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Biomedical subjects

B A Williams

Publications and source records attributed to B A Williams.

At least 91 records · Page 5Linked to original sources
PubMed1991

Preference for conditioned reinforcement.

Pigeons were presented with a concurrent-chains schedule in which both choice alternatives led to the same terminal-link stimulus, which was followed by food. Superimposed on the food-reinforced presentations of the terminal-link stimulus was a second schedule of presentations of the same stimulus that were followed by no food. The absolute number of these no-food stimulus presentations was held constant while their relative frequency assigned to one or the other choice alternative was systematically varied. Preference for a given choice alternative tracked the relative frequency of these stimulus presentations, thus demonstrating that they served as reinforcers. These results resolve conflicts in the literature regarding the effect of conditioned reinforcement on choice.

Animals↗
PubMed1991

Choice as a function of local versus molar reinforcement contingencies.

Rats were trained on a discrete-trial probability learning task. In Experiment 1, the molar reinforcement probabilities for the two response alternatives were equal, and the local contingencies of reinforcement differentially reinforced a win-stay, lose-shift response pattern. The win-stay portion was learned substantially more easily and appeared from the outset of training, suggesting that its occurrence did not depend upon discrimination of the local contingencies but rather only upon simple strengthening effects of individual reinforcements. Control by both types of local contingencies decreased with increases in the intertrial interval, although some control remained with intertrial intervals as long as 30 s. In Experiment 2, the local contingencies always favored win-shift and lose-shift response patterns but were asymmetrical for the two responses, causing the molar reinforcement rates for the two responses to differ. Some learning of the alternation pattern occurred with short intertrial intervals, although win-stay behavior occurred for some subjects. The local reinforcement contingencies were discriminated poorly with longer intertrial intervals. In the absence of control by the local contingencies, choice proportion was determined by the molar contingencies, as indicated by high exponent values for the generalized matching law with long intertrial intervals, and lower values with short intertrial intervals. The results show that when molar contingencies of reinforcement and local contingencies are in opposition, both may have independent roles. Control by molar contingencies cannot generally be explained by local contingencies.

Animals↗
PubMed1990

Enduring problems for molecular accounts of operant behavior.

Although the Associative Learner (AL) theory advocated by Shimp, Childers, and Hightower (1990) can simulate several features of human and nonhuman performance in free-operant situations, it fails to account for many of the findings that are theoretically most powerful. It underestimates the sensitivity of behavior to relative reinforcement rate and totally omits any role for incentive variables such as amount and delay of reinforcement. At present, it is not sufficiently comprehensive to serve as an adequate alternative to Herrnstein's (1961, 1970) matching theory as a general account of behavior.

Animals↗
PubMed1990

Conditioned reinforcement versus time to reinforcement in chain schedules.

Pigeons were trained on three-component chain schedules in which the initial component was either a fixed-interval or variable-interval schedule. The middle and terminal components were varied among fixed-interval fixed-interval, variable-interval variable-interval, and an interdependent variable-interval variable-interval schedule in which the sum of the durations of the two variable-interval components was always equal to the sum of the fixed-interval fixed-interval components. At issue was whether the response rate in the initial component was controlled by its time to primary reinforcement or by the temporal parameters of the stimulus correlated with the middle terminal link. The fixed-interval initial-link schedule maintained much lower response rates than the variable-interval initial-link schedule regardless of the schedules in the middle and terminal links. Nevertheless, the intervening schedules played some role: With fixed-interval schedules in the initial links, response rates were consistently highest with independent variable-interval schedules in the middle and terminal links and intermediate with the interdependent variable-interval schedules; these initial-link differences were predicted by the response rates in the middle link of the chain. With variable-interval schedules in the initial links, response rates were lowest with the fixed-interval fixed-interval schedules following the initial link and were not systematically different for the two types of variable-interval variable-interval schedules. The results suggest that time to reinforcement itself accounts for little if any variance in initial-link responding.

Animals↗
PubMed1990

Absence of anticipatory contrast in rats trained on multiple schedules.

