Increasing expression of 5-HT6 receptors in either the NAcSh dMSNs or the iMSNs does not affect operant responding on a PR schedule. (a) Cocaine infusions (mean±SEM) for the average of four PR sessions for Dyn-GFP (n=7) and Dyn-5-HT6 (n=7) (t-test, p=0.14). (b) Active lever presses (mean±SEM) for the average of four PR sessions for Dyn-GFP (n=7) and Dyn-5-HT6 (n=7) (t-test, p=0.26). (c) Cocaine infusions (mean±SEM) for the average of four PR sessions for Enk-GFP (n=12) and Enk-5-HT6 (n=14) (t-test, p=0.31). (d) Active lever presses (mean±SEM) for the average of four PR sessions for Enk-GFP (n=12) and Enk-5-HT6 (n=14) (t-test, p=0.53). (e) Increasing expression of 5-HT6 receptors the iMSNs increases preference for cocaine at a low dose. CPP score (cocaine time−saline time (s)) shown for rats with either Enk-GFP (n=8) or Enk-5-HT6 (n=8) (t-test, p=0.04). *p<0.05.