Effect of AMPH (10 mg/kg., i.p.) on extracellular DA and DOPAC measured by microdialysis in the striatum of freely moving mice. Open circles are data from wild-type mice (DAT +/+), and filled circles are data from homozygote DAT knockout mice (DAT −/−). A, Extracellular DA is increased 8- to 10-fold in wild-type mice after AMPH, whereas there is no significant difference in DA levels after AMPH in homozygotes.B, Extracellular DOPAC is decreased to approximately the same degree in both wild-type and homozygote mice. Concentrations of DOPAC in dialysates were 12.3 ± 3.5 pmol/20 μl for DAT +/+ and 5.3 ± 1.8 pmol/20 μl for DAT −/− mice. Results are the mean ± SEM of six independent experiments.