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PubMed1988

Rapid shrinkage of rat striatal extracellular space after local kainate application and ischemia as recorded by impedance.

Early changes in tissue extracellular space following exposure to the excitotoxin kainate in the striatum were compared to those following cardiac arrest of rats anesthetized by chloral hydrate. Tissue extracellular space was monitored by impedance measurements. The possible role of voltage-sensitive Na channels and energy metabolism was studied by local and systemic application of tetrodotoxine (TTX) and glucose, respectively. After both kainate intoxication and cardiac arrest the extracellular space (normally about 20%) became less than one-half within 15 min. TTX caused a delay in the effect of cardiac arrest, and a slight attenuation of that of kainate. Glucose was ineffective in both preparations. Parallel to a decrease in the extracellular space whole tissue Na/K ratio increased. These experiments show that excitotoxins and cardiac arrest cause similar (and not additive) changes in the extracellular space and that these changes are not mediated by Na channels. In cardiac arrest the onset of the extracellular space alterations is triggered by Na+ influx, thus presumably by neurotransmitter release. It is suggested that most (if not all) currently described protective measures against ischemic, hypoxic, or hypoglycemic brain damage are based on a prolongation of the time of onset leading to cell depolarization, rather than suppressing damaging processes during depolarization.

Animals↗
PubMed1993

Perivascular cells act as scavengers in the cerebral perivascular spaces and remain distinct from pericytes, microglia and macrophages.

Perivascular cells in the rat brain are an immunophenotypically defined group of cells which can be identified by their expression of the ED2 antigen. The present study investigates the role of perivascular cells as scavengers in the perivascular spaces of the rat brain and the relationship of these cells to microglia, macrophages, pericytes and smooth muscle cells. Particulate matter (Indian ink) was injected selectively into the perivascular spaces of the left caudoputamen of 59 rats. Animals were killed by cardiac perfusion of formalin or glutaraldehyde 2 h-2 years after ink injection. Cerebral hemispheres were examined histologically and immunocytochemically using the ED2 antibody for perivascular cells, ED1 for microglia and macrophages and OX-6 directed against Ia antigen [major histocompatibility complex (MHC) class II]. ED2+ perivascular cells ingested Indian ink in the perivascular spaces and expressed MHC class II antigen. Reactive microglia and macrophages in the perivascular parenchyma expressed ED1, but no ED2+ cells were seen outside the perivascular spaces. Transmission electron microscopy distinguished perivascular cells, which ingested carbon particles, from pericytes, which did not. The results of this study suggest that perivascular cells remain distinct from pericytes, microglia and macrophages and that they play a major role as scavengers in the perivascular spaces of the rat brain. This role reflects the importance of perivascular spaces as drainage pathways for soluble and insoluble material from the brain.

Animals↗
PubMed1993

Space-based visual attention models and object selection: constraints, problems, and possible solutions.

One of the functions of visual attention is the selection of object information. This seems to be in line with an influential group of attentional models that assume that attentional selection is space based. These models assume that the selection of an object in vision is realized by selection of the location of that object. Whether this relatively simple idea of space-based attention and the corresponding, more elaborated space-based models are sufficient to handle selected constraints and problems of object selection is the main issue of this article. The first step toward an answer is to describe the common computational structure of space-based attentional models. Two model classes will be distinguished: capacity-limited models (e.g., Treisman, 1988; LaBerge & Brown, 1989) and models that do not assume a capacity limitation (e.g., Van der Heijden, 1992). Next, three kinds of task and data on object selection are introduced that are especially challenging for space-based models. The first type of data refers to experiments that require selection between overlapping objects. The second type of data concerns the influence of early perceptual grouping--a strong object-defining factor--on late response competition, and the third type consists of a selection task in which a high-level (semantic) attribute defines an object and controls selection. In all three cases, problems of space-based models are analyzed and possible solutions are sketched. Finally, a brief evaluative summary is given.

Attention↗
PubMed1983

Ion activities in the lateral intercellular spaces of gallbladder epithelium transporting at low external osmolarities.

