EFFECTS OF DRUG DISCRIMINATION HISTORY ON THE GENERALIZATION OF PENTOBARBITAL TO OTHER DRUGS

In pigeons trained to discriminate between pentobarbital and saline, p entobarbital, amobarbital and diazepam substituted for pentobarbital, whereas phencyclidine (PCP) substituted in part for pentobarbital and d-amphetamine, morphine and drug vehicles did not substitute. After mo rphine replaced pentobarbital as the training drug (group A), morphine , pentobarbital and diazepam substituted, PCP substituted in part, hut not d-amphetamine, haloperidol and vehicles. After d-amphetamine repl aced pentobarbital as the training drug (group B), d-amphetamine, pent obarbital and diazepam substituted, PCP substituted in part, but not h aloperidol, morphine and vehicles. Next, morphine and d-amphetamine we re reversed as training drugs for the two groups. In group A, morphine , d-amphetamine, pentobarbital and diazepam substituted, PCP substitut ed in pall, but not haloperidol and vehicles. Similar effects were obs erved in group B. Next, birds in group A were reinforced for responses on the drug key (red key) after d-amphetamine and an the previous sal ine key (green key) after pentobarbital. In group B, morphine continue d as the training drug for the red key, whereas responses on the green key were reinforced after pentobarbital. In group A, d-amphetamine, m orphine, d-pentazocine and to some extent PCP, produced responding on the red key, whereas pentobarbital, diazepam, haloperidol and the vehi cles produced responding on the green key. Similar results were obtain ed in group B. Finally, responses were reinforced on the green key aft er pentobarbital and on the red key after saline. Group B did not lear n this discrimination. In group A, responding occurred on the red key after d-amphetamine, morphine, haloperidol and vehicles, in part after d-pentazocine, but not after pentobarbital, diazepam and PCP. These e xperiments show that drug stimuli can continue to exert stimulus contr ol over behavior for long periods, even when training with several oth er drug stimuli intervenes between tests, and the experiments also sho w that through sequential training procedures multiple drugs can serve as discriminative stimuli for the same response, even when these drug s are from different phamacological classes.