Figure 8.

Responses of fentanyl‐treated mice to acute cocaine administration. Open field tests were performed following acute cocaine (5 and 15 mg/kg) administration to investigate the effect of chronic fentanyl treatment on the response to cocaine (A). Time‐course of distance traveled (B, F), vertical activity (C, G), time spent in the central area (D, H), and stereotypic counts (E, I) are shown. Effects of acute administration of low‐dose cocaine (5 mg/kg) did not differ significantly among the three groups (B‐E). In mice with acute administration of high‐dose cocaine (15 mg/kg), cocaine‐induced hyperactivity and stereotypic counts were attenuated compared with control mice (F, I). Data are presented as means ± SEM for the indicated numbers of animals. The P values indicate treatment effect in two‐way repeated measures ANOVA. The asterisk and number sign indicate a nominally significant difference between the high‐dose group and control group or the low‐dose group and control group (P < 0.05)