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At least 253 records · Page 14Linked to original sources

PubMed1985

Differences in synaptic size in the superficial and deep layers of the molecular layer of the cerebellar cortex of the cat. An electronmicroscopic and autoradiographic study.

In a previous study observations in semithin sections of E-PTA-stained cerebellar cortex of the cat revealed differences in size of synaptic grids between the molecular and granular layer (Van der Want et al. 1984). In addition, synaptic size differences were observed between superficial and deep levels in the molecular layer. The present study was an attempt to analyze synapses in ultrathin sections of the cerebellar cortex with special emphasis on size differences of distinct types of synapses at different levels in the molecular layer. Climbing fibers were identified by means of anterograde transport of 3H-leucine injected in the inferior olive and parallel fibers were identified on account of fine structural criteria. Synaptic profiles were measured semi-automatically in the neuropil of the cerebellar cortex at the supra-Purkinje level and the subpial level. Measurements of the trace- and chordlength were obtained from random sections. The frequency distribution of the true diameters of the synapses was reconstructed with a discrete "unfolding"-procedure. The overall diameter at the superficial level was 390.2 +/- 1.5 nm, at the deep level 406.6 +/- 1.5 nm. Climbing fibers exhibited mean values of 431.9 +/- 4.7 and 461.3 +/- 4.1 nm at these levels and parallel fiber terminals mean values of 370.7 +/- 2.9 and 395.8 +/- 3.0 nm. The frequency distributions showed remarkable and statistically significant differences compared with the overall distributions observed at the superficial and the deep levels respectively. The frequency distributions of synaptic diameters at the superficial and deep levels also differ significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1980

Coronary arterial lesions in sexually mature non-layers, layers, and roosters.

The effects of hereditary hyperlipidemia on coronary artery atherosclerosis were studied in 77 White Leghorn (DeKalb strain) chickens ranging from 4 to 13 months in age. After pubescence, the plasma levels of triglyceride and cholesterol in non-laying hens ranged 2- to 3-fold and 2- to 7-fold higher compared to layers. Serial sectioning revealed that most lesions were found in the proximal portions of both the left and right coronary arteries. Ultrastructurally, lesions in the roosters contained no foam cells, whereas some foam cells and small amounts of stainable lipid were observed in the thickened intima of layers. Half of the non-layers had stenotic lesions characterized by many foam cells, necrotic foci, and heavy stromal lipid deposits. Continuous permeation of excess plasma lipids into the arterial wall appeared to be an important factor in the development of coronary lesions.

Animals↗

PubMed2003

The maize disorganized aleurone layer 1 and 2 ( dil1, dil2) mutants lack control of the mitotic division plane in the aleurone layer of developing endosperm.

The maize ( Zea mays L.) endosperm consists of an epidermal like layer of isodiametric aleurone cells surrounding a central body of starchy endosperm cells. In disorgal1 ( dil1) and disorgal2 ( dil2) mutants the control of the mitotic division plane is relaxed or missing, resulting in mature grains with disorganized aleurone layers. In addition to orientation of the division plane, both the shape and size of the aleurone cells are affected, and often more than one layer of aleurone cells is present. Homozygous dil1 and dil2 grains are shrunken due to reduced accumulation of starchy endosperm and premature developmental arrest of the embryo, and mature mutant grains germinate at a very low rate and fail to develop into plants. However, homozygous mutant plants can be obtained through embryo rescue, revealing that both mutants have an irregular leaf epidermis as well as roots with a strongly reduced number of root hairs and aberrant root hair morphology. Our results suggest the presence of common regulatory mechanisms for the control of cell division orientation in the aleurone and plant epidermis.

Alleles↗

PubMed1978

Ultrastructural studies on cerebellar histogenesis in the frog: the external granular layer and the molecular layer.

Maturational changes of the cerebellum of frog tadpoles were studied with the electron miscroscope. In the premetamorphic tadpole, parallel fiber-like processes (PFP) were present in the incipient molecular layer, long before the appearance of the external granular layer (EGL). These PFP showed synaptic contacts with the precociously developed Purkinje cell dendrites. It appears that these PFP may be responsible for inducing the precocious elaboration of the Purkinje cell dendritic arborization. In the metamorphosing tadpoles, the EGL cells migrating into the internal granular layer were frequently seen in close association with the ependymoglial cell processes, which extend from the pia down toward the ependymal surface. This observation lends support to the hypothesis that glial processes guide the migrating EGL cells.

