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PubMed1997

Allozyme polymorphism and geographic variation in the small brown planthopper, Laodelphax striatellus (Homoptera: Delphacidae).

The small brown planthopper, Laodelphax striatellus, immigrates annually into Japan over the East China Sea from the Asian mainland. It is not known whether this long-distance dispersal has any effect on the genetic structure of Japanese L. striatellus populations. The dispersal of L. striatellus is suspected to be relevant to the population dynamics of infection with the parasitic bacterium Wolbachia, which causes cytoplasmic incompatibility in L. striatellus. Wolbachia infection has spread within and among Japanese L. striatellus populations due to this cytoplasmic incompatibility. In the present study, the geographic differences among II L. striatellus populations from Japan and Taiwan was investigated using allozyme polymorphism. FST values on three enzyme loci (GPI, PGM, and AK) indicated a geographically differentiated population structure. Significant differentiation was found even among populations located along the course of the long-distance dispersal. The results indicated that long-range dispersal of L. striatellus does not occur regularly over the main islands of Japan and that it does not have a large effect on the population structure of L. striatellus. This conclusion is in agreement with the geographically variable life history of L. striatellus adapted to local climates. The short-term rice stripe epidemic, which is vectored by L. striatellus, in northwestern Kyushu, Japan, during 1985 and 1986 corresponds to these results. Based on the present findings, short-distance dispersal was considered to drive the spatial spread of Wolbachia infection among L. striatellus populations.

Alleles↗
PubMed2003

Sequence-dependent solution structure and motions of 13 TATA/TBP (TATA-box binding protein) complexes.

The TATA element is a well-known example of a DNA promoter sequence recognized by the TATA box binding protein (TBP) through its intrinsic motion and deformability. Although TBP recognizes the TATA element octamer unusually (through the minor groove, which lacks the distinctive features of the major groove), single base-pair replacements alter transcriptional activity. Recent crystallographic experiments have suggested that TATA/TBP complexes differing by a single base pair retain substantial structural similarity despite their functional differences in activating transcription. To investigate the subtle role of sequence-dependent motion within the TATA element and certain aspects of its effect on assembly of the transcriptional complex, we examine 5-ns dynamics trajectories of 13 variant TATA/TBP complexes differing from each other by a single base pair. They include the wild-type (WT) adenovirus 2 major late promoter (AdMLP) TATA element, TATAAAAG (the octamer specifies positions -31 to -24 with respect to the transcription initiation site), and the variants A31 (i.e., AATAAAAG), T30, A29, C29, G28, T28, T27, G26, T26, C25, T25, and T24. Our simulated TATA/TBP complexes develop sequence-dependent structure and motion trends that may lead to favorable orientations for high-activity variants (with respect to binding TFIIA, TFIIB, and other transcription factors), while conversely, accelerate dissociation of low-activity TATA/TBP complexes. The motions that promote favorable geometries for preinitiation complexes include small rotations between TBP's N- and C-terminal domains, sense strand DNA backbone "slithering," and rotations in TBP's H2 and H2' helices. Low-activity variants tend to translate the H1 and H1' helices and withdraw the intercalating phenylalanines. These cumulative DNA and protein motions lead to a spatial spread of complex orientations up to 4 A; this is associated with an overall bend of the variant TATA/TBP complexes that spans 93 degrees to 110 degrees (107 degrees for the crystal reference). Taken together, our analyses imply larger differences when these local structural and bending changes are extended to longer DNA (upstream and downstream) and suggest that specific local TATA/TBP motions (e.g., shifts in TBP helices and TATA bases and backbone) play a role in modulating the formation and maintenance of the transcription initiation complex.

Base Sequence↗
PubMed1986

The asymptotic speed of propagation of the deterministic non-reducible n-type epidemic.

