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PubMed1985

The relative spatial distribution of CFU-S in the mouse spleen.

Mouse spleens were separated into white and red pulp fractions and into axial and marginal fractions for analysis of the relative concentration of hemopoietic stem cells (CFU-S) with respect to their spatial distribution in the spleen. Of the total splenic CFU-S population, 80% was in the red pulp fraction. The CFU-S concentration in this fraction was 11 times higher than in the white pulp fraction, which contained lymphoid follicles, periarteriolar sheaths, surrounding marginal zones, and occasional fragments of red pulp areas. Within the red pulp, CFU-S were spatially distributed with high concentrations in the subcapsular regions and decreasing frequency toward the median intersept of the spleen, where the CFU-S frequency was about one-fifth that found in the subcapsular area. The data suggest that marginal zones contain relatively more CFU-S than the follicles themselves.

Animals↗

PubMed1985

Spatial distribution of retinol-binding protein and retinyl palmitate hydrolase activity in normal and vitamin A-deficient rat liver.

A study was conducted to explore the spatial distribution within rat liver of two proteins importantly involved in retinoid metabolism in liver, namely, retinol-binding protein (RBP) and the enzyme retinyl palmitate hydrolase (RPH). The study was conducted with both vitamin A-sufficient (control) and vitamin A-deficient rats. Livers were carefully and reproducibly dissected into 11 sections each, and RBP levels and RPH activities were measured for each section homogenate. Both RBP and RPH activity displayed highly significant spatial heterogeneity in their distributions in liver. For control rats, the mean level of RBP was 39.0 micrograms/g wet weight, with a section-to-section variation of 14.5. For deficient rats, the corresponding RBP mean and variation values were 283 and 56 micrograms/g wet weight. For RPH, the mean level was 136 pmol free fatty acids (FFA) formed/(min X mg) with a section-to-section variation of 178. Both inspection of the data and analysis of variance indicated that this significant section-to-section variation (spatial heterogeneity) did not follow a consistent anatomic pattern from rat to rat. Thus, no one specific anatomic location in the liver was consistently high or low with regard to either RBP or RPH. Since the spatial distributions of both RBP and RPH activity did not follow a consistent anatomic pattern, it is not possible to obtain an accurate measure of the total liver levels for either parameter in a homogenate made from a small section. Finally, the patterns of distribution of RBP and RPH activity observed in the liver sections from both vitamin A-sufficient and deficient rats were not significantly correlated, either directly or inversely, as determined by chi-square analysis. Thus, RBP and RPH activity levels vary independently of each other in their heterogeneous anatomic distributions in rat liver.

Animals↗

PubMed1990

Spatial distribution of modalities and receptive fields in sensorimotor cortex of awake cats.

A sample of 504 single neurons isolated in three curvilinear arrays of 10 closely spaced tracks in primary somatosensory and in pericruciate sensorimotor cortex was studied in two awake, restrained domestic cats. Modality sensitivity and receptive field size and location were assessed for each neuron, along with response adaptation rate and state of arousal at the time of recording. Reconstruction of the spatial distribution of these response properties failed to show any simple organization, beyond general somatotopy. The spatial distribution of modality sensitivities was quantitatively tested in relation to a strict columnar model and to a random model; the data could not be clearly distinguished from the random model, in any of the three recording arrays. Observations made on two or more neurons isolated simultaneously at the same recording site revealed that few shared both modality and receptive field (RF) in common. Among the simultaneously recorded neurons, five-ninths showed disparate modality sensitivities and two-thirds showed limited or no RF overlap. Many pairs of neurons showing the same modality sensitivity showed limited or no RF overlap, and many pairs showing partial or complete RF overlap showed disparate modality sensitivities. Hence, the data failed to support any model of cerebral organization that features local, bounded regions within which all neuron response properties are the same and, in particular, the model of columnar organization. On the other hand, models that feature intermingled local clusters of neurons (a cluster consists of neurons that share the same response properties) are not excluded by the data.

