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PubMed2002

Segregation and integration of visual channels: layer-by-layer computation of ON-OFF signals by amacrine cell dendrites.

The visual system analyzes images through parallel channels, and our data suggest that the first set of parallel representations of the visual world is embodied in the inner plexiform layer (IPL) of the retina, in which light-evoked excitatory inputs of the ON and OFF bipolar cells to amacrine cells (ACs) are organized in a layer-by-layer manner. Approximately 30% of ACs have narrowly monostratified dendrites in 1 of the 10 strata of the IPL, and they receive segregated bipolar cell inputs: the light-evoked excitatory cation current, DeltaI(C), in strata 1, 2, and 4 is OFF (predominantly mediated by the OFF bipolar cells), the current in strata 3 and 7-10 is ON (predominantly mediated by ON bipolar cells), and the current in strata 5 and 6 is ON-OFF (mediated by both ON and OFF bipolar cells). The remaining 70% of ACs have broadly monostratified, multistratified, or diffuse dendrites, and they integrate bipolar cell signals through layer-by-layer summation: ACs with dendrites ramified in multiple strata exhibit DeltaI(C)s that are sums of DeltaI(C)s of individual strata. The light-evoked inhibitory chloride current, DeltaI(Cl), in strata 1, 2, and 4-6 is ON-OFF (mediated predominantly by ON-OFF ACs or ON ACs plus OFF ACs), and the DeltaI(Cl) in strata 3 and 7-10 is ON (mediated predominantly by ON ACs). This indicates that the amacrine-amacrine inhibitory synaptic circuitry in the IPL is asymmetrical in favor of the ON channels.

Amacrine Cells↗

PubMed1998

[Layer thickness of dental adhesives. Relation between layer thickness and viscosity].

OBJECTIVE: To investigate the viscosity of two dental adhesives in relation to the adhesive layer thickness. DESIGN: In vitro study. METHODS: The viscosity of several dental adhesives has been determined with a reogoneometer. Both a high and a low viscous adhesive was used to restore class II preparations. These restorations were sectioned and the thickness of the adhesive layer was measured on several defined locations. A statistical analysis was performed. RESULTS: The high viscous adhesive resulted in a thinner layer along the cervical outline of the restoration. With both materials pooling occurred at the line angles of the preparation. On the flat surfaces of the preparations there was a layer of even thickness. CONCLUSION: The differences in thickness of the adhesive layer as often seen on radiographs cannot be explained solely by the use of adhesives with a different viscosity.

Dental Cements↗

PubMedDate not supplied

Comparing comfort and wearability between Type III single-layered and double-layered EVA mouthguards.

This study compared two Type III ethylene vinyl acetate (EVA) mouthguards for wearability, comfort, fit, and patient preference. Twenty-two athletes each received two custom-fabricated athletic mouthguards, a single-layered vacuum-formed EVA mouthguard and a double-layered heat- and pressure-laminated EVA type. Athletes wore each type of mouthguard for a two-week period while playing basketball. At the end of each two-week period, the athletes completed questionnaires that evaluated 17 characteristics of each mouthguard type. Data were analyzed using the binomial test for small numbers. The double-layered heat- and pressure-laminated EVA mouthguard performed as well as or better than the single-layered vacuum-formed type in 14 of the 17 categories. There was a statistically significant patient preference for the double-layered heat- and pressure-laminated mouthguard.

Athletic Injuries↗

PubMed1990

Layer-by-layer desquamation of corneal epithelium and maturation of tear-facing membranes.

A method to devitalize single layers of apically exposed rabbit corneal epithelial cells through the use of digitonin is described. Devitalized cells exfoliate spontaneously as loosely cohesive, trypan-blue-stained layers, exposing underlying viable cells. Repeated application of this devitalization-exfoliation methodology results in the gradual elimination of each of the epithelial cells. The generation of corneal surfaces composed of the tear-facing membranes of all intraepithelial cell types--subsurface, wing, and basal--is thus attainable. Exposed surfaces were studied with respect to microanatomy, the binding of lectins, and the adherence of Pseudomonas aeruginosa. Microprojections (microvilli or microplicae) were absent in the basal cells but were present in all suprabasal layers, and increased gradually in density as cells approached the surface position. Wheat germ agglutinin and concanavalin A were found to bind to the tear-facing membranes of all suprabasal cell layers. The tear-facing membrane of the basal cells, in contrast, was not labeled. Within each labeled layer, the magnitude of lectin binding differed markedly from cell to cell; lectin binding decreased as the cellular area exposed to the tear surface increased. Pseudomonas were found exclusively at microprojection-free cellular areas, suggesting that inhibition of attachment is linked to the ontogeny of these microprojections.

