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Biomedical subjects

K Arnold

Publications and source records attributed to K Arnold.

At least 127 records · Page 7Linked to original sources
PubMed1993

Error accumulation and error correction in sequential pointing movements.

Human subjects pointed, without seeing their arm, at visual targets presented in repeated sequences in a frontal plane. Required movement direction could change within the sequence by 0, 45, 90, 135 or 180 degrees. Hand position was recorded contact-free in three dimensions (3D). From the recordings, the pointing errors towards each target were transformed into a Cartesian coordinate system with the x-axis representing the mean direction of all movements towards that target. We then investigated the relationship between successive errors by applying linear regression analysis separately to the three Cartesian error components. For the x-component, we found that successive errors were positively correlated throughout the experiment, which confirms our previous finding that errors in sequential pointing tend to accumulate (Bock and Eckmiller 1986; Bock et al. 1990). Correlation dropped by nearly 50% following a direction change of 90 degrees or more, suggesting that accumulation is reduced but not abolished by large changes in movement direction. The slope of the regression line averaged 0.6, which indicates the existence of a complementary trend towards error correction, contributing about 40% towards motor performance. Changes of movement direction affected slope and correlation in a closely similar way, suggesting that reduced accumulation is paralleled by increased correction. For the y- and z-components, we found that successive errors were positively correlated as well, but were not reduced following even large direction changes. This apparent discrepancy can be resolved by assuming separate neural mechanisms for amplitude and for direction control, differing in their sensitivity to direction changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Properties of the visual channels that underlie adaptation to gradual change of luminance.

Following adaptation to a spatially uniform patch of light that is gradually brightening (or dimming), a steady test patch appears to be gradually dimming (or brightening). We measured this ramp aftereffect with a nulling method, as a function of the amplitude and temporal repetition rate of the adapting sawtooth waveform and at various retinal eccentricities and levels of dark adaptation. We conclude that the underlying visual channels respond best to large-amplitude sweeps in luminance of at least 20 dB (1 log unit); but they are fairly insensitive to the temporal rate of this sweep. The channels are present out to an eccentricity of at least 40 degrees but they almost disappear during dark adaptation. The ramp aftereffects were asymmetrical: the subjectively darkening aftereffect produced by a brightening adapting ramp was slightly stronger than vice versa.

Adaptation, Ocular↗
PubMed1993

Chitinolytic activities in Heligmosomoides polygyrus and their role in egg hatching.

The occurrence of chitin in the eggshell of Heligmosomoides polygyrus has been determined by histochemical and biochemical techniques. Approximately 5% of the egg dry weight was chitin. Staining with Calcofluor white showed the chitin in the eggshell to be more accessible to the stain after hatching or rupturing of the eggshell. Chitinolytic activity has been detected using fluorescent substrates in extracts of adult males (at low levels), females and eggs. Enzyme activity in situ, within the developing larvae, was visualised with the same substrates. It was localized in discrete granules about 1 micron in diameter which occurred as groups in areas of about 5 microns in diameter, in the posterior third of the larvae. The chitinolytic activity in the eggs increased with the age of the egg and was released into the medium when the eggs hatched. The chitinase activities were very sensitive to inhibition by allosamidin, a specific chitinase inhibitor, with an IC50 for the crude egg extract of 2.2 nM. However, treatment of eggs with 250 microM allosamidin resulted in a slowing but not cessation of egg hatching.

Acetylglucosamine↗
PubMed1993

Rickettsia-like organisms and chitinase production in relation to transmission of trypanosomes by tsetse flies.

Rickettsia-like organisms (RLO) from testse midguts and mosquito cell cultures showed high levels of endochitinase activity. A line of Glossina morsitans morsitans highly susceptible to midgut trypanosome infection and with high incidence of RLO infection showed significantly greater chitinolytic activity than G. austeni which had low RLO incidence and were correspondingly refractory to midgut infection. Midgut infection rates of Trypanosoma brucei rhodesiense in G. m. morsitans showed a dose-related increase when flies were fed N-acetyl-D-glucosamine (GlcNAc) in the infective meal and for 4 subsequent days. A model is proposed for susceptibility to trypanosome infection based on the generation of GlcNAc by RLO endochitinase activity in tsetse pupae inhibiting midgut lectin in teneral flies.

Animals↗
PubMed1993

Rapid direct reversal photography.

This is a description of a method which enables fast, direct-reversal photography of radiological images for slides and was designed to retain: (i) continued use of an existing small darkroom; (ii) use of Kodak Rapid Process copy film; and (iii) use of standard X-ray processors. By adaptation of a commercial photographic flash power pack, a flash head and a reflector it is possible to achieve a somewhat expensive but very successful system which enables the very rapid production of good quality image slides for lectures.

