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At least 199 records · Page 11Linked to original sources
PubMed1974

Discrete waves and phototransduction in voltage-clamped ventral photoreceptors.

Discrete waves in the voltage-clamped photoreceptor of Limulus are remarkably similar in all essential properties to those found in an unclamped cell. The latency distribution of discrete waves is not affected by considerable changes in the holding potential in a voltage-clamped cell. Both large and small waves occur in voltage-clamped and unclamped cells and in approximately the same proportion. Large and small waves also share the same latency distributions and spectral sensitivity. We suggest that small waves may result from the activation of damaged membrane areas. Large waves have an average amplitude of approximately 5 nA in voltage-clamped photoreceptors. It probably requires several square microns of cell membrane to support this much photo-current. Thus the amplification inherent in the discrete wave process may involve spatial spread of activation from unimolecular dimensions to several square microns of cell membrane surface. Neither local current flow, nor pre-packaging of any transmitter substance appears to be involved in the amplification process. The possible mechanisms of the amplification are evaluated with relationship to the properties of discrete waves.

Animals↗
PubMed1980

Functional importance of the taste papillae of Phormia regina M.

Electrophysiological recording from taste papillae of Phormia regina M. after stimulation with sugar (sucrose, glucose, fructose and galactose) and salt solutions (NaCl, KCl, KNO3 and CaCl2) has indicated that: 1) in all cases the responses showed a phasic onset about 30 sec in duration; 2) after sugar stimulation the phasic onset of the response was followed by a slow adapting tonic period; 3) no tonic period was present after NaCl, KCl, or KNO3 stimulation; 4) CaCl2 evoked a typical volleying activity that can be explained by a greater spatial spreading of electrotonic currents. These results indicate that the proboscis can only be maintained in an extended position (enabling food to be ingested) by rithmic firing from the papillae.

Animals↗
PubMed1995

[Prevalence of E. multilocularis in foxes in Styria taking into consideration biometrical methods].

The results of a survey covering whole of Styria/Austria, which was based on a biometrical sampling plan, showed the prevalence rate of E. multilocularis among foxes to be 3.6% (18 out of 500 examined foxes). There is however a significant regional difference in the prevalence rate. All 18 infected foxes were found in the North-West of Styria, which results in an estimated proportion of 9% in this region. The study could not reveal any significant difference between male and female foxes concerning the infection rate. The age distribution was 67 percent juvenile foxes (< 1 year) to 33 percent adults. The biometrical methods enable us to determine an exact spatial spread of the parasite and thus makes it possible to find out any potential risk for the population.

Aging↗
PubMed1999

Spatial distribution and spread of sheep biting lice, Bovicola ovis, from point infestations.

The spatial distribution of chewing lice (Bovicola ovis) on their hosts was examined in Polypay and Columbia ewes initially artificially infested on the midside or the neck. Densities of lice were determined at 69 body sites in eight body regions at approximately monthly intervals for 2 years. In the second year, half of the ewes were mated and lice were counted at 26 body sites on the resulting lambs. Polypay ewes had higher densities of lice than Columbias at most inspections but there was little effect of infestation point or mating on either numbers or the distribution of lice. During periods of high louse numbers densities were generally greatest on the sides or the back. Densities on the head were also high at times and peaked later than overall louse densities. Shearing markedly reduced density but increased the proportion of lice found on the neck, belly and lowleg sites. The distribution of lice on the lambs was similar to that on the ewes except that fewer lice were found on the head. Comparisons of lice per part with the numbers of lice extracted from clipped patches indicated that a sheep with wool bearing area of 1 m2 and a mean count of one louse per 10 cm fleece parting carried approximately 2000 lice. At most times of the year inspections for sheep lice should be concentrated on the sides and back, but in recently shorn sheep greater attention should be paid to the lower neck and ventral regions. Implications of the observed distributions of lice for the efficacy of chemical treatments are discussed.

Abdomen↗
PubMed2006

Synchrony, waves, and spatial hierarchies in the spread of influenza.

