A fluoroscopic study of the position and action of different bits in the horse's mouth     

Hilary M. Clayton BVMS  PHD  MRCVS 《Journal of Equine Veterinary Science》1985,5(2):68-77

Fluoroscopy was used to visualize the position and movements of different types of bits within the horse's oral cavity. The jointed eggbutt snaffle normally lay between the tongue and palate with the joint hanging down toward the incisor teeth. By arching and elevating the tongue the horse was able to raise the mouthpiece between the cheekteeth. The jointed mouthpiece was suspended in a more horizontal position when keepers were used with a cheek snaffle to fix the position of the bit rings relative to the cheekpieces of the bridle. In addition, the mobility of the bit within the oral cavity was reduced by using keepers. Similarly less intra-oral movement was observed in bits with an unjointed mouthpiece.The Dr. Bristol bit, which has two joints connected by an angled plate, could be attached to the bridle in two ways so that the plate lay either parallel to the tongue and palate or perpendicular to them. This would be expected to have a marked effect on the severity of action of the bit. The high tongue port of the Hannoverian pelham pressed against the palate when the reins were used, causing considerable discomfort.  相似文献   

Plasma glucose and cortisol responses to exogenous insulin in fasted donkeys     

Alison J Forhead  Hilary Dobson 《Research in veterinary science》1997,62(3):265

Susceptibility to equine hyperlipaemia is increased by poor food intake. To assess the contribution of changes in insulin sensitivity, plasma glucose and cortisol responses to an intravenous insulin challenge (0·4 kg⁻¹ bodyweight) were compared with those observed after saline administration in six donkeys fasted either overnight or for three days. Three days of fasting decreased both the rate of insulin-induced hypoglycemia and the maximal hypoglycemic response. A transitory increase in plasma cortisol which peaked within one to four hours of insulin administration was observed in three of the six overnight-fasted donkeys and in all of the three-day fasted donkeys; inter-animal variation appeared to exist in the responsiveness of the hypothalamic-pituitary-adrenocortical ( ) axis to stimulation by insulin-induced hypoglycemia. Fasting is likely to present a risk of equine hyperlipaemia, at least in part, by the reduction in tissue sensitivity to the glucoregulatory action of insulin.  相似文献   

Replacement of fishmeal in diets for Australian silver perch Bidyanus bidyanus (Mitchell). II. Effects of cooking on digestibility of a practical diet containing different starch products     

D A J Stone  G L Allan  S Parkinson  & J Frances 《Aquaculture Research》2003,34(3):195-204

Abstract The interactive effects of cooking and starch type on the dry matter, gross energy and protein digestibility of diets fed to fingerling silver perch were examined. Nine experimental diets were made: a reference diet either uncooked or cooked, six other diets comprising uncooked reference diet supplemented with 30% uncooked or cooked wheat, maize or potato starch and one diet comprising uncooked reference diet supplemented with 15% pregelatinized maize starch. Cooking involved autoclaving at 121 °C for 15 min. The indirect method was used to calculate apparent digestibility coefficients, and chromic oxide (1%) was used as the inert indicator. Both ingredient type and cooking influenced dry matter and gross energy digestibility of diets. All diets had significantly different digestibility coefficients in the following order (from most to least digestible): reference > wheat > maize > potato, for both dry matter and gross energy. Cooking significantly increased the apparent digestibility of diets for both dry matter and gross energy. There was no significant effect of ingredient or cooking or their interaction on protein digestibility. Dry matter and energy digestibility of the diet containing pregelatinized maize starch were significantly higher than for diets containing cooked or uncooked starch products. Ingredient digestibility followed the same trend as diet digestibility. The results from this study indicate that the successful use of starch in practical diets for silver perch is dependent on the origin and processing of the starch. The significant benefits of cooking in the reference diet suggest that pelleted diets should be cooked (e.g. steam conditioned or extruded).  相似文献   

A comparison of methods for soil microbial population and biomass studies     

K. H. Domsch  T. H. Beck  J. P. E. Anderson  B. Sderstrm  D. Parkinson  G. Trolldenier 《植物养料与土壤学杂志》1979,142(3):520-533

A comparison was made of 15 different techniques which are used in assessing soil microbial populations and/or biomasses. These include direct observations (fungal standing crop, fluorescein diacetate active mycelia, acridine orange stained bacteria), cultural methods (bacterial plate counts), physiological methods (total microbial, bacterial and fungal biomasses, O₂-uptake), soil enzyme analyses (dehydrogenase, catalase, alkaline and acid phosphatase, protease, amylase), and ATP-analyses. The various techniques were applied to six soils known to have different microbial characteristics. The results are discussed with respect to the convertability of counts and measurements into microbial biomasses, the variability of the techniques, the correlations within comparable groups of methods, and the practical limitations in application of individual methods to different soils.  相似文献   

Reducing endogenous tau ameliorates amyloid beta-induced deficits in an Alzheimer's disease mouse model     