A model has been formulated in to describe the spatial spread of an epidemic involving n types of individuals, when triggered by the introduction of infectives from outside. Wave solutions for such a model have been investigated in and have been shown only to exist at certain speeds. This paper establishes that the asymptotic speed of propagation, as defined in Aronson and Weinberger, of such an epidemic is in fact c0, the minimum speed at which wave solutions exist. This extends the known result for the one-type and host-vector epidemics.

Biometry↗
PubMed1983

Wave solutions for the deterministic non-reducible n-type epidemic.

A model is formulated to describe the spatial spread of an epidemic involving n types of individual. This encompasses the measles, host-vector and carrier-borne epidemics, and in addition rabies involving several species of animal. The existence, uniqueness and non-existence of wave solutions for different speeds are established for this model.

Animals↗
PubMedDate not supplied

Applications of pulsed Doppler flow mapping to left sided cardiac valvular lesions.

The flow mapping procedure has been developed in parallel to the standard pulsed Doppler procedure. It has a different purpose--picking up flow signals at the site of lesions rather than calibrating velocities--and has its own methodology, developed within the last six years. On the basis of invasive correlations performed in 267 cases of valvular heart disease, we review the three-fold purpose of the flow mapping technique: diagnosing lesions, relying on the presence of flow anomalies; assessing their severity, relying on the spatial spreading of these flow signals; and identifying the site of the lesion, which is a specific advantage, relying on the anatomical location of these flow signals and/or on the direction of the jets. For example, using this technique, it is now possible to easily differentiate a cusp tear from a leak of a bioprosthesis, to measure the size of the leaks, and to reconstruct the image of aortic or mitral stenotic areas. These optimal results are only obtained using an appropriate methodology which mainly includes a) the selection of adequate two-dimensional short axis planes in order to explore the diseased valve in its entirety, because of frequent assymetrical orifices, and to pick up the jets at their starting point, b) measurements of the abnormal areas, c) when jets are studied, a three dimensional approach is required in order to cope with the three dimensional nature of the jet and to make available the calculation of three dimensional indices of severity.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1996

Dye transfer between cells of the lens.

Dye transfer between lens fiber cells and between lens epithelial cells and underlying fiber cells was studied using a wide dynamic range-cooled CCD camera, H2O immersion objectives and image analysis techniques. Each lens was decapsulated by a new technique which leaves the epithelial cells adherent to the lens fiber mass. Lucifer Yellow CH was injected into either single epithelial cells or single fiber cells using the standard whole cell configuration of the patch voltage clamp technique. The results demonstrate extensive dye communication between fiber cells at the lens posterior surface, anterior surface, and equatorial surface. Dye transfer between deep fiber cells was also observed. Dye transfer between approximately 10% of epithelial cells and their underlying fiber cells was apparent when care was taken to yield wide dynamic range images. This was required because the relatively high concentration of dye in the epithelial cell masks the presence of much lower dye concentrations in the underlying fiber cell. A mathematical model which includes dye concentration, time, and spatial spread suggests that those epithelial cells that are coupled to an underlying fiber cell are about as well dye coupled as the epithelial cells themselves. The relatively low dye concentration in a fiber cell is due to its larger volume and diffusion of the dye along the axis of the fiber away from the fiber/epithelial junction.

Animals↗
PubMed2002

A tractable deterministic model with realistic latent period for an epidemic in a linear habitat.

This paper describes a model for the spatial spread of an epidemic in which the latent period has a Gamma distribution with arbitrary mean and variance while the infected and uninfected may have different diffusion coefficients. Using a variant of the "linear chain trick" we derive a simple algorithm for the propagation speed of the infection front. By way of verification, we show that, with suitably matched parameters, the algorithm agrees closely with speeds obtained numerically from the corresponding model in which the latent period is a constant.

Algorithms↗
PubMed1995

Different rules of spatial summation from beyond the receptive field for spike rates and oscillation amplitudes in cat visual cortex.

