Experimental study on regeneration of ascending tract after spinal cord injury with predegenerated peripheral nerve graft and NGF infusion

Objective:To explore the effects of predegenerated peripheral nerve graft (PPNG) combined with nerve growth factor (NGF) infusion on ascending sensory tract regeneration after spinal cord injury. Methods: Fifty female SD rats were randomly divided into 5 groups. Group A was treated with PPNG and NGF infusion, group B with PPNG, group C with NGF infusion, group D and group E were blank and normal control, respectively. Horseradish peroxidase-labled (HRP) tracing method was employed to evaluate the regeneration of injured nerves after 8 weeks. The extent of regeneration in and beyond the nerve graft was determined by counting the number of HRP-labeled fibers intersecting imaginary lines perpendicular to the axis of the graft and cord. For the sake of convenience, according to the relation of the PNG and spinal cord, 6 model zones were divided, including caudal of spinal cord, caudal transition zone, caudal zone in graft, rostral zone in graft, rostral transition zone and rostral of spinal cord. Results: On the transverse section of caudal zone in graft, rostral zone in graft, rostral transition zone, the fibers in group A were significantly higher than that in group B and C (P<0. 05). Conclusion: PPNG combined with NGF may significantly promote the regeneration of ascending long tract after spinal cord injury. The regenerative fibers can penetrate the 2 graft-host interface scars.

Survival of rat sciatic nerve segments preserved in storage solutions ex vivo assessed by novel electrophysiological and morphological criteria

Most organ or tissue allografts with viable cells are sto red in solutions ex vivo for hours to seve ral days.Most allografts then require rapid host revascula rization upon transplantation to maintain donor-cell functions(e.g.,cardiac muscle contra ctions,hepatic secretions).In contrast,peripheral nerve allografts stored ex vivo do not require revascularization to act as scaffolds to guide outgrowth by host axons at 1-2 mm/d,likely aided by viable donor Schwann cells.Using current storage solutions and protocols,axons in all these donor orga n/tissue/nerve transplants are expected to rapidly become non-viable due to Wallerian degeneration within days.Therefore,ex vivo storage solutions have not been assessed for preserving normal axonal functions,i.e.,conducting action potentials or maintaining myelin sheaths.We hypothesized that most or all organ storage solutions would maintain axonal viability.We examined several common organ/tissue storage solutions(University of Wisconsin Cold Storage Solution,Normosol-R,Normal Saline,and La ctated Ringe rs) for axonal viability in rat sciatic nerves ex vivo as assessed by maintaining:(1) conduction of artificially-induced compound action potentials;and(2) axonal and myelin morphology in a novel assay method.The ten diffe rent storage solution conditions for peripheral nerves with viable axons(PNVAs) diffe red in their solution composition,osmolarity(250-318 mOsm),temperature(4℃ vs.25℃),and presence of calcium.Compound action potentials and axonal morphology in PNVAs were best maintained for up to 9 days ex vivo in calcium-free hypotonic diluted(250 mOsm) Normosol-R(dNR) at 4℃.Surprisingly,compound action potentials were maintained for only 1-2 days in UW and NS at 4℃,a much shorter duration than PNVAs maintained in 4℃ dNR(9 days) or even in 25℃ dNR(5 days).Viable axons in peripheral nerve allografts are critical for successful polyethylene glycol(PEG)-fusion of viable proximal and distal ends of host axons with viable donor axons to repair segmental-loss peripheral nerve injuries.PEG-fusion repair using PNVAs prevents Wallerian degeneration of many axons within and distal to the graft and results in excellent recovery of sensory/motor functions and voluntary behaviors within weeks.Such PEG-fused PNVAs,unlike all other types of conventional donor transplants,are immune-tolerated without tissue matching or immune suppression.Preserving axonal viability in sto red PNVAs would enable the establishment of PNVA tissue banks to address the current shortage of transplantable nerve grafts and the use of stored PEG-fused PNVAs to repair segmentalloss peripheral nerve injuries.Furthermore,PNVA storage solutions may enable the optimization of ex vivo storage solutions to maintain axons in other types of organ/tissue transplants.