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PubMed2003

[A review on road ecology].

Roads are a widespread and increasing feature of most landscapes, and have great ecological effects, e.g., increased mortality of animals and plants and habitat loss from road construction, alteration of the physical and chemical environment, and changes in roadsides vegetation. The great impact on animal population includes road-kills, limiting population, road avoidance causing home arrange shift, modification of movement pattern and barrier effect subdividing habitat and populations. Roads alter landscape spatial pattern and interrupt horizontal ecological flows strongly. These impacts can be assayed by indices of road density, road-effect zone and road location. Furthermore, important applications of road ecology to planning, conservation and management are essential and potential. Road ecology presents us a surprising frontier of ecology.

Animals↗
PubMed1984

J.E. Purkynĕ's contributions to the physiology of the visual, the vestibular and the oculomotor systems.

J.E. Purkynĕ (1787-1869) was one of the leading physiologists in the first half of the 19th century, became the founder of the "exact subjectivism", and remained during his entire life a very careful observer in psychophysical experiments. He made moreover many important discoveries in anatomy, neuroanatomy, embryology and pharmacology. Despite his outstanding contributions to science, he remained in his general philosophy and feelings deeply attached to the Romantic spirit of the age. After Purkynĕ returned to Prague in 1849 he played an important role in his nation's search for a national identity and became a leading figure in the cultural and social life of Prague. Purkynĕ's contributions to the physiology of vision, the oculomotor and the vestibular systems are reviewed. In vision Purkynĕ discovered the Purkynĕ-tree, flicker patterns seen in diffuse light, moving light nebula in the Eigengrau, spatially patterned structures in pressure phosphenes, the antagonistic properties of Galvanic phosphenes with respect to current polarity, periodic afterimages, the Troxler effect for colour perception with the peripheral retina and the principle of the ophthalmoscope. The Purkynĕ-shift in chromatic sensitivity when the adaptation level shifts from scotopic to photopic vision was rediscovered by Purkynĕ. Purkynĕ was the first to describe the "Purkynĕ images" of the anterior and posterior surfaces of the cornea and the lens and the changes in the third Purkynĕ image when the eye accommodates. He described optokinetic nystagmus and optokinetic after-nystagmus and explained movement aftereffects as a habituation of the gaze motor system. Important contributions were made by Purkynĕ to the physiology of the vestibular system, but he did not propose the existence of peripheral receptors for this system. He believed that direct mechanical effects on certain parts of the brain (especially the cerebellum) are responsible for the mechanisms of vertigo. Purkynĕ's five categories of vertigo are still valid today (vertigo of motion, Galvanic vertigo, vertigo caused by general brain ischemia, height vertigo and vertigo caused by alcohol and other narcotics). Purkynĕ's contribution to sensory physiology can be considered as one of the essential foundations on which modern sensory physiology and psychophysics are built.

Adaptation, Ocular↗
PubMed2004

A combined in situ hybridization and RT-PCR method to detect spatial and temporal patterns of Noggin gene expression in embryonic and postnatal rat hippocampus.

Recent studies indicate that Noggin not only plays an important role in the early development of the nervous system, but may also plays a role in postnatal central nervous system (CNS) development. In this study, we examined the relative levels and localization of Noggin mRNA in the hippocampus of rats of different developmental stages with reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization. RT-PCR showed that the peak level of expression of Noggin mRNA was observed at embryonic day 13 (E13), subsequently gradually declined at 1-3 months (P1-3M) postnatal, and was detected only at a low level at P18M. In situ hybridization revealed that at embryonic stages, Noggin mRNA was localized throughout all hippocampal regions, whereas at early postnatal ages, Noggin mRNA was primarily localized in the anterior subiculum. At later postnatal ages, Noggin mRNA expression was obviously observed in the dentate gyrus and in the CA1-CA3 pyramidal cell layers. Taken together, our results demonstrate that Noggin is expressed in embryonic and postnatal hippocampus, and that the temporal and spatial patterns of its expression is developmentally regulated.

Aging↗
PubMed2004

Ordered patterns of liquid crystal toroidal defects by microchannel confinement.

In this article we present experimental results demonstrating an approach to controlling the size and spatial patterning of defect domains in a smectic liquid crystal (LC) by geometric confinement in surface-modified microchannels. By confining the LC 4'-octyl-4-cyanobiphenyl in mum-sized rectangular channels with controlled surface polarity, we were able to generate defect domains that are not only nearly uniform in size but also arranged in quasi-2D ordered patterns. Atomic force microscopy measurements revealed that the defects have a toroidal topology, which we argue is dictated by the boundary conditions imposed by the walls of the microchannel. We show that the defects can be considered to be colloidal objects, which interact with each other to form ordered patterns. This method opens the possibility for exploiting the unique optical and rheological properties associated with LC defects to making new materials. For example, the control of the shape, size, and spatial arrangement of the defects at the mesoscale suggests applications in patterning, templating, and when extended to lyotropic LCs, a process leading to uniform-sized spherical particles for chemical encapsulation and delivery.

