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At least 757 records · Page 42Linked to original sources
PubMed1997

Population cell differentiation of Serratia marcescens on agar surface and in broth culture.

The bacterium Serratia marcescens shows population surface migration (swarming) phenomenum on an LB swarming plate, and differentiated cells can be observed at the swarming front. How the cell population differentiates during swarming on the agar surface is not known, neither is it clear whether cells with differentiated characteristics can be observed in broth culture. To monitor the population cell differentiation in a highly sensitive way without cell destruction, experiments were designed using bacterial luciferase genes luxAB as the reporter genes to allow direct monitoring of the differentiating cells through bioluminescence. An isogenic S. marcescens strain was constructed with luxAB under the control of the promoter of flagellin gene hag (phag::luxAB). Patterns of cell differentiation were monitored either by direct X-ray film exposure and/or by Autolumat luminometer detection. Results show that population cell differentiation on the agar surface occurs first in a temporal and then spatial way during colonial growth. It was also found that cells harvested from both the spreading agar plate and broth culture showed differentiation patterns similar to those from swarming cells, suggesting that the agar surface culture may not be essential for the formation of differentiated cells.

Culture Media↗
PubMed1986

[Quantitative evaluation of the phase image in radionuclide ventriculography ].

A functional image is a representation that enhances a particular characteristic of organ behaviour (feature enhancement) with a concomitant reduction or elimination of other informations. The functional image of phase (PI), obtained by Fourier analysis, may be interpreted to represent the onset of counts reduction or contraction in each region of the heart. Phase Spreading (PS), is a parameter derived from PI and represents ventricular temporal behaviour including some spatial information. Phase analysis and PS are very sensitive tools in the diagnosis and characterization of cardiac pathology. PS is a specific indicator of CAD, allows the introduction of normal ranges and is an example of quantitative evaluation of functional images.

Coronary Disease↗
PubMed1983

Interaction between mossy fibre and climbing fibre responses in Purkinje cells.

A major problem in cerebellar physiology relates to the manner in which information from mossy fibres and climbing fibres is integrated in the efferent neurones of the cerebellar cortex, the Purkinje cells. Recent findings by Ekerot and Oscarsson [8] and by Ito, Sakurai and Tongroach [13] indicate that the important interaction between mossy fibres and climbing fibres takes place in the dendrites rather than in the Purkinje cell somata. It has been demonstrated that impulses in climbing fibres evoke not only the so-called "complex spikes" in the somata but also plateau-like depolarizations in the distal dendrites which may have durations of hundreds of ms. The plateau potentials are presumably produced by a voltage dependent calcium conductance increase which, under physiological conditions, is triggered off exclusively by the large synaptic potentials generated by climbing fibre impulses. The spread of the plateau potentials to the distal dendrites and their long duration would facilitate spatial and temporal interaction between the mossy fibre and climbing fibre inputs. The findings suggest two kinds of interaction. (1) The duration of the plateau potentials in individual dendritic branches is modulated by the local mossy fibre/parallel fibre input. Thus, it might be postulated that dendritic branches act as independent integrators of mossy fibre and climbing fibre inputs. (2) It has been suggested that interaction between mossy fibres and climbing fibres forms the basis of learning processes in the cerebellum mediated through plastic changes in the synapses between parallel fibres and Purkinje cell dendrites. The plateau potentials would influence parallel fibre synapses by increasing the intradendritic calcium which, in turn, would lastingly depress the sensitivity of the postsynaptic receptors of the parallel fibre synapses that are activated in conjunction with the climbing fibres.

Animals↗
PubMed1997

Anatomical and microstructural factors affecting the electrical activity of the heart. Experimental findings and mathematical simulations.

