Increasing 5-HT6 receptors in NAcSh iMSNs but not in the dMSNs decreased operant cocaine SA on an FR1 schedule. (a) Daily FR1 cocaine infusions (mean±SEM) for Dyn-GFP (n=7) and Dyn-5-HT6 (n=8) (two-way ANOVA, F(1,13)=0.87, p=0.37). (b) Average FR1 cocaine infusions during the last 3 days of training (mean±SEM) for Dyn-GFP (n=7) and Dyn-5-HT6 (n=8; t-test, p=0.87). (c) Daily FR1 cocaine infusions (mean±SEM) for Enk-GFP (n=12) and Enk-5-HT6 (n=14) (two-way ANOVA, F(1,24)=5.32; p=0.03). (d) Average FR1 cocaine infusions during the last 3 days of training (mean±SEM) for Enk-GFP (n=12) and Enk-5-HT6 (n=14) (t-test, p=0.015). *p<0.05.