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Biomedical subjects

A Tait

Publications and source records attributed to A Tait.

At least 55 records · Page 3Linked to original sources
PubMed1998

Vision and driving: selective effect of optical blur on different driving tasks.

A test of static (high-contrast) visual acuity is the most prevalent vision test used to screen driver license applicants worldwide, even though research has largely failed to provide convincing empirical evidence for its role in traffic accidents. The purpose of this research was to evaluate the effect of visual acuity degradation on different components of the driving task. Participants were 24 young licensed drivers (15 men, 9 women) with normal vision. Driving performance was measured while participants wore modified swimmer's goggles to which blurring lenses were affixed in amounts necessary to produce binocular visual acuity levels of 20/20, 20/40 (the prevalent acuity standard for driving), 20/100, and 20/200. Driving performance was measured using the closed-road method of Wood and Troutbeck (1994). Acuity degradation produced significant decrements in road sign recognition and road hazard avoidance as well as significant increments in total driving time. Participants' abilities to estimate whether clearances between pairs of traffic cones were sufficiently wide to permit safe passage of the vehicle and to slalom through a series of traffic cones were relatively unaffected by acuity degradation. Thus the latter tasks appear to be mediated by aspects of central and peripheral vision that are relatively unaffected by optical blur. Potential applications of this type of research include the development of procedures for defining empirically justifiable vision standards for driver licensure.

Adult↗
PubMed1997

Trypanosoma brucei: lack of cross-resistance to melarsoprol in vitro by cymelarsan-resistant parasites.

We have examined cross-resistance between trypanocidal drugs using a well-characterised drug-sensitive line, 247, and its cymelarsan-resistant derivative, 247melCyR. The cymelarsan-resistant line was cross-resistant to trimelarsen and melarsen oxide, and partially cross-resistant to two diamidines, pentamidine and berenil (diminazene aceturate). It was cross-resistant to lipid-soluble melarsoprol in vivo but to only a trivial degree in two in vitro assays. The potential role of adenosine transport in arsenical-induced killing of parasites was investigated. Adenosine, adenine, and the diamidines, but not inosine, were able to inhibit killing of drug-sensitive STIB 247 trypanosomes by cymelarsan and melarsen oxide in a concentration-dependent manner. These results are consistent with the view that these arsenical compounds enter trypanosomes via an adenosine-specific transporter. Melarsoprol-induced killing of trypanosomes was unaffected, however, by either purine and to only a slight degree by the diamidines. These data suggest that melarsoprol can enter trypanosomes by a route other than through an adenosine transporter and that there may be two mechanisms contributing to arsenical resistance in this drug-resistant line of trypanosomes.

Adenine↗
PubMed1997

Ostertagia circumcincta: isolation of a partial cDNA encoding an unusual member of the mitochondrial processing peptidase subfamily of M16 metallopeptidases.

A reverse-transcriptase polymerase chain reaction (PCR) procedure was used to isolate an Ostertagia circumcincta partial cDNA encoding a protein with general primary sequence features characteristic of members of the mitochondrial processing peptidase (MPP) subfamily of M16 metallopeptidases. The structural relationships of the predicted protein (Oc MPPX) with MPP subfamily proteins from other species (including the model free-living nematode Caenorhabditis elegans) were examined, and Northern analysis confirmed the expression of the Oc mppx gene in adult nematodes.

Amino Acid Sequence↗
PubMed1997

A computer-interfaced vertometer system for contact lenses.

BACKGROUND: The conventional vertometer (lensometer) is difficult to use for accurate measurement of contact lenses whose back vertex power (BVP) varies across the optic zone. BVPs of multifocal rigid and soft contact lenses have previously been measured using a conventional vertometer incorporating the Scheiner principle, which makes use of two light paths equidistant from the center of the lens. METHODS: We have developed a computer-based vertometer system based on the Scheiner principle which can be used to produce a profile of BVPs across rigid and soft contact lenses. A computer interface to the vertometer allows rapid acquisition of readings and software-based ray tracing derives in-air dioptric power readings across the optic zone at specific ray heights. RESULTS: Results are presented for soft and rigid, and spherical and aspheric surface contact lenses. CONCLUSIONS: The system improves the measurement resolution of a standard vertometer and shows an acceptable level of precision and accuracy for most applications.

