Development process and pathology of myelopathy due to chronic spinal cord compression have not been fully elucidated. This study was conducted in order to establish an experimental model which can efficiently produce myelopathy and be useful in the studies on myelopathy due to chronic spinal cord compression. Under electrophysiological monitoring of the spinal cord, anterior compression was produced on C5 using a plastic screw. Two weeks later, a plastic plate was inserted under the C5 arch. For the subsequent 10 months on average, walking pattern and MR images were periodically monitored. Before the sacrifice, electrophysiological test was performed and then histopathological examination was done. Palsy appeared at 5 months on average after the addition of posterior compression. Mean compression ratio of the spinal cord calculated on MR images was 34%. All animals with compression showed a high intramedullary signal intensity, and the mean contrast-to-noise ratio (CNR) in the compressed area was 49%. Electrophysiological test showed a significant decrease in the amplitude of spinal cord evoked potentials (SCEPs) at the given compression level. Histology showed flattening of the anterior horn, disappearance and necrosis of anterior horn cells in the gray matter; and demyelination and axonal degeneration in the white matter. The antero-posterior compression produces the condition of spinal canal stenosis. Repeated antero-posterior compression to the spinal cord is important in establishing myelopathy. The present animal model was evaluated to be useful in the studies on myelopathy.
In order to investigate the screening effect of a nuclear reaction in a liquid metal environment, thick-target yields of the 6 Li(d,) 4 He and 7 Li(p,) 4 He reactions were measured using a liquid Li target for incident energies between 22.5 and 70 keV. The modified SðEÞ factor [S Ã ðEÞ] for the liquid Li environment was deduced by dividing the measured yield by the energy integration of the penetration factor divided by the stopping power. It was shown that S Ã ðEÞ for the liquid environment is considerably larger than that for the atomic/molecular environment for both reactions. The difference in the screening energy between the two environments was deduced to be ÁU ¼ 235 AE 63 ( 6 Li+d) and 140 AE 82 eV ( 7 Li+p), although the screening energy for liquid Li has a large uncertainty with U liq $ 486{776 ( 6 Li+d) and 324-637 eV ( 7 Li+p) owing to the uncertainty of the astrophysical bare SðEÞ factors. This difference in the screening energy should be considered in such a way that, in liquid Li metal, conduction electrons and Li þ ions contribute to the screening in addition to bound electrons.
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