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Biomedical subjects

H A Davies

Publications and source records attributed to H A Davies.

At least 19 recordsLinked to original sources
PubMed1992

Structural asymmetry in the thalamofugal visual projections in 2-day-old chick is correlated with a hemispheric difference in synaptic density in the hyperstriatum accessorium.

Differences in visual discrimination ability between the left and right eyes of chicks, which are most prominent in young males, may result from a structural asymmetry in the organization of the visual projections from the thalamus to the visual Wulst. This asymmetry in projections is no longer present by 21 days in males when the contralateral projections from the right thalamus to the left hyperstriatum have developed. Since the asymmetry of the thalamo-hyperstriatal system results in a differential input of fibres to regions of the hyperstriatum which in turn project to the hyperstriatum accessorium (HA), one of the major differences expected within this region would be an asymmetry in the numerical density of synapses (Nv.syn/microns3). When this was examined in the hyperstriatum accessorium of 2-day-old male chicks, the density of synapses in the right HA was found to be significantly higher (22%, P less than 0.05) than in the left HA. The consequences of this asymmetry in synaptic density in the HA could be widespread and influential within the chick visual system.

Animals↗
PubMed1992

Anginal pain of esophageal origin: clinical presentation, prevalence, and prognosis.

Since 1768, when Heberden recognized a relationship of angina pectoris with eating, the close resemblance between angina-like pain of esophageal and cardiac origin has led to diagnostic confusion, with the role of the esophagus being, in turn, over- and underemphasized as a cause of symptoms. Although the classic features of angina do not distinguish the origin of the pain, certain other symptoms may identify esophageal pain. These include an inconsistent correlation of exercise with pain, periods of prolonged remission, provocation of pain by posture, association with other esophageal symptoms, relief by antacids, radiation of pain down the right arm and into the back, occurrence of pain at night, continuation of pain as a background ache, and relief from nitroglycerine delayed by 10 minutes or longer. However, while certain symptoms may alert the clinician to the possibility that angina-like pain is due to esophageal disease, no single symptom or combination of symptoms is infallible; there is no alternative to careful assessment. Esophageal disease accounts for the greatest number of patients with chest pain of unknown origin. The prevalence of angina-like esophageal pain in unselected emergency admissions with suspected myocardial infarction is 10-20%. Approximately one third or more of patients with angina and normal coronary arteries have esophageal problems. We have followed patients with angina-like esophageal pain for 9 years. Although prognosis remains good, confirming the original noncardiac diagnosis, greater than 80% of patients continue to have chest pain of undiminished intensity, and half are limited in their ability to work. Reassurance appeared to have one beneficial result: Patients were less likely to consult a physician after a positive diagnosis had been made.

Angina Pectoris↗
PubMed1992

Association of Haemophilus ducreyi with cell-culture lines.

The association of Haemophilus ducreyi with epithelial cell cultures was studied by light microscopy, electronmicroscopy and viable counts. Associated organisms were engulfed by epithelial cells and sequestered from the cell-surface environment. Large numbers of organisms within epithelial cells appeared to induce cell lysis and release of H. ducreyi. Such a mechanism occurring in vivo may assist H. ducreyi to evade the bactericidal action of polymorphonuclear leucocytes and may explain some of the tissue damage seen in genital ulcers caused by H. ducreyi.

Animals↗
PubMed1991

Permeability of human venous endothelial cell monolayers perfused in microcarrier cultures: effects of flow rate, thrombin, and cytochalasin D.

We have applied a multiple isotope dilution technique to examine junctional permeability of human umbilical vein endothelial cells (HUVEC) in vitro. Primary cultures were grown to confluence on porous Cytodex-3 microcarrier beads, packed into 0.3 ml columns (3 x 10(6) cells) and perfused at varying flow rates (0.3-1.2 ml/min) with HEPES-buffered Tyrodes solution containing unlabeled cyanocobalamin, insulin, and albumin. Columns were challenged periodically with mixtures of radioactive tracers of different molecular size. Permeability to 22Na+, [57Co]cyanocobalamin (1.3 kD), [125I]insulin (6 kD) or [125I]albumin (66 kD) was assessed relative to [131I]IgG (160 kD, impermeant reference tracer) by comparing column elution profiles. Although the single passage extraction of [125I]albumin by beads alone approximated 40%, the presence of confluent HUVEC rendered these beads effectively impermeable to albumin. High junctional extractions were measured for cyanocobalamin (0.79 +/- 0.02, n = 28) and insulin (0.51 +/- 0.05, n = 14) in cultures perfused at 0.3-0.4 ml/min, and tracer extraction decreased as perfusion rates increased. Permeability coefficients for cyanocobalamin (9.66 x 10(-5) cm/s) and insulin (4.18 x 10(-5) cm/s) increased significantly during perfusion with thrombin (10 U/ml) or cytochalasin D (1 microgram/ml), whereas permeability to albumin (0.39 x 10(-5) cm/s) remained unchanged. Morphological studies, using the glycocalyx stain ruthenium red, revealed that thrombin or cytochalasin D increased the penetration of the stain into junctions between endothelial cells.

