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  • 1
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The immature brain is prone to seizures but the underlying mechanisms are poorly understood. We explored the hypothesis that increased seizure susceptibility during early development is due to the excitatory action of GABA. Using noninvasive extracellular field potential and cell-attached recordings in CA3 of Sprague-Dawley rat hippocampal slices, we compared the developmental alterations in three parameters: excitatory actions of GABA, presence of the immature pattern of giant depolarizing potentials (GDPs) and severity of epileptiform activity generated by high potassium. The GABA(A) receptor agonist isoguvacine increased firing of CA3 pyramidal cells in neonatal slices while inhibiting activity in adults. A switch in the GABA(A) signalling from excitation to inhibition occurred at postnatal day (P) 13.5 ± 0.4. Field GDPs were present in the form of spontaneous population bursts until P12.7 ± 0.3. High potassium (8.5 mm) induced seizure-like events (SLEs) in 35% of slices at P7–16 (peak at P11.3 ± 0.4), but only interictal activity before and after that age. The GABA(A) receptor antagonist bicuculline reduced the frequency or completely blocked SLEs and induced interictal clonic-like activity accompanied by a reduction in the frequency but an increase in the amplitude of the population spikes. In slices with interictal activity, bicuculline typically caused a large amplitude interictal clonic-like activity at all ages; in slices from P5–16 rats it was often preceded by one SLE at the beginning of bicuculline application. These results suggest that, in the immature hippocampus, GABA exerts dual (both excitatory and inhibitory) actions and that the excitatory component in the action of GABA may contribute to increased excitability during early development.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Eigenschaften eines polymerisierbaren Farbstoffes, N-Methyl-N-[4-(2,5-dichlorphenyl)azophenyl]-2-aminoethyl-methacrylat (I), seine Polymerisation und die Eigenschaften des Polymerisates wurden untersucht. Die Copolymerisations-Parameter (r1, r2) von I mit Styrol (St), Methylmethacrylat, N,N-Dimethyl-2-aminoethylmethacrylat, 2,2,2-Trichlorethylmethacrylat und Methacrylsäure in benzolischer Lösung bei 50°C mit Azoisobutyronitril als Initiator, als auch die Copolymerisationsge-schwindigkeiten, wurden bestimmt. Aus den Werten r1, r2 für das System I/St wurden die Alfrey-Price Konstanten e und Q von I berechnet. Der Verzögerungseffekt der Azogruppe bei der Homo- und Copolymerisation von I wurde durch die Bestimmung der Verhaltnisse von den Geschwindigkeitskonstanten der Polymerradikaladdition an die Modell-Azoverbindung sowie an das Monomere abgeschatzt. Die Dielektrizitats-konstanten der Monomeren und ihrer Ldsungen wurden gemessen und der Einfluß der intermolekularen Wechselwirkung der Comonomeren auf die Copolymerzusam-mensetzung wurde diskutiert.
    Notes: The properties of a polymerizable dye, N-methyl-N-[4-(2,5-dichlorophenyl)azophenyl]-2-aminoethyl methacrylate (I), its homopolymerization and the properties of the homopolymer were characterized. The copolymerization parameters (r1, r2) of I with styrene (St), methyl methacrylate (MMA), N,N-dimethyl-2-aminoethyl methacrylate, 2,2,2-trichloroethyl methacrylate and methacrylic acid and the rates of copolymerization were determined in benzene solution at 50°C with 0.01 M 2,2′-azobisisobutyronitrile as initiator. The Alfrey-Price e and Q constants were calculated for I using the r1, r2 values for the system I/St. The retardative effect of the azo group in the homopolymerization and copolymerization of I was evaluated by determining the ratio of rate constants of addition of polymer radicals to the model azo compound and to the monomer in the homopolymerization of St and MMA. The relative permittivities of monomers and their solutions were measured, and the effect of the molecular interaction of comonomers on the composition of the copolymers was discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein technischer Anthrachinonfarbstoff wurde durch GPC, Massenspektroskopie und Elementaranalyse charakterisiert. Neben der polymerisierbaren Komponente, N-[4-Amino-3-methoxy-anthrachinonyl-(1)]methacrylsäureamid (I), enthielt er eine gesättigte Beimischung, N-[4-Amino-3-methoxy-anthrachinonyl-(1)]-2-chlor-2-methylpropionsäureamid (II). Es wurde die Homopolymerisation von I und die Isolierung und Charakterisierung der Beimischung II durchgeführt. Die Copolymerisation des Farbstoffs mit Styrol und Methylmethacrylat wurde untersucht, und der Verzögerungseffekt von II auf die Polymerisation dieser Monomeren wurde abgeschätzt.
    Notes: A technical dye of the anthraquinone type was analyzed by GPC, mass spectroscopy, and elemental analysis. Along with the polymerizable component, N-[4-amino-3-methoxyanthraquinonyl-(1)] methacrylamide (I), it contained a saturated admixture, N-[4-amino-3-methoxyanthraquinonyl-(1)]-2-chloro-2-methylpropionamide (II). The homopolymerization of I was carried out, and admixture II was isolated and characterized. The copolymerization of the dye with styrene and methyl methacrylate was verified, and the retardation effect of II on the polymerization of these monomers was evaluated.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Radical copolymerization of a nitro group containing azo-dye monomer (1) and methyl methacrylate leads to significantly higher polymerization rates and higher molecular weights when dispersion technique is used instead of solution polymerization. The preparation of mechanically stable coatings and free films with good mechanical properties and transparency for electro-optical investigations is possible by a spin coating technique with the dispersion copolymers. The dye side chains of these copolymers can be poled in an electric field. The orientation of the side chains leads to a change of the light absorption in the dye absorption band. Results of m-line spectroscopy show that the copolymers possess wave guiding properties.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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