Figure 6.

Effect of dopamine receptor agonists on the locomotor activity of M₄^−/− receptor mutant mice and their wild-type littermates. Mice of the indicated genotypes were injected s.c. with vehicle (Veh) or increasing doses of the following dopamine receptor agonists: apomorphine (nonselective), SKF 38393 (D1-type selective), and quinpirole (D2-type selective). Locomotor activity measurements were carried out as described in Materials and Methods. Data (number of total photobeam breaks during a 1-hr observation period) are given as means ± SEM (n ≥ 14 for each dose and genotype). ∗, P < 0.05 (Newman–Keuls post hoc comparison).