Decoupled Epineurial and Axonal Deformation in Mouse Median and Ulnar Nerves.

INTRODUCTION: Peripheral nerves accommodate mechanical loads during joint movement. Hypothesized protective features include increased nerve compliance near joints and axonal undulation. How axons perceive nerve deformation is poorly understood. We tested whether nerves increase local axonal undulation in regions of high epineurial strain, to protect nerve fibers from strain-induced damage.

METHODS: Regional epineurial strain was measured near the elbow in median and ulnar nerves of mice expressing axonal fluorescence, pre- and post-decompression. Regional axonal tortuosity was quantified under confocal microscopy.

RESULTS: Nerves showed higher epineurial strain just distal to the medial epicondyle; these differences were eliminated after decompression. Axonal tortuosity also varied regionally; however, unlike in the epineurium, was more tortuous in proximal regions.

DISCUSSION: We propose a neuromechanical model whereby axons can unravel along their entire length due to looser mechanical coupling to the peri/epineurium. Our findings have important implications for understanding nerve biomechanics and dysfunction. This article is protected by copyright. All rights reserved.