Western Blotting.

Western blot analysis was performed as reported previously (61). Mice were perfused transcardially with cold 0.9% saline solution under deep anesthesia. Whole striatum and midbrain containing the VTA and SNc were dissected. Tissues were homogenized in RIPA lysis buffer (Cell Signaling Technology), and the protein concentration for each sample was quantified with a Bio-Rad Protein Assay. Complete descriptions of Western blotting methods are provided in SI Appendix, Experimental Procedures.