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  • 1
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    Importance of AMPA receptors for hippocampal synaptic plasticity but not for spatial learning (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-06-12
    Description: Gene-targeted mice lacking the L-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit GluR-A exhibited normal development, life expectancy, and fine structure of neuronal dendrites and synapses. In hippocampal CA1 pyramidal neurons, GluR-A-/- mice showed a reduction in functional AMPA receptors, with the remaining receptors preferentially targeted to synapses. Thus, the CA1 soma-patch currents were strongly reduced, but glutamatergic synaptic currents were unaltered; and evoked dendritic and spinous Ca2+ transients, Ca2+-dependent gene activation, and hippocampal field potentials were as in the wild type. In adult GluR-A-/- mice, associative long-term potentiation (LTP) was absent in CA3 to CA1 synapses, but spatial learning in the water maze was not impaired. The results suggest that CA1 hippocampal LTP is controlled by the number or subunit composition of AMPA receptors and show a dichotomy between LTP in CA1 and acquisition of spatial memory.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zamanillo, D -- Sprengel, R -- Hvalby, O -- Jensen, V -- Burnashev, N -- Rozov, A -- Kaiser, K M -- Koster, H J -- Borchardt, T -- Worley, P -- Lubke, J -- Frotscher, M -- Kelly, P H -- Sommer, B -- Andersen, P -- Seeburg, P H -- Sakmann, B -- New York, N.Y. -- Science. 1999 Jun 11;284(5421):1805-11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Molecular Neuroscience, Max-Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10364547" target="_blank"〉PubMed〈/a〉
    Keywords: Action Potentials ; Animals ; Bicuculline/pharmacology ; Calcium/metabolism ; Dendrites/physiology/ultrastructure ; GABA Antagonists/pharmacology ; Gene Expression ; Gene Targeting ; Genes, Immediate-Early ; Glutamic Acid/pharmacology/physiology ; Hippocampus/cytology/physiology ; Long-Term Potentiation/*physiology ; *Maze Learning ; Mice ; Mice, Inbred C57BL ; Pyramidal Cells/*physiology/ultrastructure ; Receptors, AMPA/genetics/*physiology ; Receptors, N-Methyl-D-Aspartate/physiology ; Synapses/*physiology/ultrastructure ; Synaptic Transmission
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Association between brain temperature and dentate field potentials in exploring and swimming rats (1993)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1993-02-26
    Description: Attempts to correlate behavioral learning with cellular changes, such as increased synaptic efficacy, have often relied on increased extracellular potentials as an index of enhanced synaptic strength. A recent example is the enlarged excitatory field potentials in the dentate gyrus of rats that are learning spatial relations by exploration. The altered hippocampal field potentials do not reflect learning-specific cellular changes but result from a concomitant rise in brain temperature that is caused by the associated muscular effort. Enhanced dentate field excitatory potentials followed both passive and active heating and were linearly related to the brain temperature. These temperature-related effects may mask any learning-induced changes in field potential.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Moser, E -- Mathiesen, I -- Andersen, P -- New York, N.Y. -- Science. 1993 Feb 26;259(5099):1324-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Neurophysiology, University of Oslo, Norway.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8446900" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Behavior, Animal/physiology ; Body Temperature ; Cerebellar Nuclei/*physiology ; Hippocampus/*physiology ; Male ; Membrane Potentials ; Physical Exertion ; Rats ; Swimming/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of single nutrient limitation of poly-β-hydroxybutyrate molecular weight distribution in alcaligens europhus (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 46 (1995), S. 497-502 
    Details
    ISSN: 0006-3592
    Keywords: poly-β-hydroxybutyrate ; molcular weight distribution ; Alcaligens eutrophus ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of magnesium and phosphate limitation on the molecular weight distribution of poly-β-hydroxybutyrate (PHB) in Alcaligens europhus in cotinuons culture has been stuied. Conditions of nitrogen limitation both with glucose excess (above ca. 20 g/L) and without excess were investigated Under N-limitation and glucose excess, Mw decreases when the magnesium content is decreased below 50% (19.7 mg/L) of the basal medium content; this also results in a broadenng of molecular weight distribution (Mw/Mn) from 2 to 5 and a decrease in Mw fron 2 × 106 to 0.9 × 106. Below 20% of the basal content