Showing papers by "University of Hertfordshire published in 1993"

Spectral dependence of temporal point spread functions in human tissues

Abstract: We have determined the spectral dependence of the temporal point spread functions of human tissues experimentally between 740 and 840 nm in transmittance measurements on the adult head, forearm, and calf (inυivo) and the infant head (post mortem) by using picosecond laser pulses and a streak camera detector. Two parameters are extracted from the temporal point spread function; the differential path-length factor (DPF), calculated from the mean time, and the slope of the logarithmic intensity decay. In all tissues the DPF and the logarithmic slope show a reciprocal relationship and exhibit characteristics of the absorption spectra of hemoglobin. The DPF falls with increasing wavelength, the variation being typically 12%, while the logarithmic slope increases with wavelength. A quantitative analysis of the logarithmic slope spectrum significantly underestimated expected tissue chromophore concentrations. The absolute magnitudes of the DPF showed considerable intersubject variation, but the variation with wavelength was consistent and thus may be used in the correction of tissue attenuation spectra.

The relative importance of short‐ and long‐range movement of flying aphids

Abstract: Summary 1. Aphids are notorious pests of world agriculture. Even so, uncertainty persists as to their capacity for successful aerial dispersal. Evidence exists that, under some conditions, aphids can be wind-borne over long distances, i.e. hundreds of kilometers over desert or sea. It has been argued, in the recent past, that this phenomenon may be part of a strategy to locate fresh host plants in new distant areas. However, the proportion of these insects successfully colonizing new hosts is unknown. 2. Other work using meteorological backtracking has also indicated long-distance movement, but the accuracy of such predictions is dubious unless the altitude of transport is known. Mark-releaseecapture experiments with such small insects have limited potential due to large dilution effects. Static ‘snap-shots’ of demographic population densities, using suction traps, cannot accurately distinguish local aerial density fluxes and population movements from a distance. However, genetic and physiological markers may provide more direct information on population mixing; for example, some allozyme studies have shown a limited level of inter-population gene flow. 3. Under suitable conditions, aphids take off, maintain flight and alight in response to the appropriate visual and olfactory cues. Undoubtedly successful long-distance movement occurs from time to time, but its ecological relevance may have been overstated in the past. It may be selectively disadvantageous for aphids to move from areas containing their host plants. In contrast, it is advantageous for aphids to maximise their chances of survival and reproductive success by landing on suitable plant hosts at the earliest opportunity. 4. The clonal nature of aphids (a single genotype may comprise vast numbers of individuals) means that there may be advantages to phenotypic variation between individuals in the readiness to move. Recent evidence indicates that such a variation exists in the duration of the behavioural migratory phase, the initial period of maiden flight when host-plant cues are ignored and when landing is inhibited. 5. The relative biological importance of short- us. long-distance movements is reassessed with reference to plant virus epidemiology and the spread of new genotypes, e.g. insecticide resistance. It is concluded that the biological relevance of short-distance movements have a much greater impact on population and genotype distribution than long-distance movements, which may be comparatively infrequent.

Random amplified polymorphic DNA (RAPD) markers for genetic analysis in Allium

Abstract: RAPD analysis was applied to onion (Allium cepa) and otherAllium species in order to assess the degree of polymorphism within the genus and to investigate if this approach was suitable for genetic studies of onion. Seven cultivars ofA. cepa, including shallot, and single cultivars of Japanese bunching onion (A. fistulosum), chive (A. schoenoprasum), leek (A. ampeloprasum), and a wild relative of onion (A. roylei), were evaluated for variability using a set of 20 random 10-mer primers. Seven out of the twenty primers revealed scorable polymorphisms between cultivars ofA. cepa and these will be further evaluated for use in genetic mapping. Wide variations in banding profiles between species were observed with nearly every primer tested. These were assessed for use in systematic studies within the genus. Ninety-one band positions were scored (+/-) for all the cultivars studied. Genetic distances between each of the cultivars were calculated and cluster analysis was used to generate a dendrogram showing phylogenetic relationships between them. The resulting analysis was in broad agreement with previous classifications of the species studied, confirming the validity of the method. However, amongst the species studied, it placedA. roylei as the closest relative ofA. cepa, questioning the current classification of the former species in the section Rhizideum.

