Whole-cell voltage-clamp recording

Five adult Drd1-EGFP Btbd9 KO (male: n=2; female: n=3) and 6 Drd1-EGFP littermates (male: n=2; female: n=4) with an average age of 2 months were sacrificed, and their brains were rapidly removed. Coronal corticostriatal slices were used for recording spontaneous postsynaptic currents (sEPSC) for 5 mins and evoked currents from EGFP-positive MSNs. Recordings were done in the whole-cell voltage-clamp (MSN neurons were held at −70 mV) configuration, with Cesium methane sulfonate-based internal solution (in mM): 125 Cesium methane sulfonate, 8 NaCl, 10 HEPES, 4 MgATP, 0.3 NaGTP,0.2 EGTA, 0.1% Biocytin, pH 7.2. Picrotoxin (50μM; GABAa receptor blocker) was added in the artificial cerebrospinal fluid (ACSF). Paired-pulse ratios were measured by a glass electrode (3–5 MΩ) filled with the ACSF, which was placed in the white matter around 40 μm away from the recorded region to evoke currents. Currents were obtained from the dorsal-lateral striatal MSNs close to the white matter. The position of the glass electrode was carefully adjusted so as not to evoke polysynaptic responses. Two pulses (20 Hz) were given 10 times for every 10 s with 50 ms inter-pulse interval.