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C Naylor

Publications and source records attributed to C Naylor.

At least 19 recordsLinked to original sources
PubMed2005

Potential kinetic availability of metals in sulphidic freshwater sediments.

The insolubility of metal sulphides is believed to limit the bioavailability of trace metals in sulphidic sediments. However, if non-equilibrium conditions are important, metals may be more available than simple thermodynamic calculations suggest. To investigate the possible dynamic supply of Cu, Ni and Zn in a sulphidic freshwater sediment, they were measured, along with iron, manganese and sulphide, by the technique of diffusive gradients in thin-films (DGT). DGT measures the supply of solute from sediment to solution in response to a local solute sink. Release of Mn, Cu, Zn and Ni was observed at the sediment surface and attributed to the supply from reductive dissolution of manganese oxides. The depth profile of simultaneously extractable metals (SEM) for Cu and Ni followed the shape of the Mn profile more closely than the profiles of either acid volatile sulphur (AVS) or Fe, again consistent with supply from Mn oxides. Solubility calculations for a mesocosm of homogenised sediment indicated supersaturation with respect to the sulphides of Fe, Cu, Ni and Zn, yet DGT measurements demonstrated a substantial supply of both trace metals and sulphide from the solid phase to the pore waters. Ratios of metals measured in pore waters by DGT were consistent with their release from iron and manganese oxides, indicating that supply, as much as removal processes, determines the pseudo-steady state concentrations in the pore waters. The observations suggest that trace metals are not immediately bound in an insoluble, inert form when they are in contact with sulphide. This has consequences for modelling metal processes in sediment, as well as for uptake by some biota.

Acrylic Resins↗
PubMed2005

Key role of Chlamydophila psittaci on Belgian turkey farms in association with other respiratory pathogens.

Two hundred turkey sera from eight Belgian and two French farms were tested for the presence of antibodies against avian pneumovirus (APV), Ornithobacterium rhinotracheale (ORT), Mycoplasma gallisepticum, Mycoplasma meleagridis and Chlamydophila psittaci. At slaughter, C. psittaci, APV and ORT antibodies were detected in 94, 34 and 6.5% of the turkeys, respectively. No antibodies against M. gallisepticum or M. meleagridis were present. Additionally, turkeys on three Belgian farms were examined from production onset until slaughter using both serology and antigen or gene detection. All farms experienced two C. psittaci infection waves, at 3-6 and 8-12 weeks of age. Each first infection wave was closely followed by an ORT infection starting at the age of 6-8 weeks, which was still detectable when the second C. psittaci infection waves started. Animals on farm A were not vaccinated against APV leading to an APV subtype B outbreak accompanying the first C. psittaci infection wave. Despite subtype A APV vaccination on farms B and C, the second C. psittaci infection waves were accompanied (farm B) or followed (farm C) by a subtype B APV infection. On all farms respiratory signs always appeared together with a proven C. psittaci, APV and/or ORT infection. This study suggests an association between C. psittaci, APV and ORT, and indicates the multi-factorial aetiology of respiratory infections in commercial turkeys. All three pathogens should be considered when developing prevention strategies for respiratory disease.

Age Factors↗
PubMed2005

Tolerance to nicotine in mice lacking alpha7 nicotinic receptors.

RATIONALE: Previous studies have suggested that a knockout of the gene coding for alpha7 nicotinic receptor subunits influences the behaviour of undrugged mice but not the acute effect of nicotine on locomotor activity. OBJECTIVES: The present studies extend these observations to nicotine tolerance assessed by means of schedule-controlled behaviour. METHODS: Groups of alpha7-/- and alpha7+/+ mice were trained to press levers under an FR20 schedule of food reinforcement. The acute response rate-depressant effects of nicotine were determined in both genotypes and the mice were then subdivided into groups treated daily with nicotine (1.2 mg/kg/day) or saline. After 39 days of exposure to this regimen, the dose-response curves were re-determined. RESULTS: Knockout of the alpha7 gene had no consistent effect on the lever-pressing behaviour of undrugged mice and did not influence the acute, dose-related, response rate-depressant effect of nicotine (0.2-1.2 mg/kg). When dose-response curves for nicotine (0.4-2.0 mg/kg) were re-determined after daily dosing with the drug, both wild-type and knockout mice developed similar tolerance to nicotine, as shown by approximately 2.5-fold shifts to the right of the dose-response curves. CONCLUSIONS: Nicotinic receptors containing the alpha7 subunit do not play a significant role in the regulation of the lever-pressing behaviour studied or in the acute behavioural depressant effect of nicotine and the development of tolerance to that effect. Such results contrast with previous reports suggesting profound impairments in sensitivity to nicotine in nicotinic receptor beta2-/- mice.