Biphenyl Compounds↗
PubMed2004

Health and environment information systems for exposure and disease mapping, and risk assessment.

A large number of chemicals are used on a regular basis in modern society. Thousands of new chemicals are added each year, many of which may have toxic properties constituting potential health hazards. Rapid assessment of the risk associated with the use of these chemicals is therefore essential to protect people from exposure to potentially harmful substances. Exposures to chemicals (and physical agents) are typically unevenly distributed geographically as well as temporally. Disease occurrence also shows geographically varying patterns. Geographic information systems (GIS) may be used to produce maps of exposure and/or disease to reveal spatial patterns. Exposure mapping using advanced GIS modeling may enhance exposure assessment in environmental epidemiology studies. Disease maps can be valuable tools in risk assessment to explore changes in disease patterns potentially associated with changes in environmental exposures. Spatial variations in risk and trends related to distance from pollution sources may be studied using software tools such as the Rapid Inquiry Facility, developed by the U.K. Small Area Health Statistics Unit and enhanced in the European Health and Environment Information System project, for an initial quick evaluation of any potential health hazards associated with an environmental pollutant.

Cross-Sectional Studies↗
PubMed1981

Some physical, mathematical and evolutionary aspects of biological pattern formation.

An important mechanism in the generation of biological structures is the production of defined spatial patterns within initially near-uniform cells and tissues. This process can be modelled on the basis of conventional molecular kinetics if there is a short-range activating effect in conjunction with depletion or inhibition extending over a wider range ('lateral inhibition'). Such pattern-generating systems exhibit simple self-regulatory properties empirically observed in developmental biology such as polarity effects, proportion regulation and the inducibility of secondary centres. Autocatalysis and lateral inhibition have been shown to be mathematically necessary for the simplest two-factor case. Certain generalizations of these conditions to multi-component systems are possible; they are suitable for modelling intercalary regeneration. The evolution of higher organisms seems to be determined to a considerable extent by many small changes of patterns and proportions. While evolution proceeds at varying rates in the course of time, the rate-limiting steps may be due to mutations of low selection pressure. A semi-quantitative argument suggests that there might be an upper limit of evolutionarily effective genetic complexity.

Animals↗
PubMed2001

Pattern formation and localization in the forced-damped Fermi-Pasta-Ulam lattice.

We study spatial pattern formation and energy localization in the dynamics of an anharmonic chain with quadratic and quartic intersite potential, subject to an optical, sinusoidally oscillating field and a weak damping. The zone-boundary mode is stable and locked to the driving field below a critical forcing that we determine analytically using an approximate model, which describes mode interactions. Above such a forcing, a standing modulated wave forms for driving frequencies below the band edge, while a "multibreather" state develops at higher frequencies. Of the former, we give an explicit approximate analytical expression, which compares well with numerical data. At higher forcing, space-time chaotic patterns are observed.

Journal Article↗
PubMed1989

A comparison of discrimination and identification of vibrotactile patterns.

Both discrimination and identification tasks have been used to assess subjects' abilities to perceive vibratory spatial patterns presented to the skin. The present study examined discrimination and identification performance under comparable conditions. In Experiment 1, subjects attempted to discriminate a pair of patterns on some blocks of trials and to identify both members of a pair on other blocks. For both tasks, the time between the members of the pair was varied. Discrimination performance could be predicted accurately from identification data. Analysis of performance on identification trials indicated that subjects used discriminability information to identify pairs. In Experiment 2, discrimination and identification were compared when the temporal separation between patterns was fixed and a masking stimulus followed each pattern after a variable delay. Results suggest that temporal masking, rather than the time available for processing pattern information, is the major limitation in both discrimination and identification of sequences of tactile patterns.

Adult↗
PubMed1998

Diffusion MR imaging during acute subarachnoid hemorrhage in rats.

