ABSTRACT
The ultrastructure of the early regenerative response in an end-to-side neurorrhaphy
rat model was studied using transmission electron microscopy. The ipsilateral saphenous
nerve was grafted to the sciatic nerve under the following conditions: Group 1, the
epineurium and perineurium of the sciatic nerve remained intact; Group 2, an epineurial
and perineurial window was created at the site of the lateral neurorrhaphy; Group
3, the same as in Group 2 and, in addition, the sciatic nerve sustained a partial
neurectomy. Rats were perfused through the heart with fixative containing 2 percent
paraformaldehyde and 2.5 percent glutaraldehyde in 0.1 M cacodylate buffer (pH 7.4)
at 4, 8, 12, 24 and 48 hr after surgery.
In Group 1, no regenerating axons were observed and the myelin sheath in the donor
nerve did not demonstrate any degenerative changes through 48 hr. In Group 2, an increased
diameter of the unmyelinated axons and growth cones was observed in the donor nerve
proximal to the coaptation site after 12 hr. Degenerative changes in the myelin sheath
were observed after 12 hr within the several layers under the coaptation site. In
Group 3, many growth cone-like structures were observed in the area proximal to the
coaptation site after 12 hr. After 24 hr, proximal regenerating axons elongated to
the coaptation site and, at 48 hr, many regenerating nerves grew inside the Schwann
cell basement membrane of the graft nerve.
These results indicate that the perineurial window and nerve graft are the critical
conditions for inciting nerve regeneration in the donor nerve.
