Effect of partial reinforcement on tolerance to morphine-induced analgesia and weight loss in the rat

The effect of partial reinforcement on the development of tolerance to morphine-induced analgesia and weight loss was examined. Groups of rats were presented a distinctive set of environmental cues on several occasions. For one group of rats, morphine (40 mg/kg) was injected each time the cues were presented (morphine--continuous reinforcement). For a second group of rats, morphine was injected only following one of every four cue presentations …