This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System Pa 3, Subject name: Physiology
[{'content': 'Administration of which of the following will allete respiratory depression caused by opioids, without blocking their analgesic effect? \nSelect and explain. \nA. Kappa-opioid antagonist, B. Delta-opioid antagonist, C. 5-HT agonist, D. Adrenergic agonist', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Neurons in the pre-Botzinger complex (medulla) are said to be the pacemaker cells for spontaneous breathing. There are NK1 receptors (for neurokinin 1) and mu-opioid receptors on these neurons. Substance P is known to stimulate these neurons (and hence stimulate respiration; opioids inhibit respiration their action on the mu-receptors. Depression of respiration becomes a limitation for the use of opioids in the management of pain. (mu-receptor antagonist would block the effect of respiratory depression, but it will also block the analgesic effect of opioids.) 5-HT4 receptors have been shown to be present on the Pre-Botzinger neurons. Treatment with 5-HT4 agonists will block the respiratory depressant effect of opioids, without inhibiting their analgesic effect.', 'role': 'assistant'}]