Contribution of the spared primary afferent neurons to the pathomechanisms of neuropathic pain.

Neuropathic pain is caused by nervous-system lesions. Early studies on the pathomechanisms of this abnormal pain state have focused on the directly injured fibers and neurons. Here, we present recently accumulating data about the contribution of the primary afferent neurons spared from direct injury to the pathomechanisms of neuropathic pain. The phenotypic changes in the spared neurons are similar to those in the neurons in peripheral inflammation models, as opposed to those in the directly injured neurons. Electrophysiological changes and behavioral data also favor the contribution of the spared neurons. These attractive targets of study will give us new approaches for understanding the abnormal pain.