Adaptation, Physiological↗

PubMed1988

Spatial distribution of trabeculae in iliac bone from 145 osteoporotic females.

145 women showing clinical and radiological signs of involutional osteoporosis of the spine were biopsed at the ilium for histomorphometric analysis of bone mass including trabecular bone volume and parameters reflecting the spatial distribution of bony elements (mean trabecular plate thickness, density and separation). Results were compared with an age-matched population of 22 healthy females. Postmenopausal osteoporotics (i.e. younger than 75 years) were characterized by a significant reduction in trabecular bone volume, plate density and thickness, while senile osteoporotics (i.e. older than 75 years) did not exhibit any difference with controls. 51% of the osteoporotic patients had a trabecular bone volume higher than the spontaneous vertebral crush threshold defined by Meunier. Osteoporotic patients with trabecular bone volume under the vertebral crush threshold had a significant decrease in all trabecular parameters. On the opposite, patients with trabecular bone volume above the vertebral crush threshold had only a significant decrease in the number of trabeculae. A negative correlation was found between age and plate density in both osteoporotic patients and controls. A linear correlation was found between trabecular bone volume and plate density, but thickness and density of trabecular plates were not correlated. This study confirms that involutional osteoporosis is not only a decreased bone mass disorder. A modified spatial distribution of trabeculae or a mechanically less resistant bone matrix could be additional factors.

Aged↗

PubMed1991

Spatial distribution of fiber degeneration in acute hypoglycemic neuropathy in rat.

Hypoglycemia may cause axonal nerve fiber degeneration, but to do so it must be severe (less than 1.5 mmol/L) and of long duration (greater than or equal to 12 hours). Since in our previous study, systemic PO2, PCO2, pH, blood pressure, temperature, and hematocrit were maintained within physiologic limits, fiber degeneration cannot be attributed to systemic hypoxia. In this study the spatial distribution of axonal degeneration was assessed in transverse epoxy sections and teased fibers from different proximal-to-distal levels of nerves of the lower limb of the rats. Reactions in lumbar spinal motor neurons, spinal ganglia, and fasciculus gracilis were also studied. Axonal degeneration was the characteristic fiber alteration and it predominated in central fascicular distributions of distal sciatic, proximal tibial, and proximal peroneal nerves. This proximal-to-distal and central fascicular spatial distribution is not typical of distal polyneuropathy or of neuronal degeneration, but it is characteristic of a focal or multifocal nerve trunk neuropathy. Although local hypoxic-ischemic injury, possibly mediated by enhanced sympathetic tone, has not been excluded, we postulate a generalized deficiency of energy substrate manifesting itself by fiber degeneration at watershed zones of poorest perfusion.

Animals↗

PubMed1991

The male-derived genome after sperm-egg fusion: spatial distribution of chromosomal DNA and paternal-maternal genomic association.

After fusion with an egg, the haploid genome of a mammalian sperm expands from a volume of a few cubic microns to a volume of several thousand cubic microns in a fully developed zygote pronucleus. Using fluorescent in situ hybridization we studied two aspects of the chromatin organization of the sperm-derived genome during this process in a model system involving fusion of human sperm with hamster eggs. We found that (a) from the beginning of sperm head decondensation to early pronuclear stages, the hybridization signal of a probe targeted to the satellite III heterochromatin of chromosome 1 appeared as an irregularly shaped domain. In fully developed pronuclei, the signal became a fiber as much as 20-fold more extended compared with interphase somatic nuclei. The signal appeared as a string of non-uniformly distributed "beads" with interspersed gaps. A similar spatial distribution and appearance recurred after the first cleavage division. (b) Male- and female-derived genomes assembled non-randomly on the first mitotic spindle, and continued to be sequestered from each other in the nuclei of two-cell stages.

Animals↗

PubMed1990

The spatial distribution of excitatory and inhibitory inputs to ganglion cell dendrites in the tiger salamander retina.

