Fig. 4.

Locomotor activating effects of fentanyl/naltrexone mixtures. Abscissa: Dose fentanyl in mg/kg. The naltrexone dose was proportional to the fentanyl dose as indicated by fixed fentanyl/naltrexone (FENT/NTX) proportions for each mixture. Ordinate: Locomotor counts per 60 minutes. All points show mean±S.E.M. for N = 12 mice, and filled symbols indicate a significant difference compared with vehicle within each mixture as determined by repeated-measures one-way ANOVA followed by the Holm-Sidak post hoc test, P < 0.05. Statistical results are shown in Table 2.