Contact Lenses↗
PubMed1996

Conservation of neutralizing determinants between the sporozoite surface antigens of Theileria annulata and Theileria parva.

The sporozoite surface antigens SPAG-1 of Theileria annulata and p67 of Theileria parva are postulated to contain determinants necessary for host cell invasion and/or recognition and are both being considered as candidates for inclusion in subunit vaccines. Preliminary data suggest that these are related molecules. In this paper we describe the investigation of the relationship between these sporozoite antigens further by analysis of the immunological cross-reactivity using Mabs and sera raised against each antigen. The cross-reactions were examined by carrying out Western blots, IFA tests, and in vitro sporozoite neutralization assays. In addition, sequence comparison data which clearly establish that these surface antigens are encoded by related genes are presented. The regions of SPAG-1 identified as containing cross-reactive epitopes recognized by p67 antiserum correlated to regions of high predicted homology between p67 and SPAG-1, which are located at their respective N- and C-termini. Furthermore, p67 and SPAG-1 were found to contain cross-reactive determinants responsible for neutralization of sporozoite infectivity in vitro, and at least some of these were located in the C-termini of both molecules. The relevance of these findings to the possible roles for these molecules in host cell invasion is discussed.

Amino Acid Sequence↗
PubMed1996

Characterisation of cloned lines of Trypanosoma brucei expressing stable resistance to MelCy and suramin.

Two cloned drug-sensitive stocks of Trypanosoma brucei (STIB 247 and STIB 386) were each used to generate cloned lines expressing resistance to the melaminophenyl arsenical drug cymelarsan (247MelCyR and 386MelCyR) and to suramin (247SurR and 386SurR). The drug-resistance phenotypes were stable after passaging in mice in the absence of drug pressure and three of the lines were transmitted through tsetse flies with no alteration of drug-resistance. There was no evidence of cross-resistance between melCy and suramin in vivo. Twenty-four hour growth inhibition assays were conducted on bloodstream and procyclic forms in axenic in vitro cultures. Suramin-resistance was expressed in bloodstream forms but not in the procyclic stage, while the melCy-resistant lines expressed melCy-resistance in both stages. No cross-resistance between melCy and suramin was observed. Cross-resistance between melCy and another arsenical drug, melB (melarsoprol), was observed in vivo, but to only a very limited extent in vitro. We propose that this difference between the in vivo and in vitro results for melB may indicate that an alteration in a surface adenosine transporter responsible for reduced melCy uptake was bypassed by melB over 24 hours in vitro.

Animals↗
PubMed1996

The origins, dynamics and generation of Trypanosoma brucei rhodesiense epidemics in East Africa.

The history of sleeping sickness in East Africa has provoked controversy not only about the origins and spread of the disease, but also the identity of the causative organisms involved. Molecular methodology(1) has shed new light on the genetic makeup of the organisms involved in recent epidemics. Here, Geoff Hide, Andrew Tait, Ian Maudlin and Susan Welburn discuss these new data in relation to previous theories about the origins of epidemics in East Africa which emphasized the importance of the introduction of new strains.

Journal Article↗
PubMed1996

The isolation and characterization of genomic and cDNA clones coding for a cdc2-related kinase (ThCRK2) from the bovine protozoan parasite Theileria.

