Anterograde TNF alpha transport from rat dorsal root ganglion to spinal cord and injured sciatic nerve.

Tumor necrosis factor-alpha (TNF alpha) is a key modulator of painful peripheral nerve injury. We have previously shown that a tracer of TNF alpha injected at the site of rat sciatic nerve injury undergoes retrograde axonal transport to the dorsal root ganglia (DRG). To further understand the role of TNF alpha in DRG, we injected rat L5 DRG with biotinylated TNF alpha, neurobiotin, or vehicle, and detected translocation of the biotin tag by avidin-biotin histochemistry. Biotinylated TNF alpha was transported intraaxonally toward the periphery of both normal and injured nerves. It also reached the dorsal horn of the spinal cord in injured rats, but not in control rats. These findings highlight a dynamic process of TNF alpha axonal transport in the peripheral neural axis, and help explain activation of central cytokines in the pathogenesis of painful neuropathy.