Quantifying long-range dissemination of infectious diseases is a key issue in their dynamics and control. Here, we use influenza-related mortality data to analyze the between-state progression of interpandemic influenza in the United States over the past 30 years. Outbreaks show hierarchical spatial spread evidenced by higher pairwise synchrony between more populous states. Seasons with higher influenza mortality are associated with higher disease transmission and more rapid spread than are mild ones. The regional spread of infection correlates more closely with rates of movement of people to and from their workplaces (workflows) than with geographical distance. Workflows are described in turn by a gravity model, with a rapid decay of commuting up to around 100 km and a long tail of rare longer range flow. A simple epidemiological model, based on the gravity formulation, captures the observed increase of influenza spatial synchrony with transmissibility; high transmission allows influenza to spread rapidly beyond local spatial constraints.

Adult↗
PubMed2004

From spreading depression to spatial cognition.

The Laboratory of Neurophysiology of Memory started its existence in 1954 by systematic research into spreading depression of EEG activity of laboratory rodents and by the use of this remarkable phenomenon as a functional ablation method in behavioral research. Its main contributions were in the study of memory formation and consolidation, interhemispheric transfer, motor learning, conditioned taste aversion and spatial orientation and navigation. In the last five years it concentrated on navigation of rats in multiple reference frames, on electrophysiological evidence for the role of hippocampal place cells support of behavior in such dissociated frames, on the analysis of idiothetic and allothetic forms of navigation and on the mathematical methods allowing assessment of the contribution of goal directed locomotion to place cell activity. The methods used in spatial memory research in rats were used for examination of human subjects in a laboratory equipped with a tracking system for humans in the hospital Homolka. Animal models of Alzheimer disease were studied in transgenic mice with the human gene for the beta amyloid precursor protein.

Animals↗
PubMed1994

Experimental specification of cell sorting, tissue spreading, and specific spatial patterning by quantitative differences in cadherin expression.

The sorting-out of embryonic cells from a cell mixture and the selective spreading of one cell population over the surface of another have been attributed to various causes. These include differentials in chemotaxis, in cellular adhesiveness, in cell surface contractility, in speed of cell movement, and in the timing of postulated changes in cellular adhesive and motile properties. One of us earlier predicted on mathematical grounds that two motile cell types differing only in the level of expression of a single cell adhesion system should not only segregate from one another but also arrange themselves with the less cohesive cells enveloping a core of the more cohesive ones. To test these predictions, we combined two populations of L cells transfected with P-cadherin cDNA and expressing this homophilic adhesion molecule in substantially differing amounts. When the two cell populations were intermixed, they segregated to approach a sphere-within-a-sphere configuration, the cell population expressing more P-cadherin forming islands which fused to become an internal "medulla." When the two cell populations were first formed into separate aggregates which were subsequently allowed to fuse, the cell population expressing more P-cadherin was enveloped by its partner, which formed an external "cortex." These observations confirm the early prediction and support the conclusion that both morphogenetic movements and the specific anatomical configurations to which they lead can be determined by particular sets of intercellular adhesive intensities, regardless of how these are generated and in the absence of differentials in other parameters.

Animals↗
PubMed2002

RESIS3D--online information about spatial and temporal spreading of resistant pathogens.

Considering resistances of supposed or identified pathogens is of vital importance in antibiotics therapy. Additionally local details play a very important role. So the resistance situation can be different on two wards of the same facility. Furthermore it is possible that there is spatial extension of resistances across the wards that the physicians suppose a future resistance development in a specific unit. The idea of RESIS3D is to visualize spatial and temporal development of resistant pathogens and to give the attending physician (as well as the laboratory) important information for using antibiotics. RESIS3D is an addition to our computer-based therapy adviser called ICONS for calculated antibiotics therapy in intensive care medicine.

Drug Resistance↗
PubMed1994

Spatially controlled adhesion, spreading, and differentiation of endothelial cells on self-assembled molecular monolayers.

