Peripheral nerve stimulation suppression of C-fiber-evoked flexion reflex in rats. Part 1: Parameters of continuous stimulation.

Transcutaneous electrical nerve stimulation (TENS) is now a well established clinical technique to alleviate chronic pain. Its mechanism of action remains unknown and the stimulation parameters used are based on subjective reports from patients. In the present study, a systematic investigation has been performed with conditioning stimulation of different parameters delivered to a dissected skin nerve in the lightly anesthetized rat, utilizing the size of a C-fiber-evoked flexion reflex as a measure of transmission from nociceptive afferent fibers in the spinal cord. A stimulation intensity that recruited both A-beta and A-delta fibers was more effective in depressing the C-fiber-evoked reflex at all frequencies studied than were intensities activating A-beta fibers only. A stimulation frequency of 80 Hz gave the most profound inhibition. The implications for clinical treatment are discussed.