Extracellular striatal dopamine levels in response to cocaine and VU0152100 in D1-M4-KO mice. Cocaine (30 mg/kg, s.c., black circles; n=5) significantly increased extracellular dopamine compared to saline (white circles; n=4). Pretreatment with VU0152100 (1 mg/kg, i.p., grey circles; n=5) appeared to only partially reduce the effect of cocaine in D1-M4-KO mice. ##p<0.01 vs. veh-sal in D1-M4-KO mice (two-way repeated measures ANOVA followed by Bonferroni-corrected pairwise comparisons). The insert shows dopamine levels as AUC from 60–120 min in WT and D1-M4-KO mice after saline (veh-sal), cocaine (veh-coc) or cocaine+VU0152100 (VU-coc) treatment. ##p<0.01, ###p<0.001 vs. veh-sal within genotype, **p<0.01, ***p<0.001 vs. veh-coc within genotype, $$p<0.001 vs. same treatment group between genotypes (two-way ANOVA followed by Bonferroni-corrected pairwise comparisons; n=4–5). All data represent group mean ± SEM.