BACKGROUND AND PURPOSE: We analyzed the temporal and spatial pattern of water diffusion changes during acute subarachnoid hemorrhage (SAH) in rat brain to identify factors contributing to the acute pathophysiology of SAH. METHODS: Subarachnoid hemorrhage was remotely induced via perforation of the circle of Willis with an endovascular suture during MR imaging. A fast echo-planar imaging technique was used to acquire 60 maps of the apparent diffusion coefficient (ADC) beginning 1 min before and continuing for 11 min after induction of SAH. A high-resolution spin-echo diffusion sequence was used to follow diffusion changes over 6 h after SAH. Sham-operated control (n=3), nonheparinized (n=6), and heparinized (n=5) groups were studied. RESULTS: Sham-operated control animals did not show ADC changes over time. In both SAH groups, however, a sharp decline of ADC within 2 min of SAH was consistently observed in the ipsilateral somatosensory cortex. These decreases in diffusion then spread within minutes over the ipsilateral hemisphere. Similar ADC decreases on the contralateral side started with a further time delay of 1 to 3 min. From 30 min onward, the extent of the diffusion abnormality decreased progressively in the nonheparinized animals. No recovery was observed in heparinized rats. CONCLUSIONS: MR diffusion imaging allows new insight into the pathophysiology of acute SAH: The spatial and temporal pattern of diffusion changes suggests the initial occurrence of acute vasospasm and subsequently "spreading depolarization" of brain tissue. Persistent hemorrhage in heparinized animals was reflected by early decline of ADC values throughout the entire brain.

Acute Disease↗
PubMed1999

Sheep scab outbreaks in Great Britain between 1973 and 1992: spatial and temporal patterns.

In January 1973, the mange mite Psoroptes ovis was found in a sheep flock in Lancashire, UK after a 20 year period of eradication. Over the next 20 years, a total of 1480 flock outbreaks were reported, until June 1992 when the control of sheep scab was deregulated. The spatial and temporal patterns of the number of outbreaks in each month over this period were analysed using time series methods, a geographical information system (GIS) and second order approaches to the exploration of space-time interaction (K-function analysis). The monthly time series displays clear evidence of seasonal cyclicity, with most outbreaks being reported in the winter months. After removal of the summer compulsory dip in 1988 however, there is evidence of a change in the seasonal pattern, with more cases being reported in the autumn months. There is also evidence of a contribution from a sinusoidal wave with a period of 8 years, which roughly corresponds to the major changes in the national control policy. The spatial pattern also appears to expand and contract on a roughly 4 year cycle, again reflecting the oscillating periods of success and failure. Examination of the spatial and temporal pattern revealed strong evidence of space-time clustering (p < 0.001) and a major contribution to the pattern from very local (< 12 km) spread within 5 months of an arbitrary outbreak.

Animals↗
PubMed2004

A unified theory of brightness contrast and assimilation incorporating oriented multiscale spatial filtering and contrast normalization.

Brightness induction includes both contrast and assimilations effects. Brightness contrast occurs when the brightness of a test region shifts away from the brightness of adjacent regions. Brightness assimilation refers to the opposite situation in which the brightness of the test region shifts toward that of the surrounding regions. Interestingly, in the White effect [Perception 8 (1979) 413] the direction of the induced brightness change does not correlate with the amount of black or white border in contact with the gray test patch. This has led some investigators to reject spatial filtering explanations not only for the White effect but for brightness perception in general. Instead, these investigators have offered explanations based on a variety of junction analyses and/or perceptual organization schemes. Here, these approaches are challenged with a critical set of new psychophysical measurements that determined the magnitude of the White effect, the shifted White effect [Perception 10 (1981) 215] and the checkerboard illusion [R.L. DeValois, K.K. DeValois, Spatial Vision, Oxford University Press, NY, 1988] as a function of inducing pattern spatial frequency and test patch height. The oriented difference-of-Gaussians (ODOG) computational model of Blakeslee and McCourt [Vision Res. 39 (1999) 4361] parsimoniously accounts for the psychophysical data, and illustrates that mechanisms based on junction analysis or perceptual inference are not required to explain them. According to the ODOG model, brightness induction results from linear spatial filtering with an incomplete basis set (the finite array of spatial filters in the human visual system). In addition, orientation selectivity of the filters and contrast normalization across orientation channels are critical for explaining some brightness effects, such as the White effect.

Computational Biology↗
PubMed1977

Pattern and polarity of sclerites in adult abdominal segments of Calliphora erythrocephala (Diptera): anlage rotation experiments.

