On regenerative and collateral sprouting to hind limb digits after sciatic nerve injury in the rat.

PURPOSE: This study examines the proportions of regenerative and collateral sprouting to the skin after peripheral nerve injury.

METHODS

In the first experimental paradigm, primary afferent neurones were pre-labelled with Diamidino Yellow (DY), injected in digit 3, followed by sciatic nerve section and repair. After three months of regeneration, digit 3 was re-injected with Fast Blue (FB) to label regenerating cells. Fluoro-Gold (FG) was applied to the femoral (FEM) and musculocutaneous (MC) nerves four days later to quantify their contribution to the innervation. In the second experimental paradigm, sciatic nerve was first sectioned and repaired. Three months later, the sciatic was resected, and digit 3 injected with FB. After four more days, FEM and MC were resected and FG injected in all digits.

RESULTS

Neurones in dorsal root ganglion (DRG) L5 had a higher rate of correct reinnervation of digit 3 (44-72%) than neurones in DRG L4 (14-44%). Like in control cases, only occasional axons were traced from the FEM and MC. In the second experiment, only occasional labelled neurones appeared.

CONCLUSIONS

The results indicate differences in the capacity for correct peripheral sensory reinnervation between segmental levels, and that in this model collateral sprouting was practically non-existent compared to regenerative sprouting.