Animals↗
PubMed2004

Simultaneous release of sulfide with Fe, Mn, Ni and Zn in marine harbour sediment measured using a combined metal/sulfide DGT probe.

The technique of DGT (Diffusive Gradients in Thin Films) was further developed to allow simultaneous measurement of sulfide and trace metals at the same location in sediment. The new combined DGT probe consisted of a layer of gel impregnated with AgI, overlain by (1) a layer of gel containing Chelex, (2) a layer of gel and (3) a filter membrane. Diffusion of sulfide was controlled by layers (1) to (3), while diffusion of metals was controlled by layers (2) and (3). The Chelex gel trapped metals that were measured after elution with acid. The AgI gel trapped sulfide through the formation of Ag2S. This was then measured densitometrically as the colour changed from pale yellow to grey. Experiments demonstrated that concentrations of metal or sulfide measured by the combined device were no different to the concentrations measured by more conventional devices. The presence of Chelex in the gel did not impede the diffusion of sulfide. Deployment of a combined probe in marine sediment revealed simultaneous remobilisation of metals and sulfide at the same location. Solubility calculations indicated that some precipitation of amorphous FeS was probably occurring at the maxima in sulfide concentrations. There was general undersaturation with respect to NiS, but ZnS was supersaturated at all locations. There appeared to be localised active zones of organic matter decomposition, where reduction of manganese oxides, iron oxides and sulfate occurred simultaneously. Mass balance calculations indicated that Ni could not be supplied by release from decomposing organic matter. Manganese oxides were the most likely source, but supply from reductive dissolution of iron oxides could not be entirely discounted. Supply from either Fe or Mn oxides could account for the Zn maxima. Application of the newly developed combined probe provides new information that helps understanding of the complex nature of trace metal and sulfur chemistry in sediments.

Chemistry Techniques, Analytical↗
PubMed2002

Predictions of in situ solid/liquid distribution of radiocaesium in soils.

Previous work has demonstrated that plant uptake of radiocaesium (RCs) is related to the activity concentration of RCs in soil solution, which is linked to the soil/soil solution distribution coefficient, K(D). The solid-liquid distribution of RCs is generally studied in soil suspensions in the laboratory and there are few reported measurements for in situ soil solutions. From a data set of 53 different soils (contaminated with either 134CsCl or 137CsCl) used in pot trials to investigate grass uptake of RCs, we analysed the variation of in situ K(D) with measured soil properties. The soils differed widely in % clay (0.5-58%), organic matter content (1.9-96%) and pH (2.4-7.0, CaCl2). The K(D) varied between 29 and 375,000 L kg-' (median 1460 L kg(-1)). Stepwise multiple regression analysis showed a significant correlation between the log K(D) and pH (p < 0.001), log %clay (p < 0.01) and log exchangeable K (p < 0.001) (overall R2 = 0.70). The in situ K(D) values were further compared to K(D)S predicted using an existing model, which assumes that RCs sorption occurs on specific sites and regular ion-exchange sites on the soil solid phase. Sorption of RCs on specific sites was quantified from the radiocaesium interception potential (RIP) measured for each soil and the soil solution concentrations of K+ and NH4+. The in situ log K(D) correlated well with the predicted K(D) (R2 = 0.85 before plant growth, R2 = 0.83 after plant growth). However, the observations were fivefold to eightfold higher than the predictions, particularly for the mineral soils. We attribute the under-prediction to the long contact times (minimum 4 weeks) between the RCs tracers and our experimental soils relative to the short (24 h) contact times used in RIP measurements. We conclude that our data confirmed the model but that ageing of RCs in soil is a factor that needs to be considered to better predict in situ KD values.

