NTRK2 and depressive disorder: Under baseline conditions, BDNF and its receptor trkB are densely expressed in the hippocampal formation (Conner et al., 1997; Phillips et al., 1991; Quartu et al., 1999, 2013; Webster, Herman, Kleinman, & Weickert, 2006; Yan, Radeke, et al., 1997; Yan, Rosenfeld, et al., 1997), one of the key regions implicated in depression‐linked maladaptive neuronal plasticity (Dias, Banerjee, Duman, & Vaidya, 2003; Malberg, Eisch, Nestler, & Duman, 2000; Vaidya, Siuciak, Du, & Duman, 1999).