This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'Ascending pain pathway is inhibited in dorsal midbrain by \nSelect and explain. \nA. 5-HT (serotonin), B. Noradrenaline 1, C. Substance P, D. Glutamate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The cell bodies of serotonin containing neurons are localized in the raphe nuclei of midbrain and brainstem. ... Serotonin therefore acts descending pathway to modulate spinal pain signals Ref: guyton and hall textbook of medical physiology 12 edition page number:699,700,701', 'role': 'assistant'}]