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Addressing sympathetic overactivity in major depressive disorder.

In this issue of the journal, Barton et al. [1] present a remarkable study on the activation of the sympathetic nervous system in patients with major depressive disorder (MDD) and a potential beneficial effect of selective serotonin reuptake inhibitors (SSRIs). The authors applied elaborate state of the art techniques to assess sympathetic nervous system activity. Using noradrenaline isotope dilution techniques, they measured whole body and cardiac sympathetic nerve activity. Moreover, they assessed muscle sympathetic nerve activity by microneurography at the peroneal nerve. Thus, different parameters of regional and global sympathetic nerve activity were available. Representative samples were studied, 39 patients with MDD and 76 healthy controls. Interestingly, patients with MDD as whole group did not display elevated sympathetic activity compared to healthy subjects. However, the authors were able to demonstrate a bimodal distribution of cardiac and whole body sympathetic nerve activity in the patients with MDD. They were able to define a subgroup with marked sympathetic activation and a subgroup with low sympathetic activity.