TH and Parkinson disease: On the other hand, Porritt et al. (2000) found a new population of dopaminergic neurons expressing dopamine transporter (DAT) and tyrosine hydroxylase (TH) in post-mortem striatal samples of 10 PD patients, suggesting the existence of a potential endogenous compensatory mechanism in the PD striatum (Porritt et al., 2000; Table 2).