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Biomedical subjects

G M Jones

Publications and source records attributed to G M Jones.

At least 109 records · Page 6Linked to original sources
PubMed1984

Adaptive modification of the vestibulo-ocular reflex by mental effort in darkness.

The vestibulo-ocular reflex (VOR) can be suppressed in darkness if a subject tries to imagine that he looks at a head fixed target. This mental suppression of VOR was used to induce adaptive changes in VOR gain during 3 h of active head oscillations in complete darkness. VOR gain changes were tested by asking the subject to look at a visual target; then passively or actively the head was turned in darkness while the subject "fixated" the same target. Corrective saccades occurring at the end of the movement when lights were turned on give an elegant measure of VOR gain. Three hours of training induced in 3 subjects a mean of 10.9% and 11.4% decrease of VOR gain for passive and active conditions, respectively. This demonstrates that reflex adaptation can be obtained without external cues, and probably with only an internal reconstruction of target and eye movement.

Adaptation, Physiological↗
PubMed1984

A reevaluation of intervestibular nuclear coupling: its role in vestibular compensation.

Recent experimental observations indicate that pathways interconnecting the bilateral vestibular nuclei (VN) may provide positive-feedback loops for signals across the midline. The implications of such positive feedback are considered in the context of vestibular compensation. A simple conceptual model of the interconnected VN is studied analytically, based on the hypothesis that the restoration of central symmetry is achieved via changes of neural gain in closed commissural loops. A wide variety of experimental conditions related to vestibular compensation are investigated. Analytic model predictions are compared to behavioral and neurophysiological findings in the literature. The results show that organized control over commissural gains in closed loops coupling the bilateral VN is fully compatible with all phenomena cited in the article. In particular, such a mechanism for vestibular compensation can reconcile observations such as the fact that Bechterew phenomena and decompensation can both be elicited from the compensated state. Placing the site of vestibular compensation in pathways linking the VN has many implications. Other forms of central neural plasticity (e.g., vestibuloocular reflex (VOR) gain plasticity) may rely on a similar principle, since modulation of transmidline coupling can be a very powerful means of altering responses in a bilateral nervous system.

Animals↗
PubMed1984

Relationships between somatic cell counts and milk production.

The relationship between Dairy Herd Improvement program test-day milk yield and somatic cell counts in milk was analyzed in 34 dairy herds over 3 yr. Estimates of this relationship were more accurate when somatic cell counts were transformed to natural logarithms rather than actual. For 67,707 observations, test-day milk yield decreased with increasing somatic cell count. The decrease of milk yield for second and later lactations, as somatic cell count increased, was greater than for first lactations. When herds were partitioned according to herd milk production (greater than 7700, 6500 to 7700, and less than 6500 kg/yr), decrease of milk yield was linear with increasing somatic cell counts for herds averaging below 7700 kg milk. Regressions were linear, quadratic, and cubic for both parity groups in herds with high production, over 7700 kg/yr. Quarter samples were composited for each cow and cultured. Percentage of infected cows increased as somatic cell counts increased with greater infection rates above 400 X 10(3).

Animals↗
PubMed1984

Chromosomal radiosensitivity of human tumor cells during the G2 cell cycle period.

Thirteen cell lines derived from human tumors of diverse tissue origin and histopathology were compared with 12 lines of normal skin fibroblasts with respect to chromatid damage induced by 25, 50, or 100 R of X-irradiation during the G2 period of the cell cycle. Only cells in metaphase were examined, and these had been irradiated 1.5 hr before fixation. When irradiated under identical conditions, the tumor cells showed significantly more chromatid breaks and gaps than did the normal cells at all doses tested. The data suggest that the increased G2 chromosomal radiosensitivity of the tumor cells is associated with deficient DNA repair during the G2-prophase period of the cell cycle.

Cell Line↗
PubMed1983

Chromatid damage after G2 phase x-irradiation of cells from cancer-prone individuals implicates deficiency in DNA repair.

