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PubMed1990

Flow patterns and spatial distribution of atherosclerotic lesions in human coronary arteries.

To investigate the potential role of fluid mechanical factors in the localized genesis and development of atherosclerotic lesions in humans, the exact anatomic locations of atherosclerotic lesions and the flow patterns at such sites in left and right human coronary arteries were studied in detail by flow visualization and high-speed cinemicrographic techniques using five isolated, transparent human coronary arterial trees prepared postmortem. It was found that atherosclerotic plaques and wall thickenings in left and right coronary arteries were localized almost exclusively on the outer wall of one or both daughter vessels at major bifurcations and T-junctions, which left the flow-divider free of lesions, and along the inner wall of curved segments. When flow patterns in such vessels were studied in detail, it was discovered that these sites were where flow was either slow or disturbed with the formation of slow recirculation and secondary flows and where wall shear stress was low. The results indicate that the major hemodynamic factors directly related to the localization of atherosclerotic plaques and wall thickenings in the human arterial system are the low fluid velocity and the resultant low shear stress that acts on the vessel wall.

Adolescent↗
PubMed1995

Spatial distribution of connexin43, the major cardiac gap junction protein, visualizes the cellular network for impulse propagation from sinoatrial node to atrium.

Myocytes are electrically coupled by gap junctions, which are composed of low-resistance intercellular channels. The major cardiac gap junction protein is connexin43 (Cx43). The distribution of Cx43 has been studied by immunofluorescence to visualize the electrical coupling between atrial tissue and sinoatrial node. From modeling studies, this coupling was inferred to be gradual in order to shield the sinoatrial node from the atrial hyperpolarizing influence. The actual Cx43 labeling pattern did not show the expected gradient but instead a rather black and white staining in a striking pattern of strands of cells. We used an immunohistochemical marker (anti-alpha-smooth muscle actin [alpha SMA]) that specifically cross-reacts with guinea pig sinoatrial node cells together with Cx43 antibody to stain previously electrophysiologically mapped sinoatrial nodes. We found that in the guinea pig sinoatrial node the impulse originates in an alpha SMA-positive, virtually Cx43-negative, region (primary pacemaker region). The impulse then travels obliquely upward to the crista terminalis through a region where layers of alpha SMA-positive cells alternate with layers of Cx43-positive SMA-negative cells. The layers of Cx43-positive cells appear to become broader and thicker in the direction of the crista terminalis, whereas the layers of alpha SMA-positive cells become thinner and narrower. Lateral contacts between Cx43- and alpha SMA-positive cells were very sparse and only detected where the Cx43-positive strands ended (the region where alpha SMA-positive cells fill the whole space between endocardium and epicardium, ie, the putative primary pacemaker region). From these results, we conclude that the primary pacemaker is shielded from the hyperpolarizing influence of the atrium by a gradient in coupling brought about by tissue geometric factors rather than by a gradient of gap junction density.

Actins↗
PubMed1999

Incidence, evolution, and spatial distribution of functional reentry during ventricular fibrillation in pigs.

Functional reentry has been hypothesized to be an underlying mechanism of ventricular fibrillation (VF); however, its contribution to activation patterns during fully developed VF is unclear. We applied new quantitative pattern analysis techniques to mapping data acquired from a 21 x 24 unipolar electrode array (2-mm spacing) located on the ventricular epicardium of 7 open-chest, unsupported pigs. Data epochs 4 seconds long beginning 1, 10, 20, 30, and 40 seconds after electrical induction were analyzed. Reentrant circuits were automatically identified and quantified. We found that 2.3% of activation pathways could unambiguously be classified as reentrant. From scaling analysis, an additional 28% of the pathways may also have been reentrant. Reentry was short-lived with 1.5+/-1.5 (mean+/-SD) complete cycles per circuit. The fraction of reentrant pathways, number of cycles per circuit, cycle duration, and area and perimeter of the cores all increased significantly as VF progressed. Core drift speed decreased significantly. Neither the orientation of the cores nor the direction of drift was well predicted by the epicardial fiber orientation (r2=0.108 and 0.138, respectively, by linear regression). Reentrant circuits were clustered in regions of the epicardium. We conclude the following: (1) Epicardial reentry is relatively uncommon and short-lived during VF, suggesting either that sustained reentry is transmural or that mechanisms governing sustained reentry are relatively unimportant to the dynamics of VF. (2) Reentrant circuits become more common, larger, and longer-lived as VF progresses, which may explain a recently observed increase in VF organization during the first minute of VF. (3) The conditions necessary to induce and sustain reentry are distributed nonuniformly.

