Rabbit Facial Nerve Regeneration in Autologous Nerve Grafts After Antecedent Injury

Authors

  • J. Gershon Spector MD, FACS,

    Corresponding author
    1. Department of Otolaryngology–Head and Neck Surgery, Washington University School of Medicine, St. Louis, Missouri
    • J. Gershon Spector, MD, FACS, Department of Otolaryngology—Head and Neck Surgery, Washington University School of Medicine, 517 S. Euclid Avenue, Campus Box 8115, St. Louis, MO 63110, U.S.A.
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  • Patty Lee MD,

    1. Department of Otolaryngology–Head and Neck Surgery, Washington University School of Medicine, St. Louis, Missouri
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  • Albert Derby PhD

    1. Department of Biology, University of Missouri–St. Louis, St. Louis, Missouri. Dr. Lee's present address is the Department of Otolaryngology, University of New Mexico School of Medicine, Albuquerque, New Mexico
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  • This study was performed in accordance with Public Health Service Policy on Humane Care and Use of Laboratory Animals, The National Institutes of Health Guide for the Care and Use of Laboratory Animals, and the Animal Welfare Act (7 U.S.C. et seq.) The animal use protocol was approved by the Institutional Animal Care and Use Committee of Washington University Medical Center. Portions of the experiment were performed at the John Cochran Veterans Hospital in St. Louis, Missouri.

Abstract

Objective The effect of incomplete antecedent injuries on subsequent facial nerve regeneration within cable graft repairs is not known. The purpose of this study is to compare facial nerve regeneration after an immediate and delayed neural cable graft repair.

Method Rabbit facial nerve regeneration after complete transectional injuries of the buccal division was compared in two experimental models. In one, a 10-mm segment of the nerve was transected, rotated 180°, and immediately repaired as a cable graft (N=8). In the second, a preliminary nerve crush was allowed to recover over a 4-week period and a 10-mm segment of nerve centered on the crush site was then transected, rotated 180°, and delay repaired as a cable graft (N = 7). Data are presented as total numbers of regenerating myelinated axons that traverse the surgical repair to innervate the cable graft and distal nerve stumps, as well as the percentage of regenerating neurites compared with preoperative pooled and individual controls. Subpopulations of regenerating neurons are delineated to quantify the pattern of neural innervation.

Results Five weeks after cable graft repair both groups had similar myelinated outgrowth from the proximal nerve stump across the proximal anastomosis to innervate the cable graft (3995 ± 1209 vs. 3284 ± 651;P = .89). However, the delayed repair group had more intrafascicular regeneration within cable grafts (2261 ± 931 vs. 1660 ± 1169;P = .02) and distal nerve stump (1532 ± 281 vs. 445 ± 120;P = .004) than the immediate repair group. The immediate repair group had greater extrafascicular nerve regeneration in the cable graft (2335 ± 1954 vs. 437 ± 236;P = .001) and more myelin and axonal debris in pre-existing neural fascicles of the cable graft (P = .02) and distal nerve stump (463 ± 187 vs. 103 ± 87;P = .02).

Conclusions Antecedent priming lesions do not enhance axonal survival as determined by regenerating myelinated axonal counts. However, antecedent injuries enhance the efficiency of neural innervation of the affected mimetic musculature by increasing the number of myelinated intrafascicular neural regenerants in the cable graft and distal nerve stump. This is accomplished by two factors: increased perineural fibrosis and decreased intrafascicular myelin and axonal debris.

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