Drug-cue conditioning to external stimulus conditions.

Rats were trained to discriminate 0.04 mg/kg fentanyl from saline in a 2-lever procedure, and to discriminate 10 mg/kg pentobarbital from saline in a maze procedure. Stimulus generalization experiments in rats trained in this double discrimination indicate that the internal cues produced by these training drugs can be conditioned to the external stimulus conditions associated with the different discrimination procedures.