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Biomedical subjects

J Turner

Publications and source records attributed to J Turner.

At least 217 records · Page 12Linked to original sources
PubMed1994

Low-grade myxoid chondrosarcoma of the temporal bone: differential diagnosis and report of two cases.

Skull base chondrosarcoma and chordoma are rare tumors that generally have a poor prognosis. In 1973, Heffelfinger et al described a chondroid variant of chordoma, called chondroid chordoma that was found to have a significantly better prognosis than classic chordoma. However, recent evidence suggests that many of the tumors diagnosed as chondroid chordoma may, in fact, be low-grade myxoid chondrosarcomas. This report presents the diagnosis and treatment of two cases of skull base tumor that were diagnosed preoperatively as schwannoma because they were thought initially to be centred on the jugular foramen. Initial histologic evaluation suggested chondroid chordoma, but immunohistologic techniques and a review of the literature led to a diagnosis of low-grade myxoid chondrosarcoma.

Adult↗
PubMed1993

Generation of beta A4 from the amyloid protein precursor and fragments thereof.

The cellular mechanisms underlying the generation of beta A4 in Alzheimer's disease and its relationship to the normal metabolism of the amyloid protein precursor (APP) are unknown. In this report, we show that expression of the C-terminal 100 residues of APP, with (SPA4CT) or without (A4CT) a signal sequence in the N-terminal position, in human neuroblastoma cells results in secretion of a 4 kDa beta A4-like peptide. In A4CT and SPA4CT expressing SY5Y cells, beta A4 generation could not be inhibited by the lysosomotropic amines chloroquine and ammonium chloride but was inhibited by brefeldin A, monensin and methylamine. The last also selectively inhibits APP secretion in neuroblastoma cells [1]. The finding that chloroquine and ammonium chloride inhibit beta A4 generation from full length APP but not from A4CT and SPA4CT are consistent with the assumption that the two cleavages necessary to generate beta A4 operate in two different compartments. Our data suggest the cleavage which generates the C-terminus of beta A4 takes place in the same compartment (late Golgi or endosomal vesicles) in which the APP-secretase operates.

Alzheimer Disease↗
PubMed1993

Asymptomatic low bone mineral density in otherwise healthy people: four year follow up.

AIM: To determine the effect of screening a normal population for low bone density on lifestyle, subsequent bone density and fracture risk. METHOD: A cross sectional study of 726 subjects screened for low bone density identified 60 with bone density greater than one standard deviation below an age and sex matched mean. Those who accepted further assessment were followed clinically and with repeat bone densitometry for up to four years. Those declining assessment were contacted four years later and questioned about lifestyle changes and fractures. They were offered repeat bone densitometry. RESULTS: Twenty five subjects accepted intervention and were advised on lifestyle modification and treated with calcium supplements (18) calcitriol (5) or oestrogen (1). 22 of the 35 subjects who initially declined intervention volunteered to have their bone density repeated. Bone density increased in the group accepting intervention compared to the 22 subjects in the group who initially declined assessment (p < 0.05). Several laboratory investigations had a low yield. Lifestyle modification in the group declining assessment did not significantly affect subsequent bone density. Fractures occurred infrequently in both groups. CONCLUSION: After screening the normal population for low bone density, significant improvements in bone density can be achieved in patients accepting further intervention.

Adult↗
PubMed1993

Site-specific interaction of vaccinia virus topoisomerase I with base and sugar moieties in duplex DNA.

Vaccinia DNA topoisomerase specifically binds and forms a covalent adduct at DNA sites containing a conserved sequence element 5'(C/T)CCTT decreases in the scissile strand. The molecular interactions that contribute to recognition of the CCCTT motif in a synthetic DNA substrate have been examined using modification interference, modification protection, and analog substitution techniques. We report that topoisomerase makes contact with guanine nucleotide bases of the pentamer motif complementary strand (3'GGGAA) within the major groove of the DNA helix and that alteration of the binding surface by chemical modification is deleterious to the interaction. Additional contacts are made with guanine residues located outside the pentamer element. The enzyme is unable to form a covalent adduct with synthetic RNA substrates. Analysis of the cleavage of DNA duplexes containing 2'OMe sugars suggests that the inability of the vaccinia topoisomerase to cleave either an RNA duplex or an RNA:DNA hybrid can be accounted for by the interfering effects of a 2' sugar substituent at two or more sites within the pentamer. Interaction with the sugar at the +2T nucleotide appears to be the most critical, as judged by the effects of single sugar substitutions.

Base Sequence↗
PubMed1993

Arabidopsis auxin-resistance gene AXR1 encodes a protein related to ubiquitin-activating enzyme E1.

