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Biomedical subjects

D M Thompson

Publications and source records attributed to D M Thompson.

107 records · Page 6Linked to original sources
PubMed1975

Repeated acquisition of response sequences: stimulus control and drugs.

Pigeons obtained food by making four responses on three keys in a specified sequence, e.g., left, right, center, right. Under the "tandem-learning" condition, all three keys were the same color throughout the response sequence, and the sequence was changed from session to session. After total errors per session (overall accuracy) and within-session error reduction (learning) had stabilized, the effects of varying doses phenobarbital and chlordiazepoxide were assessed. For comparison, the drug tests were also conducted under a "tandem-performance" condition, in which the response sequence was the same from session to session, and under corresponding "chain-learning" and "chain-performance" conditions, where different colored keylights were associated with the response sequence. Under all four baseline conditions, the largest dose of each drug impaired overall accuracy. Under the two learning conditions, the error rate decreased across trials within each session, but the degree of negative acceleration was less in the drug sessions than in the control sessions. In contrast, under the two performance conditions, the error rate was relatively constant across trials, but was higher in the drug sessions than in the control sessions. Of the four baselines, the chain-learning condition was the most sensitive to the drug effects.

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PubMed1974

Behavioral parameters of drug action: signaled and response-independent reinforcement.

Four pigeons were initially trained under a multiple variable-interval 1-min variable-interval 1-min schedule of food reinforcement. For two of the pigeons, a signal was then presented whenever the reinforcer was available in one component; this resulted in positive contrast. For the other two pigeons, the reinforcer was presented independently of responding on a variable-time schedule in one component; this resulted in negative induction. After 30 to 50 sessions, however, a similar degree of differential responding occurred under both multiple schedules, i.e., high rates in the variable-interval component and low rates in the other component. Reinforcement frequency remained about the same in each of the schedule components. The stable performances then served as baselines for studying drug effects. In the high-rate component of both multiple schedules, small doses of d-amphetamine increased responding, whereas larger doses decreased responding. In the low-rate component of both multiple schedules, there was no rate-increasing effect at any dose of d-amphetamine; such an effect was found, however, with phenobarbital at a dose that decreased responding in the high-rate component. The drug effects thus depended on the interaction of pharmacologic variables (specific drug and dose) with behavioral variables (schedule components).

Animals↗
PubMed1972

Enhancement of progressive-ratio performance by chlordiazepoxide and phenobarbital.

The key pecking of two pigeons was reinforced with food on a progressive-ratio schedule, which required an increasing number of responses for each successive reinforcement: 8, 16, 24, 32, etc. When the subject failed to complete the next ratio in the sequence within 60 min, the session terminated. The number of responses in the final completed ratio was defined as the "breaking point". After the breaking point had stabilized (60 sessions), it served as a baseline to assess the effects of varying doses (5 to 80 mg/kg) of chlordiazepoxide and phenobarbital, administered intramuscularly 30 min before the sessions. Both drugs increased the breaking point. The dose-effect curves were inverted U-shaped, with maximum enhancement of performance occurring at 20 mg/kg for chlordiazepoxide and at 40 mg/kg for phenobarbital. A comparable enhancement was not obtained during a non-drug "probe" session, which was conducted after the subjects' body weights had been temporarily reduced from 80% to 70% of their free-feeding weights. The drug-induced enhancement of breaking point was related to the initial values of the performance and may represent a reduction in the aversiveness of the schedule.

Animals↗
PubMedDate not supplied

Role of laparoscopic ultrasound in cancer management.

Laparoscopic ultrasound (LUS) has become an important tool in the staging of hepatic, pancreatic, and gastrointestinal malignancies. It also plays an important role in the palliation and treatment of these malignancies. The use of laparoscopy and LUS in diagnosis, staging, palliation, and treatment of intra-abdominal malignancies is discussed, with a focus on the literature and our own experience.

Endosonography↗
PubMedDate not supplied

Inhibition of insect juvenile hormone epoxide hydrolase: asymmetric synthesis and assay of glycidol-ester and epoxy-ester inhibitors of trichoplusia ni epoxide hydrolase.

Juvenile hormone (JH) undergoes metabolic degradation by two major pathways involving JH esterase and JH epoxide hydrolase (EH). While considerable effort has been focussed on the study of JH esterase and the development of inhibitors for this enzyme, much less has been reported on the study of JH-EH. In this work, the asymmetric synthesis of two classes of inhibitors of recombinant JH-EH from Trichoplusia ni, a glycidol-ester series and an epoxy-ester series is reported. The most effective glycidol-ester inhibitor, compound 1, exhibited an I(50) of 1.2x10(-8) M, and the most effective epoxy-ester inhibitor, compound 11, exhibited an I(50) of 9.4x10(-8) M. The potency of the inhibitors was found to be dependent on the absolute configuration of the epoxide. In both series of inhibitors, the C-10 R-configuration was found to be significantly more potent that the corresponding C-10 S-configuration. A mechanism for epoxide hydration catalyzed by insect EH is also presented.

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