Changes in the structural properties of peripheral nerves after transection

Functional reinnervation of the canine bladder after spinal root transection and immediate end-on-end repair

The goal of this study was to transect and immediately repair ventral roots, selected by their ability to stimulate bladder contraction, to assess the feasibility of bladder reinnervation in a canine model. Brain-derived neurotrophic factor (BDNF) was delivered via an osmotic pump (0.5 or 5 mg/mL) to a cuff surrounding the reanastomosis site to the two root bundles on one side. Electrodes were implanted bilaterally immediately proximal to the site of surgical reanastomosis. Results were compared to four root-intact, control animals that also received bilateral electrode implantation. At 6-12 months post-surgery, five of eight nerve transected and repaired animals showed increased pressure and bladder emptying during electrical stimulation of the repaired ventral roots contralateral to the BDNF delivery side. Nerve tracing studies one year postoperatively determined the repaired roots to be S1 and S2 and showed regrowth of axons from the spinal cord to nerve sites proximal to the repair site and to the bladder, and the presence of neurofilament-labeled axons growing across the ventral root repair site. In conclusion, transected ventral and dorsal roots in the sacral spine can be repaired and are capable of functionally reinnervating the urinary bladder. This feasibility study paves the way for future studies utilizing other more proximal motor nerves to bypass the transection site for bladder reinnervation.

Changes in the stress relaxation properties of peripheral nerves after transection

Changes in peripheral nerve stress relaxation after transection were measured weekly for 5 weeks in the distal stumps of sciatic nerves of 50 Sprague-Dawley rats. Each week after transection the distal stumps of the transected nerves showed decreased stress relaxation compared with the freshly transected contralateral nerves after undergoing a 10% elongation. The transected side always showed less stress relaxation at 30 minutes than the intact contralateral side (average, 24%; range, 15% to 32%). A statistically significant difference in mean stress relaxation between the cut nerves and the uncut sciatic nerves occurred for weeks 1 through 4. Week 5 demonstrated a decrease in mean stress relaxation of the experimental side compared with the contralateral control side but this was not statistically significant. Decreased stress relaxation of the distal stump results in increased tension at the suture line as the nerve gap is overcome when performing a delayed neurorrhaphy at 1 to 5 weeks after transection.