Pulsed radiofrequency treatment attenuates increases in spinal excitatory amino acid release in rats with adjuvant-induced mechanical allodynia

Abstract

Excitatory amino acids (EAAs) play a critical role in the development of peripheral tactile and thermal hypersensitivity after the induction of paw inflammation in rats. We used a spinal microdialysis model to examine the effect of complete Freund's adjuvant (CFA)-induced inflammation on the spinal release of EAAs and assessed the antinociceptive effect of pulsed radiofrequency (PRF). CFA was injected into the plantar surface of the left hind paw to induce inflammation. Either the sciatic nerve of adult CFA rats in the mid-thigh, or the L4 anterior primary ramus just distal to the intervertebral foramen was treated with PRF (20 ms, 500 kHz pulses) at a rate of 2 Hz and a maximum temperature of 42°C. Concentrations of amino acids in the dialysate from the spinal microdialysis catheter and mechanical paw withdrawal threshold were determined to evaluate the analgesic effect of PRF. An intraplantar injection of CFA induced a significant release of glutamate, aspartate, and citrulline for 7 days. The behavior tests showed that PRF administered to the anterior ramus, just distal to the intervertebral foramen, significantly reduced mechanical allodynia, and microanalysis showed a significant suppression of EAAs and citrulline release. The antiallodynic effect of PRF was observed the day following CFA injection and maintained for 7 days. We showed that PRF administered adjacent to the dorsal root ganglion suppresses the release of EAAs, which may account for the PRF antiallodynic properties observed in adjuvant-induced inflammation.