The role of fentanyl training dose and of the alternative stimulus condition in drug generalization.

Different groups of rats were trained to discriminate fentanyl (F) (0.03, 0.02, or 0.01 mg/kg) from saline or to discriminate 0.03 mg/kg fentanyl (F) from alternative stimulus conditions (saline, 0.15 mg/kg nicotine, or 0.01 mg/kg F). When percentage of responses on the drug lever and percentage of time spent responding on the drug lever were used as dependent variables, it was found that training dose and alternative stimulus condition both affected the ED50 and the slope of the F generalization gradient. ED50 and slope values based on group data were not significantly different from values based on individual data. Differences between from values based on individual data. Differences between the results of the first and second 2.5-min period of the extinction test were not significant. ED50 and slope values were unaffected by the preceding training session, except in the group trained to discriminate 0.03 from 0.01 mg/kg F. A lever selection measure showed a significant effect of alternative stimulus condition on ED50 values only. Training dose and alternative stimulus condition also affected the generalization to morphine. Under none of the conditions explored in this study did generalization occur to amphetamine or nicotine. The results are discussed in terms of the relative nature of drug generalization.