This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal tract, Subject name: Pharmacology
[{'content': 'Ondansetron acts by: \nSelect and explain. \nA. Action on CTZ, B. 5-HT3 antagonism, C. D1 and D2 receptor antagonism, D. Increasing GIT motility', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ondansetron blocks the depolarizing action of serotonin through 5-HT3 receptors on vagal afferents in the gut as well as in NTS and CTZ. It donot block dopamine receptors or ACH receptors.( ref KDT 6/e p646)', 'role': 'assistant'}]