assume heterogeneity in the form of alternating patches, i.e., piecewise constant conditions. We derive implicit formulae for the persistence boundary and for the dispersion relation of the wave speed. We explicitly discuss the influence of flow speed, cross-sectional area and benthic stage on both persistence and upstream invasion speed.

Animals↗
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↗
PubMed1993

Spatial aspects of Ca2+ signalling in pancreatic acinar cells.

Secretory cells do not only respond to an agonist with a simple rise in [Ca2+]i. It is now clear that complex patterns of [Ca2+]i elevation in terms of space and time are observed in many cell types and that these patterns may be a cellular mechanism for the regulation of different responses. Ca2+ signalling in exocrine cells of the pancreas promotes the secretion of digestive enzymes and fluid. It has been shown that at high concentrations of agonist (acetylcholine or cholecystokinin) the [Ca2+]i response is initiated in the secretory pole of the cell before spreading across the whole cell. This site of initiation of the [Ca2+]i elevation is in the region where exocytotic release of enzymes occurs and is also the site of a Ca(2+)-dependent chloride channel thought to be crucially important for fluid secretion. Lower concentrations of agonist elicit [Ca2+]i oscillations with complex repetitive patterns characteristic of each agonist. At physiological agonist concentrations, we have recently described repetitive short-lasting Ca2+ spikes that are spatially restricted to the secretory pole of the cell. In addition to these spikes, cholecystokinin also promotes slow transient Ca2+ rises that result in a global rise in Ca2+. The inositol trisphosphate (InsP3) receptor plays a crucial role in all of these various agonist responses, most of which can be reproduced by the infusion of InsP3 into the cell. The high InsP3-sensitivity of the secretory pole is postulated to be due to a localization of high-affinity InsP3 receptors. We speculate that in response to cholecystokinin the short-lasting spikes elicit exocytosis from a small 'available pool' of vesicles and that the broader oscillations induce both exocytosis and cell changes that involve movement of vesicles into this 'available pool'.

Acetylcholine↗
PubMed1995

Salamander olfactory bulb neuronal activity observed by video rate, voltage-sensitive dye imaging. II. Spatial and temporal properties of responses evoked by electric stimulation.

1. Video imaging of changes in voltage-sensitive dye (VSD) fluorescence was used to analyze spatial and temporal properties of activity patterns in the in vivo salamander olfactory bulb and primordium piriform cortex after electric stimulation. Distribution of activity among and within the neuronal layers was analyzed after orthodromic stimulation of the whole olfactory nerve (ON), isolated fascicles, or local epithelial sites, and after antidromic stimulation of the medial olfactory tract (OT). 2. Optical signals propagated through the bulbar layers with a sequence that correlates with electrophysiological responses. After orthodromic stimulation, VSD responses started in the glomerular layer, spread to the deeper laminae, and, after reaching the region of mitral/tufted somata, were observed as a brief burst of activity in the OT. Compound action potentials in the ON were associated with short-duration, rapidly depolarizing optical responses in the ON layer. Responses in glomerular layer and external plexiform layer (EPL) first showed in some recordings a brief, small-amplitude hyperpolarization, followed by a period of depolarization, followed by a second, longer-lasting hyperpolarization. The periods of optical hyperpolarization could be related to events observed in intracellular mitral/tufted cell recordings. 3. With shocks delivered to the entire ON, depolarizing responses were nonhomogeneously distributed, appearing as multiple foci or bands of activity. Spatial patterns within each bulbar layer had poorly defined borders. Sites showing short-latency responses were often those with the largest and longest-lasting activity. 4. Increasing the intensity of stimulation to the ON enhanced the size and duration of the depolarizing and hyperpolarizing responses. The short-latency, early hyperpolarization was best seen with low-intensity, peripherally placed stimuli. 5. ON stimulation also elicited activity in the contralateral bulb. Activity started at the innermost layers and spread in patches to regions of the EPL just beneath the glomeruli. These had durations similar to ipsilateral responses, but longer latencies. A period of early hyperpolarization, longer than that on the ipsilateral side, was followed by prolonged depolarization and then by a second, later hyperpolarization. 6. Antidromic stimuli applied to the OT evoked optical responses consisting of a period of depolarization followed by hyperpolarization, similar to the components elicited by orthodromic stimuli. These responses had short time courses, began in the deeper layers, and spread to the superficial region of the bulb usually without reaching the glomerular region. 7. Punctate stimulation of the mucosa or nerve elicited depolarizing and hyperpolarizing events that depended on the stimulation site.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2005

Imagined rotations of self versus objects: an fMRI study.

