Behavioral Evidence for Descending Control of Nociceptive Transmission

Abstract

A major problem in the study of pain mechanisms is the development of suitable ways to measure pain. This problem is difficult enough in human subjects, who are able to describe their sensory experiences, but it becomes even more difficult in animal subjects. Animals are unable to describe their experiences, only to react to them. Furthermore, it is often necessary to use anesthetized preparations to investigate certain nociceptive mechanisms. Anesthesia by definition means that the experimental subject experiences no sensations, including pain. Investigators using animal subjects may thus be confronted with the challenge that they are attempting to study pain in the absence of pain. On the other hand, ethical considerations make it necessary to design experiments on unanesthetized animals with great care. A particularly problematic area is work on models for chronic pain. This topic is extremely important from the Standpoint of human disease, and yet there are serious questions concerning animal welfare on the one hand and human welfare on the other. Efferts have been made to develop appropriate guidelines for such studies (Bowd 1980; Covino et al. 1980; Hoff 1980; Iggo 1979; Sternbach 1976; Wall 1975; 1976). The discussion here will be concerned with tests of nociceptive responses. Emphasis will be placed on tests that are appropriate for the study of descending control of nociceptive transmission in the spinal cord, since this is the theme of this review.