Search PubMed⌕ Search

Biomedical subjects

D J Brown

Publications and source records attributed to D J Brown.

At least 91 records · Page 5Linked to original sources
PubMed1996

Theileria annulata: altered gene expression and clonal selection during continuous in vitro culture.

Kept in continuous in vitro culture, the protozoan parasite Theileria annulata gradually loses virulence when inoculated into cattle. These attenuated cell lines form the basis of the in vitro live vaccines which have been used successfully to control tropical theileriosis in several endemic regions. In the study reported here, events occurring during in vitro culture of an Indian (Hisar) cell line, which may be associated with the reduction in virulence, have been investigated. Hybridization with two polymorphic DNA probes following Southern blotting showed that selection of particular parasite genotypes occurs very rapidly with culture; a novel hybridization pattern is observed with both probes after 50-100 passages in vitro. In addition to this selection process, immunofluorescence studies using a monoclonal antibody which specifically recognizes virulent T. annulata revealed alterations in antibody reactivity following in vitro culture. This loss of reactivity was observed in three cloned cell lines derived from the early, virulent Hisar line and implies that phenotypic changes resulting from alterations to parasite gene expression are taking place during the attenuation process. When considered with the results from in vivo infections with serial passages of this cell line, it can be proposed that both altered gene expression and selection may be involved in the loss of pathogenicity of T. annulata during continuous in vitro culture.

Animals↗
PubMed1996

Functional expression of a cattle MHC class II DR-like antigen on mouse L cells.

Cattle DRA and DRB genes, cloned by reverse-transcription polymerase chain reaction, were transfected into mouse L cells. The cattle DR-expressing L-cell transfectant generated was analyzed serologically, biochemically, and functionally. Sequence analysis of the transfected DRB gene clearly showed showed that it was DRB3 allele DRB3(*)0101 , which corresponds to the 1D-IEF-determined allele DRBF3. 1D-IEF analysis of the transfectant confirmed that the expressed DR product was DRBF3. Functional integrity of the transfected gene products was demonstrated by the ability of the transfectant cell line to present two antigens (the foot-and-mouth disease virus-derived peptide FMDV15, and ovalbumin) to antigen-specific CD4(+) T cells from both the original animal used to obtain the genes, and also from an unrelated DRBF3(+) heterozygous animal. Such transfectants will be invaluable tools, allowing us to dissect the precise contributions each locus product makes to the overall immune response in heterozygous animals, information essential for rational vaccine design.

Animals↗
PubMed1996

Evaluation of [11C]RTI-121 as a selective radioligand for PET studies of the dopamine transporter.

The cocaine analogue RTI-121 (3 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid isopropyl ester), when labeled with carbon-11, was evaluated in rats as a potential PET ligand for the dopamine transporter. The compound gave in vivo striatum:cerebellum ratios that were similar to those obtained with the related ligand [11C]RTI-55 (2 beta-(4-iodophenyl)tropane-2 beta-carboxylic acid methyl ester) but showed a much greater selectivity for the dopamine compared with the 5-HT uptake site. The results indicate that [11C]RTI-121 could be used in preference to [11C]RTI-55 in man. Experimentally, [11C]RTI-121 has potential in the quantification of dopamine terminal function in rat models of disease, using a combination of autoradiography, postmortem sampling, and in vivo tomography.

Animals↗
PubMed1996

Virulence and genotype stability of Salmonella enterica serovar Berta during a natural outbreak.

Strains of Salmonella enterica serotype Berta, collected over a period of 6 years from a well documented natural outbreak in Denmark, have been characterized in order to assess the stability of chromosomal typing systems and virulence properties. Outbreak strains were identical in Pvu II and PSTI IS200 profiles, all but two strains showed the same Sma I ribotype, and all but one strain showed the same Not I pulsed field gel electrophoretic pattern, indicating that these molecular markers remained almost constant during the outbreak. In general, strains of S. Berta were found to be of moderate to low virulence; log VC10 values were found to vary between 3.0 and 4.4 after i.p. challenge of mice, and maximum CFU in internal organs of day-old chicks varied between 2 and 4 log10 units following oral challenge. The minor differences observed between strains in vivo did not correlate with differences in in vitro invasion into cultured MDCK cells, nor with in vitro growth characteristics. A succession of different plasmid profile types was observed during the outbreak but a hierarchical selection of clones based on differences in virulence was unlikely to have caused the succession of types of S. Berta during this outbreak.

Animals↗
PubMed1996

Assessment of the effect of increased dietary fibre intake on bowel function in patients with spinal cord injury.

