The link between the brain and the periphery
For decades psychiatrists and scientists have acted on the assumption that mental illnesses are caused solely by defects within the brain. However, developments in various areas of science during the last years have led to new concepts that involve the whole body in the precipitation and course of these conditions. The disciplines of endocrinology, immunology and biochemistry have revealed that the brain is holistically integrated in the most fundamental biological function of the body, which is also reflected in changes in the composition of the blood. Serum contains molecules such as hormones, cytokines and transport proteins which can act as molecular readouts of brain function and blood cells express important molecular targets for brain disorders including neurotransmitter, hormonal and cytokine receptors, as well as corresponding downstream signalling pathways.The whole body concept in psychiatry is the basis for the rationale of using blood samples in psychiatric biomarker studies. Supporting this development, recent investigations have shown that biomarkers for schizophrenia can be reliably detected in the bloodstream. This is critical as blood can be taken from living patients at progressive stages of the disease or treatment course whereas other tissues such as brain biopsies are only available at autopsies.