The ion activities in the lateral spaces of the unilateral preparation of the gallbladder of Rana catesbiana were measured by double-barrelled ion-selective microelectrodes. The bladders were bathed in a saline solution with a low osmolarity (62 mOsm) containing, in mM: 27 Na+, 27 Cl-, 2 K+, 1 Ca++, 4 HCO3-. Working at reduced osmolarities had the advantage of an increased volume transport and of widened intercellular spaces. The reference barrel recorded an electrical potential of +2.7 mV in the spaces; they contained a solution similar to the external solution. The electrodes recorded a Na+ concentration of 27 mM, a K+ concentration of 1.7 mM, a Ca++ concentration of 0.69 mM and a Cl- concentration of 28.5 mM. In the spaces there was a lower resistance between the tip of the electrode and the serosal bath than that recorded with the tip in the lumen, and injection of fluorescent dye (11 A diameter) via the electrodes did not stain the cells. The concentrations in the secretion were similar to those in the spaces. The intracellular compartment had an apparent K+ concentration of 95 mM, and the concentrations of Na+ and Cl- were both about 5 mM. These data indicate that when the gallbladder is bathed with hypotonic solutions and is transporting fluid at approximately three or four times the normal rate, there are no significant osmotic gradients between the lumen and the lateral spaces. It is suggested that transcellular transport of water is implemented by a combination of high osmotic permeabilities across both mucosal and serosal cell membranes and low reflection coefficients (for K+ salts) at the serosal cell membranes.

Animals↗
PubMed1997

Comparison of line and space bisection in evaluation of normal and amblyopic spatial vision.

BACKGROUND: Partitioning experiments have been used historically and in the recent past to evaluate space perception in visually normal and disturbed individuals. Specifically, amblyopic patients display notably distorted and/or uncertain spatial localization when assessed by either line or space bisection. METHODS: This investigation was concerned with the comparison of line bisection with space bisection. Normal and amblyopic subjects bisected horizontal lines and spaces extending 1, 2, 3 and 15 deg arc monocularly on a computer screen. Results of the two procedures were compared. RESULTS: Visually normal subjects bisected both lines and spaces without reproducible distortion, within uncertainties approximating 1-3% of their length. No differences were observed between the two procedures. Strabismic amblyopes bisected without constant distortion to either side of the geometrical mean, irrespective of direction or extent of the deviation; their uncertainty at bisecting ranged from 2% to 12%. Again, no distinction between line and space bisection could be made. CONCLUSION: We conclude that the two procedures yield comparable results.

Adolescent↗
PubMed2004

The distance from the skin to the subarachnoid space can be predicted in premature and former-premature infants.

PURPOSE: Spinal anesthesia can be technically challenging in young infants. We studied whether the distance between the skin and the lumbar subarachnoid space in premature and former-premature young infants could be predicted prior to lumbar puncture. METHODS: The distance from skin entry point to tip of the spinal needle was measured using a caliper after lumbar spinal anesthesia at the L4-5 interspace. This distance was correlated to the patient's weight, postconceptual age and lumbar ultrasonographic measurement of the skin-to-subarachnoid space and predictive statistical models were sought. RESULTS: Thirty-five premature or former-premature infants were studied. Three models were examined: all three independent variables, weight and postconceptual age only, and weight only. The model selected contained the weight and postconceptual age, because it had the highest value for adjusted R squared, as well as the lowest value for the mean squared error. Adding the ultrasonic measurement to the model worsened the results. The statistical model that described the depth of the subarachnoid space at the L4-5 level was Y = 13.19 + 0.0026 x W - 0.12 x PCA, where Y is the distance (mm) from the skin to the subarachnoid space, W is the patient's weight (g) and PCA is the postconceptual age (weeks). Adjusted R squared was 0.72, mean square error was 2.63 and P < 10(-9). CONCLUSION: The distance between the skin and the subarachnoid space at the level of L4-5 interspace can be predicted using a statistical model based on the infant's weight and postconceptual age. Spinal ultrasound has no value in L4-5 subarachnoid space depth prediction.

Anesthesia, Spinal↗
PubMed2006

Space motion sickness.

