Environmental influences upon morphine or d-amphetamine induced suppression of operant behavior

Rats trained in an operant chamber to lever press for food on a FR-30 schedule of reinforcement were given 1.0 mg d-amphetamine sulfate (IP)/kg. Injection of the drug followed by immediate placement into the operant chamber resulted in a disruption of behavior, after a 10 min latency, which lasted for approximately 25 min. Removal of the animals from the chamber soon after the onset of behavioral disruption and replacement into the chamber as soon as 2.5 min later resulted in resumption of lever pressing almost immediately. Animals left in their home cages for 10 min after being injected with d-amphetamine and then placed in the operant chamber started to bar-press almost immediately, taking an average of 4 min to receive 5 reinforcers (150 responses). A second group of rats, maintained on the same schedule of reinforcement, showed similar striking effects of delayed placement after injection with 10 mg morphine sulfate/kg. The 10 min delay resulted in a significant reversal of the behavioral suppression observed at a comparable time after injection of morphine and immediate placement into the operant chamber.