Changes in pain behavior and glial activation in the spinal dorsal horn after pulsed radiofrequency current administration to the dorsal root ganglion in a rat model of lumbar disc herniation

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Herniated discs can induce sciatica by mechanical compression and/or chemical irritation caused by proinflammatory cytokines. Using immunohistochemistry methods in the dorsal horn of a rat model of lumbar disc herniation, the authors investigated the effects of pulsed radiofrequency (PRF) current administration to the dorsal root ganglion (DRG) on pain-related behavior and activation of microglia, astrocytes, and mitogen-activated protein kinase.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>A total of 33 Sprague-Dawley rats were randomly assigned to either a sham-operated group (n = 10) or a nucleus pulposus (NP)–exposed group (n = 23). Rats in the NP-exposed group were further subdivided into NP exposed with sham stimulation (NP+sham stimulation, n = 10), NP exposed with PRF (NP+PRF, n = 10), or euthanasia 10 days after NP exposure (n = 3). The DRGs in the NP+PRF rats were exposed to PRF waves (2 Hz) for 120 seconds at 45 V on postoperative Day 10. Rats were tested for mechanical allodynia 10 days after surgery and at 8 hours, 1 day, 3 days, 10 days, 20 days, and 40 days after PRF administration. Immunohistochemical staining of astrocytes (glial fibrillary acidic protein), microglia (OX-42), and phosphorylated extracellular signal–regulated kinases (pERKs) in the spinal dorsal horn was performed at 41 days after PRF administration.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Starting at 8 hours after PRF administration, mechanical withdrawal thresholds dramatically increased; this response persisted for 40 days (p &lt; 0.05). After PRF administration, immunohistochemical expressions of OX-42 and pERK in the spinal dorsal horn were quantitatively reduced (p &lt; 0.05).</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Pulsed radiofrequency administration to the DRG reduced mechanical allodynia and downregulated microglia activity and pERK expression in the spinal dorsal horn of a rat model of lumbar disc herniation.</jats:p></jats:sec>

Comparison between bipolar pulsed radiofrequency and monopolar pulsed radiofrequency in chronic lumbosacral radicular pain

“…Increased c-fos expression was suggested to activate some pain inhibition mechanisms. Cho et al [34] reported that PRF of the DRG decreased microglia activity in the spinal dorsal horn of a rat model of lumbar disc herniation. Because microglia releases several cytokines and chemokines that mediate pain signaling, downregulation of microglia activity could possibly control neuropathic pain.…”

“…[16–18] Although the mechanism of PRF has not been clearly elucidated, the electrical field produced by PRF is known to alter pain signals. [19–21] So far, several studies have reported that PRF on the dorsal root ganglion (DRG) can effectively manage lumbosacral radiculopathy. [22–28] For PRF stimulation on the DRG, a single PRF cannula is used to produce a therapeutic electrical field.…”

Effect of bipolar pulsed radiofrequency on refractory chronic cervical radicular pain

“…They described that PRF selectively caused changes in smaller principal sensory neural fibers such as C and Aδ fibers, compared with larger nonpain-related sensory fibers such as Aβ fibers. [27] Cho et al [18] reported that PRF of the DRG decreased microglia activity in the spinal dorsal horn of a rat model of lumbar disc herniation. Because microglia are strongly responsible for the development of chronic neuropathic pain through releasing various cytokines and chemokines, which are related with pain signaling, they proposed that down-regulation of microglia can possibly prevent progression to chronic neuropathic pain.…”

“…[17] The proposed mechanism of PRF is that the electrical field produced by PRF can alter pain signals. [18–20] To date, several studies have reported that PRF stimulation of the dorsal root ganglion (DRG) can successfully manage cervical radicular pain. [6,9,21] However, in the clinical practice, despite undergoing PRF, some patients continue to complain of persisted cervical radicular pain.…”

Pulsed Radiofrequency

“…Various experimental neuropathic pain models show the pain-relieving effect of PRF on mechanical hypersensitivity, and sometimes on thermal allodynia [79][80][81][82][83][84] (Table 1). …”