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Biomedical subjects

S J Clark

Publications and source records attributed to S J Clark.

At least 37 records · Page 2Linked to original sources
PubMed2003

Responses of plants and invertebrate trophic groups to contrasting herbicide regimes in the Farm Scale Evaluations of genetically modified herbicide-tolerant crops.

Effects of genetically modified herbicide-tolerant (GMHT) and conventional crop management on invertebrate trophic groups (herbivores, detritivores, pollinators, predators and parasitoids) were compared in beet, maize and spring oilseed rape sites throughout the UK. These trophic groups were influenced by season, crop species and GMHT management. Many groups increased twofold to fivefold in abundance between early and late summer, and differed up to 10-fold between crop species. GMHT management superimposed relatively small (less than twofold), but consistent, shifts in plant and insect abundance, the extent and direction of these effects being dependent on the relative efficacies of comparable conventional herbicide regimes. In general, the biomass of weeds was reduced under GMHT management in beet and spring oilseed rape and increased in maize compared with conventional treatments. This change in resource availability had knock-on effects on higher trophic levels except in spring oilseed rape where herbivore resource was greatest. Herbivores, pollinators and natural enemies changed in abundance in the same directions as their resources, and detritivores increased in abundance under GMHT management across all crops. The result of the later herbicide application in GMHT treatments was a shift in resource from the herbivore food web to the detritivore food web. The Farm Scale Evaluations have demonstrated over 3 years and throughout the UK that herbivores, detritivores and many of their predators and parasitoids in arable systems are sensitive to the changes in weed communities that result from the introduction of new herbicide regimes.

Agriculture↗
PubMed2003

Invertebrate responses to the management of genetically modified herbicide-tolerant and conventional spring crops. I. Soil-surface-active invertebrates.

The effects of herbicide management of genetically modified herbicide-tolerant (GMHT) beet, maize and spring oilseed rape on the abundance and diversity of soil-surface-active invertebrates were assessed. Most effects did not differ between years, environmental zones or initial seedbanks or between sugar and fodder beet. This suggests that the results may be treated as generally applicable to agricultural situations throughout the UK for these crops. The direction of the effects was evenly balanced between increases and decreases in counts in the GMHT compared with the conventional treatment. Most effects involving a greater capture in the GMHT treatments occurred in maize, whereas most effects involving a smaller capture were in beet and spring oilseed rape. Differences between GMHT and conventional crop herbicide management had a significant effect on the capture of most surface-active invertebrate species and higher taxa tested in at least one crop, and these differences reflected the phenology and ecology of the invertebrates. Counts of carabids that feed on weed seeds were smaller in GMHT beet and spring oilseed rape but larger in GMHT maize. In contrast, collembolan detritivore counts were significantly larger under GMHT crop management.

Agriculture↗
PubMed2003

Invertebrate responses to the management of genetically modified herbicide-tolerant and conventional spring crops. II. Within-field epigeal and aerial arthropods.

The effects of the management of genetically modified herbicide-tolerant (GMHT) crops on the abundances of aerial and epigeal arthropods were assessed in 66 beet, 68 maize and 67 spring oilseed rape sites as part of the Farm Scale Evaluations of GMHT crops. Most higher taxa were insensitive to differences between GMHT and conventional weed management, but significant effects were found on the abundance of at least one group within each taxon studied. Numbers of butterflies in beet and spring oilseed rape and of Heteroptera and bees in beet were smaller under the relevant GMHT crop management, whereas the abundance of Collembola was consistently greater in all GMHT crops. Generally, these effects were specific to each crop type, reflected the phenology and ecology of the arthropod taxa, were indirect and related to herbicide management. These results apply generally to agriculture across Britain, and could be used in mathematical models to predict the possible long-term effects of the widespread adoption of GMHT technology. The results for bees and butterflies relate to foraging preferences and might or might not translate into effects on population densities, depending on whether adoption leads to forage reductions over large areas. These species, and the detritivore Collembola, may be useful indicator species for future studies of GMHT management.

Agriculture↗
PubMed2003

Migration and genetic structure of the grain aphid (Sitobion avenae) in Britain related to climate and clonal fluctuation as revealed using microsatellites.

