Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “layer”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77Linked to original sources
PubMed2004

Analytical investigations of tunnel magnetoresistance layers.

The basic elements of tunnel magnetoresists are two magnetic layers separated by an insulating barrier layer. The uniformity of this only 1-2 nm thick barrier layer up to dot edges and the chemical composition of the layers are properties important for the efficiency of tunnel magnetoresistance devices. These key-properties have been investigated by analytical TEM methods like high resolution TEM imaging and energy-filtered imaging. With regard to the chemical composition the TEM results have been confirmed by XPS investigations. The subsequent oxidation of the barrier is one of the most critical steps of the deposition procedure of the layer stacks. An undersized oxygen dose leads to an incomplete oxidation of the barrier layer with uncontrollable tunnel behaviour. An overdose of oxygen leads to oxygen diffusion in the layers beneath the barrier and uncontrollable magnetic hardness of the lower magnetic electrode.

Alloys↗
PubMed2001

Short-term plasticity of extrinsic excitatory inputs to neocortical layer 1.

Previous studies have shown that different pyramidal cell inputs vary in the short-term plasticity expressed when they are subjected to repetition of use. Here, we describe short-term plasticity at synapses that mediate long-range input to neocortical layer 1 and compare it with that which normally occurs in the hippocampal Schaffer collateral pathway, which also involves projection by remote inputs onto apical dendrites. We isolated tangential inputs to layer 1 in neocortical slices, stimulated these with brief 40-Hz trains, and examined postsynaptic responses by recording extracellularly from layer 1 in somatosensory, prefrontal, and visual neocortex, and intracellularly from visually identified pyramidal cell somata in layer 2/3 in somatosensory and prefrontal neocortex. Train response amplitudes were characterized by calculating paired-pulse ratios, fifth-versus-first amplitude ratios (5th/1st ratios), and a center-of-mass index "M". As expected, the hippocampal train responses facilitated strongly. In contrast, layer-1 responses displayed strong synaptic depression in all regions examined. This depression was reflected in 5th/lst ratios and M scores, but not paired-pulse ratios because it did not consistently begin until the third responses in trains. It persisted unchanged in the presence of partially blocking levels of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), but was converted to strong facilitation when slices were bathed in low-Ca++ media. Intracellularly, we observed response-train depression very similar to that recorded extracellularly. These findings show that long-range inputs to neocortical layer 1 display short-term plasticity markedly different from that which normally occurs at hippocampal Schaffer collateral synapses, but similar to that which has been described previously for excitatory inputs to pyramidal cells in deeper neocortical layers.

Afferent Pathways↗
PubMed1998

MRI anatomy of white matter layers around the trigone of the lateral ventricle.

MRI was obtained in eight normal volunteers and seven patients with brain oedema around the trigone. In addition to the conventional sequences, diffusion-weighted and intravoxel-incoherent-motion images using motion-proving anteroposterior and/or lateral direction gradients were obtained to show the white matter pathways better. Coronal proton-density-weighted images showed three thin relatively high-intensity layers in addition to the tapetum and the internal and external sagittal strata. Although they have not been confirmed anatomically, the thin layer between the internal and the external sagittal strata was corroborated by diffusion-weighted and intravoxel-incoherent-motion images, and by characteristics of the spread of oedema into the sagittal stratum. We propose that this layer be named the central sagittal lamina. The other two layers medial and lateral to the sagittal stratum were outside, but in contact with the medial and lateral parts of the sagittal stratum, respectively. We provisionally named them medial and lateral sagittal laminae; they were not evident on any other images. The low-intensity layer on T2-weighting was the internal sagittal stratum. The optic radiation, comprising the external sagittal stratum, appeared as an intermediate to slightly high-intensity layer on T2-weighted images and a low-intensity layer on T1-weighted images as did the corticospinal tract in the posterior internal capsule.

Adult↗
PubMed2001

Structure and surface energy of the surfactant layer on the alveolar surface.

