Phencyclidine established as a discriminative stimulus using ethanol as a reinforcer

Long-Evans hooded rats were initially trained to lever press, in standard, operant conditioning chambers, according to a fixed-ratio 1 (FR1) reinforcement schedule using 0.06 ml deliveries of 8% w/v ethanol as the reinforcer, during daily Monday-Friday, 1 h experimental sessions. Next, experimental sessions were reduced to 0.5 h, the FR value was increased to 5, and the rats were trained to discriminate 2.0 mg/kg s.c. phencyclidine (PCP) from saline vehicle using standard, drug discrimination training procedures, with 8% ethanol as the reinforcer. Following training, dose-response tests with PCP (0.1–4.0 mg/kg), ketamine (0.1–18 mg/kg), dexoxadrol (1.0–5.6 mg/kg) and morphine (1.0–9.0 mg/kg) were conducted. More PCP-lever presses were emitted than saline-lever presses at several doses of PCP, ketamine, and dexoxadrol, indicating generalization from the 2.0 mg/kg PCP stimulus. When morphine was tested, more saline-lever than PCP-lever presses were made, and percent PCP-lever pressing never exceeded an average of 12% at any dose tested. This study demonstrates that one drug of abuse, PCP, can serve as a discriminative stimulus when another drug of abuse, ethanol, serves as the reinforcing stimulus, and is the first explicit laboratory demonstration of drug discriminative stimulus control during drug self-administration.