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Biomedical subjects

G Brown

Publications and source records attributed to G Brown.

At least 127 records · Page 7Linked to original sources
PubMed1999

An automated radiosynthesis of 2-[11C]thymidine using anhydrous [11C]urea derived from [11C]phosgene.

2-[11C]Thymidine has been produced from [11C]methane via [11C]phosgene and [11C]urea. Anhydrous [11C]urea was prepared from [11C]phosgene by reaction with liquid ammonia. This novel approach avoids the problems associated with the synthesis of anhydrous [11C]urea from [11C]cyanide. A fully automated system based on a modular approach and under PLC control has been developed. The system provides 2-[11C]thymidine reliably and reproducibly for clinical PET studies. The radiosynthesis takes 45-50 min from [11C]methane and the average yield was 1.5-3.3 GBq (40-90 mCi). The specific radioactivity was typically in the range 29.6-51.8 GBq mumol-1 (0.8-1.4 Ci mumol-1) at EOS corresponding to 6-12 micrograms of stable thymidine. The radiochemical yield of 2-[11C]thymidine was ca. 14% from [11C]methane.

Carbon Radioisotopes↗
PubMed1999

Think before you speak: pauses, memory search, and trace redintegration processes in verbal memory span.

Immediate memory span and speed of memory search were assessed for words and nonwords of short and long spoken duration. Memory span was substantially greater for words than for nonwords and for short than for long items, though speed of memory search was unaffected by either length or lexicality. An analysis of the temporal pattern of responses in the memory span task indicated that inter-item pauses were longer between nonwords than words but that these pause durations were unaffected by item length. A model of verbal short-term memory span is described in which trace selection from a short-term store and the redintegration (restoration) of degraded phonological traces both occur in the pauses between saying successive items. Both trace selection and trace redintegration appear to play important roles in accounting for individual differences in memory span.

Adolescent↗
PubMed1999

Evolution of speckle during spinodal decomposition.

Time-dependent properties of the speckled intensity patterns created by scattering coherent radiation from materials undergoing spinodal decomposition are investigated by numerical integration of the Cahn-Hilliard-Cook equation. For binary systems which obey a local conservation law, the characteristic domain size is known to grow in time tau as R=[Btau](n) with n=1/3, where B is a constant. The intensities of individual speckles are found to be nonstationary, persistent time series. The two-time intensity covariance at wave vector k can be collapsed onto a scaling function Cov(deltat,t), where deltat=k(1/n)B(tau(2)-tau(1)) and t=k(1/n)B(tau(1)+tau(2))/2. Both analytically and numerically, the covariance is found to depend on deltat only through deltat/t in the small-t limit and deltat/t (1-n) in the large-t limit, consistent with a simple theory of moving interfaces that applies to any universality class described by a scalar order parameter. The speckle-intensity covariance is numerically demonstrated to be equal to the square of the two-time structure factor of the scattering material, for which an analytic scaling function is obtained for large t. In addition, the two-time, two-point order-parameter correlation function is found to scale as C(r/(B(n)sqaureroot[tau1(2n)+tau2(2n)]),tau1/tau2), even for quite large distances r. The asymptotic power-law exponent for the autocorrelation function is found to be lambda approximately 4.47, violating an upper bound conjectured by Fisher and Huse.

Journal Article↗
PubMed1999

Biochemical analysis of plant protection afforded by a nonpathogenic endophytic mutant of colletotrichum magna

A nonpathogenic mutant of Colletotrichum magna (path-1) was previously shown to protect watermelon (Citrullus lanatus) and cucumber (Cucumis sativus) seedlings from anthracnose disease elicited by wild-type C. magna. Disease protection was observed in stems of path-1-colonized cucurbits but not in cotyledons, indicating that path-1 conferred tissue-specific and/or localized protection. Plant biochemical indicators of a localized and systemic (peroxidase, phenylalanine ammonia-lyase, lignin, and salicylic acid) "plant-defense" response were investigated in anthracnose-resistant and -susceptible cultivars of cucurbit seedlings exposed to four treatments: (1) water (control), (2) path-1 conidia, (3) wild-type conidia, and (4) challenge conditions (inoculation into path-1 conidia for 48 h and then exposure to wild-type conidia). Collectively, these analyses indicated that disease protection in path-1-colonized plants was correlated with the ability of these plants to mount a defense response more rapidly and to equal or greater levels than plants exposed to wild-type C. magna alone. Watermelon plants colonized with path-1 were also protected against disease caused by Colletotrichum orbiculare and Fusarium oxysporum. A model based on the kinetics of plant-defense activation is presented to explain the mechanism of path-1-conferred disease protection.

