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Results for “Spatial Distribution”

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At least 181 records · Page 10Linked to original sources

PubMed1972

Spatial distribution of potential in a flat cell. Application to the catfish horizontal cell layers.

An analytical solution is obtained for the three-dimensional spatial distribution of potential inside a flat cell, such as the layer of horizontal cells, as a function of its geometry and resistivity characteristics. It was found that, within a very large range of parameter values, the potential is given by [Formula: see text] where r = rho/rho(0), z = z/rho(0), rho = (R(i)/R(m)).rho(0), delta = h/rho(0); K is a constant; J is the assumed synaptic current; rho, z are cylindrical coordinates; rho(0) is the radius of the synaptic area of excitation; h is the cell thickness; and R(i), R(m) are the intracellular and membrane resistivities, respectively. Formula A closely fits data for the spatial decay of potential which were obtained from the catfish internal and external horizontal cells. It predicts a decay which is exponential down to about 40% of the maximum potential but is much slower than exponential below that level, a characteristic also exhibited by the data. Such a feature in the decay mode allows signal integration over the large retinal areas which have been observed experimentally both at the horizontal and ganglion cell stages. The behavior of the potential distribution as a function of the flat cell parameters is investigated, and it is found that for the range of the horizontal cell thicknesses (10-50 mu) the decay rate depends solely on the ratio R(m)/R(i). Data obtained from both types of horizontal cells by varying the diameter of the stimulating spot and for three widely different intensity levels were closely fitted by equation A. In the case of the external horizontal cell, the fit for different intensities was obtained by varying the ratio R(m)/R(i); in the case of the internal horizontal cell it was found necessary, in order to fit the data for different intensities, to vary the assumed synaptic current J.

Animals↗

PubMed1992

Spatial distribution of sperm-derived chromatin in zygotes determined by fluorescence in situ hybridization.

Fluorescence in situ hybridization was used to determine the spatial distribution of chromatin in zygote pronuclei. A hybrid system involving golden hamster eggs and individual human sperm permitted use of DNA probes specific for the entire human chromosome 4, for the heterochromatic region on the long arm of the human Y chromosome and for unique DNA sequences on human chromosome 19. Chromosome 4 occupied a circumscribed domain in the pronuclei, similar to findings in somatic interphases. Unlike the situation in somatic interphases, the Y heterochromatin was extended throughout the first cell cycle. Pronuclear chromatin was extended 3- to 4-fold compared to somatic interphase chromatin. The extended pronuclear chromatin conformation is likely to affect a zygote's susceptibility to environmental hazards.

Animals↗

PubMed1993

Temporal and spatial distribution of Ixodes pacificus and Dermacentor occidentalis (Acari: Ixodidae) and prevalence of Borrelia burgdorferi in Contra Costa County, California.

The seasonal activity and spatial distribution of adult and immature Ixodes pacificus Cooley & Kohls and Dermacentor occidentalis Marx were determined along trails and on hillsides in two parks in Contra Costa County, CA. I. pacificus and D. occidentalis adults were most numerous in January and May, respectively. Adult ticks were significantly more abundant along heavily vegetated trails than on open grassy hillsides, and on the uphill versus the downhill side of trails. Five species of rodents were captured, and numbers of I. pacificus and D. occidentalis larvae per rodent were highest in May-June and July, respectively. Few nymphs were recovered either by flagging or from captured rodents. An average of 2.2 and 2.8% of the I. pacificus adults collected from the two parks were infected with the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner. The greatest risk of contracting Lyme disease from adult I. pacificus in these two Contra Costa County parks is during the winter months, especially while hiking near the uphill side of trails.

Acari↗

PubMed2001

Spatial distribution of nutritive and nonnutritive vascular routes in perfused rat hindlimb muscle using microspheres.