Audiovisual Aids↗
PubMed1993

Influence of polar polymers on the apoprotein region of human serum lipoproteins: an electron paramagnetic resonance (EPR) study.

Electron spin resonance spectroscopy was used for measurements of the surface potential and apoprotein structure of LDL and HDL in the presence of Ca2+ and dextran sulfate, heparin and chondroitin sulfate. A decrease in the absolute values of surface potential of LDL and HDL was observed after addition of Ca2+. In the presence of the negatively charged macromolecules the measured surface potential was less reduced. The spectral properties of a maleimide spin label covalently attached to the apoprotein were changed under conditions of aggregation of LDL induced by dextran sulfate, chondroitin sulfate or heparin in the presence of Ca2+. In the HDL system this effect was only observed for dextran sulfate. The influence of PEG on the spectral parameters of the spin label is dependent on the molecular weight of the polymer. PEG 400 decreased the mobility of the spin-labelled apoprotein region of LDL, whereas PEGs with higher molecular weight only slightly increased the maleimide mobility. On the other hand, the maleimide-labelled apoprotein region of HDL showed a higher sensibility to all PEGs used. Addition of PEG leads to immobilization of apoprotein A.

Apolipoproteins↗
PubMed1992

The influence of dextran sulfate on influenza A virus fusion with erythrocyte membranes.

Dextran sulfate suppresses the low pH-induced fusion of influenza virus A/Brazil 11/78 with erythrocyte membranes, as shown by fluorescence dequenching assay, using the fluorophore octadecylrhodamine B chloride (R18). Inhibition of fusion was maximal at pH 5.0, while at higher pH values (> 5.6) fusion was not affected. Hemolysis of intact red blood cells by influenza A virus at low pH values is also prevented by dextran sulfate. The inhibiting effect of the polymer is mainly ascribed to repression of virus attachment. Evidence is given that the conformational change of the virus envelope protein hemagglutinin (HA) responsible for triggering fusion is not affected by the polymer.

Anilino Naphthalenesulfonates↗
PubMed1992

Randomised trial of artesunate and mefloquine alone and in sequence for acute uncomplicated falciparum malaria.

The increasing frequency of therapeutic failures in falciparum malaria in Thailand shows an urgent need for effective drugs or drug combinations. Artesunate, a qinghaosu derivative, is effective in clearing parasitaemia rapidly, but the recrudescence rate can be as high as 50%. We have compared artesunate followed by mefloquine with each drug alone in acute, uncomplicated falciparum malaria. 127 patients were randomly assigned treatment with artesunate (600 mg over 5 days), mefloquine (750 mg then 500 mg 6 h later), or artesunate followed by mefloquine. All patients were admitted to hospital for 28 days to exclude reinfection. Cure was defined as no recrudescence during the 28 days' follow-up. The cure rates for mefloquine and artesunate alone were 81% (30/37 patients) and 88% (35/40); the combination was effective in all of 39 patients. Fever and parasite clearance times were significantly shorter in the groups that received artesunate than in the mefloquine-only group. The frequency of nausea and vomiting was slightly, but not significantly, higher among patients who received both drugs than in the other groups. The combination of artesunate followed by mefloquine is highly effective and well tolerated in patients with acute, uncomplicated falciparum malaria in Thailand.

Acute Disease↗
PubMed1992

Association of lysozyme to phospholipid surfaces and vesicle fusion.

Lysozyme-induced fusion of phosphatidylserine (PS) vesicles was studied as a function of pH. Fusion, monitored by lipid-mixing, was measured by following the dilution of pyrene-labelled phosphatidylcholine, incorporated in PS vesicles, into unlabelled bilayers. It is demonstrated that lysozyme-induced fusion is pH-dependent and significant fusion is triggered at pH 5 or below. The interaction of lysozyme with the vesicle bilayer was characterized by measuring resonance energy transfer from tryptophane, present in the protein, to pyrene. It is shown that concomitant with fusion, a strong resonance energy transfer signal appears at pH 5 or below. Furthermore, in monolayer experiments it was found that addition of lysozyme to the subphase caused an increase in surface pressure, when the pH was kept below 5.5. Very low concentrations of lysozyme sufficed to bring about the observed effects. The results are taken to indicate that lysozyme-induced fusion results from penetration of protein into the hydrophobic core of the bilayer, occurring at acidic pH.

Energy Transfer↗
PubMed1992

Motor control prior to movement onset: preparatory mechanisms for pointing at visual targets.

