TH and Parkinson disease: TH immunofluorescence analysis of striatum and substantia nigra indicated that TH was significantly decreased in the ipsilateral side striatum and substantia nigra of PD, LID, and NLID rats, suggesting that dopaminergic neurons in the substantia nigra were lost and dopamine in the striatum was decreased after striatal 6-OHDA injection, while there was no significant change in the contralateral side (Figure 1F,G).