The tryptophan link to psychopathology

In this thesis the relation between central serotonergic neurotrans-mission and behavioral correlates are investigated. The serotonergic system has been subject of psychiatric research and speculation for over 5 decades. Traditionally deficient serotonergic function is asso-ciated with depression but currently the role of serotonin in virtually any psychiatric disorder is recognized. Serotonergic neurons project extensively onto many brain regions and the anatomy of these pro-jections show remarkable similarity across species. So, the seroto-nergic system is a phylogenetically old system. Although the system is involved in many physiological processes it is the sole mediator of none of them. These properties indicate that the system plays a modulative role in brain function. Initially, the involvement of the serotonergic system in psychiatric disorders has shifted attention from its role in human non-pathologi-cal states. However, since modulation of the system is widely used to alleviate psychiatric symptoms, gaining insight into the physiology of the system may contribute to rationalisation of psychiatric treat-ment. Release of serotonin in the brain is highly dependent on plasma levels of its precursor tryptophan. After acute dietary depletion of tryptophan divergent behavioural effects have been observed in psy-chiatric patients and healthy volunteers. Longer lasting depletion of plasma tryptophan levels in non-psychiatric populations might result in more pronounced symptoms unbiassed by psychiatric diagnosis. We studied patients suffering from somatic diseases leading to modulation of plasma tryptophan levels and thus brain serotonin levels. In this way, chronic disturbances of the serotonergic system could be studied. Furthermore, these patients made it possible to study the circumstances in which the serotonergic system is com-promised providing insight in the (patho)physiological role of the system. We focused on the possible role of serotonin as a link bet-ween somatic disease and associated psychological states. This subject has been further investigated through literature research