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Biomedical subjects

A Johnston

Publications and source records attributed to A Johnston.

At least 19 recordsLinked to original sources
PubMed1992

A computational model of the analysis of some first-order and second-order motion patterns by simple and complex cells.

Although spatio-temporal gradient schemes are widely used in the computation of image motion, algorithms are ill conditioned for particular classes of input. This paper addresses this problem. Motion is computed as the space-time direction in which the difference in image illuminance from the local mean is conserved. This method can reliably detect motion in first-order and some second-order motion stimuli. Components of the model can be identified with directionally asymmetric and directionally selective simple cells. A stage in which we compute spatial and temporal derivatives of the difference between image illuminance and the local mean illuminance using a truncated Taylor series gives rise to a phase-invariant output reminiscent of the response of complex cells.

Algorithms↗
PubMed1992

The relative roles of C4A and C4B in prevention of immune precipitation, solubilisation and immune adherence.

C4A and C4B levels were measured in serum from 246 normal individuals. Complement-mediated solubilisation, assayed using alkaline phosphatase anti-alkaline phosphatase immune complexes (IC), correlated with both C4A and C4B levels. However, C4A and C4B levels showed no correlation with solubilisation of bovine serum albumin (BSA) ICs, or with the prevention of immune precipitation of BSA or alkaline phosphatase ICs, nor with immune adherence assayed using thyroglobulin and BSA ICs.

Antigen-Antibody Complex↗
PubMed1992

Dissociation of primary antigen-antibody bonds is essential for complement mediated solubilization of immune precipitates.

The role of dissociation of primary antigen-antibody bonds in the solubilization of immune complexes (IC) has been investigated using photo-affinity crosslinked IC comprising NAP15-BSA and murine monoclonal anti-DNP antibodies. Non-covalently linked IC were solubilized rapidly when incubated with normal human serum (NHS), whereas covalently-linked IC were solubilized poorly or not at all. The rate and extent of complement activation produced by incubating covalently-linked and non-covalently linked IC with NHS was similar as assessed by the production of the C1s:C1-inhibitor, C3:properdin and C5b-9 complexes and the anaphylatoxins C4a and C3a. Thus, the inability of serum to solubilize photo-affinity crosslinked IC must be due to failure of dissociation of primary antigen-antibody bonds.

Animals↗
PubMed1992

Cyclosporin monitoring: its role in autoimmune indications.

This paper describes some of the methodological problems related to the measurement of cyclosporin. The clinical value of the measurements following organ transplantation are discussed and those areas also applying to autoimmune indications are highlighted. It is concluded that the routine use of cyclosporin monitoring in samples from patients receiving the drug for autoimmune indications is unlikely to be of significant value as a guide to efficacy or toxicity. However, some settings, such as suspected poor patient compliance, for the avoidance of potential drug interactions and for research on the absorption of new formulations are considered to be useful applications of the methodology.

Autoimmune Diseases↗
PubMed1992

Recognising faces: effects of lighting direction, inversion, and brightness reversal.

When information about three-dimensional shape obtained from shading and shadows is ambiguous, the visual system favours an interpretation of surface geometry which is consistent with illumination from above. If pictures of top-lit faces are rotated the resulting stimulus is both figurally inverted and illuminated from below. In this study the question of whether the effects of figural inversion and lighting orientation on face recognition are independent or interactive is addressed. Although there was a clear inversion effect for faces illuminated from the front and above, the inversion effect was found to be reduced or eliminated for faces illuminated from below. A strong inversion effect for photographic negatives was also found but in this case the effect was not dependent on the direction of illumination. These findings are interpreted as evidence to suggest that lighting faces from below disrupts the formation of surface-based representations of facial shape.

Adult↗
PubMed1992

A placebo-controlled trial of buspirone in anxious inpatient alcoholics.

The present study is a double-blind control trial of buspirone versus placebo in highly anxious alcoholics who recently completed inpatient detoxification for alcoholism. Subjects met DSM-III-R criteria for generalized anxiety syndrome and/or other nonpanic forms of anxiety disorders and alcohol dependence. Male veterans aged 21 to 65 were randomized to 45 to 60 mg/day of buspirone (n = 33) or placebo (n = 34). Anxiety scores, as measured by the Hamilton Anxiety Scale and other anxiety measures, declined significantly for both groups, but there were no differential group differences throughout the 6-month treatment period. Survival analysis measuring time to study drop out, time to first drink, time to 5 consecutive drinking days, and time to first intoxication indicated no significant differences between groups. The number of standard drinks per drinking day for nonabstainers also did not differ between groups. In the present study anxious alcoholics taking buspirone did not receive any benefit over placebo on a number of anxiety and alcohol use measures.

Adult↗
PubMed1991

Hepatic beta-adrenoceptor adaptation during propranolol administration is impaired in aging rats.

Aging has been associated with changes in beta-adrenoceptor responses and adaptation to prolonged removal of catecholamine stimulation. We have examined the effect of chronic propranolol administration on rat hepatic membrane beta-adrenoceptor density, agonist affinity and response in young (6-7 months) and old (26-7 months) male Wistar rats. Propranolol administration via miniosmotic pumps for 7 days resulted in similar and sustained plasma propranolol levels (approximately 100 ng/ml) in old and young rats. Pretreatment beta-adrenoceptor responses to isoprenaline were significantly higher in old rats. Propranolol administration was associated with significant increases in beta-adrenoceptor response and density (Bmax) in young rats only. Cyclic adenosine 3',5'-monophosphate (cyclic AMP) responses to prostaglandin E1 (PGE1), guanosine triphosphate (GTP), 5'-guanyl-imidodiphosphate (Gpp(NH)p), forskolin and Mn2+ were not significantly different between young and old rats and were not affected by propranolol administration. Neither aging or propranolol administration was associated with a change in beta-adrenoceptor agonist affinity. These findings demonstrate elevated hepatic beta-adrenoceptor response and impaired hepatic beta-adrenoceptor adaptation to beta-adrenoceptor blockade in aging rats.

