MAPK signaling in Hdc-KO mice. (A) Phospho-T202/Y204-ERK1/2, measured in the dorsal striatum by immunostaining and cell counting by an observer blind to genotype and condition, was elevated in Hdc-KO mice and by amphetamine pretreatment (2-way ANOVA: main effect of genotype: F[1,4]=8.512, p=0.04; main effect of amphetamine: F[1,4]=96.28; p<0.001; genotype × amphetamine interaction: F[1,4]=26.59; p=0.007). (B) Elevated pT202/Y204-ERK1/2 was also seen by Western blotting in Hdc-KO mice and after amphetamine (Main effect of genotype: F[1,14]=10.47; p=0.006; main effect of amphetamine: F[1,14] =130.7; p<0.0001).