Skeletal muscle appears to have two vascular flow routes, nutritive and nonnutritive, where the balance of flow is controlled by vasoconstrictors. In the present study, spatial distributions of the two flow routes in muscles of the perfused rat hindlimb were attempted using fluorescent microspheres (15 microm in diameter). Microspheres were injected during steady-state perfusion with norepinephrine (proposed recruiter of nutritive flow), serotonin (proposed recruiter of nonnutritive flow), or vehicle. The three-dimensional location of individual microspheres in representative muscles was determined using a Fluorescent Imaging CryoMicrotome. Norepinephrine and serotonin each increased perfusion pressure (P < 0.05) but stimulated and inhibited oxygen consumption (P < 0.05), respectively. The distribution of microspheres lodged in muscle was independent of the agent used. Spatial perfusion indices for norepinephrine, serotonin, and vehicle did not differ from each other. Similarly, there was no difference in these indices for a theoretical distribution where microspheres were deliberately positioned in muscle bundle capillaries or interfibrillar connective tissue vessels. We conclude that the nutritive and nonnutritive flow routes are distributed throughout muscle sections consistent with their locations in muscle bundle capillaries and interfibrillar connective tissue, respectively.

Animals↗

PubMed2000

Relation between spatial distribution of late potentials and location of origin of premature ventricular complexes on body surface map in patients with postinfarction ventricular tachycardia.

We studied the relationship between the spatial distribution of late potentials (LPs) and the origin of premature ventricular complexes (PVCs) using body surface maps in 55 patients with postinfarction sustained ventricular tachycardia (VT). Body surface maps were recorded from 87 leads to construct departure maps during sinus rhythm and signal-averaged ECGs were recorded from 32 unipolar leads to construct a LP map. The root-mean-square values during 40 ms intervals behind the QRS end were computed as LPs. The PVC map was recorded simultaneously in 14 patients presenting PVC with similar morphology to VT during LP detection. The origin of PVC was localized at the site of isopotential minimum when the potential exceeded -0.5 mV during the early QRS period. The LP area and the departure area showed a similar distribution. However, the PVC origin was closer to the site of LP maximum than the departure minimum in 11 (79%) patients, and the spatial correlation between the LP maximum and the PVC origin was good in 12 (86%) patients. LP and PVC mapping from the body surface is feasible and of worth to predict noninvasively the site of origin of ventricular arrhythmias in patients with remote myocardial infarction and sustained VT.

Adult↗

PubMed1987

Spin-echo fluorine magnetic resonance imaging at 2 T: in vivo spatial distribution of halothane in the rabbit head.

Spin-echo 19F magnetic resonance imaging was performed at 2.0 T to explore the in vivo spatial distribution of halothane in the rabbit head. Because the halothane concentration is low in vivo, and because the measured relaxation times of the 19F resonance peak for halothane were T1 approximately equal to 1.0 sec and T2 approximately equal to 3.5-65 msec, 1-3-h imaging times were required (TR = 1 sec, TE = 9 msec) in order to obtain adequate images with a 64 X 256 raw data matrix and a 20-mm slice thickness. With this technique, halothane was primarily detected in lipophilic regions of the rabbit head, but little or no halothane was observed in brain tissue. Because T2 was shorter in brain tissue than in surrounding fat, a shorter TE than we could obtain is needed for optimal spin-echo imaging of brain halothane.

Animals↗

PubMed1994

Temporal-spatial distribution of SP-B and SP-C proteins and mRNAs in developing respiratory epithelium of human lung.

We determined the temporal and spatial distribution of surfactant protein B (pro-SP-B) and C (pro-SP-C) mRNAs and proteins by immunohistochemistry and in situ hybridization in fetal, neonatal, and adult human lung. Pro-SP-B and SP-B mRNA were detected in bronchi and bronchioles by 15 weeks' gestation. After 25 weeks, pro-SP-B, active SP-B peptide, and SP-B mRNA were co-localized in bronchiolo-alveolar portal cells and in Type II epithelial cells. In adult lung, pro-SP-B and SP-B mRNA were detected primarily in non-ciliated bronchiolar epithelial cells and in Type II cells in the alveolus. Pro-SP-C and SP-C mRNA were detected in cells lining terminal airways from 15 weeks' gestation and thereafter. After 25 weeks, SP-C mRNA and precursor protein were detected in epithelial cells of the bronchiolo-alveolar portals and in Type II cells, where expression increased with advancing gestational age. Distinct cellular patterns of staining for pro-SP-B compared with SP-B active peptide support the concept that its proteolytic processing or cellular routing may be influenced by cell type and/or cell differentiation. SP-B and SP-C are expressed primarily in distal conducting and terminal airway epithelium of human fetal lung well in advance of surfactant lipid synthesis or physiologic requirements to produce pulmonary surfactant at the time of birth.