Motion sickness remains a persistent problem in spaceflight. The present review summarizes available knowledge concerning the incidence and onset of space motion sickness and aspects of the physiology of motion sickness. Proposed etiological factors in the elicitation of space motion sickness are evaluated including fluid shifts, head movements, visual orientation illusions, Coriolis cross-coupling stimulation, and otolith asymmetries. Current modes of treating space motion sickness are described. Theoretical models and proposed ground-based paradigms for understanding and studying space motion sickness are critically analyzed. Prediction tests and questionnaires for assessing susceptibility to space motion sickness and their limitations are discussed. We conclude that space motion sickness does represent a form of motion sickness and that it does not represent a unique diagnostic entity. Motion sickness arises when movements are made during exposure to unusual force backgrounds both higher and lower in magnitude than 1 g earth gravity.

Humans↗
PubMed2005

Microbial antibiotic production aboard the International Space Station.

Previous studies examining metabolic characteristics of bacterial cultures have mostly suggested that reduced gravity is advantageous for microbial growth. As a consequence, the question of whether space flight would similarly enhance secondary metabolite production was raised. Results from three prior space shuttle experiments indicated that antibiotic production was stimulated in space for two different microbial systems, albeit under suboptimal growth conditions. The goal of this latest experiment was to determine whether the enhanced productivity would also occur with better growth conditions and over longer durations of weightlessness. Microbial antibiotic production was examined onboard the International Space Station during the 72-day 8A increment. Findings of increased productivity of actinomycin D by Streptomyces plicatus in space corroborated with previous findings for the early sample points (days 8 and 12); however, the flight production levels were lower than the matched ground control samples for the remainder of the mission. The overall goal of this research program is to elucidate the specific mechanisms responsible for the initial stimulation of productivity in space and translate this knowledge into methods for improving efficiency of commercial production facilities on Earth.

Anti-Bacterial Agents↗
PubMed2006

A temporal forecast of radiation environments for future space exploration missions.

The understanding of future space radiation environments is an important goal for space mission operations, design, and risk assessment. We have developed a solar cycle statistical model in which sunspot number is coupled to space-related quantities, such as the galactic cosmic radiation (GCR) deceleration potential (phi) and the mean occurrence frequency of solar particle events (SPEs). Future GCR fluxes were derived from a predictive model, in which the temporal dependence represented by phi was derived from GCR flux and ground-based Climax neutron monitor rate measurements over the last four decades. These results showed that the point dose equivalent inside a typical spacecraft in interplanetary space was influenced by solar modulation by up to a factor of three. It also has been shown that a strong relationship exists between large SPE occurrences and phi. For future space exploration missions, cumulative probabilities of SPEs at various integral fluence levels during short-period missions were defined using a database of proton fluences of past SPEs. Analytic energy spectra of SPEs at different ranks of the integral fluences for energies greater than 30 MeV were constructed over broad energy ranges extending out to GeV for the analysis of representative exposure levels at those fluences. Results will guide the design of protection systems for astronauts during future space exploration missions.

Computer Simulation↗
PubMed2006

Space-time clustering of glioma cannot be attributed to specific histological subgroups.

We previously showed that infectious exposures may be involved in the aetiology of adult glioma, by analysing for space-time clustering using population-based data from the South of the Netherlands. Here we extended these analyses and describe in detail the space-time clustering patterns in glioma subgroups, gender and age-categories. Knox tests for space-time interactions between cases were applied with fixed thresholds of close in space, <5 km, and close in time, <1 year apart. We used the spatial coordinates of the addresses at diagnosis in the analyses. Tests were repeated replacing geographical distance with distance to the Nth nearest neighbour. N was chosen such that the mean distance was 5 km. Data were also analysed by a second order procedure based on K-functions. There was only statistically significant space-time clustering for oligodendroglioma. Clustering was present for adults aged 30-54 years and was more pronounced among males. Given the low prior probability of an infectious aetiology for this specific subgroup, these results should probably be interpreted as false-positive. We conclude that space-time clustering of glioma cannot be attributed to a specific glioma subgroup. The observed clustering in our previous study is therefore probably an overall effect within and between glioma subgroups.

Adolescent↗
PubMed1990

Mathematical modeling of mass transfer in microvascular wall and interstitial space.

