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PubMed1997

Differential features of motor neuron disease mortality in Spain.

BACKGROUND: The objective of this study was to describe the temporal and spatial patterns of motor neuron disease (MND) in Spain. METHODS: We studied data where MND was stated as the principal cause of death in official statistics from Spain. Time trends were analysed for age-, sex-specific and age-adjusted rates for the period 1951-1990. Age-adjusted mortality and relative risk, obtained by Poisson regression adjusting for age, were calculated for each province from deaths during the period 1975-1988. Maps were constructed using log transformed rates. Statistical significance of spatial aggregation was assessed using the Ohno et al. test. RESULTS: The 1951-1990 mortality rate, age- and sex-adjusted to the European population, for the population aged > or = 40 years was 1.49 per 100,000; 1.90 and 1.21 for males and females respectively. In general, mortality increased with age. Age-adjusted rates rose until 1960, dropped by 70% during the 1960s and declined slightly over the 1951-1990 period as a whole. From 1970 onwards MND mortality rose evenly, particularly in the 60-69 age group. A North-South gradient was suggested for both sexes with statistically significant clustering in the Northern coastal regions and--for males alone--in the Midwest provinces. CONCLUSIONS: Mortality from MND in Spain displayed a magnitude and recently rising temporal trend similar to that described in several other countries. Specific traits were: a decrease during the 1960s, which has been described for Japan only, as well as spatial heterogeneity and a predominant recent increase among the 60-69 age group. The determinants of these unusual MND mortality patterns are unknown.

Adult↗

PubMed2005

Oviposition site preference and egg hatchability of Anopheles gambiae: effects of land cover types.

We studied the oviposition site preference and egg hatchability of Anopheles gambiae Giles with water collected from farmlands, forests, and natural wetlands. Water types significantly affected oviposition preference. Mosquitoes deposited significantly more eggs in rainwater in both the dry and wet seasons than waters from forests and wetlands, suggesting that An. gambiae prefers water with few impurities for oviposition. In the dry season, An. gambiae females also deposited significantly more eggs in waters from farmlands than those from forests and natural wetlands, but these differences were not statistically significant during the wet season. In both indoor and natural conditions, egg mortality in natural wetland habitats was significantly higher than in farmland habitats. The average water temperature in natural wetland habitats was significantly lower than farmland habitats in the natural conditions, but it remained the same under indoor experimental conditions, suggesting that factors other than water temperature play an important role in egg hatchability. Together with the findings from previous studies on the effects of land cover on larval survivorship, our results support the hypothesis that variations in habitat conditions induced by different land cover types contribute to the heterogeneous spatial distribution of An. gambiae larvae in the western Kenya highland.

Animals↗

PubMed2006

Thermal imaging of cucumber leaves affected by downy mildew and environmental conditions.

Pathogenesis of Pseudoperonospora cubensis causing downy mildew of cucumber resulted in changes in the metabolic processes within cucumber leaves including the transpiration rate. Due to the negative correlation between transpiration rate and leaf temperature, digital infrared thermography permitted a non-invasive monitoring and an indirect visualization of downy mildew development. Depending on the stage of pathogenesis and the topology of chloroses and necroses, infection resulted in a typical temperature pattern. Spatial heterogeneity of the leaf temperature could be quantified by the maximum temperature difference (MTD) within a leaf. The MTD increased during pathogenesis with the formation of necrotic tissue and was related to disease severity as described by linear and quadratic regression curves. Under controlled conditions, changes in temperature of infected leaves allowed the discrimination between healthy and infected areas in thermograms, even before visible symptoms of downy mildew appeared. Environmental conditions during thermographic measurement, in particular air temperature and humidity, as well as water content and age of the leaf influenced the temperature of its surface. Conditions enhancing the transpiration rate facilitated the detection of changes in leaf temperature of infected leaves at early stages of infection. As modified by environmental conditions, MTD alone is not suitable for the quantification of downy mildew severity in the field.

Cucumis sativus↗

PubMed1990

Hierarchical analysis of population genetic variation in mitochondrial and nuclear genes of Daphnia pulex.

The geographic structure of Daphnia pulex populations from the central United States is analyzed with respect to isozyme and mitochondrial DNA variation. The species complex consists of cyclic and obligate parthenogens. A hierarchical analysis of population structure in the cyclic parthenogens by using a fixation-index approach indicates that this is one of the most extremely subdivided species yet studied. This genetic structure, much of which accrues within 100 km, is certainly due in part to the limited dispersal ability of Daphnia. However, previous work has shown that fluctuating selection can account for the spatial heterogeneity in isozyme frequencies in these populations. This may explain why the population subdivision for the mitochondrial genome increases approximately three times as rapidly with distance as does that for nuclear genes, which is slower than the neutral expectation. The obligate parthenogens are shown to be polyphyletic in origin, evolutionarily young, and, in some cases, geographically widespread.