We developed an experimental preparation in which we record 1500 intramural electrograms from the ventricular walls of an isolated dog heart. The heart is plunged into an electrolytic tank shaped as a human thorax. The tank carries 1300 electrodes uniformly distributed in the conducting volume and on its surface. We obtain 2800 electric signals which enable us to define the spread of excitation and the sequence of repolarization in the heart, and to map the spatial distribution of potentials and currents in the heart, in the chest and on the body surface during a heart beat. Experimental results and mathematical simulations show that excitation, repolarization, the spatial distribution of heart potentials and the shape of the electrocardiograms are dominated by a small number of anatomical factors, namely: the geometry of the ventricles, the epi-endocardial rotation of myocardial fibers orientation in the ventricular walls, the obliqueness of the fibers relative to the epicardial surface and structure of the conduction system.

Animals↗
PubMed1990

Digital imaging system for recording rapid changes in intracellular Ca2+ concentrations triggered by electrical stimulation of cardiac myocytes.

To examine the origin and spreading of the Ca2+ transient following electrical stimulation of isolated myocyte, a system capable of recording intracellular Ca2+ distribution with sufficient temporal and spatial resolution was constructed. The system consists of a fluorescence microscope with computer-controlled pulse illumination and a digital image analyzer. The results with this new equipment show that the Ca2+ transient originates from one or a few points within a myocyte, and spreads throughout the cell. During the initial 60-msec period, the distribution of Ca2+ within a myocyte was not uniform. The system may be used for better understanding of the excitation-contraction coupling mechanism occurring within a cardiac myocyte or of changes in intracellular Ca2+ concentrations in other cells in which Ca2+ plays a crucial role in signal transduction.

Animals↗
PubMed2000

New Frontiers in the Study of Dispersal and Spatial Analysis of Epidemics Caused by Species in the Genus Phytophthora.

Diseases caused by species in the genus Phytophthora are responsible for significant economic losses on a wide range of host plants. Spatial pattern is one of the most characteristic ecological properties of a species, and reflects environmental and genetic heterogeneity and reproductive population growth acting on the processes of reproduction, dispersal, and mortality. Species of Phytophthora can be dispersed either in soil, via surface water movement down rows, from rain splash dispersal, by air, or via movement by humans or invertebrate activity. Dispersal results in patchiness in patterns of disease or inoculum in soil. In this chapter we discuss the mechanisms of dispersal of members of this important genus and describe several methods that can be used to statistically analyze data for which spatial coordinates are known. The methods include testing spatial autocorrelation for binary data or continuous data, semivariograms, and regression models for spatial data. The goal of spatial pattern analysis is to gain an understanding of the mechanisms of dispersal of propagules and to sort out the physical and biological factors that are important for spread of plant pathogens and ultimately, for disease management.

Phytophthora diseases↗
PubMed2000

Spatial risk factors related to outbreaks of contagious bovine pleuropneumonia in northern Italy (1990-1993).

In October 1990, an outbreak of contagious bovine pleuropneumonia (CBPP) was reported in Italy after an absence of approximately one century. Since October 1990, ninety-four outbreaks have occurred in Italy, of which forty-seven were concentrated in three areas of northern Italy (Lombardy region). The disease was eradicated in September 1993. The data used for the analysis were obtained from the epidemiological investigations undertaken during the outbreaks of 1990-1993. The unit of interest for the analysis is the farm. Spatial segregation of infected and uninfected farms within the study area was determined through the Pielou index of segregation. Data from herds within the same set of outbreaks were analysed through logistic regression to identify factors which could be used to discriminate between infected and uninfected herds. The study indicated a clear spatial segregation between infected and uninfected herds. The results of the analysis do not indicate the mode of disease spread. However, the study demonstrated that both aerosol and indirect transmission of the infection could have occurred, as previously documented in Africa. The possibility that indirect transmission played a prominent role in the spread of CBPP in the region of Lombardy is a completely new suggestion. Further studies are required to understand the epidemiology of CBPP in regions with intensive farming and a relatively cold climate. In particular, three aspects require consideration; firstly, animal movement among neighbouring herds could produce a pattern of disease similar to the one produced by indirect transmission (this possibility was excluded in the epidemiological outbreak investigations conducted by field veterinarians). Secondly, the methods of spatial analysis used in this study have not been previously used in the field of veterinary epidemiology. Further validation of the efficacy of these methods is thus required. Thirdly, the epidemiology of CBPP under conditions of high animal density and a relatively cool climate, as encountered in Lombardy, requires further investigation.

