Peripheral nerve autografts to the rat spinal cord: study on the origin and course of regenerating fibers.

Autologous sciatic nerve grafts were implanted to the lower thoracic spinal cord (SC) of adult rats. The grafts were longitudinally placed on both sides of the SC midline over the dura mater and their cut ends were inserted into the dorsal white matter of the SC. Eight to 60 weeks later the grafts were exposed. In a first experimental group (A) either horseradish peroxidase (HRP) or lectin conjugated horseradish peroxidase (WGA-HRP) was injected into the grafts in order to investigate the origin and the course of regenerated fibres entering the grafts. In a second experimental group (B) the SC was acutely transected between the upper and lower graft insertions and either HRP or WGA-HRP was injected into the caudal stump of the SC in order to investigate the ability of regenerating axons once entered the grafts to re-enter the SC. In group A retrogradely labelled cells were found in the SC scattered in proximity of both the caudal and rostral graft insertions and in the ventral horns as far as 30 mm rostrally to the grafts. Labelled cells were also located in the spinal ganglia, at the level of the grafts and up to 6 segments caudal to them. In group B retrogradely labelled cells were present in the SC rostrally to the transection, both in proximity of the upper graft insertions and in the ventral horns as far as 30 mm rostrally to the grafts. These findings demonstrate that PN grafts implanted to the SC of adults rats can be innervated by regenerated axons arising from both intraspinal neurons and dorsal root ganglion cells (group A); furthermore axons from intraspinal neurons entered and elongated in the grafts can re-enter the SC (group B).