The tick-transmitted protozoan parasites Theileria annulata and Theileria parva are important intracellular pathogens of domestic cattle in tropical and subtropical regions. Proliferative phases take place within both lymphocytes and erythrocytes. The lymphocyte is stimulated to enter the cell cycle by the parasite and the multinucleate parasite can establish a state in which karyokinesis and cytokinesis occur in phase with the host cell. The link between parasite nuclear division and cytokinesis is altered during the formation of merozoites (a non-dividing, invasive, extracellular stage). These features imply a high degree of control over parasite nuclear division and cytokinesis. Two different approaches have been used to identify clones from both species which are extremely highly conserved homologues. These encode a cdc2-related kinase which is > 60% identical to eukaryotic cyclin-dependent kinases of the p34cdc2/p32CDK2 subfamily. There is typical conservation of kinase domains, implying an in vivo protein kinase activity for the polypeptide. The PSTAIRE region, implicated in cyclin binding, is well conserved suggesting that ThCRK2 will bind cyclin molecules closely related to the eukaryotic A/B-type cyclins. However, there is divergence in certain key motifs potentially associated with binding of molecules that regulate the activity of the kinase. Expression patterns of RNA and protein indicate that ThCRK2 is likely to function in all dividing stages of the parasite and, taken together, the results point to a central role in the regulation of nuclear division.

Amino Acid Sequence↗
PubMed1995

Differential transcription and expression of ornithine decarboxylase in embryos of replicated mouse lines divergently selected for lean body mass.

Embryos of replicated mouse lines divergently selected for high or low lean body mass have been shown to differ approximately twofold in the activity of ornithine decarboxylase during embryogenesis and that this difference has been shown to be associated with a restriction enzyme polymorphism in the structural gene [Gray and Tait (1993) Genet. Res. 62, 31-37]. In the present paper we report that the differences in enzyme activity are due to changes in transcription and show that the enzyme produced has the same specific activity in all selected lines, precluding any significant structural change in the enzyme being associated with the differences in the structural gene.

Animals↗
PubMed1995

Trypanosoma brucei: inheritance of kinetoplast DNA maxicircles in a genetic cross and their segregation during vegetative growth.

The inheritance of maxicircle DNA was determined using a polymorphic EcoRI restriction site in the maxicircle variable region. In 11 hybrid progeny from a genetic cross of two stocks of Trypanosoma brucei, 7 progeny apparently inherited maxicircles uniparentally from either parent, in agreement with the results from previous studies, but in 4 progeny inheritance was biparental. Three subclones from 2 of these 4 progeny were made, and in these the maxicircles of only one parental type were detected. These data are considered in terms of a simple model whereby half the maxicircle genomes are inherited from each parent into progeny at meiosis with subsequent stochastic segregation at each mitotic division. This model generates a quantitative prediction as to the period of time required for fixation of inheritance to a uniparental pattern which provides a reasonable fit to the experimental data. These results provide an explanation as to why previous studies have shown that maxicircles are (apparently) inherited uniparentally: the kinetoplast is a unitary organelle inherited faithfully at cell division, but the maxicircles that it contains are best considered as a population that divides stochastically. Consideration of the model also explains why maxicircle populations are homogeneous.

Animals↗
PubMed1995

Dictyocaulus viviparus: surface antigens of the L3 cuticle and sheath.

The bovine lungworm Dictyocaulus viviparus induces a highly protective immune response in the bovine host. It is consequently a particularly useful host-parasite system for the study of those antigens and immune responses which can induce protective immunity against a parasitic nematode. We have generated monoclonal antibodies to the L3 cuticle and sheath surfaces in order to define antigens present at the host-parasite interface of infective larvae. Three monoclonal antibodies generated against the surface of the infective L3 cuticle bind to a PC-like hapten, and the presence of such an epitope exposed on the cuticular surface appears to be unique to the D. viviparus L3. Six monoclonal antibodies which bind to the surface of the L3 sheath all detect an antigen which is immunodominant in immunised cattle. The possible basis and implications of such marked antigenicity of a molecule on the L3 sheath surface are discussed.

Animals↗
PubMed1995

Immune response of lambs to vaccination with Ostertagia circumcincta surface antigens eliciting bile antibody responses.

