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Biomedical subjects

M Dixon

Publications and source records attributed to M Dixon.

At least 19 recordsLinked to original sources
PubMed1992

Hypnotic susceptibility and verbal automaticity: automatic and strategic processing differences in the Stroop color-naming task.

The original hypothesis of Dixon, Brunet, and Laurence (1990) that highly hypnotizable (HH) subjects process words more automatically than do low hypnotizable (LH) subjects was retested in a paradigm that separated strategic from automatic processes in the Stroop color-naming task. The words red and blue preceded a color patch that was red or blue. Subjects were told that the word predicted the opposite color 75% of the time. Automatic and strategic processes were assessed by varying the interstimulus interval (ISI) between the word and the color patch. Both HH and LH subjects showed significant strategic effects (faster incongruent-trial, color-naming reaction times than congruent-trial reaction times at ISIs over 400 ms), but only HH subjects showed significant automaticity (significantly faster congruent-trial reaction times than incongruent-trial reaction times at 16.7 ms, the lowest ISI).

Adult↗
PubMed1979

The effects of sodium cromoglycate on lung irritant receptors and left ventricular cardiac receptors in the anaesthetized dog.

1 The time from the injection of sodium cromoglycate 10 to 50 mug/kg into a saphenous vein, the cervical carotid arteries, the left ventricle and the aortic arch, to the onset of reflex hypotension has been measured in anaesthetized dogs. The shortest latency was 16.9 s on injection of sodium cromoglycate into the left ventricle.2 Instillation of 2% lignocaine into the pericardium of an anaesthetized dog blocked the reflex hypotensive response to sodium cromoglycate (10 to 50 mug/kg i.v.), and also prevented sodium cromoglycate (100 mug/kg) from reversing reflex bronchoconstriction induced by inhalation of an aerosol of histamine.3 The effect of sodium cromoglycate (100 mug/kg i.v.) on resting discharge and histamine-induced discharge (20 mug/kg i.v.) of five lung irritant receptors in five anaesthetized dogs has been studied. Sodium cromoglycate (100 mug/kg i.v.) did not affect the resting discharge of these receptors or their ability to respond to histamine.4 Sodium cromoglycate (100 mug/kg i.v.) increased the rate of discharge of three receptors found in the endocardium of the left ventricle of the canine heart. A solution of sodium cromoglycate (0.1%) was applied topically to one receptor and its rate of discharge was increased.5 It is suggested that in the dog, sodium cromoglycate produces reflex hypotension and reverses histamine-induced reflex bronchoconstriction by activating receptors in the left ventricle of the heart.

Action Potentials↗
PubMed1979

The effects of H1- and H2-receptor agonists and antagonists on total lung resistance, dynamic lung compliance and irritant receptor discharge in the anaesthetized dog.

1 The effects of histamine and 4 methylhistamine (i.v.) alone, and in the presence of chlorpheniramine or cimetidine, on total lung resistance (RL), dynamic lung compliance (Cdyn) and irritant receptor activity have been studied in dogs anaesthetized with chloralose. 2 Histamine produced dose-related increases in RL and irritant receptor activity with associated falls in Cdyn which were blocked by chlorpheniramine but unaffected by cimetidine. 3 4 Methylhistamine produced small insignificant changes in RL and Cdyn and small significant increases in irritant receptor activity which were reduced with chlorpheniramine but unaffected by cimetidine. 4 The results suggest that histamine increases irritant receptor activity, either directly or indirectly, via H1-receptors.

Animals↗
PubMed1979

The effects of histamine, acetylcholine and 5-hydroxytryptamine on lung mechanics and irritant receptors in the dog.

