Showing papers by "University of Hertfordshire published in 1987"

Identification and distribution of 5-HT3 receptors in rat brain using radioligand binding.

Abstract: Functional serotonin (5-hydroxytryptamine, 5-HT) receptors have been divided into three subtypes: 5-HT1,-like, 5-HT2 and 5-HT3, (ref. 1). Brain binding sites have been identified for both the 5-HT1, and 5-HT2 subtypes. Receptors of the 5-HT3 type have been characterized on isolated peripheral tissue models such as the rat vagus nerve2, guinea-pig ileum3 and isolated rabbit heart4. Using these models, selective 5-HT3 receptor antagonists such as MDL 72222 (ref. 5), ICS 205-930 (ref. 6), GR38032F (ref. 7) and BRL 43694 (ref. 8) have been developed. Recently, GR38032F, MDL 72222 and ICS 205-930 have been shown to have behavioural effects in rodents and primates that undoubtedly reflect an action in the central nervous system (refs 9–11 and unpublished observations), suggesting the existence of 5-HT3 receptors in the brain. Here we report direct evidence for the existence of 5-HT3 receptors in rat brain tissue and their distribution, based on high affinity binding of the potent 5-HT3 receptor antagonist 3H-GR65630 to homogenates of rat entorhinal cortex. Selective 5-HT3 receptor antagonists and agonists inhibited binding of 3H-GR65630 with high affinities which correlated well with their actions on the rat isolated vagus nerve2. Binding was differentially distributed throughout the brain with high concentrations in cortical and limbic areas.

A novel receptor-operated Ca2+-permeable channel activated by ATP in smooth muscle

Abstract: Receptor-operated Ca2+ entry has been proposed as a signalling mechanism in many cells1–8. Receptor-operated Ca2+ channels (ROCs) were first postulated in smooth muscle by Bolton2, van Breemen3 and Somlyo and Somlyo4, but recordings of directly ligand-gated Ca2+ current are lacking. Here we describe receptor-operated Ca2+ current evoked in arterial smooth muscle cells by ATP, a sympathetic neurotransmitter9. ATP activates channels with approximately 3:1 selectivity for Ca2+ over Na+ at near-physiological concentrations and with a unitary conductance of ∼5 pS in 110 mM Ca2+ or Ba2+. The channels can be opened even at very negative potentials and resist inhibition by cadmium or nifedipine, unlike voltage-gated Ca2+ channels; they are not blocked by Mg2+, unlike NMD A (N-methyl-D-asparate)-activated channels10,11; they are directly activated by ligand, without involvement of readily diffusible second messengers, unlike cation channels in neutrophils12 and T lymphocytes13. Thus, the ATP-activated channels provide a distinct mechanism for excitatory synaptic current and Ca2+ entry in smooth muscle.

Fluorescence and bioluminescence measurement of cytoplasmic free calcium.

Abstract: The first measurements of cytosolic free Ca2\", [Ca2\"]1, in living cells were made with aequorin in giant muscle cells (Ridgway & Ashley, 1967) in the late 1960s. During the 1970s two further methods were introduced, bis-azo absorbance dyes (mainly arsenazo III) and calciumselective microelectrodes (Ashley & Campbell, 1979). However, even as late as 1981, [Ca'1] had been reliably measured in very few cell types other than giant cells of invertebrates and the techniques were largely confined to the laboratories of those specialized in excitable cell physiology and familiar with microelectrodes or microinjection and advanced optical or electronic technologies. In 1982 a new generation of fluorescent dyes was introduced, with quin2 (Tsien et al., 1982a) and a chemical trick for loading it non-disruptively into populations of cells of any size (Tsien, 1981). This technique in its basic form is simple enough, and needs only basic laboratory instrumentation, so that it is now routinely used in hundreds oflaboratories. The technique has been rapidly developed with the invention of the superior dyes, fura-2 and indo1, and technologies for monitoring [Ca2\"], in single cells, whole fields ofidentified cells, and even localized areas within cells, and also improvements in time resolution down to the millisecond range. An outline of these developments forms part of this review. Clearly, with hundreds of papers already published we can only point out the major features, advantageous and problematic, of the technique and hope to provide a critical guide to the literature that details the important points. Another development has been the refinement of the use of the calcium sensitive photoproteins aequorin and obelin. Important novel data on microinjected small single cells are now coming from specialist laboratories and the techniques are not as fearsomely difficult as commonly thought. Part of this review is therefore devoted to an explanation of this method, its advantages and pitfalls, and its successes. We will not consider bisazo dyes or calcium-selective microelectrodes. There are several detailed accounts of these techniques and their place in relation to other approaches (e.g. Thomas, 1982; Blinks et al., 1982; Rink, 1983; Tsien & Rink, 1983). Nor will we review the fluorine derivatives of the fluorescent dyes that have provided n.m.r. probes (Metcalf et al., 1985). This review covers the technical considerations of using fluorescent and bioluminescent probes for measuring [Ca2+]1; we make no attempt to cover the extensive and proliferating data obtained from such measurements.

