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': 'In depression, there is deficiency of \nSelect and explain. \nA. 5-HT, B. Acetylcholine, C. Dopamine, D. GABA', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The 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. CSF, neurochemical, and receptor studies suppo the hypothesis that reduced central serotonin is associated with suicide. Reference: Synopsis of Psychiatry, pages 766,767.', 'role': 'assistant'}]