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Biomedical subjects

M Johnson

Publications and source records attributed to M Johnson.

At least 433 records · Page 24Linked to original sources
PubMed1994

Interaction of oddball probability and primary task type on P300 in the dual-task paradigm.

Using a dual-task paradigm with an oddball secondary task, P300 amplitude and latency were studied as a function of factorially manipulated oddball probability (low = .22, high = .44) and primary task type. In addition to a Baseline condition (oddball task only), three primary tasks were used: (1) Pure Sensory; watching a movie; (2) Pure Motor (manipulating a flashlight); and (3) Sensory/Motor (using the flashlight to trace the outlines of characters in a movie). The findings included the usual significant effects of probability on amplitude. There was also a significant effect of task type on amplitude, and a significant interaction of oddball probability with task type. In the low but not high probability condition, a pure Sensory task depressed P300 amplitude. In both probability conditions, the Sensory/motor task depressed P300 amplitude. Only task type had a significant effect on P300 latency. The results confirm the ability of other labs (using Sensory/motor primary tasks) to demonstrate P300 depression at high oddball probability, in view of the difficulty in our lab of achieving P300 depression with pure sensory tasks and high oddball probabilities. The results are discussed in terms of partial overlap of processing resource pools.

Adult↗
PubMed1994

Cytokine-induced modulation of tumor suppressor gene expression in ovarian cancer cells: up-regulation of p53 gene expression and induction of apoptosis by tumor necrosis factor-alpha.

OBJECTIVE: Our purpose was to determine the effect of tumor necrosis factor-alpha on anti-oncogene expression and to investigate the relationship between the up-regulation of the p53 tumor suppressor gene and tumor necrosis factor-alpha-mediated apoptosis in epithelial ovarian cancer cell lines. STUDY DESIGN: By means of Northern blot techniques p53 messenger ribonucleic acid expression was assayed in ovarian cancer cells. Tumor cells explanted from patients into Balb/c nude mice were exposed to supernatants from activated monocytes, activated T cells, or the recombinant cytokines interleukin-6 and tumor necrosis factor-alpha. Time- and dose-dependence of p53 up-regulation was measured. Induction of programmed cell death (apoptosis) by tumor necrosis factor-alpha was quantitated by means of a deoxyribonucleic acid fragmentation assay. RESULTS: Detectable levels of messenger ribonucleic acid for p53 were seen in ovarian cancer cells. Tumor necrosis factor-alpha induced a significant up-regulation of p53 messenger ribonucleic acid levels in ovarian cancer cells grown in nude mice and in vitro, whereas interleukin-6 did not. The maximum level of induction was 8 hours, and the up-regulation of p53 was dose dependent. In addition, tumor necrosis factor-alpha induced a dose-dependent increase in deoxyribonucleic acid fragmentation. CONCLUSION: Tumor necrosis factor-alpha induced up-regulation of p53 tumor suppressor gene expression in epithelial ovarian cancer cell lines, together with the induction of cell death by apoptosis.

Apoptosis↗
PubMed1994

HIV seroprevalence in a London same-day testing clinic.

OBJECTIVES: To determine the prevalence of HIV infection among people attending a confidential, non-genitourinary medicine based testing clinic that provides HIV antibody test results on the day of consultation. METHODS: Retrospective analysis of data collected on 2635 individuals attending the Same-Day HIV Testing Clinic at the Royal Free Hospital, London between March 1992 and February 1993. RESULTS: A total of 1612 men and 1023 women were tested for HIV antibody. The primary risk for HIV infection was heterosexual (71.7%; 1889 out of 2635) and homosexual contact (24.5%; 646 out of 2635). Fifty-four individuals were given positive HIV test results (46 men, median age 34 years; eight women, median age 27 years). Overall HIV seroprevalence was 2.0% (95% confidence interval, 1.5-2.5). HIV seroprevalence was highest among homosexual men (6.5%; 41 out of 635) and injecting drug users (5.7%; four out of 70). The rates for heterosexual men and women were 0.2% (two out of 915) and 0.7% (seven out of 974), respectively. Of the 54 individuals who were HIV-antibody-positive, 44 were Centers for Disease Control and Prevention stage II/III, eight stage IV and one was tested at the time of seroconversion (stage I; data were not available for one patient). Of the total numbers attending this clinic 27% (702 out of 2635) had previously been tested and received a negative result. Of a total of 54 HIV-antibody-positive individuals, 40% (21) had previously received a negative test result. CONCLUSIONS: The data suggest that seroprevalence amongst homosexual men attending a designated HIV testing clinic in London is lower than that reported by genitourinary clinic based testing sites. The large number of repeat testers who subsequently became infected with HIV suggests that there is a population requiring specific targetting for HIV risk reduction.

