Fig. 3.

Morphine-induced place preference in wild-type (WT) and dopamine D₃receptor knock-out (D₃KO) mice.A, Dose–response curve for the morphine-induced place preference in WT and D₃KO mice. Each pointrepresents the mean conditioning score with SEM of 8–10 mice.B, Effect of the selective μ-opioid receptor antagonist CTOP on morphine-induced place preference in D₃KO mice. CTOP (100 pmol per mouse) or saline was pretreated intracerebroventricularly 10 min before subcutaneous administration of morphine. Each column represents the mean conditioning score with SEM of 8–10 mice. *p< 0.05 versus saline group.