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
In depression, there is deficiency of 
Select and explain. 
A. 5-HT, B. Acetylcholine, C. Dopamine, D. GABA
A: 5-HT
Answer: A: 5-HT 
Explanation: 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.