Genetic structuring of populations reflects the interaction of genetic drift, mutation, migration and selection, with influences from life history. Aphids are interesting in this regard as they have the potential for unusually high levels of dispersal and natural selection, which typically counter each other. In the present study, winged grain aphids Sitobion avenae (F.) were collected in four 12.2-m high suction traps along a north-south transect in Britain in order to eliminate sampling bias from plant hosts (cereals and grasses; Poaceae), it being known that these insects show host adaptation demonstrable using molecular markers. Samples were analysed at four polymorphic microsatellite loci over two consecutive years. Population allele frequencies were similar nationally during the two years, although clonal diversity varied greatly between sites and years. In the first sampling year following a harsh winter, diversity was found to display a latitudinal clinal trend: the proportion of unique clones (genotypes) increased with latitude. However, this pattern was less apparent the following year, after a milder winter. Nonetheless, overall FST analysis showed that there was little spatial genetic structuring in either sampling year. These data support the view that the insect is highly migratory and also support a theoretical model and previous data suggesting that the reproductive mode is clinal in S. avenae. This appears to be because natural selection (reduced reproductive success of asexual genotypes under cold conditions) is sufficiently powerful to overcome the homogenizing effects of strong migration. There was no clear evidence for isolation by distance for the genetic data obtained. The data are compared with similar data from other aphid species and other insects. Only by the collection of such data sets can an accurate picture be built up relating genetic variability to flight behaviour, including migratory ambit in this group of insects since, due to their small size and rapid dilution in the air, other marking approaches are impracticable over large geographical distances.

Animal Migration↗
PubMed2002

Parametrization and validation of a force field for liquid-crystal forming molecules.

First principles density functional calculations have been carried out to determine the structures and conformational energies of a series of liquid-crystal fragment molecules. The calculations have been used to derive a molecular mechanics force field that describes a subset of commonly occurring liquid-crystal molecules. The force field has been used to carry out molecular dynamics simulations of the bulk phase for these fragment molecules. Computed densities and heats of vaporization are in good agreement with experimental data. These results should be useful in future molecular dynamics simulations of liquid-crystal systems.

Journal Article↗
PubMed2002

Right ventricular performance in hypotensive preterm neonates treated with dopamine.

Systemic hypotension with left ventricular dysfunction is a common complication of neonatal respiratory distress syndrome and is often treated with inotropic agents. Although pulmonary hypertension with elevated pulmonary vascular resistance is also an important pathophysiological finding in respiratory distress syndrome, the effect of inotropes on the right ventricle has not been studied. The aim of this study was to assess changes in right ventricular dimensions and function with inotropic therapy in hypotensive preterm infants. Hypotensive neonates with respiratory distress syndrome were studied before and 1 hour after the initiation of a dopamine infusion. Right ventricular performance was assessed by two-dimensional echocardiography using the ellipsoid approximation method. Eight hypotensive neonates were recruited with a median (interquartile range) gestation of 27 weeks (26 to 27 weeks). Right ventricular end systolic volume decreased significantly from a median (interquartile range) of 1.06 ml/kg (0.81-1.50 ml/kg) to 0.73 ml/kg (0.51-0.99 ml/kg) (p < 0.01) 1 hour following dopamine therapy. Right ventricular end diastolic volume did not change significantly. Right ventricular ejection fraction increased significantly from 0.36 (0.29-0.46) to 0.51 (0.43-0.53) ( p < 0.01). There was a trend toward an increase in right ventricular output from 90 ml/kg/min (67-115 ml/kg/min) to 112 ml/kg/min-143 ml/kg/min) (p=0.07). Dopamine increases right ventricular ejection fraction through a reduction in right ventricular end systolic volume.

Cardiotonic Agents↗
PubMed2002

Measurement of right ventricular volume in healthy term and preterm neonates.