1. The ability of histamine, acetylcholine, acetylcholine (ACh) and 5-hydroxytryptamine (5-HT) given I.V. and by aerosol to induce reflex bronchoconstriction and to activate lung irritant receptors has been studied in dogs anaesthetized with chloralose. 2. Histamine (four breaths of an aerosol from 0.0625%, 0.125% and 0.25% solutions and 5, 10 and 20 microgram kg-1 I.V.), 5-HT (four breaths of an aerosol from 0.5% or 1.0% solutions and 10, 20 and 40 microgram kg-1 I.V.) produced significant relex changes in RL (total lung resistance). The changes in RL produced by ACh (four breaths of an aerosol from 0.25%, 0.5% and 1.0% solutions, of 5, 10, 20 and 40 microgram kg-1 I.V.) were unaffected by vagal cooling. 3. The falls in Cdyn (dynamic compliance) produced by ACh given by aerosol or I.V. were unaffected by vagal cooling. The falls in Cdyn produced by histamine (10 microgram kg-1 and 40 microgram kg-1 I.V.) and 5-HT (four breaths of an aerosol generated from a 0.5% solution and 20 microgram kg-1 and 40 microgram kg-1 I.V.) were significantly reduced by vagal cooling. 4. Histamine, 5-HT and ACh given by aerosol and I.V. increased lung irritant receptor discharge. Irrespective of the route of administration, for a given change in RL histamine produced a greater increase in irritant receptor discharge than did ACh or 5-HT, which produced similar increases. 5. For a given change in RL, histamine, ACh and 5-HT were more effective in activating lung irritant receptors when given I.V. than by aerosol. 6. The mechanisms of irritant receptor activation by histamine, ACh and 5-HT and the relationship between irritant receptor discharge and reflex bronchoconstriction are discussed.

Acetylcholine↗
PubMed1979

The effect of a respiratory tract infection on histamine-induced changes in lung mechanics and irritant receptor discharge in dogs.

The effects of intravenously administered histamine on total lung resistance (RL), dynamic lung compliance (Cdyn), and the discharge of lung irritant receptors have been measured in normal dogs and in dogs whose upper respiratory tract was naturally infected with the organism Bordetella bronchiseptica. The resting values for RL and irritant receptor discharge were similar for the infected and control dogs, but Cdyn was significantly lower in the infected group of dogs. Intravenous administration of 20 microgram of histamine/kg of body weight produced significantly greater direct and reflex changes in RL in the infected dogs than in the control animals. The changes in Cdyn in both groups of animals were similar. Intravenous administration of histamine (20 microgram/kg) produced a significantly greater increase in the rate of discharge of lung irritant receptors found in infected dogs than in control dogs. A possible mechanism responsible for the hyperreactivity to histamine is seen in the hypersensitivity of the irritant receptors introduced by the epithelial lesions observed in the infected dogs.

Action Potentials↗
PubMed1978

Lung reflexes in rabbits during pulmonary stretch receptor block by sulphur dioxide.

Anaesthetized rabbits were given 200 ppm sulphur dioxide to breathe for 10 min. This abolished activity in 23 of 26 pulmonary stretch receptors, while leaving that of lung irritant receptors unimpaired. The Breuer-Hering reflex was abolished and breathing became deeper and slower. Inspiratory time (tI) was increased and expiratory time (tE) decreased. Subsequent vagotomy increased tidal volume (VT), tI and tE. In animals with stretch receptors blocked, injections of phenyl diguanide and histamine still increased breathing frequency and decreased VT, indicating that reflexes from lung irritant and J-receptors were intact. Inhalation of 8% CO2 caused a bigger increase in frequency and tidal volume in rabbits with stretch receptor block compared with controls or those after vagotomy. Induction of pneumothorax with stretch receptor block transiently prolonged tI and shortened tE; removal of the pneumothorax also transiently shortened tE and usually also decreased tI. The results suggest that lung irritant receptors reflexly shorten tE in all our experimental conditions, but have various effects on tI which may depend on the timing of the irritant receptor discharge and refractoriness of the inspiratory response.

Animals↗
PubMed1978

Posture and the composition of plasma.

