In vitro pre-degenerated nerve autografts support CNS axonal regeneration

In the present study we compared, in adult rats, the axonal regeneration of central respiratory neurons within autologous fresh (f-; grafted immediately after removal) and pre-degenerated (pd-; grafted after being stored during 3 days in saline at +8 degrees C) peripheral nerve grafts (PNGs) implanted within the C2 cervical spinal cord. The proximal end of the left peroneal nerve was implanted in the site of projection of medullary respiratory neurons (ventro-lateral quadrant) and the distal part of each nerve graft was left unconnected (blind-ended graft). PNGs were examined 2 to 4 months after grafting. Central neurons regenerating axons within the PNGs were studied by recording spontaneous unit activity from small strands teased from the grafts. In control f-PNGs (n = 9), 248 filaments had spontaneous activities, 58 of these were respiratory-related, i.e. had discharge patterns identical to those of normal respiratory (inspiratory and expiratory) neurons. The presence of regenerated nerve fibers with spontaneous unitary impulse traffic (n = 216) was found in all pd-PNGs (n = 5). Thirty-four had respiratory patterns identical to those found within f-PNGs and corresponded to efferent activity. No statistically significant differences in axonal regrowth were found between f- and pd-PNGs. In conclusion, f- and pd-PNGs were equally capable of promoting axonal regeneration of central neurons. The neural components (Schwann cells and others) required for axonal regeneration of adult central neurons are still effective following 3 days of in vitro peripheral nerve degeneration without special storage conditions (oxygenation, medium inducing ATP synthesis). These results have clinical implications for nerve graft surgery when time is required for typing the tissues of both donor and recipient (post-mortem allografts) or transportation of graft material.