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Biomedical subjects

B A Williams

Publications and source records attributed to B A Williams.

At least 127 records · Page 7Linked to original sources
PubMed1978

Metabolic consequences of mycoplasmal contamination of cell cultures.

KB cells originally derived from epitheloid carcinoma of the nasopharynx were found to be contaminated with mycoplasma. The contaminated cells showed significantly higher glycolytic (EMP) and respiratory (TCA) rates when compared with non-contaminated or 'cured' cells. The activity of the hexose monophosphate (HMP) shunt, an alternative pathway of glucose metabolism, was shown to be reasonably higher than normal KB cell levels. Treatment involving combination of heat (41 degrees C) and kanamycin (350 microgram/cm3) for 21 hours was found to adequately and selectively inactivate the mycoplasmal population. Following cure, the metabolism of the cells fell well within normal ranges. The treatment showed no deleterious effects on the KB cell population. The possibility and the significance of an independent hexose monophosphate shunt activity in the mycoplasma population in addition to the already established partial TCA and EMP activities, and the overall significance of detection of carbohydrate metabolism in these organisms, are discussed.

Cells, Cultured↗
PubMed1978

An inductively powered telemetry system for temperature, EKG, and activity monitoring.

An implant telemetry system for the simultaneous monitoring of temperature, activity, and EKG from small animals, such as rats, has recently been designed with the novel feature that instead of a battery the system is energized by an inductive field. A 250 kHz resonant coil surrounds the cage (30 X 30 X 20 cm) and provides the approximately 100 muW of power required to operate the implant transmitter while allowing the animal unrestrained movement in the cage. The implant can also be battery operated if desired RF transmission is in the 8-10 MHz band, which allows the use of a simple, essentially single IC chip, receiver.

Animals↗
PubMed1977

Diurnal rhythms of visual accommodation and blink responses: implication for flight-deck visual standards.

The major purpose of this study was to determine whether 24-h variations in accommodation responses occur and, if they do, whether they should be considered in setting visual standards for flight-deck tasks. A recently developed servo-controlled optometer and focus stimulator were used to obtain monocular accommodation response data on four college-age subjects. No 24-h rhythm in accommodation was shown. Heart rate and blink rate also were measured and periodicity analysis showed a mean 24-h rhythm for both; however, blink rate periodograms were significant (p less than or equal to 0.003) for only two of the four subjects. Thus, with the qualifications that college students were tested instead of pilots and that they performed monocular laboratory tasks imstead of binocular flight-deck task, it is concluded that 24-h rhythms in accommodation responses need not be considered in setting visual standards for flight-deck task.

Accommodation, Ocular↗
PubMed1977

Variation of forearm, hand, and finger blood flow indices with ambient temperature.

Impedance plethysmography was used to measure bilateral blood flow in the forearms, hands, and digits of seven healthy male subjects. The objectives were to determine the degree of symmetry between right and left body segments and to quantify the extent of vasomotor change at ambient temperatures ranging from 10 degrees to 46 degrees C. The mean forearm blood flow index ranged from 3.9 ml/(100 ml . min) at 10 degrees C to 7.5 ml/(100 ml . min) at 46 degrees C. Mean hand blood flow indices increased from 1.6 ml/(100 ml . min) at 10 degrees C to 10.7 ml (100 ml . min) at 46 degrees C. Finger blood flow indices in the proximal and medial phalanges of the five digits ranged from less than 1.0 ml/(100 ml . min) at 10 degrees C to over 27.0 ml/(100 ml . min) at 46 degrees C. Although each subject demonstrated variations in right and left side blood flow during any selected experiment the grouped mean flow indices exhibited no statistically significant side dominance. These experiments quantify the vasomotor alterations in the upper extremities and indicate that the more distal body segments exhibit relatively larger vasomotor responses to changes in ambient temperature than do the more proximal body segments.

Blood Flow Velocity↗
PubMed1977

Cardiovascular responses of men and women to lower body negative pressure.

Changes in blood flow and blood redistribution were measured by impedance plethysmography in the pelvic and leg regions of six male and four female subjects during three 5-min exposures to -20, -40, and -60 mm Hg lower body negative pressure (LBNP). Female subjects demonstrated significantly higher mean heart rate and lower leg blood flow indices than the male subjects during the recumbent control periods. Men had slightly higher mean resting systolic and diastolic blood pressures and higher mean control pelvic blood flow indices. Women demonstrated significantly less blood pooling in the legs and slightly less in the pelvic region than the men. All of the 18 tests with male subjects at -60 mm Hg were completed without initial signs of syncope, while only two of the tests with women were completed successfully without the subject exhibiting presyncopal conditions. The results of this study indicate that impedance plethysmography can be used to measure segmental cardiovascular responses during LBNP and that females may be less tolerant to -60 mm Hg LBNP than males.

Atmospheric Pressure↗
PubMed1976

Behavioral fever in newborn rabbits.

