Psychobiological Aspects of Somatoform Disorders: Contributions of Monoaminergic Transmitter Systems

<i>Objective: </i>To evaluate the possible biological aspects of ‘unexplained physical symptoms’, this study examined serotonergic and noradrenergic monoamino acids in somatoform disorders and/or depression. <i>Methods:</i> Blood samples of 150 subjects from 4 groups (somatization syndrome; depression; depression and somatization; controls) were analyzed for amino acids contributing to the serotonergic and noradrenergic system and peripheral muscle energy balance (tryptophan, valine, leucine, isoleucine, phenylalanine and tyrosine). <i>Results:</i> Tryptophan, branched chain amino acids and other serotonergic amino acids were decreased in patients with somatoform symptoms, even when no depression was present. <i>Conclusions:</i> We conclude that serotonergic amino acids are biological correlates of multiple unexplained symptoms. Ways of action do not only involve brain mechanisms, but also energy metabolism in peripheral muscles.