RPS6KB1 and major depressive disorder: Preclinical findings of significantly lower synaptic spine density proteins in animal depression models have been reinforced by post-mortem studies of MDD subjects who had reduced levels of PSD95 (Feyissa et al., 2009), as well as significantly lower protein levels of mTOR and p70S6K (Jernigan et al., 2011), in the PFC compared to sex- and age-matched controls.