774 occurred in a comparable manner independent of initial drug order during self-administration. The data for these two subgroups were therefore combined and averaged for each drug–cue condition (i.e., animals presented with the cocaine-paired scent were compared to the animals pre- sented with the heroin-paired scent independent of the initial order of drug exposure). Separate mixed two-factor (Group × Trial) ANOVAs were employed to analyze the behavioral effects of presenting subjects with the heroin or cocaine cue at different times after drug self-administration had terminat- ed. The impact of the cocaine-paired cue was assessed by separate ANOVAs on start latencies, run times, and retreats. The same was the case for the subjects presented with the heroin cue. For each ANOVA, there was a single independent factor (Group; i.e., different animals were tested at different withdrawal periods; 7, 14, or 21 days of extinction) and a single repeated measures factor (Trial) where cue-induced performance on test day was compared to the mean baseline performance over the prior five extinction trials. The ANOVAs on start latency data did not yield any significant main effects or interactions for either the heroin or cocaine cue (p > 0.05). Thus, neither the number of days of withdrawal nor the presentation of a drug-paired cue altered the animals’ time to initiate responding relative to baseline/extinction performance. In contrast, statistically reliable effects were identified for both run times and retreats (Figs 2 and 3, respectively). For animals presented during extinction with the cocaine cue (Fig. 2, left side), there was a statistically reliable main effect of Trial (F(1, 23) = 4.786, p = 0.04)—animals ran Fig. 2 Mean (+SEM) run times upon presentation of a cocaine- or heroin-paired olfactory cue presented to different groups of animals after 7, 14, or 21 days of non-reinforced extinction trials. Cue-induced responding (shaded bars) on test day are compared to an extinction baseline (open bars) computed as the average of the five preceding extinction trials Psychopharmacology (2011) 214:769–778 Fig. 3 Mean (+SEM) retreat frequency on test day (shaded bars) compared to baseline (open bars) of different groups of animals exposed to a cocaine- or heroin-paired cue after 7, 14, or 21 days of extinction faster (exhibited shorter run times) in the presence of the cocaine-paired cue than they did during prior non-cued extinction trials. There was no main effect of Group nor a Group × Trial interaction. The comparable ANOVA computed on the run time data for animals presented with the heroin cue (Fig. 2, right side) yielded no statistically significance results. For retreat frequency (Fig. 3), the ANOVAs yielded results comparable to those computed on run times. For the cocaine-cued animals, (Fig. 3, left side), retreats were significantly reduced in the presence of the cue (test day) compared to non-cued extinction trials (i.e., there was a strong main effect of Trial: F(1, 23) = 10.496, p = 0.004). There was again no effect of Group, and while the Group × Trial interaction was marginal (p < .07), it failed to reach statistical significance. As was the case for run times, the ANOVA computed on the data from the heroin- cued animals (Fig. 3, right side) revealed no statistically reliable effects (p > 0.05). Conditioned place preference An analysis of preconditioning baseline data confirmed that, in all three groups, there were no inherent preferences for one side of the apparatus relative to the other (Bonferroni-corrected two-tailed repeated-measures t tests). After place conditioning, both of the reinforcers that were employed in the prior runway study (1.0 mg/kg cocaine and 0.1 mg/kg heroin) produced statistically reliable increases (assessed by Bonferroni-corrected t tests) in time spent in the drug-paired environment compared to that in the vehicle-paired environment: cocaine (t(9) = 3.480, p < 0.01) and heroin (t(11) = 4.666, p < 0.001). When the two rein- forcers were directly compared against each other within the same animal, there was a slight, but non-significant