Animals↗
PubMed2002

Changes in the spatial distribution of visual attention after early deafness.

There is much anecdotal suggestion of improved visual skills in congenitally deaf individuals. However, this claim has only been met by mixed results from careful investigations of visual skills in deaf individuals. Psychophysical assessments of visual functions have failed, for the most part, to validate the view of enhanced visual skills after deafness. Only a few studies have shown an advantage for deaf individuals in visual tasks. Interestingly, all of these studies share the requirement that participants process visual information in their peripheral visual field under demanding conditions of attention. This work has led us to propose that congenital auditory deprivation alters the gradient of visual attention from central to peripheral field by enhancing peripheral processing. This hypothesis was tested by adapting a search task from Lavie and colleagues in which the interference from distracting information on the search task provides a measure of attentional resources. These authors have established that during an easy central search for a target, any surplus attention remaining will involuntarily process a peripheral distractor that the subject has been instructed to ignore. Attentional resources can be measured by adjusting the difficulty of the search task to the point at which no surplus resources are available for the distractor. Through modification of this paradigm, central and peripheral attentional resources were compared in deaf and hearing individuals. Deaf individuals possessed greater attentional resources in the periphery but less in the center when compared to hearing individuals. Furthermore, based on results from native hearing signers, it was shown that sign language alone could not be responsible for these changes. We conclude that auditory deprivation from birth leads to compensatory changes within the visual system that enhance attentional processing of the peripheral visual field.

Adult↗
PubMedDate not supplied

Spatial distribution of nociceptive neuropeptide and nerve growth factor depletion in experimental diabetic peripheral nervous system.

This study investigated the time-course of the nociceptive neuropeptide substance P and nerve growth factor (NGF), which facilitates substance P production, in lumbar and cervical dorsal root ganglia (DRG) of streptozotocin-induced diabetic rats. Levels of substance P and NGF were measured by radioimmunoassay and sandwich enzyme-linked immunosorbent assay, respectively, 2 months, 4 months and 8 months after induction of diabetes, and compared with age-matched non-diabetic control rats. At 2 months and 4 months, substance P and NGF levels were lower in the lumbar DRG of the diabetic rats than in controls. At 8 months, substance P and NGF were lower in both the lumbar and cervical DRG of the diabetic rats than in controls. These data demonstrate that a decrease in substance P levels in primary sensory neurons with NGF depletion occurs in an axonal length-dependent manner in diabetic rats, and that this decrease may be correlated with the duration of diabetes.

Animals↗
PubMed1996

Detection and spatial distribution of IL-2 receptors on mouse T-lymphocytes by immunogold-labeled ligands.

To identify the plasma membrane (PM) structures implicated in T-cell activation, we studied the distribution of interleukin-2 receptors (IL-2R) and the surface topography of lymphocytes by affinity labeling in electron microscopy (EM). In particular, we analyzed the distribution of the IL-2R alpha-chain on CTLL-2 cells (a murine cytotoxic T-cell lymphoma line). Some of our experiments were extended to the functionally and morphologically distinct cell line EL4 (a routine helper T-cell lymphoma line). As affinity ligands we used a rat monoclonal antibody (clone 7D4) reactive with the routine alpha-chain of IL-2R and recombinant mouse IL-2 (rIL-2). The distribution of IL-2R was visualized on the cell surface by ligands coupled to colloidal gold particles of different sizes. Unfixed cells were labeled with gold probes and attached to concanavalin A (ConA)-pretreated coverslips. Subsequently, the cells were prepared for EM. Examination of ultrathin sections and large surface replicas revealed a high degree of variability in cell morphology and in the density of the randomly distributed gold-labeled ligands among CTLL cells. According to their typical appearance, lymphocytes with strong receptor expression can be easily identified within the cell population. In contrast, the label on many mitogen-activated EL4 cells showed a cap-like polar distribution. The results suggest the existence of diverse distribution patterns of IL-2R on CTLL and EL4 cells. These differences are believed to reflect the different physiological roles played by T-cell subsets in the immune system.