Knockdown resistance (kdr) to DDT and pyrethroid insecticides maps to a sodium channel gene locus in the housefly (Musca domestica)

Abstract: The voltage-sensitive sodium channel is generally regarded as the primary target site of dichlorodiphenyl-trichloro-ethane (DDT) and pyrethroid insecticides, and has been implicated in the widely reported mechanism of nerve insensitivity to these compounds. This phenomenon is expressed as knockdown resistance (kdr) and has been best characterised in the housefly where several putative alleles, including the more potent super-kdr factor, have been identified. We report the isolation of cDNA clones containing part of a housefly sodium channel gene, designated Msc, which show close homology to the para sodium channel of Drosophila (99% amino acid identity within the region of overlap). Using Southern blots of insect DNA, restriction fragment length polymorphisms (RFLPs) at the Msc locus were identified in susceptible, kdr and super-kdr housefly strains. These RFLPs showed tight linkage to resistance in controlled crosses involving these strains, thus providing clear genetic evidence that kdr, and hence pyrethroid mode of action, is closely associated with the voltage-sensitive sodium channel.

An Empirical Study of Occupational Stress Transmission in Working Couples

Abstract: The associations between work demands, supports, and levels of psychological and physical health have been clearly established by research. There is growing evidence that occupational stressors are transmitted to spouses, with a possible subsequent effect on disease risks and life expectancy of both marital partners. The present study investigates the extent and direction of occupational stress transmission and the possible psychological mechanisms in a survey of 60 working couples. It analyzes the relationships between partners' psychological strain levels, investigates the accuracy of couples perceptions of each other's work stressors, and analyzes the complex interrelationships between an individual's work and the mental well-being of their spouse. Results show that work-related discussion is frequent among marital partners and that individuals have accurate perceptions of their partners' jobs. The study found evidence of transmission of stress from men to women, particularly where men have high strain...

Optical properties of brain tissue

Abstract: A rigorous technique using a Monte Carlo model has been developed to determine the optical properties of biological tissue from goniometer and integrating sphere measurements. Using these techniques, the wavelength dependence of the phase function, g-value, absorption coefficient, scattering and reduced scattering coefficient were determined for postmortem neonate and adult human brain tissue over the wavelength range of 500 to 1000 nm. Single scattering phase functions as a function of wavelength have been measured using a goniometer system and optically thin tissue slices. Spectra for the absorption and scattering coefficients have been determined from a set of integrating sphere measurements, using a white light source and a CCD spectrometer. The integrating sphere data were analyzed using a novel Monte Carlo inversion technique, which makes use of the measured phase functions and which takes into account the effects of sample geometry and the angular dependence of specular reflection. This method overcomes some of the problems and shortfalls of the analytical techniques which employ Kubelka Munk or diffusion theory. The reduced scattering coefficients for all types of brain tissue showed a linear decrease with increasing wavelength. The wavelength dependence of the scattering coefficient and the phase function is shown to be considerable, and cannot be neglected.

Inhibitors of protein kinase C. 3. Potent and highly selective bisindolylmaleimides by conformational restriction.

Abstract: The protein kinase inhibitor staurosporine has been used to design a series of selective bisindolylmaleimide inhibitors of protein kinase C (PKC). Guided by molecular graphics, conformational restriction of the cationic side chain has led to ATP competitive inhibitors of improved potency and selectivity. Two compounds have been further evaluated and were shown to inhibit PKC of human origin and prevent T-cell activation in a human allogeneic mixed lymphocyte reaction. One of these compounds was orally absorbed in mice and antagonized a phorbol ester induced paw edema in a dose-dependent manner. This compound also selectively inhibited the secondary T-cell mediated response in a developing adjuvant arthritis model in rats and provides evidence for the potential use of PKC inhibitors as therapeutic immunomodulators.

A refutation of Karasek's demand – discretion model of occupational stress with a range of dependent measures.