Rabbit pups, 12 to 72 hours old, did not develop a fever when injected intraperitoneally with a pyrogen and maintained at an ambient temperature of 32 degrees C for 2 hours. When placed in a thermally graded alleyway, animals injected with pyrogen selected gradient positions that represented significantly higher temperatures than controls injected with saline (40.4 degrees in contrast to 36.4 degrees C). Allowing the pups to remain at their selected positions for 5 minutes caused a significant increase in the rectal temperatures of the pyrogen-injected pups but not that of the controls. Thus, newborn rabbits will develop a fever by behavioral means after a single injection of an exogenous pyrogen.

Animals↗
PubMed1976

Elicited responding to signals for reinforcement: the effects of overall versus local changes in reinforcement probability.

Pigeons were studied on a three-component multiple schedule where all reinforcement was independent of responding. Two components were cued by different keylights and were associated with different rates of reinforcement. The third was always a no-key period associated with extinction. After a few sessions, pecking was elicited by the keylights signalling the reinforcement and continued to be maintained indefinitely. The duration and sequence of the three components were varied to determine if the primary controlling variable was differences in the overall probability of reinforcement, or if it was the immediate change in reinforcement signalled by the onset and/or offset of the stimulus. Both variables were found to control behavior. When 30-sec components were used, the primary controlling variable was the overall probability of reinforcement, but when 3-min components were used, overall probability had little effect. Control by local changes in reinforcement also occurred, although the type of local control varied both across subjects and experimental conditions. Some behaviors were controlled more by the change in reinforcement signalled by the onset of the stimulus, while others were controlled more by the change signalled by the offset of the stimulus.

Journal Article↗
PubMed1976

The effects of unsignalled delayed reinforcement.

Pigeons' pecks were reinforced according to a variable-interval schedule. A delay-of-reinforcement procedure was then added to the schedule, or a yoked-control procedure was arranged where the reinforcers occurred independently of responding according to the same variable-interval schedule. During the delay-of-reinforcement procedure, the first peck after a reinforcer was scheduled began a delay timer and the reinforcer was delivered at the end of the interval. No stimulus change signalled the delay interval and responses could occur during it, so that the obtained delays were often shorter than those scheduled. Responding under this procedure was highly variable but, in general, behavior was substantially reduced even with the shortest delay used, 3 sec. In addition, the rates maintained by delayed reinforcement were only slightly greater than those maintained by the yoked-control procedure, suggesting that adventitious pairings of response and reinforcer were responsible for some of the maintenance of behavior that did occur. The results challenge recent conceptions of reinforcement as involving response-reinforcer correlations and re-emphasize the role of temporal proximity between response and reinforcer.

Journal Article↗
PubMed1976

Behavioral contrast as a function of the temporal location of reinforcement.

Pigeons were trained on a multiple variable-interval variable-interval schedule of reinforcement. One component was then changed to a variation of a fixed-interval schedule in which the same rate of reinforcement was obtained as previously but the location of the reinforcer was fixed within the component. The effects of different temporal locations were compared. An increase in response rate for the unchanged variable-interval component (behavioral contrast) occurred when the reinforcer was located in the middle or at the end of the FI component, but response suppression occurred when it was located at the beginning of the component. The pattern of results cannot be explained by any previous theories of contrast. The overall response rates, and the pattern of local rates within the components, were consistent with the hypothesis that the major determinant of the contrast effect was the transition to a lower reinforcement rate following the unchanged component.

Journal Article↗
PubMed1975

The blocking of reinforcement control.

Two experiments were conducted to extend the blocking effect to the reinforcement of a response. A delayed reinforcement contingency was presented to subjects with or without a previously pretrained response available during the delay interval. The interpolated response had no scheduled effect on delivery of the reinforcer, but its availability reduced strengthening of the initial response, which completely extinguished for some subjects. The results were interpreted as support for blocking as a fundamental principle of behavior, and as evidence against the principle of reinforcement being stated solely in terms of temporal proximity between response and reinforcer.

Journal Article↗
PubMed1975

A re-examination of local contrast in multiple schedules.

Pigeons were presented with multiple schedules of alternating 90-sec components. When components in which grain was never presented alternated with components in which grain was presented on a variable-interval schedule, the average rate of responding in the variable-interval components increased, showing overall positive behavioral contrast. Unlike previous reports, this study found that the response rates for all birds increased toward the end of the variable-interval components as training proceeded. This increase in local response rate disappeared when the multiple schedule was composed solely of variable-interval components and reappeared when the variable-interval components were again alternated with extinction. This finding cannot be predicted or explained by recent theories of behavioral contrast based on autoshaping, and thus questions their sufficiency. We suggest that this local response-rate increase results from the predictable change from high to low density of reinforcement at the end of the fixed-duration component. Thus, the present effect apparently illustrates a different type of interaction between components of a multiple schedule than that described by previous theories of contrast. In a given procedure, either or both types of interaction may occur; neither provides a complete account of behavioral contrast.

Journal Article↗