Rats were trained on three- and four-component multiple schedules in which two of the components were correlated with identical reinforcement schedules that remained unchanged throughout training. These target components differed in terms of whether their respective following schedules were either higher or lower in value. Unlike corresponding experiments previously reported with pigeons, higher response rates occurred in the target component followed by a higher valued schedule than in the target component followed by the lower valued schedule. Overall contrast effects occurred independently of these sequential effects, but were inconsistent across subjects. The results suggest that the effects of a following schedule of reinforcement are opposite for pigeons and rats, and that one reason previous studies have often failed to show contrast effects with rats is that the effects of the following schedule in rats are in competition with contrast dynamics.

Animals↗
PubMed1990

Role of the carotid chemoreceptors in the respiratory response of newborn lambs to alternate pairs of breaths of air and a hypoxic gas.

We measured the reflex respiratory response to a 2-breath alternation in fractional inspired oxygen in two groups of lambs. Test runs where F(I),O2 was made to alternate (between 0.21 and 0.14) were compared with control runs in which it was held at 0.21. Within 36 h of birth we cut the carotid sinus nerves bilaterally in one group of lambs (n = 5) whilst in a second group (n = 5) sham operations were carried out. The alternating responses in seven respiratory variables were compared between test and control runs in each group of lambs at postnatal days 5-6 and again at postnatal days 10-11. In sham-operated lambs at days 5-6 there was a significant response in most respiratory variables during test runs and by days 10-11 the response was increased, primarily as a consequence of an increase in the tidal volume component of the response, indicating a postnatal maturation of the responses. The time-scale of this maturation is appropriate to that of peripheral chemoreceptor resetting. There was no significant response to the test in the denervated lambs at 5-6 days but by days 10-11 a small response was measured in some variables. Our results therefore indicate that the reflex respiratory response to alternations in FI,O2 is primarily mediated by the carotid chemoreceptors. The development of a response mediated by the aortic chemoreceptors may account for the small alternating response in the denervated lambs at days 10-11.

Animals↗
PubMed1989

Reproductive alterations in female C57BL/Crgl mice exposed neonatally to zearalenone, an estrogenic mycotoxin.

Newborn female mice were injected daily for 5 days with 1 microgram zearalenone (Z, a weakly estrogenic mycotoxin present in cereal grains), resulting in ovary-dependent reproductive tract alterations at 8 months of age. Corpora lutea were absent from 25 of 34 (74%) Z-treated mice, indicating ovarian dysfunction. Fifty-six percent of Z-treated mice had dense collagen deposition in the uterine stroma and lacked uterine glands. Squamous metaplasia of the uterine luminal epithelium was found in 59% of Z-treated mice, and altered vaginal epithelium was found in 32% (2 mice had dysplastic lesions). Ovariectomized Z-treated mice were indistinguishable from ovariectomized controls.

Animals↗
PubMed1989

The effect of chronic hypoxia upon the development of respiratory chemoreflexes in the newborn kitten.

1. We have studied the reflex respiratory responses to two-breath alternations of fractional inspired oxygen (FI,O2) in normoxic (reared in room air) and chronically hypoxic kittens (born into and reared in an FI,O2 of 0.13-0.15) on post-natal days 1, 2-3, 4-8 and 9-14. 2. Respiration was measured non-invasively in the unanaesthetized kittens. Test runs (with alternations of FI,O2 between 0.21 and 0.14) and control runs (with an FI,O2 of 0.21) were carried out during quiet sleep. 3. The degree of alternation in tidal volume, inspiratory time, expiratory time, frequency, drive, timing and instantaneous ventilation components of the respiratory response was compared during control and test runs. 4. There was little response to control runs in either group at any post-natal age. 5. In normoxic kittens we found no significant reflex response in any respiratory variable to test runs before day 4. However significant alternation was found in expiratory time, frequency and ventilation at days 4-8 and in tidal volume at days 9-14. 6. In chronically hypoxic kittens there were no significant differences between control and test runs at any of the ages studied. 7. In the normoxic group increases in the response with post-natal age probably reflect post-natal increases in the sensitivity of the peripheral chemoreceptors. The lack of development in the chronically hypoxic group may indicate abnormal function or delayed maturation of the peripheral chemoreceptor sensitivity to hypoxia. 8. The results suggest that the method can be used to detect developmental and pathological changes in the arterial chemoreflex.