In response to focal stimuli, ganglion cell dendrites receive excitation over a relatively narrow extent of the inner plexiform layer (IPL). This excitation is embedded in 2 wider lateral inhibitory regions. Here we estimate the lateral dimensions of the inhibitory regions. Ganglion cells were whole-cell patch-clamped and dendrites were identified and located in retinal slices using Lucifer yellow in the pipettes. The spatial distribution of ganglion cell dendritic sensitivity was measured with puffs of transmitter substances applied at different distances along the dendrites. All ganglion cell dendrites were sensitive to glutamate, GABA, and glycine across their full extent. The responses to puffs decreased with lateral distance from the soma and were well fit by Gaussians. The responses to puffs of potassium showed a similar decrement with distance. Since potassium channels are probably uniformly distributed along the dendrites, the similarity in profiles suggests that receptor density is also uniform along the dendrites. The spatial distribution of responses of ganglion cells to excitatory and inhibitory synaptic inputs was measured by depolarizing local populations of bipolar terminals (and subsequently local populations of amacrine cells) with transretinal current (TRC). TRC-stimulating electrodes were displaced laterally, with respect to the ganglion cell soma, to generate response profiles. We estimated the dimensions of the inhibitory and excitatory signals received by the ganglion cells by removing the contributions of their dendrites, the stimulus, and other interneurons from the response profiles. The excitatory signal extended less than 100 microns, the approximate dimensions of the ganglion cell dendrites, and corresponds roughly to the width of the bipolar inputs. The GABAergic signal extended, on average, 253 microns and glycinergic signal extended, on average, 315 microns. These inhibitory signal dimensions correspond to the width of classes of amacrine cell processes measured in other studies.

Animals↗

PubMed1987

The spatial distribution of neurons and glia in human cortex based on the poisson distribution.

A method was devised that employs deviations from the Poisson distribution to analyze the spatial arrangement of neurons and glia in human cerebral cortex. A field of randomly distributed points equal in number of a sample field of neuronal or glial cells is generated by computer, and the proportion of cells in the sample field that are closer to the nearest neighboring cells than to the nearest randomly distributed point is determined. We call this proportion the "Poisson ratio." When the cells are randomly distributed, the Poisson ratio is equal to 0.5. If the Poisson ratio is less than 0.5, the cells are farther away from one another than a random distribution would predict (exclusionary pattern); if the Poisson ratio is greater than 0.5, the cells are closer to one another than a random distribution would predict (clustering). A simple nonparametric statistical test is used to determine the significance of differences in the ratios. This method was applied to samples of human cerebral cortex in order to test the hypothesis that patients with schizophrenic psychosis may have an altered pattern of neuronal clustering. The analysis revealed that there is no difference in the nearest-neighbor distribution of either neurons or glia between psychotic patients and controls. It was found, however, that there is a highly significant difference in the spatial distribution of neurons versus glia in human cerebral cortex. Neurons of layers II to VI in the human cortex show greater-than-expected distances among them and are distributed according to an exclusionary pattern, while neurons in layer I show a clustering pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Cortex↗

PubMed1989

Spatial distribution of exercise-induced ST-segment depression and U-wave inversion in identifying the ischemic site in patients with coronary artery disease.

