BDNF and neurodegenerative disease: Although the incomplete understanding of the etiology of AD hinders the development of knowledge-based targeted therapeutics, various studies have demonstrated that alterations in the levels of specific neurotrophic factors (NTFs), such as brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), are associated with the pathogenesis of neurodegenerative diseases such as AD and Parkinson’s disease (PD) [5,7,8,9,10,11,12,13].