H reflex restitution and facilitation after different types of peripheral nerve injury and repair

This study addresses the restitution of monosynaptic H reflex after nerve injuries and their role in the recovery of walking. Adult rats were submitted to sciatic crush, complete section repaired by aligned or crossed fascicular suture, or an 8-mm resection repaired by autograft or tube repair. The sciatic nerve was stimulated proximal to the injury site and the M and H waves were recorded from gastrocnemius (GCm) and plantar (PLm) muscles at monthly intervals during 3 months postoperation. Walking track tests were also carried out and the sciatic functional index (SFI) calculated to assess gait recovery. The M and H waves reappeared in all the animals at the end of the follow-up. The H/M amplitude ratio increased during the first stages of regeneration and tended to decrease to control values as muscle reinnervation progressed. However, final values of the H/M ratio for the PLm remained significantly higher in all the groups except that with a nerve crush. The walking track pattern showed an appreciable recovery only after crush injury. Final SFI values correlated positively with the M wave amplitude and negatively with the H/M ratio. In conclusion, H reflex is facilitated after peripheral nerve injury and regeneration and tends to return to normal excitability with time. Changes in the H reflex circuitry and excitability correlated positively with the deficient recovery of walking pattern after severe nerve injury.