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  • Chemistry  (24)
  • aging  (3)
  • Conducting polymers  (2)
  • 1990-1994  (27)
  • 1
    ISSN: 1573-6903
    Keywords: Phosphate-activated glutaminase ; aging ; Fischer-344 rat ; ammonia ; glutamate ; glutamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The regulation of PAG by ammonia in whole brain (Sprague-Dawley) and regional (Fischer-344) synaptosomal preparations from adult and aged animals was assessed. Whole brain synaptosomal preparations from both age groups displayed a significant decrease in PAG activity with increasing ammonium chloride concentrations, however, the aged rats exhibited a significant attenuation in ammonia-induced PAG inhibition. PAG activity measured in synaptosomes prepared from the striatum (STR), temporal cortex (TCX) and hippocampus (HIPP) was also inhibited by ammonium chloride. The STR showed the greatest degree of ammonia-induced PAG inhibition (55%) followed by the HIPP (30–35%) and the TCX (25–30%). This reduction in PAG activity was significantly attenuated in STR from aged rats at ammonium chloride concentrations greater than 50 μM and in the TCX, PAG activity was significantly attenuated in the aged rats at ammonia concentrations of 0.5 and 1.0 mM. Ammonia regulation of PAG activity in the HIPP appeared to be unaffected by age. Ammonium chloride concentrations up to 5 mM had no effect on GLU release from cortical slices, although GLN efflux was significantly enhanced. These findings suggest that isozymes of PAG may exist in different brain regions based on their differential sensitivity to ammonia. The attenuation of ammonia-induced PAG inhibition seen in aged rats may have deleterious effects in the aged brain.
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  • 2
    ISSN: 1573-6903
    Keywords: Glutaminase ; calcium ; phosphate ; aging ; Fischer-344 ; cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Regional regulation of glutaminase by phosphate and calcium was examined in the temporal cortex (TCX), striatum (STR) and hippocampus (HIPP) from adult and aged male F344 rats. Phosphate-dependent glutaminase activity in adult rats was significantly lower (35–43%) in the HIPP (100 and 150 mM) and STR (150 mM) compared to PAG activity in the TCX. Phosphate activation in aged rats was 50–60% lower in the HIPP at concentrations greater than 25 mM compared to the aged TCX or STR. PAG activity in the TCX and STR was unaffected by age, but was significantly reduced (30–50%) in the HIPP from aged rats at phosphate concentrations of 25 mM and greater when compared to adult rats. In adult rats at concentrations of CaCl2 above 1 mM, PAG activity was significantly lower (60–75%) in the STR and HIPP when compared to the TCX. In aged rats, PAG activity (1 mM CaCl2) in the HIPP was significantly less (50%) than STR PAG activity in aged rats. Diminished PAG activity was seen only in the TCX (2.5 mM; 32%), and the HIPP (0.5 mM; 25% and 1 mM; 38%) at higher calcium concentrations compared to adult. Phosphate-independent calcium activation of PAG occurred in the HIPP but not in either the TCX or the STR. Addition of phosphate resulted in a synergistic activation of PAG in the STR and TCX, but not in the HIPP. These findings suggest that PAG is regionally regulated by phosphate and calcium, and this regulation is impaired in aged rats. These data also support the hypothesis that isozymes of PAG exist with different regulatory properties.
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  • 3
    ISSN: 1573-6903
    Keywords: Monosodium-L-glutamate ; aging ; neurotransmitters ; Fischer 344
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Peripheral administration of monosodium-L-glutamate (MSG) has been found to be neurotoxic in neonatal rats. When administered in an acute, subconvulsive dose (500 mg/kg i.p.), MSG altered neurotrnnsmitter content in discrete brain regions of adult (6 month old) and aged (24 month old) male Fischer-344 rats. Norepinephrine (NE) content was reduced in both the hypothalamus (16%) and cerebellum (11%) of adult rats, but was increased in both the hypothalamus (7%) and cerebellum (14%) of aged rats after MSG treatment. MSG also altered the dopamine content in adult rats in both the posterior cortex and the striatum, causing a reduction (23%) and an increase (12%), respectively. Glycine content in the midbrain of aged rats increased (21%) after MSG injection. Of particular interest is the widespread monoamine and amino acid deficits found in the aged rats in many of the brain regions examined. NE content was decreased (11%) in the cerebellum of aged rats. Dopamine content was reduced in both the posterior cortex (35%) and striatum (10%) of aged rats compared to adult animals. Cortical serotonergic deficits were present in aged rats with reductions in both the frontal (13%) and posterior cortex (21%). Aged rats also displayed deficits in amino acids, particularly the excitatory amino acids. There were glutamate deficits (9–18% reductions) in the cortical regions (posterior and frontal) as well as midbrain and brain stem. Aspartate, the other excitatory amino acid transmitter, was reduced 10% in the brainstem of aged rats. These data indicate that an acute, subconvulsive, dose of MSG may elicit neurochemical changes in both adult and aged male Fisher-344 rats, and that there are inherent age-related deficits in particular neurotransmitters in aged male Fisher-344 rats as indicated by the reductions in both monoamines and amino acids.
