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At least 667 records · Page 37Linked to original sources
PubMed1984

Antitubulin immunofluorescence studies of spermatogenesis in the mouse.

Immunofluorescence staining techniques, using antibodies against tubulin molecules, have been successfully used with somatic tissue culture cells. Their application to gametogenesis, however, has been more difficult, largely due to the presence of many different cell types in such a preparation. We have circumvented this problem by counterstaining with dilute hematoxylin, a biological stain that shows excellent cellular morphology without affecting the fluorescence of the antibody. We can then photograph the same field, using either ultraviolet light or conventional bright-field microscopy. Using this approach, we have examined the entire progression of murine spermatogenesis, from spermatogonial cells through mature spermatozoa. This technique has been especially valuable in the visualization of the manchette, and has allowed a reassessment of the staging of spermatid development. In the future, the antibody/hematoxylin double-staining approach will allow a more informative examination of the effects of tubulin-active mitotic poisons on mammalian germline cells.

Animals↗
PubMedDate not supplied

The morphology and physiology of a "mini-ommatidium" in the median optic nerve of Limulus polyphemus.

Examination of the Limulus median optic nerve with low-magnification light microscopy allows clear visualization of an ultraviolet-sensitive mini-ommatidium enshrouded by pigment cells, glial cells, and guanophores. Serial 1-micron sections of median optic nerves containing mini-ommatidia revealed the presence of a single, heavily pigmented photoreceptor (retinular) cell and a single, unpigmented arhabdomeric cell. Computer-assisted serial reconstructions from 1-micron sections confirmed the presence of two cells, each bearing a nucleus, and two axons leaving the mini-ommatidium. The retinular cell is morphologically similar to retinular cells from the median and lateral eyes. Its rhabdomere appears to be a continuous sheet of microvilli with much infolding. The structure of the arhabdomeric cell is nearly identical to those found in the median ocellus. As in other photoreceptors in Limulus, the retinular cell of the mini-ommatidium is innervated by efferent fibers from the brain. Each mini-ommatidium generates a single train of nerve impulses in response to light, presumably from the arhabdomeric cell. Measurement of the spectral sensitivity of the mini-ommatidium based upon a constant-response criterion indicated that the retinular cell is maximally sensitive to near ultraviolet light with lambda max = 380 nm. Comparison of intensity-response functions revealed that those of the mini-ommatidium are significantly steeper than those of the ocellus almost certainly as the result of neural processing in the ocellus which is absent in the mini-ommatidium.

Animals↗
PubMed2006

Verification of compliance with organic meat production standards by detection of permitted and nonpermitted uses of veterinary medicines (tetracycline antibiotics).

In the production of "organic" meat, one of the controlled processes is the use of veterinary drugs. Strict standards are in place as to when and how such drugs may be used. Therefore, the aim of this project was to determine whether it was possible to distinguish between a single therapeutic dose of a tetracycline (permitted under the standards) and both multiple therapeutic dosing and prophylactic dosing (not permitted). This comprised an evaluation of (i) pigs that were treated with oxytetracycline and (ii) chickens dosed with two different tetracycline antibiotics (oxytetracycline and chlortetracycline). The methodology described, using bone sectioning and examination under ultraviolet illumination (either direct observation or fluorescent microscopy), allows samples from animals that have been treated with different dosing regimes (a single therapeutic dose, two successive therapeutic doses, and long-term, low-level "prophylactic" dosing) to be assessed for compliance with organic farming regulations. Validation of the methodology by blind checks of unknown samples by a second operator has been successfully performed, and validation results are presented. The developed methodology has been shown to be applicable to a variety of species and a selection of tetracycline drugs.

Animals↗
PubMed2006

Self-organized monolayer of nanosized ceria colloids stabilized by poly(vinylpyrrolidone).

