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  • 1
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    Hypergravity exposure decreases gamma-aminobutyric acid immunoreactivity in axon terminals contacting pyramidal cells in the rat somatosensory cortex: a quantitative immunocytochemical image analysis (1998)
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    Publication Date: 2011-08-24
    Description: Quantitative evaluation of gamma-aminobutyric acid immunoreactivity (GABA-IR) in the hindlimb representation of the rat somatosensory cortex after 14 days of exposure to hypergravity (hyper-G) was conducted by using computer-assisted image processing. The area of GABA-IR axosomatic terminals apposed to pyramidal cells of cortical layer V was reduced in rats exposed to hyper-G compared with control rats, which were exposed either to rotation alone or to vivarium conditions. Based on previous immunocytochemical and behavioral studies, we suggest that this reduction is due to changes in sensory feedback information from muscle receptors. Consequently, priorities for muscle recruitment are altered at the cortical level, and a new pattern of muscle activity is thus generated. It is proposed that the reduction observed in GABA-IR of the terminal area around pyramidal neurons is the immunocytochemical expression of changes in the activity of GABAergic cells that participate in reprogramming motor outputs to achieve effective movement control in response to alterations in the afferent information.
    Keywords: Aerospace Medicine
    Type: Journal of neuroscience research (ISSN 0360-4012); Volume 53; 2; 135-42
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  • 2
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    Quantitative changes of GABA-immunoreactive cells in the hindlimb representation of the rat somatosensory cortex after 14-day hindlimb unloading by tail suspension (1996)
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    Publication Date: 2011-08-24
    Description: The present study was aimed at evaluating quantitatively gamma-aminobutyric acid (GABA) immunoreactivity in the hindlimb representation of the rat somatosensory cortex after 14 days of hindlimb unloading by tail suspension. A reduction in the number of GABA-immunoreactive cells with respect to the control animals was observed in layer Va and Vb. GABA-containing terminals were also reduced in the same layers, particularly those terminals surrounding the soma and apical dendrites of pyramidal cells in layer Vb. On the basis of previous morphological and behavioral studies of the neuromuscular system of hindlimb-suspended animals, it is suggested that the unloading due to hindlimb suspension alters afferent signaling and feedback information from intramuscular receptors to the cerebral cortex due to modifications in the reflex organization of hindlimb muscle groups. We propose that the reduction in immunoreactivity of local circuit GABAergic neurons and terminals is an expression of changes in their modulatory activity to compensate for the alterations in the afferent information.
    Keywords: Aerospace Medicine
    Type: Journal of neuroscience research (ISSN 0360-4012); Volume 44; 6; 532-9
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  • 3
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    Ion-acoustic waves in a plasma with negative ions (1991)
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    Publication Date: 2011-08-19
    Description: Propagation and damping of ion-acoustic waves have been investigated in a Q-machine plasma consisting of K(+) positive ions, SF6(-) negative ions, and electrons. The phase velocity of the ion-acoustic 'fast' mode increases with increasing epsilon, the concentration of negative ions. The wave damping decreases with increasing epsilon, and nearly disappears, for the highest wave frequencies investigated, when epsilon is more than about 0.9. Both results are in agreement with predictions from Vlasov theory.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 3; 284-287
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  • 4
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    Electrostatic ion-cyclotron waves in a two-ion component plasma (1988)
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    Publication Date: 2011-08-19
    Description: The excitation of electrostatic ion cyclotron (EIC) waves is studied in a single-ended Q machine in a two-ion component plasma (Ca+ and K+). Over a large range of relative concentrations of Cs+ and K+ ions, two modes are excited with frequencies greater than the respective cyclotron frequencies of the ions. The results are discussed in terms of a fluid theory of electrostatic ion cyclotron waves in a two-ion component plasma.
    Keywords: PLASMA PHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 16; 396-398
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  • 5
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    Transition from moving to stationary double layers in a single-ended Q machine (1990)
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    Publication Date: 2011-08-19
    Description: Large-amplitude (less than about 100 percent) relaxation oscillations in the plasma potential are known to be generated when the cold endplate of a single-ended Q machine is biased positively. These oscillations are associated with double layers that form near the hot plate (plasma source) and travel toward the endplate at about the ion-acoustic velocity. At the endplate they dissolve and then form again near the hot plate, the entire process repeating itself in a regular manner. By admitting a sufficient amount of neutral gas into the system, the moving double layers were slowed down and eventually stopped. The production of stationary double layers requires an ion source on the high-potential side of the double layers. These ions are provided by ionization of the neutral gas by electrons that are accelerated through the double layer. The dependence of the critical neutral gas pressure required for stationary double-layer formation on endplate voltage, magnetic field strength, and neutral atom mass has been examined. These results are discussed in terms of a simple model of ion production and loss, including ion losses across the magnetic field.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 2; 1936-194
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  • 6
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    Ion-beam focusing in a double-plasma device (1988)
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    Publication Date: 2011-08-19
    Description: The authors studied the propagation of a low-energy charge-neutralized ion beam injected into the target region of a long double-plasma device. A magnetic field of up to about 180 G may be applied along the axis of the device. As a result of charge exchange collisions, the ion beam is attenuated as it propagates into the target region. However, under certain conditions of magnetic field strength and neutral gas pressure, the authors have observed a `reemergence' of the beam on axis far downstream in the target. This reemergence of the ion beam is attributed to a focusing of the ions by a self-consistently produced radial ambipolar electric field. The effect may be expected to occur in other types of plasma devices as well, whenever a sufficiently large radially inward electric field is present.
