Fig. 1.

Optimization of the METH-induced locomotor sensitization protocol. Part I: protocol for METH induction of locomotor sensitization used during the light (ZT 5–7) or dark (ZT 19–21) phases. Days −3 to −1: mice handling and saline injections. Days 1–6: VEH or METH pretreatments (1.2 mg/kg, i.p.) (2.4 and 4.8 mg/kg, i.p., not shown). Locomotor activity was collected at 5 min intervals for 2 hr after treatment on Days 1, 2, 3 and 6. Day 7–10: abstinence period: no treatments. Day 11: VEH or METH challenge (1.2 mg/kg, i.p.). Locomotor activity was recorded 30 min prior to and 2 hr following treatment. Part II: ordinates represents distance traveled in 5 min intervals as a function of time (abscissae) during development (A, B) and expression (C, D) of sensitization in VEH (○) and METH (■) pretreated mice. Pretreatments were administered at times indicated by arrows under the abscissae. The main effects of drug treatment were F_(1,14) = 27.58, P < 0.05 on Day 1 (A) and F_(1,14) = 32.98, P < 0.05 on Day 6 (B). The main effects of drug pretreatment was F_(1,6) = 6.36, P < 0.05 in mice challenged with VEH and F_(1,6) = 6.36, P < 0.05 in mice challenged with METH at times indicated by arrows under the abscissae. Significance values for the main effect of drug pretreatment are noted in the upper left corners of the graphs. *P < 0.05 when compared with the corresponding VEH 5 min bin (Bonferroni test).