The results of these postmortem and animal studies showed that BDNF in the hippocampus was involved in the serotonergic system and depression pathogenesis, indicating that normalizing BDNF signal activity, followed by restoration of hippocampal atrophy and normalization of impaired serotonergic transmission, might be a novel approach to improving the symptoms of depression. This evidence concerns the gene BDNF and depressive disorder.