TH and Parkinson disease: Differences in TH expression, TH phosphorylation, and DA tissue content exist between the SN and striatum under normal [84,141,148,149,150,151,157,158], PD- [18,20,22,57,58,66,67,68,69,72,159], or aging-related conditions [54,61,84,148,149,151,159,160,161], both in animal models and in human PD [20,66,67,68,69,159] and aging [159,161,162,163].