This study used functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying two types of spatial transformations: imagined object rotations and imagined rotations of the self about an object. Participants viewed depictions of single three-dimensional Shepard--Metzler objects situated within a sphere. A T-shaped prompt appeared outside of the sphere at different locations across trials. In the object rotation task, participants imagined rotating the object so that one of its ends was aligned with the prompt. They then judged whether a textured portion of the object would be visible in its new orientation. In the self rotation task, they imagined rotating themselves to the location of the T-prompt, and then judged whether a textured portion of the object would be visible from the new viewpoint. Activation in both tasks was compared to respective control conditions in which identical judgments were made without rotation. A direct comparison of self and object rotation tasks revealed activation spreading from left premotor to left primary motor (M1) cortex (areas 6/4) for imagined object rotations, but not imagined self rotations. In contrast, the self rotation task activated left supplementary motor area (SMA; area 6). In both transformations, activation also occurred in other regions. These findings provide evidence for multiple spatial-transformation mechanisms within the human cognitive system.

Adult↗
PubMed2006

CdGAP associates with actopaxin to regulate integrin-dependent changes in cell morphology and motility.

BACKGROUND: Integrin signaling, stimulated by cell adhesion to the extracellular matrix, plays a critical role in coordinating changes in cell morphology and migration. The requisite remodeling of the cytoskeleton is controlled by the Rho family of small GTPases, which are, in turn, regulated via activation by guanine-nucleotide exchange factors (GEFs) and inactivation by GTPase-activating proteins (GAPs). However, the mechanisms contributing to the precise spatial and temporal regulation of these Rho GTPase modulators remain poorly understood. RESULTS: The Cdc42/Rac GAP CdGAP has previously been implicated as an inhibitor of growth-factor-induced lamellipodia formation. Herein, CdGAP is shown to localize to focal adhesions, potentially through its direct association with the amino terminus of actopaxin, a paxillin and actin binding protein. CdGAP activity is regulated in an adhesion-dependent manner and, through the overexpression of wild-type CdGAP and a GAP-deficient mutant, as well as RNA interference, is shown to be required for normal cell spreading, polarized lamellipodia formation, and cell migration. Introduction of an actopaxin mutant defective for CdGAP binding, or reduction of actopaxin by using RNAi, significantly attenuated these effects. CONCLUSIONS: We have established that CdGAP is an important regulator of integrin-induced Rho family signaling to the cytoskeleton and that its interaction with the focal-adhesion protein actopaxin is critical for the correct spatial and/or temporal regulation of CdGAP function. A complete understanding of the coordination of signaling events downstream of integrin engagement with the extracellular matrix will provide valuable insight into the regulation of cell migration during processes such as wound repair, development, and tumor cell metastasis.

Actinin↗
PubMed1988

Counterurbanization: spatial division of labour and regional life-cycles in Canada.

"After a discussion of major concepts of counterurbanization, a narrow definition is proposed. Various demographic and socio-economic dimensions are analysed at different scales with special regard to the Canadian heartland. The basic hypothesis suggests a temporary weakening of urban growth dynamics: decentralization, thus, is a result of locational adjustment strategies, emerging during revolutions in basic technology. The corresponding 'filtering down' processes create a selective, interregional spread of labour. However, shift analytical time series indicate that the development capacity of core regions oscillates in a life-cyclical rhythm. Counterurbanization is expected to fade out with regional adjustment to basic technological transformation."

Americas↗
PubMed1992

The effects of selective glutamate receptor antagonists on synchronized firing bursts in layer III of rat visual cortex.

