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
Antiemetic action is produced through: 
Select and explain. 
A. Decreased CTZ stimulation, B. H1 agonistic action, C. D1 antagonistic action, D. Olfactory apparatus stimulation
A: Decreased CTZ stimulation
Answer: A: Decreased CTZ stimulation 
Explanation: Mechanism of action of antiemetic drugs are: Anticholinergic e.g hyoscine H1 antihistaminics e.g promethazine,diphenyhydramine,cyclizine. 5-HT3 antagonists e.g ondansetrone,granisetron Prokinetics. 5HT4 agonists e.g cisapride. Motilin agonist e.g erythromycin. CTZ contains histamine dopamine,cholinergic,opioid and serotonin receptors.antiemetic acts by inhibiting the receptors at CTZ.( ref KDT 6/e p643)