Animals↗
PubMed1989

Characterization of a halothane-resistant strain of measles virus.

A strain of measles virus (MVr) whose replication demonstrated increased resistance to halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) exposure compared with the susceptible parental strain (MVs) is described. After exposure to a 1.2% halothane concentration, substantial amounts of the measles virus H protein were detected in MVr-infected Vero cell lysates by immunoprecipitation and polyacrylamide gel electrophoresis or by quantitative immunofluorescence staining. The protein was barely detectable in identically treated MVs-infected lysates, however. The recovery of all other measles virus proteins studied was the same in MVr- and MVs-infected cells at this anesthetic concentration. Thus, the altered expression of a single gene product appears to be responsible for the observed halothane resistance.

Animals↗
PubMed1989

Rabbit myocardial 82Rb kinetics and a compartmental model for blood flow estimation.

Quantification of regional myocardial blood flow (MBF) with rubidium-82 (82Rb) and positron emission tomography (PET) requires the validation of a tracer kinetic model that adequately describes the kinetics of 82Rb in tissue. We performed 134 82Rb kinetic experiments in 24 isolated, arterially perfused rabbit interventricular septa at different flow rates (0.5-4.5 ml.min-1.g-1) and under the following conditions: varied concentrations of glucose (2.8-11 mM), insulin (0-5 mU/ml), and potassium (5-8 mM); varied pH (7.2-7.8); varied workload; and the addition of acetylstrophanthidin (1.0 microM). The measured 82Rb tissue time-activity curves consisted of two exponential components, with half times inversely related to MBF. The size of the slow component decreased as MBF increased (from 70% at 0.3 ml.min-1.g-1 to 30% at 2.0 ml. min-1.g-1). The kinetics were not strongly dependent on the conditions studied and were consistent with a compartmental model containing two communicating compartments. The volume of the fast exchangeable compartment and the transport rate constant from the fast to the slow compartment were found to be independent of MBF. Values of MBF were estimated with the compartmental model from 82Rb kinetics, and they correlated well with the directly measured MBF (r = 0.91; slope = 1.03).

Animals↗
PubMed1989

A test of the melioration theory of matching.

Melioration theory entails that matching in concurrent schedules occurs because the subjects equalize the local reinforcement rates (reinforcers received for each alternative divided by the time allocated to each alternative). The role of local reinforcement rates was tested by using multiple schedules in which one component involved an alternative with a high absolute rate of reinforcement and a low local reinforcement rate while the second component involved an alternative with a low absolute rate and a high local rate. These alternatives were then presented simultaneously in probe trials to determine preference between them. Contrary to melioration, the absolute rate of reinforcement, not the local rate, was the controlling variable.

Animals↗
PubMed1987

Measurement of glucose and 2-deoxy-2-[18F]fluoro-D-glucose transport and phosphorylation rates in myocardium using dual-tracer kinetic experiments.

To examine the use of 2-deoxy-2-[18F]fluoro-D-glucose (2-FDG) as a glucose analog for measuring glucose utilization rate in myocardium, dual-tracer kinetic experiments with 2-FDG and 2-[3H]glucose were performed in the perfused, isolated rabbit interventricular septum to measure simultaneously the transport and phosphorylation rates of glucose and 2-FDG. Results of the present study indicated that, in the septum, the transport rate constants of 2-FDG and glucose were similar in magnitude, the phosphorylation rate constant for 2-FDG was about 60% of that of glucose, hypoxia caused an increase in phosphorylation rates of glucose and 2-FDG without affecting transport.

Animals↗
PubMed1987

Response of thermal stressed bobwhite to organophosphorus exposure.

