Figure 3.

(A) Methamphetamine-induced locomotor sensitization in wild-type (WT) and DA-βcat KO mice. Cumulative 30-min locomotor response to methamphetamine in WT (n = 16) and KO (n = 16) mice at different days after injection. (Saline) Day 1 of saline injection. D1–D5 represent five consecutive days of methamphetamine injections. C7 and C30 represent a challenge of methamphetamine injection 7 and 30 d after withdrawal. Methamphetamine exposure induced significant sensitization in both WT and DA-βcat KO mice. Induction of locomotor sensitization was less robust in KO animals, and maintenance of sensitization after a challenge injection was significantly reduced in DA-βcat KO mice. Two-way ANOVA; (*) P < 0.05, (**) P < 0.01. (B) Basal locomotor activity was measured every hour for 24 h starting at 10:00 am. There were no significant differences between the genotypes. Two-way ANOVA; P > 0.05.