NF-kB mediated CX3CL1 activation in the dorsal root ganglion contributes to the maintenance of neuropathic pain induced in adult male Sprague Dawley rats

Abstract Purpose: To evaluate the role of CX3CL1 and NF-κB in the lumbar disc herniation induced neuropathic pain. Methods: After LDH induced by implantation of autologous nucleus pulposus (NP) on the left L5 nerve root was established, mechanical thresholds and thermal hyperalgesia were tested at relevant time points during an observation period of 28 days. Expression of CX3CL1 and NF-κBin the dorsal root ganglion (DRG) were performed by using Western blotting and RT-PCR. Results: Implantation of autologous nucleus pulposus (NP) induced neuropathic pain, associated with increased mRNA and protein expression of CX3CL1 in the DRG. Moreover, intrathecal injection of neutralizing antibody against CX3CL1 could attenuates LDH-induced persistent pain hypersensitivity. Interestingly, NF-κB activation in the DRGs were found in LDH-induced neuropathic pain. Furthermore, NF-κB downregulation by p65 inhibitor PDTC markedly alleviated LDH-induced mechanical allodynia and thermal hyperalgesia in rat. Importantly, CX3CL1 neutralizing antibody (10 μg/10 μl, i.t.) reduces p-p65 protein level in DRG Conclusions: CX3XL1 could regulate LDH-induced neuropathic pain through NF-κB pathway. Targeting CX3CL1 and NF-κB may represent a potential treatment for neuropathic pain caused by LDH.

Cerebrospinal fluid-contacting nucleus mediates nociception via release of fractalkine

Increasing evidence suggests that the cerebrospinal fluid-contacting nucleus (CSF-contacting nucleus) mediates the transduction and regulation of pain signals. However, the precise molecular mechanisms remain unclear. Studies show that release of fractalkine (FKN) from neurons plays a critical role in nerve injury-related pain. We tested the hypothesis that release of FKN from the CSF-contacting nucleus regulates neuropathic pain, in a chronic constriction injury rat model. The results show that FKN is expressed by neurons, via expression of its only receptor CX3CR1 in the microglia. The levels of soluble FKN (sFKN) were markedly upregulated along with the increase in FKN mRNA level in rats subjected to chronic constriction injury. In addition, injection of FKN-neutralizing antibody into the lateral ventricle alleviated neuropathic pain-related behavior followed by reduction in microglial activation in the CSF-contacting nucleus. The results indicate that inhibition of FKN release by the CSF-contacting nucleus may ameliorate neuropathic pain clinically.