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PubMed2005

Bioaccumulation and behavioural effects of depleted uranium in rats exposed to repeated inhalations.

Depleted uranium has numerous industrial and military uses. Contamination by inhalation of airborne compounds is probably the most important route of exposure. In humans, there are no data clearly demonstrating neurotoxicity of uranium, yet some experimental studies suggest a link between neurological toxicity and uranium exposure. In this work, the bioaccumulation of uranium in male rats after exposure to repeated depleted uranium dioxide inhalation (30 min inhalation at 197 mgm(-3), 4 days a week for 3 weeks) has been studied, together with the behavioural effects. The uranium concentrations in the brain 1 day after the end of the exposure period varied as follows: olfactory bulb>hippocampus>frontal cortex>cerebellum, subsequently decreasing rapidly. The spontaneous locomotion activity of exposed rats was increased 1 day post exposure and the spatial working memory was less efficient 6 days post exposure, compared with control rats. These data suggest that depleted uranium is able to enter the brain after exposure to repeated inhalation, producing behavioural changes.

Administration, Inhalation↗
PubMed2005

Mechanism of uranium removal from the aqueous solution by elemental iron.

The effectiveness of elemental iron (Fe(0)) to remove uranium (U) from the aqueous phase has been demonstrated. While the mitigation effect is sure, discrepancies in the removal mechanism have been reported. The objective of this study was to investigate the mechanism of U(VI) removal from aqueous phases by Fe(0). For this purpose, a systematic sequence of bulk experiments was conducted to characterize the effects of the availability and the abundance of corrosion products on U(VI) removal. Results indicated that U(VI) removal reactions did not primary occur at the surface of the metallic iron. It is determined that U(VI) co-precipitation with aging corrosion products is a plausible explanation for the irreversible fixation under experimental conditions. Results of XRD analyses did no show any U phases, whereas SEM-EDX analyses showed that U tended to associate with rusted areas on the surface of Fe(0). Recovering U with different leaching solutions varied upon the dissolution capacity of the individual solutions for corrosion products, showing that the irreversibility of the removal depends on the stability of the corrosion products. U(VI) co-precipitation as removal mechanism enables a better discussion of reported discrepancies.

Adsorption↗
PubMed1980

Averages of glutamine synthetase molecules as obtained with various skin and electron dose conditions.

Averaged projections of individual glutamine synthetase molecules have been obtained by using electron microscopy and image processing. The methodology of correlation averaging under low dose conditions is described in detail. Because of their low signal-to-noise ratio, images made under low dose conditions cannot be directly interpreted in terms of high resolution features. Computer averaging of these images reveals a division of the subunit projection into two domains whose sizes agree with results of Lei et al [2] limited proteolysis experiments.

Chemical Phenomena↗
PubMed1984

A method for increasing the surface details of resin embedded viruses using Congo/Crimean haemorrhagic fever virus as a model.

The surface details of resin embedded viruses can be greatly enhanced by the use of uranyl acetate block staining. The virions are embedded in agar immediately after fixation and block stained with 3% uranyl acetate in methanol during dehydration. This technique allows those particles outside their host cells to show clearly the spikes normally seen only by the separate use of negative staining.

Bunyaviridae↗
PubMed2001

Improved determination of tributyl phosphate degradation products (mono- and dibutyl phosphates) by ion chromatography.

Tributyl phosphate (TBP) is a very important compound in the nuclear industry, particularly in the area of nuclear fuel reprocessing. This compound is used in the PUREX (plutonium and uranium refining extraction) process which consists of the extraction of uranium and plutonium from an aqueous nitric acid phase, for the purpose of recycling. But TBP may be degraded to dibutyl phosphate (DBP) and monobutyl phosphate (MBP) by dealkylation of one or two butoxy groups, respectively. We have compared and evaluated the capacity of two resins manufactured by Dionex (AS11 and AS5A) in the separation and measurement of these two degradation products. AS11 generates two interferences: nitrite/DBP and carbonate/MBP. The first one is the most serious. So, we have developed a method for oxidising nitrite ions to nitrate ions which have no trouble over the measurement. The second resin tested, AS5A, allows a very efficient separation between DBP and NO2- ions and a good separation between MBP and CO3(2-) in comparison with the AS11. The detection limits for the AS5A column are 0.13 microM for MBP and 0.71 microM for DBP (injection loop=50 microl).

Calibration↗
PubMed1983

Gap junction structures. IV. Asymmetric features revealed by low-irradiation microscopy.

Micrographs of mouse liver gap junctions, isolated with detergents, and negatively stained with uranyl acetate, have been recorded by low-irradiation methods. Our Fourier-averaged micrographs of the hexagonal junction lattice show skewed, hexameric connexons with less stain at the threefold axis than at the six indentations between the lobes of the connexon image. These substructural features, not clearly observed previously, are acutely sensitive to irradiation. After an electron dose less than that normally used in microscopy, the image is converted to the familiar doughnut shape, with a darkly stained center and a smooth hexagonal outline, oriented with mirror symmetry in the lattice. Differences in appearance among 25 reconstructed images from our low-irradiation micrographs illustrate variation in staining of the connexon channel and the space between connexons. Consistently observed stain concentration at six symmetrically related sites approximately 34 A from the connexon center, 8 degrees to the right or left of the (1, 1) lattice vector may reveal an intrinsic asymmetric feature of the junction structure. The unexpected skewing of the six-lobed connexon image suggests that the pair of hexagonal membrane arrays that form the junction may not be structurally identical. Because the projected image of the connexon pair itself appears mirror symmetric, each pair may consist of two identical connexon hexamers related by local (noncrystallographic) twofold axes in the junctional plane at the middle of the gap. All connexons may be chemically identical, but their packing in the hexagonal arrays on the two sides of the junction appears to be nonequivalent.

