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  • 1
    Electronic Resource
    Electronic Resource
    Medial septal projections to the dentate gyrus of the rat: electrophysiological analysis of distribution and plasticity (1984)
    Springer
    Experimental brain research 56 (1984), S. 243-256 
    Details
    ISSN: 1432-1106
    Keywords: Medial septum ; Hippocampus ; Dentate gyrus ; Evoked potentials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Previous electrophysiological experiments in rabbits have suggested that medial septal stimulation activates dentate granule cells and evokes an associated negative field response at the granule cell layer, without an associated “dendritic” response. Anatomical studies have suggested that septal input to the granule cells may be to stratum moleculare, or close to the cell layer, or may not exist at all. The present experiments confirmed in rats anaesthetised with urethane that medial septal stimulation elicits single action potentials from cells in the granule layer. The associated negative field potential was maximal in the granule cell layer and there was no sign of a separate dendritic potential. The fibres responsible for this potential travel to the dorsal hippocampus in the fornix superior rather than the fimbria, taking the same course as the fibres which contribute to the dense cholinesterase staining just above the granule cell layer. Stimulation at 100 Hz for 1 s of either medial septal, or perforant path, input to the dentate granule cell layer produced long term potentiation of the subsequent evoked field responses to the stimulated pathway. The responses to the non-stimulated pathway were unchanged. Paired pulse stimulation produced both homosynaptic and heterosynaptic potentiation. These data suggest that medial septal input synapses close to granule cell bodies and produces a negative field potential which is a combination of dendritic and population spike potentials. Medial septal input also appeared to produce direct activation of hilar neurones, some of which may be basket cells or other interneurones. The data also show that long term potentiation is specific to this input, perhaps dependent on presynaptic mechanisms. Paired pulse potentiation, at least in the heterosynaptic case appears to depend on postsynaptic mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236280
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Seismic character of gas hydrates on the Southeastern U.S. continental margin (1994)
    Springer
    Marine geophysical researches 16 (1994), S. 163-184 
    Details
    ISSN: 1573-0581
    Keywords: bottom simulating reflection ; gas hydrate ; amplitude blanking ; seismic characteristics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Gas hydrates are stable at relatively low temperature and high pressure conditions; thus large amounts of hydrates can exist in sediments within the upper several hundred meters below the sea floor. The existence of gas hydrates has been recognized and mapped mostly on the basis of high amplitude Bottom Simulating Reflections (BSRs) which indicate only that an acoustic contrast exists at the lower boundary of the region of gas hydrate stability. Other factors such as amplitude blanking and change in reflection characteristics in sediments where a BSR would be expected, which have not been investigated in detail, are also associated with hydrated sediments and potentially disclose more information about the nature of hydratecemented sediments and the amount of hydrate present. Our research effort has focused on a detailed analysis of multichannel seismic profiles in terms of reflection character, inferred distribution of free gas underneath the BSR, estimation of elastic parameters, and spatial variation of blanking. This study indicates that continuous-looking BSRs in seismic profiles are highly segmented in detail and that the free gas underneath the hydrated sediment probably occurs as patches of gas-filled sediment having variable thickness. We also present an elastic model for various types of sediments based on seismic inversion results. The BSR from sediments of high ratio of shear to compressional velocity, estimated as about 0.52, encased in sediments whose ratios are less than 0.35 is consistent with the interpretation of gasfilled sediments underneath hydrated sediments. This model contrasts with recent results in which the BSR is explained by increased concentrations of hydrate near the base of the hydrate stability field and no underlying free gas is required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01237512
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
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