The x axis describes AMPH dose converted from mg/kg to µmol/kg. The y axis is apparent Km ((Km)app or postdrug Km) determined from the kinetic analysis shown in Figure 4. r is the coefficient for the linear regression. (Km)app values for cocaine and nomifensine were taken from Wu et al. (2001a) after converting to µmol/kg (original drug dose: 40 and 10 mg/kg i.p., respectively). Abbreviations: AMPH, amphetamine; NOM, nomifensine; COC, cocaine; DS, dorsal striatum; VS, ventral striatum.