KCC2 function is altered specifically in D2 MSNs of R6/2 mice. A, Image showing infection site of AAV5-mCherry in the dorsolateral striatum. B, Top, Representative images of substance P expression in Drd1-Cre x R6/2 mice injected with AAV5-mCherry. B, Bottom, Representative images of A2A-receptor expression in Drd2-Cre x R6/2 mice injected with virus containing mCherry. Scale bar, 10 µm. C, Example IV curves of representative IPSCs (right) induced by electrical stimulation in the presence of glutamate blockers CNQX (10 µM) and AP-V (50 µM) at different holding potentials from −90 to −20 mV in whole-cell patch-clamp configuration with [Cl−]i = 10 mM in WT D1 MSNs (black), R6/2 D1 MSNs (pink), WT D2 MSNs (purple), and R6/2 D2 MSNs (blue). D, Summary of individual EGABA recordings obtained from all IV curves in WT D1 MSNs (n = 10), WT D2 MSNs (n = 10), R6/2 D1 MSNs (n = 11), and R6/2 D2 -MSNs (n = 11) with [Cl−]i = 10 mM (p = 0.0002; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,38) = 17.57). E, RMP from WT D1 MSNs (n = 28), WT D2 MSNs (n = 28), R6/2 D1 MSNs (n = 30), and R6/2 D2 MSNs (n = 31) with [Cl−]i = 10 mM (p = 0.4381; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,112) = 0.6057). F, Cl− driving force through GABAARs from WT D1 MSNs (n = 10), WT D2 MSNs (n = 10), R6/2 D1 MSNs (n = 11), and R6/2 D2 MSNs (n = 11) with [Cl−]i = 10 mM (p = 0.1674; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,38) = 1.981). G, Synaptic conductance from WT D1 MSNs (n = 9), WT D2 MSNs (n = 9), R6/2 D1 MSNs (n = 9), and R6/2 D2 MSNs (n = 9) with [Cl−]i = 10 mM (p = 0.4185; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,32) = 0.6717). H, Similar to D but with [Cl−]i = 30 mM, WT D1 MSNs (n = 10), WT D2 MSNs (n = 13), R6/2 D1 MSNs (n = 11), and R6/2 D2 MSNs (n = 12; p = 0.0048; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,42) = 8.868). I, Similar to E but with [Cl−]i = 30 mM, WT D1 MSNs (n = 10), WT D2 MSNs (n = 13), R6/2 D1 MSNs (n = 11), and R6/2 D2 MSNs (n = 12; p = 0.7806; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,42) = 0.07861). J, Similar to F but with [Cl−]i = 30 mM, WT D1 MSNs (n = 10), WT D2 MSNs (n = 13), R6/2 D1 MSNs (n = 11), and R6/2 D2 MSNs (n = 12; p = 0.0459; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,42) = 4.234). K, Similar to G but with [Cl−]i = 30 mM, WT D1 MSNs (n = 10), WT D2 MSNs (n = 13), R6/2 D1 MSNs (n = 11), and R6/2 D2 MSNs (n = 11; p = 0.9652; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,41) = 0.001923). L, Similar to D but using gramicidin-perforated patch-clamp configuration, WT D1 MSNs (n = 14), WT D2 MSNs (n = 11), R6/2 D1 MSNs (n = 12), and R6/2 D2 MSNs (n = 11; p < 0.0001; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,44) = 35.29). M, Similar to E but using gramicidin-perforated patch-clamp configuration, WT D1 MSNs (n = 13), WT D2 MSNs (n = 11), R6/2 D1 MSNs (n = 12), and R6/2 D2 MSNs (n = 11; p = 0.5458; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,43) = 0.3708). N, Similar to F but using gramicidin-perforated patch-clamp configuration, WT D1 MSNs (n = 13), WT D2 MSNs (n = 11), R6/2 D1 MSNs (n = 12), and R6/2 D2 MSNs (n = 11; p = 0.0077; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,43) = 7.821). O, Similar to G but using gramicidin-perforated patch-clamp configuration, WT D1 MSNs (n = 13), WT D2 MSNs (n = 11), R6/2 D1 MSNs (n = 12), and R6/2 D2 MSNs (n = 11; p = 0.1386; two-way analysis of ANOVA followed by Sidak’s multiple-comparisons test, F(1,43) = 2.277). For all panels, the circles indicate the values from single samples, and all columns represent mean ± SD. *p < 0.05, **p < 0.01 ***<0.001. For a comparison of passive membrane properties of D1 and D2 MSNs in R6/2 and WT mice, see Extended Data Table 3-1.