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Biomedical subjects

R Logan

Publications and source records attributed to R Logan.

At least 19 recordsLinked to original sources
PubMed2002

Expression and function of A1 adenosine receptors in the rat hippocampus following transient forebrain ischemia.

We investigated how transient cerebral ischemia affects the gene expression, immunoreactive protein levels, and the function of the A1 subtype of adenosine receptor in the rat hippocampus at different times following reperfusion. A1 receptor mRNA levels were altered significantly in different hippocampal subfields as early as 6 h following insult. However, these changes in mRNA levels were not paralleled at the protein level, as western blotting with A1 receptor-specific antibodies revealed that hippocampal A1 adenosine receptor prevalence did not differ from sham control at either 6 or 24 h following insult. The lack of change in A1 receptor prevalence was consistent with functional examinations, as only marginal changes were observed in the ability of A1 receptors to attenuate excitatory post-synaptic potentials in the CA1 subfield at 24 h following reperfusion. These data illustrate that although the mRNA expression levels of the A1 adenosine receptor are altered by transient cerebral ischemia, the immunoreactive prevalence and function of this receptor are maintained in the post-ischemic hippocampus at times preceding the death of the vulnerable neurons.

Animals↗
PubMed2001

The increasing problem of hepatitis C virus infection.

The widespread incidence of hepatitis C (HCV) infection throughout the community is of concern. Although many of those infected will not suffer significantly from their infection, up to one-third will have liver disease, fatigue and oral health problems. General dental practitioners need to be aware of the precautions necessary in treating people with severe liver disease. This paper discusses the issues associated with treating patients who have HCV infection including the importance of preventive programs to reduce dental pathology and maximise oral health.

Antiviral Agents↗
PubMed2001

Analysis of fluoride levels retained intraorally or ingested following routine clinical applications of topical fluoride products.

A variety of topical fluorides is now used clinically for the prevention and control of dental caries. It is essential for the dental profession to be fully aware of the relative retention rates of fluoride in saliva and thus its contact with the teeth. These may vary following the use of the different categories and concentrations of agents available and with different methods of use. It is also important to be aware of the amounts of fluoride ion ingested following use of the more concentrated forms and of the resultant elevation in total blood fluoride levels. These parameters were investigated in a series of experiments involving human volunteer subjects using a variety of topical fluoride materials commercially available in Australia. Fluoride mouthrinses appeared to provide the highest salivary retention rates per dose of all forms of topical fluoride. Ingestion rates from concentrated gels were acceptable when effective evacuation methods were applied. The use of custom-made trays resulted in a reduction in amounts of fluoride ion ingested, though simple self-application by toothbrush of smaller quantities proved to be an effective alternative in terms of amount of fluoride ion retained in saliva per amount applied and ingested. None of the concentrated gels used resulted in elevations in total blood fluoride levels which were of concern in adults. It is acknowledged that salivary retention rates of fluoride ion do not necessarily reflect the caries inhibitory effects of topical fluorides. However, these data provide some indication of possible advantages of some products and methods of application over others.

Adult↗
PubMed2001

Studies on dental erosion: an in vitro model of root surface erosion.

Most research on dental erosion has focused on erosion in enamel. However, the increasing retention of teeth into old age has increased the potential for root surface erosion. The nature and kinetics of root surface erosion have not yet been adequately explored. The objective of this project was to develop an in vitro model of root surface erosion in order to investigate the polarised light microscopy of controlled erosion and the histology and rate of demineralisation of this process in root cementum/dentine. The results demonstrate a process quite different in outcome from that in enamel erosion. Erosion results in loss of volume of enamel. However, it leaves a root surface softened though with little volume loss so long as the demineralised collagen remains hydrated. The polarised light histology was similar to that seen in root surface caries. The rate of erosive demineralisation of tooth roots by selected acids was investigated, with differing rates of demineralisation similar to that seen in enamel erosion observed. The process of erosion showed evidence of significant diffusion control.

Acetic Acid↗
PubMed2000

Altered interaction between PSD-95 and the NMDA receptor following transient global ischemia.

The postsynaptic density (PSD) is a cytoskeletal specialization involved in the anchoring of neurotransmitter receptors and in regulating the response of postsynaptic neurons to synaptic stimulation. The postsynaptic protein PSD-95 binds to NMDA receptor subunits NR2A and NR2B and to signaling molecules such as neuronal nitric oxide synthase and p135synGAP. We investigated the effects of transient cerebral ischemia on protein interactions involving PSD-95 and the NMDA receptor in the rat hippocampus. Ischemia followed by reperfusion resulted in a decrease in the solubility of the NMDA receptor and PSD-95 in 1% sodium deoxycholate, the decrease being greater in the vulnerable CA1 hippocampal subfield than in the less sensitive CA3/dentate gyrus regions. Solubilization of the kainic acid receptor GluR6/7 and the PSD-95 binding proteins, neuronal nitric oxide synthase and p135synGAP, also decreased following ischemia. The association between PSD-95 and NR2A and NR2B, as indicated by coimmunoprecipitation, was less in postischemic samples than in sham-operated controls. Ischemia also resulted in a decrease in the size of protein complexes containing PSD-95, but had only a small effect on the size distribution of complexes containing the NMDA receptor. The results indicate that molecular interactions involving PSD-95 and the NMDA receptor are modified by an ischemic challenge.

