[Serotonin now: Part 2. Behavioral genetics and psychopathology].

Several lines of evidence implicate a dysregulation of the serotonin (5-HT) system in emotional behavior and stress, and point to its relevance for the etiology and pathogenesis of various neuropsychiatric disorders. This is evidenced by behavioral pharmacology as well as genetic studies, yet the impact of genetic variation within the 5-HT system on human disorders remains controversial. The generation of tissue-specific and inducible knockout mice lacking genes belonging to the 5-HT system further established the importance of the 5-HT system for neuronal development and the regulation of emotions. This part of the review provides a summary and critical discussion of genetic, neurobiological and pharmacological studies along with recent clinical research. Together, these data underscore the complex effects of 5-HT on human behavior and psychiatric disorders. Epigenetic mechanisms add to the complexity of the 5-HT system and will be increasingly studied in the coming years. Thus, the serotonergic system still remains in the centre of current hypotheses regarding the pathogenesis of disorders with the shared feature of emotional dysregulation.