Barley mutants lacking chloroplast glutamine synthetase-biochemical and genetic analysis.

Abstract: Eight mutants of barley (Hordeum vulgare cv Maris Mink) lacking the chloroplast isozyme of glutamine synthetase (EC 6.3.1.2.) were isolated by their inability to grow under photorespiratory conditions. The cytoplasmic isozyme of glutamine synthetase was present in the leaves of all the mutants, with activities comparable to the wild-type (10-12 nanokatals per gram fresh weight). The mutant plants developed normally and were fully fertile under conditions that minimize photorespiration. In 1% O2 the rate of CO2 fixation in leaves of one of the mutants, RPr 83/32, was the same as the wild-type, but in air this rate declined to 60% of the wild-type after 30 minutes. During this time the ammonia concentration in leaves of the mutant rose from 1 to 50 micromoles per gram fresh weight. Such ammonia accumulation in air was found in all the mutant lines. In back-crosses with the parent line, F1 plants were viable in air. In the F2 generation, nonviability in air and the lack of chloroplast glutamine synthetase co-segregated, in both the lines tested. These two lines and four others proved to be allelic; we designate them gln 2a-f. The characteristics of these mutants conclusively demonstrate the major role of chloroplast glutamine synthetase in photorespiration and its associated nitrogen recycling.

Effects of the 5-HT3 receptor antagonist, GR38032F, on raised dopaminergic activity in the mesolimbic system of the rat and marmoset brain.

Abstract: 1 The ability of the selective 5-HT3 receptor antagonist GR38032F to reduce raised mesolimbic dopaminergic activity was studied in behavioural experiments in the rat and marmoset. 2 GR38032F injected into the nucleus accumbens (0.01-1 ng) or peripherally (0.01-1 mg kg-1 i.p.) inhibited the locomotor hyperactivity caused by the acute intra-accumbens injection of amphetamine (10 micrograms) in the rat. Similar treatments with sulpiride and fluphenazine also inhibited the amphetamine-induced hyperactivity. 3 The peripheral administration of GR38032F (0.001-0.1 mg kg-1 i.p., b.d.) during a 13 day period of dopamine infusion (25 micrograms 24 h-1) into the nucleus accumbens of the rat reduced the dopamine-induced hyperactivity response to control (vehicle infused) levels. Locomotor activity remained at control levels after discontinuing the dopamine/GR38032F treatment regimen. 4 The hyperactivity caused by the infusion of dopamine into the rat nucleus accumbens was also inhibited by fluphenazine (0.01-0.05 mg kg-1 i.p., b.d.), but locomotor activity was suppressed to levels below control values and a rebound hyperactivity occurred after discontinuation of the dopamine/fluphenazine treatment regimen. 5 The discontinuation of a concomitant 13 day intra-accumbens infusion of dopamine with haloperidol, 0.01 mg kg-1 i.p.t.d.s., caused a rebound hyperactivity. This hyperactivity was suppressed by GR38032F (0.001-0.1 mg kg-1 i.p.). 6 The unilateral infusion of dopamine (25 micrograms 24 h-1, 13 days) into the left amygdala of rats having right hemispheric dominance (as measured in a turn preference test) caused locomotor hyperactivity. Intraperitoneal administration of GR38032F (0.1-100 micrograms kg-1) or fluphenazine (0.025-0.1 mg kg-1), and the intra-amygdaloid injection of GR38032F (0.1-100 ng) or fluphenazine (25-500 pg), either into the infused or non-infused side, inhibited the dopamine-induced locomotor hyperactivity. 7 Marmosets receiving bilaterial infusions of dopamine (25 micrograms 24 h-1 for 13 days) into the nucleus accumbens also exhibited increased locomotor activity, GR38032F (0.1-1.0 micrograms kg-1 t.d.s.), reduced the hyperactivity to control levels with no rebound hyperactivity following the discontinuation of the dopamine/GR38032F treatment regimen. Fluphenazine (0.01-2.5 mg kg-1 i.p., t.d.s.) also inhibited the hyperactivity, but locomotor activity was reduced to values below control levels and a rebound hyperactivity followed the discontinuation of the dopamine/fluphenazine treatment. 8. It is concluded that the 5-HT3 receptor antagonist GR38032F, and the neuroleptic agents fluphenazine, sulpiride and haloperidol, can reduce raised mesolimbic dopaminergic activity in the rat and marmoset. GR38032F is distinguished from the dopamine receptor antagonists by, firstly, its ability to return the hyperactivity response to control values, without excessive suppression of locomotion even on enhanced dosage regimes and, secondly, by the lack of rebound hyperactivity following abrupt discontinuation of its treatment.

