BDNF and Parkinson disease: Neurotrophins (neurotrophic factors) have been shown to be potentially beneficial in the treatment of neurodegenerative diseases such as AD, Parkinson’s disease (PD) and Huntington’s disease (HD) because endogenous neurotrophic factors have been recognized to play critical roles in the promotion of neurogenesis, differentiation, and neuroprotection throughout the development of the central nervous system [10, 11].