Four nanometer colloidal ceria nanocrystals in a fluorite cubic structure have been synthesized via an alcohothermal treatment at 180 degrees C for 24 h from Ce(NO(3))(3)*6H(2)O in ethanol, using various alkylamines including triethylamine, butylamine, and hexadecylamine as the bases and poly(vinylpyrrolidone) (PVP) as the stabilizer. They were characterized by multiple measurements of X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), ultraviolet visible (UV-vis) spectroscopy, dynamic light scattering (DLS), and infrared spectroscopy (IR). The introduction of PVP could effectively stabilize the cerium nuclei against self-aggregation and finally lead to the formation of the CeO(2) colloids. As compared with that of their precipitated counterparts, the UV-vis spectra showed a blue-shifted absorption edge for the as-obtained colloidal nanocrystals, revealing that their surfaces were well-passivated by PVP. Four types of self-organized monolayer patterns (i.e., isolated particles, short chainlike (pseudo-1-D aggregated), pearl necklace-like (1-D aggregated), and dendritic (pseudo-2-D aggregated) alignments) appeared for the as-obtained colloidal particles on the copper TEM grids, due to the delicate balance of the attractive and repulsive forces between the PVP-passivated CeO(2) nanocrystals during the irreversible evaporation of the solvent from various colloidal solutions under ambient conditions. The type of alkylamine and the concentration of PVP were confirmed to be the crucial factors determining the oriented-aggregation dimensionality of the CeO(2) colloids. Possible interparticle interaction modes have been suggested to explain such complex self-organization patterns exhibited by the as-obtained CeO(2) nanocrystals.

Journal Article↗
PubMed2004

Structural and chemical characterization of monofluoro-substituted oligo(phenylene-ethynylene) thiolate self-assembled monolayers on gold.

Monolayers of oligo(phenylene-ethynylene) (OPE) molecules have exhibited promise in molecular electronic test structures. This paper discusses films formed from a novel molecule within this class, 2-fluoro-4-phenylethynyl-1-[(4-acetylthio)phenylethynyl]benzene (F-OPE). The conditions of self-assembled monolayer (SAM) formation were systematically altered to fabricate reproducible high-quality molecular monolayers from the acetate-protected F-OPE molecule. Detailed characterization of the F-OPE monolayers was performed by using an array of surface probes, including reflection absorbance infrared spectroscopy (RAIRS), contact angle (CA) measurements, spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and atomic force microscopy (AFM). XPS and RAIRS established that the SAM formed without removal of the F substituent and without oxidation of the thiol. The monolayer thickness, determined from SE and AFM based nanolithography, was consistent with the formation of a densely packed monolayer. The valence electronic structure of the SAM was consistent with an aromatic structure shifted by the electron-withdrawing fluorine substituent and intermolecular coupling within an oriented array of molecules.

Journal Article↗
PubMed2004

Electrostatic layer-by-layer assembled carbon nanotube multilayer film and its electrocatalytic activity for O2 reduction.

Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.

Journal Article↗
PubMed2006

Preparation and structure of a low-density, flat-lying decanethiol monolayer from the densely packed, upright monolayer on gold.

This study investigates the formation of low-density, flat-lying decanethiol chemisorbed on Au prepared by heating the surface covered with a densely packed, upright monolayer to a surface temperature above that of the onset of desorption. We determined conditions for preparing the low-density phase by observing the evolution of the photoemission spectrum as a function of the surface temperature using polarized ultraviolet light and by utilizing scanning tunneling microscopy. The preparation conditions were similar for single- and polycrystalline gold surfaces. Once the low-density decanethiol phase was formed, reflection absorption infrared spectroscopy was employed to determine the orientation of the carbon chain backbone with respect to the Au surface. The nature of the valance electronic structure for flat-lying decanethiol is described.

Journal Article↗
PubMedDate not supplied

Preparation and analgesic activity of Eudragit RS100 microparticles containing diflunisal.

Two different techniques, the quasi-emulsion solvent diffusion method and spray drying that provide polar and nonpolar preparation environments, were used to prepare microspheres from Eudragit RS100 (RS) (acrylic/methacrylic copolymer) incorporating the nonsteroidal anti-inflammatory drug diflunisal. The effects of pH on the preparation medium and drug/polymer ratio on production yield and drug incorporation, as well as on the in vitro drug release at pH 1.2 and 6.8 from tabletted microparticles, were evaluated. The drug-polymer interactions and the effect of diflunisal incorporation in the polymer matrix on drug crystallinity have been evaluated by using differential scanning calorimetry, IR and ultraviolet spectroscopy, x-ray diffraction, and microscopy analysis. A preliminary biological assay confirmed that diflunisal maintains its analgesic activity after intraperitoneal administration to rats.

Acrylic Resins↗
PubMed2003

Confined Shockley surface states on the (111) facets of gold clusters.