AIDS Serodiagnosis↗
PubMed1994

Determinants of nail thickness and length.

The determinants of final nail thickness and length at its point of detachment at the onychodermal band were studied in 20 normal great toe-nails, removed after injury, by correlating measurements of nail thickness, taken at six anatomical points, with length of nail and its lunular (matrical) and ventral nail components. Final nail thickness at the onychodermal band was related to initial thickness of the proximal matrix, and independently to the lengths of the lunula and ventral nail, but not to final nail length. There was an increase in nail thickness with age, particularly in the first two decades; this appeared not to be due to a decrease in frictional loss of nail.

Adolescent↗
PubMed1994

Evaluation of Bacillus subtilis strain IS53 for the production of Bacillus anthracis protective antigen.

An asporogenous strain of Bacillus subtilis, IS53, transformed with plasmid pPA102, produces the protective antigen (PA) component of the tripartite toxin of B. anthracis. Addition of yeast extract was required to support growth and PA production in all the media examined. Protective antigen expression was down-regulated during exponential growth and extracellular proteases caused marked degradation of the mature protein.

Antigens, Bacterial↗
PubMed1994

Effect of salmeterol on human nasal epithelial cell ciliary beating: inhibition of the ciliotoxin, pyocyanin.

1. Patients with airway infection by Pseudomonas aeruginosa have impaired mucociliary clearance. Pyocyanin is a phenazine pigment produced by P. aeruginosa which is present in the sputum of colonized patients, slows human ciliary beat frequency (CBF) in vitro and slows mucociliary transport in vivo in the guinea-pig. 2. We have investigated the effect of salmeterol, a long-acting beta 2-adrenoceptor agonist, on pyocyanin-induced slowing of human CBF in vitro. Salmeterol (2 x 10(-7) M) was found to reduce pyocycanin (20 micrograms ml-1)-induced slowing of CBF by 53% and the fall in intracellular adenosine 3':5'-cyclic monophosphate (cyclic AMP) by 26% and ATP by 29%. 3. Another beta 2-adrenoceptor agonist, isoprenaline (2 x 10(-7) M), also inhibited pyocyanin-induced slowing of CBF by 39%. 4. The effects of salmeterol (30 min preincubation) persisted after washing the cells. 5. Propranolol (10(-7) M) and the beta 2-specific antagonist, ICI 118551 (10(-6) M) blocked the protective effects of salmeterol completely, but atenolol (10(-6) M) was less effective. These results suggested that the effects of salmeterol on pyocyanin-induced effects were mediated primarily via the stimulation of beta 2-adrenoceptors. 6. Pyocyanin-induced ciliary slowing is associated with a substantial fall in intracellular cyclic AMP and ATP. Salmeterol reversed the effects of pyocyanin on cyclic AMP and ATP. 7. Mucociliary clearance is an important defence mechanism of the airways against bacterial infection. Salmeterol may benefit patients colonized by P. aeruginosa, not only by its bronchodilator action, but also by protecting epithelial cells from pyocyanin-induced slowing of CBF.

Adenosine Triphosphate↗
PubMed1994

Dynamic surface tension of surfactant TA: experiments and theory.

