P2RX4 and Parkinson disease: The relative expression of P2X4R in the PD group was significantly higher than that in the normal control group, and the number of TH positive DA neurons in the SN decreased inversely; the reduction of TH positive DA neurons in the SN was significantly more severe in the P2X4R-OE + 6-OHDA group compared to P2X4R-NC + 6-OHDA group.