Effect of High-Frequency Alternating Current on Spinal Afferent Nociceptive Transmission

Objective The study was performed to test the hypothesis that high-frequency alternating current (HFAC) ranging from 2 to 100kHz delivered to the spinal dorsal roots reduces activity of spinal wide dynamic range (WDR) dorsal horn neurons (DHNs) during noxious peripheral stimulation. Materials and Methods This hypothesis was tested in both small and large animal in vivo preparations. Single-unit extracellular spinal DHN recordings were performed in seven adult rats and four adult goats while testing various parameters of HFAC delivered to the nerve roots or dorsal root entry zone using various electrode types. Frequencies tested ranged from 2 to 100kHz but focused on the 3 to 50kHz range. This study investigated the ability of HFAC to inhibit WDR neuronal activity evoked by noxious mechanical (pinch), and electrical stimuli was tested but was primarily focused on electrical stimulation. Results Rat Study: Effects of HFAC were successfully tested on 11 WDR neurons. Suppression or complete blockade of evoked activity was observed in all 11 of these neurons. Complete data sets for neurons systematically tested with 15 baseline and post-HFAC stimulus sweeps were obtained in five neurons, the nociceptive activity of which was suppressed by an average of 69 +/- 9.7% (p < 0.0001). Goat Study: HFAC was successfully tested on 15 WDR neurons. Conclusive suppression or complete nociceptive blockade was observed for 12/15 and complete data sets with at least 20 baseline and post-HFAC stimulus sweeps were obtained from eight DHNs. For these neurons the mean activity suppression was 70 +/- 10% (p < 0.005). Conclusions Delivery of HFAC to the region of epidural nerve root or nerve root entry inhibited afferent nociceptive input and therefore may have potential to serve as an alternative to traditional spinal cord stimulation without sensory paresthesia as neuronal activation cannot occur at frequencies in this range.