Chemically modified glass substrates were used to demonstrate differential adhesion, growth, and differentiation of endothelial cells. Endothelial cells were examined for adhesion and growth on glass, glass treated with N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (EDA), or EDA with a subsequent treatment with physically adsorbed extracellular matrix components human fibronectin and heparin sulfate. EDA and EDA/human fibronectin showed similar abilities to support adhesion, spreading, and proliferation of endothelial cells. In contrast, heparin sulfate inhibited endothelial cell adhesion to EDA. Differentiation of endothelial cells resulting in precapillary cord formation was triggered by addition of basic fibroblast growth factor (bFGF). On EDA and EDA/human fibronectin bFGF causes confluent endothelial cell monolayers to differentiate and form cords, which resulted in a large-scale spatial redistribution of cells on the surface. Formation of organized neovascular assemblies was demonstrated on coplanar molecular patterns of EDA and a nonadhesive perfluorinated alkylsilane (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchloros ilane (13F). Endothelial cells preferentially adhered to the EDA lines and after 24-48 hr, microfilaments aligned with the long axes of the patterned EDA region. Finally, endothelial cells that became confluent within the confines of the EDA region (bound by the nonadhesive, 13F domains) were observed to differentiate into neovascular cords in long-term culture (7-10 days) with bFGF.

Actin Cytoskeleton↗
PubMed2001

Host spatial heterogeneity and the spread of vector-borne infection.

We analyze how spatial heterogeneity in host density affects the advance of vector-borne disease. Infection requires vector infestation. The vector spreads only between hosts occupying the same neighborhood, and the number of hosts varies randomly among neighborhoods. Simulation of a spatially detailed model shows that increasing heterogeneity in host abundance reduces pathogen prevalence. Clumping of hosts can limit the advance of the vector, which inhibits the spread of infection indirectly. Clumping can also increase the chance that the pathogen and vector become physically separated during the initial phase of the epidemic process. The latter limitation on the pathogen's spread, in our simulations, is restricted to small interaction neighborhoods. A mean-field model, which does not maintain spatial correlations between sites, approximates simulation results when hosts are arrayed uniformly, but overestimates infection prevalence when hosts are aggregated. A pair approximation, which includes some of the simulation model's spatial correlations, better describes the vector infestation frequencies across host spatial dispersions.

Analysis of Variance↗
PubMed2005

The role of spatial mixing in the spread of foot-and-mouth disease.

A model of epidemic dispersal (based on the assumption that susceptible cattle were homogeneously mixed over space, or non-spatial model) was compared to a partially spatially explicit and discrete model (the spatial model), which was composed of differential equations and used geo-coded data (Euclidean distances between county centroids). While the spatial model accounted for intra- and inter-county epidemic spread, the non-spatial model did not assess regional differences. A geo-coded dataset that resembled conditions favouring homogeneous mixing assumptions (based on the 2001 Uruguayan foot-and-mouth disease epidemic), was used for testing. Significant differences between models were observed in the average transmission rate between farms, both before and after a control policy (animal movement ban) was imposed. They also differed in terms of daily number of infected farms: the non-spatial model revealed a single epidemic peak (at, approximately, 25 epidemic days); while the spatial model revealed two epidemic peaks (at, approximately, 12 and 28 days, respectively). While the spatial model fitted well with the observed cumulative number of infected farms, the non-spatial model did not (P<0.01). In addition, the spatial model: (a) indicated an early intra-county reproductive number R of approximately 87 (falling to <1 within 25 days), and an inter-county R<1; (b) predicted that, if animal movement restrictions had begun 3 days before/after the estimated initiation of such policy, cases would have decreased/increased by 23 or 26%, respectively. Spatial factors (such as inter-farm distance and coverage of vaccination campaigns, absent in non-spatial models) may explain why partially explicit spatial models describe epidemic spread more accurately than non-spatial models even at early epidemic phases. Integration of geo-coded data into mathematical models is recommended.

Animals↗
PubMed2006

Fine-scale genetic structure among genetic individuals of the clone-forming monotypic genus Echinosophora koreensis (Fabaceae).