Roberson ED  Scearce-Levie K  Palop JJ  Yan F  Cheng IH  Wu T  Gerstein H  Yu GQ  Mucke L 《Science (New York, N.Y.)》2007,316(5825):750-754

Many potential treatments for Alzheimer's disease target amyloid-beta peptides (Abeta), which are widely presumed to cause the disease. The microtubule-associated protein tau is also involved in the disease, but it is unclear whether treatments aimed at tau could block Abeta-induced cognitive impairments. Here, we found that reducing endogenous tau levels prevented behavioral deficits in transgenic mice expressing human amyloid precursor protein, without altering their high Abeta levels. Tau reduction also protected both transgenic and nontransgenic mice against excitotoxicity. Thus, tau reduction can block Abeta- and excitotoxin-induced neuronal dysfunction and may represent an effective strategy for treating Alzheimer's disease and related conditions.  相似文献   

Evolution of supergene families associated with insecticide resistance   总被引：5，自引：0，他引：5  

Ranson H  Claudianos C  Ortelli F  Abgrall C  Hemingway J  Sharakhova MV  Unger MF  Collins FH  Feyereisen R 《Science (New York, N.Y.)》2002,298(5591):179-181

The emergence of insecticide resistance in the mosquito poses a serious threat to the efficacy of many malaria control programs. We have searched the Anopheles gambiae genome for members of the three major enzyme families- the carboxylesterases, glutathione transferases, and cytochrome P450s-that are primarily responsible for metabolic resistance to insecticides. A comparative genomic analysis with Drosophila melanogaster reveals that a considerable expansion of these supergene families has occurred in the mosquito. Low gene orthology and little chromosomal synteny paradoxically contrast the easily identified orthologous groups of genes presumably seeded by common ancestors. In A. gambiae, the independent expansion of paralogous genes is mainly a consequence of the formation of clusters among locally duplicated genes. These expansions may reflect the functional diversification of supergene families consistent with major differences in the life history and ecology of these organisms. These data provide a basis for identifying the resistance-associated enzymes within these families. This will enable the resistance status of mosquitoes, flies, and possibly other holometabolous insects to be monitored. The analyses also provide the means for identifying previously unknown molecules involved in fundamental biological processes such as development.  相似文献   

Bacterial motility: membrane topology of the Escherichia coli MotB protein   总被引：39，自引：0，他引：39  

S Y Chun  J S Parkinson 《Science (New York, N.Y.)》1988,239(4837):276-278

The MotB protein of Escherichia coli is an essential component of the force generators that couple proton movement across the cytoplasmic membrane to rotation of the flagellar motors. The membrane topology of MotB was examined to explore the possibility that it might form a proton channel. MotB--alkaline phosphatase fusion proteins were constructed to identify likely periplasmic domains of the MotB molecule. Fusions distal to a putative membrane-spanning segment near the amino terminus of MotB exhibited alkaline phosphatase activity, indicating that an extensive carboxyl-terminal portion of MotB may be located on the periplasmic side of the membrane. Protease treatment of MotB in spheroplasts confirmed this view. The simple transmembrane organization of MotB is difficult to reconcile with a role as a proton conductor.  相似文献   

Formation of ozone by irradiation of oxygen at 248 nanometers     

Freeman DE  Yoshino K  Parkinson WH 《Science (New York, N.Y.)》1990,250(4986):1432-1433

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Elemental content of vegetables, grains, and forages field-grown on fly ash amended soil   总被引：2，自引：0，他引：2  

A K Furr  T F Parkinson  W H Gutenmann  I S Pakkala  D J Lisk 《Journal of agricultural and food chemistry》1978,26(2):357-359

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Analysis of ethyl carbamate in wines using solid-phase extraction and multidimensional gas chromatography/mass spectrometry   总被引：2，自引：0，他引：2  

Jagerdeo E  Dugar S  Foster GD  Schenck H 《Journal of agricultural and food chemistry》2002,50(21):5797-5802

The method describes a rapid and accurate procedure for the analysis of ethyl carbamate in wines. The separation of the ethyl carbamate (EC), the target analyte, from alcohol and the sample matrix is a challenge to many analytical chemists. After alcohol removal from the sample, EC was extracted and concentrated by solid-phase extraction. For analysis of EC, large-volume injection on a programmable temperature vaporization (PTV) inlet was used followed by multidimensional gas chromatography/mass spectrometry (MDGC/MS) using electron-impact ionization (EI). For quantitation, the ratio of ions produced during EI at m/z 62 (EC) and 64 (isotopically labeled EC) was monitored. The use of solid-phase extraction and MDGC/MS removes the majority of the matrix interference encountered in other methods. A linear dynamic range was established from 0.387 to 1160 ng/mL, with a limit of detection at 0.1 ng/mL and limit of quantitation at 1 ng/mL.  相似文献