Polyethylene glycol treated allografts not tissue matched nor immunosuppressed rapidly repair sciatic nerve gaps, maintain neuromuscular functions, and restore voluntary behaviors in female rats

Abstract

Many publications report that ablations of segments of peripheral nerves produce the following unfortunate results: (1) Immediate loss of sensory signaling and motor control; (2) rapid Wallerian degeneration of severed distal axons within days; (3) muscle atrophy within weeks; (4) poor behavioral (functional) recovery after many months, if ever, by slowly-regenerating (∼1mm/d) axon outgrowths from surviving proximal nerve stumps; and (5) Nerve allografts to repair gap injuries are rejected, often even if tissue matched and immunosuppressed. In contrast, using a female rat sciatic nerve model system, we report that neurorrhaphy of allografts plus a well-specified-sequence of solutions (one containing polyethylene glycol: PEG) successfully addresses each of these problems by: (a) Reestablishing axonal continuity/signaling within minutes by nonspecific ally PEG-fusing (connecting) severed motor and sensory axons across each anastomosis; (b) preventing Wallerian degeneration by maintaining many distal segments of inappropriately-reconnected, PEG-fused axons that continuously activate nerve-muscle junctions; (c) maintaining innervation of muscle fibers that undergo much less atrophy than otherwise-denervated muscle fibers; (d) inducing remarkable behavioral recovery to near-unoperated levels within days to weeks, almost certainly by CNS and PNS plasticities well-beyond what most neuroscientists currently imagine; and (e) preventing rejection of PEG-fused donor nerve allografts with no tissue matching or immunosuppression. Similar behavioral results are produced by PEG-fused autografts. All results for Negative Control allografts agree with current neuroscience data 1-5 given above. Hence, PEG-fusion of allografts for repair of ablated peripheral nerve segments expand on previous observations in single-cut injuries, provoke reconsideration of some current neuroscience dogma, and further extend the potential of PEG-fusion in clinical practice.

Polyethylene glycol solutions rapidly restore and maintain axonal continuity, neuromuscular structures, and behaviors lost after sciatic nerve transections in female rats

“…In this scenario, central and/or peripheral reorganization of non-specifically PEG-fused axons observed in possible combination with slow natural regeneration of axons not PEG-fused (which could also undergo central reorganization) would explain the time lag between immediate neuronal reinnervation within minutes and extensive behavioral restoration within weeks. Our data in this study and a subsequent paper on PEG-fusion of allografts (Mikesh et al, 2018) consistently support this hypothesis. That is, immediately after PEG-fusion and at all times tested to 42d PO, axons continue to conduct action potentials, release transmitter to generate end plate potentials that cause distal muscles to contract as evidenced by CAPs, CMAPS, and muscle twitches.…”

“…Qualitatively similar results are obtained for PEG-fused and Negative Control animals after completely ablating a 5–10mm segment of a sciatic nerve and inserting an autograft or allograft to bridge the nerve gap (Sexton et al, 2012; Riley et al, 2015; Mikesh et al, 2018). These data are also similar to data published by Thayer and his collaborators for single cut (Bamba et al, 2016a, 2017; Sexton et al, 2015; ; Riley et al, 2017,) and to de Medinaceli (1983) who, perhaps inadvertently, used other fusogens in a study designed to test a device to microsuture very carefully trimmed nerve ends after a single transection.…”

“…In contrast, singly-transected Negative Control axons that are not PEG-fused do not exhibit any the phenomena 1– 5 above for 7–21d PO and show comparatively little recovery at 42d PO. These minimal recoveries are almost-certainly due to small-diameter myelinated axons regenerating by outgrowth from the severed proximal stumps, of which some may reach denervated target organs at 42d PO, as observed for allograft Negative Controls in the following paper (Mikesh et al, 2018). …”

“…These small diameter myelinated axons are almost-certainly axons regenerating by outgrowth from surviving proximal axonal stumps, a few of which may re-innervate distal muscle masses by 42d PO. Negative Control animals typically show minimal, if any, behavioral recovery by 42d PO, as measured by the SFI test compared to their SFI scores at 3d PO or to SFI values when a 5–10mm segment of sciatic nerve is ablated (Riley et al, 2015; Mikesh et al, 2018). These data are consistent with other reports that transected axons undergo Wallerian degeneration within 7 days and then slowly regrow at ~1mm/day to sometimes reinnervate denervated muscles after a month or more (Brushart, 2011).…”

“…A two-tailed Student’s t-test, a test for homoscedastic data, was used to compare mean SFI scores for each treatment group on a given post-operative day. Two-way ANOVAs were used to analyze means and standard errors of SFI scores (Bittner et al, 2012; Riley et al, 2015; Ghergherehchi et al, 2016; Mikesh et al, 2018). …”