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At least 1,135 records · Page 63Linked to original sources
PubMed1984

Calcium ultrastructural localization in Xenopus laevis eggs following activation by pricking or by calcium ionophore A 23187.

In the egg of Xenopus laevis a cortical network of smooth endoplasmic reticulum (SER) surrounds and interconnects each cortical granule (CG) (Campanella and Andreuccetti, '77). This network is a possible intracellular site of calcium storage to be called into action for CG exocytosis. In our experiments, Xenopus eggs, unfertilized or activated by pricking or by calcium ionophore A 23187, have been fixed in osmium-pyroantimonate for calcium localization. Our data show that deposits can be detected only in activated eggs. The calcium chelator edetate (EGTA) and x-ray microprobe analysis demonstrate that they contain calcium. Deposits are found on liposomes and on all intraovular cytomembranes, which therefore appear to be possible sites of calcium sequestration. In the case of ionophore-activated eggs, deposits are detectable independently of the presence of extracellular calcium. These data show that in Xenopus at activation an intracellular liberation of calcium occurs similar to that described in other species. Furthermore, the fact that antimony deposits are observed only after activation makes Xenopus eggs appropriate material in which to follow the temporal and spatial sequence of appearance of the deposits during the early stages of activation. Our results show that antimony deposits appear first in SER vesicles between the plasma membrane and CGs and then spread to the rest of the egg cytomembranes. These data corroborate our hypothesis that in Xenopus the cortical SER network is the first intracellular site where calcium is released at activation. The possible mechanism of calcium release and propagation along the egg cortex is discussed.

Animals↗
PubMed2005

Control mechanisms mediating shifts of attention in auditory and visual space: a spatio-temporal ERP analysis.

The neural systems that mediate voluntary shifts of attention to visual and auditory stimuli were investigated by examining the patterns of human brain electricity elicited by attention-directing cues in auditory and visual tasks. Several lateralized event-related potential (ERP) components were observed when participants shifted attention in expectation of visual targets (experiment 1). One component was focused over frontal cortex and a second was focused primarily over the occipital-temporal cortex but also spread to parietal regions of the scalp. Previous work has indicated that the frontal component reflects supramodal processes involved in the executive control of attention and that the posterior component reflects either spatial attentional control processes in the posterior parietal lobe or modulation of processes in visual cortex. Here, the posterior component was observed when participants shifted attention in expectation of auditory targets (experiments 2-4), but the frontal component was found only in the visual task. The posterior component seemed to be generated in parietal and occipital areas even when there was no visual information about the to-be-attended locations. These results are consistent with the view that voluntary shifts of attention are mediated by supramodal processes in the parietal lobe and that the spatial coordinates of the to-be-attended location are based on visual representations of space.

Acoustic Stimulation↗
PubMed2006

Functional consequences of blood clotting in insects.

Recent in vitro studies have revealed several important aspects of the biochemical and cellular processes involved in insect blood clotting. However, in vivo empirical studies of the functional consequences of clotting are lacking, despite the role of coagulation in wound-healing, preventing infection, and its homology with vertebrate wound repair. Here we present results of the in vivo effects of haemolymph coagulation and its consequences on the spatial disposition of immune activity, in the American cockroach Periplaneta americana. Our results demonstrate that clotting: (1) localises immune effectors in the vicinity of a breach of the cuticle; (2) restricts the spread of invasive particles across the haemocoel, and (3) is greater when wounding is associated with non-self. Our results demonstrate that haemolymph coagulation has major functional consequences, the most important of which is the compartmentalisation of the open haemocoel.

Amaranth Dye↗
PubMed2005

On the dynamics of dengue epidemics from large-scale information.

A model for the spatial and temporal dynamics of dengue fever is proposed in this article. The vector population dynamics is derived from a diffusion equation that is based on environmental parameters at the scale of a remote-sensing image. Vectors and hosts populations are then classically divided into compartments corresponding to their respective disease status. The transmission processes between hosts and vectors are described by a set of differential equations. The link between the vector population diffusion model and the compartmental model enables one to describe both the spatial and temporal dynamics of the disease. Simulations in artificial and actual landscapes show the advantage of using remotely sensed and complementary meteorological data for modelling in a realistic way the geographic spread of a vector-borne disease such as dengue fever.

