BDNF and major depressive disorder: Interestingly, (R,S)-ketamine (10 mg/kg) and its enantiomers (R)- and (S)-ketamine (10 mg/kg) significantly attenuated reduced dendritic spine density, brain-derived neurotrophic factor (BDNF) and its receptor TrkB signaling, and GluA1/PSD-95 expression in the medial prefrontal cortex (mPFC) and hippocampus (CA3 and DG) of mice with a depression-like phenotype, but did not alter the corresponding elevations in NAc25,28,49.