The present study investigated the mechanisms involved in the preparation of pointing movements in humans. We provided visual precues on the location of the upcoming target, and registered the effect of these precues on the reaction time (RT = interval between target appearance and movement onset). Generally, precues were found to reduce RT, suggesting that some aspects of the preparatory process have been advanced in time. In Exp. 1, precues fully specified the direction required for the upcoming movement while indicating only a range of movement amplitudes; in Exp. 2, precues fully specified the amplitude and indicated a range of directions. In both experiments, RT was shorter than in control trials without precues, and gradually increased with the size of the precued amplitude or direction range. This result suggests that the preparation of either parameter is possible without knowing the precise value of the other, i.e. amplitude and direction are not prepared in a fixed order. Furthermore, our results are consistent with the view that movement preparation includes a progressive contraction of the precued range towards the final value. The speed of this process can be estimated as 0.31 cm/ms for amplitude, and 1.7 deg/ms for direction ranges. In Exp. 3 and 4, precues indicated both amplitude and direction as ranges only. The size of the amplitude range was held constant while the size of the direction range was varied (Exp. 3), or vice versa (Exp. 4). Under these conditions, RT increased with the size of the varied range.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Dextran sulfate-dependent fusion of liposomes containing cationic stearylamine.

The incorporation of the positively charged stearylamine into phosphatidylcholine liposomes was studied by measuring electrophoretic mobilities. Up to a molar ratio SA/PC = 0.5 an increase of the positive zeta potential can be observed. Addition of the negatively charged macromolecule dextran sulfate leads to a change of the sign of the surface potential of the PC/SA liposomes indicating binding of the macromolecule to the surface. This process is accompanied by an increase in turbidity, which is dependent on the molecular weight of the dextran sulfate and the SA concentration (measured by turbidimetry). Using the NBD/Rh and Pyr-PC fluorescence assays the fusion of SA containing liposomes was investigated. A strong influence of the SA content and molecular weight of dextran sulfate on the fusion extent was observed. The fusion extent is proportional to the SA content in the PC membrane and the molecular weight of dextran sulfate. PC/SA/PE liposomes exhibit a higher fusion extent after addition of dextran sulfate compared to PC/SA liposomes indicating that PE additionally destabilizes the bilayer. Freeze-fracture electron microscopy reveals that the reaction products are large complexes composed of multilamellar stacks of tightly packed, straight membranes and aggregated vesicles. The tight packing of the membranes in the stacks (and the narrow contact of the aggregated vesicles) indicates a strong adherence of opposite membrane surfaces induced by dextran sulfate.

Amines↗
PubMed1992

Effect of anionic polymers on fusion of Sendai virus with human erythrocyte ghosts.

The effect of anionic polymers (dextran sulfate, heparin and chondroitin sulfate) on fusion of Sendai virus with erythrocyte ghosts was studied. The effect of pH on the activity of these anionic polymers was also investigated. In order to examine the interaction of such polymers with the Sendai virion and erythrocyte ghost surfaces, the binding of virions to erythrocyte ghosts and the aggregation of virions and/or erythrocyte ghosts were also measured with respect to the same parameters. It was found that the anionic polymers suppressed the fusion of Sendai virus with erythrocyte ghosts. The order of effectiveness of the polymers in suppression was dextran sulfate greater than heparin greater than chondroitin sulfate, for the application of a same quantity (weight/ml) of the polymers. The lower the pH of the suspending medium, the more effective were the polymers in suppressing virion-erythrocyte ghost aggregation and fusion. The suppression of fusion was dependent on the concentration of the polymers applied: the higher the concentration of the polymer applied, the more the suppression was observed. Evidence from binding studies, turbidity measurements and electrophoretic mobility measurements indicates that the anionic polymers interact preferentially with the virion surface.

Adsorption↗
PubMed1991

Role of functional groups of human plasma and luminol in scavenging of NaOCl and neutrophil-derived hypochlorous acid.