Animals↗

PubMed2003

Assessing gene expression in lung subcompartments utilizing in situ RNA preservation.

The mechanisms of toxicant-mediated lung injury and repair are influenced by the considerable spatial heterogeneity that exists within the conducting airways of the lungs. As a result of this heterogeneity, significant differences and similarities in gene expression are observed throughout lung subcompartments. RNA-based technologies such as real-time reverse transcription polymerase chain reaction (real-time RT-PCR) and cDNA microarray analysis of gene expression provide valuable clues to understanding the mechanisms of toxicant-induced injury. Isolating RNA from lung subcompartments has previously involved considerable time and labor-intensive processes that limit the number of animals that could be processed in a day. The aim of this study was to determine if intact, high-quality RNA could be preserved in situ over a period of time to delay the need to immediately perform site-specific lung subcompartment microdissections and RNA isolations. Two hours after 1-nitronaphthalene treatment, rat lungs were inflated with and stored in RNA preservation solution and stored at 4 degrees C for 7 days. RNA was isolated from the lung subcompartments isolated by microdissection. After 7 days of storage, the RNA was intact, of high quality, and could be used for real-time RT-PCR to examine heterogeneous gene expression in the lung subcompartments. In summary, this simplified technique of in situ RNA preservation and site-specific lung subcompartment microdissection allows the isolation of intact, high-quality RNA that may be used with molecular RNA-based technologies that will significantly accelerate our understanding of pulmonary injury and repair mechanisms.

Animals↗

PubMed2006

Cytochrome P450 1A4 and 1A5 in common cormorant (Phalacrocorax carbo): evolutionary relationships and functional implications associated with dioxin and related compounds.

The present study characterized cytochrome P4501A (CYP1A) isoforms from common cormorant (Phalacrocorax carbo) with regard to their evolutionary relationships and their roles in disposition of dioxin and related compounds (DRCs). Two clones isolated from a cormorant liver cDNA library were named CYP1A4 and CYP1A5 on the basis of greatest overall amino acid identity shared with chicken (Gallus gallus) CYP1A4 (78%) and CYP1A5 (78%), respectively. Spatial heterogeneity in phylogenetic signal along the sequences strongly indicated that cormorant CYP1A4 and CYP1A5 have undergone partial interparalog gene conversion, similar to chicken and mammalian CYP1As. Phylogenetic analysis of a putatively unconverted region produced a tree topology consistent with the orthology of avian CYP1A5s with mammalian CYP1A2s and avian CYP1A4s with mammalian CYP1A1s. Hepatic CYP1A4 and CYP1A5 mRNA levels in wild cormorants from Lake Biwa, Japan, were quantified to examine the effects of DRCs on isoform-specific expression and to evaluate the toxicokinetics of DRCs in which CYP1A expression is involved. Both CYP1A4 and CYP1A5 mRNA levels were positively correlated with total tetrachlorodibenzo-p-dioxin toxic equivalents and concentrations of each congener in most cases in the liver, suggesting the induction of both enzymes through a shared transcriptional mechanism. The lack of correlation of 2,3,7,8-tetrachlorodibenzofuran and 3,3',4,4'-tetrachlorobiphenyl (PCB77) to CYP1A gene expression is likely due to the rapid metabolism of these two congeners. Liver-to-muscle concentration ratios for most DRC congeners except PCB77 and mono-ortho coplanar polychlorinated biphenyls significantly increased with an elevation of CYP1A4 and CYP1A5 mRNA levels. The present data suggest that hepatic sequestration of some DRCs occurs in cormorant via binding to either CYP1A5 or both CYP1A4 and CYP1A5.

Amino Acid Sequence↗

PubMed2002

Myocardial proteome analysis reveals reduced NOS inhibition and enhanced glycolytic capacity in areas of low local blood flow.

