DDC and Parkinson disease: The results showed that co-administration of AAV8-CDNF and AAV8-AADC or AAV8-CDNF alone could improve the rotation behavior of severely lesioned PD rats, compared with the control (AAV8-RFP) group, and the combination of AAV8-CDNF and AAV8-AADC resulted in the greatest extent of motor function recovery (P < 0.05, combination group v. s. AAV8-CDNF group).