Hypochlorous acid HOCl/OCl- and other oxidants derived from stimulated polymorphonuclear leukocytes are involved in tissue damage during a number of pathological processes. In order to obtain more detailed information on possible reactions of HOCl/OCl- the effects of both NaOCl and PMN-derived hypochlorous acid on functional groups of amino acid solutions and human plasma are studied. In valine and lysine solutions NaOCl diminishes the number of amino groups in a molar ratio of 1:1 between NaOCl and amino groups. In cysteine and methionine samples the decrease of amino groups starts only after all sulfhydryl or thioether groups are oxidized by NaOCl. If freshly prepared human plasma is treated with increasing amounts of NaOCl all plasma SH groups are oxidized first, then probably the thioether groups and only after this the amino groups are affected. Furthermore, it was found, that the reactivity of luminol against NaOCl is similar to that of amino groups. Increasing amounts of SH groups of components of human plasma are oxidized by incubation with PMA-stimulated polymorphonuclear leukocytes dependent on the incubation time. Plasma amino groups are not affected under the same experimental conditions. The addition of plasma to FMLP-stimulated PMN in the presence of luminol decreases that part of chemiluminescence caused by extracellularly generated hypochlorous acid. Plasma samples pretreated with NaOCl cause a lower inhibition of light generation in FMLP-stimulated PMN only when more than 4.10(-8) mol NaOCl per mg protein are used to pretreat plasma. It is assumed that in the development of tissue injuries caused by infiltrated PMN the following sequence of damage occurs in accessible tissue regions. First, the sulfhydryl groups are oxidized, then the thioether groups, and only after this amino and other target groups are affected.

Amino Acids↗
PubMed1991

Immune-mediated hemolytic anemia in a horse.

An 18-year-old Quarter Horse gelding was determined to have immune-mediated hemolytic anemia after detection of autoagglutination of RBC spherocytosis as well as a positive direct Coombs test result. A lack of response to treatment with corticosteroids necessiated the administration of cyclophosphamide and azathioprine. The anemia resolved after treatment with chemotherapeutic drugs.

Adrenal Cortex Hormones↗
PubMed1991

The influence of particle size and multiple apoprotein E-receptor interactions on the endocytic targeting of beta-VLDL in mouse peritoneal macrophages.

Low density lipoprotein (LDL) and beta-very low density lipoprotein (beta-VLDL) are internalized by the same receptor in mouse peritoneal macrophages and yet their endocytic patterns differ; beta-VLDL is targeted to both widely distributed and perinuclear vesicles, whereas LDL is targeted almost entirely to perinuclear lysosomes. This endocytic divergence may have important metabolic consequences since beta-VLDL is catabolized slower than LDL and is a more potent stimulator of acyl-CoA/cholesterol acyl transferase (ACAT) than LDL. The goal of this study was to explore the determinants of beta-VLDL responsible for its pattern of endocytic targeting. Fluorescence microscopy experiments revealed that large, intestinally derived, apoprotein (Apo) E-rich beta-VLDL was targeted mostly to widely distributed vesicles, whereas small, hepatically derived beta-VLDL was targeted more centrally (like LDL). Furthermore, the large beta-VLDL had a higher ACAT-stimulatory potential than the smaller beta-VLDL. The basis for these differences was not due to fundamental differences in the means of uptake; both large and small beta-VLDL were internalized by receptor-mediated endocytosis (i.e., not phagocytosis) involving the interaction of Apo E of the beta-VLDL with the macrophage LDL receptor. However, large beta-VLDL was much more resistant to acid-mediated release from LDL receptors than small beta-VLDL. Furthermore, partial neutralization of the multiple Apo Es on these particles by immunotitration resulted in a more perinuclear endocytic pattern, a lower ACAT-stimulatory potential, and an increased sensitivity to acid-mediated receptor release. These data are consistent with the hypothesis that the interaction of the multivalent Apo Es of large beta-VLDL with multiple macrophage LDL receptors leads to a diminished or retarded release of the beta-VLDL from its receptor in the acidic sorting endosome which, in turn, may lead to the widely distributed endocytic pattern of large beta-VLDL. These findings may represent a physiologically relevant example of a previously described laboratory phenomenon whereby receptor cross-linking by multivalent ligands leads to a change in receptor targeting.

Animals↗
PubMed1991

Effect of dextran sulfate on fusion of Sendai virus with human erythrocyte ghosts.

The effect of dextran sulfate on the fusion of Sendai virus and erythrocyte ghosts was studied as a function of dextran sulfate concentration and pH of cell suspension solutions. In order to examine the interaction of dextran sulfate with Sendai virion and erythrocyte ghost surfaces, the turbidity of cell suspensions was also measured with respect to the same parameters as above. It was found that dextran sulfate inhibited the fusion of Sendai virus with erythrocyte ghosts. The lower the pH of the suspension solution was, the more effective was dextran sulfate in suppressing virion erythrocyte ghost fusion. Dextran sulfate of a higher molecular weight was slightly more effective in suppressing fusion than that of a lower molecular weight. From turbidity measurements of Sendai virus and erythrocyte ghost suspensions, it is likely that dextran sulfate interacts preferentially with Sendai virion surfaces and inhibits interaction between Sendai virions and erythrocyte ghosts.

Depression, Chemical↗