The plant hormone auxin has a central role in many aspects of plant growth and development. By screening for mutants of Arabidopsis that are resistant to exogenous auxin, we have identified several genes that are required for normal auxin response. One of these genes, AXR1, is defined by recessive mutations that confer auxin resistance to the roots, rosettes and inflorescences of mutant plants. In addition, axr1 mutants display a variety of morphological defects that are consistent with a reduction in auxin sensitivity. Here we isolate the AXR1 gene using a map-based approach and report that AXR1 encodes a new protein with significant sequence similarity to the ubiquitin-activating enzyme E1. The AXR1 protein is highly diverged from previously characterized E1 enzymes, however, and lacks a key cysteine residue that is essential for E1 activity. AXR1 may therefore define a new class of enzymes in the ubiquitin pathway or it may have a novel function in cellular regulation which is unrelated to ubiquitin conjugation.

Amino Acid Sequence↗
PubMed1993

The role of protein kinase C in the initial events of platelet activation by thrombin assessed with a selective inhibitor.

The role of protein kinase C (PKC) in platelet activation by thrombin was assessed using a PKC inhibitor Ro 31-7549/001 (R2) which, in vitro, shows more selectivity for PKC than other kinase inhibitors. During early (1.5 s) thrombin-induced platelet activation, when phosphorylation of 47 kDa protein (pleckstrin) and myosin light chain by PKC and myosin light chain kinase, respectively, are most readily differentiated, R2 suppressed phosphorylation of pleckstrin more effectively than myosin light chain. R2-inhibited dense granule secretion (measured 0-10 s using quenched-flow techniques) with a dose dependency similar to that for inhibition of pleckstrin phosphorylation, supporting a role for PKC in this process. R2, at 0.5 microM inhibited 47 kDa protein phosphorylation by more than 60%, but had only minimal effects on the kinetics (0-3s) of ADP-induced primary aggregation. At this same concentration, R2 potentiated the thrombin-induced rise in cytosolic calcium during early (0-15 s) activation as measured in the presence or absence of external calcium. These data support the hypothesis that activation of PKC during early platelet function helps regulate cytosolic calcium levels by limiting calcium release into the cytosol.

Blood Proteins↗
PubMed1993

Transoesophageal echocardiographic assessment of haemodynamic function during laparoscopic cholecystectomy.

We have measured cardiovascular changes associated with insufflation of carbon dioxide and the reverse Trendelenburg position during laparoscopic cholecystectomy, using transoesophageal echocardiography in 13 healthy patients. End-tidal carbon dioxide values increased after insufflation of carbon dioxide, with values significantly (P < 0.05) increased after lateral tilt positioning. Creation of a pneumoperitoneum was associated with increases (P < 0.05) in left ventricular end-systolic wall stress, concomitant with increases (P < 0.01) in peak airway pressure and systemic arterial pressure. In addition, left ventricular end-diastolic area decreased (P < 0.05) after reverse Trendelenburg positioning. Left ventricular ejection fraction was maintained throughout the study.

Adult↗
PubMed1993

Historical assessment of risk factors in screening for osteopenia in a normal Caucasian population.

BACKGROUND: Bone mineral density (BMD) can predict fracture, however, the common use of historical risk factors to predict low BMD is unproven. AIMS: To identify significant historical risk factors for osteopenia. To establish predicting equations for BMD and test their ability to identify those who should be referred for BMD scanning. METHODS: Three hundred and twenty female and 131 male volunteers underwent questionnaire assessment of risk factors and BMD by dual photon absorptiometer at hip and spine. Significant risk factors (P < 0.05) were used to construct a linear regression model to predict BMD. This was cross validated on a second sample of 107 females and 131 males selected from the electoral roll analysing the ability to detect those subjects with BMD in the lower third of the age matched normal range. RESULTS: In women lower BMD at the spine was associated with increased age, decreased weight, smoking, and delayed menarche. Lower femoral BMD was associated with increased age, decreased weight, family history, inactivity, and smoking. In men lower BMD at the lumbar spine was associated with lower weight, and inactivity. Lower BMD at the femur was associated with increased age, decreased weight, family history, and low calcium intake. When cross validated on the second sample, the models produced sensitivity of 86-89% and sensitivity of 25-46%. Referring those with these risk factors could save 10-23% on scanning. Measuring BMD at the site in question remains the only accurate way of assessing an individual's risk of osteopenia.

Adult↗
PubMed1993

Role of beta-hemolytic group C streptococci in pharyngitis: incidence and biochemical characteristics of Streptococcus equisimilis and Streptococcus anginosus in patients and healthy controls.

