Despite its dopaminotrophic benefits both in PD models and in clinical trials, the delivery of GDNF to the nigrostriatal DA system also induces adverse side effects, including hyperactivity [5,26–29], reduced levels of striatal tyrosine hydroxylase (TH)–the rate-limiting enzyme in DA synthesis [5,30], reduced food intake, and loss of body weight [6,26]. Here, TH is linked to Parkinson disease.