Animals↗
PubMed1997

Voltage signals of individual Purkinje cell dendrites in rat cerebellar slices.

For investigating neuronal information processing at the cellular level, a technique which visualizes the voltage distribution within single neurons in situ would be extremely useful. Voltage-sensitive dyes are, in principle, capable of reporting membrane potential [Cohen, L.B. and Salzberg, B.M., Rev. Physiol. Biochem. Pharmacol., 83 (1978) 35-88; Grinvald, A., Lieke, E.E., Frostig, R.D. and Hildesheim, R., J. Neurosci., 14 (1994) 2545-2568; Kleinfeld, D., Delaney, K.R., Fee, M.S., Flores, J.A., Tank, D.W. and Gelperin, A., J. Neurophysiol., 72 (1994) 1402-1419]. However, their application to single cells internally is technically difficult [Antic, S. and Zecevic, D., J. Neurosci., 15 (1995) 1392-1405; Grinvald, A., Salzberg, B.M., Lev-Ram, V. and Hildesheim, R., Biophys. J., 51 (1987) 643-651; Kogan, A., Ross, W.N., Zecevic, D. and Lasser-Ross, N., Brain Res., 700 (1995) 235-239; Zecevic, D., Nature, 381 (1996) 322-325]. An alternative strategy consists in applying the dye from the outside to all cells in the tissue, while manipulating a single cell by current injection [Krauthamer, V. and Ross, W.N., J. Neurosci., 4 (1984) 673-682; Ross, W.N. and Krauthamer, V., J. Neurosci., 4 (1984) 659-672]. Here, we modify this technique to further enhance spatial at the cost of temporal resolution [Borst, A., Z. Naturforsch., 50 (1995) 435-438]. Applied to rat cerebellar slices we demonstrate that the potential spread in individual Purkinje cells can be imaged up to even fine dendritic branches. The acquired optical signals suggest that steadily hyperpolarized Purkinje cells are electrically compact. When permanently depolarized, the somatic input resistance is significantly diminished, yet the spatial voltage drop along the dendrites remains unchanged. As demonstrated by compartmental modeling, this hints to a concentration of outward rectifying currents at the soma of the cells.

Animals↗
PubMed2007

Improvement of spatial resolution in the longitudinal direction for isotropic imaging in helical CT.

Experiments were conducted to confirm the isotropic spatial resolution of multislice CT with a 0.5 mm slice thickness. Isotropic spatial resolution means that the spatial resolution in the transaxial plane (X-Y plane) and that in the longitudinal direction (Z direction) are equivalent. To obtain point spread function (PSF) values in the X-Y-Z directions, three-dimensional voxel data were obtained by helical scanning of a bead phantom. The modulation transfer function (MTF) values were then obtained by three-dimensional Fourier transform of the PSF. Evaluation of the spatial resolution in the X-Y-Z directions by the MTF values showed that the spatial resolution in the Z direction does not depend on the reconstruction kernel used. It was also found that the spatial resolution in the Z direction, as compared with that in the X-Y plane, is superior with the standard kernel for the abdomen and is inferior with the high-definition kernel for the ears/bones. By performing sharpening filter processing in the Z direction with a high-definition kernel, comparable spatial resolution could be obtained in the X-Y-Z directions. It was confirmed that adjusting the spatial resolution in the Z direction with the reconstruction kernel used is an effective method for isotropic imaging.

Biophysical Phenomena↗
PubMed1992

Spread of synaptic activity along parallel fibres in cat cerebellar anterior lobe.