Journal Article↗
PubMed1999

The validity and reliability of an OSCE in dentistry.

The validity and reliability of a newly-developed objective structured clinical examination for 4th year dental students (OSCE(D)) were estimated by a range of quantitative and qualitative methods. The OSCE(D) consisted of 17 stations in conservation, periodontology and prosthetics. A blueprint was used to match the OSCE stations to clinical subject areas and to 7 skill clusters of clinical competence. Repeat measures of skills were undertaken in the OSCE(D) to maximise its validity and reliability. The primary purposes of the OSCE(D) were to assess clinical competence and to provide feedback to students. The results indicate that the OSCE(D) was intrinsically valid and a better predictor of performance in the final examination than either a concurrent 4th-year examination or Advanced-level university entry grades. The OSCE(D) scored relatively highly on internal consistency (Cronbach's alpha = 0.68). Intra-domain and inter-domain correlations were high and inter-examiner reliability was relatively high (eta 2 coefficients ranged from 0.00 to 0.10). There were no significant differences between performances in the morning and afternoon sessions of the examination so reproducibility is assumed to be high. Some improvement in individual stations and in inter-examiner reliability are required. A set of recommendations based on the experience of designing and testing a dental OSCE are provided.

Education, Dental↗
PubMed1999

Mature bone metaplasia in abdominal wall scar.

A 58-year-old man who had had three laparotomies for gastric surgery, developed a painful mass in the abdominal wall scar. Radiology confirmed bone formation in the scar. The bone was excised and the wound repaired. Histology confirmed metaplastic mature bone formation. This case draws the attention to the clinical condition of bone formation in midline scars. Clinically, it should be differentiated from scar recurrence following surgery for abdominal malignancy.

Cicatrix↗
PubMed1999

Rectal carcinoma: thin-section MR imaging for staging in 28 patients.

PURPOSE: To evaluate the accuracy of thin-section magnetic resonance (MR) imaging (in-plane resolution, 0.6 x 0.6 mm) in the preoperative assessment of the depth of extramural tumor infiltration, which is a major prognostic indicator in rectal cancer. MATERIALS AND METHODS: In a prospective study of 28 consecutive patients, preoperative MR imaging was performed. The tumor stage according to the TNM classification system and the measured depth of extramural tumor invasion in matched MR images and histopathologic slices were compared. RESULTS: Preoperative MR imaging correctly indicated the histopathologic tumor stage in all 25 patients in whom comparisons were possible. The difference between the depth of extramural tumor measured on preoperative MR images and corresponding measurements on histopathologic slices of the resection specimen ranged from -5.0 mm to +5.5 mm (mean difference, +0.13 mm; 95% CI: -2.72, +2.98 mm), indicating good agreement. The mesorectal fascia, and the relation of the tumor to it, could be visualized in every case. In all five patients with involvement of the circumferential excision margins of resection specimens, extensive extramural invasion was identified on preoperative MR images. CONCLUSION: Preoperative thin-section MR imaging accurately indicates the tumor stage of rectal cancer and depth of extramural tumor infiltration. It provides valuable information for identifying T3 tumors for preoperative adjuvant therapy in patients who are at high risk of failure of complete excision.

Female↗
PubMed1999

Tumor, normal tissue, and plasma pharmacokinetic studies of fluorouracil biomodulation with N-phosphonacetyl-L-aspartate, folinic acid, and interferon alfa.