We measured spike rates in parallel with visually induced oscillations of multi-unit activity (MUA) and local field potentials (LFP) from cortical areas 17 and 18 of anesthetized cats. Variations in the three response types were systematically correlated with stimulus size and placement. Oscillation amplitudes of both MUA and LFP were on average low with stimuli covering just the receptive field and they increased progressively with larger stimuli, whereas average spike rates rather decreased monotonically with stimulus sizes beyond the receptive field (area 18) or reached a plateau with stimuli in the far surround (area 17). Thus, spike rates and oscillation amplitudes follow different rules of spatial summation. Since the spatial spread of the synchronized components of oscillations roughly matches the horizontal divergence zone of the pyramidal cells' axonal collaterals in area 17 and 18, the interconnected system of neighbouring columns seems to constitute a functional unit, within which the oscillations could exert their functional role.

Animals↗
PubMedDate not supplied

The "deterministic simple epidemic" unmasked.

We derive a simple but surprising connection between the "deterministic epidemic with recovery" and the spatial birth-and-death process, and discuss its implications for the use of nonlinear differential equation models for the spatial spread of epidemics. This paper consists of a manuscript dating back to 1977, which has been widely referred to in the literature but not previously published, and its more recent extension to include recovery/death in the processes considered, with some additional comments. To aid reference, we retain the original title.

Communicable Diseases↗
PubMed1990

Nonlinear analysis of spatial vision using first-and-second-order Volterra transfer functions measurement.

The harmonic input method of nonlinear system identification is modified to allow the Volterra series approach to be used for psychophysical investigation of various aspects of human pattern vision in the spatial frequency domain. While it is well known that only one modulation transfer function provides a complete characterization of a linear system, a number of multidimensional transfer functions are needed to identify a nonlinear system. We have shown, that so far as the contrast sensitivity to sine-wave gratings may be used for an empirical estimate of the first-order modulation transfer function of the human visual system, the contrast sensitivity to difference harmonics may be used as an empirical estimate of the second-order modulation transfer function. A difference harmonic arises from a mixture of two sine-wave gratings resulting from the nonlinearity of the visual system. Difference harmonic, experienced as some periodic beatlike structure, may still be observed if frequencies of the component gratings are higher than the maximum visual acuity. The visibility of the low-frequency beatlike pattern produced by pairs of sine-wave gratings, which themselves are of spatial frequencies too high to be resolved, could be accounted for either by a difference frequency distortion product (Burton, 1973) or by a special beat detector (Derrington & Badcock, 1985). We found that increasing the contrast of one component grating may be compensated for by reducing the contrast of the other component grating, the beatlike pattern being at threshold. This is exactly what would be expected if the beatlike pattern is detected because of the difference harmonics produced by nonlinearity of the visual system. We have determined contrast thresholds for the difference harmonics which occur between two unresolved different spatial frequencies. The contrast sensitivity function for difference harmonics was found to have a marked similarity both in the shape and position of peak sensitivity to the contrast sensitivity function for single sine-wave gratings. Another important characteristic of the contrast sensitivity function for difference harmonics is that it depends only on the frequency difference, delta f = f1 - f2, rather than on the value of either f1 or f2. All this indicates that a difference harmonic arises from local nonlinearities in the visual system. More specifically, the visual system may be represented as a cascade system, composed of a linear system with transfer function O (f) followed by a nonlinear element, r(.), without spatial spread in cascade with another linear system with transfer function P (f).(ABSTRACT TRUNCATED AT 400 WORDS)

Contrast Sensitivity↗
PubMed1994

Mechanisms of vertical phoria adaptation revealed by time-course and two-dimensional spatiotopic maps.

The spatial spread of short term phoria adaptation was measured in response to either a single vertical disparity presented at a single eye position, or, vertical disparities of opposite sign presented at two different locations along either the primary vertical or horizontal meridians or along an oblique axis. The spread of adaptation to eye positions not specifically adapted was assessed by measuring phoria across a two-dimensional surface. The change in phoria was uniform across the field in response to a single disparity. With two disparities, adaptation conformed to the stimulus demand in the direction in which the disparity varied but was uniform in the orthogonal direction. The time-course of the adaptation indicated the presence of two mechanisms, a global one which shifted the phoria uniformly across the field and a local one which selectively adjusted the phoria to the position dependent demands of the disparity stimulus.

