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Biomedical subjects

G M Jones

Publications and source records attributed to G M Jones.

At least 127 records · Page 7Linked to original sources
PubMed1980

Prediction of silage digestibility and intake by chemical analyses or in vitro fermentation techniques.

Chemical analyses and in vitro fermentations were on three corn silages, four legume-grass silages, and four corn-hay crop silage mixtures which had been fed to sheep for 21 days. In vivo data were collected for voluntary silage intake and apparent digestibility of energy. Forage nutritive value was expressed as digestible energy intake. Multiple regression equations were developed to determine the more reliable methods to evaluate voluntary intake, digestibility, and nutritive value of silage. Equations for quadratic response surfaces accounted for 71 to 79% of variation in in vivo data compared to 54 to 70% of variability accountable by simple linear regression equations. Dry matter, crude protein, cell wall, acid-detergent fiber, and acid-detergent lignin contents of silage accounted for greater variability in silage intake, digestibility, and nutritive value than did any in vitro method either alone or in combination with chemical analysis. The results support Crampton's concept of nutritive value index, which is now expressed in the relative feed value system proposed by the American Forage and Grassland Council for differences between forages.

Animal Feed↗
PubMed1980

Evaluation and clinical application of a dextran-charcoal method for measuring bound testosterone in human plasma.

A method for rapidly determining bound and free testosterone in human plasma is evaluated and described, in which dextran-coated charcoal is used to separate bound and free testosterone. Intra- and inter-assay CV's were 1.9 and 3.8%, respectively. At least 50% of the "bound" testosterone was associated with species that behaved like sex steroid hormone-binding globulin on Sephadex G-25 chromatography and polyacrylamide gel electrophoresis. Bound and free testosterone concentrations were determined in normal men, normal women (during the menstrual cycle and during normal pregnancy), and in women with various degrees of hirsutism. We conclude that determining the circulating proportions of bound and free testosterone is helpful in the diagnostic evaluation of hirsutism in women, and in the investigation of normal and pathological conditions where androgen concentrations may be altered.

Charcoal↗
PubMed1980

Susceptibility to fluorescent light-induced chromatid breaks associated with DNA repair deficiency and malignant transformation in culture.

The increased susceptibility of mouse cells to fluorescent light-induced chromatid damage following their spontaneous malignant transformation in culture could result from loss or inactivation of catalase that decomposes the photoproduct H2O2 or from impaired capacities to repair DNA damage. No consistent change in catalase activity with respect to neoplastic state could be established. To interpret the cytogenetic damage in terms of DNA strand breaks, we determined the incidence of chromatid breaks induced by light exposure during the G1 and late S-G2 phases of the cell cycle in normal and malignant derivatives of a C3H mouse cell line. Chromatid breaks at metaphase following light exposure during G1 would result from DNA strand breaks, cross-links, or base damage, whereas breaks following exposure during late S-G2 would result from single-or double-strand breaks. Both G1 and late S-G2 were susceptible in malignant cells but only G1 in normal. Since caffeine inhibits DNA repair, we compared its effects on light-induced chromatid damage in the normal and malignant cells to assess their DNA repair capacities. Treatment of normal cells with caffeine (50 microgram/ml) directly following five hr of light exposure in G1 increased the chromatid damage to that in malignant cells exposed with or without caffeine. Similarly, treatment of normal cells with caffeine during late S-G2 exposure increased chromatid damage to a level not significantly different from that in malignant cells exposed without caffeine. Caffeine had little influence on chromatid damage in malignant cells. The increased susceptibility of malignant mouse cells to fluorescent light-induced chromatid breaks thus appears to result from impaired capacities to repair DNA damage.

Animals↗
PubMed1979

Visible light-induced DNA crosslinks in cultured mouse and human cells.

Cool-white fluorescent light induces crosslinks in DNA when proliferating cells are exposed at 37 degrees C for 20 h to 4.6 J/m2/s in culture medium supplemented with fetal bovine serum. Using the Kohn alkaline elution technique, we now find that: 1. Increased light intensity increases DNA crosslinks. 2. The crosslinking is medium-mediated. 3. Oxygen enhances the crosslinking. 4. The extent of crosslinking is decreased at high cell density. 5. The crosslinks can be removed by digestion with proteinase K (0.02 to 0.50 mg/ml). 6. Human cell lines including those derived from adult prostate, fetal lung (IMR-90) and mixed fetal tissues are susceptible to light-induced crosslinks. 7. Crosslinkage is not decreased by addition of catalase to the medium and the effective wavelength is probably between 450 nm and 490 nm. From these results we conclude that the mechanism of light-induced crosslinks differs from that of light-induced chromatid breaks and that the major lesion observed is protein-DNA cross-linkage rather than DNA strand breaks.