It is common for constipation to occur following severe spinal cord injury (SCI). Although a bowel management program including a high fibre diet is an integral part of rehabilitation, the effect of a high fibre diet on large bowel function in SCI has not been examined. The aims of this study were to assess the nutrient intake of SCI patients, to determine baseline transit time, stool weight and evacuation time and to assess the effect of addition of bran on large bowel function. Eleven subjects, aged 32 +/- 10.5 years participated in the study. The level of injury ranged from C4 to T12; only one patient had an incomplete injury. Baseline mean energy intake was 7823 +/- 1443 kJ/d, protein intake 93 +/- 21 g/d, carbohydrate intake 209 +/- 39 g/d and mean dietary fibre intake 25 +/- 8 g/d. Mean baseline stool weight was 128 +/- 55 g/d and bowel evacuation time was 13 +/- 7.4 min/d. Three subjects who consumed < 18 g dietary fibre/d had low stool weights of 60-70 g/d and two had very delayed transit times that were too slow to enable quantitation. Mean mouth to anus transit time was 51.3 +/- 31.2 h, mean colonic transit time 28.2 +/- 3.5 h, right colonic transit time 5.9 +/- 4.5 h, left colonic transit time 14.5 +/- 5.2 h and rectosigmoid colonic transit time 7.9 +/- 5.6 h. Following the addition of bran, dietary fibre intake significantly increased from 25 g/d to 31 g/d (P < 0.001). However, the mean colonic transit time increased from 28.2 h to 42.2 h (P < 0.05) and rectosigmoid colon transit time increased from 7.9 to 23.3 h (P < 0.02). Stool weight, mouth to anus, left and right colon transit time and evacuation time did not change significantly. Results of this study suggest that increasing dietary fibre in SCI patients does not have the same effect on bowel function as has been previously demonstrated in individuals with 'normally functioning' bowels. Indeed the effect may be the opposite to that desired. This preliminary study highlights the need for further research to examine the optimal level of dietary fibre intake in SCI patients.

Adult↗
PubMed1996

The potentials of virtual environments in the education and training of people with learning disabilities.

The expansion of 'care in the community' has highlighted the need for more effective educational and training media for people with learning disabilities, and this paper suggests that virtual environments (VEs) may help to meet this need. Firstly, key terms (virtual environment, cyberspace and artificial reality) are defined. Secondly, aspects of developmental and cognitive psychological theories and principles of computer-assisted learning are presented that suggest that VEs might be an especially valuable educational media for people with learning disabilities. Thirdly, the existing literature in this field is reviewed. Fourthly, ethical issues associated with the use of VE, both generally and specifically by people with learning disabilities are discussed. Fifth, possible future developments of VEs, both in education and through their convergence with technologies of miniaturization, are suggested. It is concluded that VEs are an effective, affordable, accessible and safe training and educational media for people with learning disabilities, although further research will be required to realise their full potentials.

Computer Systems↗
PubMed1996

Input impedance and reflection coefficient in fractal-like models of asymmetrically branching compliant tubes.

A mathematical model is described, based on linear transmission line theory, for the computation of hydraulic input impedance spectra in complex, dichotomously branching networks similar to mammalian arterial systems. Conceptually, the networks are constructed from a discretized set of self-similar compliant tubes whose dimensions are described by an integer power law. The model allows specification of the branching geometry, i.e., the daughter-parent branch area ratio and the daughter-daughter area asymmetry ratio, as functions of vessel size. Characteristic impedances of individual vessels are described by linear theory for a fully constrained thick-walled elastic tube. Besides termination impedances and fluid density and viscosity, other model parameters included relative vessel length and phase velocity, each as a function of vessel size (elastic nonuniformity). The primary goal of the study was to examine systematically the effect of fractal branching asymmetry, both degree and location within the network, on the complex input impedance spectrum and reflection coefficient. With progressive branching asymmetry, fractal model spectra exhibit some of the features inherent in natural arterial systems such as the loss of prominent, regularly-occurring maxima and minima; the effect is most apparent at higher frequencies. Marked reduction of the reflection coefficient occurs, due to disparities in wave path length, when branching is asymmetric. Because of path length differences, branching asymmetry near the system input has a far greater effect on minimizing spectrum oscillations and reflections than downstream asymmetry. Fractal-like constructs suggest a means by which arterial trees of realistic complexity might be described, both structurally and functionally.

Arteries↗
PubMed1996

Serial passage of tobacco rattle virus under different selection conditions results in deletion of structural and nonstructural genes in RNA 2.

