PENTOBARBITAL DISCRIMINATION AND GENERALIZATION TO OTHER DRUGS UNDER MULTIPLE FIXED-RATIO FIXED-INTERVAL SCHEDULES

Pigeons were trained to discriminate 5 mg/kg pentobarbital from saline under several multiple fixed-ratio fixed-interval schedules of food p resentation. The following schedules were studied: multiple fixed-rati o 40 fixed-interval 18 s (mult FR40 FI18), mult FR10 FI18 s, mult FR10 FI180 s and mult FR90 FI10 s. After responding stabilized under each multiple schedule, generalization curves were determined for pentobarb ital, amobarbital, diazepam, phencyclidine and d-amphetamine. Pentobar bital generated dose-dependent increases in responding under all sched ule components; however, there was more responding on the drug key aft er low doses of pentobarbital under FI components than under FR compon ents, except for the FR90 component of the mult FR90 FI10 schedule. Th is tendency for more responding on the drug key after low doses of pen tobarbital under FI components than under FR components generally was observed for low doses of all of the drugs. Examination of data from i ndividual subjects revealed that there was a greater tendency for bird s to distribute responding on both keys (mixed responding) under FI co mponents than under FR components, where responding after each dose wa s confined largely to one of the two response keys. Analysis of local rates of responding within the FI component of the schedules showed th at responding under the FT components developed the typical FI scallop at all FI-component durations. These data suggest that FI schedules w ith values between 10 and 180 s generate similar dose-effect curves wi th higher rates of responding on the drug key after low doses of drugs than under FR schedules with low response requirements; however, unde r schedules with higher FR requirements, the dose-effect curves for so me drugs begin to look more like those under FI schedules.