Animals↗

PubMed1981

[Layer-by-layer analysis of transcallosal responses in the cat sensomotor cortex].

Transcallosal responses to stimulation of the cortex at the depth of 0.5 mm had the least phase I and the greatest phase II as compared with their values at a deeper stimulation. The maximal phase II occurred at the 1 mm stimulation. At a fixed depth of stimulation the maximal amplitude of the phase I coincided with the depth of stimulation. At 1 and 2 mm stimulations, the second maximum of the responses occurred at the depth of 2 and 1 mm, resp. The data obtained suggest that the callosal connections are organized in a "layer--to--layer" way, and that there are some cross--connections between the layers III and V ("one layer--another layer").

Animals↗

PubMed1991

Thin-layer chromatographic analyses of lipids in different layers of porcine epidermis and oral epithelium.

Frozen cryosections were cut parallel to the surface of porcine skin and palatal, buccal and floor-of-mouth mucosa so as to provide separate samples representing various epithelial layers. The samples were dried, extracted with chloroform:methanol, and the lipids were chromatographed on silica gel plates in various solvent systems. After charring, lipids were quantified with a scanning densitometer. Overall, greater differences in proportions and distributions of lipid components were evident between keratinized and non-keratinized epithelia than between epidermis and keratinized oral epithelium. For epidermis and palate there was an increase in neutral lipids, including ceramides, from the deeper layers to the surface; ceramides were most abundant in surface layers. In buccal epithelium there was a distinct increase in glycosylceramides toward the surface, and in both non-keratinized regions ceramides were present in only very small amounts. The results suggest that although neutral lipids may be associated with a superficial barrier layer in skin and oral mucosa, there are differences in the composition of this barrier between keratinized and non-keratinized epithelia.

Animals↗

PubMed1977

Preparation of plates with a permanent adsorbent layer and their application in the analytical thin-layer chromatography of lipids.

Experimental conditions for preparing the thin-layer chromatographic plates with a permanent adsorbent layer (PAL) have been established; the particles of this layer are firmly bound to each other and to the glass support by means of fused glass powder. To prepare the PAL plates, a mixture of Woelm silica gel and glass powder (1:3, w/w) of particle size 7+/-1 mum was suspended in toluene and spread on the plates, yielding PALs of thickens 150-250 mum. The plates were heated in an electric furnace at 675 degrees for 20 min. In the separation of neutral lipids, a PAL thus prepared is equal in efficiency and selectivity to silica gel layers prepared in the usual manner.

Adsorption↗

PubMed2003

Dopaminergic amacrine cells in the inner nuclear layer and ganglion cell layer comprise a single functional retinal mosaic.

Many types of retinal neuron are distributed in an orderly manner across the surface of the retina. Indeed, the existence of such regularity amongst a population of neurons, termed a retinal mosaic, may be a defining feature of functionally independent types of retinal neuron. We have examined the spatial distribution of dopaminergic amacrine cells in the ferret retina both in the inner nuclear layer (INL) and in the ganglion cell layer (GCL) to determine whether the cells in each layer form an independent retinal mosaic as evidence of whether they should be considered as two separate types. Ferret retinas contain approximately 1,900 dopaminergic amacrine cells, of which 27% are located in the GCL, and the rest in the INL. Based on analysis of their Voronoi domains as well as autocorrelation analysis and tests for complete spatial randomness, we found that the distribution of INL cells was statistically regular, while that of the GCL cells was not. However, by using cross-correlation analysis, these two groups of cells were found to be spatially dependent: an exclusion zone was detected in the cross-correlogram of roughly the same size as that found in the autocorrelograms of both INL and GCL cells. Such a pattern would be expected if dopaminergic amacrine cells in the INL and GCL were members of a single regular population differing only in their somatic depth. By using computer simulations, we tested this hypothesis directly, confirming that a random assignment of 27% from the total population produces cross-correlograms that are indistinguishable from those of the biological mosaics. We conclude, therefore, that the cells in the two layers form a single functional population; those in the GCL appear to be misplaced. Somatic positioning with respect to depth within the retina is not, by itself, a reliable guide for functional classification.

