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Biomedical subjects

B Dixon

Publications and source records attributed to B Dixon.

At least 73 records · Page 4Linked to original sources
PubMed1997

Continuous, pulsed or single acute irradiation of a transplanted rodent tumour model.

BACKGROUND: Recent advances in remote afterloading pulsed mode brachytherapy have provided a much needed tool for the radiation oncologist. It has the versatility of optimised physical dose distribution along with improved staff radiation protection and patient nursing. PURPOSE: This preliminary study was designed to explore the radiobiological equivalence between conventional continuous low dose rate tumour irradiation (CLDR) and the new technique of pulsed dose irradiation (PDR). MATERIALS AND METHODS: Subcutaneous isogenic sarcomas transplanted in female John's Strain Wistar rats were irradiated locally with acute, pulsed or continuous interstitial low dose-rate exposures at 9-11 mm mean diameter. RESULTS: As expected, single acute doses (5-40 Gy) were more effective (P < 0.01) in achieving tumour growth delay (1.4 days/Gy) than CLDR exposure (4-51 Gy) over 24-48 h (0.93 days/Gy). However, PDR treatment (8 hourly fractions/day) at high dose-rate (8-48Gy) over 8-72 h was significantly (P = 0.01) more effective (1.66 days/Gy) than CLDR but not acute exposures. CONCLUSIONS: These data suggest that, clinically a significantly improved therapeutic ratio may also be achievable with pulsed high dose rate brachytherapy, and that further radiobiological studies with in-vivo tumour models are needed.

Animals↗
PubMed1997

Cardiopulmonary and anesthetic effects of propofol in wild turkeys.

OBJECTIVE: To determine safety, anesthetic variables, and cardiopulmonary effects of i.v. infusion of propofol for induction and maintenance of anesthesia in wild turkeys. ANIMALS: 10 healthy, adult wild turkeys. PROCEDURE: Anesthesia was induced by i.v. administration of propofol (5 mg/kg of body weight) over 20 seconds and was maintained for 30 minutes by constant i.v. infusion of propofol at a rate of 0.5 mg/kg/min. Heart and respiratory rates, arterial blood pressures, and arterial blood gas tensions were obtained prior to propofol administration (baseline values) and again at 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 minutes after induction of anesthesia. All birds were intubated immediately after induction of anesthesia, and end-tidal CO2 concentration was determined at the same time intervals. Supplemental oxygen was not provided. RESULTS: Apnea was observed for 10 to 30 seconds after propofol administration, which induced a decrease in heart rate; however, the changes were not significant. Compared with baseline values, respiratory rate was significantly decreased at 4 minutes after administration of propofol and thereafter. Systolic, mean, and diastolic pressures decreased over the infusion period, but the changes were not significant. Mean arterial blood pressure decreased by 30% after 15 minutes of anesthesia; end-tidal CO2 concentration increased from baseline values after 30 minutes; PO2 was significantly decreased at 5 minutes after induction and thereafter; PCO2 was significantly (P < 0.05) increased after 15 minutes of anesthesia; and arterial oxygen saturation was significantly (P < 0.05) decreased at the end of anesthesia. Two male turkeys developed severe transient hypoxemia, 1 at 5 and the other at 15 minutes after induction. Time to standing after discontinuation of propofol infusion was 11 +/- 6 minutes. Recovery was smooth and unremarkable. CONCLUSION: Propofol is an effective agent for i.v. induction and maintenance of anesthesia in wild turkeys, and is useful for short procedures or where the use of inhalational agents is contraindicated.

Anesthesia, Intravenous↗
PubMed1996

Identification and characterization of a new major histocompatibility complex class I gene in carp (Cyprinus carpio L.).

In this study we report the finding of three representatives of a new group of major histocompatibility complex class I sequences in carp: Cyca-12 (Cyca-UA1*01), a full-length cDNA; Cyca-SP1 (Cyca-UAW1), a polymerase chain reaction (PCR) fragment from cDNA; and Cyca-G11 (Cyca-UA1*02), a partial genomic clone. Comparison of the amino acid sequences of Cyca-12, Cyca-SP1, and Cyca-G11 with classical and non-classical class I sequences from other species shows considerable conservation in regions that have been shown to be involved in maintaining the structure and function of class I molecules. The genomic organization of Cyca-12 has been elucidated by analysis of a partial genomic clone (Cyca-G11, in combination with PCR amplifications on genomic DNA of a homozygous individual. Although the genomic organization is similar to that found in class I genes from other species, the 3' untranslated region contains an intron which is unprecedented in class I genes, and intron 2 is exceptionally large (+/-14 kilobases). Southern blot analysis indicates the presence of multiple related sequences. In phylogenetic analyses, the Cyca-UA sequences cluster with class I genes from zebrafish and Atlantic salmon, indicating that the ancestral gene arose before the salmonid/cyprinid split, approximately 120-150 million years ago. The previously reported class I Cyca-Z genes from carp and Caau-Z genes from goldfish cluster as a completely separate lineage. A polyclonal antiserum (anti-Cyca12) was raised against a recombinant fusion protein containing most of the extracellular domains of Cyca-12. The antibodies showed substantial reactivity to the recombinant protein and an Mr 45000 protein in membrane lysates of spleen and muscle, as well as to determinants present on leucocytes in fluorescence-activated cell sorter analyses. Erythrocytes and thrombocytes were found to be negative.

Amino Acid Sequence↗
PubMed1996

Evolution of MHC class II beta chain-encoding genes in the Lake Tana barbel species flock (Barbus intermedius complex).

Major histocompatibility complex (MHC) class II protein polymorphism is maintained in allelic lineages which evolve in a trans-specific manner, passing from one species to descendant species. Selection pressure on peptide binding residues should be greatest during speciation, when organisms move into new environments and their MHC molecules encounter new pathogens. The isolation of MHC genes from teleost fishes, the most diverse group of vertebrates, has created possibilities for testing this hypothesis. The large barbels of Lake Tana have undergone an adaptive radiation within the last 5 million years, producing 14 morphotypes which inhabit different ecological niches within the lake. We studied the variability in class II beta chain-encoding genes of four of these morphotypes using polymerase chain reaction amplification and DNA sequencing. The sequences obtained were orthologous to four of the known class II genes from the common carp, from which barbels diverged approximately 32 million years ago. When subjected to phylogenetic analysis, the 48 sequences clustered into groups which represent allelic lineages. A comparison of nonsynonymous and synonymous substitutions between the peptide binding region codons and non-peptide binding region codons of these sequences revealed that they are under strong selective pressure.

Amino Acid Sequence↗
PubMed1995

Horror bacteria.

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Anti-Bacterial Agents↗
PubMed1995

Response of a rodent fibrosarcoma to photodynamic therapy using 5-aminolaevulinic acid or polyhaematoporphyrin.

The effects of 5-aminolaevulinic acid (ALA)-based photodynamic therapy (PDT) on the growth of an intradermal rat fibrosarcoma have been determined following topical, intravenous, or intratumour application of ALA. The pattern of tumour growth was identical following each type of therapy and we conclude that the efficacy of ALA-PDT is independent of the route of drug administration, at least in this tumour system. We have also compared the efficacy of interstitial ALA-based PDT with similar therapy using a conventional photosensitizer, polyhaematoporphyrin (PHP). ALA-PDT was less effective than PHP-based therapy at inhibiting the growth of a subcutaneous rat fibrosarcoma at light doses over 300 J. It is suggested that protoporphyrin IX photo-bleaching may limit the effectiveness of treatment, whilst the more bleach-resistant PHP may continue to be effective at higher light doses.

Aminolevulinic Acid↗