The majority of unmyelinated afferent axons in human ventral roots probably conduct pain.

Three patients with intractable chest pain had undergone dorsal rhizotomy. None had obtained relief, but all three had developed dysesthesia and hyperesthesia, in addition to the original pain persisting in the supposedly deafferented area. Dorsal ganglionectomy was performed for these 3 patients in 1976 and they were followed for 3 years. Following ganglionectomy two of the three developed total anesthesia, including loss of dysesthesia, hyperesthesia, and the original pain. Light and electron microscopical examination of the ventral roots removed at the time of ganglionectomy showed that unmyelinated axons constituted approximately 25% of the total fiber count. Two ventral roots from one patient who previously had serendipitous removal of dorsal ganglia showed a marked reduction in the population of unmyelinated axons. The observations support Coggeshall's contention that the majority of unmyelinated axons in the ventral roots are sensory and probably conduct pain.