A bubble surfactometer was used to measure the surface tension of an aqueous suspension of surfactant TA as a function of bubble area over a range of cycling rates and surfactant bulk concentrations. Results of the surface tension-interfacial area loops exhibited a rich variety of phenomena, the character of which varied systematically with frequency and bulk concentration. A model was developed to interpret and explain these data and for use in describing the dynamics of surface layers under more general circumstances. Surfactant was modeled as a single component with surface tension taken to depend on only the interfacial surfactant concentration. Two distinct mechanisms were considered for the exchange of surfactant between the bulk phase and interface. The first is described by a simple kinetic relationship for adsorption and desorption that pertains only when the interfacial concentration is below its maximum equilibrium value. The second mechanism is "squeeze-out" by which surfactant molecules are expelled from an interface compressed past a maximum packing state. The model provided good agreement with experimental measurements for cycling rates from 1 to 100 cycles/min and for bulk concentrations between 0.0073 and 7.3 mg/ml.

Biological Products↗
PubMed1994

Somatic symptoms in generalized anxiety disorder with and without comorbid psychiatric disorders.

The authors compared the distribution of somatic symptoms associated with generalized anxiety disorder in 28 patients with "pure" generalized anxiety disorder and 77 patients with generalized anxiety disorder plus comorbid current or lifetime psychiatric diagnoses. They found no significant differences in individual symptom endorsement between the two groups, indicating that the basic symptoms of generalized anxiety disorder are specific to the disorder itself.

Adult↗
PubMed1994

Platelet-derived growth factor is an autocrine growth stimulator in retinal pigmented epithelial cells.

The retinal pigmented epithelium (RPE) plays a major role in normal and exaggerated retinal wound repair; the latter can result in epiretinal membrane formation and loss of vision. The RPE forms a stable monolayer of highly differentiated cells that proliferates only during wound repair. The mechanism underlying the change to the proliferating phenotype is unknown. When grown on a plastic substratum, cultured RPE cells mimic the proliferating phenotype in situ; they escape density arrest and proliferate in serum-free medium. In this study, we have demonstrated that a platelet-derived growth factor (PDGF) autocrine loop is involved in RPE growth in serum-free medium, because: (1) RPE cells secrete PDGF into their media and express PDGF receptors; (2) the PDGF receptors on RPE cells are autophosphorylated in serum-free medium and suramin, an agent that displaces PDGF and other growth factors from their receptors, blocks the autophosphorylation; and (3) a neutralizing antibody to PDGF significantly decreases RPE growth in serum-free medium. When a linear scrape is made in an RPE monolayer, the cells migrate and proliferate to fill in the gap mimicking wound repair in situ. Cells along the edge of the scrape show increased expression of PDGF and PDGF-beta receptors, and increased staining for proliferating cell nuclear antigen. Immunohistochemistry and in situ hybridization demonstrate expression of PDGF in ganglion cells and cells of retinal blood vessels. PDGF is not detected in the outer retina or RPE in untreated eyes, but is detected in RPE participating in wound repair, either adjacent to laser burns or underlying retinal detachment. PDGF and PDGF receptors are also expressed in RPE in epiretinal membranes removed during vitreous surgery. These data suggest that PDGF is an autocrine stimulator of growth in RPE that plays a role in retinal wound repair and epiretinal membrane formation.

Animals↗
PubMed1994

Estimates of population smoking prevalence: self-vs proxy reports of smoking status.

OBJECTIVES: In the face of rising costs of surveillance systems, it is time to reexamine the feasibility of including proxy respondents in surveys designed to provide population estimates of smoking prevalence. METHODS: Data are from the California. Tobacco Surveys, which are random-digit dialed telephone surveys. One adult provided demographic information and smoking status for all household residents. Additionally, some adults were selected for in-depth interviews that also included smoking status questions. We matched information from proxy respondents and self-respondents and evaluated smoking status discrepancies between them relative to demographic and other factors (n = 2930 matched pairs) in 1992. We address the potential bias these discrepancies might introduce into the population estimate of smoking prevalence. RESULTS: Overall, the discrepancy between proxy report and self-report was 4.3%, and it increased particularly when the self-respondent reported nondaily smoking or recent quitting. Discrepancies acted in both directions, and the net bias was that the screener survey overestimated smoking prevalence by 0.1% in 1992 (0.3% in 1990). CONCLUSIONS: Smoking status questions can be added to ongoing surveys such as the census or labor force surveys; one adult could provide smoking status for all household members.

Adult↗
PubMed1994

Hemoglobinuria in rats: a sensitive test of renal filtering and absorption of PEG-hemoglobin, a red blood cell substitute.

