BDNF and Alzheimer disease: Apart from Aβ-induced toxicity, dendritic spine and associated synaptic alterations could be associated with reduced levels of BDNF in MCI and AD patients, reinforced by the neuroprotective effects of the neurotrophin reported in experimental AD models (Peng et al., 2005; O’Bryant et al., 2009; Caccamo et al., 2010; Jiao et al., 2016).