Peripheral Mechanisms of Sensitization and Hyperalgesia

Abstract

Classical textbooks of neuroanatomy and neurophysiology discuss pain pathways in a relatively straightforward manner. Thus it is stated that noxious stimuli activate unmyelinated fibers in the periphery. These in turn contact second order neurons in the spinal cord dorsal horn. The latter are cells at the origin of the spinothalamic tract which project to the lateral and medial thalamic nuclei. Precisely what is the cortical target of these thalamic regions and, in fact, whether there is a cortical contribution to pain is still controversial. This view of the pain transmission network is clearly a ″labelled line″ view. In other words, the implication is that there are specific cells in the nervous system which respond to noxious stimuli; and when they are activated pain is produced. Recent studies, however, have taken a very different view of the organization of pain transmission networks. This lecture will address some of these observations.