1. Mossy fibre evoked activity in the cerebellar cortex elicited by peripheral electrical stimulation was studied in chloralose anesthetized cats. The distribution of intracortical field potentials in the C3 and D zones was mapped in order to determine if there is a spread of synaptic activity outside the mossy fibre termination area. This area was identified by the presence of short latency synaptic field potentials in the granular layer. 2. Molecular layer field potentials were recorded up to 1.5 mm outside the mossy fibre termination area. The latencies of these potentials increased with increasing distance from the mossy fibre termination area, corresponding to a conduction velocity of about 0.4 m/s. 3. Recordings from Purkinje cells, within and outside the mossy fibre termination area, revealed an increase of simple spike activity at latencies corresponding to those of the field potentials in the same location. 4. From the spatial and temporal characteristics of the evoked activity, it is concluded that a mossy fibre input results in spread of synaptic activity along the parallel fibres. 5. The findings are discussed in relation to the recently discovered microzonal organization of the C3 zone. It is proposed that the organization of this zone offers a possibility for the control of muscle synergies, each synergy being represented by a mossy fibre input and the specific set of microzones activated by this input via the parallel fibres.

Animals↗
PubMed2002

Spatially explicit models of Turelli-Hoffmann Wolbachia invasive wave fronts.

This paper examines different mathematical models of insect dispersal and infection spread and compares these with field data. Reaction-diffusion and integro-difference equation models are used to model the spatio-temporal spread of Wolbachia in Drosophila simulans populations. The models include cytoplasmic incompatibility between infected females and uninfected males that creates a threshold density, similar to an Allee effect, preventing increase from low incidence of infection in the host population. The model builds on an earlier model (Turelli & Hoffmann, 1991) by incorporating imperfect maternal transmission. The results of simulations of the models using the same parameter values produce different dynamics for each model. These differences become very marked in the integro-difference equation models when insect dispersal patterns are assumed to be non-Gaussian. The success or failure of invasion by Wolbachia in the simulations may be attributed to the insect dispersal mechanism used in the model rather than the parameter values. As the models predict very different outcomes for the integro-difference models depending on the underlying assumptions of insect dispersal patterns, this emphasizes that good field data on real (rather than idealized) dispersal patterns need to be collected before models such as these can be used for predictive purposes.

Animals↗
PubMed2002

Spatial and temporal traction response in human airway smooth muscle cells.

Tractions that cells exert on their substrates are essential in cell spreading, migration, and contraction. These tractions can be determined by plating the cells on a flexible gel and measuring the deformation of the gel by using fluorescent beads embedded just below the surface of the gel. In this article we describe the image correlation method (ICM) optimized for determining the displacement field of the gel under a contracting cell. For the calculation of the traction field from the displacement field we use the recently developed method of Fourier transform traction cytometry (FTTC). The ICM and FTTC methods are applied to human airway smooth muscle cells during stimulation with the contractile agonist histamine or the relaxing agonist isoproterenol. The overall intensity of the cell contraction (the median traction magnitude, the energy transferred from the cell to the gel, and the net contractile moment) increased after activation with histamine, and decreased after treatment with isoproterenol. Cells exhibited regional differences in the time course of traction during the treatment. Both temporal evolution and magnitude of traction increase induced by histamine varied markedly among different cell protrusions, whereas the nuclear region showed the smallest response. These results suggest that intracellular mediators of cell adhesion and contraction respond to contractile stimuli with different rates and intensities in different regions of the cell.

Adrenergic beta-Agonists↗
PubMed2004

Epidemic spreading in a hierarchical social network.

A model of epidemic spreading in a population with a hierarchical structure of interpersonal interactions is described and investigated numerically. The structure of interpersonal connections is based on a scale-free network. Spatial localization of individuals belonging to different social groups, and the mobility of a contemporary community, as well as the effectiveness of different interpersonal interactions, are taken into account. Typical relations characterizing the spreading process, like a range of epidemic and epidemic curves, are discussed. The influence of preventive vaccinations on the spreading process is investigated. The critical value of preventively vaccinated individuals that is sufficient for the suppression of an epidemic is calculated. Our results are compared with solutions of the master equation for the spreading process and good agreement of the character of this process is found.

