ABSTRACT
Pain in humans has been defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” (Merskey et al., 1979). In animals, pain must be inferred from observed behaviour. In the overwhelming majority of studies where conscious animals are employed, stimulation is of short duration and terminates as soon as the subject displays a response taken to indicate pain. Tissue damage is usually avoided. The animals are as a rule healthy and frequently adapted to the test situation so that fear and anxiety is reduced. Thus, “pain” in the experimental situation differs significantly from pain in the clinic. Still, experiments using animal models have provide valuable insight into the physiology of pain and the mechanisms of action of analgesics and thereby contributed to the advancement of the clinical treatment of pain. A striking example is the demonstration of a spinal site of action of opiates and subsequent administration of these drugs at the level of the spinal cord for pain control (Yaksh, 1981).