Amacrine Cells↗

PubMed2006

Defoliation and plasmid delivery with layer-by-layer coated colloids.

The uptake of polyelectrolyte multilayer coated colloids into cells, subsequent defoliation and plasmid delivery was studied by means of confocal microscopy and flow cytometry. Silica particles coated layer-wise with protamine and dextran sulfate were given to HEK 293T cells. Optimum uptake was found with protamine as the top layer. The particle uptake likely follows an non-receptor-mediated endocytotic pathway. Defoliation of polyelectrolyte multilayer coated particles within cells was demonstrated by the release of incorporated plasmids as indicated by the expression of plasmid encoded proteins using the enhanced green fluorescence proteine (pEGFP-C1) plasmid and a red fluorescence protein (pDsRed1-N1) plasmid. This proves, together with the direct observation of fluorescent layer debris, the defoliation of coated particles and the release of layer components into the cytoplasm. Particle uptake and GFP expression.

Animals↗

PubMed2002

Layer-by-layer self-assembled ultrathin multilayer films of lanthanide polyoxometalates and poly(allylamine hydrochloride) and their photoluminescent properties.

Ultrathin multilayer films of two lanthanide polyoxometalates (LPOMs), K(17)[Eu(P(2)W(17)O(61))(2)] (EPW) and K(13)[Eu(SiW(11)O(39))(2)] (ESW), and poly(allylamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. UV-vis spectroscopy and ellipsometry respectively show that the absorbance values at characteristic wavelengths and the thicknesses of the multilayer films increase linearly with the number of LPOM/PAH bilayers, suggesting that the deposition process is linear and highly reproducible from layer to layer. Average thicknesses of ca. 3.4 and 2.4 nm were determined for the EPW/PAH and ESW/PAH bilayers by ellipsometry, respectively. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide the surface morphology of the LPOM/PAH films, indicating that the film surface is relatively uniform and smooth. The photoluminescent properties of these films have also been investigated by fluorescence spectroscopy. The LPOM/PAH multilayer film has a good thermal stability as shown by UV-vis, X-ray photoelectron, and fluorescence spectra.

Journal Article↗

PubMed2002

Accounting for diffuse layer ions in triple-layer models.

The triple-layer model is one of the most widely used surface complexation models for adsorption on mineral surfaces. In current implementations, the accounting of ions in the diffuse layer may be neglected, resulting in a charge imbalance in the modeled solution as well as errors in mass balance, particularly in low ionic strength solutions when mineral-specific surface area is large. This paper introduces an internally consistent scheme for modeling diffuse layer ions in the triple-layer model. Model calculations illustrate the difference between the proposed and previous implementations using an idealized example. The guarantee of charge balance on both sides of the interface assures that pH is accurately modeled. This may be important in reactive transport simulations, such as modeling adsorption in low ionic strength variable charge soil solutions.

Journal Article↗

PubMed1995

Quantitative assessment of lateral interaction as determined by computerized quantitative layer-by-layer perimetry.

BACKGROUND: Quantitative layer-by-layer perimetry is a psychophysical technique which assesses lateral interaction in human vision. In prior designs of this technique the test procedure was time-consuming and quantitative assessment of the results was not possible. In order to shorten test duration and provide quantitative experimental data, a new computerized version of the technique has recently been developed. METHODS: A mathematical model for describing lateral interaction as assessed by computerized quantitative layer-by-layer perimetry was developed, and experimental data from the testing of 18 normal persons were fitted to the model. Two descriptive parameters of, respectively, lateral stimulation and lateral inhibition were for each test point related to the differential light sensitivity and to the eccentricity in the visual field. RESULTS: The two parameters describing lateral stimulation could not be reliably estimated. However, the two parameters describing lateral inhibition showed, respectively, a positive correlation with the differential light sensitivity in the visual field and a significant decline with increasing eccentricity in the visual field. CONCLUSION: The technique and the mathematical model employed are suitable for quantitative assessment of lateral inhibition in human vision.

