THE FUNCTION OF THE NON-MYELINATED FIBERS OF THE DORSAL ROOTS

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Abstract
On the basis of the identification previously made of the so-called "C" wave of the nerve action potential as that assignable to non-myelinated fibers, no sensory or reflex effects can be elicited from stimulation of these fibers after differentially blocking all myelinated fibers in the saphenous nerves of dogs and rabbits by means of pressure. Nerve response beyond the block was followed by means of the cathode ray oscillograph with the nerve in functional connection with the body, after partial recovery from ether anesthesia. Release of pressure to permit only B fibers (small myelinated) to take effect, results upon stimulation in respiratory, vasomotor and motor responses, and obvious pain as anesthesia is reduced. Stimulation of the depressor nerve in rabbits results in a relative increase of volume of the plethysmographed sympathec-tomized limb as compared with the denervated limb. During perfusion of both hind limbs, depressor nerve stimulation results in an uncompensated increase of flow through the sympathectomized limb with dorsal roots intact, as compared with the denervated limb. This increase has a latent period of several seconds, reminiscent of the latent period of "antidromic" dorsal root vasodila-tion, and cannot be assigned to lowering of systemic blood pressure. It is apparently due to reflex activation of non-myelinated fibers over synapses within the spinal cord. Since no afferent function, and certainly not pain, can be assigned to dorsal root non-myelinated fibers, and since their presumed antidromic action can be initiated reflexly, they are concluded to be motor fibers, here as in the autonomic system.