In the heart, in situ local myocardial blood flow (MBF) varies greater than 10-fold between individual areas and displays a spatially heterogeneous pattern. To analyze its molecular basis, we analyzed protein expression of low and high flow samples (300 mg, <50% or >150% of mean MBF, each n=30) of six beagle dogs by 2-D polyacrylamide gel electrophoresis (380 +/- 78 spots/gel). In low flow samples, dimethylarginine dimethylaminohydrolase (DDAH1) was increased greatly (+377%, compared with high flow samples). This increase resulted in a 75% reduction of asymmetric dimethylarginine (ADMA), the potent endogenous inhibitor of NO synthase, whereas eNOS showed no difference. Low flow samples exhibited enhanced expression of GAPDH (+89%) and phosphoglycerate kinase (+100%), whereas hydroxyacyl-CoA dehydrogenase, electron transfer flavoprotein, myoglobin, and desmin were decreased. Assessing local MBF on different days within 2 weeks revealed a high degree of MBF stability (r2 > 0.79). Thus, stable differences in local MBF are associated with significant differences in local gene and protein expression. In low flow areas, the increased DDAH1 reduces ADMA concentration and NOS inhibition, which strongly suggests enhanced NO formation. Low flow areas are also characterized by a higher glycolytic and a lower fatty acid oxidation capacity. Both the shift in substrate utilization and the rise in NO may contribute to the known lower oxygen consumption in these areas.

Amidohydrolases↗

PubMed1994

Surgical stimulation induces changes in brain electrical activity during isoflurane/nitrous oxide anesthesia. A topographic electroencephalographic analysis.

BACKGROUND: The aim of this study was to investigate topographic changes in electroencephalographic (EEG) power and frequency induced by abdominal surgery during anesthesia with 0.6% or 1.2% isoflurane in 66% nitrous oxide. METHODS: Forty-six patients (aged 41 +/- 13 yr) scheduled for elective abdominal surgery were studied. The trachea of each patient was intubated and the lungs ventilated. Patients were randomly assigned to one of four groups: anesthesia was maintained with 0.6% (group 1, n = 12; group 2, n = 11) or 1.2% end-tidal isoflurane (group 3, n = 12; group 4, n = 11) in 66% nitrous oxide. Data were recorded over 20 min. Groups 1 and 3 were studied without surgery (as controls). In groups 2 and 4 recording was started 6 min before skin incision. The EEG was acquired via 17 scalp electrodes placed in standard International 10-20 locations (reference Cz). Absolute and relative power densities were calculated in selected frequency bands. EEG maps of spectral power densities were coded according to a continuous color spectrum. RESULTS: During baseline recordings, alpha activity was dominant at frontal areas in groups 1 and 2. In comparison, in groups 3 and 4, delta and theta activities were dominant at frontal leads. In group 2, the start of surgery resulted in increases in delta activity and decreases in alpha activity that were most dominant frontally (delta +181% and alpha -61%, F3). The delta shift was attenuated at 1.2% isoflurane (group 4, delta +44%, F3), but decreases in alpha activity (-53%, F3) were comparable to those in group 2. The EEG response in all frequency bands was attenuated at parietotemporal recording sites at both isoflurane concentrations. CONCLUSIONS: The current data demonstrate graded EEG responses induced by abdominal surgery during anesthesia with 0.6% or 1.2% isoflurane in 66% nitrous oxide. Spatial heterogeneities in absolute spectral power densities were reflected by color changes in the EEG maps. The topographic EEG analysis indicates that these changes were most dominant at frontal areas. The increases in delta and decreases in alpha activities may be related to intraoperative "paradoxical" electrophysiologic arousal phenomena.

Adult↗

PubMed2001

Physiology of pulmonary perfusion: new concepts.

Regional pulmonary perfusion is spatially heterogeneous. The classic assumption has been that this is due to the influence of gravity. In the past decade, a new concept has emerged, stressing the fractal geometric properties of the pulmonary vascular tree. Studies that support the gravitational concept tend to have been elaborated using a lower resolution of measurement whereas experiments with high resolution measurements often yield results that contradict the gravitational hypothesis.

Journal Article↗

PubMed2000

Quantitative tagged magnetic resonance imaging of the normal human left ventricle.

Magnetic resonance imaging with tissue tagging is a noninvasive technique for measuring three-dimensional motion and deformation in the human heart. Tags are regions of tissue whose longitudinal magnetization has been altered before imaging so that they appear dark in subsequent magnetic resonance images. They then move with the underlying tissue and serve as easily identifiable landmarks within the heart for the detailed detection of motion. Many different motion and strain parameters can be determined from tagged magnetic resonance imaging. Strain components that are based on a high density of tag data, such as circumferential and longitudinal shortening, or parameters that are combinations of multiple strain components, have highest measurement precision and tightest normal ranges. The pattern of three-dimensional motion and strain in the heart is important clinically, because it reflects the basic mechanical function of the myocardium at both local and global levels. Localized abnormalities can be detected and quantified if the pattern of deformation in a given heart is compared to the normal range for that region, because normal motion and strain in the left ventricle is spatially heterogeneous. Contraction strains typically are greatest in the anterior and lateral walls and increase toward the apex. The direction of greatest contraction lies along a counter clockwise helix from base to apex (viewed from the base) and approximates the epicardial muscle fiber direction. This fiber geometry also results in long-axis torsion during systole. Ejection is accomplished primarily by radially inward motion of the endocardium and by descent of the base toward the apex during systole.