Animals↗

PubMed1995

Two-layer versus one-layer closure in transverse island flap repair of posterior hypospadias.

Despite its prevalence for more than two decades, one-stage repair of moderately severe hypospadias is still associated with a high complication rate. A retrospective study of 103 cases of posterior hypospadias treated exclusively with the Duckett transverse island flap procedure was conducted to analyze factors that might affect the morbidity. The latter included the age of the patients, the anatomical variants of the hypospadias, the suture materials and the technique used, the length of the urethral tube, and the methods and duration of urinary diversion. The fistula rate was 24% (25/103), and the overall complication rate was 31% (32/103). The patients in the glanular-subcoronal-penile variant had a significantly lower overall complication rate than those in the penoscrotal-scrotal variant (21% versus 39%, P < .05). The patients with a neourethra shorter than 3 cm also had significantly less complications than those with a neourethra longer than 3 cm (25% versus 47%, P < .05). The only procedural factor that makes a difference is the method of skin closure to form the neourethra. Two-layer closure resulted in a significantly lower fistula rate and overall complication rate than one-layer closure (13% versus 34% and 15% versus 45%, P < .025 and P < .005, respectively). The study confirms the value of two-layer closure in the transverse island flap repair of posterior hypospadias.

Adolescent↗

PubMed2005

Multilayer membranes for glucose biosensing via layer-by-layer assembly of multiwall carbon nanotubes and glucose oxidase.

A bilayer of the polyelectrolytes poly(dimethyldiallylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) was formed on a 3-mercapto-1-propanesulfonic-acid-modified Au electrode. Subsequently, multiwall carbon nanotubes (MWCNTs) wrapped by positively charged PDDA were assembled layer-by-layer with negatively charged glucose oxidase (GOx) onto the PSS-terminated bilayer. Electrochemical impedance spectroscopy and atomic force microscopy were adopted to monitor the regular growth of the PDDA-MWCNTs/GOx bilayers. Using GOx as a model enzyme, the assembled multilayer membranes showed some striking features such as the adsorbed form of GOx on individual MWCNT, uniformity, good stability, and electrocatalytic activity toward oxygen reduction. Based on the consumption of dissolved oxygen during the oxidation process of glucose catalyzed by the immobilized GOx, a sensitive amperometric biosensor was developed for the detection of glucose up to 5.0 mM with a detection limit of 58 microM. The sensitivity increased with increasing sensing layers up to five bilayers. Ascorbic acid and uric acid did not cause any interference due to the use of a low operating potential. The present method showed high reproducibility for the fabrication of carbon-nanotubes-based amperometric biosensors.

Biosensing Techniques↗

PubMed2005

Natural polyelectrolyte films based on layer-by layer deposition of collagen and hyaluronic acid.

The aim of the present work was to assemble extracellular matrix components into polyelectrolyte multilayers using the layer-by-layer deposition method. The films are constructed with type-I collagen and hyaluronic acid. The construction exhibits the general features observed during polyelectrolyte multilayer buildup: alternate positive and negative values of the zeta potential of the film during its construction and regular increase of the film thickness with the number, n, of deposition step. This increase is shown to be linear with n. As expected for a linearly growing film, the confocal microscopy shows that when the film is brought in contact with a collagen solution, collagen does not diffuse into the film but interacts only with its outer layer. However, the films are not constituted of homogeneously distributed polyanion/polycation complexes as it is usually observed, but they are formed of fibers as imaged by AFM. The typical width of these fibers increases with the number of deposition steps. Finally, it is found that chondrosarcoma cells spread well and synthesize extracellular matrix components only on the collagen ending films, whereas no cellular matrix was found for HA ending ones. Such architectures may be further functionalized by inclusion of active drugs, peptides, proteins..., and could be used as tunable biomaterial interfaces.

Biocompatible Materials↗

PubMed2006

Layer-by-layer self-assembled multilayer films of carbon nanotubes and platinum nanoparticles with polyelectrolyte for the fabrication of biosensors.

