Inhibition of NF-kappaB prevents mechanical allodynia induced by spinal ventral root transection and suppresses the re-expression of Nav1.3 in DRG neurons in vivo and in vitro

doi:10.1016/j.brainres.2010.09.048

Brain Research

Volume 1363, 6 December 2010, Pages 151-158

https://doi.org/10.1016/j.brainres.2010.09.048 Get rights and content

Abstract

Activation of nucleus factor-kappaB (NF-κB) in the dorsal root ganglia (DRG) is critical for development of neuropathic pain. The underlying mechanisms, however, are largely unknown. In the present work we tested if the activation of NF-κB is required for re-expression of Nav1.3, which is important for development of neuropathic pain, in uninjured DRG neurons. We found that intrathecal injection of pyrrolidine dithiocarbamate (PDTC), a NF-κB inhibitor, completely blocked the mechanical allodynia induced by L5 ventral root transection (L5-VRT), when applied 30 min before or 8 h after operation, but at 7 d after L5-VRT the same manipulation had no effect on established allodynia. Pre-treatment with PDTC also prevented the re-expression of Nav1.3 induced by L5-VRT. As our previous work has shown that up-regulation of tumor necrosis factor-alpha (TNF-α) in DRG is responsible for the re-expression of Nav1.3 in uninjured DRG neurons following L5 ventral root injury, we investigated whether activation of NF-κB is essential for the up-regulation of Nav1.3 by TNF-α. Results showed that application of rat recombinant TNF-α (rrTNF) into the cultured normal adult rat DRG neurons increased the immunoreactive (IR) of Nav1.3 localized mainly around the cell membrane and pre-treatment with PDTC blocked the change dose-dependently. The data suggested that injury to ventral root might lead to neuropathic pain and the re-expression of Nav1.3 in primary sensory neurons by activation of NF-κB.

Research Highlights

►Blockade of NF-κB attenuates the mechanical allodynia induced by motor neuron injury. ►Blockade of NF-κB inhibits re-expression of Nav1.3 in DRG neurons following L5-VRT. ►Blockade of NF-κB inhibits the re-expression of Nav1.3 in cultured DRG neurons.

Introduction

It is well-established that peripheral nerve injury induces neuropathic pain by triggering the abnormal spontaneous discharges of action potentials (ectopic discharges) (Govrin-Lippmann and Devor, 1978, Wall and Gutnick, 1974), which occur in both injured site and dorsal root ganglion (DRG) (Blumberg and Janig, 1984, Devor et al., 1992). At present, it is generally accepted that abnormal expression of voltage-gated sodium channels may play an important role in the generation of ectopic discharge. Nav1.3, a subtype of tetraodontoxin-sensitive (TTX-S) sodium channel, which is normally expressed at relatively high level in embryonic nervous system and is barely detectable in the DRGs of adult rats (Beckh et al., 1989, Waxman et al., 1994). Following peripheral nerve injury, however, Nav1.3 is re-expressed in DRG neurons (Black et al., 1999, Dib-Hajj et al., 1996, Dib-Hajj et al., 1999, Kim et al., 2001, Lindia et al., 2005, Waxman et al., 1994). Importantly, inhibition of Nav1.3 re-expression by intrathecal injection of Nav1.3 specific antisense oligodeoxynucleotides attenuates mechanical allodynia and thermal hyperalgesia produced by peripheral nerve injury and reduces the hyperresponsiveness of dorsal horn neurons (Hains et al., 2004). Our recent work has shown that selective injury of motor fibers, but leaving sensory neurons intact by L5 ventral root transection (L5-VRT), which leads to neuropathic pain (Li et al., 2002, Xu et al., 2006), also induces the re-expression of Nav1.3 at both mRNA and protein level in uninjured L4 and L5 DRGs. The time course of the channel expression is parallel to the behavioural signs of neuropathic pain (He et al., 2010).

Previously we have shown that L5-VRT up-regulates tumor necrosis factor-alpha (TNF-α) and TNF receptor 1 (TNFR1) in uninjured DRGs (Xu et al., 2006) and that the increased TNF-α is responsible for the up-regulation of Nav1.3 in uninjured DRG neurons (He et al., 2010). However, the signal transduction mechanism underlying the re-expression of Nav1.3 triggered by TNF-α is still unknown. A large body of studies has demonstrated that the activation of nucleus factor-kappaB (NF-κB) (Ledeboer et al., 2005, Ma and Bisby, 1998, Sun et al., 2006, Tegeder et al., 2004) is required for the development of neuropathic pain. TNF-α may activate NF-κB by binding to TNFR1 (Baud and Karin, 2001) and initiate the transcription of a wide variety of target genes (Pahl, 1999). In the present work we tested whether activation of NF-κB is required for mechanical allodynia induced by L5-VRT and the re-expression of Nav1.3 in DRG neurons.

Section snippets

Blockade of NF-κB attenuates the mechanical allodynia induced by motor neuron injury

In consistency with our previous work (Xu et al., 2006), selective damage of motor neurons by L5-VRT resulted in decreased paw withdrawal threshold bilaterally. The changes in paw thresholds were detected ipsilaterally at 15 h and contralaterally at 24 h (P < 0.05 versus pre-operation), lasting at least for 4 weeks. In contrast, no changes in paw withdrawal thresholds were detected in sham-operated rats (data not shown). The results indicated that injury to motor neurons but not operation might

Discussion

In the present study, we demonstrated that intrathecal injection of NF-κB inhibitor (PDTC) prevented mechanical allodynia and re-expression of Nav1.3 in DRG neurons produced by L5-VRT. PDTC depressed the up-regulation of Nav1.3-IR triggered by rrTNF in cultured adult DRG neurons dose-dependently. The data suggested that injury to ventral root might lead to the re-expression of Nav1.3 in primary sensory neurons by activation of NF-κB.

Animals

Male Sprague–Dawley rats weighing 130–150 g were used. The rats were housed in separated cages. The room temperature was kept at 24 ± 1 °C and humidity 50–60% under a 12:12 light–dark cycle. The animals were allowed to access food and water ad libitum. All experimental procedures were approved by the Local Animal Care Committee and were carried out in accordance with the guideline of the National Institutes of Health on animal care and the ethical guidelines for investigation of experimental pain

Acknowledgments

Funding for this study was provided by the National Natural Science Foundation of China (nos. 30900436, 30770705, and 30570599).

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Research ReportInhibition of NF-kappaB prevents mechanical allodynia induced by spinal ventral root transection and suppresses the re-expression of Nav1.3 in DRG neurons in vivo and in vitro

Abstract

Research Highlights

Introduction

Section snippets

Blockade of NF-κB attenuates the mechanical allodynia induced by motor neuron injury

Discussion

Animals

Acknowledgments

Trends Cell Biol.

Pain

J. Neurosci. Meth.

Pain

Pain

Pain

Pain

Brain Res.

Pain.

Brain Res. Mol. Brain Res.

Pain

Pain

Exp. Neurol.

Pain

Pain

Brain Res.

Mol. Ther.

Eur. J. Pharmacol.

Br. J. Anaesth.

Exp. Neurol.

Research Report
Inhibition of NF-kappaB prevents mechanical allodynia induced by spinal ventral root transection and suppresses the re-expression of Nav1.3 in DRG neurons in vivo and in vitro