Fig. 4.

Cocaine dose-effect functions under a FR 1 schedule of reinforcement in wild-type (WT), heterozygous (HET), and DATki mice. Abscissa shows the unit dose of cocaine in saline (milligrams per kilograms per infusion); S designates saline. Ordinate shows the cocaine reinforcers earned per hour. Wild-type mice and heterozygous mice self-administered cocaine showing a typical inverted U-shaped dose-effect curve. The DATki mice never self-administered cocaine, but only showed suppression of behavior at high doses. ∗, p < 0.05; ∗∗, p < 0.01; ∗∗∗, p < 0.001 versus saline, two-sided paired-sample t test. Data are group means; bars represent one S.E.M.