The role of previous nociceptive input in development of autotomy following cordotomy

Intractable pains have been described after surgical or accidental lesions in the peripheral or central nervous system. The possible contribution of antecedent injury to the appearance of these pains was examined in an animal model for chronic pain which involved observing self-mutilation or autotomy behavior in rats. Various combinations of previous injury, selective spinal cut, and peripheral denervation were carried out on rats. Injuries ranged from mild to moderate and were produced by nociceptive stimuli from formaldehyde injection, induced local arthritis, or hot water application. Selective spinal cuts included either a dorsal column (DC), a dorsal quadrant which included a DC and a dorsolateral funiculus, an anterolateral column (ALC), or a hemisection. In rats without prior exposure to injury the various types of spinal cuts were not associated with any autotomy. In rats with prior exposure to formaldehyde injection, autotomy was associated only with spinal cuts that involved the ALC. In an otherwise similar group of rats but with prior induction of local arthritis, a stronger association of ALC lesion and autotomy was observed. In an earlier study, rats with ALC lesion prior to denervation showed reduced autotomy. In this study, we demonstrated that in rats with previous exposure to heat injury, an ALC lesion was strongly associated with autotomy. Autotomy was absent, however, in rats with heat injury only. These findings strongly suggest that pain resulting from previous exposure to injury produces a memory trace in the central nervous system which can account for the phantom pains encountered in various clinical conditions.