Eighty-seven unipolar electrocardiograms were simultaneously recorded before and after symptom-limited treadmill exercise in 75 patients with coronary artery narrowing (greater than equal to 70%) and without previous myocardial infarction. Body surface distributions of ST segment depression were divided into 3 types; upper, lower, and diffuse types. Body surface distributions of U-wave inversion were divided into 2 types; upper, and lower types. These distribution patterns were compared with the location of ischemia determined by T1-201 exercise myocardial perfusion imaging. For ST-segment depression, a considerable number of patients had diffuse-type ST depression, whether the site of ischemia was anterior (22/32, 69%), inferior (18/27, 67%) or both (5/5, 100%). However, upper-type ST depression was associated with anterior ischemia, and lower-type ST depression, with inferior ischemia. The sensitivity and specificity of the spatial distribution of ST depression in identifying the myocardial ischemic site were 27% and 95% for anterior ischemia. The sensitivity and specificity of the spatial distribution of St depression in identifying the myocardial ischemic site were 27% and 95% for anterior ischemia respectively, and 28% and 88% for inferior ischemia, respectively. The incidence of U-wave inversion was moderate (29/75, 39%), but the distribution pattern was specific for the site of ischemia; upper-type U inversion associated with anterior ischemia, and lower type with inferior ischemia. The sensitivity and specificity were 59% and 100% for anterior ischemia respectively, and 22% and 100% for inferior ischemia respectively. By a combination of ST-depression and U-inversion, the sensitivity and specificity were 78% and 95% for anterior ischemia, and 44% and 88% for inferior ischemia. Body surface electrocardiographic mapping provided important information in the non-invasive diagnosis of the site of myocardial ischemia.

Adult↗

PubMed1975

Pattern of spatial distribution in Drosophila melanogaster.

The effect of temperature and sex on spatial distribution of Drosophila melanogaster adults was studied in a specially designed apparatus. It was observed that individuals tend to aggregate in sections of the sphere independently of sex and temperature. Nevertheless, decrease in temperature increase aggregation. The mobility of both males and females indicates a negative geotactic tendency.

Animals↗

PubMed1990

Spatial distribution of muscle fibers within the territory of a motor unit.

The spatial distribution of muscle fibers belonging to a motor unit was studied in the soleus (SOL) and tibialis anterior (TA) of adult cats to provide a detailed description of the spatial patterns which exist within the territory of a motor unit. Glycogen depletion of the motor unit was achieved through repetitive stimulation of either the intracellularly identified motoneuron or the functionally isolated motor axon. Muscle fibers belonging to the stimulated unit were identified in serial cross-sections, and in the cross-section which contained the most depleted fibers the centroid of each depleted fiber was determined. Subsequently, three spatial analyses, ie, a quadrat analysis, a point-to nearest neighbor analysis and an interfiber distance analysis, were used to determine if motor unit fibers were distributed randomly throughout the territory of the unit. Motor unit fibers tended to be localized within the muscle cross-section and were not evenly or homogeneously distributed throughout the territory. In general, the analyses suggested that motor unit fibers may be arranged in clusters or subgroups of varying size. The data demonstrate three different quantitative analyses for studying the organization of muscle fibers of normal motor units, which can be used for objective assessment and diagnosis of neuromuscular diseases.

Animals↗

PubMed1990

Spatial distribution of intracellular, free Ca2+ in isolated rat parotid acini.

The spatial distribution of intracellular, free Ca2+ ([Ca2+]i) in rat parotid acini was measured by imaging fura-2 fluorescence from individual acinar cells by means of a digital imaging microscope. Upon cholinergic stimulation in a Krebs-Ringer bicarbonate buffer at (37 degrees C), [Ca2+]i increased synchronously at both the basolateral and luminal membranes as well as in all cells of the secretory endpiece, reaching peak [Ca2+]i levels 1 s after stimulation. Atropine addition caused a rapid down-regulation of [Ca2+]i, which, however, never reached prestimulatory levels. When acini were stimulated in a medium containing 5 nM Ca2+, the Ca2+ mobilization arising from internal pools caused an increase in [Ca2+]i predominantly near the basolateral area, where the endoplasmic reticulum is located, and standing Ca2+ gradients were observed for up to 10 s. A mathematical model is developed to simulate the time courses of the Ca2+ profiles through the cytoplasm using estimated values of the Ca2+ diffusion coefficients and the cytosolic Ca2+ buffering capacity. It is concluded that under physiological conditions, the Ca2+ release from the endoplasmic reticulum is responsible for the activation of the basolaterally located K+ channels. Furthermore, Ca2+ influx from the interstitium is responsible for much of the rise in [Ca2+]i near the luminal membranes, where the Cl- channels are supposed to be located.

