GDNF and Parkinson disease: For example, neurotropic factors, such as glial cell-line derived neurotropic factor (GDNF), neurturin (NTN), or vascular endothelial growth factor (VGEF) produced by transfected neural stem cells (NSC) [34]–[36] and bone marrow-derived macrophages and microglia [37], [38] were used in PD mouse models.