This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaesthesia, Subject name: Pharmacology
[{'content': 'Muscular rigidity caused by opioids is due to the agonistic effect on which receptor? \nSelect and explain. \nA. Mu, B. Kappa, C. Delta, D. Sigma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (A) Mu(Ref: Miller 7th/e p781)Truncal rigidity caused by highly lipid soluble opioids like fentanyl is supraspinal in origin. It is mainly caused by stimulation of mu receptors whereas kappa and delta receptors tend to reduce the rigidity.', 'role': 'assistant'}]