To test how hippocampal FTO contributes to depression-like behaviors, we employed recombinant adeno-associated virus (rAAV) as a transgenic tool to specifically knock down mouse FTO overexpressed in the hippocampus of wild-type C57BL/6 mice and to specifically knock out Fto in the hippocampus of Fto flox/flox mice. This evidence concerns the gene FTO and major depressive disorder.