Key role of the dorsal root ganglion in neuropathic tactile hypersensibility

Cutting spinal nerves just distal to the dorsal root ganglion (DRG) triggers, with rapid onset, massive spontaneous ectopic discharge in axotomized afferent A-neurons, and at the same time induces tactile allodynia in the partially denervated hindlimb. We show that secondary transection of the dorsal root (rhizotomy) of the axotomized DRG, or suppression of the ectopia with topically applied local anesthetics, eliminates or attenuates the allodynia. Dorsal rhizotomy alone does not trigger allodynia. These observations support the hypothesis that ectopic firing in DRG A-neurons induces central sensitization which leads to tactile allodynia. The question of how activity in afferent A-neurons, which are not normally nociceptive, might induce allodynia is discussed in light of the current literature.