Cesium Radioisotopes↗
PubMed2000

Duration of cross-protection between subtypes A and B avian pneumovirus in turkeys.

The degree and duration of clinical and virological cross-protection between avian pneumovirus subtypes A and B were examined in two-week-old pneumovirus antibody-free turkeys. The turkeys were inoculated with either a virulent subtype A (Belgian isolate A/T6/96), a virulent subtype B (Belgian isolate B/T9/96), an attenuated subtype A or an attenuated subtype B, and challenged homologously and heterologously with virulent avian pneumovirus two, five and 11 weeks after inoculation. Birds inoculated with virulent A or B virus showed typical respiratory signs from three to seven days after inoculation. After challenge, no clinical signs were observed in any of the groups, and no virus was isolated from the turkeys that had been initially inoculated with a virulent strain. Virulent virus was recovered from the birds that had been initially inoculated with attenuated subtypes and challenged five and/or 11 weeks later with a heterologous virulent strain. Birds challenged after five weeks showed a serological booster reaction only when they had been inoculated initially with a virulent or attenuated subtype B and challenged with subtype A. Seroconversion was observed in all the groups challenged after 11 weeks except when they had been inoculated initially with attenuated subtype B and challenged with subtype B.

Animals↗
PubMed1999

Discrimination and self-administration of nicotine by inbred strains of mice.

These studies aim to characterize the discriminative stimulus effects of nicotine in two inbred strains of mice that differ in many pharmacological responses, and to investigate the feasibility of IV self-administration studies with nicotine in one of the strains. For discrimination studies, three groups of C57BL/6 and one group of DBA/2 mice were trained in a two-lever operant conditioning paradigm with a tandem VI-30" FR-10 schedule of food reinforcement. After 40 training sessions, accuracy reached 57.5, 77.5 and 90.0% in C57BL/6 mice trained with (-)-nicotine (SC) in doses of 0.4, 0.8 and 1.6 mg/kg, respectively (n = 8). DBA/2 mice trained with 0.8 mg/kg nicotine attained similar (73.3 %) accuracy (n = 9). Results from extinction tests showed that all groups of mice yielded orderly dose-response curves for nicotine (0.03-1.6 mg/kg), but stimulus control remained notably weaker for the mice trained with 0.4 mg/kg nicotine than for any other group. Overall rates of responding in the undrugged state were lower for DBA/2 than for C57BL/6 mice; DBA/2 mice were also slightly less sensitive than C57BL/6 mice to the response rate-reducing effect of nicotine. The nicotine antagonist mecamylamine (1.5 mg/kg SC) blocked the discriminative stimulus effect of the training dose of nicotine in all groups. The results of the IV self-administration study suggest that nicotine (0.1 mg/kg) can serve as a positive reinforcer in drug-naive C57BL/6J mice (n = 13). Behaviour maintained by 0.1 mg/kg nicotine injections was significantly greater than behaviour maintained by vehicle injections, and it was maintained under an intermittent schedule of reinforcement (FR4). The methods described provide possible approaches for genetic analyses of strain differences in sensitivity to the discriminative and reinforcing stimulus properties of nicotine.

Animals↗
PubMed1998

On the mechanism of the reaction catalyzed by glucose 6-phosphate dehydrogenase.

The catalytic mechanism of glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides was investigated by replacing three amino acids, His-240, Asp-177, and His 178, with asparagine, using site-directed mutagenesis. Each of the mutant enzymes was purified to homogeneity and characterized by substrate binding studies and steady-state kinetic analyses. The three-dimensional structure of the H240N glucose 6-phosphate dehydrogenase was determined at 2.5 A resolution. The results support a mechanism in which His-240 acts as the general base that abstracts the proton from the C1-hydroxyl group of glucose 6-phosphate, and the carboxylate group of Asp-177 stabilizes the positive charge that forms on His-240 in the transition state. The results also confirm the postulated role of His-178 in binding the phosphate moiety of glucose 6-phosphate.

