Rapid, effective, and long‐lasting behavioral recovery produced by microsutures, methylene blue, and polyethylene glycol after completely cutting rat sciatic nerves

Abstract

Behavioral function lost in mammals (including humans) after peripheral nerve severance is slowly (weeks to years) and often poorly restored by 1-2-mm/day, nonspecifically directed outgrowths from proximal axonal stumps. To survive, proximal stumps must quickly repair (seal) plasmalemmal damage. We report that, after complete cut- or crush-severance of rat sciatic nerves, morphological continuity, action potential conduction, and behavioral functions can be consistently (>98% of trials), rapidly (minutes to days), dramatically (70-85% recovery), and chronically restored and some Wallerian degeneration prevented. We assess axoplasmic and axolemmal continuity by intra-axonal dye diffusion and action potential conduction across the lesion site and amount of behavioral recovery by Sciatic Functional Index and Foot Fault tests. We apply well-specified sequences of solutions containing FDA-approved chemicals. First, severed axonal ends are opened and resealing is prevented by hypotonic Ca²⁺-free saline containing antioxidants (especially methylene blue) that inhibit plasmalemmal sealing in sciatic nerves in vivo, ex vivo, and in rat B104 hippocampal cells in vitro. Second, a hypotonic solution of polyethylene glycol (PEG) is applied to open closely apposed (by microsutures, if cut) axonal ends to induce their membranes to flow rapidly into each other (PEG-fusion), consistent with data showing that PEG rapidly seals (PEG-seals) transected neurites of B104 cells, independently of any known endogenous sealing mechanism. Third, Ca²⁺-containing isotonic saline is applied to induce sealing of any remaining plasmalemmal holes by Ca²⁺-induced accumulation and fusion of vesicles. These and other data suggest that PEG-sealing is neuroprotective, and our PEG-fusion protocols that repair cut- and crush-severed rat nerves might rapidly translate to clinical procedures.

Axonal Fusion via Conduit-Based Delivery of Hydrophilic Polymers

“…The ability to immediately regain nerve function after injury to a segment of a peripheral nerve would revolutionize current nerve repair strategies. We have previously described a technique that allows early physiologic and behavioral recovery after nerve transection by fusing the cut ends of the axons back together with the hydrophilic polymer, polyethylene glycol (PEG) [4]. We then expanded that strategy and the current report describe how both physiologic and behavioral recovery can be immediately restored across a nerve gap using a fresh nerve autografts and this PEG fusion technique [29].…”

Peripheral Nerve Reconstruction after Injury: A Review of Clinical and Experimental Therapies

“…Preliminary studies have been promising demonstrating a small improvement in gait function after nerve crush injury (axonotmesis) and a 13-fold improvement after neurotmesis injury, compared to standard of care microsurgery [70, 71]. A recent study reported that compound action potentials could be recorded distal to a 10-mm nerve graft repair up to 7 days after surgery [72].…”

Advances in peripheral nerve regeneration as it relates to VCA

“…A specific sequence of antioxidases and polyethylene glycol has now been developed to lead to optimal axonal fusion. 53 This study demonstrated almost immediate restoration of electrophysiology (compound action potentials) across the repair site following fusion as well as dramatic improvement in functional recovery (gait function) in a rat model of sciatic nerve repair when polyethylene glycol fusion was used. This repair method was recently used in humans for the first time, in digit re-implantation, with positive results, but requires further clinical study to determine its long-term efficacy and widespread application.…”