Adaptation, Physiological↗
PubMed1991

Seroepidemiology of hepatitis B infection in children in Vanuatu. Implications for vaccination strategy.

Four hundred and eighty-two unvaccinated children from three different age groups (12-18 months, 30-42 months, 54-115 months) in a hepatitis B virus (HBV) endemic area were tested for markers of HBV infection. HBV seromarkers were detected in 52.3% of children and 26.9% were hepatitis B surface antigen (HBsAg) positive. Evidence of infection was related to age, with HBV seromarker rates highest (67.5%) in school children aged 56-115 months. The HBsAg positive rate was highest (30.1%) in children 30-42 months of age. However, even children in the youngest age group (12-18 months) had high seromarker (26.8%) and HBsAg positive (17.0%) rates. A high proportion of HBsAg positive children (83.8%) were also hepatitis Be antigen (HBeAg) positive. Mothers of children in the youngest age group (12-18 months) were also tested, and 24.5% were HBsAg positive. Factors associated with higher rates of infection in children included maternal HBeAg positivity (for children in the youngest age group), increasing age, and residence on the islands of Emao or Nguna. Higher rates of HBsAg positivity were associated with these factors and with being male. Crossinfection between children is probably the most important source of infection, based on the evidence of the high rate of HBeAg positivity in children and the rising infection rate with age. A possible vehicle of spread is through skin infections and skin sores which are highly prevalent in children in Vanuatu. Since this study indicates that both perinatal and early child-to-child transmission are occurring, the most practical strategy to prevent the majority of infections is to vaccinate all children, commencing at birth and completing the course early in the first year of life.

Child↗
PubMed1991

The effect of age on the pharmacokinetics of pentisomide.

The effects of age on the pharmacokinetics of pentisomide (CM7857), an orally effective antiarrhythmic agent, were studied in two groups of volunteers. Sixteen young volunteers (mean age 26.4 years) and 10 elderly volunteers (mean age 67.8 years) received a single 200 mg oral dose of pentisomide. Mean AUC was larger and terminal elimination half-life longer in the elderly subjects, due to a decrease in total plasma clearance of pentisomide in the elderly. This decrease was due to a reduction in renal clearance of the drug which was paralleled by a significantly lower creatinine clearance in the elderly subjects. Dosage reduction, or a reduced frequency of dosing of pentisomide would be necessary in the elderly or those with impaired renal function.

Administration, Oral↗
PubMed1991

Prenatal diagnosis for dystrophia myotonica using the polymerase chain reaction.

The polymerase chain reaction has been used to detect an abundant class of short repeat DNA families of the form (dC-dA)n.(dG-dT)n, known as microsatellites. These units are found throughout the human genome and have been characterized for several loci including APOC2 on chromosome 19q12-q13.2. The locus APOC2 is linked to the gene for dystrophia myotonica and a microsatellite within this locus was used to derive polymorphisms in a family to predict the inheritance of the disease. Chorionic villus sampling (CVS) was performed at 15 1/2 weeks' gestation. Following DNA extraction from the CVS material and parental blood samples, microsatellite analysis was carried out by the polymerase chain reaction.

Adult↗
PubMed1991

Monitoring cyclosporin: is it still important?

This paper reviews the current data which provide a rationale for the measurement of cyclosporin as a guide to therapy. Methodological problems related to sample matrix and analytical technique are considered, and the most commonly used methods considered. Factors which could influence the clinical interpretation of cyclosporin measurements are examined, including other drug therapy, compliance with therapy, cyclosporin metabolites, pharmacokinetic variables and sample timing. It is concluded that, whilst isolated measurements do not offer a definitive diagnostic tool, taken in context they can be of considerable value in optimising therapy.

Cyclosporine↗
PubMed1991

Concentration of metronidazole in cervical mucus and serum after single and repeated oral doses.

The disposition of metronidazole in cervical mucus and serum after single and repeated oral doses (400 mg) was investigated in six healthy female subjects. Metronidazole reached higher concentrations in serum than cervical mucus after both single and repeated oral doses. Metronidazole concentrations in both cervical mucus and serum were high enough to be trichomonicidal and bactericidal. After oral administration, metronidazole concentrations in cervical mucus are due to diffusion rather than ion trapping.

Administration, Oral↗
PubMed1991

Plasma metronidazole concentrations after single and repeated vaginal pessary administration.

Metronidazole concentrations in plasma were measured by h.p.l.c. in 12 healthy female volunteers after single and repeated vaginal administration of 500 mg metronidazole pessaries. The area under the plasma concentration-time curve (AUC(0,12 h) was 8.4 +/- 3.9 micrograms ml-1 h (mean +/- s.d.) on day 1 and 20.6 +/- 7.1 micrograms ml-1 h (mean +/- s.d.) on day 5. The peak plasma drug concentration on day 1 was 1.2 +/- 0.6 micrograms ml-1 (mean +/- s.d.) and on day 5 it was 2.0 +/- 0.7 micrograms ml-1 (mean +/- s.d.). The plasma concentration of metronidazole at steady state was above the minimum inhibitory concentration (MIC) for anaerobic Streptococci and Clostridium tetani. These results demonstrate much lower systemic exposure than after oral administration.

Adult↗