Stability of the stimulus properties of drugs over time.

Three separate groups of rats were trained to discriminate the stimulus effects of either 600 mg/kg ethanol (n = 5), 0.8 mg/kg d-amphetamine (n = 8) or 1.0 mg/kg 1-(3-trifluoromethylphenyl)piperazine (TFMPP; n = 10). Once criterion performance was attained, each group was tested with various doses of the drug used in their training, thus allowing for calculations of dose-response curves and ED50 values. A second dose-response relationship was established at a later time, averaging over a year later, and this result was compared to the initial curve. In none of the three groups was there substantial change in the sensitivity of the rats to different doses of the drug used in training as indicated by similar ED50 values. These results suggest that the drug discrimination procedure is stable over a period of continuous training and testing.