PURPOSE: To evaluate the effect of N-phosphonacetyl-L-aspartate (PALA), folinic acid (FA), and interferon alfa (IFN-alpha) biomodulation on plasma fluorouracil (5FU) pharmacokinetics and tumor and liver radioactivity uptake and retention after [18F]-fluorouracil (5-[18F]-FU) administration. PATIENTS AND METHODS: Twenty-one paired pharmacokinetic studies were completed on patients with colorectal, gastric, and hepatocellular cancer, utilizing positron emission tomography (PET), which allowed the acquisition of tumor, normal tissue, and plasma pharmacokinetic data and tumor blood flow (TBF) measurements. The first PET study was completed when the patient was biomodulator-naive and was repeated on day 8 after the patient had been treated with either PALA, FA, or IFN-alpha in recognized schedules. RESULTS: TBF was an important determinant of tumor radioactivity uptake (r = .90; P < .001) and retention (r = .96; P < .001), for which radioactivity represents a composite signal of 5-[18F]-FU and [18F]-labeled metabolites and catabolites. After treatment with PALA, TBF decreased (four of four patients; P = .043), as did tumor radioactivity exposure (five of five patients; P = .0437), with no change in plasma 5FU clearance. With FA treatment, there were no differences observed in whole-body metabolism, plasma 5FU clearance, or tumor and liver pharmacokinetics. IFN-alpha had measurable effects on TBF and 5-[18F]-FU metabolism but had no apparent affect on liver blood flow. CONCLUSION: The administration of PALA and IFN-alpha produced measurable changes in plasma, tumor, and liver pharmacokinetics after 5-[18F]-FU administration. No changes were observed after FA administration. In vivo effects may negate the anticipated therapeutic advantage of 5FU biomodulation with some agents.

Adult↗
PubMed1999

Bacillus anthracis: medical issues of biologic warfare.

Recent world events refocused attention on the possibility of nations engaging in biologic warfare, including an attack with Bacillus anthracis. The single available anthrax vaccine in the United States for human use, formerly known as MDPH-PA, has decreased ability to protect laboratory animals against virulent B. anthracis strains, especially compared with new vaccines being developed. Studies with these vaccines, however, have several shortcomings. The pathogenesis, diagnosis, treatment, and prophylaxis of anthrax are discussed, as well as the implications that an attack with B. anthracis would place on the health care system.

Anthrax↗
PubMed1999

A personal philosophy and model of nursing.

Understanding the relationships and conflicts between nursing professionals, their health care clients, wellness, and the environment is a major component of any nursing philosophy. This understanding is a fundamental element in The Brown Human Cell Model, a personal philosophy of nursing. The objectives of this model are to assist in obtaining a clearer understanding of the conflicts the nursing professional will encounter with the health care clients, their wellness, and environment. Nursing, client, wellness, and environment are defined according to the personal attitudes, behavior, beliefs, and values of the author. Many factors and essential components were borrowed from other nursing theories in forming this philosophy and model. The model is a replica of a human cell, significant in defining how nursing, client, wellness, and environment relate to a continuum of health.

Communication↗
PubMed1999

Clofibric acid: a potential therapeutic agent in AML and MDS.

Differentiation therapy using retinoic acids (RAs) or 1alpha25-dihydroxyvitamin D3 (D3) is an attractive alternative to chemotherapy in acute myeloid leukaemia (AML) and myelodysplastic syndromes (MDS). However, with the exception of RA therapy for acute promyelocytic leukaemia (APL), RAs and D3 are not potent enough at doses that can be tolerated by patients. We demonstrate that clofibric acid (CA) enhances the response of HL60 cells to all-trans RA and D3. Our findings and those of others in the field lead us to suggest that combination therapy using all-trans RA and CA should be considered as potential therapy for AML and MDS.

Aged↗
PubMed1999

The critical region of overlap defining the AZFa male infertility interval of proximal Yq contains three transcribed sequences.