A one-dimensional, unsteady-state mathematical model was developed to describe the transfer of macromolecules across a microvascular wall and into the interstitial space. The proposed theoretical model accounts for both molecular diffusion and convective transfer through the microvascular wall as well as in the interstitial space. The resulting partial differential equations were simultaneously solved using the Laplace transform method. The inversion of the Laplace transformed equations was obtained by using contour integration in the complex region. The final solution is represented by two equations expressing the macromolecule concentration in the microvascular wall region and in the interstitial space, respectively, as functions of time, spatial coordinate, macromolecule concentration in the microvascular wall at the plasma-wall interface, wall thickness, wall-interstitial space equilibrium constant for the macromolecules, ratio of the cross-sectional area of the two regions, sieving coefficients, diffusivity coefficients, and average fluid velocity terms in the two regions. Plots of the macromolecule concentration in both regions as a function of time are presented and discussed for selected values of the parameters. An analytical expression for the total amount of mass which has accumulated in a portion of the interstitial space at any given time was also derived and used to determine the average fluid velocity term and the diffusivity coefficient for each of the two regions from published experimental data (A. Y. Bekker, A. B. Ritter, and W. N. Durán, 1989, Microvasc. Res. 34, 200-216). A numerical nonlinear regression method was used for this purpose. The values for the diffusivity coefficients found in this work for this particular data set compare favorably with the results previously obtained by other workers in similar systems. It is expected that our model will be used in the future to describe the dynamics of mass transfer across a microvascular wall and into the interstitial space, on the basis of the molecular diffusion and/or convective transport mechanisms, thus contributing to the solution of the controversy regarding the nature of the transfer mechanism controlling macromolecule transport in living systems.

Animals↗
PubMedDate not supplied

Catecholamines and their enzymes in discrete brain areas of rats after space flight on biosatellites Cosmos.

The activity of the catecholaminergic system was measured in the hypothalamus of rats which had experienced an 18.5-19.5-day-long stay in the state of weightlessness during space flights on board Soviet biosatellites of the type Cosmos. In the first two experiments, Cosmos 782 and 936, the concentration of norepinephrine and the activities of synthesizing enzymes tyrosine hydroxylase and dopamine-beta-hydroxylase and of the degrading enzyme monoamine oxidase were measured in the total hypothalamus. None of the given parameters was changed after space flight. In the light of the changes of these parameters recorded after exposure to acute stress on Earth, this finding indicates that long-term state of weightlessness does not represent an intensive stressogenic stimulus for the system studied. In the space experiment Cosmos 1129, the concentration of norepinephrine, epinephrine, and dopamine was studied in isolated nuclei of the hypothalamus of rats within 6-10 hr following return from space. Norepinephrine was found to be significantly reduced in the arcuate nucleus, median eminence and periventricular nucleus, epinephrine in the median eminence, periventricular and suprachiasmatic nuclei, whereas dopamine was not significantly changed after space flight. The decreased catecholamine levels found in some hypothalamic nuclei of rats which had undergone space flight indicate that no chronic intensive stressor could have acted during the flight, otherwise the catecholamine concentration would have been increased in the nuclei. The decreased levels must have been induced by the effect of a stressogenic factor acting for a short time only, and that either during the landing maneuver or immediately after landing. Thus long-term exposure of the organism to the state of weightlessness does not represent a stressogenic stimulus for the catecholaminergic system in the hypothalamus, which is one of the regulators of the activation of neuroendocrine reactions under stress.

Animals↗
PubMed1989

Human dimensions in space development.

Space exploration is now moving beyond the stage when technical development dominated research. As thinking shifts towards the problems of long-term colonization of the Solar System, the biological and behavioural sciences must make major contributions. This article outlines some of the issues which must be addressed, such as group behaviour and dynamics in space flight, the environment created at space stations and other outposts, recruitment and training of suitable spacefarers, and the planning and governing of space settlements. Ten dimensions of the human aspect of space habitation are described and an indication given of how they may form the basis for a new taxonomy of space planning, operations and management.

Communication↗
PubMed1984

Radiation risk estimation and its application to human beings in space.

