640 research outputs found
Self-Similar Collapse of Scalar Field with Plane Symmetry
Plane symmetric self-similar solutions to Einstein's four-dimensional theory
of gravity are studied and all such solutions are given analytically in closed
form. The local and global properties of these solutions are investigated and
it is shown that some of the solutions can be interpreted as representing
gravitational collapse of the scalar field. During the collapse, trapped
surfaces are never developed. As a result, no black hole is formed. Although
the collapse always ends with spacetime singularities, it is found that these
singularities are spacelike and not naked.Comment: latex, two figure
Amphiphysin I and regulation of synaptic vesicle endocytosis
Amphiphysin I, known as a major dynamin-binding partner localized on the collars of nascent vesicles, plays a key role in clathrin-mediated endocytosis (CME) of synaptic vesicles. Amphiphysin I mediates the invagination and fission steps of synaptic vesicles by sensing or facilitating membrane curvature and stimulating the GTPase activity of dynamin. Amphiphysin I may form a homodimer by itself or a heterodimer with amphiphysin II in vivo. Both amphiphysin I and II function as multilinker proteins in the clathrin-coated complex. Under normal physiological conditions, the functions of amphiphysin I and some other endocytic proteins are known to be regulated by phosphorylation and dephosphorylation. During hyperexcited conditions, the most recent data showed that amphiphysin I is truncated by the ca2-dependent protease calpain. Overexpression of the truncated form of amphi-physin I inhibited transferrin uptake and synaptic vesicle endocytosis (SVE). This suggests that amphi-physin I may be an important regulator for SVE when massive amounts of Ca2 flow into presynaptic terminals, a phenomenon observed in neurodegenerative disorders such as ischemia/anoxia, epilepsy, stroke, trauma and Alzheimer's disease. This review describes current knowledge regarding the general properties and functions of amphiphysin I as well as the functional regulations such as phosphorylation and proteolysis in nerve terminals.</p
多価不飽和脂肪酸の神経芽腫細胞(Neuro2a)におけるアポトーシス抑制効果
Neuronal apoptosis is involved in neurodegenerative diseases such as Alzheimer's disease and Parkinson.s disease. An efficient means of preventing it remains to be found. Some n-3 polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA, 22 : 6n-3) and eicosapentaenoic acid (EPA, 20 : 5n-3) have been reported to be protective against the neuronal apoptosis and neuronal degeneration seen after spinal cord injury (SCI) [1]. However, it is unclear which kinds of PUFAs have the most potent ability to inhibit neuronal apoptosis and whether the simultaneous treatment of PUFAs inhibits the apoptosis. In the present study, we compared the abilities of various n-3- and n-6- PUFAs to inhibit the apoptosis induced after the administration of different apoptotic inducers, etoposide, okadaic acid, and AraC, in mouse neuroblastoma cells (Neuro2a). Preincubation with DHA (22 : 6n-3), eicosapentaenoic acid (EPA, 20 : 5n-3), alpha-linolenic acid (alpha-LNA, 18 : 3n-3), linoleic acid (LA, 18 : 2n-6), arachidonic acid (AA, 20 : 4n-3), and gamma-linolenic acid (gamma-LNA, 18 : 3n-6) significantly inhibited caspase-3 activity and LDH leakage but simultaneous treatment with the PUFAs had no effect on the apoptosis of Neuro2a cells. There were no significant differences of the anti-apoptotic eff ect among the PUFAs. These results suggest that PUFAs may not be effective for inhibiting neuronal cell death after acute and chronic neurodegenerative disorders. However, dietary supplementation with PUFAs may be beneficial as a potential means to delay the onset of the diseases and/or their rate of progression
Cosmology in nonrelativistic general covariant theory of gravity
Horava and Melby-Thompson recently proposed a new version of the
Horava-Lifshitz theory of gravity, in which the spin-0 graviton is eliminated
by introducing a Newtonian pre-potential and a local U(1) gauge field
. In this paper, we first derive the corresponding Hamiltonian,
super-momentum constraints, the dynamical equations, and the equations for
and , in the presence of matter fields. Then, we apply the theory to
cosmology, and obtain the modified Friedmann equation and the conservation law
of energy, in addition to the equations for and . When the spatial
curvature is different from zero, terms behaving like dark radiation and
stiff-fluid exist, from which, among other possibilities, bouncing universe can
be constructed. We also study linear perturbations of the FRW universe with any
given spatial curvature , and derive the most general formulas for scalar
perturbations. The vector and tensor perturbations are the same as those
recently given by one of the present authors [A. Wang, Phys. Rev. D{\bf 82},
124063 (2010)] in the setup of Sotiriou, Visser and Weinfurtner. Applying these
formulas to the Minkowski background, we have shown explicitly that the scalar
and vector perturbations of the metric indeed vanish, and the only remaining
modes are the massless spin-2 gravitons.Comment: Revtex4, no figures. Gauge freedom was clarified and typos were
corrected. Version to appear in Physical Reviews
Weak antilocalization and electron-electron interaction in coupled multiple-channel transport in a BiSe thin film
Electron transport properties of a topological insulator BiSe thin
film are studied in Hall-bar geometry. The film with a thickness of 10 nm is
grown by van der Waals epitaxy on fluorophlogopite mica and Hall-bar devices
are fabricated from the as-grown film directly on the mica substrate. Weak
antilocalization and electron-electron interaction effects are observed and
analyzed at low temperatures. The phase-coherence length extracted from the
measured weak antilocalization characteristics shows a strong power-law
increase with decreasing temperature and the transport in the film is shown to
occur via coupled multiple (topological surface and bulk states) channels. The
conductivity of the film shows a logarithmically decrease with decreasing
temperature and thus the electron-electron interaction plays a dominant role in
quantum corrections to the conductivity of the film at low temperatures.Comment: 12 pages, 5 figure
Inhibitory effect of polyunsaturated fatty acids on apoptosis induced by etoposide, okadaic acid and AraC in Neuro2a cells
Neuronal apoptosis is involved in neurodegenerative diseases such as Alzheimer's disease and Parkinson.s disease. An efficient means of preventing it remains to be found. Some n-3 polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA, 22 : 6n-3) and eicosapentaenoic acid (EPA, 20 : 5n-3) have been reported to be protective against the neuronal apoptosis and neuronal degeneration seen after spinal cord injury (SCI) [1]. However, it is unclear which kinds of PUFAs have the most potent ability to inhibit neuronal apoptosis and whether the simultaneous treatment of PUFAs inhibits the apoptosis. In the present study, we compared the abilities of various n-3- and n-6- PUFAs to inhibit the apoptosis induced after the administration of different apoptotic inducers, etoposide, okadaic acid, and AraC, in mouse neuroblastoma cells (Neuro2a). Preincubation with DHA (22 : 6n-3), eicosapentaenoic acid (EPA, 20 : 5n-3), alpha-linolenic acid (alpha-LNA, 18 : 3n-3), linoleic acid (LA, 18 : 2n-6), arachidonic acid (AA, 20 : 4n-3), and gamma-linolenic acid (gamma-LNA, 18 : 3n-6) significantly inhibited caspase-3 activity and LDH leakage but simultaneous treatment with the PUFAs had no effect on the apoptosis of Neuro2a cells. There were no significant differences of the anti-apoptotic eff ect among the PUFAs. These results suggest that PUFAs may not be effective for inhibiting neuronal cell death after acute and chronic neurodegenerative disorders. However, dietary supplementation with PUFAs may be beneficial as a potential means to delay the onset of the diseases and/or their rate of progression
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