The position of deletion breakpoints in a series of four AZFa male infertility patients has been refined using new markers derived from BAC clone DNA sequence covering the AZFa male infertility interval. The proximal half of the AZFa interval is occupied by pseudogene sequences with homology to Xp22. The distal half contains an anonymous expressed sequence tag (named AZFaT1) found transcribed in brain, testis, and skeletal muscle and the DFFRY and DBY genes. All the patients have AZFaT1 and DFFRY deleted in their entirety and three patients additionally have DBY deleted. The three patients with AZFaT1, DFFRY, and DBY deleted show a severe Sertoli cell only syndrome type I phenotype, whereas the patient that has retained DBY shows a milder oligozoospermic phenotype. The expression of DBY in a cell line from this latter patient is unaltered; this shows that it is the loss of genes lying within the deletion that is responsible for the observed oligozoospermia. RT-PCR analysis of mouse testis RNA from normal and XXSxr(a) mice (devoid of germ cells) has shown that Dby is expressed primarily in somatic cells and that the level of expression is unaltered during germ cell differentiation. This contrasts with Dffry where no transcripts are detectable in XXSxr(a) mouse testis and expression occurs specifically in testis mRNA in a germ cell dependent fashion.

Adult↗
PubMed1999

Disruption of operant oral self-administration of ethanol, sucrose, and saccharin by the AMPA/kainate antagonist, NBQX, but not the AMPA antagonist, GYKI 52466.

BACKGROUND: AMPAergic transmission has been suggested to be important in mediating the rewarding effects of drugs. We therefore examined the role of non-NMDA glutamate-receptors in mediating the reinforcing properties of ethanol in an oral self-administration paradigm. METHODS: The competitive antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline) and the non-competitive antagonist, GYKI 52466 (1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5H2,3- be nzodiazepine), were administered to animals previously trained to self-administer ethanol, sucrose, or saccharin, on a progressive ratio schedule. RESULTS: GYKI 52466 (5 & 10 mg/kg) had no effect on operant responding for ethanol, but increased spontaneous locomotor activity, whereas the highest doses of NBQX (3 & 6 mg/kg) significantly decreased operant responding and correspondingly decreased the breaking point in responding for ethanol on a progressive ratio schedule. NBQX (but not GYKI 52466) also significantly decreased operant responding for a food reinforcer (sucrose) as well as for a sweet tasting reinforcer (saccharin). Doses of NBQX that disrupted operant performance caused a significant reduction in locomotor activity, indicating that NBQX decreased ethanol self-administration only at doses which disrupt motor activity. CONCLUSIONS: These results suggest non-NMDA glutamate-receptors may not have a specific role in the maintenance of responding for an ethanol reinforcer, but may generally disrupt operant performance. Because, unlike GYKI 52466, NBQX possesses an action at central kainate receptors, these results suggest that kainate, but not AMPA (alpha-amino 3-hydroxy-5-methyl-4-isoxazole propionate) receptors may be important in mediating the reinforcing effects of ethanol.

Animals↗
PubMed1998

Identification of a retinoic acid responsive aldoketoreductase expressed in HL60 leukaemic cells.

Neutrophil and monocyte differentiation can be induced in HL60 leukaemia cells by all-trans-retinoic acid (ATRA) and 1alpha,25-dihydroxyvitamin D3 (D3), respectively, whose differentiating effects can be enhanced by exposure to 'anti-inflammatory agents' and steroids. We have provided evidence that this potentiation is via inhibition of the activity of an enzyme of the aldoketoreductase (AKR) family, but had failed to identify expression of known AKRs in HL60 cells. In this study, we have identified a previously unclassified aldoketoreductase family member (termed HAKR e) that is expressed in HL60 cells. HAKR e is dramatically and transiently up-regulated in HL60 cells within 24 h of exposure to ATRA, further supporting the proposition that a member(s) of this family of enzymes play(s) a role in controlling cell growth and/or differentiation.

Blotting, Northern↗
PubMed1998

Project-based learning.

Architecture and nursing and midwifery students worked with employers from local trusts on a project exploring design issues for a new maternity unit. Marlene Sinclair and George Brown report on how it was organised, and the benefits for students and employers.

Architecture↗