Adaptation, Ocular↗
PubMed1996

Binocular rivalry with isoluminant stimuli visible only via short-wavelength-sensitive cones.

To test whether the binocular contour rivalry mechanism is tritanopic, we presented isoluminant, rival stimuli visible only via the short-wavelength-sensitive (S) cones. We stimulated only the S cones with violet gratings superimposed on a bright yellow field that adapted the responses of the middle- and long-wavelength-sensitive (M and L) cones. We found that an S-cone grating presented to one eye rivalled with an orthogonal grating presented to the other. Rivalry persisted over a range of luminances and contrasts of the S-cone stimuli, and was greater than could be accounted for by nonrival fading. The spatial spread of rivalry from S-cone stimuli is similar to that for the same stimuli when visible also to the M and L cones (luminance stimuli). We found that an S-cone stimulus would rival with a luminance stimulus, and exploited this to determine the equivalent luminance contrast of S-cone stimuli by putting them in a rivalry competition with luminance stimuli. For rivalry, the equivalent luminance contrast of isoluminant, S-cone stimuli is much less than their S-cone contrast. The existence of rivalry with isoluminant stimuli, along with earlier evidence that such stimuli can support stereopsis, challenges the view that an achromatic channel alone drives certain higher level functions such as depth perception.

Contrast Sensitivity↗
PubMed1983

The postoperative classification for uterine cervical cancer and its clinical evaluation.

A postoperative classification for uterine cervical cancer has been made in consideration of the spatial spreading of cancer, biological malignancy of 120 cases which were treated with radical hysterectomy and pelvic lymphadnectomy. This classification corresponds extremely well to prognosis. The 5-year survival of the cases with prognostic index (P.I.) 9 or less was 96.1%, while those with P.I. above 10 showed 31.8%. In the Shinshu University School of Medicine clinic, this classification has become indispensable for decision of postoperative irradiation, selection of irradiation methods, and chemotherapeutic agents. Using this classification for individualized therapy, the survival rate was elevated in advanced cancer, class III or IV, with lymph node metastasis and P.I. above 10.

Adenocarcinoma↗
PubMed1991

Activity-dependent modulation of nerve terminal excitation in a mammalian peptidergic system.

Transmitter release at nerve terminals is triggered by voltage-gated calcium influx upon arrival of an action potential. Changes in coupling between axonal impulse discharge and depolarization of the nerve ending might therefore regulate exocytotic secretion. In the magnocellular neurosecretory system of the rat, the pattern of electrical activity can modify the duration of action potentials within individual nerve endings, and alter the spatial spread of excitation into the branching terminal field of neurohypophysial axons. The observed effects are consistent with the effects of firing rate and pattern on peptide release, indicating that activity-dependent changes in axon-terminal coupling may modulate secretion in this neuroendocrine system.

Animals↗
PubMed1993

The functions of thrombospondin and its involvement in physiology and pathophysiology.

The thrombospondin family of molecules is expressed in many different tissues. Its expression is highly regulated by different hormones and cytokines and is developmentally controlled. It can bind to many different cell types, probably via an array of receptors which are similarly regulated. The level of thrombospondins in body fluids and their distribution in tissue change in correlation with various pathological states. It is linked to the growth of primary tumors and to metastasis, to development of the atherosclerotic plaque, to malaria infection and other diseases. The role(s) of thrombospondin(s) are by and large unknown, though specific interaction seem to affect particular cell functions. The wide-spread spatial and temporal regulation, multiple interactions and correlation with major diseases imply important roles in cell function and call for concerted effort to unravel the mystery.