Pharmacological characterization of 5-hydroxytryptamine-induced depolarization of the rat isolated vagus nerve.

Abstract: A study has been made of the pharmacology of the 5-hydroxytryptamine (5-HT)-induced depolarization responses that can be recorded extracellularly from the rat isolated cervical vagus nerve. Phenylbiguanide (PBG) and 2-methyl-5-hydroxytryptamine (2-methyl-5-HT) were found to mimic the effects of 5-HT on the vagus nerve. Their EC50 values were respectively 2.0 fold and 3.9 fold greater than that of 5-HT. Metoclopramide behaved as a reversible competitive antagonist of depolarization induced by PBG and 2-methyl-5-HT, with pKB values of 6.48 +/- 0.04, respectively. These agreed well with the pKB value of 6.60 +/- 0.04 obtained previously for metoclopramide against 5-HT on the rat vagus nerve. 5-HT, PBG and 2-methyl-5-HT had no demonstrable agonist effects at non-5-HT receptors on the rat vagus nerve. Tropacaine and m-chlorophenylpiperazine were found to behave as reversible competitive antagonists of 5-HT-induced depolarization of the vagus nerve. The pKB values were 6.29 +/- 0.03 and 6.90 +/- 0.03, respectively. Quipazine, MDL 72222 and ICS 205-930 were also shown to be effective antagonists of 5-HT on the vagus nerve. However, although these compounds were highly potent, they all caused a marked concentration-dependent reduction in the amplitude of the maximum response to 5-HT. This behaviour was not consistent with a simple reversible competitive mechanism. The results are discussed with reference to the current classification of mammalian peripheral neuronal 5-HT receptors.

Transformations of the explanatory variables in the logistic regression model for binary data

Abstract: SUMMARY Some results are presented on improving the fit of the logistic regression model for binary data by transforming the vector of explanatory variables. The methods are based on consideration of the distributions of these variables conditional on outcome group. The transformations required are the functions of the explanatory variables which appear in the log density ratio of the conditional distributions.

Physico‐chemical factors affecting uptake by roots and translocation to shoots of weak acids in barley

Abstract: The uptake from solution of maleic hydrazide, flamprop and a series of phenoxyacetic acids by roots, and their subsequent translocation to shoots, was measured in barley. Both uptake and translocation increased as the pH of the solution decreased, the magnitude of the change varying amongst the chemicals tested. Uptake by roots could be accounted for by the ion-trap mechanism, which assumes that entry of the chemicals occurs largely by passive diffusion of the undissociated form of the acids, with passage of the anions across the cell membranes being very slow. The ratio of the permeability of the cell membranes to the undissociated and dissociated forms of the acids was estimated from the accumulation in roots, and in the phenoxyacetic acid series this ratio was maximal (4×105) for compounds of intermediate lipophilicity. Maleic hydrazide and flamprop had much lower ratios, 1.8×102 and 103 respectively; the value for flamprop was much less than for phenoxyacetic acids of similar lipophilicity, such as 2, 4- dichlorophenoxyacetic acid, indicating that lipophilicity may not be the sole factor determining the behaviour of weak acids in plants. Translocation to shoots was approximately proportional to the chemical concentrations in the roots.

