BDNF and Parkinson disease: The transplantation studies, using NSCs, showed an increase in several secreted neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor, and ciliary neurotrophic factor and, subsequently, resulted in neuroprotective effects in neurodegenerative disorders, such as spinal cord injury, ischemic stroke, Huntington’s disease, Parkinson’s disease, and demyelinating disorders [33,58,67,68,69].