Fig. 5.

Blocking D₁ or D₂ receptors in mPFC impaired stimulus discrimination. (A) Schematic diagram showing bilateral cannula placement for mice receiving injections of Sal (n = 6), D₁⁻ (n = 8), or D₂⁻ (n = 9) in mPFC (black, green, and red, respectively). (B) Mice learned a two-tone discrimination task (CS⁺, rewarded; CS⁻, unrewarded). (Bottom) Traces show typical licking behavior on d8 for a mouse in each group (CS⁺, thick lines; CS⁻, thin dotted lines), using the same color code as in A. (C and D) Progression of learning is shown across sessions (x axis) as the average percentage of rewarded CS⁺ presentations (C) and CS⁺ vs. CS⁻ discrimination score (D). Data are presented as mean (solid circles) ± SEM (error bars), with the same color code as in A. Note that although the percentages of rewarded CS⁺ were similar between groups, discrimination (disc.) scores were significantly different [F(2,19) = 6.924, P = 0.015; Sal 0.59 ± 0.09 vs. D₁⁻ 0.22 ± 0.04, t(12) = 3.53, P = 0.008; vs. D₂⁻ 0.19 ± 0.04, t(13) = 3.99, P = 0.003; Bonferroni corrected post hoc t tests on d10]. Several mice receiving D₁⁻ or D₂⁻ receptor antagonists (n = 4 and n = 6, respectively) were further trained without drug infusion (yellow shaded area in D) until they reached the same discrimination level as controls (D₁⁻, 0.59 ± 0.11; D₂⁻, 0.59 ± 0.09). (E) CS⁺ vs. CS⁻ discrimination scores for sessions where these mice received alternating injections of Sal and D₁⁻ or D₂⁻. No difference was observed between treatments [Sal vs. D₁⁻: 0.62 ± 0.05 and 0.61 ± 0.04, t(14) = 0.04, P = 0.49; Sal vs. D₂⁻: 0.58 ± 0.04 and 0.54 ± 0.05, t(22) = 0.87, P = 0.21]. Data are presented as mean ± SEM across mice and sessions.