[Major depressive disorders and BDNF (brain-derived neurotrophic factor)].

We reviewed the pre-clinical and clinical papers demonstrating that BDNF plays a role in the pathophysiology of major depressive disorders. Experimental studies suggest that BDNF expression is induced by chronic antidepressant treatments, and that BDNF itself have antidepressant activity in animal models of depression. Furthermore, BDNF may protect neurons against stress-induced damage, and affect neurogenesis in the adult hippocampus. Our clinical study showed that serum levels of BDNF in drug naive patients with depression were significantly decreased as compared with normal controls. These findings suggest that low BDNF levels may play a pivotal role in the pathophysiology of major depression. It is unclear whether low BDNF levels are primary or secondary in patients with depression. One hypothesis would be that reduced BDNF might reflect a genetic vulnerability in patients with depression. Another possible explanation would be that stress-induced BDNF reductions might cause neuronal damage, which would in turn lead to acquired biological vulnerability. In order to determine the precise mechanism underlying the relationship between reduced BDNF levels and the etiology of major depression under both genetic and environmental backgrounds, further detailed study will be necessary.