of magnesium (7.9 mg/L) these two trends were reversed. This behaviour was not observed in the absence of glucose excess, phshate had virtually no effect on PHB Mw or its distribution, whereas wih no (or little) glucose excess Mw of the PHB decreased with phosphate concentrations below 50% of the basal level (0.705 g/L). Hence, in continuous or fed-batch cultures, in addition to nitrogen limitation to alklow for PHB accumulation, it is necesary to control both the addition of glucose (no excess) and also to maintain magnesium limitation (ca. 25% of basal medium level, 9.9 mg/L) and phosphate above 50% of he basal level (0.705 g/L). Thus, when broadening of molecular weight destribution (increase in Mw/Mn) is observed at the end of fed-batch culture it is probably caused by phosphate limitation and/or glucose excess. © 1995 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260460514
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  • 4
    Electronic Resource
    Electronic Resource
    Flow-induced crystallization of polypropylene in stretched ribbons (1976)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 16 (1976), S. 217-221 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: Ribbons of molten polypropylene have been extruded into a thermostatted chamber and subjected to elongations ranging as high as 4400-fold. Some of these ribbons have been shown to possess the unusual ability of recovering nearly all of the strain from large levels of stretch (≤100 percent). This property, as well as the magnitude of the tensile yield drop, has been found to be directly proportional to the uniaxial character of the flow present at the moment of crystallization. The structure in the final solid films has been characterized by wide angle X-ray diffraction and crystal orientation distribution. Both of these factors have been found to be proportional to the character of flow at the moment of crystallization. Finally, the temperature in the thermostatted chamber has been shown to affect the character of the flow.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760160316
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  • 5
    Electronic Resource
    Electronic Resource
    Crystal nucleation in sheared polymer melts (1978)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 18 (1978), S. 215-221 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: A semiquantitative procedure has been developed for analyzing crystal nucleation in undercooled polymer melts that are undergoing flow. This analysis was applied to the specific ease of molten high density polyethylene experiencing low levels of shearing flow. A custom-made concentric cylinder viscometer, which could be operated by the Rheometrics mechanical spectrometer instrument, was used to make simultaneous measurements of transmitted torque and optical anisotropy in isothermal melts, The result of the analytical procedure developed here was molecular Size-dependence of chain distensions caused by prevailing shear. This distribution function was verified by testing against experimentally obtained values of birefringence. Total entropy reduction resulting from this distorted state was then calculated, and the corresponding increase in free energy was found to be at least enough to account for comparable crystal nucleation rates in flowing melts at higher temperatures and in quiescent melts at lower temperatures.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760180308
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  • 6
    Electronic Resource
    Electronic Resource
    Polypropylene fibers melt-spun in the presence of torsional shear (1975)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 19 (1975), S. 1755-1766 
    Details
    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: Melt-spun fibers of isotactic polypropylene have been formed using specific combinations of shearing and elongational flow. Such rheological conditions were achieved with a take-up device capable of subjecting molten polymer filaments continuously to various combinations of torsional and elongational strains. Relationships were determined between mechanical properties of the resulting fibers and their molecular organizations. The results obtained indicated that these flow fields would produce fibers whose mean-preferred-chain-orientation directions ranged between being tilted radially from a direction parallel with the fiber axis (no torsional shear strain imposed) and having some additional tilt that is tangential with respect to the fiber circumference (some torsional shear strain imposed). It is not possible to resolve the observed helical chain tilts into contributions from crystalline and amorphous regions, respectively.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1975.070190625
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