The surface energy of the alveolar surfactant layer is determined in the scope of a modification of the structural model of Larsson et al. [(1999) J Disp Sci Technol 20:1-12], according to which this layer is built up of a lipid monolayer adsorbed at the hypophase/air interface and supported by a network of lipid bilayers immersed into the hypophase, i.e., the alveolar liquid. Formulae are derived for the dependence of the specific surface energy of the surfactant layer on the distance between the bilayers constituting the layer. It is shown that at equilibrium this energy can have values comparable with or less than 1 mJ/m2 needed for normal functioning of the alveolus during the respiration cycle. The specific surface energy of the surfactant layer with monolayer-bilayer structure can have such low values only if the layer is of optimal thickness and if the specific line energy of the monolayer-bilayer contact lines is negative and that of the bilayer-bilayer contact lines is positive. It is found that in dynamic regime the change in the specific surface energy of the alveolar surfactant layer with bilayer-monolayer structure is in qualitative agreement with that determined experimentally during lung inflation and deflation.

Kinetics↗
PubMed2006

The membranous layer of superficial fascia: evidence for its widespread distribution in the body.

A discrete membranous layer, "stratum membranosum", in human subcutaneous tissue is classically described as confined to the lower anterior abdominal wall and perineum and referred to as Scarpa's and Colles' fasciae, respectively. Evidence for its existence elsewhere in the body is scanty and therefore the present study was undertaken. Dissection of six embalmed adult cadavers, along with ultrasound imaging on four living subjects, were carried out to determine the existence, topography, and thickness of the membranous layer of superficial fascia in different regions of the body. In all six cadavers, a continuous layer of fibrous membrane in the superficial fascia was found consistently in all the dissected regions of the body and was also confirmed by ultrasonography. The arrangement and thickness of this membranous layer varied according to body region, body surface, and gender. It was thicker in the lower than in the upper extremity, on the posterior than anterior aspect of the body, and in females than in males. The mean thickness of the membranous layer ranged from 39 to 189 mum, being thickest in the leg and thinnest over the dorsum of the hand. The membranous layer was observed to have two or even three components in regions such as the breast, back, thigh, and arm and was seen to split, forming special compartments around subcutaneous major veins of upper and lower extremities, with fibrous septa extending to attach to the vessel wall. Functionally, the membranous superficial fascia may play a role in the integrity of the skin and support for subcutaneous structures particularly veins, by ensuring their patency. Understanding the topographic anatomy of this fascial layer may help explain body-contour deformities and provide the anatomic basis for surgical correction.

Abdominal Wall↗
PubMed2000

Blood-derived macrophage layers in the presence of hydrocortisone support myeloid progenitors in long-term cultures of CD34+ cord blood and bone marrow cells.

Monocytes/macrophages secrete various cytokines that induce proliferation of colony-forming unit granulocyte-macrophage (CFU-GM) in short-term assays. To determine whether macrophages also support proliferation of more primitive progenitors, i.e., cells that give rise to colony forming cells in a 5-week long-term culture (LTC), we established plastic-adherent macrophage layers from human peripheral blood (PB) and filgrastim (G-CSF)-mobilized progenitor cell collections in the presence of hydrocortisone, and compared these layers with bone marrow (BM) stroma regarding their suitability to support proliferation and differentiation of CD34+ BM and cord blood (CB) cells in 5-week LTCs. CD34+ cells were seeded onto irradiated macrophage and BM stromal layers, as well as without any preformed layer. After 5 weeks, colony formation (CFU-GM, BFU-E/CFU-E) and cell expansion were determined. CD34+ cells from BM and CB yielded more CFU-GM and total nucleated cells at 5 weeks in the presence of both types of adherent layer compared with cultures without a layer (p<0.05). For CD34+ BM cells, macrophage layers were superior to BM stroma in enhancing CFU-GM and CFU-E/BFU-E output (p < 0.05). In contrast, BM stroma was favorable compared with macrophages concerning nucleated cell expansion from CD34+ CB cells (p = 0.027). The macrophage nature of PB-derived adherent cells was confirmed immunocytochemically by positive staining for CD68, Ki-Mlp, CD31, CD54, inconstant staining for CD14, and negative staining for CD1a, CD3, CD15, CD34, and CD62E. Cytochemical reactions were positive for alpha-naphthyl acetate esterase and negative for peroxidase and periodic acid-Schiff, consistent with the immunophenotype. In conclusion, the results show that blood-derived macrophages support CFU-GM generation from CD34+ CB and BM progenitors for 5 weeks in vitro. Differential effects on proliferation and maturation of BM versus CB progenitors are discussed.

