Animal models of chronic pain: scientific and ethical issues.

Chronic pain is a major health care problem throughout the world. Available data indicate that acute pain syndromes cont~bute significantly to health care costs but that chronic or recurrent pain produces an even greater economic burden in addition to social and psychological problems [8,19]. As the medical and scientific community has become aware that chronic pain is different from acute pain and has its own high economic and social costs, there has developed increased interest in research focused on the etiology and treatment of chronic pain. In this paper, we will focus on the implications this interest in chronic pain has for the conduct of basic research in animals. The importance and nature of the clinical problem have raised questions about the need to develop animal models to study the pathophysiological processes that may be unique to chronic pain. However, the development and use of models in which animals are exposed to persistent painful stimuli present serious and difficult ethical problems that require continuing discussion among scientists [2,3,6]. Some definitions are in order before discussing these issues. We accept the definition of the Taxonomy Committee of the IASP: (pain is) ‘an unpleasant sensory and emotional experience as-