Adult↗

PubMed1995

Cell layer-specific expression of cyclic nucleotide phosphodiesterases in rat arteries: molecular cloning using isolated cell layers from paraformaldehyde-fixed tissues.

We describe a method for the isolation of small quantities of large poly (A)+ mRNA from blood vessels of the rat as well as from distinct cell layers of the rat aorta. The poly (A)+ mRNA isolated by this method is suitable for use in reverse transcription polymerase chain reaction (RT-PCR) amplification of low abundance messages. In this method, anesthetized rats are perfused with ice-cold phosphate-buffered paraformaldehyde to allow for the in situ fixation of many of the main arteries of the rat. Following the in situ fixation of the rat vasculature, selected blood vessels can be removed, cleaned, and poly (A)+ mRNA purified. In addition, the distinct cell layers of the paraformaldehyde-fixed aorta can be mechanically separated and poly (A)+ mRNA purified selectively from each. The application of this method to the study of enzymes involved in cyclic nucleotide-mediated cell-signaling is illustrated by the cloning of two cyclic AMP phosphodiesterases from rat arteries, and from the selective amplification of message for these enzymes from different cell layers isolated from the rat aorta. This method should be applicable to determine if selected mRNAs are present in selected blood vessels of the rat, or within distinct cell layers of particular large blood vessels.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed2005

Amperometric biosensor for choline based on layer-by-layer assembled functionalized carbon nanotube and polyaniline multilayer film.

Conducting polymer film was prepared by electrochemical polymerization of aniline. Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. By using the layer-by-layer method, homogeneous and stable MWNTs and polyaniline (PANI) multilayer films were alternately assembled on glassy carbon (GC) electrodes. Conducting polymer of PANI had three main functions: (i) excellent antiinterference ability, (ii) protection ability in favor of increasing the amount of the MWNTs immobilized on GC electrodes, and (iii) superior transducing ability. The protection effect of PANI film and the electrostatic interaction between positively charged PANI and negatively charged MWNTs both attributed to immobilizing abundant MWNTs stably, thereby enhancing the catalytic activity. The layer-by-layer assembled MWNTs and PANI-modified GC electrodes offered a significant decrease in the overvoltage for the H2O2 and were shown to be excellent amperometric sensors for H2O2 from +0.2V over a wide range of concentrations. As an application example, by linking choline oxidase (CHOD), an amplified biosensor toward choline was prepared. The choline biosensor exhibited a linear response range of 1x10(-6) to 2x10(-3) M with a correlation coefficient of 0.997, and the response time and detection limit (S/N=3) were determined to be 3 s and 0.3 microM, respectively. The antiinterference biosensor displays a rapid response and an expanded linear response range as well as excellent reproducibility and stability.

Alcohol Oxidoreductases↗

PubMed2006

Thicker carotid intima layer and thinner media layer in subjects with cardiovascular diseases. An investigation using noninvasive high-frequency ultrasound.

BACKGROUND: The thickness of the arterial intima increases and that of the media decreases with increasing age and degree of atherosclerosis. Separate estimates of the individual intima and media layers might therefore be more appropriate than the commonly used method estimating the combined intima-media thickness (IMT). METHODS AND RESULTS: One hundred consecutive 70-year-old subjects from the PIVUS study were investigated. Separate estimates of the thickness of the carotid artery intima and media wall layers were carried out noninvasively using 25MHz high-frequency ultrasound. Subjects with a diagnosis of cardiovascular disease (CVD), coronary heart disease (CHD), myocardial infarction (MI) or stroke had a significantly thicker intima layer (all P<0.0001) and a thinner media layer (all P<0.05) than healthy subjects. The intima/media thickness ratio also differed significantly between subjects with and without a diagnosis of CVD (0.43+/-0.20versus 0.75+/-0.48, P=0.0002). Subjects with hypertension or hyperlipidemia also had a thicker carotid intima than subjects without these diagnoses (P<0.0005 for both). None of the corresponding intima+media thickness values differed significantly. Similar results were obtained in women and men. CONCLUSION: Separate assessment of carotid artery intima and media thickness using noninvasive high-frequency ultrasound appears to be of potential value, as a striking difference in intima thickness and the intima/media thickness ratio was found between subjects with and without CVD.

Aged↗

PubMed2006

Layer-by-layer films of hemoglobin or myoglobin assembled with zeolite particles: electrochemistry and electrocatalysis.