Identification of an aphid sex pheromone

Abstract: Although aphids reproduce asexually on their host plants during the summer, many species migrate to a winter host where sexual reproduction occurs. Males of certain species locate mates by means of a sex attractant pheromone released from the hind legs of the females1–4. Here we report the identification of such a pheromone from the vetch aphid Megoura viciae. Extracts of the excised legs of sexual females were analysed by gas chromatography-coupled single cell recording techniques (GC-SCR)5 and by gas chromatography-coupled mass spectrometry (GC-MS). A tentative identification by MS analysis of the two active components as specific isomers of the monoterpenoids nepetalactone (I), a known cat attractant, and nepetalactol (II) was confirmed by comparison with authenticated compounds isolated or synthesized from natural products. Although neither compound was attractive to males when presented alone in the laboratory bioassay, a mixture of the two components produced a response equal to that elicited by the female leg extract. Thus the sex pheromone of M. viciae comprises a synergistic mixture of the nepetalactone I and the nepetalactol II. The identification of aphid sex pheromones will provide a further means of investigating and manipulating the behaviour of these ubiquitous pests.

Field Modelling of Fire in Forced Ventilated Enclosures

Abstract: This paper describes the application of the Fire Research Station's field model JASMINE to the prediction of conditions in a forced ventilated experimental fire test at the Lawrence Livermore National Laboratory. The combustion model of Magnussen and Hjertager based on eddy-break-up concepts has been used to describe the non-spreading pool fire. Comparison between measurements and predictions are shown to be in reasonable agreement and areas requiring further research indicated.

Cimetidine and chlorpheniramine in the treatment of chronic idiopathic urticaria: a multi‐centre randomized double‐blind study

Abstract: One hundred and twenty patients with chronic idiopathic urticaria, who entered a study at five centres (Sheffield, London, Bristol, Cardiff and Leeds) were treated with therapeutic doses of the H1 antagonist chlorpheniramine for 6 weeks. Histamine H1 non-responders (40 patients) were entered into a double-blind study and received chlorpheniramine plus cimetidine 400 mg q.d.s. (21 patients) or chlorpheniramine plus placebo (19 patients) for a further 8 weeks. The most important response measure was the change from baseline of the total symptom score: an assessment of the number and duration of new weals and degree of itching. There was a statistically significant difference between the average response in the two treatment groups in favour of chlorpheniramine plus cimetidine after 4 and 8 weeks' treatment (P less than 0.05 and P less than 0.01, respectively). No significant side-effects related to treatment were noted.

An analysis of morphological development stages in Avalon winter wheat crops with different sowing dates and at ten sites in England and Scotland

Abstract: An experiment to measure the variation in the phenological and apical development ofwinter wheat (cv. Avalon) in England and Scotland is described. Ten sites which ranged from Aberdeen (57·2° N), the most northerly, to Newton Abbot (50·6° N), the most southerly, were included in the survey, and at each site seed was hand-sown in mid-September, October and November 1983. Developmental stages and sampling procedures were precisely defined to ensure uniformity in scoring by the observers at each site. Temperatures during the growing season were in line with the long-term means, though spring was cooler at all sites and summer warmer at most. The range of monthly-mean temperatures between sites was about the same as the difference between consecutive months. The method of analysis of development rates and durations was in terms of thermal time, modified by sensitivity to photoperiod and a vernalization requirement that slowed early development until a number of days of low temperatures had been experienced. In general, crops at northern sites developed more slowly than those in the south and particularly the south-west of England. There was less variation in the timing of apical stages for later sowings. Developmental rates responded linearly to temperature and photoperiod, with the base temperature increasing for later phases of development. The effect of photoperiod in modifying the rate of development was apparent for all developmental phases from emergence to anthesis, longer days accelerating development, but there was no effect on the duration of the grain-filling period. Vernalization exerted its effect solely within the phase from emergence to double ridge, and had a major influence on the variation between sites only for the first sowing.

The performance of optical phase-locked loops in the presence of nonnegligible loop propagation delay

Abstract: The optical phase-locked loop is analyzed taking into account shot noise, phase noise, and loop propagation delay. The degradation of loop phase error due to propagation delay is evaluated in terms of the delay bandwidth product \omega_{n} \cdot \tau_{D} . This product was found to have a maximum value of 0.736 for absolute loop stability. The resulting effect on a Costas loop system optimized for zero time delay is discussed. It is found that in order to maintain a 10-9BER system performance with \xi = 1/2^{0.5}, R = 0.85 A/W, P_{DATA} = -59.2 dBm, and a 1-MHz beat linewidth, the delay time must be kept below 1.8 ns. If the beat linewidth increases to 15 MHz this figure drops to 0.12 ns.