Albumins↗
PubMed1991

Intracellular location of mycoplasmas in cultured cells demonstrated by immunocytochemistry and electron microscopy.

Mycoplasma fermentans (strain 'incognitus') was incubated with HeLa cells for up to 96 h. After 24 h, mycoplasma organisms were demonstrated intracellularly by immunocytochemistry using mule anti-M. fermentans antiserum and gold labelling on ultrathin sections of both Lowicryl K4M and Araldite-embedded HeLa cells, the latter being treated with hydrogen peroxide. The Araldite-embedded cells were fixed with glutaraldehyde and osmium tetroxide in the presence of ruthenium red to stain the mucopolysaccharide surface components of both the procaryotic and eucaryotic cells. Intracellular localization of some M. fermentans organisms was confirmed by exclusion of ruthenium red from their membranes. Various numbers of mycoplasma organisms were seen per cell and occasionally some were within vacuoles, the membranes of which were also unstained by ruthenium red. The PG18 strain of M. fermentans and a strain of M. hominis were also detected intracellularly using similar methodology and homologous mule or rabbit antisera. The occasional presence of both apparently normal and some denser degenerate mycoplasmas in the same cell may indicate gradual degradation by phagolysosomal digestion.

HeLa Cells↗
PubMed1990

The 70 kilodalton iron regulated protein of Neisseria meningitidis is not the human transferrin receptor.

Neisseria meningitidis is able to chelate iron from human transferrin (HTF), the main sequestrator of extracellular iron in vivo. Previous workers have reported that a ca. 70 kilodalton (kDa) iron regulated outer membrane protein (FeRP-70) is a highly specific receptor for HTF. We have examined the interaction between the iron regulated outer membrane proteins (OMP's) and HTF, using HTF and rabbit anti HTF, as well as gold labelled HTF (Au-HTF) to blot OMP's of various serogroups and serotypes of N. meningitidis. Also, we used monospecific rabbit anti FeRP-70 in competitive experiments to determine the role of FeRP-70 in HTF-binding. Single proteins (molecular weights range ca. 60 to ca. 90 kDa) were identified in the OMP's from each strain which reacted with HTF. HTF failed to block the reaction between FeRP-70 and the OMP's, conversely anti FeRP-70 failed to block the HTF-binding reaction. We believe that the 70 kDa iron regulated protein of N. meningitidis is not a human transferrin receptor.

Adolescent↗
PubMed1990

Detection of capsule in strains of Clostridium difficile of varying virulence and toxigenicity.

Nine toxigenic and six non-toxigenic strains of Clostridium difficile, of varying virulence in the hamster model of antibiotic-associated colitis, were examined for the presence of a capsule. Antibody stabilisation of the capsule with heterologous and/or homologous antiserum fixed in glutaraldehyde, or direct fixation in glutaraldehyde/diamine, were used with added ruthenium red to stain the capsular glycocalyx. All strains possessed a capsule which was either loose-knit or compact, sometimes with attached globular masses. Better capsule preservation was achieved in some strains with glutaraldehyde/diamine/ruthenium red fixative than with homologous or heterologous antibody stabilisation. The possession of a capsule following in vitro growth does not appear to correlate with the virulence status of these strains of C. difficile.

Animals↗
PubMed1989

Epitopes of serogroup B Neisseria meningitidis analysed in vitro and directly from cerebrospinal fluid.

Two type B15 P1.16 strains of Neisseria meningitidis were examined by immunogold electron microscopy for accessibility of two outer membrane protein (OMPs) to monoclonal antibodies. Both strains exhibited cell-to-cell variation of one epitope of the Class 3 OMP (P3.15) and one of the Class 1 OMPs (P1.16) when grown in vitro. One strain, a nasopharyngeal isolate revealed this variation to be growth-phase independent and double labelling of both epitopes showed independent variation. CSF containing N. meningitidis was stored in liquid nitrogen without laboratory processing at the time of isolation of the second strain. Direct analysis of the organisms showed no cell-to-cell variation and immunoglobulin G on the surface. However, while there were similar labelling densities of the Class 1 epitope in vivo compared with either strain grown in vitro, there was a lower labelling density of the Class 3 epitope in vivo that was not caused by freeze-thawing. This reduction may be due to decreased expression of this epitope in vivo which casts doubts on the use of the Class 2/3 OMP as a vaccine candidate.

