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Biomedical subjects

D C Elliott

Publications and source records attributed to D C Elliott.

At least 37 records · Page 2Linked to original sources
PubMed1986

Relationship of gastrointestinal histology and mucus antiparasite activity with the development of resistance to trichostrongyle infections in sheep.

Changes in the numbers of globule leucocytes, mast cells, eosinophils and goblet cells in the gastrointestinal mucosa were examined in relation to the development of resistance and elimination of nematodes in grazing sheep in their first year of life. Sheep immunised against Trichostrongylus colubriformis, and sheep treated with dexamethasone were also examined. A strong association between resistance to infection and the presence of globule leucocytes was found. In contrast, the numbers of mast cells or goblet cells were not correlated with resistance. Globule leucocyte and eosinophil numbers were also correlated with antiparasite activity in mucus. Immunising infections of T. colubriformis given to 10-month-old sheep, their duration limited by thiabendazole treatment, gave rise to considerable immunity to homologous challenge infections. Larvae that developed to the 4th stage were as effective at stimulating immunity as those that developed to the 5th stage. Dexamethasone treatment abrogated resistance to trickle challenge infection with T. colubriformis and reduced mucosal globule leucocyte and mast cell numbers. After cessation of drug treatment, the re-establishment of resistance and adult worm elimination were associated with repopulation of the mucosa with large numbers of globule leucocytes and high antiparasite activities in mucus.

Animals↗
PubMed1986

Tapeworm (Moniezia expansa) and its effect on sheep production: the evidence reviewed.

Literature relating to the effects of the tapeworm Moniezia expansa on sheep is reviewed. While there are many claims of adverse effects by this organism, none of these withstand critical scrutiny. The balance of evidence indicates that M. expansa infections are generally harmless, even when the tapeworms are present in large numbers in young lambs, and that there is no justification for treating sheep for M. expansa on the basis of any likely benefit to the health or production of the animals. No published experimental results can be found to support claims that heavy M. expansa infections sometimes exacerbate losses from other causes. Anthelmintics for investigative use, and some aspects of the classification, life history and biology of M. expansa and of its intermediate host are also discussed.

Journal Article↗
PubMed1984

Tapeworm (Moniezia expansa) in sheep: anthelmintic treatment studies to assess possible pathogenic effects and production loss in young infected animals in the field.

Niclosamide and cupric acetoarsenite were both effective in removing tapeworm (Moniezia expansa) from unweaned lambs. In four trials there was no significant liveweight gain in niclosamide-drenched, compared with undrenched, animals. Post-mortem examination for tapeworm showed that although one lamb contained 200 ml (bulk volume) of strobila, 50% of 49 infected animals contained 50 ml or less. The greatest number of scoleces in one animal was 41, and 65% of lambs contained four or fewer. M.expansa is not indicated as a cause of diarrhoea in lambs.

Journal Article↗
PubMed1983

The production of developmental defects of enamel in the incisor teeth of penned sheep resulting from induced parasitism.

Thirty-four sheep were infected with nematode parasites (Trichostrongylus spp. and Ostertagia circumcincta) during central incisor formation. The tooth enamel was examined for defects of mineralization at eruption and compared with that of 14 control sheep. The type and number of parasites given, the duration of the infection and the age of the sheep were varied. Sheep receiving high doses of parasites e.g. 200,000 T. vitrinus + 20,000 O. circumcincta showed severe systemic effects (debilitation, scouring and weight loss) which were of short duration (7-10 days) as the infections were terminated by anthelmintic treatment. Hypoplastic enamel (a break in continuity) was induced in all 5 sheep infected at 8 1/4-9 months of age and demarcated opacities (an alteration in the translucency) in 3 out of 4 sheep infected at 10 months of age. Sheep given 150,000 or 40,000 T. colubriformis showed less obvious systemic effects although the weight loss continued in some sheep for up to 54 days. Although opacities of the enamel in the form of parallel lines, sometimes with localized increase in width or with a diffuse opacity superimposed, were seen by microscopic examination (X 10) of teeth in this group, many of the teeth from the control sheep showed similar lesions. Only the hypoplastic lesions can be attributed with confidence to the experimental manipulations.

Animals↗
PubMed1983

Inhibition of cytokinin-regulated responses by calmodulin-binding compounds.

Two classes of compounds which bind to calmodulin in a calcium-dependent manner (neuroleptic drugs and local anaesthetics) were used to investigate the possible involvement of a calcium-dependent regulator protein in the action of the plant hormones cytokinins.The cytokinin-induced synthesis of betacyanin in Amaranthus tricolor seedlings was used as one test system. The calmodulin antagonists inhibited betacyanin synthesis with the following order of potency: fluphenazine > trifluoperazine = pimozide > chlorpromazine > dibucaine > penfluridol > haloperidol > tetracaine, over a concentration range (IC(50)) of 0.1 to 0.6 millimolar. Red light and fusicoccin increase betacyanin accumulation and are synergistic with cytokinins. These red light- and fusicoccin-dependent inductions were inhibited by lower concentrations of the drugs than cytokinin-dependent induction, and the order of potency of the drugs was not precisely the same. The results are compatible with the hypothesis that cytokinins may act, at least in part, by changing ion fluxes, with the additional involvement of a calmodulin.The second cytokinin-regulated response studied was growth in soybean callus culture. In this system, inhibition was observed with lower concentrations of drugs than in cytokinin-dependent betacyanin synthesis with an order of inhibitory potency of pimozide = trifluoperazine > penfluridol > chlorpromazine > haloperidol > tetracaine. The effective concentration range (IC(50)) was from 0.07 to 0.5 millimolar.Inhibition of betacyanin synthesis by 0.15 millimolar trifluoperazine and of soybean callus growth by 2 millimolar tetracaine were both reversible.