Animals↗
PubMed1989

Direct and transcallosal contribution to the cortical visual evoked response in rats.

The averaged visually evoked cortical potential (VECP) in response to contrast reversal of a grating was measured on striate cortex over a range of spatial frequencies and contrasts. The response to binocular or monocular stimulation was almost abolished by unilateral section of the optic tract on the side of the recording, indicating that the transcallosal pathway makes little contribution to the VECP. Additional section of the corpus callosum, and application of spreading depression to the normal hemisphere shows that the small response following tract section was transcallosal. It was confined to stimuli of low spatial frequencies and high contrast.

Animals↗
PubMed1999

Differentiating between clonal growth and limited gene flow using spatial autocorrelation of microsatellites

In plant populations alleles often deviate from a random distribution and reveal positive autocorrelation at short distances. In species with both clonal and sexual reproduction, such clustering may be because ramets of the same genet were sampled at nearby locations. Alternatively, clustering may be the result of limited gene flow through pollen or seeds (isolation-by-distance). Here, we modify a conventional spatial autocorrelation analysis using the join-count statistic in order to differentiate between these two causes of genetic structure. We examined the distribution of seven microsatellite loci representing 37 alleles in a 20 x 80 m plot of a perennial population of eelgrass Zostera marina L. In analysing join-counts between all like genotypes we found significant genetic autocorrelation among ramets at distances between 1 and 7 m (P < 0. 001). We then excluded joins between clonemates which were identified from the expected likelihood of their seven-locus genotypes. Without joins within genets, no autocorrelation was evident, indicating that most of the significant genetic clustering was caused by clonal spread. At distances up to 27 m, alleles were distributed at random, indicating a panmictic population at this spatial scale. These results illustrate the need for an a priori estimation of genet-ramet structure in clonally reproducing plants in order to avoid erroneous inferences about putative gene flow at various spatial scales.

Journal Article↗
PubMed1997

Effects of spatial frequency, duration, and contrast on discriminating motion directions.

The minimum speed required for discriminating the direction of drifting gratings was measured at a variety of spatial frequencies, display durations, and contrasts. As was reported previously, speed thresholds were relatively constant for middle and high spatial frequencies, but speed threshold was found to be almost inversely proportional to spatial frequency in the range of 0.25 to 1.0 c/deg. Speed threshold was also found to be inversely proportional to duration between 73 and 40 ms. These results at low frequencies and short durations are shown to be consistent with limits set by the spread of energy in the stimuli, producing velocity uncertainty. A quantitative model of temporal filtering is presented that largely accounts for results at all spatial frequencies and durations by the inclusion of constant positional noise. A discussion includes the possible roles of magnocellular and parvocellular mechanisms in mediating speed thresholds.

Contrast Sensitivity↗
PubMed2000

Xylem conduits of a resurrection plant contain a unique lipid lining and refill following a distinct pattern after desiccation.

