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  • Collateral specificity  (1)
  • Ephaptic transmission  (1)
  • amplitude blanking  (1)
  • 1
    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
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ephaptic interactions contribute to paired pulse and frequency potentiation of hippocampal field potentials (1984)
    Springer
    Experimental brain research 54 (1984), S. 567-570 
    Details
    ISSN: 1432-1106
    Keywords: Hippocampus ; Frequency potentiation ; Transmembrane potential ; Ephaptic transmission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The contribution of ephaptic interactions to potentiation of the hippocampal CA1 extracellular population spike during paired pulse or frequency stimulation of stratum radiatum (SR) inputs was investigated using the in vitro hippocampal slice preparation. Records of the transmembrane potential revealed a depolarizing wave with an amplitude and latency that varied directly with that of the extracellular population spike. Paired pulse or repetitive stimulation of SR resulted in a potentiation of the population spike amplitude and a corresponding increase in the amplitude of the TMP depolarizing wave. Action potentials generated during the stimulus train consistently arose from the peak of the depolarizing wave. It is proposed that ephaptic interactions contribute to potentiation of the extracellular population spike through recruitment of subthreshold neurons within the population during repetitive afferent stimulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00235482
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Collateral specific long term potentiation of the output of field CA3 of the hippocampus of the rat (1986)
    Springer
    Experimental brain research 62 (1986), S. 250-258 
    Details
    ISSN: 1432-1106
    Keywords: Longterm potentiation ; Hippocampus ; Collateral specificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Long term potentiation (LTP) in response to brief high frequency trains has been reported for many pathways in the hippocampus. The mechanisms involved are still unclear. The present experiments set out to confirm reports in the literature that LTP of output from CA3 neurons can be specific to particular collaterals. Single pulses delivered to area CA3 produced field responses nearly simultaneously in area CA1 and in the lateral septum (LS). High frequency stimulation of CA3 produced long term potentiation of CA1 but not LS responses. The CA1 response to stimulation of the contralateral hippocampus did not potentiate when the CA1 response to CA3 stimulation showed long term potentiation. The CA1 and LS responses to CA3 stimulation showed similar strength-duration, strength-amplitude and frequency following characteristics. Their latencies were comparable to the latencies of antidromic activation of CA3 cells from CA1 and LS. Movement of stimulating electrodes to the region of the Schaffer collaterals increased the latency of the LS response and decreased the latency of the CA1 response but left the sum of these latencies unchanged. It was concluded that the CA3 and Schaffer stimulation were activating LS and CA1 collaterals of the same CA3 neurons. CA1 and LS responses to CA3 stimulation showed somewhat different paired pulse and frequency potentiation characteristics. These data confirm reports in the literature that long term potentiation is both input-specific and collateral-specific. The mechanisms of long term potentiation are likely, therefore, to be limited to changes at specific synaptic junctions, e.g. changes in sensitivity of specific postsynaptic receptor sites or changes in transmitter release, which can depend on functional or organisational differences between two collaterals of the same neuron.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238844
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    Paper (German National Licenses)
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