Abstract: Summary Karasek's (1979) demand-discretion model of occupational stress has been highly influential but has been criticized as confounding social class variables (Payne and Fletcher, 1983), ignoring the curvilinearity of relationships (Warr, 1991), and because it has inconsistently predicted heart disease (Ganster and Fusilier, 1989). The present study examines the ability of the model to predict raised blood pressure (a risk factor in the development of CHD), anxiety, depression, job and life satisfaction, in a large heterogeneous sample of over 3000 people. It examines the predictability of the model for men and women, taking occupational classification (manual and non-manual workers) into account, to allow some control over social class confounding. It also examines nonlinear relationships in the data. The study showed that demands and discretion do separately predict psychological strain, job and life satisfaction, though they account for a very small percentage of the variance. There was no evidence of interactive effects which are central to the model. Where the model was able to predict blood pressure, relationships were consistently in the opposite direction to that hypothesized. There was also little evidence of curvilinear relationships. Interpersonal support was found to add significantly to the predictability of the dependent variables. The findings cast doubt on Karasek's model and suggest that emphasis should be shifted to those models which are more encompassing of support factors.

Functional characterization of three adenosine receptor types

Abstract: 1. The purpose of the present study was to classify adenosine receptors into A1 and A2 subtypes in a wide range of isolated tissues and cell types (rat adipocytes and atria, guinea-pig ileum and atria (A1); guinea-pig aorta, dog coronary artery and human platelets and neutrophils (A2)) using the R- and S-diastereoisomers of N-phenylisopropyladenosine (PIA), N-cyclopentyladenosine (CPA), the novel compound, N-[(1S,trans)-2-hydroxycyclopentyl]adenosine (GR79236), N-[(2-methylphenyl)methyl]adenosine (metrifudil), 2-(phenylamino)adenosine (CV1808), and 2[[2-[4-(2-carboxyethyl)phenyl]ethyl]amino]-N- ethylcarboxamidoadenosine (CGS21680); N-ethylcarboxamidoadenosine (NECA) was used as a standard. 2. Results obtained in all tissue preparations previously reported to contain A1-receptors could be described by a single rank order of agonist potency: CPA > or = GR79236, R-PIA > or = NECA >> S-PAI > or = metrifudil > or = CV1808, CGS21680. 3. In contrast, two distinct rank orders of agonist potency were observed in preparations previously reported to contain A2-receptors. In dog coronary artery, human neutrophils and platelets the rank order of potency was: CV1808, CGS21680 > or = NECA > R-PIA > or = metrifudil > or = CPA > GR79236 S-PIA. However, in guinea-pig aorta the rank order was: NECA > metrifudil > R-PIA, CPA > CV1808, GR79236 > or = S-PIA, CGS21680. 4. The results of this study are consistent with the existence of three types of adenosine receptor: A1-and two subtypes of A2-receptor. The receptor present in dog coronary artery, human platelets and neutrophils, probably corresponds to the A2a subtype, whilst that present in the guinea-pig aorta may be of the A2b subtype.

The occultation of 28 Sgr by Titan

Abstract: We present a comprehensive analysis of data obtained during the 1989 July 3 occultation of 28 Sgr by Titan. The data set includes 23 lightcurves from 15 separate stations, spanning wavelengths from 0.36 to 0.89 micron. A detailed model of the structure of Titan's atmosphere in the altitude range 250 to 450 km is developed, giving the distribution of temperature, pressure, haze optical depth, and zonal wind velocity as a function of altitude and latitude. Haze layers detected in Titan's stratosphere are about one scale height higher than inferred from Voyager data, and show a wavelength dependence indicative of particle sizes on the order of 0.1 micron. A marked north-south dichotomy in haze density is observed with a transition to lower density south of about -20 deg latitude. Zonal wind speeds are inferred from global distortions from spherical symmetry and are of the order of 100 m/s with significant increase toward higher latitudes. Titan's high atmosphere shows substantial axial symmetry; the position angle of the symmetry axis is equal to the position angle of Saturn's spin axis to within about 1 deg.

Paradoxical facilitation of pilocarpine-induced seizures in the mouse by MK-801 and the nitric oxide synthesis inhibitor L-NAME.

