NTRK2 and major depressive disorder: The TrkB agonist LM22A has been intranasally administered to rodents (Massa et al., 2010), showing promising results by activating TrkB, PI3K-Akt, and Ras-MAPK pathways, which play a critical role in MDD (Reichardt, 2006; Dietz et al., 2009; Duman and Aghajanian, 2012; Lu et al., 2014).