GDNF and neurodegenerative disease: Extensive preclinical research carried out on GDNF for its restorative function in Parkinson’s Disease (PD) [5,6,7,8] and its crucial role for the maintenance of adult catecholaminergic neurons in the nigrostriatal system [9] have shown promise and generated great interest in using GDNF as a therapeutic agent for intervention in neurodegenerative diseases such as PD.