Antigens, CD34↗
PubMed2002

Genes and derived amino acid sequences of S-layer proteins from mesophilic, thermophilic, and extremely thermophilic methanococci.

Cells of methanococci are covered by a single layer of protein subunits (S-layer) in hexagonal arrangement, which are directly exposed to the environment and which cannot be stabilized by cellular components. We have isolated S-layer proteins from cells of Methanococcus vannielii ( T(opt.)=37 degrees C), Methanococcus thermolithotrophicus ( T(opt.)=65 degrees C), and Methanococcus jannaschii ( T(opt.)=85 degrees C). The primary structure of the S-layer proteins was determined by sequencing the corresponding genes. According to the predicted amino acid sequence, the molecular masses of the S-layer proteins of the different methanococci are in a small range between 59,064 and 60,547 Da. Compared with its mesophilic counterparts, it is worth noting that in the S-layer protein of the extreme thermophile Mc. jannaschii the acidic amino acid Asp is predominant, the basic amino acid Lys occurs in higher amounts, and Cys and His are only present in this organism. Despite the differences in the growth optima and the predominance of some amino acids, the comparative total primary structure revealed a relatively high degree of identity (38%-45%) between the methanococci investigated. This observation indicates that the amino acid sequence of the S-layer proteins is significantly conserved from the mesophilic to the extremely thermophilic methanococci.

Amino Acid Sequence↗
PubMed2006

Structural, chemical and biological properties of carbon layers sputtered on polyethyleneterephtalate.

Carbon layers on polyethyleneterephtalate (PET) backing were prepared by sputtering from graphite target. UV-VIS, Raman spectroscopy, RBS (Rutherford backscattering) and ERDA (Elastic Recoil Detection Analysis) techniques were used for the characterization of the layers. Surface morphology of the layers was determined by AFM technique and the adhesion of 3T3 mouse fibroblasts on the layers was studied in vitro. It was found that the properties of the deposited carbon layer depend on the sputtering time. The concentration of conjugated double bonds, fraction of amorphous hydrogenated carbon (a-C:H) containing oxygen and surface roughness are increasing functions of the sputtering time. The changes of the layer surface morphology with increasing sputtering time were also observed. For the sputtering times up to 30' the number of adhering 3T3 cells increases with increasing sputtering time. For longer sputtering times, however, the cell adhesion becomes lower probably due to unfavorable changes in roughness and morphology of the layer.

3T3 Cells↗
PubMed1979

Exchange and interactions between lipid layers at the surface of a liposome solution.

Lipid organization and lipid transport processes occurring at the air-water interface of a liposome (lipid vesicle) solution are studied by conventional surface pressure-area measurements and interpreted by an adequate theory. At the interface of a dioleoyl phosphatidylcholine vesicle solution, used for demonstration, a well defined two layer structure selfassembles: vesicles disintegrate at the interface forming a surface-adsorbed lipid monolayer, which prevents further disintegration beyond about 1 dyne/cm surface pressure. A layer of vesicles now assembles in close association with the monolayer. This layer is in vesicle diffusion exchange with the solution and in lipid exchange with the monolayer. The lipid exchange occurs exclusively between the monolayer and the outer lipid layer of the vesicles; it is absent between outer and inner vesicle layers. Equilibration of the lipid density in the monolayer with that in the vesicle outer layer provides a coherent and quantitative explanation of the observed hysteresis effects and equilibrium states. The correspondence between monolayer and vesicle outer layer is traced down to equilibrium constants and rate constants and their dependences on surface pressure, vesicle size and concentration. Other alternate realizations of surface structure and exchange, including induced lipid flip-flop within vesicles or vesicle monolayer adhesion or fusion are potential applications of the proposed analysis.

