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  • 1
    Electronic Resource
    Electronic Resource
    Glutamate Uptake by Squid Nerve Fiber Sheaths (1996)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 67 (1996), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The squid giant nerve exhibits neuron-Schwann cell interactions that appear to involve glutamate as a mediator; however, there is no information available about the possible fate of the released glutamate. In this study, it is demonstrated that the periaxonal sheaths of the extrasynaptic regions of squid giant nerves (where the glial cells are located) possess the capacity to transport glutamate. In whole intact nerves incubated with low-glutamate concentrations for long periods of time, the majority of the glutamate incorporated into the tissue was found in the sheaths. Axoplasm-free sheaths incubated for long periods of time with low concentrations of glutamate were able to accumulate this amino acid against a large apparent concentration gradient. Sheath glutamate uptake occurred in a sodium-dependent fashion over a wide concentration range and displayed both high- and low-affinity components. Glutamate uptake at concentrations below the Km of the high-affinity component was independent of homoexchange and displayed a specificity that is similar to that described for high-affinity glutamate transport in mammalian brain. It is proposed that the sheath transport systems may be involved in the regulation of glutamate levels in the intercellular clefts of the nerve fiber, as part of the glutamatergic neuron-glial signaling mechanisms in the squid giant nerve fiber.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1996.67020787.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Aspartate Aminotransferase and Glutamate Dehydrogenase Activities in the Squid Giant Nerve (1995)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 64 (1995), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The present study sought to investigate the presence and distribution of some enzymatic activities involved in the metabolism of glutamate in the giant nerve fiber of the tropical squid Sepioteuthis sepioidea. Specific activities of aspartate aminotransferase and glutamate dehydrogenase were evaluated in homogenates of the isolated giant fiber, extruded axoplasm, and axoplasm-free giant nerve fiber sheaths. The activities of both enzymes were present in the tissue. The specific activity of aspartate aminotransferase was similar in axoplasm and sheaths. However, the specific activity of glutamate dehydrogenase was an order of magnitude higher in the sheaths. This finding is discussed in the framework of the hypothesis that proposes that a differential distribution of the enzymes of the glutamatergic system between the axonal and neuroglial compartments forms part of a system of communication between these cells whose neuronal signal may be glutamate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1995.64010437.x
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Performance and Early Results from the Golf Instrument Flown on the Soho Mission (1997)
    Springer
    Solar physics 175 (1997), S. 207-226 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract GOLF in-flight commissioning and calibration was carried out during the first four months, most of which represented the cruise phase of SOHO towards its final L1 orbit. The initial performance of GOLF is shown to be within the design specification, for the entire instrument as well as for the separate sub-systems. Malfunctioning of the polarising mechanisms after 3 to 4 months operation has led to the adoption of an unplanned operating sequence in which these mechanisms are no longer used. This mode, which measures only the blue wing of the solar sodium lines, detracts little from the detection and frequency measurements of global oscillations, but does make more difficult the absolute velocity calibration, which is currently of the order of 20%. Data continuity in the new mode is extremely high and the instrument is producing exceptionally noise-free p-mode spectra. The data set is particularly well suited to the study of effects due to the excitation mechanism of the modes, leading to temporal variations in their amplitudes. The g modes have not yet been detected in this limited data set. In the present mode of operation, there are no indications of any degradation which would limit the use of GOLF for up to 6 years or more.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004911408285
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Global Oscillations at Low Frequency from the SOHO mission (GOLF) (1995)
    Springer
    Solar physics 162 (1995), S. 61-99 
    Details
    ISSN: 1573-093X
    Keywords: sun ; helioseismology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The GOLF experiment on the SOHO mission aims to study the internal structure of the sun by measuring the spectrum of global oscillations in the frequency range 10−7 to 10−2 Hz. Bothp andg mode oscillations will be investigated, with the emphasis on the low order long period waves which penetrate the solar core. The instrument employs an extension to space of the proven ground-based technique for measuring the mean line-of-sight velocity of the viewed solar surface. By avoiding the atmospheric disturbances experienced from the ground, and choosing a non-eclipsing orbit, GOLF aims to improve the instrumental sensitivity limit by an order of magnitude to 1 mm s−1 over 20 days for frequencies higher than 2.10−4 Hz. A sodium vapour resonance cell is used in a longitudinal magnetic field to sample the two wings of the solar absorption line. The addition of a small modulating field component enables the slope of the wings to be measured. This provides not only an internal calibration of the instrument sensitivity, but also offers a further possibility to recognise, and correct for, the solar background signal produced by the effects of solar magnetically active regions. The use of an additional rotating polariser enables measurement of the mean solar line-of-sight magnetic field, as a secondary objective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00733427
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  • 5
    Electronic Resource
    Electronic Resource
    Tri-Phonic Helioseismology: Comparison of Solar p Modes Observed by the Helioseismology Instruments Aboard SOHO (1997)
    Springer
    Solar physics 175 (1997), S. 311-328 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The three helioseismology instruments aboard SOHO observe solar p modes in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series of two months duration are compared and confirm that the instruments indeed observe the same Sun to a high degree of precision. Power spectra of 108 days are compared showing systematic differences between mode frequencies measured in intensity and in velocity. Data coverage exceeds 97% for all the instruments during this interval. The weighted mean differences (V-I) are −0.1 µHz for l=0, and −0.16 µHz for l=1. The source of this systematic difference may be due to an asymmetry effect that is stronger for modes seen in intensity. Wavelet analysis is also used to compare the shape of the forcing functions. In these data sets nearly all of the variations in mode amplitude are of solar origin. Some implications for structure inversions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004949832159
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    First Results on it p Modes from GOLF Experiment (1997)
    Springer
    Solar physics 175 (1997), S. 227-246 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The GOLF experiment on the SOHO mission aims to study the internal structure of the Sun by measuring the spectrum of global oscillations in the frequency range 10-7 to 10-2 Hz. Here we present the results of the analysis of the first 8 months of data. Special emphasis is put into the frequency determination of the p modes, as well as the splitting in the multiplets due to rotation. For both, we show that the improvement in S/N level with respect to the ground-based networks and other experiments is essential in achieving a very low-degree frequency table with small errors ∼ 2 parts in 10-5). On the other hand, the splitting found seems to favour a solar core which does not rotate slower than its surface. The line widths do agree with theoretical expectations and other observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004942929956
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    First View of the Solar Core from Golf Acoustic Modes (1997)
    Springer
    Solar physics 175 (1997), S. 247-265 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract After 8 months of nearly continuous measurements the GOLF instrument, aboard SOHO, has detected acoustic mode frequencies of more than 100 modes, extending from 1.4 mHz to 4.9 mHz. In this paper, we compare these results with the best available predictions coming from solar models. To verify the quality of the data, we examine the asymptotic seismic parameters; this confirms the improvements achieved in solar models during the last decade. Using the GOLF set of frequencies for l=0, 1, 2, 3 combined with the LOWL second year data set for l 〉 3 we then carry out inversions to infer properties of the solar core. This largely confirms the previous results down to around 0.1 R⊙, while there remain differences, even closer to the centre, where the present study shows an extreme sensitivity of the inversion results to the values of the frequencies. We finally consider physical processes which may influence directly or indirectly the solar core structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004992727541
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    Paper (German National Licenses)
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