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Biomedical subjects

D McCarthy

Publications and source records attributed to D McCarthy.

At least 145 records · Page 8Linked to original sources
PubMed1982

Independence of stimulus discriminability from absolute rate of reinforcement in a signal-detection procedure.

Three experiments are reported in which two pigeons were trained to detect differences in stimulus duration under varying levels of absolute rate of reinforcement. Two red stimuli, differing in duration, were arranged probabilistically on the center key of a three-key chamber. On completion of the center-key duration, the center keylight was extinguished and the two side keys were illuminated white. Correct responses were left-key pecks following the shorter duration and right-key pecks following the longer duration. In Experiment 1, relative rate of reinforcement for correct responses was held constant and absolute rate of reinforcement was varied in seven conditions from continuous reinforcement to a variable-interval 90-second schedule. In Experiment 2, relative rate of reinforcement was manipulated across three different absolute rates of reinforcement (continuous reinforcement, variable-interval 15-second, and variable-interval 45-second). Stimulus discriminability was unaffected by changes in absolute or relative rates of reinforcement. Experiment 3 showed that discriminability was also unaffected by arranging the same consequences (three-second blackout) for unreinforced correct responses and errors.

Animals↗
PubMed1981

Intrinsically stable IgG aggregates.

Measurement of the absorbance due to light scattering at 40 nm proved to be a simple and reliable way of assessing the extent of aggregation in heat-treated IgG solutions. Using this technique the rate of aggregation was demonstrated to be markedly temperature dependent with a sharp inflexion in the curve close to 63 degrees C. During heating at 63 degrees C the concentration of unaggregated IgG fell in a manner consistent with a first-order process and the mean size of the IgG aggregates increased with time. IgG aggregates could be selectively removed from heat-treated IgG solutions and concentrated by precipitation with 3.5% polyethylene glycol without altering their size distribution. Furthermore, and in contrast with a previous report, the IgG aggregates examined in this study were remarkably stable in the absence of any other protein such as serum albumin. In consequence, several important practical recommendations concerning the production of heat-aggregated IgG for use in immune complex assays are made.

Centrifugation, Density Gradient↗
PubMed1981

The effect of IgG aggregate size and concentration on reactivity in immune complex assays.

The reactivity of heat-aggregated IgG of known size, in the Raji cell assay, the C1q binding assay and the C1q solid phase radioimmunoassay as a function of concentration, has been investigated. Marked differences were found in the way that the three assays behave when the IgG concentration and aggregate size are varied. These findings indicate the pitfalls in attempting to express the results of immune complex assays performed on biological fluids in terms of equivalent concentrations of aggregated IgG.

Antigen-Antibody Complex↗
PubMed1981

Transformation of Haemophilus influenzae by plasmid RSF0885 containing a cloned segment of chromosomal deoxyribonucleic acid.

A plasmid containing a single cloned insertion of Haemophilus influenzae chromosomal deoxyribonucleic acid that carried a novobiocin resistance marker was 2.6 times larger than the parent plasmid, RSF0885, which conferred ampicillin resistance. The most frequent type of transformation by this plasmid (designated pNov1) was the transfer of novobiocin resistance to the chromosome, with the loss of the plasmid from the recipient. In accord with this observation, after radioactively labeled pNov1 entered a competent cell, it lost acid-insoluble counts, as well as biological activity. The level of ampicillin transformation, which involved establishment of the plasmid, was almost two orders of magnitude lower than the level of novobiocin transformation. Both types of transformation were depressed profoundly in rec-1 and rec-2 mutants. Ampicillin transformants of wild-type cells always contained plasmids that were the same size as pNov1, although most of these transformants were not novobiocin resistant. Plasmid pNov1 in wild-type cells but not in rec-1 or rec-2 cells often recombined with the chromosome, causing a homologous region of the chromosome to be substituted for part of the plasmid, as shown by restriction and genetic analyses. Our data suggested that plasmid-chromosome recombination took place only around the time when the plasmid entered a cell, rather than after it became established.

Ampicillin↗
PubMed1981

Transformation of Haemophilus influenzae by plasmid RSF0885.

Plasmid RSF0885, which conferred ampicillin resistance, transformed competent Haemophilus influenzae cells with low efficiency (maximum, less than 0.01%). As judged by competition experiments and uptake of radioactivity, plasmid RSF0885 deoxyribonucleic acid was taken up into competent H. influenzae cells several orders of magnitude less efficiently than H. influenzae chromosomal deoxyribonucleic acid. Plasmid RSF0885 transformed cells with even lower efficiency than could be accounted for by the low uptake. Transformation was not affected by rec-1 and rec-2 mutations in the recipient, and strains cured of the plasmid did not show increased transformation. Plasmid molecules cut once with a restriction enzyme that made blunt ends did not transform. Transformation was favored by the closed circular form of the plasmid.

Bacteriophages↗
PubMed1981

Characterization of somatostatin-like components in the tumors and plasma of a patient with a somatostatinoma.

