Almost all elderly people show brain atrophy and cognitive dysfunction, even if they are saved from illness, such as cardiac disease, malignancy and diabetes. Prevention or delay of brain senescence would therefore enhance the quality of life for older persons. Because oxidative stress has been implicated in brain senescence, we investigated the effects of green tea catechin (GT-catechin), a potential antioxidant, in senescence-accelerated (SAMP10) mice. The mouse is a model of brain senescence with short life span, cerebral atrophy and cognitive dysfunction. Mice were fed water containing 0.02% GT-catechin from 1- to 15-month-old. The mean dose was about 35 mg/kg/day. We found that daily consumption of GT-catechin prevented memory regression and DNA oxidative damage in these mice. GT-catechin did not prolong the lifetime of SAMP10 mice, but it did delay brain senescence. These findings suggest that continued intake of GT-catechin might promote healthy ageing of the brain in older persons.

Measurements of complex dielectric constant c*, shear viscosity , and complex shear modulus G* were carried out on narrow molecular weight distribution cis-polyisoprenes (cts-PI) to determine their dielectric relaxation, g(r), and viscoelastic relaxation, H(t), spectra. For each sample the spectra were compared over a wide range of time scale covering the wedge-type to the box-type region of the viscoelastic spectrum. The viscoelastic relaxation time, tv, agreed with the dielectric normal-mode relaxation time, , while the relaxation time at the maximum of the wedge-type spectrum agreed with the dielectric segmental-mode relaxation time, t8. In the wedge-type region, the slope of the log H(t) vs log plot changed at the time scale of the transition from the Rouse-like motions to the segmental motions as decreased.For unentangled cts-PIs with a molecular weight, Mw, less than the characteristic molecular weight, Mc, the observed agreed with the longest Rouse relaxation time calculated with i?o. For entangled cts-PIs with Mw > Mc, the shape of the spectra H(t) and g(r) differed in the terminal region.

ABSTRACT:The dielectric behavior of six-arm star-shaped cis-polyisoprenes (6S-PI) with the arm molecular weight MP ranging from 3.5 x 10 3 to 21 x 10 3 was compared with that of corresponding linear cis-polyisoprenes (L-PI) which were precursors for the arms. In the entangled regime, the normal mode relaxation time '" of 6S-PI was longer and its dependence on molecular weight was stronger for 6S-Pls than for L-Pls. However, an exponential increase of 'n with MP which is characteristic of a highly entangled star chains was not clearly observed for the 6S-Pls examined, because MP was not large enough. In the non-entangled regime, the relaxation time 'ns at an iso-friction state of 6S-PI was close to that of corresponding L-PI, as suggested by the RouseHam theory. However, the relaxation mode distribution for 6S-PI was broader than that of L-PI. A model calculation using Rouse-Ham dynamics suggested that the distribution of arm length could possibly lead to a substantial broadening for the relaxation mode distribution.

Surgery with needle aspiration of the gas resulted in clinical improvement in all cases, confirming that intraspinal gas is an important cause of lumbar radiculopathy. The composition of the gas in one patient was analyzed by gas chromatography, which revealed an overwhelming preponderance of nitrogen. A relationship between a gas-containing pseudocyst in the spinal canal and a degenerated intervertebral disc was identified, a key finding for understanding the precise nature of this disorder. Intradiscal gas formation and its outward migration as a sequel of intervertebral disc degeneration also has been addressed in this report.

Viscoelastic properties of binary blends composed of narrow molecular weight distribution (MWD) 4-arm star polystyrenes (2-chain) of molecular weight (MW) M2 and narrow MWD linear polystyrenes (1-chain) of Ml were examined and compared with binary blends of narrow MWD linear polystyrenes of M2 and M1. In these blends, the volume fraction 4z of the 2-chain was kept small so that the 2-chains were entangling only with the matrix 1-chains but not with themselves. When the MW of the components of these dilute blends were such that M, < Ml << M,, with M, being the characteristic MW, the star 2-chain exhibited Rouse-Ham-like relaxation modes with the (weight average) relaxation time proportional to 42OMl3MZ2 and the compliance proportional to 4z-1M,0M2 Similar behavior was also found in the dilute blends of linear chains.These results suggest that the star as well as the high-MW linear (2-) chain in the dilute blend with Mz >> Ml > M, may relax as the surrounding 1-chains diffuse away so that the 1-2 entanglement has become ineffective.In the framework of the generalized tube model, this relaxation mechanism corresponds to the tube renewal mode. The limiting ratio of M2/Ml, for which these power laws are valid, is smaller for the star/linear chain blends than that for the linear chain blends. This is because the intrinsic relaxation time of the star 2-chain of M, is longer than that of the linear 2-chain of the same M2, observed in the bulk states. Thus, the star 2-chain exhibits the Rouse-Ham modes more easily than the corresponding linear 2-chain in the same matrix 1-chains.