Directional specificity of regenerating primary sensory neurons after peripheral nerve crush or transection and epineurial suture A sequential double-labeling study in the rat

Clinical and experimental observations have demonstrated that peripheral nerve transection generally results in lasting disturbed sensory discrimination whereas nerve crush is followed by more or less complete functional restoration. This has been explained by an increased misdirection of regenerating fibers after transection as compared to crush injury. In the present study, sequential double-labeling was used to investigate the relative proportions of peripherally misdirected sensory fibers in the sural and tibial nerve branches after crush or transection of the parent sciatic nerve in the rat. Control experiments showed that 0.21% ± 0.12 (mean ± S.D.) of all labeled tibial and sural neurons normally send axons to both nerves. After sciatic nerve crush or transection, 1.31% ± 0.78 and 3.79% ± 3.01, respectively, of all labeled tibial and sural axons were double-labeled indicating previously sural axons now having an axon in the tibial. Statistically significant differences in the percentages of bidirectional sciatic sensory neurons were found between the normal controls and after crush injury (P < 0.01) or transection injury (P < 0.001), respectively, but not between transection and crush (P > 0.05). The results indicate that the number of sensory neurons having an axon in two peripheral nerves is normally very small, that a substantial number of sensory axons become misdirected after both crush and transection with resuture, and that the number of misdirected fibers in the major sciatic branches after these types of injury is similar.