For a group of normal medical students, we examined the effect of posture on the concentration of a number of constituents in plasma. On standing, there is a significant increase in plasma total protein, albumin, calcium, alkaline phosphatase, bilirubin, and cholesterol--all proteins or substances bound to protein. Although it is possible to make an allowance for postural variations in plasma calcium, no correction is possible for changes in protein concentrations and care is needed whenever the precise values are important, as in the follow-up of patients with the nephrotic syndrome.

Adult↗
PubMed1977

Varicose veins in tropical Africa.

1259 Tanzanians in a provincial town were examined for varicose veins. 5-5% (6-1% of men and 5-0% of women) of the 1000 people aged eighteen years and over had varicose veins. This prevalence is intermediate between that reported for minimally developed areas (0-1%-0-4%) and the age-adjusted rate reported for Michigan (12-3%). The Tanzanian diet included some refined carbohydrate, and the mean daily stool weight (228 g) indicated a fibre content intermediate between that of traditional African communities (490 g) and western countries (115 g). These findings are consistent with the hypothesis relating varicosities to a fibre-depleted diet. Life-long use of the squatting position for defaecation did not protect against the development of varicose veins.

Adolescent↗
PubMed1977

The isolation and partial characterization of the major glycoprotein (LGP-I) from the articular lubricating fraction from bovine synovial fluid.

The articular lubricating fraction from bovine synovial fluid was prepared by repeated fractionation in three consecutive CsCl density gradients to remove completely traces of hyaluronic acid. The major glycoprotein consituent (LGP-I) was then isolated by repeated gel-permeation chromatography. The yield of the LGP-I component was about 20 mg/litre of synovial fluid. Sedimentation-equilibrium measurements showed that this glycoprotein was homogeneous and the mol.wt. was calculated to be 227500. Amino acids represented 43% (w/w) and carbohydrate constituents 44% (w/w) of the molecule. Threonine, glutamic acid, proline and lysine (224, 127, 242 and 128 residues/1000 residues respectively) were the major amino acids. Galactosamine, galactose and N-acetylneuraminic acid (202, 162 and 114 residues/molecule of LGP-I component respectively) accounted for 98% of the total carbohydrate residues present. Small amounts of mannose and glucosamine (1 and 9mol respectively/mol of LGP-I component) were also present. After treatment of LGP-I component with alkali and NaB3H4 radioactivity was incorporated into alpha-aminobutyric acid and alanine in a molar ratio of 4:1, and radioactive galactosaminitol was isolated by ion-exchange chromatography from a cleaved oligosaccharide fraction. These data demonstrate the presence of threonine and serine -O-GalNAc linkages, but only 25% of the theoretical likages involving threonine were cleaved by a beta-elimination reaction. Digestion of LGP-I component with Pronase followed by chromatography on DEAE-cellulose yielded glycopeptide fractions with a similar amino acid and carbohydrate composition to the intact molecule. Treatment of desialylated and intact LGP-I component with galactose oxidase followed by reduction with NaB3H4 revealed the presence of 52mol of terminal galactose in the intact molecule and 153mol of galactose/mol of LGP-I component after treatment with neuraminidase. The data indicate the LGP-I component is composed of a single polypeptide chain containg more than 150 oligaosaccharide side chains composed of O-GaINAc-Gal distributed over the length of the peptide chain and that terminal sialic acid residues are linked to galactose in two-thirds of these side chains.

Amino Acids↗
PubMed1976

Radioimmunological identification of tropoelastin.

Antiserum was prepared in sheep against insoluble elastin isolated from embryonic-chick aortae. In an indirect immunoprecipitation test, the antiserum reacted quantitatively with small amounts of radioactively labelled purified tropoelastin prepared from embryonic-chick aortae. The antiserum did not cross-react with chick procollagen, and the antiserum uas used to identify radioactively labelled tropoelastin secreted by chick aorta cells in suspension culture.

Animals↗