Animals↗
PubMed1999

Assessment of mitral regurgitant jets by three-dimensional color Doppler.

BACKGROUND: Color Doppler echocardiography is a standard technique for assessing mitral regurgitation before and after mitral valvuloplasty. Mitral valve prolapse produces complex eccentric jet flows that cannot be visualized and measured by two-dimensional color Doppler echocardiography. The aim of this study was to evaluate the clinical impact of three-dimensional color Doppler echocardiography, a new technique developed at our institution, for assessing mitral regurgitation. METHODS: Forty-five patients with mitral regurgitation underwent intraoperative transesophageal echocardiography and three-dimensional Doppler data acquisition. The grade of mitral regurgitation was assessed by angiography. The jet areas were calculated by planimetry from conventional color Doppler; the jet volumes were obtained by three-dimensional Doppler data. RESULTS: New patterns of mitral regurgitant flows were recognized according to the origin, direction, and spatial spreading into the left atrium. Conventional jet areas failed to separate the groups of patients with different degrees of regurgitation, whereas the jet volumes were able to divide patients with different regurgitation grades. No significant correlation was found between jet area and angiographic grading (r = 0.63, p = NS). Jet volumes were significantly correlated to angiography (r = 0.89, p < 0.001). CONCLUSIONS: Three-dimensional color Doppler echocardiography revealed new patterns of regurgitant flow and allowed a more accurate semiquantitative assessment of complex asymmetrical regurgitant jets.

Blood Flow Velocity↗
PubMed2003

Mathematical model of the spatio-temporal dynamics of second messengers in visual transduction.

A model describing the role of transversal and longitudinal diffusion of cGMP and Ca(2+) in signaling in the rod outer segment of vertebrates is developed. Utilizing a novel notion of surface-volume reaction and the mathematical theories of homogenization and concentrated capacity, the diffusion of cGMP and Ca(2+) in the inter-disc spaces is shown to be reducible to a one-parameter family of diffusion processes taking place on a single rod cross section; whereas the diffusion in the outer shell is shown to be reducible to a diffusion on a cylindrical surface. Moreover, the exterior flux of the former serves as a source term for the latter, alleviating the assumption of a well-stirred cytosol. A previous model of visual transduction that assumes a well-stirred rod outer segment cytosol (and thus contains no spatial information) can be recovered from this model by imposing a "bulk" assumption. The model shows that upon activation of a single rhodopsin, cGMP changes are local, and exhibit both a longitudinal and a transversal component. Consequently, membrane current is also highly localized. The spatial spread of the single photon response along the longitudinal axis of the outer segment is predicted to be 3-5 microm, consistent with experimental data. This approach represents a tool to analyze point-wise signaling dynamics without requiring averaging over the entire cell by global Michaelis-Menten kinetics.

Animals↗
PubMed1997

Improved model of thromboembolic stroke and rt-PA induced reperfusion in the rat.

We report the technical details and validation of an improved rat model for thromboembolic stroke and rt-PA induced reperfusion, which closely resembles clinical embolic stroke. The middle cerebral artery (MCA) was proximally occluded by injection of twelve medium sized (1.5 x 0.35 mm), fibrin-rich autologous blood clots. On inspection, densely packed clot material was found at the ipsilateral MCA origin in all untreated animals. Autoradiographic rCBF measurements showed severe ischemic deficit throughout the ipsilateral MCA territory in untreated animals. The volume in which flow values fell below 30 ml/100 g per min was 54 +/- 14% of the hemispheric volume. In all rt-PA treated animals the proximal MCA was recanalised, and the volume with flow values below 30 ml/100 g per min was reduced to 29 +/- 17%. Histological findings paralleled the spatial spread of the CBF deficit. The rat model presented is well-suited for investigations of the specific pathophysiology of thromboembolic stroke. Furthermore it allows detailed studies of thrombolytically induced reperfusion, beyond the question of successful recanalisation.

Animals↗