Pulsed Radiofrequency Improves Neuropathic Pain in Chronic Constriction Injury Rats through the Upregulation of the Transcription and Translation Levels of Glial Cell Line-Derived Neurotrophic Factor

Abstract

Background: Several studies in recent years have confirmed that the direct application of pulsed radiofrequency (PRF) on peripheral nerve compression points can alleviate hyperalgesia in animal models of neuropathic pain (NP). However, the mechanism underlying the treatment of peripheral nerves by PRF is unclear. Objectives: We aim to observe changes in pain behavior after the application of PRF on the ligation site of the sciatic nerves (SNs) of rats with chronic constriction injury (CCI) and to investigate the effects of PRF on the transcription and translation levels of glial cell line-derived neurotrophic factor (GDNF) in nerve tissues at the treatment site. Study Design: A randomized, experimental trial. Setting: Experimental Animal Center, Beijing Tiantan Hospital. Methods: Ninety-six adult male Sprague-Dawley rats were randomly divided into 4 groups: sham-sham (SS) group, sham-PRF (SP) group, CCI-sham (CS) group, and CCI-PRF (CP) group. The right SNs of rats in the CS and CP group were ligated to establish the CCI model. The right SNs in the SS and SP groups were isolated and exposed but without being ligated. On the fourteenth day after CCI/sham operation, PRF treatment was performed on the midpoint of the ligation sites of the SN in the CP group and the corresponding sites in the SP group. The electrode was only placed at the ligation sites of the SN in the CS group and the corresponding sites in the SS group without current being applied. The 50% paw withdrawal threshold (50%PWT) and thermal withdrawal latency (TWL) of rats in all of the groups were measured. The transcription and translation levels of GDNF of the PRF/sham treatment sites were measured before and after treatment by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assays (ELISAs). Results: The 50%PWT value of the hind paws of rats in the CP group gradually increased on day 6 after the PRF treatment and was significantly higher than that in the CS group (6 days after treatment P < 0.05; 14 days after treatment P < 0.01). The TWL value in the CP group was higher than that in the CS group 2 days after treatment (P < 0.05) and was significantly higher (P < 0.01) from day 6 until the end of the experiment. On the day 6 and 14 after PRF treatment, the mRNA and protein expression levels of GDNF at the ligation sites of the SNs of rats in the CP group were higher than both the levels before treatment and those in the CS group (P < 0.01). Limitations: The efficacy of PRF treatment in the CCI model was only tested within 14 days, and the changes in GDNF levels were only tested at 3 time-points before and after treatment. Conclusions: The direct application of PRF on SN ligation sites in the CCI model can safely and effectively alleviate NP. One of the mechanisms of this effect could be the upregulation of the transcription and translation of GDNF in compressed SNs. Key words: Pulsed radiofrequency, chronic constriction injury, sciatic nerve, 50% paw withdrawal threshold, thermal withdrawal latency, glia cell line-derived neurotrophic factor, reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay