Spinal cord mechanisms of hyperalgesia and allodynia: Role of peripheral input from nociceptors

This chapter focuses on the role of peripheral activity from nociceptors in the development and maintenance of hyperalgesic states. In psychophysical terms, hyperalgesia and allodynia are best understood as the consequences of the leftward shift that occurs, following a peripheral injury, in the curve that relates stimulus intensity to pain sensation. This shift causes the lower portion of the pain curve to fall in the innocuous stimulus intensity range (allodynia), whereas the top portion shows an increased pain sensation to noxious stimuli (hyperalgesia). Allodynia and hyperalgesia provide protective mechanism to the organism, preventing the individual from stimulating an injured area and in so doing help the healing process. In addition, a new model for the spinal cord mechanisms of allodynia is described in the chapter. This model has been recently proposed and is based on central presynaptic interactions at the spinal level between low threshold mechanoreceptors and nociceptors. © 1996 Elsevier Science B.V.