Kinetics↗
PubMed1988

Comparative assessment of the resistance of the unstirred water layer to solute transport between two different intestinal perfusion systems.

The resistance of the unstirred water layer to solute transport was estimated in two different intestinal single-pass perfusion systems for a comparative study, using D-glucose as a model compound. One is a well established perfusion system in anesthetized rats as a standard (system A). The other is the one in unanesthetized rats for comparison (system B). It was demonstrated that in system B as well as in system A the resistance of the unstirred water layer to D-glucose transport should be taken into account and this resistance, accordingly, the effective thickness of the unstirred water layer (delta) which is assumed to be in proportion to its resistance, could be described as a function of the perfusion rate by using a film model. The delta decreased with increasing perfusion rate and was larger in system A than in system B at each perfusion rate; 785 microns in system A versus 319 microns in system B at the perfusion rate of 0.16 ml/min and 337 microns versus 184 micron at that of 2.95 ml/min. Thus in system B the effective thickness, accordingly, the resistance, of the unstirred water layer was reduced to about 50% of that in system A, but the resistance of the unstirred water layer could still account for 85% of the total resistance at the maximum as far as D-glucose absorption was concerned, while 93% in system A. These results suggest that, compared with perfusion experiments in anesthetized rats (system A), the resistance of the unstirred water layer is reduced but cannot be left out of consideration even if perfusion experiments are performed in unanesthetized rats (system B). And the lower resistance of the unstirred water layer in system B was attributed to a turbulent flow in contrary to a laminar flow in system A.

Animals↗
PubMed1984

Phenytoin preferentially suppresses epileptiform activity in the superficial cortical layers of the cat.

Clinically, phenytoin is thought to be useful in controlling seizure activity by preventing it's spread from the focus to neighboring tissue. Experimentally, it has been suggested that phenytoin's principal action is no longer polysynaptic pathways with primary foci affected less than surrounding tissue. In this study, we present data confirming these basic experimental conclusions in foci induced in striate neocortical layer 4 of the cat. By using discrete penicillin microinjections strategically placed into this most penicillin-sensitive neocortical layer and recording simultaneously from several layers, we have been able to expand upon these conclusions by identifying this differential action at the interlaminar level. Epileptiform activity recorded from superficial laminae bordering layer 4, and into which layer 4's primary projections terminate, is suppressed preferentially by phenytoin. These superficial layers are also those that project into neighboring areas of the cat visual cortex. It would appear, then, that phenytoin begins protecting the cortex from seizure spread at the first synaptic termination into which this layer 4 primary focus projects. A discussion of the basic mechanisms of action that may be responsible for these results is also presented.

Animals↗
PubMed1987

Immunocytochemical localization of LANT-6-like immunoreactivity within neurons in the inner nuclear and ganglion cell layers in vertebrate retinas.

LANT-6 is a hexapeptide (H-Lys-Asn-Pro-Tyr-Ile-Leu-OH) isolated from chicken small intestine, which resembles the COOH-terminal half of neurotensin, except for the amino acid substitutions Lys/Arg and Asn/Arg. The present report concerns the immunocytochemical staining of vertebrate retinas using an antiserum directed against LANT-6. In the retinas from goldfish, bird and turtle, cells in both the inner nuclear and ganglion cell layers were labeled, but in the frog no cells were labeled specifically and in the rat only cells in the ganglion cell layer were labeled. Labeled cell bodies in the inner nuclear layer gave rise to processes which were seen primarily within the following laminas of the inner plexiform layer (IPL): in the goldfish, lamina 3; chicken, laminae 1, 3 and 4; and turtle, laminae 3, 4 and 5. The cell bodies of the labeled neurons in the ganglion cell layer gave rise to dendrites which entered the IPL and axons which descended to the optic fiber layer. The cells with LANT-6-like immunoreactivity were distributed in both the central and peripheral parts of the retina in all the species examined except frog. Measured by radioimmunoassays, the levels of LANT-6-like-immunoreactivity in extracts of turtle, chicken, and goldfish retinas were 5-30 times those for neurotensin-like immunoreactivity, however no LANT-6-like immunoreactivity was detected in frog. Multiple chromatographic analyses indicated that while the LANT-6-like immunoreactivity in chicken retina was indistinguishable from synthetic LANT-6, LANT-6-like immunoreactivity in turtle and goldfish retinas was primarily associated with large molecular forms. Treatment of turtle LANT-6-like immunoreactivity with pepsin, an enzyme known to mimic processing for neurotensin precursors, yielded 3 major peptides, one of which co-chromatographed with synthetic LANT-6. The present immunocytochemical localization of LLI within cells in the inner nuclear and ganglion cell layers, coupled with the biochemical characterization of LANT-6 in the vertebrate retinas and brains, suggests that neuropeptides such as LANT-6 may play a role in visual processing both within the retina and within the visual pathways to the brain.

