Exposure to galactic cosmic radiation (GCR) is considered to be a potential health risk in long-term space travel, and it represents a significant risk to the central nervous system (CNS). The most harmful component of GCR is the HZE [high-mass, highly charged (Z), high-energy] particles, e.g. (56)Fe. In ground-based experiments, exposure to HZE-particle radiation induces pronounced deficits in hippocampus-dependent learning and memory in rodents. The mechanisms underlying these impairments are mostly unknown, but some studies suggest that HZE-particle exposure perturbs the regulation of long-term potentiation (LTP) at the CA1 synapse in the hippocampus. In this study, we irradiated rats with 60 cGy of 1 GeV (56)Fe-particle radiation and established its impact on hippocampal glutamatergic neurotransmissions at 3 and 6 months after exposure. Exposure to 60 cGy (56)Fe-particle radiation significantly (P < 0.05) reduced hyperosmotic sucrose evoked [(3)H]-glutamate release from hippocampal synaptosomes, a measure of the readily releasable vesicular pool (RRP). This HZE-particle-induced reduction in the glutamatergic RRP persisted for at least 6 months after exposure. At 90 days postirradiation, there was a significant reduction in the expression of the NR1, NR2A and NR2B subunits of the glutamatergic NMDA receptor. The level of the NR2A protein remained suppressed at 180 days postirradiation, but the level of NR2B and NR1 proteins returned to or exceeded normal levels, respectively. Overall, this study shows that hippocampal glutamatergic transmission is sensitive to relative low doses of (56)Fe particles. Whether the observed HZE-particle-induced change in glutamate transmission, which plays a critical role in learning and memory, is the cause of HZE-particle-induced neurocognitive impairment requires further investigation.
The radiative transport equation is solved in the three-dimensional slab geometry by means of the method of rotated reference frames. In this spectral method, the solution is expressed in terms of analytical functions such as spherical harmonics and Wigner d-functions. In addition, the eigenvalues and eigenvectors of a tridiagonal matrix and certain coefficients, which are determined from the boundary conditions, must also be computed. The Green's function for the radiative transport equation is computed and the results are compared with diffusion approximation and Monte Carlo simulations. We find that the diffusion approximation is not quite correct inside the slab, even when the light emitted from the slab is well described by the diffusion approximation. The solutions we obtain are especially convenient for solving inverse problems associated with radiative transport.
A microscopic model of the molecular magnet V 15 is used to study mechanisms for the adiabatic change of the magnetization in time-dependent magnetic fields. The effects of the Dzyaloshinskii-Moriya interaction, the most plausible source for the energy-level repulsions that lead to adiabatic changes of the magnetization, are studied in detail. We find that the energy-level repulsions that result from this interaction exhibit a strong dependence on the direction of the applied field. We also discuss the role of magnetic anisotropy in the molecule Mn 12-acetate.
Prefractionation procedures facilitate the identification of lower‐abundance proteins in proteome analysis. Here we have optimized the conditions for immobilized metal affinity chromatography (IMAC) to enrich for phosphoproteins. The metal ions, Ga(III), Fe(III), Zn(II), and Al(III), were compared for their abilities to trap phosphoproteins; Ga(III) was the best. Detailed analyses of the pH and ionic strength for IMAC enabled us to determine the optimal conditions (pH 5.5 and 0.5 m NaCl). When whole cell lysates were fractionated in this way, about one‐tenth of the total protein was recovered in the eluate, and the recovery of phosphorylated extracellular signal‐regulated kinase (ERK) was more than 90%. Phosphorylated forms of ribosomal S6 kinase (RSK) and Akt were also enriched efficiently under the same conditions. Our Ga(III) IMAC and a commercially available purification kit for phosphoproteins performed similarly, with a slight difference in the spectrum of phosphoproteins. When phosphoproteins enriched from NIH3T3 cells in which ERK was either activated or suppressed were analyzed by two‐dimensional fluorescence difference gel electrophoresis, phosphorylated ERK was detected as discrete spots unique to ERK‐activated cells, which overlapped with surrounding spots in the absence of prefractionation. We applied the same technique to search for Akt substrates and identified Abelson interactor 1 as a novel potential target. These results demonstrate the efficacy of phosphoprotein enrichment by IMAC and suggest that this procedure will be of general use in phosphoproteome research.
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