Considering that BDNF plays a critical role in the pathophysiology of depression and is closely related to activated microglia in the hippocampus, we measured hippocampal protein and mRNA levels of BDNF and its high-affinity receptor TrkB to determine whether hippocampal BDNF contributes to sex differences in depressive-like behaviour. The gene discussed is BDNF; the disease is major depressive disorder.