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At least 73 records · Page 4Linked to original sources

PubMed1985

Spatial distribution of capillaries in rat nerves: correlation to ischemic damage.

Computerized imaging was used to assess the spatial distribution of capillaries (number, density, and intercapillary distance) in normal rat sciatic nerve and its branches, to be able to make inferences about their distribution to central fascicular degeneration typical of ischemic nerve injury. Capillary density was significantly less in the central regions of fascicles than in outer contour areas in sciatic and proximal tibial nerves, the difference being greater in large fascicles. The mean of the minimum intercapillary distance was significantly greater in the central fascicular region of fascicles of the sciatic but not of the tibial and peroneal nerves. These anatomic characteristics may be a factor in ischemic-induced central fascicular degeneration. A decrease in the number of capillaries in a region might lead to impaired oxygen diffusion when blood flow to the region is compromised.

Animals↗

PubMed1990

Detection of the spatial distribution of late potentials by body surface mapping using forty-five unipolar, leads.

For evaluating the spatial location of late potentials (LPs), the authors designed a new system for the body surface mapping of signal-averaged, filtered ECGs using forty-five thoracic unipolar leads (5 x 9 array). The signals from patients with old myocardial infarction (MI, N = 7) and arrhythmogenic right ventricular dysplasia (ARVD, N = 1) were amplified and passed through a bandpass (100-300 Hz) filter. The departure maps, LP isopotential maps, and LP30 area maps were generated and superimposed. The LP30 duration was determined as the section between the filtered QRS endpoints and points thirty milliseconds (ms) before. Isopotential maps of the LPs showed distinct positive and negative regions. In 7 cases with MI, the extreme was related to the zones indicated by the departure maps, and the LP30 area maps also corresponded to the departure areas. In 1 case of ARVD, endocardial fragmented activity directly recorded at the right ventricle closely corresponded with the region on the LP30 area map. In conclusion, body surface LP isopotential maps and LP30 area maps may provide useful information concerning the spatial distribution of endocardial fragmentation.

Arrhythmias, Cardiac↗

PubMed1986

Temporal and spatial distribution of intracellular potentials during generation and spread of epileptogenic discharges.

This chapter addresses the characteristics and spatial distribution of intracellular potentials, the spread of paroxysmal depolarization shifts (PDSs) through the cortex, the extracellular field potentials in three dimensions, and the concentrations of penicillin in direct contact with elements in the epileptogenic focus. Data are presented that show that there are several types or gradations of PDS intensities within each focus; PDS types are distributed in groups related to their distance from the center of the focus and to the concentration of the epileptogenic drug; the morphology and repetition rate of electroencephalogram (EEG) spikes are related to features of the intracellular potentials; a mathematical model can estimate the distribution of concentrations of penicillin within the focus over long periods; no barriers impede diffusion of penicillin either at the cortical surface or at the boundary between gray and white matter; the potential field of the EEG spike is defined in three dimensions; and PDSs spread through the focus at the rate of 0.25 m/sec.

Action Potentials↗

PubMed1982

Spatial distribution and timing of transmitted and reflexly generated urethral pressures in healthy women.

We localized the temporal and spatial distribution of pressures in the urethra to identify their contribution to continence. With the data obtained we resolved the timing between the passively transmitted and actively generated urethral pressures. Data were obtained from 11 healthy female volunteers, with a mean age of 22 years. Simultaneous measurements of bladder and urethral pressures were taken from subjects during the Valsalva maneuver and coughing, and then holding with the subject in the supine, standing and sitting positions. The ratio of urethral to bladder pressure increase and the latency between these pressure increases were analyzed. A biphasic pressure distribution results from coughing with subjects in all positions. The first phase occurs at the normalized distance of 10 to 15 per cent from the bladder neck, where the ratio of urethral to bladder pressure increase is 0.8. The second phase occurs at 60 to 70 per cent of the urethral length and has a 1.5 to 1.7 ratio of urethral to bladder pressure increase, indicating the presence of pressure magnification. Simultaneous latency measurements indicate that the pressure increase in the urethra precedes that of the bladder by 240 plus or minus 30 msec. in the region that exhibits maximum pressure magnification. These results indicate that a fast-acting contraction occurs in the distal third of the urethra, which contributes reflexly to the compressive forces of the proximal urethra, thereby preventing urine loss during stress.

Adolescent↗

PubMed1992

Spatial distribution of tumor-specific monoclonal antibodies in human melanoma xenografts.