The anlagen of imaginal histoblasts in the abdominal segments of Calliphora (higher Diptera) present an interesting problem, which bears on recent concepts employed in the consideration of spatial patterning in insects. They differ from imaginal discs with respect to larval organization and activity, and in the absence of the progressive pattern of genetic determination during the larval period, characteristic of imaginal discs. How is the adult pattern in the abdominal segments determined? The experiments presented here seek to clarify the spatial parameters involved in control of adult pattern and polarity in the adult segment. A series of 180 degrees rotations of hypodermal grafts bearing the anlagen singly, or in combination, or of larval intersegmental hypodermis, indicate that polarity is determined within the anlagen through interaction with local larval epidermis either before or during histoblast migration. The nature of the sclerites, too, is primarily carried by the anlagen rather than determined by intersegmental information. The whole question of 'determination of polarity' is set out more carefully than hitherto in the light of (a) observations of the movement of epidermal cells in other systems in response to disturbance of pattern, and (b) the obvious vectorial nature of the phenomenon, which cannot be a genetic matter, but one of cell axes and of the relation of cells to segment/organism. The demonstration that (i) hemitergite and hemisternite are primarily determined by the anlagen themselves, and not by larval intersegmental membranes; and (ii) evidence indicates an influence of epidermal cells of the larva on the differentiation (as well as polarity) of imaginal histoblasts, leads to the conclusion that neither of two models considered will account for the establishment of the adult abdominal pattern among the histoblasts at metamorphosis. These models are (a) of a segmental gradient, set by the intersegmental boundaries of the previous instar, to which imaginal cells respond by interpretation of positional information; and (b) of progressive compartmentalization of pattern within the anlagen, without reference to epidermal context.

Abdomen↗
PubMed2005

Ecologic covariates of hookworm infection and reinfection in rural Kwazulu-natal/south Africa: a geographic information system-based study.

Information on hookworm infection and re-infection in a cohort of primary school children and interview data on their socioeconomic background and behavior were combined with environmental data using a geographic information system (GIS). Multivariate models served to explore the covariation of environmental and infection patterns adjusted for possible confounders. Our aim was to identify environmental factors that might serve to predict infection and thus guide control efforts when epidemiologic information is insufficient. Furthermore, we wanted to establish whether soil type has a genuine influence on hookworm infection. Prevalence maps and spatial statistics showed considerable spatial clustering of infection in the small ( approximately 28 x 16 km) study area. The multivariate logistic regression models showed strong positive associations of infection at baseline (baseline prevalence = 83.2%) with settlement density (odds ratio [OR] = 1.24, 95% confidence interval [CI] = 1.10-1.38) and vegetation density (OR = 1.66, 95% CI = 1.25-2.22) and a strong negative association with the clay content of the soil (OR = 0.67, 95% CI = 0.62-0.73). Similar but weaker correlations were found after re-infection. Socioeconomic status and behavior did not seem to confound these associations. Spatial analysis of the model residuals suggested that because the models accounted for most of the spatial pattern, the model standard errors were not affected by spatial clustering. Our study shows that the pattern of hookworm infection is strongly influenced by several environmental factors. The GIS-aided prediction of areas in need of treatment is therefore a promising tool to guide control efforts when epidemiologic information is insufficient.

Child↗
PubMed1989

Tubulin isotype usage in vivo: a unique spatial distribution of the minor neuronal-specific beta-tubulin isotype in pheochromocytoma cells.

The neuronal cells of vertebrates express two beta-tubulin isotypes, called Class II and Class III, that are neuronal specific. In order to determine the distribution of the minor Class III isotype, site-directed antibodies were raised to synthetic peptides representing the carboxyl terminal, isotype-defining domains of the tubulins. These antibodies were applied to PC12 cells at various stages of differentiation. The Class III isotype was found to be expressed in undifferentiated PC12 cells as well as in cells at every stage of differentiation. The concentration of the Class III isotype, relative to the total beta-tubulin complement, did not change significantly. Indirect double immunofluorescence microscopy demonstrated that the Class III isotype was found in the soma and the neurites of differentiated PC12 cells; this spatial pattern of Class III expression paralleled the total beta-tubulin pattern. Although the anti-Class III antiserum could stain in vitro assembled neuronal microtubules in a filamentous pattern, a close examination of the Class III staining pattern in flattened PC12 cells revealed that this isotype was not incorporated into the nonaxoplasmic array of microtubules. Rather, the Class III isotype was localized in a nonfilamentous, granular pattern that was not readily extracted with nonionic detergent. Cells treated with taxol and then flattened and stained showed that the Class III isotype could be induced to assemble into microtubule bundles by taxol. Thus, the minor neuronal beta-tubulin isotype appears to be spatially specialized in its pattern of expression.

Adrenal Gland Neoplasms↗
PubMed1979

Patterns of cell proliferation in the retina of the clawed frog during development.