Immune responses to surface antigens of infective larvae of Ostertagia circumcincta recognized by bile antibodies of sheep immune to challenge were studied in 5-month-old Finn-Dorset male lambs. The sheep were vaccinated subcutaneously with 2 doses of 25 micrograms/kg body weight of surface proteins immunoprecipitated by bile antibodies derived from protected lambs. These antigens were purified from immune complexes by affinity chromatography and then injected with beryllium hydroxide as an adjuvant. The immunized lambs were challenged with 5 x 10(4) L3 and the worm burdens evaluated on day 21 post challenge. These were significantly (P < 0.01) lower in the vaccinated group than in the challenged controls (72% protection). The mucosal and bile IgM, recognizing the L3 surface, showed significantly higher levels in the vaccinated lambs compared to the challenge controls. Mucosal and bile IgA antibody levels against the same antigens were low and no significant differences were observed between vaccinated and control lambs.

Animals↗
PubMed1995

Increased expression and activity of ornithine decarboxylase in chicks genetically selected for rapid growth rate.

Polyamines are essential requirements for cell proliferation and their role in stimulation of RNA, DNA, and protein synthesis is clearly established. Ornithine decarboxylase is a key enzyme in the biosynthesis of the polyamines and its activity is regulated in response to factors that stimulate cell proliferation. Steady-state ODC mRNA levels and enzyme activity were measured in muscle of chicks genetically selected for increased growth rate or for egg production. In muscle, muscle satellite cells and myotubes, two ODC mRNA transcripts are present of molecular size 2.05 and 1.75 kb. Northern blotting analysis suggest that these transcripts are produced as a result of using different polyadenylation sites. Between day 1 and day 6 after hatching, a period of rapid muscle growth in these animals, a peak in muscle ODC mRNA levels is followed by a peak in enzyme activity in both lines. Significantly higher ODC mRNA levels and enzyme activity are associated with selection for rapid growth in the broiler line. The results are consistent with other data showing that ODC is a major factor in cell growth and provide further evidence that it is a candidate 'trait-gene' for growth.

Animals↗
PubMed1995

An immunodominant antigen on the Dictyocaulus viviparus L3 sheath surface coat and a related molecule in other strongylid nematodes.

Monoclonal antibody 2A6 binds to the surface of the Dictyocaulus viviparus L3 sheath and identifies a molecule which is highly antigenic in both infected and vaccinated cattle. Immunogold electron microscopy reveals that the antibody binds to a highly stable surface coat overlying the epicuticle of the L3 sheath. The binding to the cuticular surface is stage specific, being restricted to the surface of the L3 sheath, although the antigen can be detected on Western blots of parasite homogenates from the L1 stage. Immunofluorescence on live parasites demonstrates that the antibodies also bind to the L3 sheath surface of many other strongylid nematodes. The antigen detected by 2A6 differs in molecular weight between the species; in D. viviparus the antigen is poorly resolved between 29 and 40 kDa by SDS-PAGE whereas in nematodes from the family Trichostrongyloidea a single band or doublet of approximately 20 kDa is detected, suggesting that a related molecule is present in these species. Although infection and vaccination with D. viviparus elicits a strong immune response to the L3 sheath antigen this does not appear to be the case following infection with other strongylid nematodes.

Animals↗
PubMed1995

Women consultants, their background and training: some myths explored.

This paper aims to show what choices (both personal and professional) the many women who achieve National Health Service (NHS) consultant status make, and how some of the factors that affect this also influence merit awards. Over 2200 women and 200 men holding consultant contracts within the NHS were asked (through an anonymous postal questionnaire) about the personal choices they had made and other factors that had influenced their career. Findings from the 1654 respondents show that women reach consultant grade at about the same time as their male contemporaries, but are more likely to be in anaesthetics, radiology, pathology or psychiatry. Many women choose these specialities because they fit best with family commitments. The remaining women are more likely to work in the female-orientated specialities of paediatrics and obstetrics and gynaecology than other medical or surgical specialities. They are less likely to receive a merit award.

Career Choice↗