NTRK2 and Alzheimer disease: Furthermore, in human AD post-mortem tissue, BDNF mRNA and protein, as well as its precursor form, pro-BDNF, its receptor tropomyosin receptor kinase B (TrkB) and activation of downstream signaling molecules such as cAMP response element binding (CREB) protein, are all decreased (Phillips et al., 1991; Yamamoto-Sasaki et al., 1999; Holsinger et al., 2000; Siegel and Chauhan, 2000; Peng et al., 2005).