Animals↗
PubMed1983

Visualization of longitudinally-oriented intermediate filaments in frozen sections of chicken cardiac muscle by a new staining method.

When ultrathin frozen sections of chicken cardiac muscle were osmicated, dehydrated in ethanol, embedded in ethyl cellulose, and stained with acidic uranyl acetate, filaments of 10-12 nm width were visualized in wide interfibrillar spaces. Immunostaining of the frozen sections for desmin resulted in exclusive labeling of such filaments. These observations indicated that longitudinally oriented networks of intermediate filaments were present in the interfibrillar spaces, in addition to the transversely oriented networks that surround myofibrils at the level of Z band. As in skeletal muscle (Tokuyasu, K. T., A. H. Dutton, and S. J. Singer, 1983, J. Cell Biol. 97:1727-1735), desmin in chicken cardiac muscle is believed to be largely, if not entirely, in the form of intermediate filaments.

Animals↗
PubMed1984

A quantitative ultrastructural evaluation of the cell organelle specificity of the uranaffin reaction in normal human platelets.

The purpose of this study was to determine the normal variation in the number of uranaffin-positive organelles in normal human platelets and to study the effect of pH and fixation on the uranaffin reaction. The normal variation in uranaffin organelles was determined by studying platelets from nine normal subjects. At pH 3.9, the mean number of reactive sites/platelet profile was 0.43 +/- 0.10 when platelets were fixed with lower glutaraldehyde concentrations and 0.56 +/- 0.24 with higher glutaraldehyde concentrations. Fixed platelets were reacted at pH 2.8, 3.9, 5.0, and 7.0 with four different uranaffin procedures that varied in the extent of fixation and rinse steps (isotonic saline vs. cacodylate buffer). The number of uranaffin-positive sites in 200 platelet profiles was scored under the electron microscope. There was a progressive increase in the number of reactive sites/platelet profile as the pH increased from 2.8 to 7.0. In general, higher pH favored granule matrix and core staining, whereas low pH favored both the staining of granule membranes and their contents. The uranaffin reaction showed organelle specificity when run under certain experimental conditions. At low pH and using isotonic saline in the rinse steps, only the dense bodies and ribosomes stained. The biochemical content of the dense body responsible for uranaffin reactivity is discussed.

Blood Platelets↗
PubMed1982

Specificity of stain distribution in electron micrographs of protein molecules contrasted with uranyl acetate.

The mechanism of contrast enhancement of protein molecules by negative staining with uranyl acetate has been investigated by analysing electron micrographs of microcrystals of the human immunoglobulin Dob. Digitally filtered micrographs were compared systematically with idealized reference images which were constructed computationally, starting from knowledge of the primary sequence and three-dimensional crystal structure of this IgG molecule. By separately modelling negative staining as bulk exclusion of heavy metals, and positive staining as the specific decoration of charged amino acid residues, and then combining these simulated images, we were able to assess quantitatively the amount of positive staining present in micrographs of ostensibly 'negatively stained' proteins. At a resolution of 2 nm, we find that the experimental images do indeed exhibit predominantly negative staining, the best matches being obtained by simulations which also include a minor contribution (10-40%) of positive staining. We have also compared two independent measures for the significant resolution present in images of periodic biological specimens: (i) the outermost visible orders of optical diffraction patterns, and (ii) the band-limited resolutions of the idealized simulations when they most closely match the experimental images. These criteria observe close correspondence, thus vindicating the traditional practice of inferring resolution from the optical diffraction spectra of indirectly represented (stained) objects.

Computers↗
PubMed1985

Lowicryl K4M embedding of brain tissue for immunogold electron microscopy.

We present methods for embedding brain tissue in Lowicryl K4M embedding medium and localizing antigens using postembedding immunogold techniques. After perfusion fixation with 4% paraformaldehyde and 0.1% glutaraldehyde in 0.1 M cacodylate buffer, blocks of rat brain were placed in 2% aqueous uranyl acetate for 1 hour, dehydrated in 50%, 70%, and 95% ethanol, infiltrated with Lowicryl/ethanol mixtures (1:2 for 10 min, 1:1 for 15 min) and 100% Lowicryl (20 min and 25 min). Polymerization was carried out under UV light for 24-48 hours at room temperature. Several neural antigens, including three different synaptic vesicle proteins and an enzyme associated with the postsynaptic density, were localized by this technique, indicating that this procedure may have wide applicability.

Acrylic Resins↗
PubMed1982

Use of hydrogen peroxide to accelerate staining of ultrathin Spurr sections.

Pretreatment of ultrathin Spurr sections of glutaraldehyde-osmium fixed tissue with hydrogen peroxide significantly reduces the time required to stain with ethanolic uranyl acetate and lead citrate for electron microscopy. Micrographs compare contrast obtained by this method with that obtained using conventional staining times. Reasons for the facilitating action of hydrogen peroxide are suggested.

Citrates↗