Generalization study with some narcotic and nonnarcotic drugs in rats trained for morphine-saline discrimination.

Rats were trained to lever-press on an FR-10 schedule for food reinforcement, and to respond differentially on two levers while discriminating the effects of morphine (10 mg/kg) injection from those of saline (1 ml/kg). Following discrimination training, the morphine stimulus was generalized to propoxyphene, methadone, fentanyl, and sulfentanyl in a dose-dependent manner, and saline was generalized to alcohol, pentobarbital, azaperone, clonidine, naloxone, and p-chloroamphetamine. p-Chloroamphetamine failed to block the morphine stimulus.