Tyrosine hydroxylase (TH) is the rate-limiting enzyme and one of the most important factors in catecholamine biosynthesis including dopamine (DA). Any change in TH expression or activity has a significant impact on DA production and therefore is of great importance in the pathogenesis of Parkinson’s disease. Depending on the duration and intensity of the stimuli triggering TH modulation, this complex and multilevel process is categorized into short and long-term changes in which TH synthesis and activity, respectively, are affected. In this chapter, each of these modulating pathways is explained in detail.
