TH and Parkinson disease: Of note, in an AAV-α-syn-induced rat PD model, we observed large amounts of AAV 9-α-syn infected TH+ neurons and a certain amount of AAV 9-α-syn infected Iba-1+ microglia in the SN (Fig. 7i), suggesting that there might be two reasons for causing α-syn-induced microglia inflammation by mGluR5 degradation: (1) α-syn released from AAV 9-α-syn infected neurons could be engulfed by microglia, resulting in neuroinflammation, and (2) AAV 9-α-syn infected microglia could lead to neuroinflammation.