Fetal valproate syndrome: is there a recognisable phenotype?

Abstract: Four infants who were exposed to sodium valproate or valproic acid during pregnancy are described. Common facial features in the three surviving infants include epicanthic folds, a flat nasal bridge, a broad nasal base, anteverted nostrils, a shallow philtrum, and a thin upper lip with a thick lower lip. Ridging of the metopic suture, congenital heart defect, postaxial polydactyly, and hypospadias were additional features in individual cases. In agreement with previous authors, we feel that there is a distinctive 'fetal valproate' phenotype.

Inheritance of linear type traits in dairy cattle and correlations with milk production

Abstract: Records on 18 939 Friesian-Holstein cows classified for 16 linear-type traits and total score in first lactation by the British Friesian Cattle Society and similarly on 13 192 cows in second lactation were analysed to estimate heritabilities and genetic correlations among the linear traits. These comprised progeny of 542 and 477 young sires, respectively, together with older sires included to increase connections. Correlations of type with milk production traits and correlations between type in first and second lactations were estimated from subsets (of about one-half) of the data. Effects due to proportion of Holstein in the sires were removed.Heritabilities of the linear traits were similar in first and second lactations, ranging from under 0·15 for one of the leg traits to about 0·5 for stature. Genetic correlations between traits in first and second lactation were generally over 0·75, whereas phenotypic correlations for most traits ranged from 0·3 to 0·6. Genetic and phenotypic correlations among the linear traits were generally low, except for those involving size.Phenotypic correlations between linear traits and milk yield and composition were all small, none exceeding 0·3. Genetic correlations were generally almost as small: taking first and second lactations together, the only consistent non-negligible correlations with yield were for angularity (+0·3), fore-udder attachment (–0·2) and udder depth (–0·4). The linear traits are not useful predictors of yield.

The effect of GR38032F, novel 5‐HT3‐receptor antagonist on gastric emptying in the guinea‐pig

Abstract: The effects of GR38032F a novel, selective and potent 5-hydroxytryptamine (5-HT3)-receptor antagonist on gastric emptying in the guinea-pig were investigated and compared to those of metoclopramide and haloperidol. Both GR38032F and metoclopramide increased gastric emptying in a dose-dependent manner. In contrast, haloperidol was ineffective. GR38032F was about 200 times more potent than metoclopramide in enhancing gastric emptying over the 2 h period studied.

Structure and function of SV40 large-T antigen

Abstract: The small eukaryotic DNA tumour virus, SV40, has long provided a very useful model for the study of eukaryotic DNA replication and cellular transformation The viral gene product, large-tumour (large-T) antigen, is essential for the initiation of viral DNA replication and the initiation and maintenance of SV40-virus-mediated cellular transformation The large-T antigen is a complex multifunctional protein, and to delineate its activity more precisely in viral DNA replication and cellular transformation, small functional domains of the protein have been expressed in Escherichia coli and analysed by using a very extensive library of anti-T monoclonal antibodies

The effect of insect pollination on plant development and seed production in winter oil-seed rape (Brassica napus L.)

Abstract: The effect of insect pollination on plant development and seed yield of winter oil-seed rape, cultivar Jet Neuf, was investigated by comparing plots caged with a honeybee colony, plots caged to exclude insects and plots uncaged and 'open-pollinated' by naturally occurring insects. Plants in the bee-pollinated plots finished flowering earlier, showed more advanced pod growth, and were shorter than those in the plots without bees. Pods from the plots with honeybees contained more seed post-flowering than those from plots without honeybees but the proportion of them that grew into mature seeds for harvest was determined by water availability during seed growth.

Mapping soil fertility at Broom's Barn by simple kriging

Abstract: Simple kriging is a technique for estimating values of continuous random spatial variables from data without bias and with minimum variance. The procedure is illustrated by a case study in which three properties of soil fertility, available phosphorus, exchangeable potassium and pH in the topsoil, are mapped using data from Broom's Barn Experimental Station. The soil on the station, covering 77 ha, had been sampled at 40-m intervals. Semi-variograms of the properties were determined from the measurements and kriged values estimated at 10-m intervals on a square grid. These values were then contoured to produce maps of the properties and also reliability maps showing the estimation variances.