Abstract: The sensitivity of pilocarpine-induced seizures to NMDA receptor blockade with MK-801, or to inhibition of synthesis of the second messenger nitric oxide (NO) with N ω - nitro- L -arginine methyl ester ( L -NAME), was studied in mice. The NO precursor L -arginine (100–500 mg/kg, IP) and L -NAME (1–125 mg/kg, IP) had no overt effects on animals' behaviour by themselves, while MK-801 (0.1–0.8 mg/kg, IP) caused motor excitability at low doses and sedation and paraplegia at high ones. Contrary to expectation, MK-801 and L -NAME failed to protect mice against limbic motor seizures induced by pilocarpine (400 mg/ kg, IP), and L -arginine was not proconvulsant in mice challenged with a threshold convulsant dose of the cholinomimetic (100 mg/kg, IP). Surprisingly, both MK-801 and L -NAME were found to be proconvulsant when injected in conjunction with 100 mg/kg pilocarpine, and in both cases this convulsant action synergised with that produced by the dopamine D1 agonist SK&F38393 (10 mg/kg, IP). Concomitant administration of L -arginine (500 mg/kg) prevented the convulsant effect of 5 mg/kg L -NAME but was ineffective against 25 mg/kg L -NAME and MK-801. It is concluded that glutamate, acting through the NMDA receptor and NO production, normally suppresses epileptogenesis in the mouse pilocarpine model of limbic epilepsy.

A potent new class of kappa-receptor agonist: 4-substituted 1-(arylacetyl)-2-[(dialkylamino)methyl]piperazines.

Abstract: The synthesis of 4-substituted 1-(arylacetyl)-2-[(alkylamino)methyl]piperazines (10-22, 26, 27, and 30-33) and their activities as kappa-opioid receptor agonists are described. This includes a range of 4-acyl and 4-carboalkoxy derivatives with the latter series showing the greatest kappa-agonist activity. In particular, methyl 4-[(3,4-dichlorophenyl)acetyl]-3-[(1-pyrrolidinyl) methyl]-1-piperazinecarboxylate (18) displays exceptional potency and selectivity. It showed the following activities in functional in vitro assays: rabbit vas deferens (kappa-specific tissue) IC50 = 0.041 nM, rat vas deferens (mu-specific tissue) IC50 > 10,000 nM, and hamster vas deferens (delta-specific tissue) IC50 > 10,000 nM. Compound 18 is also a highly potent antinociceptive agent, as determined in the mouse acetylcholine-induced abdominal constriction test: ED50 = 0.000 52 mg/kg, sc. The activity of 18 resides solely in its 3(R)-enantiomer. The kappa-agonist activity in both the 4-acyl and the 4-carbamate series is sensitive to the size of the 4-substituent. In addition, it would appear that an appreciable negative electrostatic potential in this region of the molecule is an important requirement for optimal potency.

Inhibition of cytochrome P450 reductase by the diphenyliodonium cation. Kinetic analysis and covalent modifications.

Abstract: Diphenyliodonium has been shown to be an irreversible, time-dependent inhibitor of NADPH cytochrome P450 oxidoreductase (EC 1.6.2.4) with the Ki for diphenyliodonium chloride being 2.8 mM. Kinetic studies have indicated that diphenyliodonium interacts with the reduced enzyme and NADPH is essential for inactivation to take place. Cytochrome c acts as a competitive substrate. The use of radiolabeled diphenyliodonium has enabled two sites of covalent modification to be identified. Isolation of radiolabeled cofactor followed by mass spectrometry has shown that a phenyl group is added to FMN while the FMN is effectively trapped in the reduced state. Trypsin digestion of S-carboxymethylated P450 reductase after inhibition with radiolabeled inhibitor shows covalent modification of the protein. Purification of a single radiolabelled peptide followed by automated Edman degradation has enabled identification of the second site of covalent attachment as Trp 419.

