Using the Neuromuscular Junction Cellular Response to Predict Functional Recovery AfterNerve Grafting in a Mice Experimental Model.

Abstract

Functional recovery following peripheral nerve injury worsens with increasing time of denervation prior to repair. Denervated muscle undergoes progressive atrophy that limits the extent to which motor end plates can be reinnervated. The aim of this study is to assess nerve injuries reconstructed at different time points, and identify various neural and muscle-based markers to predict functional outcome, including an in-depth look at the neuromuscular junction. Adult wild type C57BL/6J mice received surgery on the sciatic nerve and were divided into five groups: 1) Nerve cut and repaired, 2) Acute: nerve cut and immediately repaired with 1cm autograft, 3) Subacute: nerve grafted two weeks after injury, 4) Delayed (D): nerve grafted four weeks after injury, 5) Nerve cut and capped. Functional recovery was measured by treadmill and electrodiagnostic tests. Nerves were harvested for histology evaluation, and leg muscles for histology evaluation and NMJ immunofluorescent staining of motor end plate innervation and terminal Schwann cells (tSC). Delayed graft group performed worst in nearly all parameters. Subacute graft group shared more similarities with the acute group, especially the tSC response (Subacute 48% vs Acute 51%) and motor end plate innervation pattern (Subacute 75% vs Acute 72%). Only parameters to elucidate differences were muscle weight and motor end plate fragmentation. Traditional axon count failed to capture differences between the three groups. tSC activity and NMJ innervation pattern can be used as predictive markers of functional recovery that captures differences between acute, subacute and delayed nerve injuries.