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  • 4
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Collagen-silicone composites were fabricated and tested for biocompatibility by subcutaneous implantation in rats. The silicone component consisted of addition cure or condensation cure sheets. The collagen component was either (a) a sponge layer 2 mm thick, (b) a thin film 12-20 μm thick, or (c) residual collagen bonded to or incorporated in the silicone rubber. Collagen sponges were mechanically bonded to silicone sheets, and collagen thin films and residual collagen were physically and chemically attached to epoxyderivatized silicone sheets. Analysis of implanted samples showed that reduced capsule formation occurred around collagen spongesilicone, compared to control silicone sheets. Only where the underlying silicone sheet, or interpenetrating silicone, was exposed to the tissue, did limited capsule formation occur. In contrast, thin capsule developed completely around silicone coated with a thin collagen film and around silicone bonded to residual collagen. Sponge-silicone composites and control silicone sheets were free of acute and chronic inflammation, except for occasional foreign body giant cells in sponge adjacent to silicone. Silicone coated with micron-thick collagen films exhibited some inflammation, but residual collagen-silicone did not. This study suggests that, to prevent capsule formation, a collagen coat must be of minimum thickness and surface coverage sufficient to prevent any contact between silicone and tissue. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 35 (1994), S. 197-205 
    ISSN: 0959-8103
    Keywords: polyaniline ; inverse chromatography ; thin layer chromatography ; amino acids ; characterisation of chemical interactions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Inverse thin layer chromatography is used to characterise the chemical interactions that occur on polyaniline that has been electrochemically deposited on to a support. Amino acids are used as the molecular probe species by which the retention behaviour can be related to particular chemical interactions. The mobile phase is also varied, with respect to its polarity and pH, in order to add a further dimension to the qualitative information that is obtained. Anion exchange interactions are found to be the dominant interaction type. However, the behaviour seems to be different to that which occurs on conventional anion exchange materials. The behaviour was dependent upon the number of negative sites and also their spatial arrangement. A configurational-selective ionic interaction with the polaron lattice of the polyaniline is proposed. The response of the anion exchange behaviour to a change of pH suggested that protonated sites remained within the polymer, even at high pH values (c 9).
    Additional Material: 4 Ill.
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  • 6
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: An analytical strategy for quantifying the diffusion of 18O in small, melt-grown single-crystal Yba2Cu3O7-x superconductors by image depth profiling SIMS is presented. This technique was used to obtain data for both in-depth (along the c-axis) and lateral (in theab-plane) diffusion from one superconducting crystal. Cross-sectional images, generated from the image depth profiling data, revealed features of the diffusion processes that would not have been apparent in a standard depth profile. Retrospective selected area depth profiling was used to remove the influence of background species, edge effects and imperfections in the crystals, resulting in processed depth profiles with greater dynamic range. These techniques also were used to study the diffusion behavior of fluorine that was unexpectedly incorporated into the superconduting crystals during preparation. Finally, the influence of detector artifacts on the analytical results was evaluated.
    Additional Material: 13 Ill.
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  • 7
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The relatively low levels of human salivary proteins in whole saliva as compared to the ductal secretions may be related to their interaction with oral bacteria. These interactions are thought to play an important role in the microbial colonisation of the mouth, and salivary proteins adsorbed to oral surfaces have been implicated in adherence. In this study we attempted to investigate the prevalence of interactive strains by screening a range of oral bacteria. Parotid saliva was incubated with bacterial suspensions and consequent alterations to the salivary protein profile determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A number of salivary components were found to be preferentially removed, particularly by those species known to be primary colonisers of clean tooth surfaces.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Brookfield, Conn. : Wiley-Blackwell
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Plastisol rheological characteristics are of prime importance to the formulator and processor. As the formulas become more complicated, interactions can occur between ingredients that have significant effects on rheology. This paper explores aspects of the resin-CaCO3 filler interaction. Experiments investigating some of the effects of resin-filler interaction on rheological behavior have been performed. The experiments indicate that particle size distributions of the resin and filler, as they relate to packing efficiency, have a significant effect on rheological behavior, especially at high filler concentrations. The effects of particle packing vs. oil absorption are also investigated and discussed.
    Additional Material: 6 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Advanced Materials 6 (1994), S. 798-802 
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 4 Ill.
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  • 10
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Injectable collagen is a concentrated dispersion of collagen fibers in aqueous solution that is used to correct dermal contour defects through intradermal injection. The effect of hydrophobic forces on the rheology of concentrated dispersions of collagen fibers was studied by dynamic rheological measurements over temperatures ranging from 283 to 308 K. The results are interpreted in terms of the associated relaxation time spectra and the theory of Kamphuis et al. for concentrated dispersions. Increases in fiber rigidity are seen from a progressive decrease in the slope of the linear log G′ (or G″) vs. log ω data recorded for these dispersions as temperature is increased. A molecular interpretation of this result was obtained by treating collagen fibers as a liquid crystalline phase of rigid-rod collagen molecules that have phase-separated from aqueous solution. Hydrophobic forces affect the volume fraction of water that is present in the phase-separated fibers, which, in turn, affects the rigidity of the fibers. Distinct yielding behavior (in the nonlinear viscoelastic region) occurs at temperatures above 293 K and reflects a gel transition. Thermal gelation of collagen dispersions is proposed to proceed through hydrophobically driven mechanisms of increased fiber rigidity and enhanced interfiber attractive forces. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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