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Biomedical subjects

J R Turner

Publications and source records attributed to J R Turner.

At least 127 records · Page 7Linked to original sources
PubMed1984

Temporal consistency of individual differences in cardiac response to a video game.

Three experiments are reported which examined the temporal stability of cardiac reactions to a video game of the 'space invaders' genre. Experiment 1 also addressed the matter of inter-task consistency; in addition to the video game, subjects were presented with an unsignalled reaction time task and led to believe that relatively quick reactions attracted financial reward, while slower ones brought either a burst of loud noise or withdrawal of money previously earned. Forty-two male subjects were tested on both tasks on two occasions, a week apart. Of the two tasks, the video game elicited the greater reactivity. In addition, individual variations in reactivity showed striking temporal stability for both tasks. However, inter-task consistency was much less marked; in fact, a significant inter-task correlation was obtained only on the first occasion of testing. It is probable that limited consistency here was in some measure due to the ineffectiveness of our reaction time task in eliciting substantial reactivity. Finally, reactivity was independent of baseline heart rate level. In experiment 2, three extreme high and three extreme low cardiac reactors were selected from an initial sample of 23 male subjects, on the basis of reactivity during an initial session with the video game, and subsequently studied during four further sessions. Once more, impressive stability of heart rate reactivity was apparent over sessions. In experiment 3, we examined the reliability of individual variations in cardiac reactivity in women and the issue of whether temporal stability is constrained by menstrual cycle effects. Twenty-four females were tested on the video game both preovulatory and postovulatory, with half being tested first during the preovulatory phase and half being tested first during the postovulatory phase. Again, the most striking finding was the marked stability of individual variations in cardiac reactivity over both time and menstrual cycle phase.

Adolescent↗
PubMed1981

Procedure for assay of tobramycin in serum containing moxalactam.

Moxalactam was examined as a substrate for 11 beta-lactamases. Hydrolysis was shown only with the beta-lactamase from Bacillus cereus, a nonpathogenic bacterium. Tobramycin was assayed in tobramycin-moxalactam mixtures by using this beta-lactamase.

Anti-Bacterial Agents↗
PubMed1980

Oscillations of frequency in Batesian mimics, hawks and doves, and other simple frequency dependent polymorphisms.

It is customary to infer the properties of the internal equilibria produced by frequency dependent selection from the properties of the boundary equilibria (often called the "invasion" criterion). This paper demonstrates that there are some circumstances that there is a truly stable, unique, internal equilibrium. For two alleles with complete dominance, if phenotype fitness declines monotonically with increasing frequency, then the internal point of equal phenotype fitness is the unique internal equilibrium of the genes, and is not unstable; this criterion may also be met if the fitness of one phenotype increases with frequency. It must be truly stable, in the sense of not producing oscillations, if the decline of fitness is linear or convex upwards and no phenotype is lethal at any frequency; the hawk-dove game complies with both conditions, and at least the second condition is likely to be met in most of the models encountered in sociobiology. However, an equilibrium which induces damped oscillations, or perhaps even complex limit cycles, is possible if at least one phenotype can be lethal at high frequency, or if the decline in fitness is strongly curvilinear and concave upwards. One case of curvilinear frequency dependence, a dimorphic batesian mimic with a non-mimetic form, is examined in detail. Although oscillations about the recessive or Y-linked, this will only occur when selection coefficients are very large, and (except for Y-linkage) only if both sexes can be mimetic. As selection is density as well as frequency dependent, such conditions may be produced in the real world by large fluctuations in population size.

Adaptation, Biological↗
PubMed1980

Thyroid uptake of 123I in a normal population.

Iodine 131 for thyroidal uptake and scan exposes the thyroid to potentially carcinogenic doses of radiation. Iodine 123, on the other hand, compares equally with 131I for uptake studies yet reduces thyroid radiation exposure substantially. Reported fluctuations in normal thyroidal iodine uptake over the past decade, as well as possible radiation injury with 131I, prompted examination of uptake values in a normal population using 123I. The normal range defined in 100 euthyroid subjects was 1% to 8.8% at two hours, and 4% to 27% for the 24-hour uptake. These results are significantly lower than observed eight years ago in this area. No relationship was noted between uptake values and thyroid indices, age, sex, ponderal index, estrogen ingestion, or urinary iodine excretion. Purified 123I appeared to provide clinically reliable results with a substantial reduction in potential radiation injury.

Female↗
PubMed1979

Contrasted modes of evolution in the same genome: allozymes and adaptive change in Heliconius.