Platinum nanoparticle-doped chitosan (CHIT) solution can be easily prepared by treating the CHIT solution with aqueous H2PtCl6 solution followed by chemical reduction of Pt(IV) with NaBH4. Multiwalled carbon nanotubes (MWCNT) are then dispersed in the nanoparticle-doped solution. The resulting Pt-CNT-CHIT material brings new capabilities for electrochemical devices by using the synergistic action of Pt nanaoparticles and CNT. Positively charged Pt-CNT-CHIT solution and negatively charged poly(sodium-p-styrenesulfonate) salt (PSS) have been employed to fabricate stable ultrathin multilayer films on gold electrode and quartz glass slides in a layer-by-layer fashion. Cyclic voltammetric and UV-vis adsorption spectroscopy confirms the consecutive growth of the multilayer films. The modified gold electrode allows low-potential detection of hydrogen peroxide with high sensitivity and fast response time. With the immobilization of cholesterol oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to cholesterol has been constructed. In pH 6.98 phosphate buffer, almost interference free determination of cholesterol has been realized at 0.1 V vs. SCE with a linear range from 0.01 to 3mM and response time<30s. With the immobilization of another cholesterol esterase enzyme layer, the biosensor was used to determine total cholesterol in serum samples with satisfactory results.

Biosensing Techniques↗

PubMed2006

Layer-by-layer assembly of cationic lipid and plasmid DNA onto gold surface for stent-assisted gene transfer.

Intravascular stent-assisted gene transfer is an advanced approach for the therapy of vascular diseases such as atherosclerosis and stenosis. This approach requires a stent that allows local and efficient administration of therapeutic genes to the target cells at the vascular wall. To create such a stent, a method was developed for loading plasmid DNA onto the metal surface. The method involves the formation of self-assembled monolayer on the noble metal surface followed by electrostatic layer-by-layer (LBL) assembly of a cationic lipid/plasmid DNA complex and free plasmid DNA. In this in vitro feasibility study, the thin plainer film and the wire of gold were used as a substrate. The LBL assembly process was characterized by surface plasmon resonance spectroscopy and static contact angle measurement. Plasmid DNA loaded in the multilayer exhibited improved resistance against nuclease digestion. When cultured directly on the DNA-loaded surface, cells were transfected to express exogenous gene in the DNA loading-dependent manner. Plasmid DNA could also be transferred to endothelial cells from its apical side by placing the DNA-loaded gold wire onto the cell layer.

Cations↗

PubMed2006

Surface modification of poly(tetramethylene adipate-co-terephthalate) membrane via layer-by-layer assembly of chitosan and dextran sulfate polyelectrolyte multiplayer.

The improvement of hydrophilicity and hemocompatibility of poly(tetramethylene adipate-co-terephthalate) (PTAT) membrane was developed via polyelectrolyte multilayers (PEMs) immobilization. The polysaccharide PEMs included chitosan (CS, as a positive-charged and antibacterial agent) and dextran sulfate (DS, as a negative-charged and anti-adhesive agent) were successfully prepared using the aminolyzed PTAT membrane in a layer-by-layer (LBL) self-assembly manner. The obtained results showed that the contact angle of as-modified PTAT membranes reached to the steady value after four bilayers of coating, hence suggesting that the full coverage was achieved. It could be found that the PTAT-PEMs membranes with DS as the outmost layer could resist the platelet adhesion and human plasma fibrinogen (HPF) adsorption, thereby prolonging effectively the blood coagulation times. According to L929 fibroblast cell growth inhibition index, the as-prepared PTAT membranes exhibited non-cytotoxic. Overall results demonstrated that such an easy, valid and shape-independent processing should be potential for surface modification of PTAT membrane in the application of hemodialysis devices.

Adipates↗

PubMed2006

Preparation of insulin nanoparticles and their encapsulation with biodegradable polyelectrolytes via the layer-by-layer adsorption.

To develop a new polypeptide delivery system, insulin nano-aggregates with sizes of 100-230nm were prepared by the salting out method with NaCl and encapsulated via the layer-by-layer (LbL) adsorption to provide the insulin nanoparticles shelled with two oppositely charged polyelectrolytes. Poly(alpha,beta-l-malic acid) (PMA) and water-soluble chitosan (WSC) as the weak polyelectrolytes with good biodegradability and biocompatibility in vivo were chosen to be the encapsulating materials of the LbL adsorption. In the preparation of the insulin nano-aggregates, the NaCl concentration and pH in the medium obviously affected yield and particle size of the insulin nano-aggregates. After eight adsorption cycles of the polyelectrolytes on the insulin nano-aggregates, the insulin-polyelectrolyte nanoparticles with the sizes of 100-250nm were obtained with about 20% insulin loss. The insulin release from the nanoparticles was mostly pH-dependent owing to sensitivity of the weak polyelectrolytes to pH. Insulin was hardly released from the nanoparticles in a medium at pH 4-5 while it could be released at pH 7.4, corresponding to the pH of the human blood and the body fluid. A burst effect was also observed although it could be reduced via increasing the polyelectrolyte layers of PMA and WSC assembled on insulin nano-aggregates.

