IL6 and major depressive disorder: Furthermore, we measured the plasma levels of the inflammatory cytokine interleukin-6 (IL-6) and synaptic proteins (i.e., α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor A1 [GluA1] and postsynaptic density 95 [PSD-95]) in the prefrontal cortex (PFC) since the expression of these synaptic proteins was decreased in the PFC from rodents with depression-like phenotypes [26, 27].