BDNF and major depressive disorder: Further research focused on ketamine, brain-derived neurotrophic factor (BDNF), and the role of neuroplasticity on the pathomechanism of depression, seemed to contradict the model of inhibition of glutamatergic signaling; this suggested the activation of glutamatergic transmission as the key mechanism behind the rapid-acting antidepressant effect [11, 13, 14].