Adult↗

PubMed1997

The spectrum and spatial distribution of cyanogen in comet Hale-Bopp (C/1995 O1) at large heliocentric distance.

Optical spectra of comet Hale-Bopp (C/1995 O1) at a heliocentric distance of 6.45 astronomical units showed emission from cyanogen gas. The spatial distribution of cyanogen was considerably more diffuse and extended compared to the spatial profile of the dust or grains which were sharply peaked near the center. This behavior is consistent with comets at smaller heliocentric distances suggesting the same or a similar formation mechanism. A cyanogen gas production rate of (1.2 +/- 0.3) x10(26) molecules per second was derived. A model band profile derived from fluorescence equilibrium calculations for the comet's heliocentric velocity and distance agrees with the observed band profile.

Cosmic Dust↗

PubMed1983

Spatial distribution of proliferating cells in avian sarcoma virus-induced gliomas.

We studied the regional distribution of proliferating tumor cells in five avian sarcoma virus-induced gliomas. The labeling index and spatial distribution of [3H]thymidine (dThd)-labeled tumor cells were determined in serial sections of each tumor with a computer-assisted digitizing system. The density of [3H]dThd-labeled cells showed marked regional variation in each tumor, and the ratio of the density of [3H]dThd-labeled cells in tumor periphery to tumor center varied from 0.86 to 1.38. The labeling index generally, but not always, reflected [3H]dThd-labeled cell density. This study indicates that proliferating pools of glioma tumor cells exhibit regional variability in concentration and that the highest numbers of proliferating cells may be predominantly located in central regions of tumor and not in tumor periphery as assumed previously. In all tumors, large numbers of proliferating cells were present in all parts of the tumor.

Animals↗

PubMed1995

Spatial distribution of cardiac transmembrane potentials around an extracellular electrode: dependence on fiber orientation.

Recent theoretical models of cardiac electrical stimulation or defibrillation predict a complex spatial pattern of transmembrane potential (Vm) around a stimulating electrode, resulting from the formation of virtual electrodes of reversed polarity. The pattern of membrane polarization has been attributed to the anisotropic structure of the tissue. To verify such model predictions experimentally, an optical technique using a fluorescent voltage-sensitive dye was used to map the spatial distribution of Vm around a 150-microns-radius extracellular unipolar electrode. An S1-S2 stimulation protocol was used, and vm was measured during an S2 pulse having an intensity equal to 10x the cathodal diastolic threshold of excitation. The recordings were obtained on the endocardial surface of bullfrog atrium in directions parallel and perpendicular to the cardiac fibers. In the longitudinal fiber direction, the membrane depolarized for cathodal pulses (and hyperpolarized for anodal pulses) but only in a region within 445 +/- 112 microns (and 616 +/- 78 microns for anodal pulses) from the center of the electrode (n = 9). Outside this region, vm reversed polarity and reached a local maximum at 922 +/- 136 microns (and 988 +/- 117 microns for anodal pulses) (n = 9). Beyond this point vm decayed to zero over a distance of 1.5-2 mm. In the transverse fiber direction, the membrane depolarized for cathodal pulses (and hyperpolarized for anodal pulses) at all distances from the electrode. The amplitude of the response decreased with distance from the electrode with an exponential decay constant of 343 +/- 110 microns for cathodal pulses and 253 +/- 91 microns for anodal pulses (n = 7). The results were qualitatively similar in both fiber directions when the atrium was bathed in a solution containing ionic channel blockers. A two-dimensional computer model was formulated for the case of highly anisotropic cardiac tissue and qualitatively accounts for nearly all the observed spatial and temporal behavior of vm in the two fiber directions. The relationships between vm and both the "activating function" and extracellular potential gradient are discussed.