Female↗

PubMed1996

Survey of 222Rn concentrations in dwellings and soils in the Dutch Belgian border region.

222Rn levels in dwellings and soil gas have been investigated in the Eijsden-Visé region, located at the Dutch-Belgian border, in order to analyze the relationship between domestic radon levels and soil gas radon levels, in view of the fact that the local geology varies substantially from uranium-rich to uranium-poor rocks and soils. During February 1992, charcoal detectors were exposed for 24 h in 116 dwellings in the township of Visé, a radon prone area in Belgium. As expected, the results show a large regional variation, with an averaged indoor air radon level of 116 Bq m-3. In the nearby township of Eijsden, the Netherlands, an area with a lower radiation level, similar measurements by means of charcoal detectors in 42 dwellings during March 1993, resulted in an averaged indoor 222Rn concentration of 46 Bq m-3. Furthermore, in the same region time-integrated radon measurements were performed in 15 dwellings on different floors. These results indicate that a gradient in indoor air radon concentration exists from basement to upper floor level. In addition, a significant positive correlation has been found between radon gas levels of soils surrounding 26 houses and indoor air radon levels. The variation in indoor air radon levels in the region under study is mainly due to the variation of the radon levels in the soils. A soil gas radon survey is suitable for prescreening of the radon potential of an area taking into account the spatial heterogeneity of the local geology.

Air Pollutants, Radioactive↗

PubMed2000

Magic-angle effect in magnetic resonance imaging of articular cartilage: a review.

RATIONALE AND OBJECTIVES: The laminar appearance of articular cartilage in magnetic resonance (MR) images has been a source of confusion, especially concerning the number, intensity, thickness, and origin of the layers. The laminar appearance is associated with the magic-angle effect in the MR imaging (MRI) of articular cartilage. METHODS: This article introduces the topic with background information about cartilage and the magic-angle effect and then reviews the literature about the magic-angle effect. The review concludes with a brief discussion of the future directions of study and the potential clinical relevance of the laminae in MR images of articular cartilage. CONCLUSIONS: The magic-angle effect is commonly seen in MR images of several tissues. The direct cause of the laminar appearance of articular cartilage is the T2 relaxation anisotropy in the tissue, which is closely linked to the structure of the collagen fibers, their orientation in the magnetic field, and the water-proteoglycan interaction that amplifies the prevailing orientation of the collagen fiber network. The laminar appearance of cartilage has an intrinsic spatial heterogeneity over the two-dimensional joint surface, which leads to inconsistencies in the reported total number of cartilage laminae and the laminar patterns observable in MRI, depending on where the sample was taken. Two additional thin, low-intensity laminae may also be visible at the boundaries of the cartilage with fluid and with bone; whether these boundary laminae are identified and counted with the others may introduce inconsistency in the results reported by various researchers.

Cartilage, Articular↗

PubMed2005

Modelling predation as a capped rate stochastic process, with applications to fish recruitment.

Many mathematical models use functions the value of which cannot exceed some physically or biologically imposed maximum value. A model can be described as 'capped-rate' when the rate of change of a variable cannot exceed a maximum value. This presents no problem when the models are deterministic but, in many applications, results from deterministic models are at best misleading. The need to account for stochasticity, both demographic and environmental, in models is therefore important but, as this paper shows, incorporating stochasticity into capped-rate models is not trivial. A method using queueing theory is presented, which allows randomness and spatial heterogeneity to be incorporated rigorously into capped rate models. The method is applied to the feeding and growth of fish larvae.

Animals↗

PubMed1999

The effects of local spatial structure on epidemiological invasions.

Predicting the likely success of invasions is vitally important in ecology and especially epidemiology. Whether an organism can successfully invade and persist in the short-term is highly dependent on the spatial correlations that develop in the early stages of invasion. By modelling the correlations between individuals, we are able to understand the role of spatial heterogeneity in invasion dynamics without the need for large-scale computer simulations. Here, a natural methodology is developed for modelling the behaviour of individuals in a fixed network. This formulation is applied to the spread of a disease through a structured network to determine invasion thresholds and some statistical properties of a single epidemic.

Communicable Disease Control↗

PubMed2004

Stochastic and spatial dynamics of nematode parasites in farmed ruminants.