Quantitative assays of the spatial pattern of cell production in the developing retina of Xenopus have been made using 3H-thymidine labelling and colcemid blockade of mitosis. Reconstructions were made from serial sections showing the position of every mitotic figure in the retina. After stage 54 the number of mitotic figures decreases at the dorsal margin of the retina and increases at the ventral margin. The ventral:dorsal ratio of mitoses reaches 10:1 by metamorphosis. Density of mitotic figures is maximum at the point of entry of the ophthalmic vessels at the ventral margin. In spite of asymmetrical production of retinal cells the cell density remains constant throughout the retina, probably as a result of displacement of retinal cells dorsally to compensate for the relatively greater proliferation ventrally. It is also proposed that the asymmetrical retinal growth serves to maintain the relationship between each point in visual space and corresponding points in the two retinae as the eyes are displaced dorsally on the head during metamorphosis.

Animals↗
PubMed1997

Pattern formation triggered by rare events: lessons from the spread of rabies.

Understanding of large-scale spatial pattern formation is a key to successful management in ecology and epidemiology. Neighbourhood interactions between local units are known to contribute to large-scale patterns, but how much do they contribute and what is the role of regional interactions caused by long-distance processes? How much long-distance dispersal do we need to explain the patterns that we observe in nature? There seems to be no way to answer these questions empirically. Therefore, we present a modelling approach that is a combination of a grid-based model describing local interactions and an individual-based model describing dispersal. Applying our approach to the spread of rabies, we show that in addition to local rabies dynamics, one long-distance infection per 14000 km2 per year is sufficient to reproduce the wave-like spread of this disease. We conclude that even rare ecological events that couple local dynamics on a regional scale may have profound impacts on large-scale patterns and, in turn, dynamics. Furthermore, the following results emerge: (i) Both neighbourhood infection and long-distance infection are needed to generate the wave-like dispersal pattern of rabies; (ii) randomly walking rabid foxes are not sufficient to generate the wave pattern; and (iii) on a scale of less than 100 km x 100 km, temporal oscillations emerge that are independent from long-distance dispersal.

Animals↗
PubMed1990

Expression of a MyoD family member prefigures muscle pattern in Drosophila embryos.

We have isolated a Drosophila gene that is expressed in a temporal and spatial pattern during embryogenesis, strongly suggesting an important role for this gene in the early development of muscle. This gene, which we have named nautilus (nau), encodes basic and helix-loop-helix domains that display striking sequence similarity to those of the vertebrate myogenic regulatory gene family. nau transcripts are initially localized to segmentally repeated clusters of mesodermal cells, a pattern that is reminiscent of the expression of the achaete-scute genes in the Drosophila peripheral nervous system. These early nau-positive cells are detected just prior to the first morphological evidence of muscle cell fusion and occupy similar positions as the later-appearing muscle precursors. Subsequently, nau transcripts are present in at least a subset of growing muscle precursors and mature muscle fibers that exhibit distinct segmental differences. These observations establish nau as the earliest known marker of myogenesis in Drosophila and indicate that this gene may be a key determinant of pattern formation in the embryonic mesoderm.

Amino Acid Sequence↗
PubMed1993

DNA replication in fertilized eggs of the starfish Asterina pectinifera.

Early starfish embryos were labeled with 5-bromo-2'-deoxyuridine (BrdU; the thymidine analogue) for 3-4 min of pulse, and the BrdU incorporated into newly replicated DNA was immunocytochemically detected with anti-BrdU antibody. Series of optical sections of the stained embryos observed with a confocal laser scanning microscope (CLSM) were collected, and three-dimensional images of the chromatin and the incorporated BrdU were reconstructed on a computer display. The distribution of the DNA replication sites and the chromatin structure were investigated from a three-dimensional point of view. The oocytes fertilized during maturation and the eggs fertilized after maturation were examined for the timing of S phase, DNA replication pattern, and chromatin distribution in the nucleus. Duration of the first S phase between the two types of embryos differed in the first S phase, but was the same in the second and third S phases. We observed a successive change in the distribution of DNA replication sites from a "uniform" to a "condensing" pattern during a single S phase traverse, except in the first S phase of the eggs fertilized after maturation. These two patterns of DNA replication almost coincided with chromatin visualized by anti-single-stranded DNA antiserum. The apparent change in the pattern of DNA replication sites thus simply reflects the change in the spatial distribution of chromatin. The spatial pattern of DNA replication at the first S phase of the eggs fertilized after maturation was unique in that the whole nucleus was a mosaic of two distinct regions, each supposedly derived from the female and male pronuclei. The putative female region had a fibrillar pattern of DNA replication sites confined to the periphery of the nucleus, while the male region showed condensed sites of DNA replication, which persisted longer than the sites in the female pronuclear region. We discuss such a singularity of the first S phase in starfish eggs on the basis of the temporal relation between the progress of maturation and the time of activation.

Animals↗