Do small riverine fish move inshore at night

Abstract: We tested the hypothesis that numbers of small fish increase along river banks with decreasing light levels. Fish were sampled every 3h over a 24-h period (30–31 August 1992) along two adjacent stretches of bank (one shallow sand, one steep boulder) on the R. Morava near Breelav, Czech Republic. The size of fish was significantly greater along the boulder bank than along the sand bank. Numbers of fish along the steep boulder bank did not increase with decreasing light levels, except in Rhodeus sericeus and perch Perca fluviatilis, which were significantly more abundant at night. Along the shallow sand bank, all species increased in number at night, most significantly so. As light levels decreased, numbers of whitefin gudgeon Gobio albipinnatus and roach Rutilus rutilus decreased along the boulder bank, as their numbers increased along the sand bank, suggesting a dusk migration to the sand bank to avoid predation. This assumption was corroborated by the significantly higher number of potentially piscivorous fishes (P. ftuviatilis and chub Leuciscus cephalus≥ 80 mm) along the boulder bank during the night.

Electronic marking instrument

Abstract: A hand-held marking device comprises an electrically actuated writing head (20) for making marks on a writing surface and a sensor (40) for detecting when the writing head is moving in any direction in a plane parallel to the surface. The device includes means (57) for causing the head to be actuated when the sensor detects relative movement of the writing head and the surface. The writing head can be arranged to be able to make a plurality of different types or sizes of marks on a writing surface, in which case means (53-55) are provided for selecting which of the different mark types or sizes is to be made.

Investigations into factors determining the duration of action of the β2-adrenoceptor agonist, salmeterol

Abstract: 1. This study has explored the mechanism underlying the long duration of action of the beta 2-adrenoceptor agonist, salmeterol. 2. Salmeterol, salbutamol and isoprenaline caused a concentration-related inhibition of electrically-induced contractile responses of the guinea-pig superfused trachea preparation. The effects of both isoprenaline and salbutamol were rapid in onset and rapidly reversed upon removal of the agonist. In contrast, the effects of salmeterol were slower in onset and could not be reversed by superfusion of the tissue with agonist-free Krebs solution even for periods of up to 10 h. 3. The effects of salmeterol were, however, readily reversed by a number of beta-adrenoceptor blocking drugs, as was the effect of a continuous infusion of isoprenaline. Upon removal of the antagonist, however, the effects of salmeterol and of the isoprenaline infusion were reasserted at a rate which was inversely related to the lipophilicity of a beta-adrenoceptor blocking drugs. 4. Salmeterol inhibited the binding of [125I]-(-)-iodopindolol (100 pM) to rat lung membranes (pIC50 7.1), with isoprenaline (pIC50 6.2) and salbutamol (pIC50 5.1) having lower potencies. The inhibition of binding by salmeterol was apparently non-competitive, whereas that produced by salbutamol and isoprenaline was competitive in nature. 5. Isoprenaline and salbutamol rapidly dissociated from their binding sites, whereas in marked contrast, the binding of salmeterol showed no dissociation for periods of up to 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Ion distribution in cereal leaves: pathways and mechanisms

Abstract: Measurement of ion concentrations in the vacuoles of different cell types in cereal leaves using a variety of techniques indicates that ions are differentially distributed between different cell types. Thus mesophyll cells are enriched in P but contain relatively little Ca 2+ or Cl - , whereas the reverse is true for epidermal cells. Solutes reach the leaf via the transpiration stream and we consider three possible pathways which they could follow from the xylem to leaf cells. The first is a fully apoplastic mesophyll pathway in which both water and solutes move together through the leaf apoplast passing bundle sheath, mesophyll and epidermis in turn. The second is a partly symplastic mesophyll pathway in which ions and water pass into the symplast at the mestome/bundle sheath cells. Water continues to sites of evaporation via either a transcellular or symplastic pathway, but ions may be secreted back to the mesophyll apoplast and move to the epidermis along an extracellular route. The third is a vein extension pathway which provides a diffusional pathway for ions to the epidermis. A testable hypothesis for the roles of the pathways in supplying solutes to the mesophyll and epidermis is proposed and the implications of each of these pathways for transport systems in individual cell types is discussed.

