ABSTRACT

In this chapter, the authors review their knowledge of the “building blocks” of the descending modulatory system within the rostral ventromedial medulla (RVM) and focuses on information gained from recent work using pharmacological tools and single unit recording in this region. The ultimate goal is to place this system into a behavioral context, with an understanding of how the different elements of the RVM might be recruited to regulate nociception in different behavioral states. The recognition that electrical or glutamate stimulation or opioid microinjection into the RVM produces a potent analgesia led to the view that this region constituted an “analgesia center”, distinct from the less differentiated reticular core. The function of a modulatory network depends not only on the intrinsic properties of the constituent neurons, but also on the anatomical and functional connections among these neurons and how these combine to give rise to measurable effects on behavior.