Single Afferent Nerve Fibers in the Spinal Dorsal Roots Activated by Manual Acupuncture Needle Stimulation in Frog's Hind Limbs.

Abstract

The present experiment aimed to determine what kinds of afferent nerve fibers in dorsal roots are stimulated during manual stimulation with an acupuncture needle by using single nerve unit recording techniques in bullfrogs. An acupuncture needle was inserted into a hind limb via the skin to the muscles and was manually twisted right and left at a frequency of about 1Hz. Dorsal roots of the 8th and 9th spinal nerves were cut close to their entrance into the spinal cord and dissected to record single unitary afferent activity. The conduction velocity of the single nerve fiber was measured. A total of 30 units were successfully dissected and all of those responded to manual twisting stimulation of the acupuncture needle in a hind limb. All of the dissected fibers had their receptive fields only at the unilateral side ipsilateral to the recording site never contralateral. The conduction velocities of all 30 units ranged between 5.3 ‑ 40.7 m/s. The reports by Erlanger et al. 1 2 which showed the maximum conduction velocities of Aα β δ and C afferent fibers in bullfrogs to be about 48.2 m/s 28.7 m/s 13.6 m/s and 0.7 m/s respectively indicated that all 30 units dissected at the dorsal roots and responding to manual acupuncture stimulation were Aα β δ fibers. We could not record single nerve unitary activity of C fibers probably because of technical difficulties. We conclude that manual acupuncture needle stimulation to the hind limbs excites single unitary afferent fibers of Aα β and δ fibers in the dorsal roots of bullfrogs.