Animals↗
PubMed2000

Altered association of protein tyrosine kinases with postsynaptic densities after transient cerebral ischemia in the rat brain.

Transient cerebral ischemia results in an increase in the tyrosine phosphorylation of proteins associated with postsynaptic densities (PSDs). The authors investigated the possible mechanisms behind this increase by analyzing isolated PSDs for protein tyrosine kinase activity and for the presence of specific tyrosine kinases. Transient (15 minutes) global ischemia was produced in adult rats by four-vessel occlusion, and PSDs were isolated immediately after ischemia or after 20 minutes or 6 hours of reperfusion. Tyrosine phosphorylation of several PSD proteins, including the N-methyl-D-aspartate (NMDA) receptor subunits NR2A and NR2B, was enhanced relative to shams after 20 minutes of reperfusion and underwent a further increase between 20 minutes and 6 hours. The ability of intrinsic PSD tyrosine kinase to phosphorylate PSD proteins, including the NMDA receptor, increased threefold after ischemia. Whereas PSD-associated proline-rich tyrosine kinase 2 (PYK2) and gp145TrkB were elevated immediately after the ischemic event, increases in Src and Fyn were not apparent until 6 hours of reperfusion. The level of PSD-associated pp125FAK decreased after ischemia. The results demonstrate that ischemia results in selective changes in the association of protein tyrosine kinases with the PSD which may account for ischemia-induced increases in the tyrosine phosphorylation of PSD proteins.

Animals↗
PubMed2000

Comparison of tests for assessment of Helicobacter pylori eradication: results of a multi-centre study using centralized facility testing.

BACKGROUND: The accuracy of diagnostic tests to assess Helicobacter pylori eradication has rarely been performed. AIM: To compare the tests most commonly used for this purpose, i.e. histology, culture and (13)C urea breath test performed in centralized facilities. METHODS: Prospective study where patients were included in four centres and diagnostic tests performed centrally by biologists experienced in the field. Gastric biopsies were obtained from antrum and corpus (two for histology, two for culture from each site) 4-6 weeks after an eradication treatment. The definition of a gold standard for H. pylori-positive patients was either a positive culture or both positive histology and urea breath test results. RESULTS: Ninety-seven patients for whom data on histology, culture and (13)C urea breath test were available were included. The majority were females (60%) suffering from non-ulcer dyspepsia (52%) and having received proton-pump inhibitor-based triple therapy (62%). Forty-one per cent of the patients were H. pylori-positive according to the gold standard. The sensitivities were 90%, 95% and 92.5% and the specificities 100%, 98.2% and 100% for culture, histology and (13)C urea breath test, respectively. CONCLUSION: All the methods had excellent specificity but the sensitivity ranged between 90 and 95%. The combination of two techniques which increases the sensitivity to virtually 100% is recommended in situations where the eradication treatment requires a precise evaluation such as in clinical trials.

Breath Tests↗
PubMed1998

Diagnosis of Helicobacter pylori in Britain.

The prevalence of Helicobacter pylori infection in the United Kingdom (UK) is similar to that of other developed Western countries with H. pylori infection a major cause of morbidity from peptic ulcer disease and gastric cancer. Guidelines for testing and treating H. pylori have been published and recommend eradicating H. pylori infection in all patients with peptic ulcer disease. With the increasing efficacy and tolerability of H. pylori treatment and the development of near patient tests there is considerable demand for H. pylori testing for screening as well as pre- and post-treatment. In the future this may change the current pattern of testing towards increased population-based non-invasive testing. Currently most investigation for H. pylori occurs within and is funded by the government health-care system. As no one test is suited to all clinical situations, numerous tests for detecting H. pylori are available; however, growing concern about an increasing endoscopy workload has led to the development of screening protocols for endoscopy based on H. pylori status. In the future, the role of H. pylori testing in the management of dyspepsia may also change based on the results of decision analysis models and community-based trials which are currently being performed in the UK.

Decision Support Techniques↗
PubMed1997

The effect of long-term omeprazole on the glucose-hydrogen breath test in elderly patients.

OBJECTIVE: to test whether omeprazole taken for longer than 1 month causes an increase in the rate of small bowel bacterial overgrowth in elderly subjects. SUBJECTS: 44 elderly people, 22 taking omeprazole, 22 not taking omeprazole or H2 receptor antagonists. MAIN OUTCOME MEASURES: rate of positive glucose-hydrogen breath tests; anthropometric measures and blood tests reflecting malabsorption. RESULTS: there was no difference in the rate of positive tests between those taking omeprazole (45%) and those not taking it (59%). The omeprazole group had significantly lower serum albumin concentrations. There was no difference in body mass index, mid-arm circumference, arm fold thickness, adjusted calcium concentration or haemoglobin levels. CONCLUSIONS: omeprazole does not cause increased bacterial shall bowel overgrowth in elderly subjects.

Aged↗