Ten lines of skin fibroblasts from individuals with genetic disorders predisposing to a high risk of cancer were compared with nine lines from normal adult donors with respect to chromatid damage after x-irradiation [25, 50, and 100 rad (0.25, 0.50, and 1 gray)] during G2 phase. The 10 cell lines represented five genetic disorders: Bloom syndrome, familial polyposis, Fanconi anemia, Gardner syndrome, and xeroderma pigmentosum, complementation groups A(XP-A), C(XP-C), E(XP-E), and variant (XP-Va). The incidence of chromatid breaks in all cancer-prone lines except XP-E and XP-A was significantly higher than in the normal lines. The incidence of chromatid gaps in all cancer-prone lines except XP-A and XP-Va was significantly higher than in the normal lines. Because each chromatid apparently contains a single continuous DNA double strand, chromatid breaks and gaps represent unrepaired DNA strand breaks arising directly or indirectly during excision repair of x-ray-induced DNA damage. These cytogenetic data together with results from use of the DNA repair inhibitor arabinofuranosyl cytosine (cytosine arabinoside) suggest that cells from all of these cancer-prone individuals are deficient in some step of DNA repair, predominantly excision repair operative during the G2-prophase period of the cell cycle. It appears that these DNA repair deficiencies are associated with a genetic predisposition to a high risk of cancer.

Abnormalities, Multiple↗
PubMed1982

Metabolic profiles in Virginia dairy herds of different milk yields.

This study examined metabolic profiles of commercial dairy herds differing in milk production. Thirty herds were selected with 10 herds averaging more than 7258 kg milk, 10 herds between 6350 and 7258 kg, and 10 herds averaged below 6350 kg. In each herd, 28 cows were selected for blood sampling, which was collected every 3 mo during 12 mo. Cows varied in estimated relative producing ability. Metabolic profiles were established for 19 blood components. Differences among treatment means were significant between high and low producing herds and little between profiles for milking and pregnant nonlactating cows. Metabolic profiles of problem herds remained within normal ranges for all herds except one. Profiles of herds with breeding or mastitis problems remained in the normal range. Metabolic profile testing was of limited value in screening a dairy herd for potential problems or deficiencies.

Animals↗
PubMed1982

Repair of chromosome damage induced by X-irradiation during G2 phase in a line of normal human fibroblasts and its malignant derivative.

A line of normal human skin fibroblasts (KD) differed from its malignant derivative (HUT-14) in the extent of cytogenetic damage induced by X-irradiation during G2 phase. Malignant cells had significantly more chromatid breaks and gaps after exposure to 25, 50, or 100 rad. On the assumption that each chromatid contains a single continuous DNA double helix, chromatid breaks would represent unrepaired DNA double-strand breaks; the gaps may represent single-strand breaks. Results from alkaline elution of cellular DNA immediately after irradiation showed that the normal and malignant cells in asynchronous population were equally sensitive to DNA single-strand breakage by X-irradiation. Caffeine or beta-cytosine arabinoside (ara-C), inhibitors of DNA repair, when added directly following G2 phase exposure, significantly increased the incidence of radiation-induced chromatid damage in the normal cells. In contrast, similar treatment of the malignant cells had little influence. Ara-C differed from caffeine in its effects; whereas both agents increased the frequency of chromatid breaks and gaps, only ara-C increased the frequency of gaps to the level observed in the irradiated malignant cells. Addition of catalase, which destroys H2O2, or mannitol, a scavenger of the derivative free hydroxyl radical (.OH), to the cultures of malignant cells before, during, and following irradiation significantly reduced the chromatid damage; and catalase prevented formation of chromatid gaps. The DNA damage induced by X-ray during G2 phase in the normal KD cells was apparently repaired by a caffeine- and ara-C-sensitive mechanism(s) that was deficient or absent in their malignant derivatives.

4-Nitroquinoline-1-oxide↗
PubMed1981

Light-induced chromatid damage in human skin fibroblasts in culture in relation to their neoplastic potential.

Skin fibroblasts from ataxia telangiectasia and xeroderma pigmentosum (XP) donors and from the XP sib (possible heterozygote), all genetically predisposed to a high risk of cancer, show an increased susceptibility to light-induced chromatid breaks after culture in vitro. Light-induced chromatid breaks were shown previously to result from generation of hydrogen peroxide (H2O2) during light exposure. The level of susceptibility attained is significantly higher than that observed in 13 lines of fibroblasts from normal skin of donors ranging in age from 3 days to 92 years or from fetal skin tested at various population doubling levels. Two lines of normal skin fibroblasts transformed by chemical carcinogens to neoplastic cells also show a significant increase in susceptibility as compared with their untransformed controls. These data indicate for human cells, as reported earlier for mouse cells, an association between enhanced susceptibility to light-induced chromatid damage and neoplastic potential; this association is further supported by the high susceptibility of cells derived from a human adenocarcinoma. Two observations are consistent with the concept that the increased susceptibility does not result from greater initial damage to the DNA of the neoplastic cells. First, activities of the ubiquitous H2O2 scavenging enzyme, glutathione peroxidase, are similar in the paired normal and neoplastic cell populations. Second, cells of the paired lines are equally sensitive to DNA breakage by exogenous H2O2. The enhanced susceptibility associated with neoplastic potential may result from an impaired capacity to repair DNA rather than a greater initial sensitivity of the neoplastic cells to the damaging agent.

