The brain-derived neurotrophic factor (BDNF) seems to be implicated in the neurobiology of depression. The aim of the study was to assess the relationship between the improvement of depressive symptoms during a one-year antidepressant treatment and serum and plasma BDNF levels.

Plasma and serum BDNF levels were assayed using the ELISA method, in 15 drug-free patients with major depression and in 15 healthy control subjects. Blood samples were collected at the baseline and the 2nd week, 1st, 3rd, 6th and 12th month of antidepressant treatment. Patients were naturalistically treated with selective serotonin reuptake inhibitors and tricyclic antidepressants at variable dosage.

At baseline, the mean serum and plasma BDNF levels were significantly lower (p<.05) than those found in the control subjects. However, from the 1st month of treatment, patient plasma BDNF levels did not differ significantly from the values reported in healthy control subjects (p=.079). On the contrary, at each evaluation time, serum BDNF levels in patients were significantly lower than those of the control subjects.

Untreated depressed patients showed reduced baseline serum and plasma BDNF levels, as compared with control subjects. The normalization of plasma BDNF up to the values found in control subjects occurred after 1 month of antidepressant treatment. On the contrary, at every time assessment, patient's serum BDNF levels were lower than those of control subjects suggesting that serum BDNF might represent a non-specific trait marker of depression.