Changes in Spinal Cord Expression of Fractalkine and its Receptor in a Rat Model of Disc Herniation by Autologous Nucleus Pulposus

Abstract

Study Design. Behavior, mRNA and immunohistochemical assessment of the expression of fractalkine (CX3CL1) and its receptor (CX3CR1) in a rat model of disc herniation by autologous nucleus pulposus (NP) implantation. Objective. To evaluate the changes in expression of fractalkine and its receptor in the spinal cord and their association with pain behavior in a rat model of disc herniation. Summary of Background Data. Chemokines have recently been implicated in the pathophysiology of neuropathic pain. They mediate astrocytic migration and microglial proliferation, which are involved in the regulation of nociceptive transmission. Fractalkine is a chemokine, which participates in the mechanisms of neuropathic pain as a mediator of neuron-glia interactions. Methods. Sixty-six rats (NP-treated = 47, sham = 19) were implanted with autologous NP (approximately 3 mg) on the left L5 nerve root, just proximal to the dorsal root ganglion and tested for thermal hyperalgesia and mechanical allodynia before surgery and on days 1, 5, 10, 20, and 30 after surgery. The changes of expression of fractalkine and its receptor in the spinal cord were studied using real time PCR and immunohistochemistry. Results. Rats developed ipsilateral mechanical allodynia at day 1 and bilateral thermal hyperalgesia at day 5 after surgery, and these changes in sensitivity persisted throughout the observation period. The expression of mRNA for fractalkine in the spinal cord was increased by day 5 and remained upregulated for the duration of the experiment. The immunostaining for fractalkine increased in neurons and astrocytes and that for the fractalkine receptor increased in microglia in the dorsal horn ipsilateral to the disc herniation. Conclusion. Our results indicate that autologous implantation of NP induces thermal hyperalgesia and mechanical allodynia, and leads to an upregulation of fractalkine and its receptor in spinal neurons and glia, implicating fractalkine in association with radicular pain.