This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Ascending pain pathway is inhibited in dorsal midbrain by encephalin anda) 5-HT (serotonin)b) Noradrenalinec) Substance Pd) Glutamatee) Adenosine \nSelect and explain. \nA. ac, B. a, C. ab, D. bc', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Opioid interneurons inhibit the spinothalamic pain transmission after activation by serotonin and noradrenaline.', 'role': 'assistant'}]