To maximize nuclei viability, we followed a harvesting protocol similar to the one outlined in Davenport et al.70 Briefly, animals were initially sedated with ketamine (15 mg/kg IM), and then ventilated and further anesthetized with isoflurane. The animals were transported to a surgery suite and placed in a stereotaxic frame (Kopf Instruments). We removed the calvarium and then perfused the circulatory systems with 3-4 liters of ice cold artificial cerebrospinal fluid (ACSF; 124 mM NaCl, 5 mM KCl, 2 mM MgSO4, 2 mM CaCl2, 23 mM NaHCO3, 3 mM NaH2PO4, 10 mM glucose; pH 7.4, osmolarity 290–300 mOsm) oxygenated with 95 % O2:5 % CO2. We then opened the dura and removed the brain. We sliced on the custom brain matrix into 4 mm slabs along the rostral-caudal axis. We removed three striatal regions – the caudate nucleus, putamen, and ventral striatum – under a dissection microscope for nuclei isolation. Monkeys B and K, for FISH, were perfused with 4% paraformaldehyde (PFA, Sigma-Aldrich, Cat# P6148) in phosphate buffered saline (PBS, Fisher scientific, Cat# BP243820) supplemented with 10% sucrose (Sigma-Aldrich, Cat# S8501). The brain was post-fixed with 4% PFA and cryopreserved with a gradient of sucrose (10%, 20%, 30%) in PBS.