Aspartic Acid↗
PubMed1998

Use of a satellite-derived land cover map to estimate transport of radiocaesium to surface waters.

During the weeks to months after the deposition of radioactive fallout, the initial concentration of radioactivity in rivers and lakes declines as a result of flushing and removal to bottom sediments. In the long-term, however, radioactivity in the water body can remain at significant levels as a result of secondary contamination processes. In particular, it is known that soils contaminated by long-lived radionuclides such as 137Cs and 90Sr provide a significant source to surface waters over a period of years after fallout. Using The Land Cover Map of Great Britain, a satellite-derived land cover map as a surrogate indicator of soil type, we have related catchment land cover type to long-term 137Cs activity concentrations in 27 lakes in Cumbria, UK. The study has shown that satellite-derived maps could be used to indicate areas vulnerable to high long-term 137Cs transport to surface waters in the event of a nuclear accident. In these Cumbrian lakes, it appears that residual 137Cs levels are determined by transfers of 137Cs from contaminated catchments rather than within-lake processes. Only three of the cover types, open shrub moor, bog and dense shrub moor, as identified by the satellite, are needed to explain over 90% of the variation in long-term 137Cs activity concentrations in the lakes, and these have been shown to correlate spatially with occurrence of organic soils.

Cesium Radioisotopes↗
PubMed1997

Towards the routine application of nucleic acid technology for avian disease diagnosis.

The use of nucleic acid technology (polymerase chain reaction, probing, restriction fragment analysis and nucleotide sequencing) in the study of avian diseases has largely been confined to fundamental analysis and retrospective studies. More recently these approaches have been applied to diagnosis and what one might call real-time epidemiological studies on chickens and turkeys. At the heart of these approaches is the identification and characterisation of pathogens based on their genetic material, RNA or DNA. Among the objectives has been the detection of pathogens quickly combined with the simultaneous identification of serotype, subtype or genotype. Nucleic acid sequencing also gives a degree of characterisation unmatched by other approaches. In this paper we describe the use of nucleic acid technology for the diagnosis and epidemiology of infectious bronchitis virus, turkey rhinotracheitis virus (avian pneumovirus) and Newcastle disease virus.

Animals↗
PubMed1993

Freeze-dried Chlorella vulgaris as food for Daphnia magna Straus in toxicity testing.

The continuous culture of fresh green algae for use as food for Daphnia magna in toxicity tests is labor intensive. The possibility of using freeze-dried Chlorella vulgaris as an off-the-shelf food was investigated. The performance of D. magna provided with freeze-dried food was investigated over several generations and was found to satisfy the current EC validity criteria. However, a number of life-history parameters, for example, fecundity and neonate size, were significantly reduced when compared to animals fed fresh algae. The effect of freeze drying on cell size and availability are investigated and discussed in relation to daphnid performance.

Animals↗
PubMed1993

Variation in the development of cadmium resistance in Daphnia magna straus; effect of temperature, nutrition, age and genotype.

The extent to which responses to toxicants can be modified by the environment and genotype of Daphnia magna is important for interpreting the results from ecotoxicity tests. Variation in the development of cadmium resistance and its relevance for survivorship has been investigated in two genetically distinct clones of D. magna. Cadmium resistance was induced by pre-exposing daphnids to a sublethal concentration of a Cd/Zn mixture and thereafter cadmium tolerance was assessed in standard acute tests. The results showed that the ability to develop cadmium resistance is affected by temperature, but there is no consistent pattern for maternal nutrition. The age of the daphnids had no apparent effect on the development of cadmium resistance. Differences in the induction of cadmium resistance between clones were seen only under resource depression.

Journal Article↗
PubMed1992

Frozen algae as food for Daphnia magna Straus in toxicity testing.

As EC validity criteria for the production of Daphnia magna neonates in standard toxicity tests set fecundity minima which must be attained, it is important that culture conditions provide an adequate ration of high quality food. Maintaining a steady supply of fresh algae can be problematical so the possibility of using frozen food was investigated. The performance of three generations of D. magna fed on diets of fresh or frozen Chlorella was compared. There were no significant effects on fecundity due to food type or generation. Cumulative fecundity (over 21 days) on fresh or frozen food exceeded 120 neonates per female and satisfied that EC validity criterion (60 neonates per female). In addition criteria relating to survival and variability were met. We conclude that frozen Chlorella are an acceptable substitute for fresh algae.

