BDNF and Alzheimer disease: Apelin-13 administration ameliorated STZ-induced decrease of hippocampal BDNF and p-TrkB expression, and TrkB blocker K252a antagonized apelin-13-mediated amelioration of STZ-induced cognitive deficits, which is consistent with previous data showing the requirement for BDNF in anti-AD-like responses (Tapia-Arancibia et al., 2008).