This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mood disorders, Subject name: Psychiatry
[{'content': 'Increase in suicidal behaviour is due to \nSelect and explain. \nA. Increase in serotonin, B. Decrease in serotonin, C. Increase in noradrenaline, D. Reactive depression', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Karolinska Institute in Sweden first noted that low concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the lumbar cerebrospinal fluid (CSF) were associated with suicidal behavior. This finding has been replicated many times and in different diagnostic groups.CSF, neurochemical, and receptor studies suppo the hypothesis that reduced central serotonin is associated with suicide. Reference: Synopsis of Psychiatry, page 766, 767.', 'role': 'assistant'}]