Animals↗
PubMed1999

Mucosal mast cell secretion processes imaged using three-photon microscopy of 5-hydroxytryptamine autofluorescence.

The secretion process of the mucosal mast cell line RBL-2H3 was imaged using infrared three photon excitation (3PE) of serotonin (5-hydroxytryptamine, 5-HT) autofluorescence, a measurement previously difficult because of the technical intractability of deep UV optics. Images of prestimulation 5-HT distributions were analyzed in loaded cell populations (those incubated in a 5-HT-rich medium overnight) and in unloaded populations and were found to be strictly quantifiable by comparison with bulk population high-performance liquid chromatography measurements. Antigenically stimulated cells were observed to characteristically ruffle and spread as granular 5-HT disappeared with no detectable granule movement. Individual cells exhibited highly heterogeneous release kinetics, often with quasi-periodic bursts. Neighboring granule disappearances were correlated, indicative of either spatially localized signaling or granule-granule interactions. In one-half of the granule release events, weak residual fluorescence was visible suggestive of leftover 5-HT still bound to the granule matrix. The terminal stages of secretion (>300 s) consisted primarily of unresolved granules and remainder 5-HT leakage from already released granules.

Animals↗
PubMed1996

Triple helix formation of procollagen type I can occur at the rough endoplasmic reticulum membrane.

One key problem in understanding the biosynthesis of collagens remains the assembly of the three alpha-chains. How and when are the different gene products selected, aligned, and folded into a triple helix? As the spatial arrangement during biosynthesis might be important, we concentrated on whether the rough endoplasmic reticular membrane is involved in this process. Microsomes were prepared from biosynthetically labeled chick tendon fibroblasts. Vesicles were spread as a monomolecular film which was then transferred over several compartments of a filmbalance containing fresh subphase. Fluorograms of the surface film showed that the monolayer contains procollagen chains. When the monolayer was transferred onto a chymotrypsin/trypsin-containing subphase, the gel bands of the proalpha-chains were shifted into the position of mature alpha-chains, indicating that only the propeptides were digested and the collagenous regions were protected due to triple helix formation. Our results suggest that newly synthesized proalpha-chains can associate as trimers and fold into a triple helical conformation while they are still associated with the membranes of the rough endoplasmic reticulum. These processes also occur when interchain disulfide linkage is inhibited, indicating that chain selection and registration is not dependent on formation of covalent bonds among the carboxyl propeptides.

Animals↗
PubMed1999

mtDNA history of the Cayapa Amerinds of Ecuador: detection of additional founding lineages for the Native American populations.

mtDNA variation in the Cayapa, an Ecuadorian Amerindian tribe belonging to the Chibcha-Paezan linguistic branch, was analyzed by use of hypervariable control regions I and II along with two linked regions undergoing insertion/deletion mutations. Three major maternal lineage clusters fit into the A, B, and C founding groups first described by Schurr and colleagues in 1990, whereas a fourth lineage, apparently unique to the Cayapa, has ambiguous affinity to known clusters. The time of divergence from a common maternal ancestor of the four lineage groups is of sufficient age that it indicates an origin in Asia and supports the hypothesis that the degree of variability carried by the Asian ancestral populations into the New World was rather high. Spatial autocorrelation analysis points out (a) statistically significant nonrandom distributions of the founding lineages in the Americas, because of north-south population movements that have occurred since the first Asian migrants spread through Beringia into the Americas, and (b) an unusual pattern associated with the D lineage cluster. The values of haplotype and nucleotide diversity that are displayed by the Cayapa appear to differ from those observed in other Chibchan populations but match those calculated for South American groups belonging to various linguistic stocks. These data, together with the results of phylogenetic analysis performed with the Amerinds of Central and South America, highlight the difficulty in the identification of clear coevolutionary patterns between linguistic and genetic relationships in particular human populations.

Base Sequence↗
PubMed2004

Origin, diffusion, and differentiation of Y-chromosome haplogroups E and J: inferences on the neolithization of Europe and later migratory events in the Mediterranean area.