In the rat visual cortex in vitro, single-shock stimulations applied to the border between layer VI and the white matter evoke synchronized burst-firing by units in layer III. We have examined the effects of glutamate receptor antagonists on this activity, with antagonists applied via the bath to allow correlation of effects with concentrations. All synaptically driven components (recorded extracellularly as field potential 'S2' spikes, dipoles 'W1' and 'W2', and coinciding single-unit spikes) were inhibited by greater than 90% in 1.0 mM kynurenic acid and in 3 or 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, which selectively blocks AMPA/kainate receptors). S2 spike amplitudes were reduced by half in 0.7 microM CNQX. 2-Amino-5-phosphonovalerate (APV), a specific blocker of NMDA receptors, did not prevent S2 spike burst or horizontal spread of bursting within layer III. However, APV reduced the duration of synchronized bursts and the slower potentials which followed. In Mg(2+)-free medium, new components appeared which were APV-sensitive: (1) low amplitude spikes, distributed spatially like S2 spike, but recurring more slowly, and (2) slow potentials, distributed spatially like W1 and W2 potentials, but lasting for hundreds of milliseconds. The amplitudes of these spikes were reduced by half in 3 microM D-APV. Our data imply that: (1) glutamate receptors play a major role in mediating local, excitatory neurotransmission in the supragranular layers of neocortex, with NMDA and AMPA/kainate subtypes each subserving somewhat different functions; (2) AMPA/kainate receptors mediate rapid excitatory transmission between layer III neurons, responsible for driving the first 15 ms of synchronized bursts; (3) currents gated by NMDA receptors determine the duration of coherent firing bursts, and drive asynchronous neuronal firing following bursts; and (4) under conditions which circumvent block by extracellular Mg2+, activation of NMDA receptors greatly enhances and prolongs the response to single-shock stimulations. In vivo, activation of layer III neurons is likely to depend significantly upon currents gated by NMDA receptors whenever repetitively firing excitatory inputs summed over several tens of milliseconds provide enough depolarization to lift block by extracellular Mg2+.

2-Amino-5-phosphonovalerate↗
PubMed2006

Control of cell adhesion on poly(methyl methacrylate).

Keratoprostheses have been constructed from a wide variety of transparent materials, including poly(methyl methacrylate) (PMMA). However, the success of keratoprosthesis has been plagued by numerous shortcomings that include the weakening of the implant-host interface due to weak cell adhesion and opaque fibrous membrane formation over the inner surface of the implant due to fibroblast attachment. An effective solution requires a surface modification that would selectively allow enhanced cell attachment at the implant-host interface and reduced cell attachment over the interior surface of the implant. Here, we have developed a novel and simple peptide conjugation scheme to modify PMMA surfaces, which allowed for region-specific control of cell adhesion. This method uses di-amino-PEG, which can be grafted onto PMMA using hydrolysis or aminolysis method. PEG can resist cell adhesion and protein adsorption. The functionalization of grafted di-amino-PEG molecules with RGD peptide not only restored cell adhesion to the surfaces, but also enhanced cell attachment and spreading as compared to untreated PMMA surfaces. Long-term cell migration and micropatterning studies clearly indicated that PEG-PMMA surfaces with and without RGD conjugation can be used to differentiate cell adhesion and control cell attachment spatially on PMMA, which will have potential applications in the modification of keratoprostheses.

Actins↗
PubMed2005

Evoked phase synchronization between adjacent high-density electrodes in human scalp EEG: duration and time course related to behavior.

OBJECTIVE: Data from a previous event-related potential (ERP) study in visual-perceptual grouping [Nikolaev AR, van Leeuwen C. Flexibility in spatial and non-spatial feature grouping: an event-related potentials study. Brain Res Cogn Brain Res 2004;22:13-25] were re-analyzed to identify event-related dynamics of phase-synchronization. METHODS: In 20 Hz activity, uniform spreading of phase synchronization in closely spaced (approximately 2 cm) scalp electrodes appears and disappears spontaneously. The lengths of synchronized activity intervals and how they vary as a function of stimulus presentation were compared between task and control conditions. RESULTS: Synchronization reached a maximum in the task condition about 180 ms post-stimulus onset, coinciding with the peak N180 ERP marking the deployment of task-specific attention. Synchronized intervals were longer in the task than in the control condition. Long (above 80 ms) intervals occurred at a stable rate before and just after stimulus onset, but steeply decreased 200-400 ms afterwards. CONCLUSIONS: Perceptual tasks lead to longer synchronized intervals in early visual areas. Attention deployment resets the ongoing synchronization. Event-related activity, besides low-frequency ERP, consists of high-frequency short and long synchronized intervals corresponding to evoked bursts and ongoing oscillations, respectively. SIGNIFICANCE: High-density scalp recorded EEG revealed synchronization dynamics in a local, early visual area of cortex that can be interpreted as modulation of spontaneous ongoing task-related processes by attention.

Adult↗
PubMed1997

Spatial resolution of the variable-period x-ray standing-wave method as applied to model membranes.

