Horizontal locomotor activity after a single administration of saline (A), 5 mg/kg methamphetamine (B) and 10 mg/kg methamphetamine (C) in mice pretreated with 10 mg/kg PTIQ or vehicle (i.e. saline). Values are shown as the mean ± SEM (n = 8). METH, methamphetamine; PTIQ, 4-phenyl-1,2,3,4-tetrahydroisoquinoline. *P < 0.05, compared with saline-pretreated mice (post-hoc Bonferroni/Dunn test).