Taking into account the interstrain differences observed in anxious and depressive-like behaviors and studies that propose alterations in cell proliferation, Bdnf expression and neuronal morphology in the hippocampus as playing a role in the etiology of depression (Jacobs et al., 2000; Groves, 2007; Bessa et al., 2009), we next analyzed these parameters. This evidence concerns the gene BDNF and major depressive disorder.