Animals↗
PubMed1979

Tibialis anterior response to sudden ankle displacements in normal and Parkinsonian subjects.

It is well known that in Parkinsonian subjects with akinesia, reaction times are increased but reflex latencies remain normal. We have attempted to use this knowledge to distinguish between 'reflex' and 'voluntary' components of the electromyographic (EMG) response to ankle displacement. The EMG and torque responses of tibialis anterior (TA) to randomly applied servo-controlled plantar-flexing displacements of the ankle with and without the subject's intentional opposition were examined in 9 Parkinsonian and 9 age-matched normal humans. To obtain a measure of akinesia, the response latency to a visual stimulus was subsequently measured in the same subjects. Three principal findings emerged. (1) The intermediate latency EMG component (PSR) of the response evoked by ankle displacement with the subject instructed to relax was more regularly evoked and of lower threshold in Parkinsonians than in normals. This finding corresponds to the enlarged M2 component in upper limb muscles. However, the facilitation of PSR was not found to be associated with an increase in torque. In fact, the patients did not exhibit more stiffness than normals under our experimental conditions. (2) Mean latency estimate of the PSR was indistinguishable between Parkinsonians and normals. This finding puts the PSR in the nature of a reflex. Indeed, in accordance with reflex behaviour which is proportional to input characteristics, its area increased linearly with increase in the magnitude of displacement velocity. (3) In contrast, the 'late' EMG response (FSR) evoked by opposing sudden ankle displacement exhibited a significantly longer latency in 6 out of 8 Parkinsonians than normals. In the same patients, the EMG response latency to a visual signal was similarly increased. The delay of FSR in akinesia patients thus argued against its being a stereotyped reflex. The result is discussed with reference to the recent finding that preprogrammed responses are delayed in Parkinsonians.

Adult↗
PubMed1979

Soluble cyclic AMP-dependent protein kinases from chick kidney. Effects of dilution and non-protein inhibitors.

Cyclic AMP-dependent protein kinases prepared from crude cytosols of chick kidney, rat kidney and rat liver were found on dilution to exhibit complex kinetics. Dilution of the cytosols appears to increase the state of activation of the enzymes. This effect was due to the presence of inhibitory agents in the cytosol which had a greater inhibitory effect on the cyclic AMP-dependent than on the cyclic AMP-independent enzyme. Two types of inhibitory activity were found by column chromatography, one resistant to trichloroacetic acid precipitation and boiling but affected by trypsin digestion and the other resistant to boiling and trypsin digestion but precipitated by trichloroacetic acid. Inhibitory activity corresponding to the former characteristics has been described previously but the presence of additional soluble inhibitory agents in the cytosol has not been documented. The complete characterisation of this previously undescribed inhibitory activity requires further investigation. The relevance of such cytosolic inhibitory activity to the interpretation of states of activation of protein kinase enzymes is discussed.

Adenosine↗
PubMed1979

Relationship between cerebral blood flow changes and cortical extracellular fluid pH during cerebral metabolic depression induced by althesin.

Baboons anaesthetized with halothane and nitrous oxide in oxygen were given Althesin 0.05 ml kg-1 i.v. Cerebral blood flow (c.b.f.) was measured by an electromagnetic flowmeter and by xenon clearance whilst extracellular fluid (e.c.f.) pH of the parietal cortex was measured with a micro pH electrode. Carotid blood flow (carBF) began to decrease and carotid vascular resistance (carVR) to increase 2.0 s (SEM 0.3) after the slowing of the e.e.g. produced by Althesin, while e.c.f. pH began to change to alkaline 10.5 s (SEM 1.0) after the e.e.g. change. The first statistically significant increase in mean e.c.f. pH occurred 25 s after the Althesin-induced change in the e.e.g. The duration of the changes in carVR and e.c.f. pH were 7 and 5 min respectively. It is concluded that the change in e.c.f. pH cannot have initiated the increase in carVR which followed the cerebral matabolic depression produced by Althesin. The later alkaline shift in e.c.f. pH may, however, have maintained the increased carVR during the duration of cerebral metabolic depression produced by Althesin.

