NTRK2 and major depressive disorder: Brain-derived neurotrophic factor (BDNF) and TrkB play crucial roles in cognition, memory, and depression (Duman and Monteggia, 2006; Rantamaki and Castren, 2008; Nagahara and Tuszynski, 2011), driven at least in part by downstream effectors, including VGF (non-acronymic) (Bonni et al., 1995; Alder et al., 2003).