NEW STRATEGIES FOR THE TREATMENT OF MOOD DISORDERS: VAGUS NERVE STIMULATION FOR THE TREATMENT OF RESISTANT DEPRESSION

Depression is a severe psychiatric disorder, in which a third of patients do not achieve remission, despite the wide variety of therapeutic strategies that are currently available. Vagus nerve stimulation (VNS) has shown promise in treating resistant-depressed patients, and it has been approved as an adjunctive treatment for resistant depression. However, the mechanism of action by which VNS exerts its antidepressant effects has remained elusive. The present chapter was aimed first at introducing VNS, beginning from the anatomy of the vagus nerve, the surgical procedure of the stimulator implantation, and the rationale leading to the use of VNS for the treatment of resistant depression. A second goal of this chapter was to review what has been done so far in clinical and preclinical research, from neuroimaging, neurochemical, molecular and electrophysiological studies, in order to understand the mechanism of action of VNS. These studies reported an effect of VNS on brain regions, such as limbic structures, involved in mood regulation. Furthermore an influence of VNS on all three central monoamine systems (serotonin, norepinephrine, and, dopamine) implicated in the pathophysiology of depression and that are especially targeted by antidepressant medications has been revealed, contributing to the clinical efficacy of this approach. Finally, this chapter described the stimulation parameters of this therapy and the results of different studies aimed at characterizing the optimal VNS parameters to treat resistant depression and to potentially minimize and/or even prevent stimulation-related side effects, thus improving patients’ quality of life.

Keywords: Serotonin (5-HT), norepinephrine (NE), depression, antidepressant drugs, electroconvulsive treatment (ECT), A, B, and C-fibes of vagus nerve, nucleus of the solitary tract (NTS) of medulla oblongata (MO), vagus nerve stimulation (VNS).