Animals↗
PubMed2005

Habitat characterization and spatial distribution of Anopheles sp. mosquito larvae in Dar es Salaam (Tanzania) during an extended dry period.

INTRODUCTION: By 2030, more than 50% of the African population will live in urban areas. Controlling malaria reduces the disease burden and further improves economic development. As a complement to treated nets and prompt access to treatment, measures targeted against the larval stage of Anopheles sp. mosquitoes are a promising strategy for urban areas. However, a precise knowledge of the geographic location and potentially of ecological characteristics of breeding sites is of major importance for such interventions. METHODS: In total 151 km2 of central Dar es Salaam, the biggest city of Tanzania, were systematically searched for open mosquito breeding sites. Ecologic parameters, mosquito larvae density and geographic location were recorded for each site. Logistic regression analysis was used to determine the key ecological factors explaining the different densities of mosquito larvae. RESULTS: A total of 405 potential open breeding sites were examined. Large drains, swamps and puddles were associated with no or low Anopheles sp. larvae density. The probability of Anopheles sp. larvae to be present was reduced when water was identified as "turbid". Small breeding sites were more commonly colonized by Anopheles sp. larvae. Further, Anopheles gambiae s.l. larvae were found in highly organically polluted habitats. CONCLUSIONS: Clear ecological characteristics of the breeding requirements of Anopheles sp. larvae could not be identified in this setting. Hence, every stagnant open water body, including very polluted ones, have to be considered as potential malaria vector breeding sites.

Animals↗
PubMed1993

Function and spatial distribution in developing chick retina of the laminin receptor alpha 6 beta 1 and its isoforms.

We have recently shown that the laminin-binding integrin receptor, alpha 6 beta 1, is prominently expressed in the developing chick retina, and its expression and activity are regulated during development on both retinal ganglion cells and other neural retinal cells. In the present study, we show that antibodies specific for the extracellular portion of the chick alpha 6 subunit dramatically inhibit interactions in vitro between embryonic day 6 neural retinal cells and laminin, showing that alpha 6 beta 1 functions as an important laminin receptor on developing retinal neurons. In previous work, we showed that alpha 6 mRNA levels on retinal ganglion cells decrease dramatically after E6 during the period that RGC axons innervate the optic tectum. In the present study, we show decreases in alpha 6 mRNA are not prevented by ablation of the optic tectum, indicating that tectal contact is not the major cause of this decrease. Within the embryonic retina, the alpha 6 subunit is codistributed, in part, with laminin, suggesting that it functions as a laminin receptor during retina development in vivo. Furthermore, two isoforms of the alpha 6 protein with distinct cytoplasmic domains generated by differential splicing have quite different distribution patterns in the retina, suggesting that these two isoforms may have different functions during retinal development.

Amino Acid Sequence↗
PubMed2005

Alix regulates cortical actin and the spatial distribution of endosomes.

Alix/AIP1 is a proline-rich protein that has been implicated in apoptosis, endocytic membrane trafficking and viral budding. To further elucidate the functions of Alix, we used RNA interference to specifically suppress its expression. Depletion of Alix caused a striking redistribution of early endosomes from a peripheral to a perinuclear location. The redistribution of endosomes did not affect transferrin recycling or degradation of endocytosed epidermal growth factor receptors, although the uptake of transferrin was mildly reduced when Alix was downregulated. Quantitative immunoelectron microscopy showed that multivesicular endosomes of Alix-depleted cells contained normal amounts of CD63, whereas their levels of lysobisphosphatidic acid were reduced. Alix depletion also caused an accumulation of unusual actin structures that contained clathrin and cortactin, a protein that couples membrane dynamics to the cortical actin cytoskeleton. Our results suggest that Alix functions in the actin-dependent intracellular positioning of endosomes, but that it is not essential for endocytic recycling or for trafficking of membrane proteins between early and late endosomes in non-polarised cells.