Host-parasite systems provide powerful opportunities for the study of spatial and stochastic effects in ecology; this has been particularly so for directly transmitted microparasites. Here, we construct a fully stochastic model of the population dynamics of a macroparasite system: trichostrongylid gastrointestinal nematode parasites of farmed ruminants. The model subsumes two implicit spatial effects: the host population size (the spatial extent of the interaction between hosts) and spatial heterogeneity ('clumping') in the infection process. This enables us to investigate the roles of several different processes in generating aggregated parasite distributions. The necessity for female worms to find a mate in order to reproduce leads to an Allee effect, which interacts nonlinearly with the stochastic population dynamics and leads to the counter-intuitive result that, when rare, epidemics can be more likely and more severe in small host populations. Clumping in the infection process reduces the strength of this Allee effect, but can hamper the spread of an epidemic by making infection events too rare. Heterogeneity in the hosts' response to infection has to be included in the model to generate aggregation at the level observed empirically.

Animal Husbandry↗

PubMed2005

Amplification of individual preferences in a social context: the case of wall-following in ants.

Amplification processes are an essential component of the collective phenomena observed in social and gregarious species. In this paper, we tested the hypothesis that a weak individual wall-following tendency in ants can be amplified by communication through chemical trails, leading to a response to the spatial heterogeneities at the collective level. In our experiments, ants had to cross a diamond-shaped bridge along either of two branches of equal length to get from their nest to a food source. Two types of bridge were used: control bridges without a wall, and experimental bridges equipped with a wall along the inner edge of one of their branches. On the control bridges, ants collectively chose either branch of the bridge in most experiments, whereas on the experimental bridges, the branch with the wall was selected almost systematically. A mathematical model is proposed to assess, in various conditions, the importance of the amplification effect of the chemical trail on the wall-following tendency observed at the individual level. The model highlights the fact that the amplification process can lead to an overestimation of individual capabilities and, thus, that the results of experiments investigating individual preferences at group level in animals must be interpreted with caution.

Animal Communication↗

PubMed2007

Experimentally induced change in infectious period affects transmission dynamics in a social group.

A key component of any epidemiological model is the infectious period, which greatly affects the dynamics and persistence of an infection. Social organization, leading to behavioural and spatial heterogeneities among potential susceptibles, interacts with infectious period to create different risk categories within a group. Using the honeybee (Apis mellifera) colony as a social model, a protocol that creates different infectious periods in individual bees and another that follows the diffusion of a transmittable tracer within a colony, we show experimentally how a short infectious period results in an epidemic process with low prevalence confined only to individuals at the outer edge of a group, while a long infectious period results in high prevalence distributed more universally among all the group members. We call this finding an evidence of 'organizational immunity' in a social network and propose that the honeybee colony provides a unique opportunity to test its role in social transmission processes.

Animals↗

PubMed1981

On pattern formation mechanisms for lepidopteran wing patterns and mammalian coat markings.

The patterns on wings of Lepidoptera can be generated with a few pattern elements, but no mechanism has been suggested for producing them. I consider two of the basic patterns, namely, central symmetry and dependent patterns. A biochemically plausible model mechanism is proposed for generating major aspects of these patterns, based on a diffusing morphogen that activates a gene or colour-specific enzyme in a threshold manner to generate a stable heterogeneous spatial pattern. The model is applied to the determination stream hypothesis of Kühn & von Engelhardt (Wilhelm Roux Arch. Entw Mech. Org. 130, 660 (1933)), and results from the model compared with their microcautery experiments on the pupal wing of Ephestia kühniella. In the case of dependent patterns, results are compared with patterns on specific Papilionidae. For the same mechanism and a fixed set of parameters I demonstrate the important roles of geometry and scale on the spatial patterns obtained. The results and evidence presented here suggest the existence of diffusion fields of the order of several millimetres, which are very much larger than most embryonic fields. The existence of zones of polarizing activity is also indicated. Colour patterns on animals are considered to be genetically determined, but the mechanism is not known. I have previously suggested that a single mechanism that can exhibit an infinite variety of patterns is a candidate for that mechanism, and proposed that a reaction-diffusion system that can be diffusively driven unstable could be responsible for the laying down of the spacing patterns that generates the pre-pattern for animal coat markings. For illustrative purposes I consider, a practical reaction mechanism, which exhibits substrate inhibition, and show that the geometry and scale of the domain (part of the epidermis) play a crucial role in the structural patterns that result. Patterns are obtained for a selection of geometries, and general features are related to the coat colour distribution in the spotted Felidae, giraffe, zebra and other animals. The patterns depend on the initial conditions, but for a given geometry and scale are qualitatively similar, a positive feature of the model and a necessary model attribute in view of the pattern individuality on animals of the same species.

Animals↗