Journal Article↗
PubMed1983

Calmodulin-binding drugs affect responses to cytokinin, auxin, and gibberellic Acid.

Trifluoperazine, a phenothiazine tranquilizer, and tetracaine, a local anesthetic, have been found to inhibit a variety of plant hormone responses at concentrations compatible with their known inhibition of Ca(2+)-calmod-ulin-dependent enzyme activities. Among these responses are cytokinin-dependent betacyanin synthesis and increase in fresh weight in Amaranthus tricolor cotyledons, auxin-dependent increase in length of wheat coleoptile segments and gibberellic acid-dependent induction of alpha-amylase synthesis in barley aleurone layers. The reversibility of some of these inhibitory effects has been demonstrated, indicating that, up to a point, a generalized membrane destruction can be ruled out. The evidence, taken in conjunction with numerous examples from the literature showing calcium involvement in the action of all of the plant hormones, support a unifying theory of hormone action.

Journal Article↗
PubMed1982

Inhibition of cytokinin action and of heat/aging induced potential for cytokinin action by inhibitors of membrane synthesis and function.

Data to support the hypothesis that cytokinin action, in inducing the biosynthetic pathway involved in betacyanin synthesis in Amaranthus tri-color seedlings, is dependent on both membrane synthesis and function is presented. The experimental system included a pretreatment of heat shock (40 degrees C) and aging of cotyledon explants. This produced the conditions necessary for the full expression of cytokinin potential during the subsequent betacyanin induction. Cerulenin, an inhibitor of fatty acid and sterol synthesis, inhibited both the heat-induced potential for cytokinin action and the benzyladenine-dependent induction itself. This was also true of metyrapone, an inhibitor of hydroxylation reactions involving cytochrome P450. Gammexane, an inhibitor of phospholipid turnover, impaired the heat-induced process but not the benzyladenine-dependent betacyanin accumulation. This was also the case with 2-isopropyl-4-dimethylamino-5-methyl phenyl-1-piperidine carboxylate methyl chloride, an inhibitor of the cyclization steps in sterol and gibberellin synthesis. Filipin at 100 micrograms per milliliter inhibited both processes, particularly the heat-induced potential. The effect of various steroids and fatty acids on induction is recorded together with experiments aimed at using them to reverse some of the inhibitions. The effect of cerulenin on heat-induced potential was partially reversed by preparations of Amaranthus lipids. Some reversal of the filipin effects was obtained with beta-sitosterol and stigmasterol. It is concluded that menbrane synthesis is stimulated during the heat/aging pretreatment and during the induction and that some membrane function(s) is necessary for subsequent cytokinin action.

Journal Article↗
PubMed1980

Apneic spells in progressive dialysis encephalopathy.

A 53-year-old patient with progressive dialysis encephalopathy is discussed. In addition to the clinical features previously described in this syndrome, the patient had spells of sudden respiratory arrest in close association with the episodic EEG abnormalities characteristic of the syndrome.

Apnea↗
PubMed1979

Ionic Regulation for Cytokinin-dependent Betacyanin Synthesis in Amaranthus Seedlings.

Potassium ions at low concentrations stimulate cytokinin-dependent betacyanin synthesis in Amaranthus tricolor seedlings more than other alkali metal ions when tested as the chloride salts. The sequence of relative stimulation is K(+) > Rb(+) > (Na(+) = Li(+)). Calcium and Mg(2+) ions are inhibitory at concentrations > 1 millimolar when tested as chlorides. Anions also have an effect on the degree of alkali metal stimulation in the order PO(4) (3-) > NO(3) (-) > Cl(-). The high activity of phosphate may be partly due to its chelating effect on inhibitory Ca(2+) ions, or to effects on K(+) uptake. A mixture of Na(+) and K(+) in the presence of phosphate is more effective than either cation alone. This result may be due either to effects on tyrosine transport or on the potassium uptake system. Phytochrome-dependent betacyanin synthesis shows the same stimulation by Na(+) plus K(+). The effect of a number of inhibitors of transport systems on betacyanin accumulation is reported. The possible role of the ionic environment of cells in their metabolic regulation is discussed, particularly in relation to cytokinin action.

Journal Article↗
PubMed1979

Analysis of Variability in the Amaranthus Bioassay for Cytokinins: Effects of Water Stress on Benzyladenine- and Fusicoccin-dependent Responses.