Adsorption↗

PubMed2005

Morphology characterization of layer-by-layer films from PAH/MA-co-DR13: the role of film thickness.

We report on the use of dynamic scale theory and fractal analyses in the study of distinct growth stages of layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and a side-chain-substituted azobenzene copolymer (Ma-co-DR13). The LBL films were adsorbed on glass substrates and characterized with atomic force microscopy with the Ma-co-DR13 at the top layer. The granular morphology exhibited by the films allowed the observation of the growth process inside and outside the grains. The growth outside the grains was found to follow the Kardar-Parisi-Zhang model, with fractal dimensions of ca. 2.6. One could expect that inside the grains the morphology would be close to a Euclidian surface with fractal dimension of ca. 2 for any growth stage. The latter, however, was observed only for thicker films containing more than 10 bilayers. For thinner films the morphology was well described by a self-affine fractal. Such dependence of the growth behavior with the film thickness is associated with a more complete coverage of adsorption sites in thicker films due to diffusion of polymer molecules.

Azo Compounds↗

PubMed2006

Layer-by-layer assembly of mucin and chitosan--Influence of surface properties, concentration and type of mucin.

Bovine submaxillary mucin (BSM) and chitosan were used to build layer-by-layer structures on solid substrates. The build-up was monitored using in situ ellipsometry to obtain time resolved values of the thickness and adsorbed amount. Additionally surface morphology during build-up was studied by atomic force microscopy (AFM). It was found that the adsorbed amount of the film increases approximately linearly with each deposition cycle on hydrophobized silica whereas construction on silica was found not to be possible at the experimental conditions used. We conclude that sufficient amount of the first mucin layer is crucial for the subsequent multilayer formation. The complex build-up kinetics on hydrophobized silica is characterized by adsorption and redissolution processes and the overall growth is the sum of both processes. AFM imaging on hydrophobized silica also confirmed the presence of redissolution processes and chitosan addition led to a reduction both in the number of surface aggregates and in the roughness of the surface. The present work also shows that by adjusting the relative concentrations of the polyelectrolytes it is possible to change the growth rate considerably. The final structures after deposition of 8 bilayers were found to have a high content of water and film stability test revealed that a substantial amount dissolves when increasing electrolyte concentration or pH of the ambient solution. Human mucin from saliva (MUC5B) was also used to create multilayers with chitosan on hydrophobized silica and it was revealed that no redissolution appears to be present in this system.

Adsorption↗

PubMed2006

New loading process and release properties of insulin from polysaccharide microcapsules fabricated through layer-by-layer assembly.

Polysaccharide multilayer microcapsules were fabricated in aqueous media by the layer-by-layer self-assembly of chitosan (CHI) and sodium alginate (ALG) on melamine formaldehyde (MF) microparticles of 2.1 microm diameter as templates, followed by removal of the templates through dissolving at low pH. The loading process was observed with the confocal laser scattering microscope (CLSM) using fluorescence labeled insulin. Insulin was spontaneously loaded into the ALG/CHI microcapsules at pH below its isoelectric point of 5.5 where insulin was positively charged and the loading capacity increased with pH decreasing from 4.0 to 1.0. Because there exited a negatively charged complex of ALG/MF residues inside the microcapsules formed during the MF particle dissolution. A novel two-temperature loading procedure was proposed as loading at 20 degrees C for the first hour and at a higher loading temperature for the second hour. This procedure was very significant that increasing the second loading temperature from 20 to 60 degrees C not only increased the insulin loading capacity, but also slowed down its release rate. The release rate of insulin at pH 7.4 was found much faster than that at pH 1.4 due to the positive charges on the insulin. Cross-linking the ALG in the microcapsule shell with calcium ions (Ca(2+)) or re-sealing the microcapsules with additional layers also remarkably decreased the insulin release rate. The results provide a simple method to control the loading and release of protein molecules within these polysaccharide microcapsules.

Alginates↗

PubMed2001

Direct electrochemistry of hemoglobin in layer-by-layer films with poly(vinyl sulfonate) grown on pyrolytic graphite electrodes.

