Changes in axonal impulse conduction correlate with sensory modality in primary afferent fibers in the rat.

Conduction velocity was measured in vivo in single cutaneous afferent fibers of rat sciatic nerve that were characterized by natural stimulation. During sustained electrical stimulation, impulses slowed less and propagated more reliably in cold fibers (both A delta and C) than in nociceptive fibers of similar conduction velocity. Velocity in cold fibers tended to stabilize after an initial decrease rather than decrease throughout the stimulation as for nociceptive fibers. The slowing correlated with axon modality and hence with natural firing pattern, raising the possibility that impulse activity can determine conduction properties of axons.