Another possible explanation for the discrepancy regarding the role of BDNF in depression involves serotonergic- and dopaminergic-dependent mechanisms; for example, in a different depression model, olfactory bulbectomy, endogenous BDNF levels increase in an attempt to counteract the bulbectomy-induced loss in serotonergic function in the PFC and hippocampus [77]. Here, BDNF is linked to major depressive disorder.