Given our data suggesting that MSCs mediate 5-HTDRN neuronal activation and behavioral improvements via the BDNF-TrkB axis of lung afferents, we hypothesized that inhalation of the TrkB agonist, 7, 8-DHF, could improve depressive and anxiety-like behaviors and thus represent a promising treatment for depression. The gene discussed is BDNF; the disease is major depressive disorder.