Cocaine- and methylphenidate-conditioned place preferences in DAT knockout mice. (A) Conditioned place preference induced by cocaine in wild type (+/+, open bars) and heterozygous (+/−, gray bars) and homozygous (−/−, black bars) DAT knockout mice. Time scores shown represent differences between post-conditioning (Post) and pre-conditioning (Pre) time spent in the cocaine-paired environment. Wild-type mice displayed significant place preference associated with 5 and 10 mg/kg cocaine, whereas heterozygous and homozygous animals showed significant place preference associated with 10 mg/kg cocaine. ∗ P < 0.05 vs. saline-injected group by ANOVA; n = 8–23 mice per genotype. The following data show the real mean time scores ± SEM (sec) of pre-conditioning (Pre) and post-conditioning (Post) sessions on initially nonpreferred compartment in each genotype. Wild-type [Pre/Post], heterozygote [Pre/Post], homozygote [Pre/Post]: saline ([411.4 ± 30.0/382.8 ± 50.4], [387.0 ± 36.0/392.6 ± 47.2], [408.6 ± 29.1/364.6 ± 65.0]), cocaine 5 mg/kg ([304.1 ± 35.0/489.0 ± 67.8], [354.4 ± 37.7/495.9 ± 70.7], [348.2 ± 29.1/455.0 ± 114.8]), cocaine 10 mg/kg ([336.7 ± 25.6/526.0 ± 59.2], [327.9 ± 26.0/655.9 ± 64.9], [328.7 ± 26.9/597.5 ± 50.5]). (B) Conditioned place preference induced by methylphenidate in wild type (+/+, open bars) and heterozygous (+/−, gray bars) and homozygous (−/−, black bars) DAT knockout mice. Time scores shown represent differences between post-conditioning (Post) and pre-conditioning (Pre) time spent in the cocaine-paired environment. All three genotypes displayed significant place preference associated with 5 mg/kg methylphenidate. ∗∗, P < 0.01; ∗, P < 0.05 vs. saline-injected group by ANOVA; n = 12–21 mice per genotype. The following data show the real mean time scores ± SEM (sec) of pre-conditioning (Pre) and post-conditioning (Post) sessions on initially nonpreferred compartment in each genotype. Wild-type [Pre/Post], heterozygote [Pre/Post], homozygote [Pre/Post]: saline ([411.4 ± 30.0/382.8 ± 50.4], [387.0 ± 36.0/392.6 ± 47.2], [408.6 ± 29.1/364.6 ± 65.0]), methylphenidate 5 mg/kg ([356.6 ± 34.6/562.5 ± 68.3], [367.4 ± 22.1/552.6 ± 56.0], [376.6 ± 38.7/533.0 ± 77.2]).