Alfaxalone Alfadolone Mixture↗
PubMed1979

Increased susceptibility of mouse cells to fluorescent light-induced chromosome damage after long-term culture and malignant transformation.

Exposure of mouse cells in culture to fluorescent light has been shown to produce chromatid breaks and exchanges. Hydrogen peroxide formed in the cell during illumination has been implicated as the causative agent. The present results indicate that susceptibility to light-induced chromosome damage increases with time in culture and seems to be associated with or requisite for the spontaneous malignant transformation of mouse cells. All three cell lines followed during long-term culture that either became tumorigenic or showed cytological evidence of neoplastic transformation developed a concomitant increase in susceptibility. In three additional cell lines, susceptibility to light-induced chromatid damage was significantly increased in the spontaneously transformed malignant cells as compared with their nonneoplastic precursors. The increased susceptibility is not simply the result of long-term culture, since three other nonneoplastic cell lines after prolonged culture were significantly less susceptible than their malignant counterparts. Increased susceptibility to light-induced chromatid damage could result from impaired DNA repair or from the loss of defense mechanisms for destroying H2O2 or scavenging free radicals.

Animals↗
PubMed1978

Fluorescent light-induced chromosome damage and its prevention in mouse cells in culture.

Twenty-hour-exposure to fluorescent light produces chromatid breaks in a line of adult mouse lung cells grown in Dulbecco-Vogt medium supplemented with fetal bovine serum. The light-induced damage appears to be enhanced by increasing the concentration of oxygen in the gas phase of the culture. The effective wavelength(s) of light is in the visible range between 400 and 450 nm andis probably the mercury emission peak at 405 or 436 nm. Addition of catalase or glutathione with ascorbic acid to the culture medium reduced the number of chromatid breaks to a level not significantly different from that in the shielded cultures. It thus appears that the production of H2O2 in the culture medium or in the cell is responsible for the chromatid breaks. Most of the chromosomal abnormalities observed in long-term culture of mouse cells may result from exposure of cells or medium to fluorescent room lights in the presence of atmospheric oxygen. These genetic abnormalities can be minimized by shielding cells and medium from light, lowering the PO2 of the medium, and including reducing agents such as glutathione and ascorbic acid in the medium formulation.

Ascorbic Acid↗
PubMed1978

Fluorescent light-induced DNA crosslinkage and chromatid breaks in mouse cells in culture.

A single 20-hr exposure of mouse cells derived from embryonic or lung tissue to cool-white fluorescent light (4.6 W/m2) causes both DNA damage and chromosome aberrations including chromatid breaks, exchanges, and minutes. In Kohn's alkaline elution technique, the DNA from exposed cells elutes more slowly than that from shielded cells. Because larger molecular weight DNA elutes slower than smaller, we interpret these results to mean that the DNA in cells exposed to light is crosslinked. The estimated frequency of crosslinks is sufficient to account for the number of chromatid breaks observed. The types of chromosome aberrations produced by light indicate that the primary lesion results in chromatid rather than chromosome breaks, and the results suggest an influence of cell density in that cells in densely populated cultures showed few or no chromatid breaks after irradiation. The present results, together with observations from the literature, suggest that the DNA crosslinkage and the chromosome aberrations produced by light may be related.

Cells, Cultured↗
PubMed1977

Plasticity in the adult vestibulo-ocular reflex arc.

Human subjects with maintained reversal of their horizontal field of vision exhibit very substantial adaptive changes in their 'horizontal' vestibulo-ocular reflex (v.o.r.). Short durations (8 min) of vision reversal during natural head movement led to 20% v.o.r. attenuation while long periods (4 weeks) eventually led to approximate reversal of the reflex. The reversed condition is approached by a complex, but highly systematic, series of changes in gain and phase of the reflex response relative to normal. Recovery after return to normal vision exhibits a similar duration, but different pattern, to that of the original adaptation. A chronic cat preparation with long-term optical reversal of vision has now been developed and shows similar adaptive and recovery changes at low test stimulus amplitudes, but different patterns of adaptive response at high amplitudes. An adaptive neural model employing known vestibulo-ocular pathways is proposed to account for these experimentally observed plastic changes. The model is used to predict the adapted response to patterns of stimulation extending beyond the range of experimental investigation.

Adaptation, Physiological↗