Increased activation of nuclear factor kappa B in rat lumbar dorsal root ganglion neurons following partial sciatic nerve injuries

Abstract

Nuclear factor kappa B (NF κB) is a transcription factor which can be activated by some neurotrophic factors and cytokines, and then translocated into the nucleus. We examined NF κB immunoreactivity (IR) in L4 and L5 dorsal root ganglion (DRG) cells of normal rats, and 2 weeks after complete sciatic nerve transection (CSNT), partial sciatic nerve ligation (PSNL) and chronic constriction injury (CCI). In the normal DRG, 45% of the neurons were NF κB-IR (IR in cytoplasm only or in both cytoplasm and nucleus). Only 18% were activated NF κB-IR cells (IR in both cytoplasm and nucleus). Two weeks after CSNT, PSNL and CCI, there was no significant difference in the percentages of NF κB-IR neurons between the ipsilateral and contralateral DRG. However, the percentages of the activated NF κB-IR neurons in the ipsilateral DRG of PSNL (30%) and CCI (33%) rats, but not in CSNT (24%) rats, were significantly increased, compared with the contralateral DRG. Ultrastructurally, NF κB-IR was localized to the endoplasmic reticulum and Golgi apparatus. In activated cells, IR was also observed in the nuclei. Two weeks after CCI, NF κB-IR was stronger in the axons and Schwann cells in the proximal stump of the injured sciatic nerves than in uninjured contralateral nerves. In some Schwann cells surrounding unmyelinated fibers, the nuclei were also NF κB-IR, suggesting that these cells were activated by CCI. NF κB activation increased in DRG neurons and Schwann cells 2 weeks following partial sciatic injuries, possibly in response to cytokines and neurotrophins produced by endoneurial cells in the partially injured nerve during Wallerian degeneration.