Serum levels of brain-derived neurotrophic factor are unchanged after transcranial direct current stimulation in treatment-resistant depression

Background Brain-derived neurotrophic factor (BDNF) plays an important role in differentiation and repair of neurons in the adult brain. BDNF serum levels have been found to be lower in depressed patients than in healthy subjects. In a couple of studies, effective antidepressant treatment including electroconvulsive therapy led to an increase in BDNF serum levels. As transcranial direct current stimulation (tDCS) is currently discussed as novel therapeutic intervention in major depression, we investigated BDNF serum levels during tDCS in therapy-resistant depression. Methods Twenty-two patients with a major depressive episode participated in a double-blind placebo-controlled trial and received randomized cross over treatment with 2 weeks active and 2 weeks sham tDCS (1 or 2 mA for 20 min, anode over the left dorsolateral prefrontal cortex, cathode right supraorbital cortex). Results Clinical assessment only showed a modest and non-significant improvement in HAMD, BDI and CGI in both groups. BDNF serum levels were measured at baseline, after 2 and after 4 weeks. There was neither a significant change of BDNF levels following active tDCS, nor were severity of depressive symptoms and BDNF levels correlated. Limitations The small sample size, its heterogeneity, the short observation period and a cross-over design without an interval between both conditions. Conclusions tDCS did not change BDNF serum levels unlike other established antidepressant interventions in this treatment resistant sample. However, larger studies are needed.