BACKGROUND: Pulmonary hypertension is associated with worse perinatal outcomes in infants with respiratory disorders. In such infants right ventricular dysfunction may result in poor pulmonary blood flow. OBJECTIVE: To evaluate the practicability and repeatability of echocardiographic measurements of right ventricular volume in healthy term and preterm neonates, and to follow changes in right ventricular volume over the first 2 days of life. METHODS: Serial echocardiographic examinations were performed on day 0, 1, and 2 on healthy term and preterm neonates. Two methods of estimating right ventricular volume were assessed: the ellipsoid approximation and Simpson's stacked discs methods. Systolic and diastolic volumes on days 1 and 2 were compared with baseline values on day 0. Term and preterm volumes were compared at the same time points. RESULTS: Thirty five infants were recruited, 18 term and 17 preterm. Right ventricular volumes were significantly lower on day 1 and day 2 than baseline in both term and preterm infants. Median (interquartile range) end systolic and diastolic volumes for term infants on days 0, 1, and 2 were 1.04 (0.88-1.44), 0.82 (0.70-1.03), 0.92 (0.72-0.97) ml/kg and 2.21 (2.10-2.75), 2.05 (1.81-2.38), 1.91 (1.81-2.13) ml/kg respectively. In preterm infants the values were 1.09 (0.91-1.16), 0.72 (0.54-0.91), 0.61 (0.54-0.76) ml/kg and 2.09 (1.71-2.25), 1.47 (1.23-1.98), 1.43 (1.22-1.78) ml/kg respectively. CONCLUSION: Right ventricular volume decreases over the first 2 days of life in healthy term and preterm infants.

Cardiac Output↗
PubMed2001

Loss of annexin II heavy and light chains in prostate cancer and its precursors.

Annexin II mRNA coding for a calcium binding protein was found to be absent in prostate cancer by subtractive hybridization and Northern analysis. In contrast to high expression in normal and benign hyperplastic glandular and basal epithelium, Annexin II heavy (p36) and light (p11) chains in 31/31 prostate cancer specimens were lost immunohistochemically. In glands involved by prostate intraepithelial neoplasia, 65% lost both chains in glandular epithelial cells, whereas basal cells were all positively stained. Southern analysis of cancer DNA showed no noticeable deletion in p36 gene. LNCaP cells treated with 5-azacytidine re-expressed p36, suggesting methylation could be responsible for the silencing.

Adult↗
PubMed2001

Bisulfite genomic sequencing: systematic investigation of critical experimental parameters.

Bisulfite genomic sequencing is the method of choice for the generation of methylation maps with single-base resolution. The method is based on the selective deamination of cytosine to uracil by treatment with bisulfite and the sequencing of subsequently generated PCR products. In contrast to cytosine, 5-methylcytosine does not react with bisulfite and can therefore be distinguished. In order to investigate the potential for optimization of the method and to determine the critical experimental parameters, we determined the influence of incubation time and incubation temperature on the deamination efficiency and measured the degree of DNA degradation during the bisulfite treatment. We found that maximum conversion rates of cytosine occurred at 55 degrees C (4-18 h) and 95 degrees C (1 h). Under these conditions at least 84-96% of the DNA is degraded. To study the impact of primer selection, homologous DNA templates were constructed possessing cytosine-containing and cytosine-free primer binding sites, respectively. The recognition rates for cytosine (>/=97%) and 5-methylcytosine (>/=94%) were found to be identical for both templates.

5-Methylcytosine↗
PubMed2001

Hepatitis B vaccination practices in hospital newborn nurseries before and after changes in vaccination recommendations.

BACKGROUND: Routine use of hepatitis B vaccine for low-risk newborns was suspended on July 7, 1999, because of concern about the potential risk of thimerosal, a mercury-containing vaccine preservative. Reinstatement of the birth dose was recommended when a thimerosal-free vaccine became available. OBJECTIVE: To explore changes in hepatitis B vaccination practices for newborns related to the revised recommendations for low-risk infants (in this study, the terms newborn and infant are used interchangeably). DESIGN: A telephone survey of a random sample of 1000 US hospitals. PARTICIPANTS: Nurse managers, nursery directors, and staff nurses of the newborn nurseries. MAIN OUTCOME MEASURES: Nursery vaccination practices before and after July 7, 1999, and the availability and use of thimerosal-free vaccine. RESULTS: Interviews were conducted with 773 (87%) of 886 eligible hospitals. Before July 7, 1999, 78% of the hospitals reported vaccination practices that were consistent with recommendations at that time, although only 47% vaccinated all low-risk infants at birth. After July 7, 1999, almost all hospitals discontinued vaccination of low-risk infants, in accordance with the recommendation change; however, there was a 6-fold increase in the number of hospitals that were not vaccinating all high-risk infants. After the introduction of thimerosal-free vaccine, only 39% of the hospitals reported vaccinating all low-risk infants. CONCLUSIONS: Most hospital nurseries altered their newborn hepatitis B vaccination practices consistent with changes in national recommendations. However, unintended consequences included the failure of some hospitals to continue vaccinating all high-risk infants and the delay in reintroducing vaccination for low-risk newborns after the introduction of a thimerosal-free vaccine. Assessments of the appropriateness of this country's response to the threat of thimerosal in vaccines should consider these findings.