The RNA genome of tobacco rattle virus (TRV) is bipartite. RNA 2 of the nematode-transmissible TRV isolate PPK20 encodes the viral coat protein (cp) and proteins with molecular weights of 29,400 and 32,800 (29.4K and 32.8K proteins). When this isolate was serially passaged in tobacco by using phenol-extracted RNA as the inoculum in each transfer, defective interfering (DI) RNAs rapidly accumulated. A number of these DI RNAs were cloned. Six DI RNAs had single internal deletions in RNA 2 that removed most of the cp gene, the 29.4K gene, and the 5' half of the 32.8K gene. The borders of the deletions in these DI RNAs were found to be flanked in the genomic RNA 2 by short nucleotide repeats or sequences resembling the 5' end of TRV genomic and subgenomic RNAs. Two DI RNAs were found to be recombinants containing a 5' sequence derived from RNA 2 and a 3' sequence derived from RNA 1. When serial passage of TRV isolate PPK20 was carried out by using leaf homogenates as inocula in each transfer, accumulation of a DI RNA (designated D7) with a functional cp gene was observed. The deletion in D7 covered the 3' end of the cp gene, the 29.4K gene, and the 5' half of the 32.8K gene. An infectious cDNA clone of D7 RNA was made. In mixed infections, D7 RNA rapidly outcompeted RNA 2 but did not compete with RNA 1. The deletion in D7 RNA abolished the nematode transmissibility of the PPK20 isolate. These results may explain the observation that many laboratory isolates of tobraviruses have lost their nematode transmissibility and contain RNA 2 molecules of widely different lengths.

Culture Media↗
PubMed1996

Cleavage of structural components of mammalian vitreous by endogenous matrix metalloproteinase-2.

Our goal was to determine if the major endogenous vitreous matrix metalloproteinase (MMP-2) could digest known collagenous components of the vitreous body. Matrix metalloproteinase-2 and its associated inhibitors were isolated from porcine vitreous by affinity column chromatography. The inhibitors were inactivated by chemical modification with dithiothreitol and iodoacetamide. The latent MMP-2 was then activated with the organomercurial, p-aminophenyl mercuric acetate (APMA). Bovine vitreous fibrillar collagens (types II, V/XI and IX) were isolated by pepsin extraction and differential salt precipitation. Intact type IX collagen was purified by selective salt precipitation followed by ion exchange and size exclusion chromatography. These isolated collagens were incubated for 6 to 24 h with different concentrations of activated MMP-2, and the extent of collagen degradation was analyzed. Activated MMP-2 was also introduced into freshly isolated vitreous gels and the degree of liquefaction was determined. Our results showed that the activated MMP-2 has no apparent effect upon type II collagen but can degrade type V/XI collagen and type IX collagen fragments (COL2 and COL2 + COL3). In addition, when the type IX collagen was in the intact helical form, MMP-2 appeared to selectively digest alpha 3 (IX) chains. This suggested that vitreous MMP-2 preferentially cleaved certain vitreous collagen chains into large fragments rather than small peptides. MMP-2 also disrupted the vitreous gel in vitro, releasing proteins but not hexuronic acid or sulfated glycosaminoglycans into the liquefied supernatant. We conclude that MMP-2 activity should be considered as a potential mechanism of vitreous liquefaction that is seen in aging and various pathological states.

Aging↗
PubMed1996

Vocational achievements following spinal cord injury in Australia.

This study describes the vocational achievements in a sample (n = 139) of Australian persons with spinal cord injuries. The post-accident and employment achievements (February-March 1993) were represented by significant diversity in outcomes. Around one-third of subjects went on to obtain further qualifications since their injury, and around 31% were employed full-time or part-time. The majority of subjects utilized informal means of returning to work. Around two-thirds of those employed indicated that they were in a preferred occupation and their median length of employment was 108 months. The hours of work varied greatly but were centred around a median of 38 hours (i.e. a full-time job). A model of diverse employment outcomes and achievement following spinal cord injury is proposed.

Adolescent↗
PubMed1996

Cleavage of human corneal type VI collagen alpha 3 chain by matrix metalloproteinase-2.

The human cornea contains significant amounts of type VI collagen and matrix metalloproteinase-2 (MMP-2), but there has been no established relation between these two components. The objective of this study was to determine whether corneal type VI collagen was susceptible to digestion by MMP-2. Human corneas were frozen and then pulverized in liquid nitrogen. The type VI collagen was isolated by sequential extractions with sodium chloride buffer, guanidinium chloride solution, and guanidinium chloride/dithiothreitol solution. Visualization of type VI collagen alpha 3(VI) chain was made by using Western blots with specific monoclonal antibodies. The extracts were incubated up to 24 h with isolated, activated MMP-2. Within 4 h of incubation, two lower molecular weight bands (approximately 190 and 170 kDa) appeared. These bands increased in intensity with time but were not further digested into smaller fragments. This cleavage activity was inhibited by ethylenediaminetetraacetic acid (EDTA). Because type VI collagen represents approximately 25% of the corneal dry weight, its degradation properties may be important for the integrity of the stroma in scarring episodes and corneal diseases, such as keratoconus.

Animals↗
PubMed1995

24-hour service.

Explore the source record for details and available documents.

Animals↗
PubMed1995

Identification of two binding proteins for halogenated aromatic hydrocarbons in the hard-shell clam, Mercenaria mercenaria.

