Effects Of High Voltage Pulsed Radiofrequency On The Ultrastructure And The Nav1.7 Level Of Dorsal Root Ganglion In Rats With Spared Nerve Injury

Objective: The aim of this study was to compare the analgesic efficacy between standard voltage and high voltage pulsed radiofrequency(PRF)in rats with spared nerve injury(SNI),and observe the changes of ultrastructure and Nav1.7 level in the dorsal root ganglion(DRG).Methods: Herein,a total of 120 adult male Sprague-Dawley(SD)rats were randomly assigned in 5 groups as follows: Sham,SNI,Free-PRF,standard-voltage PRF(SV-PRF),and high voltage PRF(HV-PRF).All rats(except for those in Sham group)were subjected to SNI.The standard voltage and high voltage PRF therapy applied to the left L5 DRG was performed in the SV-PRF group and HV-PRF group on day 7 after nerve injury,whereas no PRF was concurrently delivered in the Free-PRF group.The paw mechanical withdrawal threshold(PMWT)was detected before SNI(baseline)and on days 1,3,7,8 10,14 and 21.The ultrastructural changes of L5 DRG were analyzed with transmission electron microscopy on day 21.Meanwhile,the expression levels of Nav1.7 in left L5 DRG were detected by immunofluorescence and Western blot on days14 and 21.Results:(1)PMWT:The baselines of PMWT in rats showed no significant difference among groups(P > 0.05).Compared with Sham group,PMWT in other four groups were significantly decreased(P < 0.01)after SNI.There were no significant differences in the PMWT at every time point between SNI group and Free-PRF group(P>0.05).Compared with Free-PRF group,PMWT in SV-PRF group and HV-PRF group were both significantly increased after the treatment of PRF(P< 0.01).Meanwhile,the PMWT was significantly higher in HV-PRF group than that in SV-PRF group on days14 and 21.(2)the changes of ultrastructure in L5 DRG: The soma and nerve fibers of left L5 DRG in both SNI and Free-PRF groups were acutely damaged,and some of the nerve fiber myelin sheaths were completely destroyed after nerve injury compared with those in Sham group.While in SV-PRF and HV-PRF groups,nerve fibers were noticeably repaired compared with those in SNI and Free-PRF groups.Meanwhile,there was a significant ultrastructural improvement in left L5 DRG in HV-PRF group compared to that in SV-PRF group.(3)Expression of Nav1.7 in L5 DRG: Compared with Sham group,the expression of Nav1.7 in left L5 DRG were significantly increased in other four groups on days 14 and 21(P < 0.01).Whereas,there were no significant differences in the expression of Nav1.7 in left L5 DRG between SNI group and Free-PRF group on days 14 and 21(P>0.05).And the expression of Nav1.7 in left L5 DRG was significantly downregulated in SV-PRF group and HV-PRF group than that in Free-PRF group(P < 0.01).Meanwhile,there was a significant lower of Nav1.7 level in HV-PRF group compared to that in SV-PRF group(P < 0.05).Conclusion: The analgesic efficacy of high voltage PRF was superior to standard voltage PRF.The underlying mechanisms of these effects may be associated with the improvement of ultrastructure and the downregulation of Nav1.7 in DRG.