Animals↗

PubMedDate not supplied

Comparison of electrophysiological and histochemical methods for assessing the spatial distribution of muscle fibres of a motor unit within muscle.

The spatial distribution of muscle fibres of a motor unit has been examined in patients with a variety of neuromuscular disorders using the fibre density (FD) technique of single fibre EMG and the enclosed fibre count (EFC) method, and the results of the two approaches compared. Agreement between the findings occurred in 64% of cases; an increase in both parameters was seen only in neurogenic conditions. FD was found to be more sensitive to minor disturbances of motor unit architecture as seen in myopathies and mild neurogenic states, and this factor together with sampling differences accounted for most of the discrepancies between the two methods. The finding of normal FD and EFC values in the presence of fibre type disproportion helped to exclude reinnervation as the cause by confirming the predominantly diffuse distribution of muscle fibres.

Adenosine Triphosphatases↗

PubMed1978

Spatial distribution of pulmonary blood flow in dogs in increased force environments.

Spatial distribution of pulmonary blood flow (SDPBF) during 2- to 3-min exposures to 6-8 Gy acceleration was studied, using radioactive microspheres in dogs, and compared to previously reported 1 Gy control distributions. Isotope distributions were measured by scintiscanning individual 1-cm-thick cross sections of excised, fixed lungs. Results indicate: 1) the fraction of cardiac output traversing left and right lungs did not change systematically with the duration and magnitude of acceleration; but 2) the fraction is strongly affected by the occurrence or absence of fast deep breaths, which cause an increase or decrease, respectively, in blood flow through the dependent lung; and 3) Gy acceleration caused a significant increase in relative pulmonary vascular resistance (PVR) in nondependent and dependent regions of the lung concurrent with a decrease in PVR in the midsagittal region of the thorax. Result 3 may be mediated primarily by changes in regional alveolar volume and geometry in the nondependent hemithorax conbined with hydrostatic effects of extravascular fluid and active hypoxic response in the dependent region and is superimposed on, and may override, hydrostatic effects of perfusion pressures on SDPBF during acceleration.

Adaptation, Physiological↗

PubMed1990

Components of field potentials evoked by white matter stimulation in isolated slices of primary visual cortex: spatial distributions and synaptic order.

1. We have recorded profiles of the spatial distributions of extracellular field potentials in transverse slices of rat primary visual cortex. Responses were evoked by electrical stimulation near the white matter/layer VI border and sampled from layers I to V along the radial axis orthogonal to the laminae and intersecting the stimulation site ("on-beam" recording). To assess the activity of "horizontal" connections, we also recorded profiles along axes parallel to the cortical lamination ("off-beam" recording), usually in layer III. Overall, our goal was to extend understanding of the physiology and organization of neocortical circuitry and to provide a basis for comparisons of data from different experiments and experimenters when neocortical field potentials are used in studies of plasticity and pharmacology. 2. Responses were highly specific with respect to the cortical layers. We distinguish four major components: two kinds of population spike ("S1" and "S2") and two slower waveforms ("W1" and "W2"). The latter appear to represent flow of current in apical dendrites of the supragranular layers. Component W1, the earliest slow component, is a synaptically driven field potential dipole that is positive in layer I and negative in layer II. Based on estimates of current source densities (CSDs), we attribute this to entry of depolarizing current into dendrites and/or cell somata in layer II, ascending intradendritic current, and passive depolarization of inactive dendritic membrane in layer I. Component W1 rises during the 20 ms after stimulation and falls during the 50-100 ms thereafter. Component W2 is also positive in layer I but maximally negative in layer III. It rises for approximately 100 ms after stimulation and decays during the following 400-800 ms. 3. Component S1 does not depend on synaptic transmission because it persists during the application of glutamate receptor antagonists or medium that is low in Ca2+. This component is largest in layer III, radial to the site of stimulation. There, it is a negative deflection, typically 1-2 mV in amplitude and lasting roughly 2 ms, with a latency to peak between 2 and 4.5 ms. Component S1 is most likely a population spike due to synchronized firing of cell somata activated antidromically via unmyelinated efferent axons. 4. Component S2 is a short (less than 20 ms) burst of population spikes specifically in layer III. Individual S2 spikes closely resemble S1 spikes, and we propose that the same neuronal population generates both. However, S2 spikes require glutamatergic synaptic transmission.(ABSTRACT TRUNCATED AT 400 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1990