Earlier studies have reported an unusually high incidence of gonadal tumors in marine bivalves in areas of potentially high exposure to herbicides including 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophe-noxyacetic acid. Some herbicides can be contaminated by halogenated aromatic compounds including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Most of the effects of planar halogenated aromatic compounds, including carcinogenic effects in vertebrates, appear to be mediated through binding to the aryl hydrocarbon receptor. The current study investigated whether halogenated aromatic hydrocarbon-binding proteins are present in the marine bivalve, Mercenaria mercenaria. We used the TCDD photoaffinity analog 2-azido-3-[125I]-iodo-7, 8-dibromodibenzo-p-dioxin to detect the presence of two proteins (28 and 39 kDa) in cytosols prepared from M. mercenaria that specifically bound this ligand. Expression of these proteins is tissue-dependent with the highest concentrations being observed in gill and gonadal tissue. Gonadal tissue also exhibited gender-specific expression with female clams exhibiting higher levels of the 39-kDa protein. Gender-and tissue-specific expression are consistent with the hypothesis that these proteins might be involved in the carcinogenic response observed in clams exposed to herbicides.

Affinity Labels↗
PubMed1995

A qualitative ecological model to support mariculture pond water quality management.

A qualitative model of the ecology of a mariculture pond is described. The model represents ecological relationships in the form of a network of tableaux of inference rules which are scanned by a deductive reasoning mechanism to compute the values of pond water quality indicators, make forecasts and determine appropriate corrective and/or preventative maintenance actions.

Ecosystem↗
PubMed1995

Sequence of RNA 2 of a nematode-transmissible isolate of tobacco rattle virus.

Tobacco rattle virus (TRV) isolate PPK20 is transmitted by Paratrichodorus pachydermus nematodes. The factor(s) determining vector transmissibility has been shown to be located on TRV RNA 2. Sequence determination revealed that PPK20 RNA 2 contains three open reading frames encoding the coat protein (cp) and proteins with molecular masses of 29.4 and 32.8 kDa. The 29.4 and 32.8 kDa protein-coding genes showed no significant sequence similarity to any other known tobravirus gene. A full-length cDNA of PPK20 RNA 2 cloned between the 35S promoter and nos terminator infected plants when co-inoculated with PPK20 RNA 1. Deletions in the reading frames of the 29.4 and 32.8 kDa proteins revealed that these sequences are dispensable for replication of PPK20 RNA 2 in plants. Subgenomic RNAs for translation of cp and the putative 29.4 and 32.8 kDa proteins were detected in infected leaves. The possible role of PPK20 RNA 2 non-structural genes in TRV vector transmission is discussed.

Amino Acid Sequence↗
PubMed1995

Sequence comparison of RNA2 of nematode-transmissible and nematode-non-transmissible isolates of pea early-browning virus suggests that the gene encoding the 29 kDa protein may be involved in nematode transmission.

A cDNA clone containing the complete coding region of RNA2 of the newly described TPA56 isolate of pea early-browning virus (English serotype, PEBV-E) has been obtained. A plasmid (pFLA56) containing this clone together with the 5' and 3' non-coding regions of PEBV isolate SP5 (the type isolate of PEBV-E) and flanked by the CaMV 35S promoter and NOS terminator is infectious when co-inoculated onto plants with pCaN1, an infectious clone of PEBV SP5 RNA1. Virus containing RNA2 derived from the cDNA clone of the TPA56 isolate is transmitted by Trichodorus primitivus nematodes, whereas virus containing RNA2 from a clone of the SP5 isolate is not transmitted. Sequencing revealed 11 differences out of 3374 nucleotides between the transmissible TPA56 and non-transmissible SP5 clones. However, only three of the base changes affected the amino acid sequences of virus gene products. A single, conservative amino acid change was present in the virus coat protein. Two non-conservative changes occurred in the protein of molecular mass 29.6 kDa expressed from an open reading frame located down-stream of the coat protein gene, suggesting that it has a function in nematode transmission and that changes in this protein prevent vector transmission of the SP5 isolate of PEBV.

Animals↗
PubMed1995

The effect of levcromakalim (BRL 38227) on bladder function in patients with high spinal cord lesions.

The effects of the potassium channel opener levcromakalim (BRL 38227) 7.5 micrograms kg-1 were examined on urodynamic variables and blood pressure during inflow and voiding cystometry in six high spinal cord lesion patients. Levcromakalim administration significantly increased the duration of bladder contraction (197 +/- 128 s to 267 +/- 167 s, P < 0.05) and also reduced blood pressure (126 +/- 13/67 +/- 9 mm Hg to 104 +/- 25/52 +/- 12 mm Hg) but was without effect on other urodynamic parameters. Because of concerns about hypotensive responses, further studies involving higher doses of levcromakalim should be considered only if the drug was administered intravesically.

Adult↗