Butterflies in the South American genus Heliconius have undergone a spectacular adaptive radiation (with convergent evolution between some lines) in their color patterns; this has been produced by natural selection for muellerian mimicry. The genetic basis of this radiation, shown by crossing highly differentiated races within two of the species, is homozygosity for alternative alleles at some half dozen loci. In complete contrast, allozyme loci in these butterflies are strongly heterozygous and show only frequency differences (never amounting to homozygosity of alternative alleles) between races; the amount of allozyme divergence is the same between races of H. erato and H. sara, although in color pattern the first forms marked races and the other does not. For the allozymes, there is a strong correlation over loci for rate of divergence between species and average heterozygosity. This is not true of the genes controlling color pattern. Heterozygosity of the enzymes is correlated with subunit molecular weight. Thus, different parts of the genome can evolve in different ways simultaneously; genes controlling color pattern in the "classical" mode, and allozymes in a different mode in which the rate of evolution is related to their heterozygosity (a "balance" or "neutral" mode).

Animals↗
PubMed1979

Lack of correlation between beta-lactamase production and susceptibility to cefamandole or cefoxitin among spontaneous mutants of Enterobacteriaceae.

A large number of cultures of gram-negative bacteria were examined for their susceptibility to various concentrations of cefamandole, cefoxitin, carbenicillin, and nalidixic acid. Heterogeneity of susceptibility was demonstrated in individual cultures to all of these antibiotics. Resistant clones isolated from cefamandole or cefoxitin plates were examined for beta-lactamase production. Approximately 13% of 262 resistant clones acquired the ability to produce a beta-lactamase. Examination of the substrate profile of the beta-lactamases from some of these clones revealed no change in the specific activity of these enzymes for cefamandole, cephaloridine, or compound 87/312 as compared with their parental enzymes. This study clearly shows that some resistant clones do not produce beta-lactamases, whereas some susceptible strains produced significant amounts of these enzymes. We conclude from these findings that little correlation exists between beta-lactamase production and decreased susceptibility to cefamandole or cefoxitin. The results suggest the possibility that characteristics other than beta-lactamase production may be responsible for resistance in Enterobacteriaceae.

Cefamandole↗
PubMed1979

The treatment of hypertension with propranolol and bendrofluazide.

In 101 hypertensive patients, the effects of a combination of propranolol and bendrofluazide were compared with those of each drug alone. After an introductory period with a placebo, the patients received, in a double-blind randomized trial, propranolol 80 mg twice a day, bendrofluazide 2.5 mg twice a day, or both drugs together twice daily. The combination produced significantly greater reductions in lying, standing, and post-exercise systolic and diastolic blood pressure than either drug separately. Side-effects were minimal and the combination was well accepted by patients.

Adult↗
PubMed1978

A simple and inexpensive method for the recording of scintillation camera data at low and moderate count rates.

In a small routine nuclear medicine department the majority of imaging on a gamma camera involves count rates within about 15 000 CPS. The analogue approach described enables images within this range to be recorded without loss of uniformity or resolution. The equipment needed is only two channels per isotope of an instrumentation recorder and simple additional pulse shaping circuitry. For information about an area of interest simple comparators and a pen recorder may be used. The major cost would be the instrumentation recorder (at present a suitable 40 kHz machine is available for about 3000 lbs.). The additional electronics may be quite easily built in a small department at nominal cost, and the rate meter and pen recorder are likely to be found in most departments. The approach has gross limitations and could not be used for studies above about 20 000 CPS, it would only be suitable for slow dynamic studies such as renograms, but the simplicity of the method, the immediate replay on site, and almost instant quantitative data after a patient study without any need for programming, together with the very low cost, make this system attractive for a small routine department without access to a digital computer.

Scintillation Counting↗
PubMed1978

A32390A, a new biologically active metabolite. III. In vitro and in vivo antifungal activity.

A32390A, an isonitrile-containing derivative of mannitol, represents a new class of antifungal antibiotics. In vitro antifungal activity of A32390A was found against Candida albicans, Cryptococcus neoformans and Histoplasma capsulatum. In vivo antifungal activity of A32390A was demonstrated in mice infected with C. albicans. Accumulative doses of 37.5 approximately 600 mg/kg, administered subcutaneously over a 24-hour period, showed significant activity without demonstrating toxicity. A32390A was effective, but not as effective as amphotericin B, in reducing the number of Candida cells isolated from the kidney of infected mice. Urinary excretion of A32390A accounted for only 10% of the administered dose. Improved bioavailability of A32390A was accomplished when the antibiotic was combined with polyvinyl pyrrolidone (PVP) in a solid dispersion. Administration of A32390A as a 10% dispersion in PVP resulted in increased urinary excretion of the drug and reduced the amount of drug required for in vivo activity.

Animals↗
PubMed1977

Delineation of the relative antibacterial activity of cefamandole and cefamandole nafate.

