Sensitization to AMPH- and METH-induced locomotion (A) and rearing (B), represented as the difference between activity during the 60-min period following the challenge (day 11) and acute (day 2) injections (n = 8 rats/group). Statistical analysis, which was performed on the raw data from the two injection days (see Results), revealed statistically significant sensitization for locomotion in all groups except the 0.5 mg/kg METH, Sā group; sensitization to drug-induced rearing was only evident in the 0.5 mg/kg AMPH, S+ and the 1.0 mg/kg METH, S+ groups. The only significant difference in the magnitude of sensitization was between the 0.5 and 1.0 mg/kg dose of METH in the absence of the stimuli (Sā). * p < 0.05