BDNF and nervous system disorder: Impaired BDNF/TrkB signaling is associated with several neurological disorders, including neurodegenerative, neurodevelopmental, and neuropsychiatric diseases (for review see Duman et al. 2019; Gupta et al. 2013; Li and Pozzo-Miller 2014; Zuccato and Cattaneo 2009), characterized, among others, by dendritic spine alterations (for review see Bloss et al. 2011; Qiao et al. 2016; Xu et al. 2014).