Spatial distribution and temporal changes of pulmonary thallium uptake in myocardial perfusion studies.

Spatial distribution and temporal changes in pulmonary thallium uptake were assessed in 24 normal subjects and 35 patients with coronary artery disease (CAD). In studies carried out directly after stress and 3 h later, pulmonary Tl uptake was assessed as body surface area corrected absolute pulmonary uptake in the upper, middle and lower right lung regions, and in the total right lung and upper left lung. Pulmonary/myocardial (PM) uptake ratios for these 5 regions were calculated as mean pulmonary/mean background-corrected myocardial uptake. Additionally, wash-out was assessed for each region and for the myocardium. In normal subjects, the initial pulmonary Tl uptake, the PM ratios and Tl wash-out were greater in the lower lung regions than in the upper. In the late studies, no significant differences in Tl content or PM ratios were found among the regions. In patients with CAD, initial pulmonary Tl uptake and PM ratios were greater in the lower than in the upper regions, and higher than for the normal subjects in all pulmonary regions (P less than 0.001). Tl wash-out was significantly higher in the low and middle regions versus the upper region (P less than 0.001) and higher in all regions than in normal subjects (P less than 0.001). In the late studies no significant differences in Tl content or PM ratios were found between any pulmonary regions. Pulmonary Tl content was, in all regions, higher in CAD than in normal subjects (P less than 0.01), as were the PM ratios (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗

PubMed1992

[Spatial distribution of the action potentials of the sural nerve].

We investigated the spatial distribution of the sural nerve sensory nerve action potential (SNAP) in 25 healthy subjects between 21 and 50 years. Stimulation was achieved through surface electrodes at the lateral malleolus. Recordings were made 15-18 cm proximal to the site of the stimulation from different positions on a line perpendicular to the sural nerve using needle electrodes insulated except for the tip. The amplitude of the SNAP decreased on both sides of the potential of highest amplitude. 10 mm lateral to the potential of highest amplitude the mean amplitude was reduced to 55%. The latency of the first positive phase decreased within increasing distance from the largest SNAP. We explained this with different influence of more distal, earlier depolarized nerve segments on the locally generated SNAP. In 20 subjects we performed an additional recording using an uninsulated needle electrode that was placed 3-4 cm subcutaneously perpendicular to the sural nerve. The latency of the SNAP recorded in this way was similar to the latency of the largest SNAP using the insulated needle electrode; however, the amplitude was smaller by 19%. We recommend for clinical practice to use the uninsulated needle in case the SNAP is smaller than 4 microV.

Action Potentials↗

PubMed1991

Spatial distributions of inelastic events produced by electrons in gaseous and liquid water.

The spatial distributions of ionizations and other inelastic events in charged-particle tracks are important quantities that influence the final outcome of radiation interaction. Calculations of such distributions are presented for the tracks of electrons in the energy range 100 eV to 10 keV in liquid water and water vapor, and the results are compared. The distributions include the frequency of nearest-neighbor distances for all inelastic events, the mean nearest-neighbor distances for ionizations and for all inelastic events as a function of electron energy, the frequency of distances between all ionizations and all inelastic events, and the farthest distances between all inelastic events in electron tracks. The physical differences between liquid water and water vapor are discussed in terms of the respective inverse mean free paths, the collision spectra, and the nonlocalization of energy losses that are likely to occur in the liquid.

Electrons↗