The number of human beings likely to spend time in space will increase as time goes on. While exposures vary according to missions, orbits, shielding, etc., an average space radiation fluence (ignoring solar flares, radiation belts and anomalous regions in space) in locations close to earth is about 10 rad/year with a quality factor of about 5.5. The potential effects of exposure to these fluences include both non-stochastic effects and stochastic effects (cancer and genetic damage). Non-stochastic effects, damage to the lens of the eye, bone marrow or gonads, can be avoided by keeping radiation limits below threshold values. Stochastic effects imply risk at all levels. The magnitude of these risks has been discussed in a number of reports by the UNSCEAR Committee and the BEIR Committee in the USA during 1970-1980. The uncertainties associated with these risks and information which has become available since the last BEIR report is discussed. In considering reasonable limits for exposure in space, acceptable levels for stochastic risks must be based on appropriate comparisons. In view of the limited term of duty of most space workers, a lifetime limit may be appropriate. This lifetime limit might be comparable in terms of risks with limits for radiation workers on the ground but received at a higher annual rate for a shorter time. These and other approaches are expected to be considered by an NCRP Committee currently examining the problem of space radiation hazards.

Astronauts↗
PubMed1989

Radiation biology in space: a critical review.

A short summary of the results of radiobiological studies in space or on respective particles on ground will be given. Among the various types of radiation in space, the effect of heavy ions with high energy (HZE-particles) are most essential. Thus, radiobiology in space concerns mostly to the effect of these particles, in cells and in whole organism. Cell death, mutation and malignant transformation are the relevant endpoints, with can be studied on ground with heavy ions of different energy with suitable accelerators or in space, especially by the BIOSTACK concept. In space, however, the effect of microgravity has to be considered as well and there are hints, that under weightlessness the biological effect of radiation may be enhanced. There are still open questions to be answered concerning radioprotection of man in space. Further experiments are necessary.

Animals↗
PubMed1994

Issues and problems for radiobiological research in space.

The uniqueness of the space radiation field creates specific problems in the evaluation of hazards to men and materials. Comprehensive measurements of all physical parameters are necessary but not sufficient. Particular attention has to be paid to variables like solar flares by applying fast-responding active dosimetry. The assessment of biological consequences poses even more problems. There are no human data for the kinds of particles seen in space and they will presumably never be available. The only reasonable approach is therefore to use the information obtained for other radiations and check their applicability for the space situation. This involves both the study of fundamental processes in ground experiments as well as their verification in space missions. Special emphasis has to be laid on the modification of radiation effects by flight-dynamic factors and microgravity. Radiation protection guidelines for space flights cannot simply be transformed from existent regulations designed for radiation workers on earth but have to be tailored to the specific situation in space.

Aerospace Medicine↗
PubMed1990

Right perirenal space. Computed tomography evidence of communication between the bare area of the liver.

Computed tomography (CT) images from one cadaver and 11 patients with perirenal fluid collection were reviewed to study whether the right perirenal space communicates with the bare area of the liver. CT of a cadaver obtained after meticulous right perirenal injection of contrast media showed that contrast media extended superiorly into the bare area of the liver. CT of 11 patients with right perirenal hemorrhage or infection showed that fluid collection within the right perirenal space continued upward, crossing the coronary ligament, extending into the bare area of the liver. The inferior vena cava were completely or partially surrounded by fluid. CT of two patients with bleeding hepatocellular carcinoma showed that blood in the bare area continued extending downward into the perirenal space. We conclude that the right perirenal space is open toward the bare area of the liver and fluid collection within one space may communicate with the other space across the coronary ligament.

Cadaver↗
PubMed2003

Representation and constraints: the inverse problem and the structure of visual space.

Visual space can be distinguished from physical space. The first is found in visual experience, while the second is defined independently of perception. Theorists have wondered about the relation between the two. Some investigators have concluded that visual space is non-Euclidean, and that it does not have a single metric structure. Here it is argued (1) that visual space exhibits contraction in all three dimensions with increasing distance from the observer, (2) that experienced features of this contraction (including the apparent convergence of lines in visual experience that are produced from physically parallel stimuli in ordinary viewing conditions) are not the same as would be the experience of a perspective projection onto a frontoparallel plane, and (3) that such contraction is consistent with size constancy. These properties of visual space are different from those that would be predicted if spatial perception resulted from the successful solution of the inverse problem. They are consistent with the notion that optical constraints have been internalized. More generally, they are also consistent with the notion that visual spatial structures bear a resemblance relation to physical spatial structures. This notion supports a type of representational relation that is distinct from mere causal correspondence. The reticence of some philosophers and psychologists to discuss the structure of phenomenal space is diagnosed in terms of the simple materialism and the functionalism of the 1970s and 1980s.

Humans↗