SLC6A4 and major depressive disorder: On the other hand, the preclinical SERT study is in agreement with a metanalysis of 18 studies with 364 MDD patients and 372 healthy subjects that found significant reductions SERT availability in subcortical regions like amygdala, midbrain, striatum, thalamus and brainstem of depressed patients, and no changes in SERT in cortical areas [92].