Operant place conditioning measures examined using morphine reinforcement

A new place conditioning procedure for assessing drug reinforcement, based on drug administration following chamber entry, was examined in rats and compared to conditioned place preference (which is based on chamber exposure of drugged animals). Besides relative time subsequently spent in the morphine chamber, choices between the drug and nondrug chambers were recorded during the time test and during a discrete-trials choice test. In some experiments, either choices or latencies of chamber entry were recorded during training. Most choice and latency measures showed larger reinforcement effects than did time spent. Placement training was somewhat less effective than operant place conditioning overall, but produced significant time differences and discrete-trial choices in four of five groups. With intravenous morphine, the lengthy chamber exposures generally used in conditioned place preference were unnecessary.