American Society for Peripheral Nerve

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Brief Electrical Stimulation Enhances Axon Regeneration through a Nerve Graft
Kevin Zuo, MD1; Golsa Shafa, BSc2; Kira Antonyshyn, BSc1; Katelyn Chan, B.Eng BioSci3; Tessa Gordon, PhD4; Gregory H. Borschel, MD3
1University of Toronto, Toronto, ON, Canada, 2Hospital for Sick Children, Toronto, ON, Canada, 3Division of Plastic and Reconstructive Surgery, The Hospital for Sick Children, Toronto, ON, Canada, 4Division of Plastic and Reconstructive Surgery, University of Toronto, Toronto, ON, Canada

INTRODUCTION
Nerve graft reconstruction of gap defects may result in variable outcomes. Electrical stimulation (ES) at 20 Hz for 1 hour significantly enhances axon regeneration following nerve crush and nerve transection/repair. Few studies have examined the effect of ES in nerve grafting. Furthermore, it is not known if a second, delayed session of ES has added benefit to an initial session of ES in staged surgical procedures such as cross face nerve grafting for facial reanimation. The objectives of this rodent nerve autograft study were to evaluate if ES enhances axon regeneration and if there is added benefit of a second, delayed session of ES (serial ES) on axon regeneration as compared to a single session only of ES.

MATERIALS & METHODS
Transgenic thy1-GFP rats were randomized to control (sham ES + sham ES), single ES (ES + sham ES), or serial ES (ES + ES). A 5 mm defect in the right common peroneal (CP) nerve was reconstructed with a reversed 20 mm left CP autograft. Stainless steel electrodes placed proximal to the graft were connected to a Grass SD9 stimulator. Rats received either 1 hour of ES (20 Hz, 3-5 V, 0.1 ms pulses) or sham ES (stimulator not turned on) prior to wound closure. After 4 weeks, the right CP was re-exposed, electrodes were placed again, and rats received either ES or sham ES for 1 hour. At 6 weeks post initial surgery, CP nerve was retrograde labeled to enumerate motor and sensory neurons with regenerated axons (mean SD).

RESULTS
Significantly more motoneurons regenerated axons in rats that received single ES (314 70) or serial ES (292 60) compared to rats receiving only sham ES (182 72, p=0.0002). There was no significant difference in regenerated motoneurons between single and serial ES. For regenerated sensory neurons, when compared to sham ES (544 165), there were significantly greater sensory neurons in serial ES (769 188, p=0.03) but not single ES (754 144, p =0.06). There were no significant differences in muscle mass ratios of tibialis anterior or extensor digitorum longus.

CONCLUSIONS
ES enhances axon regeneration following immediate nerve autografting. After one session of ES at the time of graft reconstruction, a second session of delayed ES does not further increase axon regeneration. Future studies are needed to assess functional outcome. ES is a clinically translatable technique that may have a role in nerve gap reconstruction.


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