Positively charged hemoglobin (Hb) or myoglobin (Mb) at pH 5.0 in solutions and negatively charged zeolite particles in dispersions were alternately adsorbed onto solid surfaces forming [zeolite/protein](n) layer-by-layer films, which was confirmed by quartz crystal microbalance (QCM) and cyclic voltammetry (CV). The protein films assembled on pyrolytic graphite (PG) electrodes exhibited a pair of well-defined, nearly reversible CV peaks at about -0.35 V vs. SCE at pH 7.0, characteristic of the heme Fe(III)/Fe(II) redox couples. Hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)) in solution were catalytically reduced at [zeolite/protein](7) film modified electrodes, and could be quantitatively determined by CV and amperometry. The shape and position of infrared amide I and II bands of Hb or Mb in [zeolite/protein](7) films suggest that the proteins retain their near-native structure in the films. The penetration experiments of Fe(CN)(6)(3-) as the electroactive probe into these films and scanning electron microscopy (SEM) results indicate that the films possess a great amount of pores or channels. The porous structure of ]zeolite/protein](n) films is beneficial to counterion transport, which is crucial for protein electrochemistry in films controlled by the charge-hopping mechanism, and is also helpful for the diffusion of catalysis substrates into the films. The proteins with negatively charged net surface charges at pH 9.0 were also successfully assembled with like-charged zeolite particles into layer-by-layer films, although the adsorption amount was less than that assembled at pH 5.0. The possible reasons for this were discussed, and the driving forces were explored.

Adsorption↗

PubMed2004

Enzyme-mediated amperometric biosensors prepared with the Layer-by-Layer (LbL) adsorption technique.

Glucose oxidase (GOD) has been immobilized in Layer-by-Layer (LbL) films, adsorbed alternately with poly(allylamine) hydrochloride (PAH) layers, onto an ITO substrate modified with a Prussian Blue (PB) layer. The ITO/PB/GOD-PAH heterostructures were tested in amperometric glucose biosensors, with a high sensitivity of 16 microA mmol(-1)lcm(-2) and a limit of detection of 0.20 mmoll(-1) being achieved. This high sensitivity is attributed to the ultrathin nature of the film in addition to the low operating potentials that could be used due to the efficient catalysis of H(2)O(2) produced in the enzymatic reaction in the presence of Prussian Blue. The biosensors are highly selective to glucose, as demonstrated by the lack of interference from possible interferents such as ascorbic and uric acids and acetominophen. The stability of the biosensors was checked by observing an almost constant sensitivity for a period of approximately 20 days, thus indicating a stable adsorption of GOD.

Adsorption↗

PubMed2005

Catechol biosensing using a nanostructured layer-by-layer film containing Cl-catechol 1,2-dioxygenase.

The detection of aromatic compounds from pesticides and industrial wastewater has become of great interest, since these compounds withstand chemical oxidation and biological degradation, accumulating in the environment. In this work, a highly sensitive biosensor for detecting catechol was obtained with the immobilization of Cl-catechol 1,2-dioxygenase (CCD) in nanostructured films. CCD layers were alternated with poly(amidoamine) generation 4 (PAMAM G4) dendrimer using the electrostatic layer-by-layer (LbL) technique. Circular dichroism (CD) measurements indicated that the immobilized CCD preserved the same conformation as in solution. The thickness of the very first CCD layers in the LbL films was estimated at ca. 3.6 nm, as revealed by surface plasmon resonance (SPR). PAMAM/CCD 10-bilayer films were employed in detecting diluted catechol solutions using either an optical or electrical approach. Due to the mild immobilization conditions employed, especially regarding the pH and ionic strength of the dipping solutions, CCD remained active in the films for periods longer than 3 weeks. The optical detection comprised absorption experiments in which the formation of cis-cis muconic acid, resulting from the reaction between CCD and catechol, was monitored by measuring the absorbance at 260 nm after film immersion in catechol solutions. The electrical detection was carried out using LbL films deposited onto gold-interdigitated electrodes immersed in aqueous solutions at different catechol concentrations. Using impedance spectroscopy in a broad frequency range (1Hz-1kHz), we could detect catechol in solutions at concentrations as low as 10(-10) M.

Adsorption↗