The phylogeography of Y-chromosome haplogroups E (Hg E) and J (Hg J) was investigated in >2400 subjects from 29 populations, mainly from Europe and the Mediterranean area but also from Africa and Asia. The observed 501 Hg E and 445 Hg J samples were subtyped using 36 binary markers and eight microsatellite loci. Spatial patterns reveal that (1). the two sister clades, J-M267 and J-M172, are distributed differentially within the Near East, North Africa, and Europe; (2). J-M267 was spread by two temporally distinct migratory episodes, the most recent one probably associated with the diffusion of Arab people; (3). E-M81 is typical of Berbers, and its presence in Iberia and Sicily is due to recent gene flow from North Africa; (4). J-M172(xM12) distribution is consistent with a Levantine/Anatolian dispersal route to southeastern Europe and may reflect the spread of Anatolian farmers; and (5). E-M78 (for which microsatellite data suggest an eastern African origin) and, to a lesser extent, J-M12(M102) lineages would trace the subsequent diffusion of people from the southern Balkans to the west. A 7%-22% contribution of Y chromosomes from Greece to southern Italy was estimated by admixture analysis.

Africa, Northern↗
PubMed2000

Functional and molecular properties of human astrocytes in acute hippocampal slices obtained from patients with temporal lobe epilepsy.

PURPOSE: The specific role of glial cells in epilepsy is still elusive. In this study, functional properties of astrocytes were investigated in acute hippocampal brain slices obtained from surgical specimens of patients with drug-resistant temporal lobe epilepsy (TLE). METHODS: The patch-clamp technique together with a single-cell reverse transcription-polymerase chain reaction approach were used to combine functional and molecular analysis in the same individual cell in situ. RESULTS: In patients with Ammon's horn sclerosis, the glial current patterns resembled properties of immature astrocytes in rodent hippocampus. Depolarizing voltage steps activated delayed rectifier and transient K+ currents as well as tetrodotoxin-sensitive Na+ currents. Hyperpolarizing voltages elicited inward rectifier K+ currents. Comparative recordings were made in astrocytes from patients with lesion-associated TLE that lacked significant histopathological hippocampal alterations. The inward rectifier K+ current density was significantly smaller in astrocytes from the sclerotic group compared with lesion-associated TLE patients. CONCLUSIONS: During normal development of rodent brain, astroglial inward rectification gradually increases. It thus appears that astrocytes in human sclerotic tissue reexpress an immature current pattern. Reduced astroglial inward rectification in conjunction with seizure-induced shrinkage of the extracellular space may lead to impaired spatial K+ buffering. This will result in stronger and prolonged depolarization of glial cells and neurons in response to activity-dependent K+ release and may thus contribute to seizure generation and spread in this particular condition of human TLE.

Action Potentials↗
PubMed2005

Modelling the spread of foot-and-mouth disease in Australia.

Preparedness for an incursion of an exotic animal disease is of key importance to government, industry, producers and the Australian community. An important aspect of Australia's preparedness for a possible incursion of foot-and-mouth disease is investigation into the likely effectiveness and cost-efficiency of eradication strategies when applied to different regional outbreak scenarios. Disease modelling is a tool that can be used to study diseases such as foot-and-mouth disease to better understand potential disease spread and control under different conditions. The Australian Government Department of Agriculture, Fisheries and Forestry has been involved with epidemiologic simulation modelling for more than 10 years, and has developed a sophisticated spatial model for foot-and-mouth disease (AusSpread) that operates within a geographic information system framework. The model accommodates real farm boundary or point-location data, as well as synthesised data based on agricultural census and land use information. The model also allows for interactions between herds or flocks of different animal species and production type, and considers the role that such interactions are likely to play in the epidemiology of a regional outbreak of foot-and-mouth disease. The user can choose mitigations and eradication strategies from those that are currently described in Australia's veterinary emergency plan. The model also allows the user to evaluate the impact of constraints on the availability of resources for mitigations or eradication measures. Outputs include a range of maps and tabulated outbreak statistics describing the geographic extent of the outbreak and its duration, the numbers of affected, slaughtered, and, as relevant, vaccinated herds or flocks, and the cost of control and eradication. Cost-related outputs are based on budgets of the value of stock and the cost of mitigations, each of which can be varied by the user. These outputs are a valuable resource to assist with policy development and disease management.