The time-dependent (1-72-h) spatial distribution of three biotinylated anti-melanoma monoclonal antibodies (MAbs), a control MAb, and several macromolecular tracers was studied in two small (4-12-mg), well-characterized human melanoma xenografts (SK-MEL-2, M21) growing in the s.c. space of athymic nude mice. The specific MAbs (436, IND1, and 9.2.27) recognize two different melanoma cell surface antigens (Mr 125,000 glycoprotein melanoma-associated antigen and high molecular weight melanoma-associated antigen) and have equilibrium association constants differing by two orders of magnitude (10(8)-10(10) M-1). SK-MEL-2 tumors were poorly vascularized and were composed of one or several collections of tumor cells with few intratumor blood vessels. In contrast, M21 tumors induced a strong angiogenic response and were organized into multiple small tumor cell nests separated from each other by fine blood vessels. Neither tumor developed extensive connective tissue stroma. In both tumors, hyperpermeable blood vessels were concentrated at the tumor-host interface but some intratumor vessels in M21 tumors were also leaky. Macromolecular tracers extravasated extensively from leaky vessels into tumor stroma but penetrated poorly into tumor parenchyma. All three tumor-specific MAbs stained tumor cell surfaces in a time-dependent fashion such that one-half or more of all tumor cells were stained by 24-48 h. Tumor cell staining was favored by increased density of tumor cell antigens but, at the doses studied, was little affected by differences in affinity among tumor-specific antibodies. The distribution of MAb staining was nonuniform in two respects: (a) peripherally situated tumor cells were more likely to be stained than centrally placed cells, and only in the smallest tumors did MAb reach centrally placed tumor cells; and (b) staining was nonuniform in different parts of the same tumor. The inhomogeneity of tumor cell staining by tumor-specific MAb was attributable to several factors, including: tumor blood vessel number, distribution, perfusion and permeability; distribution of tumor connective tissue stroma; small volume of the parenchymal interstitial space and relatively impaired diffusion of macromolecules in that space (low effective diffusivity of MAb); and interactions between specific MAbs and tumor cells. Of these factors, those associated with the parenchymal compartment apparently were rate limiting, and strategies that enhance parenchymal penetration are likely to improve solid tumor therapy with MAbs.

Animals↗

PubMed1985

[Spatial distribution of light intensity with a phototherapy halogen lamp].

The spatial energy distribution under a phototherapy unit fitted with a special halide lamp (ex. Hereaus, "Photo-Therapie 800") is particularly uneven, with a pronounced decrease in energy towards the edges. With a correct positioning of the child in the centre of the luminous cone however, the energy of the effective light is still distinctly higher than that received from a phototherapy unit fitted with 6 blue fluorescent tubes (Philips 20W/52 BAM blue). With the addition of lateral aluminium reflectors, not only is the effective energy intensity increased, but also the spatial energy distribution becomes more even, so that a very exact positioning of the child is no longer required.

Bilirubin↗

PubMed1988

Fertilization alters the spatial distribution and the density of voltage-dependent sodium current in the egg of the ascidian Boltenia villosa.

The spatial distribution of voltage-dependent ionic currents was characterized in Boltenia villosa eggs before and after fertilization using two-microelectrode voltage clamp of paired animal-vegetal halves of eggs (merogones) made surgically. Major voltage-dependent conductances in the Boltenia egg are a transient inward Na current, a transient inward Ca current, and an inwardly rectifying K current. These currents were randomly distributed along the animal-vegetal axis in the unfertilized egg. When paired merogones (surgically prepared egg fragments) were made at the vegetal cap stage, 15-30 min after fertilization, Ca and K currents remained randomly distributed along the animal-vegetal axis. In contrast, the relative Na current density was found to be twofold lower in the vegetal vs the animal merogones made at the vegetal cap stage. By making pairs of merogones from unfertilized eggs and subsequently fertilizing one merogone of a pair, we showed that this change in current density ratio was due to a loss of absolute Na current density in the vegetal hemisphere shortly after fertilization. These results also show that this loss was intrinsic to the vegetal hemisphere, rather than being determined solely by the point of sperm entry. A second decrease in Na current was observed during the hour before first cleavage, 60-120 min after fertilization (M.L. Block and W.J. Moody, 1987, J. Physiol. 393, 619-634), both in fertilized eggs and in animal merogones fertilized after isolation. This second loss of Na current was not observed in vegetal merogones fertilized after isolation or in either animal or vegetal merogones made from fertilized eggs at the vegetal cap stage. Possible mechanisms for te rapid (complete by 40 min after fertilization) and the late (occurring from ca. 60 to 120 minutes after fertilization) Na current losses are discussed.

Action Potentials↗

PubMed1979

Origin and spatial distribution of maternal messenger RNA during oogenesis of an insect, Oncopeltus fasciatus.

