DRD2 and Parkinson disease: Using stereological approaches and single-neuronal injections performed on striatal sections from sham and 6-hydroxydopamine (6-OHDA)-lesioned double BAC transgenic mice (Drd1a-tdTomato/Drd2-EGFP), we show that the D1/D2 MSNs are affected differently than the D1 and D2 MSNs by striatal DA deafferentation that characterizes PD.