Stable layer-by-layer electroactive films were grown on pyrolytic graphite (PG) electrodes by alternate adsorption of layers of polyanionic poly(vinyl sulfonate) (PVS) and positively charged hemoglobin (Hb) from their aqueous solutions. Cyclic voltammetry (CV) of [PVS/Hb]n films showed a pair of well-defined and nearly reversible peaks at about - 0.28 V vs. SCE at pH 5.5, characteristic of Hb heme Fe(III)/Fe(II) redox couple. The process of (PVS/Hb) bilayer growth was monitored and confirmed by CV, X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. While the amount of Hb adsorbed in each bilayer was the same, the amount of electroactive Hb in each bilayer decreased dramatically with increase of the number of bilayer, and electroactivity was just extended to 8 [PVS/Hb] bilayers. CVs of [PVS/Hb]8 films maintained stable in buffers containing no Hb. Positions of Soret band of Hb in [PVS/Hb]n films grown on transparent glass slides suggest that Hb in the films keeps its secondary structure similar to its native state in a wide pH range. Trichloroacetic acid and nitrite were catalytically reduced by [PVS/Hb]8 films with significant lowering of the electrode potential required.

Catalysis↗

PubMed2002

Calcium currents in rat entorhinal cortex layer II stellate and layer III pyramidal neurons in acute brain slice.

The entorhinal cortex (EC) is an essential relay station in neocortical - hippocampal information transfer and memory functions. Layer II stellate and layer III pyramidal neurons show specific damage in Alzheimer's disease and epilepsy, respectively. Using whole cell patch clamp recording in rat brain slices we here demonstrate that high voltage activated Ca(2+)-currents (I(Ca)(2+)) are about 1.6-fold bigger in stellate cells than in pyramidal neurons while current density is equal in both cell types. In stellate cells I(Ca)(2+) shows stronger inactivation with depolarization, block of I(Ca)(2+) by Ni(2+) (300 and 600 microM) is more effective, and this block decreases more for currents evoked from a less negative holding potential than in layer III pyramidal neurons. These data indicate distinct molecular composition of Ca(2+)-channels and can partially explain stronger increases of [Ca(2+)](i) during 10 Hz firing activity in EC pyramidal versus stellate neurons.

Animals↗

PubMed2001

Layer-by-layer self-assembly of glucose oxidase and Os(Bpy)2CIPyCH2NH-poly(allylamine) bioelectrode.

The uptake of glucose oxidase (GOx) onto a polycationic redox polymer (PAA-Os)-modified surface, by adsorption from dilute aqueous GOx solutions, was followed by the quartz crystal microbalance (QCM) and shows double exponential kinetics. The electrochemistry of the layer-by-layer-deposited redox-active polymer was followed by cyclic voltammetry in glucose-free solutions, and the enzyme catalysis mediated by the redox polymer was studied in beta-D-glucose-containing solutions. AFM studies of the different layers showed the existence of large two dimension enzyme aggregates on the osmium polymer for 1 microM GOx and less aggregation for 50 nM GOx solutions. When the short alkanethiol, 2,2'-diaminoethyldisulfide was preadsorbed onto gold, a monoexponential adsorption law was observed, and single GOx enzyme molecules could be seen on the surface where the enzyme was adsorbed from 50 nM GOx in water.

Biosensing Techniques↗

PubMed2005

Silver nanowire layer-by-layer films as substrates for surface-enhanced Raman scattering.

In this paper, the fabrication of highly stable, surface-enhanced Raman scattering (SERS) active dendrimer/silver nanowire layer-by-layer (LBL) films is reported. Ag nanowires, approximately 100 nm in diameter, were produced in solution and transferred, using the LBL technique, onto a single fifth-generation DAB-Am dendrimer layer on a glass substrate. The Ag nanowires, and the resulting LBL films were characterized using UV-visible surface plasmon absorbance, while the LBL films were further characterized by atomic force microscopy measurements and surface-enhanced Raman and resonance Raman scattering of several analytes. The dendrimer was found to effectively immobilize the Ag nanowires with increased control over spacing and aggregation of the particles. These films are shown to be excellent substrates for SERS/SERRS measurements, demonstrating significant enhancement, and trace detection capability. Several trial analytes were tested using a variety of excitation energies, and results confirmed effective enhancement of Raman signals throughout the visible range (442-785 nm) with different molecules. Analytes were deposited onto the enhancing Ag nanowire LBL films surface using both casting and Langmuir-Blodgett monolayer transferring techniques.

Dendrimers↗