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  • Occupational Health and Environmental Toxicology  (2)
  • Rostral ventrolateral medulla  (2)
  • 1
    ISSN: 1432-1106
    Keywords: Ventrolateral periaqueductal grey matter ; Nucleus raphe magnus ; Nucleus raphe obscurus ; Rostral ventrolateral medulla ; GABA ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Experiments were carried out in urethane-anaesthetised rats to determine whether the inhibition of neurones in the rostral ventrolateral medulla (RVLM) induced by stimulation in the ventrolateral periaqueductal grey matter (PAG), is mediated via a relay in the medullary raphe nuclei. Electrical stimulation in the ventrolateral part of the PAG (20-ms trains, 7 pulses, 5–100 μA) inhibited ongoing activity of neurones in the RVLM for periods of 10–120 ms (mean 43.6 ms). The duration of the inhibition was reduced by 51.1% after microinjection of GABA (40–160 nmol in volumes of 200–400 nl, 9/12 sites), but not 165 mM NaCl (8/8 sites) in nucleus raphe magnus (NRM) and the rostral half of nucleus raphe obscurus (NRO). In a further series of experiments, activation of neuronal perikarya at 17 sites in NRM or NRO by microinjection of d,l-homocysteic acid (5–40 nmol in volumes of 50–400 nl) inhibited ongoing activity of 9 out of 14 neurones in the RVLM, the other 5 being excited. We suggest that the inhibitory effect on neurones in the RVLM, which can be evoked by stimulation in the ventrolateral PAG, is mediated indirectly by activation of an inhibitory projection to the RVLM from NRM and the rostral half of NRO.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 422 (1992), S. 93-97 
    ISSN: 1432-2013
    Keywords: 5-Hydroxytryptamine ; 5-HT1A receptor ; Rostral ventrolateral medulla ; Rat ; Sympathoexcitatory drive
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In rats anaesthetised with urethane, iontophoretic application of 5-hydroxytryptamine (5-HT) and the 5-HT1A agonists buspirone, flesinoxan and 8-hydroxy-2-(di-n-propylamino)-tetralin inhibited ongoing or amino-acid-evoked activity of neurons in the rostral ventrolateral medulla (RVLM) including barosensitive cells with spinally projecting axons. More than 90% of cells tested were inhibited by these agonists. In 5/9 cells the inhibition was reduced after intravenous spiperone (0.6 mg/kg). These results suggest that the sympathoinhibitory effects produced by microinjection of 5-HT1A agonists into the RVLM are due to a direct inhibitory action on neurons that send excitatory projections to the spinal sympathetic outflow.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 13 (1992), S. 237-246 
    ISSN: 0197-8462
    Keywords: windows ; transient response ; chemical reaction model ; rate constant ; transcription ; teratogenesis ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Data in the literature imply that the relationship between exposure and bio-effect involves more than a simple time integral of the field strength to which the living system has been subjected. Windows - ranges in which the system exhibits enhanced sensitivity - have been reported for power (or field strength), frequency, and the duration of the exposure. In this paper we show that such isolated window effects can be accounted for by recognizing the transient character of the response of the biological system. The principal assumption here is that the direct effect of the field is to increase the rates of production and degradation of mRNA or proteins. In this paper we review and extend the mathematical model that quantifies this. The model predicts that, for a given field strength, certain optimum relatively short duration exposures cause significantly larger bio-effects than exposure for much longer or much shorter times. The thinking embodied in the model should provide a framework for obtaining a meaningful working definition of “effective dose” and for predicting the response of subjects to environmental electromagnetic fields. It should help in deciding the relevant variables in the design and analysis of epidemiological studies. 1992 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0197-8462
    Keywords: dosimetry ; magnetic field exposure ; induced current ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: In-vitro studies of biological effects of electromagnetic fields are often conducted with cultured cells either in suspension or grown in a monolayer. In the former case, the exposed medium can be assumed to be homogeneous; however, eventually the cells settle to the bottom of the container forming a two layer system with different dielectric and conductive properties. In the present work the effect of this separation on the electric field distribution is calculated and experimentally measured at selected positions for a commonly used exposure configuration. The settled cell suspension is modeled by a well-defined two layer system placed in a rectangular container with the base of the container parallel to the direction of the magnetic field. Theoretical calculations based on numerical techniques are done for various two layer systems with different conductivities in each layer. The agreement between the theoretical calculations and the experimental measurements is within ± 1.5 mV/m, or 10% of the maximum induced field when the conductivity of the lower layer is ten times that of the upper layer. This result is well within experimental error. When the thickness of one of the layers is small compared to the thickness of the other layer, it is found that the electric field distribution is essentially that of the homogeneous case. The latter situation corresponds to a typical cell exposure condition. © 1993 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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