Data Collection↗
PubMed2001

Reference ranges for thyroid function tests in premature infants beyond the first week of life.

OBJECTIVES: To establish reference ranges for the more sensitive assays of thyrotropin and the best available assays of free thyroxine in premature infants after the first week of life. STUDY DESIGN: Free thyroxine measurements by direct equilibrium dialysis and thyrotropin measurements by third generation immunometric assay were measured in 120 healthy premature infants 25 to 36 weeks' gestation at birth and every 3 weeks until hospital discharge. Infants were stratified by postconceptional age. Differences in free thyroxine and thyrotropin levels among groups were determined by ANOVA. Correlations between hormone measurements and gestational and postnatal ages were sought by linear regression analysis. Reference ranges were determined as arithmetic (free thyroxine) and geometric (thyrotropin) mean+/-2 SD ranges. RESULTS: From 120 infants, 164 samples were obtained and grouped by postconceptional age at sampling. Free thyroxine was not different among postconceptional age groups and did not correlate with gestational or postnatal age. The free thyroxine reference range based on these data was 10 to 33 pmol/l (0.8 to 2.6 ng/dl). Thyrotropin did not correlate with gestational age. There was a clinically trivial but statistically significant (r(2)=0.03, p<0.05) correlation of thyrotropin with postnatal age. The thyrotropin reference based on these data was 0.8 to 12 mU/l. CONCLUSIONS: Free thyroxine was closely regulated in these premature infants and levels were similar to those in older children and adults, once the natal surge in thyrotropin has subsided. After the first week of life a single range for each hormone appeared appropriate for all premature infants until 40 weeks postconceptional age.

Female↗
PubMed2001

Population-scale laboratory studies of the effect of transgenic plants on nontarget insects.

Studies of the effects of insect-resistant transgenic plants on beneficial insects have, to date, concentrated mainly on either small-scale "worst case scenario" laboratory experiments or on field trials. We present a laboratory method using large population cages that represent an intermediate experimental scale, allowing the study of ecological and behavioural interactions between transgenic plants, pests and their natural enemies under more controlled conditions than is possible in the field. Previous studies have also concentrated on natural enemies of lepidopteran and coleopteran target pests. However, natural enemies of other pests, which are not controlled by the transgenic plants, are also potentially exposed to the transgene product when feeding on hosts. The reduction in the use of insecticides on transgenic crops could lead to increasing problems with such nontarget pests, normally controlled by sprays, especially if there are any negative effects of the transgenic plant on their natural enemies. This study tested two lines of insect-resistant transgenic oilseed rape (Brassica napus) for side-effects on the hymenopteran parasitoid Diaeretiella rapae and its aphid host, Myzus persicae. One transgenic line expressed the delta-endotoxin Cry1Ac from Bacillus thuringiensis (Bt) and a second expressed the proteinase inhibitor oryzacystatin I (OC-I) from rice. These transgenic plant lines were developed to provide resistance to lepidopteran and coleopteran pests, respectively. No detrimental effects of the transgenic oilseed rape lines on the ability of the parasitoid to control aphid populations were observed. Adult parasitoid emergence and sex ratio were also not consistently altered on the transgenic oilseed rape lines compared with the wild-type lines.

Animals↗
PubMed2001

Temporal changes in insulin sensitivity following the development of acute liver failure secondary to acetaminophen.

