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Biomedical subjects

D A Overton

Publications and source records attributed to D A Overton.

13 recordsLinked to original sources
PubMed1979

Drug discrimination training with progressively lowered doses.

Rats were trained to discriminate drug from no-drug conditions in a two-lever operant task. Moderately high dosages were used initially. Whenever the discrimination was learned, training was continued with progressively reduced dosages. Eventually the rats discriminated extremely low doses of phenobarbital, chlordiazepoxide, cyclazocine, and fentanyl.

Animals↗
PubMed1979

Correlations between psychiatric diagnosis and some quantitative EEG variables.

Several methods of quantitative analysis were applied to the left parietal 'resting' EEGs of 48 nonpatient controls and 90 undrugged psychiatric inpatients. Patient and control groups, matched for age and sex, differed as follows: (a) Mean frequency was lower and frequency variability was greater in the total patient group than in controls. (b) Mean amplitude was higher and mean frequency lower in chronic schizophrenics than in controls; the amplitude differences were contributed mainly by female patients. (c) Amplitude and frequency means of nonpsychotic patients were intermediate between those of chronic schizophrenics and controls. (d) Mean amplitudes were greater and frequency variability was less in neurotics than in controls.

Adult↗
PubMed1979

Investigation of narcotics and antitussives using drug discrimination techniques.

Rats learned drug discriminations in a shock-escape T-maze task. They were trained to turn right in the maze following injection of a drug (D) and left when no injection (N) was given. Number of training sessions before criterion performance (STC) was used to indicate degree of discriminability of the training drug. STC decreased monotonically as dosage increased, and reached a minimum of 3 to 26 with various agonists. Most agonists were not highly discriminable. Daily maintenance injections of morphine, 200 to 600 mg/kg, increased the STC of morphine, 15 mg/kg, significantly, but complete tolerance to discriminable drug actions was not observed. After rats discriminated D vs. N, they were tested with novel drugs to determine which would elicit D choices. Most morphine-like agonists substituted for one another during substitution tests; the tested agonists included alphaprodine, codeine, fentanyl, heroin, meperidine, methadone, morphine, piminodine and propoxyphene. In a few instances, one of these agonists failed to substitute for another. Naloxone and naltrexone antagonized the discriminable effects of morphine. Cyclazocine, levallorphan, naltrexone, dextromethorphan, ethoheptazine and the narcotic agonists did not substitute for one another, suggesting that six dissimilar discriminable effects were produced by these drugs.

Analgesics, Opioid↗
PubMed1978

Discriminable effects of antihistamine drugs.

Rats were trained to discriminate drug vs. no-drug in a shock-escape T-maze task; a right turn was required when rats were drugged and a left turn when undrugged. The three antihistamine drugs pyrilamine, dimenhydrinate (Dramamine) and diphenhydramine (Benadryl) were discriminated after an average of 20 training sessions indicating that their effects were only moderately discriminable. After criterion performance was achieved under the training conditions, substitution tests were conducted during which rats received a novel drug and were then run in the maze with both goals accessible. Rats trained with antihistamine drugs made drug choices during tests with other antihistamines. Rats trained with other types of drugs made no-drug choices during tests with antihistamines. The results suggest that the antihistamines share a discriminable effect which is relatively unique to that class of drugs.

Animals↗
PubMed1977

Comparison of ethanol, pentobarbital, and phenobarbital using drug vs. drug discrimination training.

Rats learned drug vs. drug (D vs. D) or drug vs. no drug (D vs. N) discriminations in a T-maze shock escape task with various doses of pentobarbital, phenobarbital, or ethanol. Dose-effect curves were obtained for each drug using D vs. N training. After D vs. N training with any one of these drugs, rats made D choices during substitution tests with the other two drugs, suggesting drug interchangeability. D vs. D training also showed that pentobarbital and phenobarbital were virtually indistinguishable from one another. However, ethanol was readily discriminated from pentobarbital, showing that the two drugs differed. The results show the utility of D vs. D training as a method for studying drug differences that may be too small to detect with substitution tests.

Animals↗
PubMed1977

Discriminable effects of antimuscarinics: dose response and substitution test studies.

In a shock escape T-maze task, rats were trained to turn right following one drug treatment and left following a second drug treatment. The specific drug and dose conditions were the only discriminative cues available to the animals. The number of training sessions before criterion performance indicated the discriminability of the two training conditions. Drug vs no drug training showed that discriminability was proportional to dosage for low doses, but was constant over a range of higher doses. Such an asymptote of discriminability was observed with scopolamine, atropine, benactyzine and Ditran (JB 329), and was shown not to result from tolerance. High dose vs low dose discriminations involving scopolamine were learned very slowly if both doses were within the asymptotic range; this indicates that similar discriminable effects were produced by high and low doses. To compare various drugs, substitution tests were administered to trained rats. The four antimuscarinic drugs generally substituted for one another but did not mimic and were not mimicked by drugs in other pharmacological classes. Some exceptions to this pattern were noted. The discriminable effects of scopolamine were partially antagonized by physostigmine. The results indicate that the antimuscarinic drugs share discriminable actions probably produced by their anticholinergic actions. The asymptote of action at high doses appears genuine, possibly reflecting receptor saturation.

Animals↗
PubMed1976

Discriminable effects of benzodiazepines.

In a shock-escape T-maze task, rats rapidly discriminated diazepam, flurazepam and chloridazepoxide from no drug. The discriminable effects of these benzodiazepines were not completely interchangeable with those of barbiturate anesthetics. The dose-response curve for diazepam asymptoted over the range 15 to 100 mg/kg, ip whereas dose-response curves for flurazepam and chloridazepoxide were more linear.

Anti-Anxiety Agents↗
PubMed1975

Psychiatric diagnosis and EEG-evoked response relationships.

This study was conducted to determine whether the patterning of EEG and somatosensory evoked response (SER) variables, as determined by the correlations between them, differs with respect to psychiatric diagnosis. Subjects were 43 nonpatients and 90 psychiatric inpatients. SER modified recovery function recordings provided 36 variables, reflecting amplitude and its variations with different stimulus conditions. A 10-min left parietal EEG was quantitatively analyzed to give mean amplitude and frequency and variability measures. Correlations between EEG and ER variables were compared both for unmatched groups of nonpatients, schizophrenics, psychotic depressions, and nonpsychotics and for smaller age and sex-matched diagnostic groups. The results revealed a number of correlation differences between clinical groups. The nature of the differences suggested diagnostic specificity for EEG-ER patterning, which may provide a new, psychiatrically relevant electrophysiological variable.

Adolescent↗
PubMed1975

A comparison of the discriminable CNS effects of ketamine, phencyclidine and pentobarbital.

In a shock-escape T-maze task, rats were required to learn drug discriminations involving various doses of pentobarbital, phencyclidine and ketamine. Repeated training sessions were administered. Typically a right turn in the maze was required during drug sessions and a left turn was required during alternate no drug sessions. Results were as follows: 1. Linear dose effect curves relating discriminability (sessions to criterion) to dosage were obtained with all three drugs. 2. Phencyclidine and ketamine produced much more 'response randomization' than did pentobarbital at doses matched for discriminability. 3. Phencyclidine and ketamine tended to mimic each other's discriminable effects, but neither mimicked or was mimicked by pentobarbital. 4. Drug vs drug training demonstrated that phencyclidine and ketamine differed discriminably from each other.

Animals↗