Characterization of the inhibitory prostanoid receptors on human neutrophils

Abstract: 1. We have evaluated the effects of various prostanoid agonists on the release of leukotriene B4 (LTB4) and superoxide anions (O2-) from human neutrophils stimulated with opsonized zymosan (OZ) and formyl-methionyl-leucyl-phenylalanine (FMLP), respectively. 2. Prostaglandin E2 (PGE2) and PGD2 inhibited both OZ-induced LTB4 release (EC50 0.72 microM and 0.91 microM respectively), and FMLP-induced O2- release (EC50 0.42 microM and 0.50 microM respectively). PGF2 alpha, the TP-receptor agonist, U46619, and the IP-receptor agonist, iloprost, were also active, but were all at least an order of magnitude less potent than PGE2 and PGD2. 3. The EP2/EP3-receptor agonist, misoprostol, and the selective EP2-agonist, AH13205, were both effective inhibitors of LTB4 release, being approximately equipotent with and 16-times less potent than PGE2, respectively. In contrast, the EP1/EP3-receptor agonist, sulprostone, had no inhibitory activity at concentrations of up to 10 microM. 4. The selective DP-receptor agonist, BW245C, inhibited LTB4 release, (EC50 0.006 microM) being approximately 50 times more potent than PGD2. BW245C also inhibited O2- release, and this inhibition was antagonized competitively by the DP-receptor blocking drug, AH6809 (pA2 6.6). 5. These data indicate the presence of both inhibitory EP- and DP-receptors on the human neutrophil. The rank order of potency of EP-receptor agonists suggest that the EP-receptors are of the EP2-subtype.

Damaris cudworth, lady masham: Between platonism and enlightenment

Abstract: (1993). Damaris Cudworth, lady Masham: Between Platonism and enlightenment. British Journal for the History of Philosophy: Vol. 1, No. 1, pp. 29-54.

A pheromone trap for dispersal of the pathogen Zoophthora radicans Brefeld. (Zygomycetes: Entomophthorales) amongst populations of the diamondback moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae)

Abstract: A sex pheromone trap designed as a novel pathogen delivery system is described. The strategy envisaged for its use is that male Plutella xylostella moths attracted to the pheromone enter the trap and are dosed with the fungus Zoophthora radicans. After habituation to the pheromone, the moths leave the trap and disperse to the crop carrying the fungal inoculum to susceptible larvae, thus initiating or enhancing an epizootic. A fluorescent marker in the trap was used to demonstrate that moths entered and exited from the trap and carried particles to crop plants at least 5 m away. As a preliminary study, this work shows the potential of this strategy for disseminating Z. radicans in populations of P. xylostella In addition, it could be considered as a model system with implications for other pest species where a pheromone and virulent pathogen are known.

The authentication of Basmati rice using near infrared spectroscopy

Abstract: The feasibility of using near infrared transmission spectroscopy to discriminate between Basmati and other long-grain rice samples was investigated. A discriminant rule was derived using the Fisher linear discriminant function calculated from the first few principal component scores of the NIR spectra. The discriminant rule was assessed by cross-validation. Nine Basmati and 53 other rice samples were classified correctly from NIR spectra measured on 200 g bulk samples but 8% of the Basmatis and 14% of the others were misclassified on the basis of spectra of individual grains. Using average spectra from 23 grains resulted in correct classification of 16 Basmatis but a 20% error rate on 100 other samples.

Movement of nonionic organic chemicals in agricultural soils

Abstract: During the last decade, it has been reported that groundwater, surface water, food crops, livestock, and human tissue have all been contaminated with organic chemicals. Although much of the early work focused on pesticides, more recent studies have shown that a wider range of anthropogenic organic chemicals, many of which are designated as priority pollutants, also have been detected. Clearly, the movement of these chemicals through soil governs their potential to be transferred into water courses and foodchains. This review presents an overview of recent advances in sorption/desorption and transport phenomena. Theories currently being invoked to explain the mechanisms of sorption/desorption are discussed and their classification and numerical characterization are described. Water movement and its implications for solute transport are discussed, with emphasis being placed on the importance of soil structure. Finally, the impact of intrinsic factors, such as spatial and temporal variability of wea...