BACKGROUND AND AIMS: For rare endemics or endangered plant species that reproduce both sexually and vegetatively it is critical to understand the extent of clonality because assessment of clonal extent and distribution has important ecological and evolutionary consequences with conservation implications. A survey was undertaken to understand clonal effects on fine-scale genetic structure (FSGS) in two populations (one from a disturbed and the other from an undisturbed locality) of Echinosophora koreensis, an endangered small shrub belonging to a monotypic genus in central Korea that reproduces both sexually and vegetatively via rhizomes. METHODS: Using inter-simple sequence repeats (ISSRs) as genetic markers, the spatial distribution of individuals was evaluated using Ripley's L(d)-statistics and quantified the spatial scale of clonal spread and spatial distribution of ISSR genotypes using spatial autocorrelation analysis techniques (join-count statistics and kinship coefficient, F(ij)) for total samples and samples excluding clones. KEY RESULTS: A high degree of differentiation between populations was observed (phi(ST(g)) = 0.184, P < 0.001). Ripley's L(d)-statistics revealed a near random distribution of individuals in a disturbed population, whereas significant aggregation of individuals was found in an undisturbed site. The join-count statistics revealed that most clones significantly aggregate at < or = 6-m interplant distance. The Sp statistic reflecting patterns of correlograms revealed a strong pattern of FSGS for all four data sets (Sp = 0.072-0.154), but these patterns were not significantly different from each other. At small interplant distances (< or = 2 m), however, jackknifed 95% CIs revealed that the total samples exhibited significantly higher F(ij) values than the same samples excluding clones. CONCLUSION: The strong FSGS from genets is consistent with two biological and ecological traits of E. koreensis: bee-pollination and limited seed dispersal. Furthermore, potential clone mates over repeated generations would contribute to the observed high F(ij) values among genets at short distance. To ensure long-term ex situ genetic variability of the endangered E. koreensis, individuals located at distances of 10-12 m should be collected across entire populations of E. koreensis.

Conservation of Natural Resources↗
PubMed1988

Differential spatial displacement discrimination thresholds for Gabor patches.

Differential spatial displacement discrimination thresholds were determined for a configuration of three identical Gaussian modulated patches of sinusoidal grating presented with equal orientation and at threshold luminance contrast. The patches were arranged one above the other at equal spatial intervals. The orientation of the bars of the sinusoidal grid constituting the patches was orthogonal to the axis joining the centres of the outer two patches. Thresholds were determined for displacements of the middle patch both orthogonal to and along the axis joining the outer two patches. Thresholds for both tasks were obtained as a function of both the spatial frequency of the sinusoidal grating and the spatial scale parameter of the Gaussian envelope of the patches. We found that the differential spatial displacement discrimination thresholds for both tasks are a constant fraction of the spatial scale parameter of the Gaussian envelope of the sinusoidal grating patches and are independent of the spatial frequency of the modulated grating. We conclude that the human visual system is capable of assigning a single location tag to an entire Gaussian modulated patch of sinusoidal grating. The accuracy with which the relative position of such a Gabor patch can be determined in a constant fraction of its spatial extent (spread of the Gaussian spatial envelope).

Adult↗
PubMed2002

The urban spread of visceral leishmaniasis: clues from spatial analysis.

BACKGROUND: The pattern of spread of visceral leishmaniasis in Brazilian cities is poorly understood. METHODS: We used geographic information systems and spatial statistics to evaluate the distribution of 1061 cases of visceral leishmaniasis in Teresina, Brazil, in 1993 through 1996. RESULTS: A locally weighted (LOESS) regression model, which was fit as a smoothed function of spatial coordinates, demonstrated large-scale variation, with high incidence rates in peripheral neighborhoods that bordered forest land and pastures. Moran's I indicated small-scale variation and clustering up to 300 m, roughly the flight range of the sand fly vector. CONCLUSIONS: Spatial analytical techniques can identify high-risk areas for targeting control interventions.

Brazil↗
PubMed1976

A simulation spatial model of the spread of foot-and-mouth disease through the primary movement of milk.

