The effect of pulsed radiofrequency current on mechanical allodynia induced with resiniferatoxin in rats.
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 microg/kg) under 2 to 3% sevoflurane anesthesia. Rats in group S(2) (n = 5) were assigned to receive PRF current to the right sciatic nerve for 2 minutes 1 week after RTX treatment; rats in group M(2) (n = 6), PRF current for 2 minutes 3 weeks after RTX treatment; rats in group L(2) (n = 7), PRF current for 2 minutes 5 weeks after RTX treatment; rats in group S(4) (n = 5), PRF current for 4 minutes 1 week after RTX treatment; rats in group S(6) (n = 5), PRF current for 6 minutes 1 week after RTX treatment; and rats in group S(0) (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 S(2), S(4), S(6), and M(2), 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 S(2) were significantly higher than those in groups M(2) and L(2). Between groups M(2) and L(2), significant differences were found 1, 2, 4, and 5 weeks after PRF procedures. The ipsilateral-contralateral paw withdrawal thresholds in group S(6) were significantly higher than those in groups S(2) and S(4) 5 weeks after PRF procedures. No significant difference was found between groups S(2) and S(4) 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.
Tanaka
Nobuhiko
N
Department of Anesthesiology and Intensive Care, Faculty of Medicine, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan. nobut@med.miyazaki-u.ac.j
Yamaga
Masaharu
M
Tateyama
Shingo
S
Uno
Takeshi
T
Tsuneyoshi
Isao
I
Takasaki
Mayumi
M
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004224:Diterpenes; D004558:Electric Stimulation; D007839:Functional Laterality / Q000187:drug effects; D018737:Hand Strength; D006358:Hot Temperature; D008297:Male; D009498:Neurotoxins; D010146:Pain / Q000139:chemically induced* / Q000532:radiotherapy*; D010147:Pain Measurement / Q000187:drug effects; D010812:Physical Stimulation; D011846:Radio Waves; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects
D004224:Diterpenes; D009498:Neurotoxins; C024353:resiniferatoxin