Actins↗
PubMed2005

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

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

Arabidopsis↗
PubMed1993

F-actin content and spatial distribution in resting and chemoattractant-stimulated human polymorphonuclear leucocytes. Which role for intracellular free calcium?

Intracellular free calcium concentration ([Ca2+]i) plays a pivotal role for many responses in polymorphonuclear leucocytes (PMNs) stimulated by chemoattractants such as N-formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe). The importance of [Ca2+]i in the morphological polarization was investigated by using calcium-manipulated PMNs. We loaded human PMNs with BAPTA/AM to buffer or chelate [Ca2+]i in the presence or the absence of extracellular calcium by using fluo-3/AM as calcium indicator. The shape changes of PMNs were determined by microscopic examination, and membrane ruffling by right-angle light-scatter changes. Actin polymerization and F-actin distribution were recorded by staining PMNs with bodipy-phallacidin and quantified by quantitative fluorescence microscopy. We found that calcium-free incubation of PMNs loaded or not with 50 microM BAPTA/AM did not modify morphological polarization, membrane ruffling, actin assembly and F-actin distribution of PMNs stimulated with fMet-Leu-Phe, suggesting that these responses were probably functionally linked. It should be noted that incubation of PMNs in calcium-free conditions resulted in a radial distribution of F-actin and a moderate polymerization of actin, but not in morphological polarization of PMNs. Moreover, both calcium-sensitive and calcium-insensitive mechanisms of actin polymerization were additive, and inhibitable by 5 micrograms/ml cytochalasin B.

Actins↗
PubMed1996

Spatial distribution of fluorescently labeled actin in living Dictyostelium amoebae.

Actin from Dictyostelium was labeled with iodoacetamide tetramethylrhodamine (IAR). The labeled actin retained the ability to polymerize into filaments. The labeled actin was introduced into Dictyostelium cells by electroporation. The introduced IAR-labeled actin was diffusely distributed in the cytoplasm but some of it was concentrated in small and large projections at the cell periphery. IAR-labeled actin was concentrated in pseudopods and in the tail cortical region in actively migrating cells. Intense fluorescence due to labeled actin appeared rapidly and disappeared during the extension and retention of pseudopods. During cytokinesis, IAR-labeled actin was concentrated in both polar regions and slightly concentrated in the furrow region. However, the ratio of intensities due to IAR-labeled actin and fluorescently labeled bovine serum albumin that had been introduced simultaneously into cells showed the absence of any concentration of IAR-labeled actin in the furrow region. Staining of fixed cells with fluorescently labeled phalloidin revealed that filamentous actin was rich in the furrow region. These observations indicate that actin is concentrated at this region in higher ratio of filamentous actin to monomeric actin than in other regions of the cytoplasm. Image analysis revealed that the concentration of IAR-labeled actin was high in a pseudopod of an actively migrating cell. Comparisons with staining by fluorescently labeled phalloidin of fixed cells revealed that there was a decreasing gradient in the concentration of filamentous actin from the tip to the base of a pseudopod. These results reveal the high rate at which actin is coordinately organized during mitosis and locomotion in highly motile Dictyostelium cells.

Actins↗
PubMed2003

[Real-time detection of neurotransmitter release and its spatial distribution].

Neurotransmitters have been well known as information carriers for a long time. Recently, some of the research indicated their neurotoxicity, while some indicated their neurotrophic actions. It is very important to understand the role of neurotransmitters. Glutamate is one of the most important excitatory neurotransmitter in the brain. We developed a novel measurement method for glutamate. The method we describe here is based on the enzyme-mediated electrochemical detection. Glutamate oxidase and horseradish peroxidase were deposited together with polymer-mediator on the electrode. We applied this idea on ITO multi-array electrode and developed a 64 channel multi-array sensor. The sensor permits us to detect glutamate release from multiple regions simultaneously in real time. As it is possible to illustrate the distribution of glutamate release, the sensor could be used not only in the pharmacological field, but also in medical treatment in the near future.

Animals↗