Adult↗
PubMed1988

Mucosal association by Clostridium difficile in the hamster gastrointestinal tract.

For many organisms, mucosal association is an important virulence determinant. Although studied in detail for other intestinal pathogens, this aspect of pathogenicity has not been studied for Clostridium difficile. We compared the ability of an avirulent non-toxigenic strain (M-1), a highly virulent toxigenic strain (B-1), and a poorly virulent toxigenic strain (BAT) of C. difficile to adhere to different regions of the gastrointestinal tract of hamsters pre-treated with clindamycin. Strain B-1 associated with the gut mucosa significantly better than strain M-1 (p less than 0.001) for all sites other than the caecum, and achieved significantly higher levels in the caecal contents (p less than 0.001). The same was true when strain B-1 was compared with strain BAT except that there was no significant difference for the large bowel mucosa. To assess the possible role of toxin in promoting mucosal association, e.g., by compromising host defences or exposing masked adherence sites, strain M-1 was given to animals after intra-caecal administration of crude toxin preparations from strain-B1, which were heat-inactivated in control experiments. The addition of this toxin increased significantly the mucosal association of M-1 for the small bowel only, whereas the inactivated toxin had no significant effect. These results imply that there may be intrinsic differences between strains in their ability to colonise and associate with the gut mucosa, which may partly depend on their ability to produce toxin. These differences do not correlate with cell-surface hydrophobicity or the presence of plasmids, flagella or fimbriae.

Animals↗
PubMed1988

Computerized and telemetric management of diabetic pregnancy in Cambridge.

In order to optimize the quality of our care, we have used the Ames Memory Glucometer in our computerized management of 17 insulin-dependent diabetic pregnancies. Patients measured their own blood glucose levels on 4.5 +/- 1.2 (SD) occasions per day, and six of them transmitted their blood glucose measurements telemetrically from home into a hospital-based computer on a total of 42 occasions. We achieved near-optimal blood glucose levels and normal HbA1 levels throughout most of these 17 pregnancies. Average blood glucose levels were 6.4 +/- 0.9 mmol/l in the first, 5.9 +/- 1.2 mmol/l in the second, 5.4 +/- 1.0 mmol/l in the third trimester. Corresponding values for HbA1 were 8.0 +/- 1.5%, 6.5 +/- 0.8%, and 6.2 +/- 0.4%. Average insulin requirement doubled during pregnancy, but fell to 74% of the pre-pregnancy dosage by one week after delivery. The average gestational age at delivery was 38.9 +/- 1.3 weeks, and we had no perinatal deaths. Two of the babies were macrosomic, even though their mothers had good diabetic control. Four patients were delivered by Caesarean section. However we achieved a vaginal delivery in 93% of those in whom it was planned. Our computerized system of managing diabetic pregnancies was efficient, safe, and popular with our patients.

Blood Glucose↗
PubMed1987

Trial of nifedipine for prevention of oesophageal spasm.

We have used a placebo controlled trial to investigate the effect of long-term administration of nifedipine in the prevention of symptomatic episodes of oesophageal spasm. Diary card scoring was used to assess symptoms in 8 patients with oesophageal spasm who were each given nifedipine and placebo for at least 6 weeks. No significant differences in symptoms between the nifedipine and placebo treatment periods were seen.

Adult↗
PubMed1986

A numerical taxonomic study of anaerobic gram-negative bacilli classified as Bacteroides ureolyticus isolated from patients with non-gonococcal urethritis.

A numerical taxonomic study of 64 strains of anaerobic Gram-negative bacilli isolated from men with non-gonococcal urethritis, two unclassified laboratory strains of 'corroding bacilli', and 12 other strains of anaerobic Gram-negative bacilli, including nine received as anaerobic curved rods and three as 'Bacteroides corrodens' (B. ureolyticus), isolated from women with bacterial vaginosis, was undertaken. Seventeen reference anaerobic strains belonging to the genera Bacteroides, Fusobacterium, Mobiluncus, Mitsuokella and Wolinella were included. Morphological, biochemical and physiological characteristics were examined in 103 tests. The resemblance between the 95 strains was calculated using the SSM, SJ and DP coefficients for cluster analyses based on the UPGMA method. All three approaches gave similar groupings, and the estimated average probability of test error was 2.46%. The strains fell into 10 phenons. The unclassified strains from men and three from women with lower genital-tract infections, and the laboratory strains of 'corroding bacilli' clustered in one phenon with the reference strains of B. ureolyticus, indicating that they correspond to B. ureolyticus. The other unclassified strains of anaerobic curved rods clustered as a distinct phenon. They correspond to species of the newly described genus Mobiluncus. The taxonomic data and the compilation of diagnostic tables serve as a useful guide for the laboratory identification of clinical isolates regarded as B. ureolyticus.

Bacteroides↗