Ultrastructural observations on the progress of nerve degeneration and regeneration at the suture site following vagal-hypoglossal nerve coaptation in cats.
Nerve degeneration and regeneration have been investigated at the suture site following proximal-to-distal vagal-hypoglossal nerve coaptation (VHC) in cats at different time points (from 3 to 315 days postoperatively; dpo). Massive axonal degeneration and myelin breakdown and removal of degraded neural debris were observed during the first 2 weeks postoperatively. This was followed by active Schwann cell multiplication and inflammatory cell invasion at 14 dpo. Schwann cells appeared mobile, and were guided to the newly developed growth cones, dividing them into axonal sprout clusters. At 18 dpo, the migrating Schwann cells were confined to the preexisting basal lamina scaffolds, forming bands of Bungner. It is suggested that the latter may play a key role in navigating the regenerating axons to their newly acquired target organ at 22 dpo. Remyelination of axons was not observed till 46 dpo. Compared with the rapid axonal reaction in other models of nerve injury, the degeneration process in VHC was protracted and, furthermore, regeneration and remyelination were delayed. The subtle remodeling of the nerve in cross-coaptation may be far greater than previously recognized, and this may have clinical importance since patients undergoing nerve crossover microsurgery exhibit delayed motor rehabilitation, apparently as a direct result of a change in target innervation. Defining the mechanisms underlying the neuroplastic program could thus potentially improve the prognosis of crossover of two different peripheral nerves.
Hu
Ming-E
ME
Department of Anatomy, Faculty of Medicine, Chung-Shan Medical University, 402 Taichung, Taiwan, ROC.
Tyan
Yeu-Sheng
YS
Hsu
Peng-Wei
PW
Hsu
Jee-Ching
JC
Chang
Hung-Ming
HM
Ling
Eng-Ang
EA
Lan
Chyn-Tair
CT
D000818:Animals; D002415:Cats; D005260:Female; D007002:Hypoglossal Nerve / Q000473:pathology / Q000601:surgery* / Q000648:ultrastructure*; D008297:Male; D023421:Models, Animal; D009410:Nerve Degeneration / Q000473:pathology; D009416:Nerve Regeneration; D013537:Sutures / Q000009:adverse effects*; D013997:Time Factors; D014630:Vagus Nerve / Q000473:pathology / Q000601:surgery* / Q000648:ultrastructure*