BDNF and depressive symptom measurement: In addition to its interactions with NMDA receptors, ketamine influences the activity and expression of brain-derived neurotrophic factor (BDNF) [78], eukaryotic elongation factor 2 and mechanistic target of rapamycin (mTOR), which modulate synaptic plasticity, a process implicated in the pathogenesis of depression [79] and addiction [75].