The levels of mRNA were measured by real-time quantitative PCR; mRNA levels were normalized to 18s RNA. Data represent means ± SEM of fold changes relative to the controls (n = 6 rats per group). Statistical significance was determined by ANOVA followed by protected least-squares difference (PLSD). $ = p <0.05, M vs. C; # = p < 0.05, M vs. M + S. Abbreviations are C, control; S, SCH23390; M, methamphetamine, and M + S, methamphetamine plus SCH23390.