    Keywords: PLASMA PHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 16; 590-596
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  • 7
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    Regulation of collagenase-3 and osteocalcin gene expression by collagen and osteopontin in differentiating MC3T3-E1 cells (2002)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Both collagenase-3 and osteocalcin mRNAs are expressed maximally during the later stages of osteoblast differentiation. Here, we demonstrate that collagenase-3 mRNA expression in differentiating MC3T3-E1 cells is dependent upon the presence of ascorbic acid, is inhibited in the presence of the collagen synthesis inhibitor, 3,4-dehydroproline, and is stimulated by growth on collagen in the absence of ascorbic acid. Transient transfection studies show that collagenase-3 promoter activity increases during cell differentiation and requires the presence of ascorbic acid. Additionally, we show that, in differentiating MC3T3-E1 cells, collagenase-3 gene expression increases in the presence of an anti-osteopontin monoclonal antibody that binds near the RGD motif of this protein, whereas osteocalcin expression is inhibited. Furthermore, an RGD peptidomimetic compound, designed to block interaction of ligands to the alpha(v) integrin subunit, increases osteocalcin expression and inhibits collagenase-3 expression, suggesting that the RGD peptidomimetic initiates certain alpha(v) integrin signaling in osteoblastic cells. Overall, these studies demonstrate that stimulation of collagenase-3 expression during osteoblast differentiation requires synthesis of a collagenous matrix and that osteopontin and alpha(v) integrins exert divergent regulation of collagenase-3 and osteocalcin expression during osteoblast differentiation.
    Keywords: Aerospace Medicine
    Type: The Journal of biological chemistry (ISSN 0021-9258); 277; 27; 24788-98
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  • 8
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    Plasma density fluctuations observed during Space Shuttle Orbiter water releases (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observations by the Langmuir probe on the Plasma Diagnostics Package flown as part of the Spacelab 2 mission in the summer of 1985 show a strong increase in the level of turbulence near the Shuttle Orbiter during operations in which liquid water is released. The spectrum of the plasma density fluctuations peaks at the lowest frequencies measured (a few Hz) and extends up to a few kHz, near the lower hybrid frequency. Two potential mechanisms for generating the plasma turbulence are suggested which are both based on the production of water ions as a result of charge exchange with the ambient oxygen ions in the ionosphere. The first mechanism proposed is the ion-plasma instability which arises from the drift of the contaminant with respect to the ambient oxygen ions. The other mechanism proposed is the Ott-Farley instability, which is a result of the ring distribution formed by the 'pick-up' water ions.
    Keywords: PLASMA PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 12081-12
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  • 9
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    Plasma density, temperature and turbulence in the wake of the Shuttle Orbiter (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: In situ observations of the plasma density, temperature, and turbulence in the near wake, midwake, and far wake of the Shuttle Orbiter are presented. The results show that the plasma disturbances produced by the passage of the Orbiter extend downstream for a distance of several hundred meters behind the Orbiter. It is found that the electron density profile exhibits nonmonotonic behavior, and that most of the 6-40-Hz turbulence in the wake is confined to a region about 20 m downstream of the Orbiter. The saturation Delta N(e)/N(e) spectra rapidly decline in the 10,000-100,000-Hz decade, both in the ambient ionosphere and in the wake.
    Keywords: PLASMA PHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 37; 1001-101
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  • 10
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    Influence of the ion/neutral atom mass ratio on the damping of electrostatic ion-cyclotron waves (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The damping of electrostatic ion-cyclotron waves by ion-neutral collisions was studied in a single-ended Q machine. The amplitudes of K(+) and Cs(+) electrostatic ion-cyclotron waves were measured as a function of neutral pressure in helium, neon, argon, krypton, and xenon. For each ion/neutral atom combination, the electrostatic ion-cyclotron wave amplitude maximizes at a neutral pressure that scales monotonically with the m(+)/m(n) mass ratio. This result is interpreted by considering the dynamics of elastic collisions between the ions and the neutral atoms.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids (ISSN 0031-9171); 30; 3304-330
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