The Effect of Pulsed Radiofrequency Current on Mechanical Allodynia Induced with Resiniferatoxin in Rats

Abstract

In Brief BACKGROUND: Pulsed radiofrequency (PRF) is a popular pain treatment modality. The effect of PRF current on neuropathic pain has not been examined in detail. We investigated the effect of PRF current on mechanical allodynia induced with resiniferatoxin (RTX) in rats, especially regarding the influence of the duration of allodynia before PRF procedures and that of exposure time to PRF. METHODS: Adult male Sprague-Dawley rats (weighing 250–400 g) received a single intraperitoneal injection of RTX (200 μg/kg) under 2 to 3% sevoflurane anesthesia. Rats in group S2 (n = 5) were assigned to receive PRF current to the right sciatic nerve for 2 minutes 1 week after RTX treatment; rats in group M2 (n = 6), PRF current for 2 minutes 3 weeks after RTX treatment; rats in group L2 (n = 7), PRF current for 2 minutes 5 weeks after RTX treatment; rats in group S4 (n = 5), PRF current for 4 minutes 1 week after RTX treatment; rats in group S6 (n = 5), PRF current for 6 minutes 1 week after RTX treatment; and rats in group S0 (n = 3), no PRF current was delivered. Instead, the needle and electrode were inserted at proper points for 6 minutes 1 week after RTX treatment. All rats were evaluated for sensitivity to mechanical stimulation with von Frey filaments and to thermal stimulation with a thermal testing apparatus and for motor function using placing and grasping reflexes before injection of RTX, every week after injection of RTX, and 1, 2, 3, 4, and 5 weeks after PRF treatment. RESULTS: The paw withdrawal thresholds of both hindpaws 1 week after RTX treatment were significantly lower than the pre-RTX baseline in all groups. In groups S2, S4, S6, and M2, after PRF procedures, the ipsilateral paw withdrawal thresholds significantly increased. A statistically significant difference was detected between the PRF-treated and PRF-untreated hindpaws. The ipsilateral–contralateral paw withdrawal thresholds after PRF procedures in group S2 were significantly higher than those in groups M2 and L2. Between groups M2 and L2, significant differences were found 1, 2, 4, and 5 weeks after PRF procedures. The ipsilateral–contralateral paw withdrawal thresholds in group S6 were significantly higher than those in groups S2 and S4 5 weeks after PRF procedures. No significant difference was found between groups S2 and S4 at any time. After PRF procedures, no difference in the withdrawal latency after heat stimulation and no motor disturbance were observed at any time in all groups. CONCLUSIONS: PRF treatment was more effective when applied in the early stages of mechanical allodynia (1 week) in rats. Increased exposure time to PRF current from 2 to 6 minutes showed a significant antiallodynic effect without motor impairment. We propose the application of PRF current for 6 minutes adjacent to the nerve as soon as possible when allodynia appears. Published ahead of print July 2, 2010