The use of only the upper part of the hypocotyl and the cotyledons in the Amaranthus tricolor bioassay for cytokinins, instead of the whole seedling, was found to reduce the endogenous response and give a higher benzyladenine-dependent response. There is no marked difference in the uptake or metabolism of benzyladenine in whole seedlings compared with that in excised cotyledons.Analysis of variability in the bioassay showed that water availability to the cut seedlings and to whole seedlings is a major factor in the amounts of betacyanin accumulated during the subsequent induction period. The increase in the amount of betacyanin accumulated in response to benzyladenine, following conditions of water stress, is not correlated with differences in benzyladenine uptake. Endogenous production and fusicoccin stimulation is also increased following water loss by cut seedlings. Possible explanations for this stress induction may be found in responses of active transport to changes in turgor pressure.Although pretreatment of the roots of seedlings with mannitol stimulated subsequent induction by excised cotyledons, the presence of mannitol during the induction period inhibited the accumulation of betacyanin. This inhibition is not due to any effect on benzyladenine uptake. The susceptibility of amino acid uptake and polysome profiles to water stress suggests that the inhibition of betacyanin synthesis, a process dependent on protein synthesis, may be due to inhibition either of precursor (tyrosine) uptake or of the synthesis or activity of some enzyme in the pathway.

Journal Article↗
PubMed1979

Analysis of variability in the amaranthus betacyanin assay for cytokinins: effects of "aging" excised cotyledons.

"Aging" of excised cotyledons plus the top part of the hypocotyl of Amaranthus tricolor seedlings was carried out by washing in distilled H(2)O for varying periods. This led to increased betacyanin accumulation during the subsequent 24-hour induction period in the presence of tyrosine and Na(+) + K(+) phosphate. Endogenous accumulation as well as that dependent on added benzyladenine and on added fusicoccin was stimulated. This stimulation could not be due to a carryover of a wound-induced burst of ethylene since 2-chloroethylphosphonic acid (Ethrel) was shown to be extremely inhibitory to betacyanin synthesis if present during the induction process. It is possible that a wound-induced burst of ethylene could give rise to increased betacyanin synthesis as an after effect. The procedure for obtaining good induction with the most reproducible results is described.

Journal Article↗
PubMed1979

Temperature-dependent Expression of Betacyanin Synthesis in Amaranthus Seedlings.

Two phenomena related to temperature effects have been observed during the induction of betacyanin synthesis by a cytokinin (benzyladenine) in Amaranthus tricolor seedlings. One is a total inhibition of betacyanin accumulation at a temperature (39 C) at which seedling growth is unimpaired, and where there is still adequate uptake of benzyladenine. The other is the apparent induction of a higher potential for subsequent betacyanin synthesis following pretreatment of the seedlings at an elevated temperature.

Journal Article↗
PubMed1979

Temperature-sensitive Responses of Red Light-dependent Betacyanin Synthesis.

Amaranthus tricolor half-seedlings show a greater accumulation of betacyanin in response to a defined period of red light if given a pretreatment at an elevated temperature (40 C). Red light given before the shift to 40 C is ineffective. The maximum response is achieved after a 2-hour shift to 40 C and if the red light is given 1 hour after return to the germination temperature (25 C). The effect on red light induction of betacyanin synthesis and on fusicoccin induction by these conditions is similar, whereas the increase in cytokinin-dependent synthesis is greater. Both phytochrome-cytokinin synergism and fusicoccin-cytokinin synergism are changed in the same manner by this treatment. Phytochrome and fusicoccin responses are inhibited similarly by carbonyl-cyanide-p-trifluoromethoxy-phenylhydrazone.If the seedlings are again returned to 40 C after the 25 C shift there is an inhibition of betacyanin synthesis. The interpretation of these results is that a shift to 40 C induces the formation of some component necessary for the full expression of phytochrome potential, that for the maximum formation or action of this component it is necessary for the seedlings to spend 1 to 2 hours at a lower temperature (for example 25 C) before red light is given and that for the subsequent processes in betacyanin synthesis an elevated temperature is inhibitory.

Journal Article↗
PubMed1975

Evidence against an involvement of cyclic nucleotides in the induction of betacyanin synthesis by cytokinins.

1. A wide range of purine bases, nucleosides and cyclic nucleotides were shown to induce betacyanin synthesis in Amaranthus seedlings. 2. The induction of pigment by benzyladenine, dibutyryl cyclic AMP or cyclic AMP was not potentiated by aminophylline. Aminophylline was shown to inhibit Amaranthus cyclic AMP phosphodiesterase activity. 4. Incubation of seedlings with aminophylline inhibited the conversion of 6-[G--3H]benzyladenine into presumed 9- and 7-glucosylbenzyladenine. 5. Induction of betacyanin synthesis by 6-benzyladenine or by exposure to red light was not accompanied by changes in the total cyclic AMP content in seedlings. 6. It is concluded that the inducers tested act as cytokinin analogues; no evidence was obtained to support cyclic AMP as an intermediate in the induction process.

3',5'-Cyclic-AMP Phosphodiesterases↗