Animals↗
PubMed1987

Gene flow and the geographic structure of natural populations.

There is abundant geographic variation in both morphology and gene frequency in most species. The extent of geographic variation results from a balance of forces tending to produce local genetic differentiation and forces tending to produce genetic homogeneity. Mutation, genetic drift due to finite population size, and natural selection favoring adaptations to local environmental conditions will all lead to the genetic differentiation of local populations, and the movement of gametes, individuals, and even entire populations--collectively called gene flow--will oppose that differentiation. Gene flow may either constrain evolution by preventing adaptation to local conditions or promote evolution by spreading new genes and combinations of genes throughout a species' range. Several methods are available for estimating the amount of gene flow. Direct methods monitor ongoing gene flow, and indirect methods use spatial distributions of gene frequencies to infer past gene flow. Applications of these methods show that species differ widely in the gene flow that they experience. Of particular interest are those species for which direct methods indicate little current gene flow but indirect methods indicate much higher levels of gene flow in the recent past. Such species probably have undergone large-scale demographic changes relatively frequently.

Animals↗
PubMed1997

Structure-based rationale for the rescue of systemic movement of brome mosaic virus by spontaneous second-site mutations in the coat protein gene.

We describe spontaneous second-site reversions within the coat protein open reading frame that rescue the systemic-spread phenotype and increase virion stability of a mutant of brome mosaic virus. Based on the crystal structure of the related cowpea chlorotic mottle virus, we show that the modified residues are spatially clustered to affect the formation of hexamers and pentamers and therefore virion stability.

Bromovirus↗
PubMed2002

Superresolution in far-field imaging.

We demonstrate the feasibility of achieving superresolved images by using Fourier-plane phase masks and image multiplication, which together create effective point-spread functions that are not positive definite and therefore cannot be created by any single Fourier plane mask in a linear system. Three different configurations were investigated, all of which gave a spatial resolution exceeding that corresponding to the full open aperture of the optical system. One price that must be paid for the superresolution is inefficient use of the light source.

Journal Article↗
PubMed1996

[Diagnostic imaging of osteoid osteoma].

Conventional radiography, bone scintigraphy and Computed Tomography (CT) are the most useful tools to identify osteoid osteomas. We examined 26 patients (14 men and 12 women) with osteoid osteoma in different skeletal sites (13 femora, 3 tibiae, 3 hands, 2 peroneal bones, 2 humera, 2 spines and 1 talus) and compared the diagnostic yield of the above techniques. The fundamental radiographic findings in this benign bone lesion are the presence of a "nidus", with or without calcifications, perilesional sclerosis and periosteal new bone formation. Four patients in our series had soft tissue edema. In the majority of cases, conventional radiography is the imaging method of choice, because it is easily available and its diagnostic yield is adequate (17 patients in our series), especially if combined with bone scintigraphy-whose high diagnostic sensitivity was proved in all of our patients. CT is recommended for its better spatial resolution, in view of surgery, especially when soft tissues are involved. MRI is a highly valuable tool in bone tumor staging because it demonstrates cortical involvement and intramedullary and soft tissue spread. However, MR findings might be misinterpreted as indicating a more aggressive pathologic process.

Adolescent↗
PubMed1990

Spatial dynamics of intracellular calcium in agonist-stimulated vascular smooth muscle cells.

Vasoconstrictor agonists stimulate smooth muscle contraction by inducing a rise in intracellular free Ca2+. Digital-imaging microscopy of fura-2 fluorescence from single vascular smooth muscle cells cultured from the human internal mammary artery has allowed us to record the subcellular alterations in Ca2+ that occur immediately after stimulation by receptor agonists. The thrombin-induced rise in cytoplasmic free Ca2+ begins in a discrete region typically located close to the end of the cell. Subsequently, this region of elevated Ca2+ expands until Ca2+ is elevated throughout the cell cytoplasm. The rate of spreading in the region of elevated Ca2+ in a linear direction averaged 10.1 microns/s, enabling it to traverse the length of most cells within approximately 5 s, and involved rises in Ca2+ of between 200 and 500 nM. In some cells, the Ca2+ rise began at both ends and collided midway. Similar dynamic changes in the spatial distribution of Ca2+ were recorded in cells stimulated by acetylcholine. The novel observation that vasoconstrictor agonists induce an elevation of Ca2+ in a localized region which subsequently expands throughout the cytoplasm of single smooth muscle cells may provide new insight into the nature of Ca2+ signaling in vascular tissue.

