system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Site of action of opioid receptor is:
assistant
The correct answer is  Opioid receptors subtypes "u" and "k" receptors ;high density of u receptor detected in periaqueductal gray,thalamus,nucleus tract us solitarus ,nucleus ambiguous,area postrema. Ref KD Tripathi 8th ed.