Abstract: The rostral ventromedial medulla is one of the key structures in descending pain modulation system. It receives inputs the thalamus, the periaqueductal gray, and parabrachial nucleus, and sends descending projections through the dorsolateral funiculus and ventrolateral funiculus to the spinal dorsal horns. The rostral ventromedial medulla is thought to be the final relay in descending modulation of pain. The neurons in this region can be classified into On-cells, Off-cells and Neutral cells according to the changes in the firing activity before tail flick. This review mainly focuses on pain modulation functions and potential analgesia mechanisms of On-cells and Off-cells.

Key words: rostral ventromedial medulla, On-cell, Off-cell, opioid receptor, pain