Animals↗
PubMed1992

Induction of cadmium tolerance in two clones of Daphnia magna straus.

1. The abilities of two different genotypes of Daphnia magna to develop cadmium resistance through physiological adaptation, after pre-exposure to sublethal concentrations of Cd, Zn and Cd/Zn mixtures, was investigated. 2. The induced elevation in cadmium tolerance was shown to be associated with an increase in the body concentration of metallothionein-like proteins. 3. The highly significant difference in acute responses to cadmium between the two clones reduced after pre-exposure. 4. Differences in cadmium tolerance were shown to be associated with differences in cadmium uptake.

Animals↗
PubMed1990

Effect of stress on a freshwater benthic detritivore: scope for growth in Gammarus pulex.

Scope for growth (SfG), a measure of energy balance (between food intake and metabolic output) within animals, has been used as an indicator of pollution stress in marine systems. However, it has not been used commonly in freshwater systems and here we investigate the sensitivity of SfG in Gammarus pulex, a benthic freshwater crustacean, under conditions often associated with pollution. The effects of four specific substances were investigated; a metal (zinc), an organic (3,4-dichloroaniline), and two dissolved gases (oxygen and ammonia). In all cases SfG was reduced by the stress, primarily due to a depression in energy intake. Only with ammonia was energy output (respiration) significantly affected.

Ammonia↗
PubMed1990

Field deployment of a scope for growth assay involving Gammarus pulex, a freshwater benthic invertebrate.

Scope for growth (SfG) is a measure of the energy balance of an animal (i.e., the difference between energy intake and metabolic output). The SfG of marine invertebrates, particularly the mussel Mytilus edulis, has been successfully used as the basis of a field bioassay to detect a range of stresses both natural (temperature, food, salinity) and anthropogenic (hydrocarbons, sewage sludge). SfG of the freshwater amphipod Gammarus pulex was found to be a sensitive indicator of stress under laboratory conditions and here we describe the field deployment of this technique and present data from three field trials. In every case, SfG was reduced at the downstream polluted site compared with that at an upstream reference site. This reduction in SfG was the result of a decrease in energy intake (absorption) rather than an increase in energy expenditure (respiration).

Animals↗
PubMed1989

Comparative studies on mannosylphosphoryl dolichol and glucosylphosphoryl dolichol synthases.

Factors affecting the synthesis of mannosylphosphoryl dolichol and glucosylphosphoryl dolichol hen oviduct microsomes were compared in order to gain insight into the properties of their respective synthases. A stabilized form of mannosylphosphoryl dolichol synthase, but not glucosylphosphoryl dolichol synthase, was released from microsomes by freezing the membranes after exposure to the detergent CHAPSO. The activation energy for mannosylphosphoryl dolichol synthesis in membranes was 9.4 glucosylphosphoryl dolichol synthesis in membranes had a similar activation energy, 8.1 kcal/mol, but below 18 degrees C the value was 16.7 kcal/mol. Tryptic digestion of sealed microsomes preferentially inactivated mannosylphosphoryl dolichol synthase; however, both synthases were equally inactivated in detergent-permeabilized microsomes. Periodate-oxidized UDP-Glc was used to probe the topological orientation of glucosylphosphoryl dolichol synthase in rat liver microsomes. Sealed microsomes treated with oxidized UDP-Glc were inactive in synthesis of glucosylphosphoryl dolichol. However, when these treated microsomes were permeabilized, glucosylphosphoryl dolichol synthase activity was readily detected. From these studies we conclude that although mannosyl- and glucosylphosphoryl dolichol synthases catalyze chemically similar reactions in the endoplasmic reticulum, they differ in several respects. These differences were interpreted in terms of a topological model in which the active sites of the two enzymes reside on opposite faces of the endoplasmic reticulum, with that of the glucosyl lipid synthase facing the lumen and that of the mannosyl lipid synthase facing the cytosol.

Animals↗