Low frequency brief electrical stimulation to enhance axon regeneration after transection and nerve grafting

Zuo, Kevin 1, 2, 3 ; Gordon, Tessa 2, 3 ; Borschel, Gregory 1, 2, 3

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto; 2. Neurosciences & Mental Health, SickKids Research Institute; 3. Division of Plastic & Reconstructive Surgery,, Department of Surgery, University of Toronto

Injuries to the peripheral nervous system are common and lead to paralysis, sensory impairment, and functional disability. Peripheral nerves possess innate regenerative capacity; however, even with meticulous surgical repair, this is a very slow process and long distances of regeneration for end organ reinnervation inevitably result in an unsatisfactory patient outcome. A novel strategy of enhancing nerve regeneration is brief electrical stimulation (ES) at 20 Hz for 1 hour at the time of surgical repair. Brief ES has demonstrated effectiveness in accelerating nerve regeneration in both acute and chronic models of animal nerve injury and is now being used clinically in patients. The mechanism of action occurs at the level of the cell body with upregulation of mitogens and cytoskeletal proteins. While the current clinical paradigm is ES at 20 Hz for 1 hour, shorter durations have not been investigated and if proven effective, could improve operating room efficiency and reduce healthcare resources. Furthermore, ES has not been investigated in nerve grafts, which are pivotal when transected nerve stumps cannot be directly re-approximated.

Aims and Hypotheses

Aim 1: To determine the effect of brief ES at 20 Hz for 30 minutes versus 1 hour in enhancing nerve regeneration after cut and repair nerve injury.

Hypothesis 1: Brief ES at 20 Hz for 30 minutes enhances nerve regeneration to an extent comparable to that of brief ES at 20 Hz for 1 hour.

Aim 2: To determine the effect of brief ES at 20 Hz for 1 hour to enhance nerve regeneration using a nerve graft in a nerve gap defect.

Hypothesis 2: Brief ES at 20 Hz for 1 hour enhances nerve regeneration through a nerve graft.

Methods

For Aim 1, Sprague-Dawley rats underwent common peroneal (CP) nerve transection and immediate surgical repair, followed by electrical stimulation with insulated stainless steel electrodes at the repair site at 20 Hz, 0.1 ms pulse width, 3 V to achieve visible tetanic contractions, and a duration of either 30 minutes or 1 hour. A control group of animals did not receive ES.

For Aim 2, a gap defect was created in the CP nerve and a nerve graft from the contralateral leg was surgically interposed to restore continuity. Animals were randomized to receive either 1 hour of ES at 20 Hz, 0.1 ms pulse width, 3 V or 1 hour of sham ES, during which electrodes were connected to a stimulator that was not turned on.

After 2 weeks (Aim 1) or 6 weeks (Aim 2), retrograde labelling was performed 10 mm distal to the injury site to enumerate regenerated motor and sensory neurons under fluorescence microscopy of spinal cord ventral horn and dorsal root ganglia, respectively. Secondary outcome measures include fresh muscle mass ratio and quantitative histomorphometry for axon number, density, diameter, and myelin sheath thickness.

Results

Surgeries have been completed for Aims 1 and 2. The results are currently being collected and will be available at the time of iARC for presentation.