Fig. 4. Lack of CIN D2Rs decreases delay, but not probabilistic, discounting.

A ChAT-IRES-Cre mice were crossed to Drd2^loxP/loxP mice to obtain mice lacking D2Rs in CINs (CIN-D2KO). CIN-D2KO and control Drd2^loxP/loxP mice increased preference for the large reward with training in the absence of delays to either reward option (session block effect: F _{(6, 78)} = 9.206, p < 0.0001; Tukey’s test showed significant within session effects in both groups between session blocks 1 and 7 (adjusted p values < 0.001), but no effect of genotype: F _{(1, 13)} = 1.651, p = 0.2213, and no genotype x session block interaction: F _{(6, 78)} = 0.607, p = 0.7237). B Compared to Drd2^loxP/loxP mice, CIN-D2KO mice showed greater preference for the large reward at longer delays (decreased delay discounting). Delay effect: F _{(5, 65)} = 72.56, p < 0.0001; genotype x delay: F _{(5, 84)} = 4.756, p < 0.001, * denotes significant interaction. Drd2^loxP/loxP, n = 8 (5 females, 3 males); CIN-D2KO, n = 7 (4 females, 3 males). One Drd2^loxP/loxP did not reach the criterion of ≥50% large choice on Session Block 7 and was excluded from the analysis. C, D Two-way ANOVA showed a significant main effect of delay on median press latency during forced trials (F _{(5, 65)} = 2.628, p = 0.0317), but no genotype effect: F _{(1, 13)} = 0.05419, p = 0.8195; genotype x delay interaction: F _{(5, 65)} = 0.5731, (p = 0.7203) or during free choice trials (genotype effect: F _{(1, 13)} = 0.5917, p = 0.4555; genotype x delay interaction: F _{(5, 65)} = 0.4477, p = 0.8135). No delay effect was seen during free choice trials (F _{(5, 65)} = 1.349, p = 0.2554). Values expressed as mean of median latencies ± S.E.M. E, F No significant group differences were observed in either distance traveled in 5-min bins over a 90-min period in an open field using a different cohort of mice (genotype effect: F (1, 14) = 0.1786, p = 0.6790; virus x delay interaction: F _{(17, 238)} = 0.7946, p = 0.7946), or in mean total distance traveled over 90-min (t ₍₁₄₎ = 0.4226, p = 0.6790). n = 8 mice per group (4 females, 4 males/ group). G Using a third cohort of mice, no significant group differences were found in the preference between reward options during training (when both options were given at 100% probability). Session block effect: F _{(6, 72)} = 0.7816, p = 0.5871; genotype (F _{(1, 12)} = 0.3588, p = 0.5603); genotype x session block interactions (F _{(6, 72)} = 0.9471, p = 0.4672) were observed. H No significant group differences were observed in probabilistic discounting in same cohort as in G (probability effect): F _{(6, 72)} = 14.26, p < 0.0001; genotype x probability: F _{(6, 72)} = 0.9263, p = 0.4814, Drd2^loxP/loxP, n = 8 (4 females, 4 males); CIN-D2KO, n = 6 (3 females, 3 males), 1 CIN-D2KO did not reach the criteria of ≥ 50% large choice on Session Block 7 and was excluded from the analysis.