Fig. 2.
Progressive failure of regenerating axons to grow through an autograft into the distal nerve stump and to reinnervate denervated muscles after delayed nerve repair. (a) The experimental protocol was to tease Sprague–Dawley rat ventral roots to evoke and record isometric contractile force from muscle fibers in the reinnervated tibialis anterior (TA) muscle that were reinnervated by single tibial (Tib) axons (motor units) at least 6 months after cross-suturing the proximal tibial (Tibp) nerve stump to the distal common peroneal (CPd) nerve via a CP nerve autograft (CPg) taken from the contralateral hindlimb. The cross-suture took place either (a) immediately or after a delay of up to 500 days, resulting in (b) chronic TIB axotomy, (c) chronic CP graft denervation, or (d) chronic TA muscle denervation. The relative contributions of (b) chronic axotomy, (c) chronic CP nerve denervation, and (d) TA muscle denervation to the decline in the number of regenerating Tib nerves that reinnervated the denervated TA muscle (motor unit number) are seen with each contributing to the progressive failure of nerve regeneration