Immunohistochemical detection of tyrosine hydroxylase (TH), a marker of dopaminergic neurons [24], showed that striatal 6-OHDA injections resulted in a dramatic loss of dopaminergic neuron in the SN and dopaminergic neuron degeneration in the striatum of PD, LID, and NLID rats on the side ipsilateral to the injection site (Figure 1C). This evidence concerns the gene TH and Parkinson disease.