Affective disorders and aggression disorders: evidence for a common biological mechanism.

Ever since the discovery that the classical antidepressants--tricyclics and MA oxidase inhibitors--exert an influence on central 5-HT, this neurotransmitter has been studied in depression, particularly in those forms responsive to this type of treatment. This chapter reviews the evidence in favor of a relationship between depression and central 5-HT dysfunctions. Most of the findings have been derived from patients with depression as the principal diagnosis. Some data have originated from patients suffering from a somatic illness and from depression as well. Both peripheral and central data are discussed. Although no single 5-HT-related finding in depression has so far been unequivocally established, the available evidence, in balance, justifies the tentative conclusion that disturbances in 5-HT metabolism can occur in depression. Lowered CSF 5-HIAA, the major indicator of disturbed central 5-HT metabolism in depression, has also been reported in aggression disorders, both in patients who had committed suicidal acts and in those with outward-directed aggression. The finding can not be explained by a concomitant state of depression. Rather than to discard the classical 5-HT-depression hypothesis, in favor of a 5-HT-aggression hypothesis, the hypothesis is launched that disturbances in serotonergic regulation can give rise to both mood and aggression disorders. This would provide a biological explanation for the clinical observation that those disorders frequently go hand in hand.