[The importance of the kynurenine pathway in depressive disorders].

Depressive disorders are the most frequently diagnosed mental disorder. It is assumed that the etiology of depression is multifactorial and the individual theories complement each other. Referring to the neurochemical hypothesis of the underlying depressive disorder, the relationship between lowering levels of serotonin, norepinephrine, dopamine and a change in mood is suggested. Particular attention has been given to serotonin, called the happiness hormone, which is synthesized from the exogenous amino acid tryptophan. The main methods of antidepressant treatment, in particular the use of serotonin reuptake inhibitors (SSRIs), take into account the concept of monoamine deficiency in patients with depression. However, an insufficient response in some patients to antidepressants (the existence of a refractory depression), indicates the importance of looking for other possible causes for the development of this disease and thus alternative treatment methods. It is indicated that in patients with depression there are disorders of tryptophan metabolism, ie the redirection of tryptophan from the serotonin synthesis pathway to the kynurenine pathway, which is the source of neuroactive compounds in the central nervous system, so-called. kynurenin m.in. kynurenic acid, 3-hydroxycinurenine, quinoline acid. It has been proved that certain metabolites of this cycle of transformations have neuroprotective and other neurotoxic properties. For this reason, it seems reasonable to summarize the research published so far on this subject.