Somatostatin-like immunoreactive polypeptides with approximate molecular weights of 1,500-2,000 (peak I), 2,500-3,500 (peak II), and 10,000-15,000 (peak III) were isolated from the peripheral plasma and from extracts of tumor tissue of a patient with a pancreatic somatostatinoma and hepatic metastases. The peak I component had approximately the same molecular charge as somatostatin, but the peak II component was appreciably more basic. The peak III component was heterogeneous with respect to charge and dissociated into smaller immunoreactive polypeptides during isoelectric focusing or after treatment with strongly denaturing solvents. In plasma, the levels of the larger molecular weight components (peak II and peak III), relative to that of the somatostatin-size component (peak I), were higher than in tissue extracts, suggesting a lower rate of clearance of the larger polypeptides from the circulation. In response to a nutrient stimulus, the peak I component increased to a greater extent than the larger components. Plasma levels of larger immunoreactive polypeptides relative to the peak I component in patient's plasma were higher after complete resection of the pancreatic tumor than preoperatively, suggesting that the rate of release of these putative precursor forms from the metastases was greater than from the primary tumor.

Chemical Phenomena↗
PubMed1980

On the discriminability of stimulus duration.

The performance of pigeons trained to detect differences in the duration of stimuli was analysed using a matching model of signal detection. Two white stimuli, S1 and S2, differing in duration, were arranged with equal probability on the center key of a three-key chamber. S1 was systematically varied from 5 seconds to 25 seconds while S2 remained constant at 30 seconds. On completion of the center-key stimulus, a peck on the center key turned on the two red side keys. A left-key response was "correct" when S1 had been in effect on the center key and a right-key response was "correct" on S2 trials. A correct response produced a 3-second magazine light accompanied intermittently by food. Incorrect responses produced 3-second blackouts. Detection performance was measured under two procedures. In the first, the obtained reinforcement ratio was uncontrolled by allowing the number of food reinforcements obtained for correct left- and right-key responses to vary as the stimuli were changed. In the second procedure, the presentation of food reinforcement was controlled by holding the obtained reinforcement ratio constant. Discriminability changed as a function of stimulus differences under both procedures. No such trend was found in response bias.

Animals↗
PubMed1980

Independence of sensitivity to relative reinforcement rate and discriminability in signal detection.

Six pigeons were trained to detect differences between two white stimuli, S1 and S2, differing in duration and arranged probabilistically on the center key of a three-key chamber. Detection performance was measured at two levels of discriminability. At one level, S1 was five seconds and S2 was thirty seconds. At the other level, S1 was twenty seconds and S2 was thirty seconds. The procedure was a standard signal-detection yes-no design in which stimulus-presentation probability was varied from .1 to .9 at both discriminability levels. On completion of the center-key stimulus, a peck on the center key darkened the center-key light and turned on the two red side keys. A left-key response was "correct" on S1 trials, and a right-key response was "correct" on S2 trials. Correct responses produced food reinforcement on a variable-ratio 1.3 schedule. Incorrect responses produced three second blackout. Discriminability was higher for the five-second versus thirty-second conditions than for the twenty-second versus thirty-second conditions, but there were no differences in sensitivity of behavior to reinforcement variation for the two stimulus pairs. Response bias was a function of the relative reinforcement rate for correct choice responses.

Animals↗
PubMed1980

Reinforcement for errors in a signal-detection procedure.

Six pigeons were trained on a signal-detection procedure. They were required to peck the left key when a 5-second white light had been presented, and the right key when a 10-second light had been presented. These two correct responses were followed by food reinforcement with a probability of .7. Errors, left responses after the 10-second stimulus or right responses after the 5-second stimulus, were initially followed by a 3-second blackout of the chamber. In nine subsequent experimental conditions, errors were followed by food reinforcement with increasing probability while the probability of reinforcement for correct responses was kept constant. The percentage of correct responses decreased as error reinforcement probability increased. A matching model of detection performance, in which discrimination is a joint function of stimulus discriminability and stimulus-reinforcement association, provided a convincing fit to the data and to two sets of published data. The model also fitted published data on multiple and multiple-concurrent free-operant performance. This description of detection performance in terms of matching offers both accurate prediction of complex behavior and measures of discriminability with wide generality.

Journal Article↗
PubMed1979

Pneumatosis coli in adult acute myeloid leukaemia.

Three cases of pneumatosis coli (PC) in adult patients with acute myeloid leukaemia seen over the last five years in Hammersmith Hospital are reported. Although definite conclusions are impossible, we suggest that that pneumatosis could be due to damage to the bowel mucosa as a result of the disease or the treatment. The literature is reviewed and discussed in an inconclusive attempt to discover the source of the gas.

Adolescent↗
PubMed1979

Relationship between the single-breath N test and age, sex, and smoking habit in three North American cities.

This report describes a collaborative study conducted in Montreal, Canada, Portland, Ore., and Winnipeg, Canada, to establish the relationship between the single-breath N2 test and age, sex, and smoking and to determine the prevalence of functional abnormalities in these populations. In nonsmokers, age-related regressions for closing volume, closing capacity, and the slope of phase III obtained from the single-breath N2 test, plus the ratio of the I-s forced expiratory volume to the forced vital capacity had very similar slopes, suggesting that differences in geographic location, climate, air pollution, and occupation had no effect on lung function detectable by these tests. Among the 6 city/six groups there was no systematic difference in the prevalence of functional abnormalities between the cities, but closing capacity expressed as a percentage of total lung capacity was abnormal most often in men and the slope of the alveolar plateau was abnormal most often in women. The prevalence of respiratory symptoms within different smoking categories was similar in the 3 cities. Although the number of cigarettes smoked had a significant effect on every test except the ratio of the I-s forced expiratory volume to forced vital capacity in men, the effect of age was considerably greater than the effect of smoking, and the dose-response relationship was weak. We conclude that additional factors may interact with smoking to place a smoker at risk of developing chronic airflow limitation.

Adult↗