ABSTRACT

Opioid analgesic drugs have been clearly demonstrated to produce antinociception by acting at specific sites in the brainstem (Porreca and Burks, 1993) and spinal cord (Yaksh, 1993). It is presumed that these exogenously applied drugs mimic the actions of endogenously released opioid peptides such as the enkephalins and ^-endorphin. However, it is not clear where the pain modulatory neurons that contain endogenous opioid peptides are located or how they function to modulate nociception. The purpose of this chapter is to review the current state of understanding related to the location and function of enkephalin-containing neurons that are involved in modulating nociception. In addition, the results of recent experiments are described that define a previously unidentified group of enkephalin neurons in the dorsolateral pontine tegmentum that also appear to modulate nociception.