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Biomedical subjects

J R Phillips

Publications and source records attributed to J R Phillips.

At least 37 records · Page 2Linked to original sources
PubMed1995

Form deprivation myopia: elastic properties of sclera.

Thinning of the posterior sclera may imply that stretching and/or weakening of the sclera plays a role in axial elongation of myopic eyes. We investigated the elastic stress-strain properties of sclera from developing tree shrew eyes made myopic by monocular deprivation (MD) of form vision. Five days of MD induced a relative myopia (mean +/- SEM) of -5.6 D +/- 0.6 D (retinoscopy) and a vitreous chamber elongation (deprived minus control) of 106 +/- 14 microns, n = 10 (ultrasonography). Posterior scleral test samples (2 mm wide) cut from myopic eyes were significantly thinner than their contralateral eye controls (149 +/- 4 microns versus 164 +/- 4 microns, n = 10, P < 0.01) when measured with a force-controlled micrometer. However, posterior sclera from control eyes was significantly thicker than that from age-matched normal eyes (164 +/- 4 microns versus 149 +/- 3 microns, n = 10, P < 0.01). Under uniaxial tension, posterior scleral samples from myopic eyes failed at 18% lower load (162 g versus 198 g) and extended approximately 25% more than controls at a load corresponding to 20 mm Hg intraocular pressure. These differences were largely accounted for by the differences in scleral thickness. Finite element modelling of tree shrew eyes using the material properties summarised above, implies that simple elastic stretching of the sclera accounts for less than 20% of the observed difference in axial length between myopic and contralateral control eyes.

Animals↗
PubMed1994

MRI scanner transport system.

A computer-controlled transport system has been designed and tested for small bore magnetic resonance scanners for animal research. The transport system allows remote animal positioning based on scout images using a graphic interface. The design utilized commercially available components suitable for use in the scanner's strong magnetic field. Tests indicate positioning accuracy of the transport system to be within 0.13 mm.

Animals↗
PubMed1993

Methylene blue and rose bengal photoinactivation of RNA bacteriophages: comparative studies of 8-oxoguanine formation in isolated RNA.

Several reactive oxygen species, including singlet oxygen (1O2) and hydroxyl free radical (.OH), may potentially be involved in the photoinactivation of viruses by agents such as methylene blue (MB) and rose bengal (RB). Both 1O2 and .OH also mediate the formation of 8-oxoguanine (8-oxoGua) in DNA and RNA. Evidence that MB-or RB-induced bacteriophage (R17 or Q beta) inactivation and 8-oxoGua formation in RNA result from 1O2 rather than .OH was obtained utilizing complementary experimental approaches which show that: (i) the rate of phage photoinactivation by MB was unchanged by the presence of iron chelators or by different temperatures in the 13-37 degrees C range; (ii) MB- and RB-mediated rates of 8-oxoGua formation in isolated RNA have very little, if any, temperature dependence, in contrast to a significant temperature dependence of 8-oxoGua formation by a .OH generating system, the ultraviolet light irradiation of H2O2; and (iii) deuterium oxide (D2O) enhanced the RB-mediated rate of phage photoinactivation and 8-oxoGua formation in isolated RNA. The presence of superoxide dismutase in the RB photoinactivation reaction did not alter the rate of phage inactivation. The data suggest that 8-oxoGua serves as a marker that correlates qualitatively with 1O2-mediated lethal lesions in RNA bacteriophages.

Centrifugation, Density Gradient↗
PubMed1993

Texture perception and afferent coding distorted by cooling the human ulnar nerve.

The roughness of standardized surfaces (embossed dot arrays or gratings) was compared by scanning them with the little finger of either hand while the ulnar nerve was cooled unilaterally at the elbow; both hands remained warm. Across-hand comparison of roughness showed that a given surface felt smoother on the cooled side. When the surfaces were adjusted to feel equally rough, that on the cooled side would normally have felt appreciably rougher. The effect of the nerve cooling on axonal conduction was monitored during the psychophysical experiments by stimulating the ulnar nerve above the cooled region and recording the EMG of an ulnar-innervated hand muscle. During cooling, large myelinated axons remained unblocked, but prolongation of their absolute refractory period to 5-10 msec left them unable to transmit trains of impulses at high frequencies (Wedensky inhibition). By varying the length of nerve cooled and the cooling temperature, it was shown that the perceptual effects were not due to an increase in the normal temporal dispersion of impulses transmitted by different-sized afferents. The effect of increasing the absolute refractory period on the signals from the various types of cutaneous afferent was modeled mathematically, using earlier human single-fiber responses to dot arrays. It is concluded that the reduction of perceived roughness with nerve cooling is due to Wedensky inhibition, and that the percept of roughness is related to the local contrast in the afferent spatiotemporal image.

Adult↗