Effect of pulsed radiofrequency application to dorsal root ganglias on neuronal Nav1.8 expression in a rat model of inflammatory pain

Objective To evaluate the effect of pulsed radiofrequency application to dorsal root ganglions (DRGs)on neuronal Nav1.8 expression in a rat model of inflammatory pain. Methods Twenty-four adult male Sprague-Dawley rats, aged 6-8 weeks, weighing 200-250 g, were randomly divided into 4 groups (n=6 each)using a random number table: control group (group C), inflammatory pain group (group IP), pulsed radiofrequency group (group PR), and inflammatory pain+ pulsed radiofrequency group (group IP+ PR).2.5% formalin 100 μl was injected into the plantar surface of the right hindpaw to induce inflammatory pain.Pulsed radiofrequency was applied on L4, 5 DRGs at 42 ℃ for 180 s starting from 4 days after formalin injection.At 1 day before formalin injection (T0), and 1, 3, 5 and 7 days after formalin injection (T1-4), the mechanical paw withdrawal threshold (MWT)and thermal paw withdrawal latency (TWL)were measured in the right hindpaw.After the last measurement of pain threshold, the rats were sacrificed, and the DRGs of the L4, 5 were removed for determination of Nav1.8 mRNA expression (by real-time reverse transcriptase-polymerase chain reaction)and Nav1.8 protein expression (by Western blot). Results Compared with group C, the MWT was significantly decreased, and the TWL was shortened at T1-4, and the expression of Nav1.8 protein and mRNA was up-regulated in IP and IP+ PR groups (P<0.05). Compared with group IP, the MWT was significantly increased, and the TWL was prolonged at T1-4, and the expression of Nav1.8 protein and mRNA was down-regulated in group IP+ PR (P<0.05). Conclusion The mechanism by which pulsed radiofrequency application to DRGs reduces inflammatory pain is probably related to down-regulation of neuronal Nav1.8 expression in rats. Key words: Catheter ablation; Sodium channels; Ganglia, spinal; Neurons; Inflammation; Pain