A computer model was constructed to mimic the 1967-8 foot-and-mouth epizootic in Shropshire and Cheshire, but the daily spatial distribution of outbreaks was randomized. This pattern of outbreaks was then examined to determine what percentage of outbreaks would fulfil and arbitrary set of criteria for milk-lorry-borne disease, or the primary movement of milk. Some 21% of herds visited subsequent to a 'source farm' were affected, as were 4% of herds visited after any infected herd. The relevance of these results to the true risk of disease through the primary movement of milk off affected farms is discussed.

Animals↗
PubMed1997

The role of vitronectin in the attachment and spatial distribution of bone-derived cells on materials with patterned surface chemistry.

In recent years a central objective of tissue engineering has been understanding the interaction of cells with biomaterial surfaces. In this study we examined the protein adsorption events necessary to control the attachment and the subsequent spatial distribution of bone-derived cells exposed to chemically modified surfaces. Silane chemistry and photolithography techniques were used to create substrates with alternating regions of an aminosilane, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (EDS), along side an alkylsilane, dimethyldichlorosilane (DMS), on quartz surfaces. Sera depleted of fibronectin (Fn), vitronectin (Vn), or both were used to determine if these proteins were necessary for the initial attachment and spatial distribution of bone-derived cells exposed to modified surfaces in vitro. The kinetics and mechanisms of the spatial distribution of cells were examined using light microscopy and digital image acquisition and subsequently were analyzed. Compared to complete serum, the use of serum depleted of fibronectin with vitronectin included had minimal effect on the cell attachment, spreading, and spatial distribution on the EDS regions of the surface. However, the use of serum depleted of vitronectin with or without fibronectin included resulted in greatly reduced cell attachment and spreading. Thus the presence of vitronectin was required for the attachment, spreading, and spatial distribution of bone-derived cells exposed to EDS/DMS-patterned surfaces.

Adsorption↗
PubMed2007

Spatial bridges and the spread of Chlamydia: the case of a county in Sweden.

OBJECTIVES: The so-called small-world effect can have a great impact on efforts to control the incidence and prevalence of sexually transmitted infections. This is because a small number of so-called spatial bridgers (individuals who, through sexual contacts, interconnect geographically distant areas) can drastically lower the average path length in the sexual network and, as a result, make locally based intervention programs much less effective. The objectives of this study were to analyze the sociodemographic characteristics of these bridgers and to compare the result with the remaining study population. The purpose was to determine whether it is possible to identify them for targeted intervention programs. STUDY DESIGN: During 2001, contact tracing was performed in approximately 98% of all cases with positive test results in Värmland County. The sexual networks obtained constituted a study population of 851 individuals. Statistical analysis was used to characterize individuals engaged in spatial bridging behavior. RESULTS: Approximately 8% of the study population was characterized as spatial bridgers. Using multivariate analysis, we found almost no significant differences between these individuals and the rest of the study population when it came to sociodemographic variables, including education, economy, and ethnicity. CONCLUSION: The number of spatial bridgers is high enough to create a small-world network with links that can fuel the endemic chlamydia in Värmland County. Sociodemographic information could not be used to characterize spatial bridgers. In interventions against chlamydia, spatial bridgers shall be considered as potentially important for sustaining the disease.

Adolescent↗
PubMed2004

Modelling the establishment and spread of autotetraploid plants in a spatially heterogeneous environment.

The establishment and spread of autotetraploids from an original diploid population in a heterogeneous environment were studied using a stochastic simulation model. Specifically, we investigated the effects of heterogeneous habitats and nonrandom pollen/seed dispersal on the critical value (micro) of unreduced 2n gamete production necessary for the establishment of autotetraploids as predicted by deterministic models. Introduction of a heterogeneous environment with random pollen/seed dispersal had little effect on the micro value. In contrast, incorporating nonrandom pollen/seed dispersal into a homogeneous environment considerably reduced the micro value. Incorporating both heterogeneous habitats and nonrandom pollen/seed dispersal may lead either to an increase or to a decrease in the micro value compared to that with random dispersal, indicating that the two factors interact in a complex way.

Biological Evolution↗