Animals↗

PubMed1991

Spatial distribution of recurrent inhibitory synapses on spinal motoneurons in the cat.

1. Intracellular staining of Renshaw cells and alpha motoneurons was used to determine the spatial distribution of recurrent inhibitory synapses on spinal motoneurons in the cat. In each experiment, a Renshaw cell and one or more possible target motoneurons were labeled with horseradish peroxidase after physiological identification. 2. Paris of labeled neurons were reconstructed and measured at the light microscopic level. As defined by light microscopy, presumed synaptic contacts between nine Renshaw cells and 10 postsynaptic motoneurons were observed. On average, each Renshaw cell made three synaptic contacts (range 1-9) on each motoneuron. 3. Electron microscopic confirmation of several presumed contacts provided evidence that the appositions identified by light microscopic criteria are genuine contacts between Renshaw cell boutons and the labeled motoneuron. 4. All of the identified synapses observed in these experiments were located on motoneuron dendrites, between 65 and 706 microns from the soma. Use of a simplified cable model indicated that the synapses are electrotonically close to the soma, the average location being approximately 0.25 length constants from the soma (range 0.04-0.82 lambda). 5. These observations provide direct evidence to support the hypothesis that Renshaw cell synapses on motoneurons are located on the dendrites and not on the cell body (whereas reciprocal inhibitory synapses, from Ia inhibitory interneurons, are predominantly located on the soma). The functional significance of the observed distribution of Renshaw inhibitory synapses is discussed. One possibility is that the recurrent inhibitory pathway selectively inhibits particular dendritic inputs.

Animals↗

PubMed1998

Spatial distribution of yolk platelets and fat droplets in oocytes and cleaving embryos of the common frog (Rana temporaria) and toad (Bufo bufo).

Animal-vegetal gradients of fat droplets and yolk platelets have been quantitatively determined in mature oocytes and in cleaving embryos in two anuran species Rana temporaria and Bufo bufo using stereological methods. Volume densities Vv which describe properly the amount of nutrients in embryos have been used during the measurements. The embryos till the stage of late blastula are spherical: the spherical form is not distorted even by blastocoel forming eccentrically, in the animal hemisphere. Increased diameters during cleavage, which have been observed in the two species, can be ascribed to growth of the blastocoel and increased number of blastomeres while the quantity of the cytoplasm does not increase. The volume densities of yolk platelets and fat droplets per unit of cytoplasm volume remains constant throughout the cleavage. Volume densities change along the animal-vegetal axis in accordance with the course of the 3rd polynomial depending on the distance of the area under study from the vegetative pole f: y-->Vv, f = ay3 + by2 + cy + d. Parameters of fitting functions a, b, c and d change considerably during development of the embryo, which proves reorganisation of the cytoplasm during cleavage: the most significant changes occur from fertilisation to the four-cell stage and during growth of the blastocoel from morula to late blastula stage. Distortion of the axial symmetry of yolk platelet distribution in embryos occurring after fertilisation is not extensive in the two studied species. The mathematical model of spatial distribution of yolk platelets and fat droplets in oocytes and cleaving embryos in the studied anuran species was proposed using the above data.

Animals↗

PubMed1983

Quantitative spatial distributions of calcium, phosphorus, and sulfur in calcifying epiphysis by high resolution electron spectroscopic imaging.

