4.5 Depression and levels of BDNF
As with monoamine levels, researchers have tried to establish whether there is a relationship between levels of BDNF and depression. BDNF levels in the blood of patients with major depression are abnormally low (Sen et al., 2008), and post-mortem studies show low levels of BDNF in the hippocampus and prefrontal cortex of depressed patients (Martinowich et al., 2007).
Such findings suggest that BDNF levels are correlated (associated) with mood, and have led to the neurotrophic hypothesis of mood disorders. In essence, the hypothesis states that ‘reduced brain BDNF levels predispose to depression, whereas increases in brain BDNF levels produce an antidepressant action’ (Duman and Monteggia, 2006). This may sound like a remarkably similar approach to that of the monoamine hypothesis, in that the level of a neurochemical, or neurotransmitter, in this case BDNF, again seems the focus of a hypothesis to explain depression. Indeed the hypothesis has been criticised for this limited viewpoint on aetiology.
However, a major difference between the simple monoamine hypothesis and the neurotrophic hypothesis is that levels of BDNF have been linked to a complex series of processes involving the birth and death of neurons in some parts of the brain, and the experience of stress has been linked to such effects. Hence there is a strong potential for psychosocial factors to link into the neurotrophic model, as you will see now.