Polyethylene glycol fusion repair of severed rat sciatic nerves reestablishes axonal continuity and reorganizes sensory terminal fields in the spinal cord.

ABSTRACT: Peripheral nerve injuries result in the rapid degeneration of distal nerve segments and immediate loss of motor and sensory functions; behavioral recovery is typically poor. We used a plasmalemmal fusogen, polyethylene glycol (PEG), to immediately fuse closely apposed open ends of severed proximal and distal axons in rat sciatic nerves. We have previously reported that sciatic nerve axons repaired by PEG- fusion do not undergo Wallerian degeneration, and PEG-fused animals exhibit rapid (within 2-6 weeks) and extensive locomotor recovery. Furthermore, our previous report showed that PEG-fusion of severed sciatic motor axons was non-specific, i.e., spinal motoneurons in PEG- fused animals were found to project to appropriate as well as inappropriate target muscles. In this study, we examined the consequences of PEG-fusion for sensory axons of the sciatic nerve. Young adult male and female rats (Sprague-Dawley) received either a unilateral single cut or ablation injury to the sciatic nerve and subsequent repair with or without (Negative Control) the application of PEG. Compound action potentials recorded immediately after PEG-fusion repair confirmed conduction across the injury site. The success of PEG-fusion was confirmed through Sciatic Functional Index testing with PEG-fused animals showing improvement in locomotor function beginning at 35 days postoperatively. At 2-42 days postoperatively, we anterogradely labeled sensory afferents from the dorsal aspect of the hindpaw following bilateral intradermal injection of wheat germ agglutinin conjugated horseradish peroxidase. PEG-fusion repair reestablished axonal continuity. Compared to unoperated animals, labeled sensory afferents ipsilateral to the injury in PEG-fused animals were found in the appropriate area of the dorsal horn, as well as inappropriate mediolateral and rostrocaudal areas. Unexpectedly, despite having intact peripheral nerves, similar reorganizations of labeled sensory afferents were also observed contralateral to the injury and repair. This central reorganization may contribute to the improved behavioral recovery seen after PEG-fusion repair, supporting the use of this novel repair methodology over currently available treatments.

Polyethylene glycol fusion repair of severed sciatic nerves accelerates recovery of nociceptive sensory perceptions in male and female rats of different strains.

ABSTRACT: Successful polyethylene glycol fusion (PEG-fusion) of severed axons following peripheral nerve injuries for PEG-fused axons has been reported to: (1) rapidly restore electrophysiological continuity; (2) prevent distal Wallerian Degeneration and maintain their myelin sheaths; (3) promote primarily motor, voluntary behavioral recoveries as assessed by the Sciatic Functional Index; and, (4) rapidly produce correct and incorrect connections in many possible combinations that produce rapid and extensive recovery of functional peripheral nervous system/central nervous system connections and reflex (e.g., toe twitch) or voluntary behaviors. The preceding companion paper describes sensory terminal field reorganization following PEG-fusion repair of sciatic nerve transections or ablations; however, sensory behavioral recovery has not been explicitly explored following PEG-fusion repair. In the current study, we confirmed the success of PEG-fusion surgeries according to criteria (1-3) above and more extensively investigated whether PEG-fusion enhanced mechanical nociceptive recovery following sciatic transection in male and female outbred Sprague-Dawley and inbred Lewis rats. Mechanical nociceptive responses were assessed by measuring withdrawal thresholds using von Frey filaments on the dorsal and midplantar regions of the hindpaws. Dorsal von Frey filament test was a more reliable method than plantar von Frey filament test to assess mechanical nociceptive sensitivity following sciatic nerve transections. Baseline withdrawal thresholds of the sciatic-mediated lateral dorsal region differed significantly across strain but not sex. Withdrawal thresholds did not change significantly from baseline in chronic Unoperated and Sham-operated rats. Following sciatic transection, all rats exhibited severe hyposensitivity to stimuli at the lateral dorsal region of the hindpaw ipsilateral to the injury. However, PEG-fused rats exhibited significantly earlier return to baseline withdrawal thresholds than Negative Control rats. Furthermore, PEG-fused rats with significantly improved Sciatic Functional Index scores at or after 4 weeks postoperatively exhibited yet-earlier von Frey filament recovery compared with those without Sciatic Functional Index recovery, suggesting a correlation between successful pPEG-fusion and both motor-dominant and sensory-dominant behavioral recoveries. This correlation was independent of the sex or strain of the rat. Furthermore, our data showed that the acceleration of von Frey filament sensory recovery to baseline was solely due to the PEG-fused sciatic nerve and not saphenous nerve collateral outgrowths. No chronic hypersensitivity developed in any rat up to 12 weeks. All these data suggest that PEG-fusion repair of transection peripheral nerve injuries could have important clinical benefits.