Electron spectroscopic imaging, a new technique that permits the quantitative detection of the spatial distributions of atomic elements at high resolution, has been applied to the epiphyseal zone of hypertrophy in the mouse for the visualization of calcium, phosphorus, and sulfur. Longitudinally sectioned epiphyseal growth plates reveal a developmental sequence in the longitudinal septum leading from a noncalcified matrix to a calcified matrix. During the early stages of this transition, matrix granules containing highly localized concentrations of P (200-400 atoms/nm2) are found spatially separate from Ca-containing sites. These Ca localizations displayed a concentration range of 20-350 atoms/nm2 and a complete spatial overlap with sulfur. At these sites, S levels range from 10 to 200 atoms/nm2. At a later stage, and therefore more proximal to the zone of provisional calcification, the usual scattered, irregularly shaped mineral deposits are found. These sites contain a virtual superposition of Ca with both P and S. The Ca/P and Ca/S ratios of these mineral deposits are predominantly 1.0 with only minor, locally varying ratios present.

Animals↗

PubMed1982

Spatial distribution of [14C]-lidocaine and blood flow in transmural and lateral border zones of ischemic canine myocardium.

The purpose of this study was to determine the spatial distribution of lidocaine relative to blood flow in ischemic, normal and border zone canine myocardium. Ischemic zone tissue was distinguished from normal zone tissue by a special microsphere technique in adjacent sections 4 to 5 mm wide from the center to the lateral border of the ischemic region in 14 open chest dogs. Gamma-labeled microspheres were separated by a special technique from carbon-14 ([14C])-lidocaine in the same tissue sample. Blood flow (mean value +/- 1 standard deviation) was reduced to 46 +/- 25 percent of normal in the ischemic subepicardium and 17 +/- 18 percent of normal in the subendocardium. [14C]-lidocaine was 0.56 +/- 0.12 microgram/g in normal myocardium 10 minutes after bolus injection of [14C]-lidocaine; it was reduced to 91 +/- 15 percent of normal in ischemic subepicardium and 58 +/- 12 percent of normal in the subendocardium. Blood flow and lidocaine concentration were uniformly lowest in gross samples from the central and intermediate ischemic zones, and highest in the gross samples from the border normal zone (p less than 0.05). The values for flow and lidocaine in samples from the border ischemic zone were intermediate, that is, higher than values from central ischemic (p less than 0.05) and lower than values from border normal zone samples (p less than 0.05). However, the labeling technique for normal zone tissue revealed that the values of blood flow and lidocaine in the gross samples from the lateral border of the ischemic zone were intermediate between those of adjacent ischemic and normal samples because of the mixture of overlapping normal and ischemic tissues components--not because of a unique mildly ischemic region. Both blood flow and lidocaine concentration were lower in the subendocardial third than in the subepicardial third of the ischemic zone (p less than 0.05) even after the contribution of normal zone tissue was subtracted, suggesting a gradient of ischemia across the transmural border zone. In conclusion, lidocaine is distributed uniformly in ischemic components from the center to the lateral border of the ischemic zone, but there is an endocardial to epicardial gradient. Both lateral and transmural border zone distributions must be considered to understand the mechanisms of drug effects in myocardial ischemia.

Animals↗

PubMed2000

Changes in the kinetics of dopamine release and uptake have differential effects on the spatial distribution of extracellular dopamine concentration in rat striatum.

The objective of this study was to examine whether the limited diffusion distance of dopamine in rat striatum produces spatial heterogeneity in the extracellular dopamine concentration on a dimensional scale of a few micrometers. Such heterogeneity would be significant because it would imply that the concentration of dopamine at a given receptor depends on the receptor's ultrastructural location. Spatially resolved measurements of extracellular dopamine were performed in the striatum of chloral hydrate-anesthetized rats with carbon fiber microdisk electrodes. Dopamine was monitored during electrical stimulation of the nigrostriatal pathway before and after administration of drugs that selectively affect the kinetics of evoked dopamine release and dopamine uptake. The effects of nomifensine (20 mg/kg), L-DOPA (250 mg/kg), and alpha-methyl-p-tyrosine (250 mg/kg) on the amplitude of the stimulation responses were examined. The outcome of these experiments was compared with predictions derived from a mathematical model that combines diffusion with the kinetics of release and uptake. The results demonstrate that the extracellular dopamine concentration is spatially heterogeneous on a micrometer scale and that changing the kinetics of dopamine release and uptake has different effects on this spatial distribution. The impact of these results on brain neurochemistry is considered.