Animals↗
PubMed1988

Changes in inner plexiform layer thickness following neonatal visual cortical ablation in cats.

The effect of visual cortex removal at 5-7 days of age on the development of the inner nuclear and inner plexiform layers of the cat's retina was examined in animals which had survived 9-36 months after the cortical removal. The lesions were unilateral so that only the nasal or the temporal region of each retina was affected, and the affected regions were positively identified by HRP injection into the optic tract either ipsilateral or contralateral to the ablated hemisphere. Small sections of retina straddling the naso-temporal boundary were then embedded in plastic and sectioned radially for analysis. In this way, comparisons could be made between areas of retina which were closely matched in terms of location as well as histological history. Cells in the inner nuclear layer in affected regions of retina appeared normal both in number and size, even though ganglion cell density in these areas was clearly reduced. This indicates that, at least at this age, the survival of inner nuclear layer cells does not depend on the availability of ganglion cells as synaptic targets. Paradoxically, in the affected regions of retina there was an increase in the width of the inner plexiform layer which was not associated with any change in the thickness of other, more distal retinal layers. This could be due either to an increased growth of surviving ganglion cells and/or inner nuclear layer cells, or to an increase in the survival of cells in the ganglion cell layer, perhaps displaced amacrine cells, which have a greater dendritic volume than the lost ganglion cells.

Animals↗
PubMed1988

In vitro formation of the "S" layer, a unique component of the fertilization envelope in Xenopus laevis eggs.

The extracellular matrix (ECM) of unfertilized Xenopus laevis eggs consists of an elaborate filamentous network in the perivitelline space (PS) and a thick fibrillar vitelline envelope (VE), with a thin layer of horizontal filaments (HF) separating the two. At fertilization this ECM is converted into the fertilization envelope (comprised of the fertilization (F) layer and altered VE), and a third layer, the smooth (S) layer, is formed at the upper boundary of the PS (Larabell and Chandler, 1988). In this report, we use quick-freeze, deep-etch, rotary-shadow electron microscopy to show that an intact S layer can be formed in vitro by incubation of unfertilized eggs in an exudate obtained from cortical granules. Within 5 min numerous 36-nm-diameter particles assemble in a highly ordered array at the microvillar tips. These particles appear to "melt" and to form patches of smooth material and within 10 min one continuous sheet has formed. The presence of the VE is required for formation of the S layer, and we suggest that the HF layer is the site of assembly.

Animals↗
PubMed1987

Effects of hypercholesterolemia on the microsomal membrane fluidity of intimal-medial versus medial layers of swine aorta: implications for the pathogenesis of vasospasm.

The hypothesis was examined that hypercholesterolemia induces a decrease in arterial microsomal membrane fluidity. To investigate this hypothesis, the fluorescence anisotropy (r) of 1,6-diphenylhexa-1,3,5-triene was measured in aortic microsomes isolated from the intimal-medial (IM) and medial (M) layers of swine thoracic aortas. After 10 weeks of feeding a high fat (10% lard) diet, serum cholesterol increased 2.3-fold compared to 3.6-fold in pigs fed a similar diet supplemented with 2% cholesterol. Based upon differences in r, the membrane fluidity of the IM layer was significantly less than the M layers. The membrane fluidity of the IM layer was inversely related to the severity of hypercholesterolemia regardless of dietary treatment. There were no differences in membrane fluidity among the three dissected M layers and the membrane fluidity of these layers was refractory to changes in serum cholesterol. A decrease in the membrane fluidity of the IM layer may contribute to the abnormal regulation of vascular tone which underlies the development of vasospasm in atherosclerotic arteries.

