Plasma neurotransmitters and functional illness

Although the concept of functional illness has blurred boundaries, some consensus exists on its understanding among clinicians. In short, it is easier to conceive than to define functional illness. Semantic and conceptual discussion concerning this issue have been endless. Many links exist that connect brain and body (mind and organs, psyche and soma). Amongst them, neurotransmitters, released by peripheral neurons and some glandular cells (adrenal, enterochromaffin cells, mast cells), are diverted into the bloodstream. Although neurotransmitters cannot cross the blood-brain barrier, basic and clinical research has progressively established the relationship between central and peripheral neurochemical activities. Hence, it is possible to obtain some approach to the central profile through the measurement of circulating neurotransmitters. However, this approach is more reliable if we can measure all circulating factors and, in addition, test the responses to different kinds of challenges (stressors, drugs, etc.). All diseases (somatic, psychiatric and psychosomatic) present some kind of plasma neurotransmitter disturbance; however, only in some has the whole abnormal profile been established. Technical difficulties as well as expensive procedures have interfered with the generalization of this research area. In the present review article, we summarize data quoted from current scientific literature reporting exhaustive research in this area.