Animals↗

PubMed2000

Spatial distributions of expansion rate, cell division rate and cell size in maize leaves: a synthesis of the effects of soil water status, evaporative demand and temperature.

The spatial distributions of leaf expansion rate, cell division rate and cell size was examined under contrasting soil water conditions, evaporative demands and temperatures in a series of experiments carried out in either constant or naturally fluctuating conditions. They were examined in the epidermis and all leaf tissues. (1) Meristem temperature affected relative elongation rate by a constant ratio at all positions in the leaf. If expressed per unit thermal time, the distribution of relative expansion rate was independent of temperature and was similar in all experiments with low evaporative demand and no water deficit. This provides a reference distribution, characteristic of the studied genotype, to which any distribution in stressed plants can be compared. (2) Evaporative demand and soil water deficit affected independently the distribution of relative elongation rate and had near-additive effects. For a given stress, a nearly constant difference was observed, at all positions of the leaf, between the relative elongation rates of stressed plants and those of control plants. This caused a reduction in the length of the zone with tissue elongation. (3) Methods for calculating cell division rate in the epidermis and in all leaf tissues are proposed and discussed. In control plants, the zone with cell division was 30 mm and 60 mm long in the epidermis and in whole tissues, respectively. Both this length and relative division rate were reduced by soil water deficit. The size of epidermal and of mesophyll cells was nearly unaffected in the leaf zone with both cell division and tissue expansion, suggesting that water deficit affects tissue expansion rate and cell division rate to the same extent. Conversely, cell size of epidermis and mesophyll were reduced by water deficit in mature parts of the leaf.

Cell Division↗

PubMed2000

Spatial distribution of GC- and AT-rich DNA sequences within human chromosome territories.

Previous topological analyses of DNA sequence organization in the interphase chromosome mainly focused on the spatial distribution of individual gene copies within chromosome territories. In order to achieve a more comprehensive view into the subchromosomal arrangement of DNA, we isolated the GC-richest/gene-richest fraction (H3 isochores) as well as AT-richest/gene-poorest fraction of human genomic DNA (L1+L2 isochores) and visualized the respective DNA within individual chromosome territories by means of dual-color FISH. Application of confocal laser scanning microscopy and dedicated 3D image analysis software, which differentiated territory subvolumes by peeling shells one voxel in width, revealed a significant difference in the intraterritorial distribution of these two DNA sequence classes. While the H3 isochores were found localized in all subvolumes of the territories at similar frequency, simultaneously detected L1+L2 isochores were observed more to the interior of the same chromosome territories. Thus the GC-rich sequences display a much higher variability in their intraterritorial localization than AT-rich DNA fragments.

Chromosomes, Human↗

PubMed1995

Semi-automatic data acquisition for quantitative neuroanatomy. MicroTrace--computer programme for recording of the spatial distribution of neuronal populations.

We present a computer programme, MicroTrace, designed for user-guided digitisation of objects in biological sections. The programme is optimised for recording the spatial distribution of neuronal structures, such as large populations of tracer-labelled cell bodies or axonal plexuses, regional borders, and surfaces. System requirements are a PC running Microsoft Windows, a microscope equipped with stepping motors, and a drawing tube. A computer generated drawing area, surrounded by menus and icons, is projected into the microscope field of view via the drawing tube. Different 'object' icons are assigned to individual object categories (cell types, surfaces, etc.). Digitisation is performed by pointing the cursor at objects in the section. Computer graphical symbols are superimposed on the digitised objects. All object categories are digitised, before moving the stage to other fields of view by manipulating the joystick or scroll bars. Movement of the microscope stage is accompanied by a translation of the graphical image, so that continuous feedback on the progress of the digitisation is provided. MicroTrace can readily be adapted to the specific needs of the user. We show its use in different experimental neuroanatomical techniques. Two-dimensional images and three-dimensional reconstructions of neuronal distribution and surfaces are demonstrated.

Animals↗