A series of model membranes as Langmuir-Blodgett (LB) films composed of long-chain zinc alkanoates (saturated fatty acid salts) was used to evaluate the spatial resolution of the variable-period x-ray standing-wave (XSW) technique. The chain length dependence of the zinc mean position (z) above the supporting substrate demonstrates that it is possible to detect differences in (z) of 1-2 A. Thus 1-2 A is the spatial resolution of the method in the current application. The data show that the chain tilt angle is chain length dependent, varying from 40 degrees to 0 degrees for alkanoates 18 and 24 carbon atoms long, respectively. The spread about the mean position of the zinc in the film, sigma(in), was found to be independent of chain length at 10.0 A for all members of the series. Sigma(in) was shown to be insensitive to the presence of a "spacer" omega-tricosenoic acid (omegaTA) bilayer placed between the zinc alkanoate LB film and the coated gold mirror. However, an overlayer of omegaTA sharpened the zinc ion distribution and lowered the chain tilt angle. This study provides important information regarding sample composition and constitution that facilitates membrane structure determination by XSWs.

Fatty Acids, Nonesterified↗
PubMed2001

Learning deficits in mice with persistent Borna disease virus infection of the CNS associated with elevated chemokine expression.

Borna disease virus (BDV) is a highly neurotropic RNA virus that causes a CD8(+) T cell-mediated neurological disease in certain mouse strains. We established asymptomatic persistent central nervous system (CNS) infections in mutant C57BL/10J mice that lack functional CD8(+) T cells. When analyzed at adult age for spatial learning abilities in a water maze, BDV-infected mice showed slightly impaired escape performance while their exploratory behavior in an openfield test was indistinguishable from uninfected control mice. Histological and molecular biological analysis revealed extensive viral spread throughout the CNS of infected animals. Most neurons of the hippocampus contained viral antigen, but there was no overt loss of neurons from this structure. We found almost unchanged levels of the proinflammatory cytokines IL-1beta and TNF-alpha, but clearly increased levels of the chemokines IP-10 and RANTES in brains of infected mice. Re-examination of water maze data revealed that only infected mice with IP-10 transcript levels above a certain threshold showed impaired performance, whereas the performance of infected mice with lower IP-10 levels was indistinguishable from uninfected controls. This suggests that BDV infection can disturb the function of the mammalian CNS without causing overt neuronal loss, and that the magnitude of virus-induced chemokine production in the CNS correlates with the degree of impairment.

Animals↗
PubMed2004

Tilt and rotational pitch angle of membrane-inserted polypeptides from combined 15N and 2H solid-state NMR spectroscopy.

Knowledge of the alignment of alpha-helical polypeptides with respect to the membrane surface and their dynamics in the membrane are key to understanding the functional mechanisms of channels, antibiotics, and signal or translocation peptides. In this paper polypeptides have been labeled with [3,3,3-(2)H(3)]alanine as well as with (15)N at single site amide positions and reconstituted into oriented phospholipid bilayers. A transmembrane and two amphipathic helical polypeptides with the deuterium label at orthogonal positions have been investigated by deuterium and proton-decoupled (15)N solid-state NMR spectroscopy. The (15)N chemical shift measurements and the deuterium quadrupole splitting exhibit a highly complementary functional dependence with respect to the spatial alignment of the polypeptide. Therefore, the combination of these two measurements allows one to determine both the tilt and the rotational pitch angle with high precision. In addition, the deuterium line shape is very sensitive to mosaic spread and the relative orientation of the peptide. The solid-state NMR measurements indicate that the model sequences exhibit a small degree of mosaicity, when at the same time the phospholipid headgroup region is significantly distorted. Furthermore, the (2)H solid-state NMR spectra reveal small orientational and dynamic differences when the fatty acyl chain composition of the phosphatidylcholine bilayers is modified.

Alanine↗
PubMed1992

Detection of cortical spreading depression in the anaesthetised rat by impedance measurement with scalp electrodes: implications for non-invasive imaging of the brain with electrical impedance tomography.

The possible use of impedance measurement with scalp electrodes to detect intracranial events non-invasively was investigated by measuring the localised impedance changes during cortical spreading depression (CSD) in anaesthetised rats. Impedance was measured over ipsilateral fronto-parietal cortex by a four electrode method operating at 50 kHz with electrodes spaced 0.5 mm apart. Cortical impedance increased by 39% of the resting level during CSD. With scalp electrodes placed on abraded skin, an unexpected impedance decrease of 0.8% occurred, which correlated spatially and temporally with CSD. CSD was accompanied by a small rise in temperature; when scalp temperature was held constant by warming the scalp, no impedance change greater than baseline variability (+/- 0.1% of the resting impedance level) was observed. The non-invasive detection of CSD in migraine in humans may be possible by measuring the characteristic temperature-related impedance changes with Electrical Impedance Tomography and scalp electrodes.

Anesthesia, Inhalation↗