Constant and intermittent cold stressed juvenile northern bobwhite (Colinus virginianus) were exposed to chlorpyrifos, an organophosphorus insecticide, following avian dietary LC(50) test procedures. Chlorpyrifos concentrations ranged from 100 to 1000 ppm; ambient temperatures (T(a)) included 35.0 (control), 32.5, 30.0 and 27.5 degrees C. Survival decreased significantly under constant cold conditions. Non-survivors averaged 33% weight loss, but survivor weight dropped with increasing dose and decreasing T(a). Control quail at all temperatures maintained a constant body temperature (T(b)); however, T(b) of dosed quail fell with increasing dose and decreasing T(a). Non-surviving cold stressed quail had higher cholinesterase (ChE) activity that non-survivors at 35 degrees C; in addition, dead quail failed to average the 50% inhibition of ChE used to implicate a ChE depressant in death. Daily exposure of quail to 12 h of warmth increased survival. Survivors of intermittent cold stress experienced less weight loss than constant cold survivors due to reduced metabolic costs. Synergistic effects were evident in juvenile northern bobwhite exposed simultaneously to chlorpyrifos and cold stress; however, mortality and certain sublethal effects were mitigated when cold exposure was intermittent.

Journal Article↗
PubMed1987

Effects of delayed conditioned reinforcement in chain schedules.

The contingency between responding and stimulus change on a chain variable-interval 33-s, variable-interval 33-s, variable-interval 33-s schedule was weakened by interposing 3-s delays between either the first and second or the second and third links. No stimulus change signaled the delay interval and responses could occur during it, so the obtained delays were often shorter than the scheduled delay. When the delay occurred after the initial link, initial-link response rates decreased by an average of 77% with no systematic change in response rates in the second or third links. Response rates in the second link decreased an average of 59% when the delay followed that link, again with little effect on response rates in the first or third links. Because the effect of delaying stimulus change was comparable to the effect of delaying primary reinforcement in a simple variable-interval schedule, and the effect of the unsignaled delay was specific to the link in which the delay occurred, the results provide strong evidence for the concept of conditioned reinforcement.

Animals↗
PubMed1986

An equation for behavioral contrast.

Pigeons were trained on a three-component multiple schedule in which the rates of reinforcement in the various components were systematically varied. Response rates were described by an equation that posits that the response-strengthening effects of reinforcement are inversely related to the context of reinforcement in which it occurs, and that the context is calculated as the weighted average of the various sources of reinforcement in the situation. The quality of fits was comparable to that found with previous quantitative analyses of concurrent schedules, especially for relative response rates, with over 90% of the variance accounted for in every case. As with previous research, reinforcements in the component that was to follow received greater weights in determining the context than did reinforcements in the preceding component.

Animals↗
PubMed1984

Isolation of a virus from chimpanzee liver cell cultures inoculated with sera containing the agent of non-A, non-B hepatitis.

A membrane-coated virus having a diameter of 85-90 nm and containing a 40-45 nm core was found to replicate in cell cultures derived from chimpanzee liver after inoculation of serum containing infective non-A, non-B (NANB) hepatitis viruses from two independent sources. Replication of this agent was not observed when the same cells were inoculated with a chloroform-extracted inoculum or were left uninoculated. Replication involves assembly of virus cores on tubular structures similar to those seen in liver cells of chimpanzees infected with most isolates of NANB virus.

Animals↗
PubMed1984

Hypothermic and antipyretic effects of ACTH (1-24) and alpha-melanotropin in guinea-pigs.

Intracerebroventricular administration of adrenocorticotropin (ACTH 1-24) and alpha-melanotropin (alpha-MSH), peptides which occur naturally in brain induced dose-related hypothermia in guinea-pigs at room temperature (21 degrees C) and also produced greater hypothermia at low (10 degrees C) ambient temperature. However, when the experiments were repeated in a warm (30 degrees C) environment, no effect on body temperature was observed. These results indicate that the peptides did not reduce the central set-point of temperature control. The hypothermia induced by ACTH and alpha-MSH was not mediated via histamine H1- or H2-receptors and serotonin since the H1-receptor antagonist, mepyramine, the H2-receptor antagonist, cimetidine, and the serotonin antagonist, methysergide, had no antagonistic effects. The peptides were antipyretic since they reduced pyrogen-induced-fever and hyperthermia due to prostaglandin E2, norepinephrine and dibutyryl cAMP, at a dose which did not affect normal body temperature. The powerful central effects of these peptides on normal body temperature, fever and hyperthermia, together with their presence of the brain regions important to temperature control, suggest that they participate in thermoregulation.

Adrenocorticotropic Hormone↗