In order to investigate the origin and spatial distribution of maternal mRNA during oogenesis, in situ hybridization with [3H]-poly(U) was utilized for the detection of poly(A)-containing RNA [poly(A)+RNA] in histological sections of Oncopeltus fasciatus ovaries. In the germarium poly(A)+RNA was found to accumulate in the trophocyte cytoplasm concomitant with the maturation of these cells. Poly(A)+RNA was also detected in the trophic cores and nutritive tubes suggesting that these channels participate in the transport of trophocyte-derived mRNA to the oocytes. Although large amounts of poly(A)+RNA were also detected in the cytoplasm of the follicle cells, particularly during late vitellogenesis when pseudopod-like processes projected into the ooplasm, no evidence was obtained for the transport of poly(A)+RNA from these processes to the oocytes. The content of poly(A)+RNA in the oocyte cytoplasm continually increased during oogenesis. In stage 2--4 oocytes poly(A)+RNA accumulation occurred in the apparent absence of transcriptional activity in the germinal vesicle nuclei suggesting that most maternal mRNA molecules synthesized during early oogenesis are of trophocyte origin. Poly(A)+RNA also continued to accumulate after chorion formation, when the nutritive tubes are longer active in RNA transport. This implies that other sources of maternal mRNA may exist during late oogenesis. The distribution of poly(A)+RNA molecules in the oocyte cytoplasm appeared to be uniform throughout oogenesis with one exception. During late vitellogenesis poly(A)+RNA activity was significantly enhanced in the anterior and posterior periplasmic cytoplasms relative to the lateral periplasm and the endoplasm. After chorion formation these variations disappeared. The results suggest that maternal mRNA molecules arise from at least 2 sources during oogenesis. During late vitellogenesis these molecules appear to be subject to differential localization in the polar perimeters of the oocyte cytoplasm.

Animals↗

PubMed1990

Spatial distribution of the capacity to initiate a secondary embryo in the 32-cell embryo of Xenopus laevis.

To examine the spatial distribution of dorsal determinants in the early embryos of Xenopus laevis, individual cells from the 32-cell embryo were transplanted into the same tier of the ventral side of a synchronous recipient. Their abilities to initiate a secondary embryo were measured by the incidence of secondary embryos and by the length of the secondary axis relative to the primary embryo. The ability was found to be localized in all cells (A1, B1, C1, and D1) of the dorsal most column and in the vegetal cells (C2 and D2) of the dorsolateral column. Transplanted C1 (subequatorial) cells caused the highest incidence of a secondary embryo and the average relative length of the secondary embryo was also greatest. Effectiveness decreased in the order: D1, B1, D2, C2, and A1. When these results were compared with Dale and Slack's fate map of the 32-cell embryo, it was concluded that the distribution of dorsal determinants is unique and does not coincide with the prospective regions for any tissues, though it is somewhat similar to the prospective region of dorsal endoderm or notochord. From these results it seems that dorsal determinants do not determine a particular tissue in an embryo but rather the "dorsal" region of an embryo.

Animals↗

PubMed1989

The molluscicidal properties of Ambrosia maritima L. (Compositae). 4. Temporal and spatial distribution of Biomphalaria alexandrina in Egyptian village irrigation systems with reference to schistosomiasis transmission control.

Data on the temporal and spatial distribution of Biomphalaria alexandrina were collected throughout one year in two village irrigation systems near Alexandria, Egypt. Snails bearing Schistosoma mansoni cercariae were found from May to December but about 80% of annual transmission potential was confined from June to August. Although snail infection rates were generally 0-2%, higher rates were recorded and tended to be associated with smaller number snail collections. Infected snails were found in most canal and drain types and were judged to be present across most of the irrigated area of each village. In view of the dispersed nature of both infected snails and human-water contact in the area, it is suggested that schistosomiasis transmission is more widespread than focal. Effective transmission control using molluscicides should therefore require application to all village irrigation water-courses. The difficulties these various findings might impose on the use of commercial molluscicides are discussed and some possible advantages of the alternative plant molluscicide, Ambrosia maritima are noted.

Animals↗

PubMed1990

The spatial distribution of attention during covert visual orienting.

Many studies of covert orienting of visual attention in response to informative pre-cues have focused on the spatial distribution of improved or impaired performance. One can find at least four different models in the literature, each describing a different distribution: the fixed gradient spotlight; the zoom lens spotlight; the hemifield activation hypothesis; and the flexible allocation of resources model. In previous work examining procedural details that might have led to the formulation of the hemifield activation hypothesis, it was postulated (Klein and McCormick 1989) that under conditions of uncertainty about which of two locations to attend, an observer may focus attention on a visual channel (i.e., midlocation placement of a fixed gradient spotlight) that is spatially intermediate. The present experiment was designed to distinguish among the four models of attentional distribution, and to test the midlocation placement strategy. Our findings show support for midlocation placement, demonstrate evidence against flexible allocation and hemifield activation, but could not differentiate between fixed gradient and zoom lens variants of the spotlight model.

Attention↗

PubMed1987

Spatial distribution of disease: three case studies.

Maps transformed so as to have constant density of residential population were used to analyze the spatial distribution of disease in three specific areas. Each area had received recent attention because of suspected environmental pollution. The area adjacent to the Rocky Flats Facility (CO) was examined to identify any association between possible plutonium releases and increases in lung cancer or leukemia incidence. The industrial area of northern Contra Costa County (CA) was studied to explore a relationship between petrochemical industrial emissions and histologic-specific lung cancers. Finally, a suspected increase in the risk of congenital cardiac defects possibly related to pollution of the Santa Clara County (CA) water supply was investigated. No evidence of elevated risk of disease was found to be associated with either the Rocky Flats Facility or the polluted water of Santa Clara County. An increase in lung cancer, found by other investigators in earlier years, was shown to persist in association with industrial emissions in Contra Costa County.

Adult↗

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↗

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↗

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↗

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↗

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↗