Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophic factor that enhances survival and morphological differentiation of dopaminergic neurons and increases their high-affinity dopamine uptake. GDNF is a glycosylated, disulfide-bonded homodimer that is a distantly related member of the transforming growth factor-beta superfamily. The GDNF family members (consists of GDNF, neurturin, artemin and persephin) are structurally similar to transforming growth factor-beta. Unlike other members of the TGF-beta superfamily, which signal through the receptor serine-threonine kinases, GDNF family ligands activate intracellular signalling cascades via the receptor tyrosine kinase Ret. GDNF family ligands binds to GDNF family receptor alpha (GFRalpha) and then the GDNF family ligand-GFR alpha complex binds to and stimulates autophosphorylation of Ret.