The axial and radial refilling with water of cut dry branches (up to 80 cm tall) of the resurrection plant Myrothamnus flabellifolia was studied in both acro- and basipetal directions by using 1H-NMR imaging. NMR measurements showed that the conducting elements were not filled simultaneously. Axial water ascent occurred initially only in a cluster of a very few conducting elements. Refilling of the other conducting elements and of the living cells was mainly achieved by radial extraction of water from these initial conducting elements. With time, xylem elements in a few further regions were apparently refilled axially. Radial water spread through the tissue occurred almost linearly with time, but much faster in the acropetal than in the basipetal direction. Application of hydrostatic pressure (up to 16 kPa) produced similar temporal and spatial radial refilling patterns, except that more conducting elements were refilled axially during the first phase of water rise. The addition of raffinose to the water considerably reduced axial and radial spreading rates. The polarity of water climbing was supported by measurements of the water rise in dry branches using the 'light refraction'(and, sometimes, the 'leaf recurving') method. Basipetal refilling of the xylem conduit exhibited biphasic kinetics; the final rise height did not exceed 20-30 cm. Three-cm-long branch pieces also showed a directionality of water climbing, ruling out the possibility that changes in the conducting area from the base to the apex of the branches were responsible for this effect. The polarity of water ascent was independent of gravity and also did not change when the ambient temperature was raised to c. 40 degrees C. At external pressures of 50-100 kPa the polarity disappeared, with basipetal and acropetal refill times of the xylem conduit of tall branches becoming comparable. Refilling of branches dried horizontally (with a clinostat) or inverted (in the direction of gravity) showed a pronounced reduction of the acropetal water rise to or below basipetal water climbing level (which was unaffected by this treatment). Unlike water, benzene and acetone climbing showed no polarity. In the case of benzene, the rise kinetics (including the final heights) were comparable with those measured acropetally for water, whereas with acetone the rise height was less. Transmission electron microscopy of dry branches demonstrated that the inner surfaces of the conducting tracheids and vessels were lined with a continuous osmiophilic (lipid) layer, as postulated by the kinetic analysis and light microscopy studies. The thickness of the layer varied between 20 and 80 nm. The parenchymal and intervessel pits as well as numerous tracheid corners contained opaque inclusions, presumably also consisting of lipids. Electron microscopy of rehydrated plants showed that the lipid layer was either thinned or had disintegrated and that numerous vesicle-like structures and lipid bodies were formed (together with various intermediate structural elements). These, many other data and the physical-chemical literature imply that several (radial) driving forces (such as capillary condensation, Marangoni forces, capillary, osmotic and turgor pressure forces) operate when a few conducting elements become axially refilled with water. These forces apparently lead to an avalanche-like radial refilling of most of the conducting elements and living cells, and thus to the removal of the 'internal cuticle' and of the hydrophobic inclusions in the pits. The polarity of water movement presumably results from high resistances in the basipetal direction, which are created by local gradients in the thickness of the lipid film as a result of draining under gravity in response to drought. There are striking similarities in morphology and function between the xylem-lining lipid film and the lung surfactant film lining the pulmonary air spaces of mammals.

Acetone↗
PubMed1975

Nonlinear mathematical models for the origin of asymmetry in biological molecules.

The origin of chemical chirality is probably associated with a difference in the initial concentrations of two separate populations of primeval organic molecules and possible even two types of primeval organisms and amplified by nonlinear kinetic processes leading to the death of one population. This theory, as originally developed by F. C. Frank of the University of Bristol, is reviewed in this paper with additional derivations, discussions and generalizations. The possible effect of asymmetry in the rate constant is compared to the role of statistical fluctuations, and it is shown, that within the simple model investigated here that the role of statistical fluctuations is much more important for the death of one isomer. In the unlikely absence of any fluctuations, the non-linear kinetic processes amplify the asymmetry in the rate constant and lead to the death of one enanthiomorph. The role of spatial diffusion is discussed, and it is shown that in the presence of a local excess of one enanthiomorph this excess would have spread in space and grown, destroying the opposite enanthiomorph. If the total population of both enanthiomorphs was exactly composed of equal parts of both types, but local fluctuation increased one type at one place and decreased the same type at a different location, the diffusion and growth rate would have caused spatial separation in the population of both enanthiomorphs. For general nth order nonlinear symmetric rate processes (incorporating multitudes of reactions and general diffusion), it is shown that if initially two populations of enanthiomorphs were exactly the same at all locations, then for all times both populations would have increased and remained equal to each other. Mathematical model was constructed for stereoscopic autocatalysis suggested by Calvin. It was found that under certain special local conditions in the presence of large fluctuation it is possible indeed to have growth of only one type of isomer. Various approximate methods and numerical solutions are presented in order to facilitate the handling of nonlinear rate equations.

Cells↗