The biochemical characteristics and the isolation rates of the two Lancefield group C streptococcal species (S. equisimilis and S. anginosus) from patients with pharyngitis and asymptomatic controls were compared. Some 239 strains of beta-hemolytic group C streptococci were isolated from 1,480 patients (209 strains) with pharyngitis and 227 controls (30 strains). A total of 44 strains displayed broad hemolysis, were Voges-Proskauer test negative, and produced glucuronidase. Some 72.7% of these strains also fermented ribose. A second group of 159 strains was Voges-Proskauer test positive and glucuronidase negative; 98.8% also displayed minute hemolysis and only 3.7% fermented ribose. These two groups represent typical large-colony S. equisimilis and small-colony S. anginosus, respectively. A small number of strains (36 in total) exhibited intermediate characteristics; morphologically, all 36 strains resembled S. anginosus, but 6 strains biochemically resembled S. equisimilis. No strains of S. equisimilis fermented sorbitol (unlike S. zooepidemicus) and all fermented trehalose (unlike S. equi). The structural carbohydrate profiles of S. equisimilis and S. anginosus both included galactosamine (consistent with their being group C organisms), but the profiles were not distinguishable. In total, 78.5% of strains from controls and 83.3% of strains from patients were determined to be the species S. anginosus. S. equisimilis was isolated from 3.0% of patients and 2.2% of controls, and S. anginosus was isolated from 11.1% of patients and 11.0% of controls. Thus, S. equisimilis and S. anginosus are both members of the normal flora of asymptomatic individuals. The incidence and biochemical characteristics of these two species are similar in patients who are healthy and those who have disease. However, a companion article provides clinical evidence associating S. equisimilis (but not s. anginosus) with pharyngitis.

Adult↗
PubMed1993

Incidental information processing: effects of mood, sex and caffeine.

This experiment assessed the effects of various parameters on incidental information processing. Participants from a nonclinical population were asked to fill out mood and personality questionnaires before completing a simple explicit and implicit memory task. It was predicted that participants with more depressive symptoms would show lower implicit memory scores. A number of sex differences were revealed: data from male participants supported the prediction; however, female participants showed a negative correlation between increasing depressive mood symptoms and implicit memory; sex differences were also present along other cognitive dimensions. Socioeconomic effects and hemispheric biases were factors considered as possible explanations for these sex differences; hemispheric bias could have resulted in differential female/male strategies being used; these may have been responsible for the consistently higher female scores found throughout the experiment. It is also suggested that implicit memory might have a separate store; this may be influenced by the default/habitual preference for a particular processing strategy (unique to the individual participant and/or the presence of depressive symptoms).

Adult↗
PubMed1993

Myonecrosis of the middle cerebral artery with thrombosis and cerebral infarction following resection of meningioma.

The authors report the clinical, radiological and pathological findings in a case of myonecrosis of the right middle cerebral artery following resection of a right temporal lobe meningioma. Postoperatively, the 64 yr old female patient developed a left hemiplegia and died with a massive pulmonary embolus on the eighth day. At postmortem examination the right middle cerebral artery showed recent necrosis of the wall in the area of previous surgery, with thrombosis of the artery and a large right parietal lobe cerebral infarct. Although myonecrosis of arteries has been described in a variety of settings, we know of no previous reported case following a routine neurosurgical procedure. We propose a dual pathogenesis of vasospasm plus damage to the external layers of the arterial wall at surgery and discuss the possible mechanisms based on a review of the literature.

Brain Neoplasms↗
PubMed1993

Passing the MCQ.

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Educational Measurement↗
PubMed1993

A comparison of the 8-hydroxydeoxyguanosine and micronucleus techniques for the assessment of X-ray and UV induced genotoxicity.

A comparison was made of the relative sensitivities of the cytokinesis-block micronucleus and the 8-hydroxydeoxyguanosine assays for the assessment of X-ray and UV-induced genotoxicity in mouse splenocytes in vitro. A detectable (p < 0.05) increase in micronuclei occurred at about 1/5 the X-ray exposure required to induce a significant increase in the level of 8-hydroxydeoxyguanosine. With UV radiation a significant (p < 0.05) rise in micronuclei was achieved at about 1/10th the dose needed to produce a detectable increase in 8-hydroxydeoxyguanosine levels. The data confirm the value of the cytokinesis-block micronucleus technique for the detection of genotoxicity at low-level X-irradiation, and indicate that it is more sensitive for that purpose than the 8-hydroxydeoxyguanosine assay. The data also demonstrate, for the first time, the production of 8-hydroxydeoxyguanosine by UVA/B-irradiation of intact cells, but point again to a more sensitive assessment of UV-related genotoxicity by the cytokinesis-block micronucleus method.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1993

Effect of bowel cleansing and colonoscopy on serum CEA levels.

A group of patients being investigated for various forms of colonic pathology showed an apparent rise in serum carcinoembryonic antigen (CEA) level following bowel cleansing at the time of colonoscopy, as compared with the 'resting' level. The rise was particularly marked in a small group of patients with colonic polyps or previous colonic resection for carcinoma, suggesting a need for careful timing in the taking of blood samples. The findings may also have diagnostic importance in identification of patients at higher risk of malignant disease of the colon.

Adult↗
PubMed1992

Hard and fast.

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Surgery Department, Hospital↗