Hemoglobinuria, defined as hemoglobin or hemoglobin subunits in the urine, is an easily monitored, sensitive indicator of renal handling of hemoglobin-based blood substitutes. Hemoglobin tetramer dissociation increases filtration by the kidneys. When the rate of filtration exceeds reabsorption, hemoglobinuria occurs. This study investigates the renal filtration and absorption of polyethylene glycol-modified bovine hemoglobin by monitoring for hemoglobinuria in several model systems.

Absorption↗
PubMed1994

Normal oxygen tension restored in the ischemic rat liver model by PEG-hemoglobin.

Cell damage initiated during ischemia, as a result of oxygen depletion, continues during reperfusion, and recovery is dependent on the length of the ischemic period. This study investigates the effect of polyethylene glycol-modified hemoglobin (PEG-Hb) on recovery of tissue oxygen tension after induced ischemia.

Alanine Transaminase↗
PubMed1994

Abortion caused by Brucella abortus biovar 1 in a free-ranging bison (Bison bison) from Yellowstone National Park.

A near-term aborted bison (Bison bison) fetus was collected near Old Faithful geyser in Yellowstone National Park, Wyoming (USA). On necropsy, the fetus liver had a small capsular tear, and there was a small quantity of blood in the peritoneal cavity. Microscopic lesions included mild, purulent bronchopneumonia and mild, multifocal, interstitial pneumonia. Brucella abortus biovar 1 was isolated from fetal abomasal contents, lung, and heart blood.

Abortion, Veterinary↗
PubMed1994

Bacteria-host relationships in the bivalve mollusc Loripes lucinalis.

Loripes lucinalis, a lucinid species found in reduced sediments, contains endosymbiotic bacteria within specialized gill cells which contribute to the bivalve's nutrition. An additional bivalve-bacteria association can be seen in the digestive gland where large inclusion bodies filled with rickettsia- or chlamydia-like organisms are observed in the duct and tubule cells. Despite indications of a possible energy parasitism on the part of these endocellular digestive gland bacteria, the digestive epithelium of the host is not significantly damaged by the infection suggesting that this is a generalized and normal bivalve-bacteria association in adults of this species.

Alphaproteobacteria↗
PubMed1994

Role of the 5-HT2 receptor in the methamphetamine-induced neurochemical alterations.

The possibility that serotonin (5-HT) modulates dopamine (DA) synthesis by acting at 5-HT2 receptor sites during methamphetamine (METH) treatment was investigated. The neostriatal accumulation of 3,4-dihydroxyphenylalanine was not altered by ritanserin (1 mg/kg i.p.), a 5-HT2/1c receptor antagonist, or by METH (15 or 25 mg/kg s.c.), which indicates that METH-induced DA and 5-HT release did not invoke increased DA synthesis. Interestingly, the combined treatment of METH with ritanserin reduced 3,4-dihydroxyphenylalanine formation. We also examined the possibility that 5-HT2 receptors participate in the mechanism by which METH alters central tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH) activities as well as the concentration of neurotensin-like and substance P-like immunoreactivity. Five administrations of METH given at 6-hr intervals reduced neostriatal TH and TPH activity to 27 and 13% of control, respectively, 18 to 20 hr after the last drug administration; ritanserin failed to alter these decreases significantly. Ritanserin also failed to alter the METH-induced increase in neostriatal neurotensin-like immunoreactivity or in nigral neurotensin-like immunoreactivity and substance P-like immunoreactivity. Finally, the administration of ICS 205-930, a 5-HT3/4 receptor antagonist, also failed to prevent the METH-induced decrease in TH and TPH activities at doses below 200 micrograms/kg, whereas a dose of 500 micrograms/kg potentiated the effect of METH. These results suggest that 5-HT2 does not modulate DA synthesis nor does it mediate the changes in central TH and TPH activity, or neurotensin-like immunoreactivity and substance P-like immunoreactivity content induced by METH. Because 3,4-methylenedioxymethamphetamine is reported to stimulate DA synthesis by a 5-HT2 receptor-dependent mechanism, these observations suggest that METH and 3,4-methylenedioxymethamphetamine regulate the central dopaminergic system in a different manner.

Animals↗