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Collateral and terminal sprouting of rat facial nerve axons into fresh or predegenerated nerve grafts after end-to-side neurorrhaphy
Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Department of Biomedicine and Surgery, Plastic Surgery, Hand Surgery and Burns. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedicine and Surgery, Plastic Surgery, Hand Surgery and Burns. Linköping University, Faculty of Health Sciences.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In spite of a continuous technical refinement the results of microsurgical facial nerve repair remain unsatisfactory. This situation prompted the present study, which evaluates axonal regeneration into a rat facial nerve branch after crossfacial end-to-side neurorrhaphy in adult rats. A fresh (group A, 12 rats) or predegenerated (group B, 12 rats) sural nerve graft (SNG) was sutured to a perineurial window in the mandibular branch (MB) of the right facial nerve. It was then tunneled under the chin and sutured to the distal stump of the cut left MB. Twelve weeks after grafting some rats were prepared for electron microscopy (EM). EM examination showed that distal to the window the right MB contained mainly myelinated axons with relatively thick sheaths. Aberrant small-diameter axons with thin sheaths were also observed in most specimens. The counts revealed a total average of about 1 800 axons (14 % unmyelinated) in both groups. In the SNG thin myelinated and unmyelinated axons predominated. The counts showed 900-1 000 axons (63-68% unmyelinated) with no significant difference between the groups. The left MB contained some thin myelinated axons and many unmyelinated axons. The number of axons was 1 200-1300 (81-83% unmyelinated). Again, the two groups did not differ. Other rats were subjected to retrograde tracing. The SNG-right MB coaptation was exposed and each nerve was cut off. Two or 3 days after application of fast blue (FB) to the right MB and fluoro-ruby (FR) to the SNG the animals were perfused with paraformaldehyde and the brain stem was transversely cryosectioned. Counts of labeled motoneurons were used to calculate the percentage of motoneurons with different tracer combinations. The results showed FBlabeling only (motoneurons with axons in the right MB distal to the coaptation) in 5-11% of the counted profiles, FR-labeling only (motoneurons with axons in the SNG) in 43-54% of the profiles, and a combined FB- and FR-labeling (motoneurons with axons in the right MB as well as in the SNG) in 41-46% of the profiles. The two groups did not differ statistically in this respect. We conclude that (i) coaptation of a SNG to the MB of the facial nerve in an end-toside fashion is followed by growth of myelinated and unmyelinated axons from the donor nerve into the graft; (ii) these axons originate from facial motor axons; (iii) some 50% of the traced facial neurons project into the SNG only, 45% project into the SNG and into the MB and 5% project into the MB only; (iv) predegeneration of the SNG does not enhance the number of axons in the graft.

National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-81520OAI: diva2:553101
Available from: 2012-09-18 Created: 2012-09-18 Last updated: 2012-09-18Bibliographically approved
In thesis
1. Facial nerve injury and microsurgical repair: Experimental and clinical studies
Open this publication in new window or tab >>Facial nerve injury and microsurgical repair: Experimental and clinical studies
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Facial palsy is a relatively common clinical condition with a variety of causes. Irrespective of its etiology, facial palsy always represents a very serious problem for the patient. This underlines the need for more effective treatment procedures. Retrospective evaluation of a clinical material of 16 patients with facial palsy treated at the University Hospital of Linköping during the period 1990-2000 showed that to improve the results of microsurgical nerve repair experimental research - controlled studies on homogeneous materials - is imperative.

To produce relevant experimental data we used a rat model. Dissections showed that the mandibular branch (MB) of the rat facial nerve is suitable for experimental studies. Electron rnicroscopy revealed that the normal rat MB contains some 2,200 axons, 1,825 of which are myelinated and show a unimodal size distribution with a mode at 4.5 µm. It was also found that the normal rat MB contains myelinated and unmyelinated sympathetic axons and that about half the C-fibers in the normal rat MB belong to capsaicin-sensitive putative polymodally nociceptive sensory neurons. Importantly, repair of the MB through transmedian grafting in one stage and in two stages, respectively, had largely similar outcomes in terms of anatomy.

These data evoked questions concerning the functional outcome of the two types of repair. Electrophysiological analysis (force recordings andelectromyography) revealed that repair of the rat MB through transmedian grafting in one stage gives a somewhat better functional restoration than repair in two stages.

The observations on the rat MB called for experimental studies on the effects of denervation and repair on mimic muscle. We found that the rat dilator naris muscle (DNM) is suitable for that purpose. The normal DNM contains 1,200 fast MyHC fibers with MyHC IIB fibers predominating. It is a very fast contracting muscle without static functions. A brief denervation of the DNM followed by spontaneous reinnervation by the MB did not influence fiber number, had long-term effects on fiber diameter, and had little effect on fiber types. Fiber number, fiber diameter, and occurrence of fiber types in the DNM remained abnormal both after immediate and delayed surgical repair of the MB. Long-term denervation of the DNM had severe effects on qualitative histology, fiber number, fiber diameter and fiber type distribution. Hence, a long delay between facial nerve injury and repair reduces the chances of restoring normal facial muscle function.

Conventional cross facial grafting includes division of a facial nerve branch (the donor nerve) on the intact side of the face. This non-optimal situation prompted us to test cross-facial grafting with a less traumatic end-to-side procedure in the rat. After coaptation of a sural nerve graft to the rat MB in an end-to-side fashion, including opening of a perineurial window, axons in the donor nerve emitted myelinated and umnyelinated sprouts into the graft. A predegenerated graft did not stimulate sprouting more than a fresh graft. Retrograde tracing with fast blue and fluoro-ruby showed that many sprouts originate from facial motor axons. Of all traced facial motoneurons 50% projected exclusively into the graft, 45% projected into the graft and the donor MB and 5% projected exclusively into the donor MB. This shows that the end-to- side procedure can be used for cross-facial repair of the rat MB.

Altogether these results provide new experimental data, which hopefully will contribute to improvements of the microsurgical treatment of patients with facial palsy.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2002. 97 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 716
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-25666 (URN)10042 (Local ID)91-7373-159-5 (ISBN)10042 (Archive number)10042 (OAI)
Public defence
2002-02-22, Berzeliussalen, Hälsouniversitetet, Linköping, 09:00 (Swedish)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-09-18Bibliographically approved

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