Acetylcholine↗
PubMed2000

Imaging extracellular waves of glutamate during calcium signaling in cultured astrocytes.

A growing body of evidence proposes that glial cells have the potential to play a role as modulators of neuronal activity and synaptic transmission by releasing the neurotransmitter glutamate (Arague et al., 1999). We explore the spatial nature of glutamate release from astrocytes with an enzyme-linked assay system and CCD imaging technology. In the presence of glutamate, L-glutamic dehydrogenase (GDH) reduces NAD(+) to NADH, a product that fluoresces when excited with UV light. Theoretically, provided that GDH and NAD(+) are present in the bathing saline, the release of glutamate from stimulated astrocytes can be optically detected by monitoring the accumulation of NADH. Indeed, stimuli that induce a wave of elevated calcium among astrocytes produced a corresponding spread of extracellular NADH fluorescence. Treatment of cultures either with thapsigargin, to deplete internal calcium stores, or with the membrane-permeant calcium chelator BAPTA AM significantly decreased the accumulation of NADH, demonstrating that this fluorometric assay effectively monitors calcium-dependent glutamate release. With a temporal resolution of 500 msec and spatial resolution of approximately 20 micrometer, discrete regions of glutamate release were not reliably resolved. The wave of glutamate release that underlies the NADH fluorescence propagated at an average speed of approximately 26 micrometer/sec, correlating with the rate of calcium wave progression (10-30 micrometer/sec), and caused a localized accumulation of glutamate in the range of 1-100 microM. Further analysis of the fluorescence accumulation clearly demonstrated that glutamate is released in a regenerative manner, with subsequent cells that are involved in the calcium wave releasing additional glutamate.

Animals↗
PubMedDate not supplied

Tissue engineering human placenta trophoblast cells in 3-D fibrous matrix: spatial effects on cell proliferation and function.

Nonwoven polyethylene teraphathalate (PET) fabrics with different porosities and knitted fabric were used as support matrixes to grow human trophoblast cells to study the spatial effects of fibrous matrix on cell adhesion, spatial organization, proliferation, and metabolic functions. In general, cells grown on 2-D surface and knitted fabric had faster metabolic rates and also showed higher proliferation activities as detected by cyclin B assay. For nonwoven PET fibers, matrix porosity had profound effects on cell morphology, spatial organization, and proliferation. Cells grown in a low-porosity fibrous matrix formed small aggregates ( approximately 100 cells per aggregate), whereas cells grown in high-porosity matrix formed big aggregates ( approximately 1000 cells per aggregate). This was attributed to the difference in pore volume or averaged fiber distance, which dictated a cell's ability to cross over and form a bridge between adjacent fibers. The high-porosity matrix had a relatively poor surface accessibility for cells to attach and spread, which are essential for cell proliferation. Dual staining with PI and BrdU showed that 60% of cells in the small aggregates found in the low-porosity matrix were proliferating, while only 18% of cells in the large aggregates found in the high-porosity matrix were proliferating. These results suggest that spatial characteristics of fibrous matrix are important to cell proliferation and function and should be considered in tissue-engineering human cells.

Biocompatible Materials↗
PubMed2005

High-capacity spatial contextual memory.

Humans show implicit memory for complex spatial layouts, which aids in subsequent processing of these layouts. Research efforts in the past 5 years have focused primarily on a single session of training involving a dozen repeated displays. Yet every day, people encounter many more visual layouts than were presented in such experiments. In this study, we trained subjects to learn 60 repeated displays, randomly intermixed within 1,800 nonrepeated displays, spread over 5 consecutive days. On each day, the subjects conducted visual search on 360 new displays and a new set of 12 repeated displays, each repeated 30 times. Contextual memory was observed daily. One week after the fifth session, the subjects still searched faster on the repeated displays learned previously. We conclude that the visual system has a high capacity for learning and retaining repeated spatial context, an ability that may compensate for our severe limitations in visual attention and working memory.

Adult↗