Combining low-temperature scanning tunneling microscopy and spectroscopy with high-resolution ultraviolet photoemission, we have revealed a confined Shockley surface state on the (111) facets of gold clusters with about N=10(4) atoms grown in nanopits on highly oriented graphite. With tunneling spectroscopy, we observed energy dependent nodal patterns in the dI/dV maps, which are in quantitative agreement with the two-dimensional confinement of the surface state within the hexagonal facet area. The results indicate that the lattice of the ionic cores influences the electronic properties of the clusters significantly.

Journal Article↗
PubMed2006

Preparation of poly(diiododiacetylene), an ordered conjugated polymer of carbon and iodine.

Conjugated organic polymers generally must include large substituents for stability, either contained within or appended to the polymer chain. In polydiacetylenes, the substituents fulfill another important role: During topochemical polymerization, they control the spacing between the diyne monomers to produce an ordered polymer. By using a co-crystal scaffolding, we have prepared poly(diiododiacetylene), or PIDA, a nearly unadorned carbon chain substituted with only single-atom iodine side groups. The monomer, diiodobutadiyne, forms co-crystals with bis(nitrile) oxalamides, aligned by hydrogen bonds between oxalamide groups and weak Lewis acid-base interactions between nitriles and iodoalkynes. In co-crystals with one oxalamide host, the diyne undergoes spontaneous topochemical polymerization to form PIDA. The structure of the dark blue crystals, which look copper-colored under reflected light, has been confirmed by single-crystal x-ray diffraction, ultraviolet-visible absorption spectroscopy, and scanning electron microscopy.

Journal Article↗
PubMed2000

Strength of irradiated bone.

A surface of the bone is a site, where the highest mechanical tensions are developed. Therefore, this place has a special importance to provide the strength. The latter depends on a bone tissue atomic/molecular structure. The present report reviews recent results demonstrating how damaged atomic/molecular bonds situated in the surface layer (interface) of the bone have an influence on its strength. The bonds were excited owing to ultraviolet radiation (UR) supplied by a Mercury tube. As the result the strength was decreased. To explore the reason of this phenomenon the atomic force microscopy operated in a tapping mode (AFM) and photoelectron (PE)/exoelectron (EE) analysis was applied. AFM demonstrated a surface topography varied from a homogenize to an island-type under UR. Such a behavior was repeated periodically in monotonically increased radiation exposure. Selective etching of the bone evidenced that reconstruction of the interface layer coupling mineral and organic phases stipulated such a synergetic. EE demonstrated a concentration of destroyed bonds also had a similar regularity depended on exposure. PE measurements discovered responsible for this centres placed at 5.35 and 5.65 eV below a vacuum level.

Animals↗
PubMed1975

Detection by electron microscopy of photo-induced denaturation in lambda DNA.

We have used an electron microscope to study localized denatured regions in ultraviolet-irradiated DNA. DNA from bacteriophage lambda was UV-irradiated and then prepared for electron microscopy after fixing in buffered (pH 9.5) formaldehyde solutions at 25 degrees C. The denatured regions observed corresponded to those described by Inman and Schnös (1) who used alkaline denaturation to preferentially destroy thymine-adenine base pairing. In UV-irradiated DNA, pairs of neighboring thymine residues are converted into photodimers; hence, loss of hydrogen bonding most likely occurs in thymine-rich regions and denaturation results. Conceivably, photo-induced denaturation may under some circumstances represent a more convenient method than alkaline denaturation for mapping thymine-rich regions in DNA.

Coliphages↗
PubMed1994

Ultraviolet-B irradiation deforms the configuration of elastic fibers during the induction of actinic elastosis in rats.

We used scanning electron microscopy combined with perfusion fixation, resin injection and a selective digestion procedure to determine the effects of ultraviolet-B (UVB) radiation on the three-dimensional architecture of elastic fibers of rat skin. Chronic irradiation with a suberythematous dose of UVB (3 times/week for 12 weeks) produced a tortuous deformation of the superficial elastic fibers in the skin of the rat sole which normally are linearly arranged. Using computer analysis, we evaluated 40 individuals elastic fibers every 3 weeks for 12 weeks following the irradiation. This procedure confirmed the increasing tortuosity of the fibers, which was related to a decline in the elastic property of the skin in situ. Fine elastic branches developed among the deformed fibers and eventually anastomosed to produce an irregular network in the superficial dermal connective tissue, which may correspond to the development of actinic elastosis, that is, the UV-related accumulation of elastic fiber material.

Animals↗