Animals↗
PubMed1991

A reappraisal of the magnitude and implications of the intestinal unstirred layer.

Until recently, a variety of studies had suggested that luminal stirring in the jejunum is relatively poor, with unstirred layers of about 600 microns reported for humans and 300-900 microns for animals. Unstirred layers of this magnitude would markedly retard the absorption of all solutes, and diffusion through this layer would be the rate-limiting step in the uptake of all rapidly absorbed compounds. As a result, luminal stirring, rather than epithelial transport, would be the major variable influencing absorption rate. However, recent studies in dogs and humans have shown that the unstirred layer has a maximal apparent thickness of only about 40 microns. This layer is far thinner than what can be achieved in vitro with vigorous stirring with a magnetic bar, suggesting that some unique stirring mechanism, perhaps villous contractions, is responsible for this extraordinarily efficient mixing. A 40-microns unstirred layer would produce only about 1/15 the resistance of the previously reported 600 microns value; with this thinner layer, alterations in either luminal stirring or epithelial function could readily influence the absorption rate of rapidly transported compounds.

Animals↗
PubMed1992

Shaking of the intact rat and intestinal angulation diminish the jejunal unstirred layer.

A sizeable pre-epithelial diffusion barrier (unstirred layer) is present during perfusion of the rat jejunum. In the present study, three rapidly transported compounds, CO, [14C]warfarin, and glucose (5.5 mmol/L), were used as probes to assess the ability of manipulations to reduce the unstirred layer. This layer was 700-800 microns thick in a 30-cm jejunal segment perfused in conventional fashion on the abdominal wall. Placement of four sharp angulations in the segment or replacement in the abdominal cavity reduced the maximal unstirred layer to 200-400 microns. Increasingly rapid shaking of the anesthetized, intact rat on a platform shaker produced progressively thinner unstirred layers. At 250 revolutions per minute, the maximal layer ranged from 32 to 68 microns for the three probes and may have been appreciably less if the epithelium offered appreciable resistance. Shaking yields a > 15-fold reduction in unstirred layer resistance and provides a means for measuring this resistance and for obtaining more accurate assessment of the true in vivo transport Michaelis constant (Km) of any compound.

Animals↗
PubMed1996

Modeling axi-symmetrical joint contact with biphasic cartilage layers--an asymptotic solution.

The articular contact surfaces in human and animal joints are highly variable. Articular cartilage thickness and the material properties of the cartilage vary as a function of location in the joint and may also change in the pathologic state. In order to study practical joint contact problems, we extended the model for the contact of two biphasic cartilage layers proposed by Ateshian et al. [J. Biomechanics 27, 1347-1360 (1994)] by combining the assumption of the kinetic relationship from classical contact mechanics with the joint contact model for biphasic articular cartilage. In order to illustrate the characteristics of the proposed model, the contact problem was solved numerically for different curvatures of the contact surfaces, and for different thicknesses and material properties of the cartilage layers. Each cartilage layer was assumed to have constant thickness within the contact region. The contact radius, the relative displacement between the contacting bodies, contact pressure, and the stress distributions within the cartilage layers were calculated by applying a step load for a time period of 200 s. The contact radius was found to be sensitive to the change in thickness of the cartilage, and was not very sensitive to the change in the material property of the cartilage. The peak effective stress and the maximal shear stress were predicted to occur at the cartilage-bone interface for all simulated cases, which is in agreement with other theoretical research and supports the experimental findings in the literature on the origins of cartilage damage. For articular cartilage layers of different thicknesses, the stresses in the thick layer were found to be higher than those in the thin layer. Compared to other models of joint contact, the present model offers more possibilities for investigating practical applications, such as simulating the effects associated with cartilage degeneration in diseases such as osteoarthritis, and comparing theoretical predictions with experimental measurements of pressure distribution and contact area in joints.

Cartilage, Articular↗