Adult↗
PubMed1981

Differential visual adaptation of vertical canal-dependent vestibulo-ocular reflexes.

Reversing vision in the horizontal (left-right) plane in humans induces adaptive mechanisms and even reversal of the horizontal vestibulo-ocular reflex (HVOR). The present experiments were aimed at investigating if such adaptive modifications could be observed in the frontal plane by reversal of the torsional visual world movements. Torsional vestibulo-ocular reflex (TVOR) was measured in one subject who wore Dove prisms for 19 days. The gain of TVOR was tested in the dark with the head leaned backward and rotating around an earth vertical axis with sinusoidal rotation (1/6 HZ). The gain decreased from 0.27 to 0.13 at 70 degrees peak-to-peak amplitude, and from 0.3 to 0.11 at 45 degrees peak-to-peak amplitude after 19 days of prism-wearing. Full gain recovery was observed 10 days after prism removal. The results are compared with the observation that in the same situation the vertical VOR (up-down) is not reversed (Dove prisms do not reverse visual images in this plane). As the same four (vertical) canals produce both reflexes, it is suggested that central neuronal mechanisms allow the recognition of the geometrical pattern of visual reversals and selectively adapt the reflex in the relevant planes.

Acclimatization↗
PubMed1980

The plate-implant as a bioassay for the neoplastic potential of cultured cells.

One objective of this study was to test the plate implant as an in vivo bioassay for the neoplastic state with pairs of cell lines that were non-tumorigenic and tumorigenic when inoculated in suspension at various sites. Each pair originated from a common cell pool or from one cell derived from normal rat or mouse embryonic tissue. The implantation of cells attached to polycarbonate plates was compared with the subcutaneous injection of comparable numbers of cells in suspension or the intraocular injection of 10(5) cells. In addition, some implants of glass helices with attached cells were made into syngeneic mice and compared with injection of comparable cell numbers intramuscularly into X-irradiated hosts. A total of 10 lines or clones were tested on plates. Of four lines that were non-tumorigenic when inoculated in suspension either subcutaneously or intraocularly, two were tumorigenic when implanted subcutaneously attached to plastic plates. The remaining two are the first permanent rodent lines that have not been tumorigc on plastic plates. Of the remaining six lines, all were tumorigenic on plates and two produced sarcomas at a higher frequency on plates than in suspension. Cytologic diagnoses of the cells implanted on plates, subcutaneously and intraocularly, correlated best with the results from plate implants. Of three mouse lines implanted on helices, two were equally tumorigenic in suspension and on helices, whereas the third was tumorigenic on helices only. The plate implant was more satisfactory technically than the helices and proved to be one of the most sensitive bioassays for the neoplastic state of cultured cells.

Animals↗
PubMed1980

Expanding food-animal veterinary services through nutritional consultation.

Practitioners can increase their value to their clients as well as increase the gross veterinary product by developing supplemental expertise in nontraditional disciplines. This can be accomplished through continuing education and the utilization of technical support services such as the professional nutritionist. In addition, contemporary technology such as the electronic moisture tester and the pH meter can be implemented in the acquisition of nutritional diagnostic data. A comprehensive herd health program is precisely the delivery system into which such complimentary expertise can be integrated successfully.

Animal Feed↗
PubMed1980

Computerized feeding management systems for economic decision-making.

Linear programming has been useful in the formulation of feeding guidelines for lactating cows. The most economical rations can be fed. Newer feeding management systems are being developed as new nutritional findings permit greater refinement. This report describes the use of computerized feeding management systems in helping dairy farmers make sound economic decisions. Such procedures are useful to the feed industry, dairy consultants, and in development of extension education programs.

Animals↗