Insulin resistance in chronic liver disease (CLD) is well documented. This study investigated whether similar changes occur in acute liver failure (ALF). Patients with ALF (n = 10) were recruited within 72 hours of their peak prothrombin time (range 42-120 seconds). All patients were ventilated for encephalopathy (grade III-IV). Peripheral and endogenous insulin sensitivity were assessed by a hyperinsulinemic euglycemic clamp (Human Actrapid 1.5 mU/min/kg) with an infusion of D-[6,6-(2)H(2)] glucose. The clamp was performed on day 0 and then on day 7 and day 14. During the insulin infusion, the mean total peripheral glucose uptake (area under the curve [AUC]) was 1,422 (SD, 1,253), 2,244 (SD, 1,392), and 4,500 (SD, 1,120) micromol/kg on days 0, 7, and 14, respectively. Significant changes occurred from day 0 to 14 (day 14-day 0: 3,078 [95% CI, 1,798 to 4,359]; P =.001) and day 7 to 14 (day 14-day 7: 2,256 [95% CI, 923 to 3,589]; P =.001). No significant difference in endogenous glucose production was demonstrated over time. Mean peripheral insulin sensitivity altered over time, increasing from 0.09 (SD, 0.09) micromol/kg/min/mU/L on day 0 to 0.24 (SD, 0.16) on day 7 and 0.5 (SD, 0.1) on day 14. Significant changes occurred between days 0, 7, and 14 (day 7-day 0: 0.15 [95% CI, 0.04 to 0.26], P =.006; day 14-day 0: 0.4 [95% CI, 0.28 to 0.5], P =.001; day 14-day 7: 0.2 [95% CI, 0.12 to 0.38], P =.001). This study demonstrates that in ALF, impaired peripheral uptake of glucose occurs, peripheral insulin sensitivity being restored at 2 weeks in subjects who survived.

Acetaminophen↗
PubMed2001

The effect of natural enemies on the spread of barley yellow dwarf virus (BYDV) by Rhopalosiphum padi (Hemiptera: Aphididae).

The effects of two natural aphid enemies, adult Coccinella septempunctata Linneaus, a predator, and Aphidius rhopalosiphi de Stefani Perez, a parasitoid, on spread of barley yellow dwarf virus (BYDV) transmitted by the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) were studied under laboratory conditions. Predators or parasitoids were introduced to trays of durum wheat seedlings and the patterns of virus infection were observed after two, seven and 14 days of exposure. More plants were infected with BYDV in control trays without A. rhopalosiphi than in trays with the parasitoid present, both seven and 14 days after the introduction of parasitoids. Patterns of virus infection were found to be similar over time in trays with a parasitoid present and in control trays. More plants were infected in trays with C. septempunctata present than in control trays, both two and seven days after the introduction of the coccinellid. The spread of virus infections progressed differently over time for the two treatments (predator and parasitoid), differences between treatments being most marked after two days and seven days, when more plants exposed to predators but fewer exposed to parasitoids were infected with BYDV compared to their respective controls. However, by the 14th day 88% of all plants were infected and there was no significant difference between the two treatments. The role of natural enemies in spread of BYDV is discussed.

Animals↗
PubMed2001

Measurement of intraosseous pressures generated by the Wand, high-pressure periodontal ligament syringe, and the Stabident system.

Intraosseous pressure generated by the use of three anesthetic systems-the Wand; a hand-operated high-pressure periodontal ligament (PDL) syringe; and the Stabident system-were studied in fresh mandibles of 14 large swine. The mandibles were drilled and tapped in one area of both the right and left posterior molar regions. Pressure gauges were attached via threaded fittings. Pressures during injection were recorded for the Wand first, then the PDL syringe, and finally Stabident. Results showed averages of 8.3 mm Hg generated by the Wand, 16.3 mm Hg with the high-pressure PDL syringe, and 43.7 mm Hg from the Stabident system. Results were corroborated with data from three human cadaver mandibles.

Analysis of Variance↗
PubMed2001

Degradation of the sealing properties of a zinc oxide-calcium sulfate-based temporary filling material by entrapped cotton fibers.

During root canal therapy cotton may be placed in the pulp chamber before placement of a temporary filling. This study evaluated the effect on the sealing of a zinc oxide-calcium sulfate-based temporary filling material when fibers of the internal cotton passed through the filling material and reached the external surface of the temporary filling. Glass tubes were filled with a 3.5 mm thickness of the temporary filling incorporating a bundle of cotton fibers that passed from the inner surface of the restoration to the outer surface. The time for methylene blue stain to penetrate the filling was compared among four groups. Group 1 (large bundles of fibers) had 20 to 40 fibers, group 2 (medium bundles) had 10 to 15 fibers, group 3 (small bundles) had 3 to 5 fibers, and group 4 (negative controls) had no cotton fibers. All samples with cotton fibers leaked within 12 min. None of the negative controls leaked within the 21 -day observation time. These results demonstrate that even a very small amount of cotton trapped between the wall of the tube and the filling material dramatically reduced the sealing quality of the temporary restoration.

Calcium Sulfate↗