By conventional laboratory evaluation procedures, the in vitro antibacterial activities of cefamandole and its O-formyl ester, cefamandole nafate, appear virtually identical. When the activities of these two compounds were examined for their ability to lyse log-phase cultures of susceptible bacteria, however, cefamandole was found to be about 10 times more active than cefamandole nafate. Cefamandole nafate was shown to be rapidly converted to cefamandole in bacteriological media, with a half-life of less than 1 h at a pH of 7.0 or above. At pH 6.0, in log-phase inhibition experiments, however, cefamandole nafate is more stable, allowing delineation of the activity between cefamandole and cefamandole nafate. The efficacy of cefamandole was identical to that of cefamandole nafate in treating experimental animal infections, indicating that rapid conversion of cefamandole nafate to cefamandole occurs in vivo.

Animals↗
PubMed1976

Substrate inhibition of beta-lactamases, a method for predicting enzymatic stability of cephalosporins.

Selected cephalosporins, including cefamandole, cephaloridine, cephaloglycin, and cefoxitin, were examined for their ability to inhibit the enzymatic activity of and act as substrates for beta-lactamases produced by Enterobacter cloacae and Staphylococcus aureus. Enzyme inhibition was determined by Michaelis-Menten kinetic measurements and by a spot plate assay using a chromogenic substrate (Glaxo compound 87/312). These two methods provide comparable estimates of kinetic parameters. Inhibition of beta-lactamase, as measured by these two methods, was generally found to correlate with resistance to hydrolysis and is proposed as a preliminary method of assessing susceptibility of cephalosporins to beta-lactamase hydrolysis. Four 7-alphaOCH(3), 7-alphaH cephalosporin analogue pairs were also examined. The presence of the 7-alphaOCH(3) substituent invariably resulted in reduced susceptibility to enzymatic hydrolysis, regardless of the other C7 substituent. The 7-alphaOCH(3) compounds were also better inhibitors than were their 7-alphaH analogues, with the exception that 7-alphaOCH(3) compounds having C7 adipic acid substituents were less inhibitory to the S. aureus enzyme than were the corresponding 7-alphaH analogues. Response of these two enzymes to 7-alphaOCH(3) and 7-alphaH cephalosporins suggests that beta-lactamase hydrolysis of these compounds involves attack at the alpha side of the betalactam ring.

Amidohydrolases↗
PubMed1976

Colonization of the intestinal tract of conventional mice with Candida albicans and treatment with antifungal agents.

Conventional mice inoculated with Candida albicans per os were unable to maintain this organism in the intestinal tract as judged by decreasing numbers of yeast recoverable from feces. After inoculation with 10(7) cells/mouse, fecal counts ranged from 10(5) cells per g of feces to 5 x 10(3) cells per g of feces during a 12-day experimental period. Addition of various antibiotics to the drinking water did not result in any improvement in maintenance or stability of the gut population. A combination of X irradiation and administration of tobramycin or gentamicin, however, resulted in a stable population of C. albicans in the intestinal tract, with cell counts in the feces remaining constant at a level of about 10(6)/g of feces for a period of 10 to 15 days. The usefulness of this model in assessing the effect of experimental drugs on C. albicans infections of the gut was demonstrated by the fact that treatment with a new antifungal antibiotic (A9145), amphotericin B, 5-fluorocytosine, or nystatin resulted in a reduction in the fecal counts of C. albicans from experimentally infected animals.

Animals↗
PubMed1975

Absence of crossing-over in female butterflies (Heliconius).

Absence of recombination between linked markers in female Heliconius is suggested by coupling backcross broods in H. erato, by a repulsion F2 in H. melpomene, and by other crosses with this species. No recombinants have been found in the offspring of doubly heterozygous females in either species. This supports the contention that the absence of chiasmata at oogenesis in these bufferflies prevents genetic crossing-over. Chiasmata are absent in all the female Lepidoptera examined by Suomalainen and others, but Ephestia seems to show the absence of chiasmata but the presence of genetic recombination in the female, and therefore would repay further study.

Animals↗
PubMed1975

Rapid detection of ampicillin-resistant Haemophilus influenzae and their susceptibility to sixteen antibiotics.

Ampicillin-resistant and -susceptible strains of Haemophilus influenzae were tested for susceptibility to 16 antibiotics. Chloramphenicol and a new cephalosporin, cefamandole, were most active with minimal inhibitory concentrations (MICs) for all bacteria tested between 0.5 to 2.0 mug/ml. All but two organisms were susceptible to tetracycline. Ampicillin-resistant strains of H. influenzae were less susceptible (MIC, 4 to 32 mug/ml) to carbenicillin and ticarcillin than ampicillin-susceptible organisms (MIC, 0.25 to 1.0 mug/ml). A rapid assay for beta-lactamase, utilizing a chromogenic cephalosporin substrate, detected enzyme production in all 17 ampicillin-resistant strains of H. influenzae.

Ampicillin↗