Changes in a rat facial muscle after facial nerve injury and repair

This study describes changes in a rat facial muscle innervated by the mandi bular and buccal facial nerve branches 4 months after nerve injury and repa ir. The following groups were studied: (A) normal controls; (B) spontaneous reinnervation by collateral or terminal sprouting; (C) reinnervation after surgical repair of the mandibular branch; and (D) chronic denervation. The normal muscle contained 1200 exclusively fast fibers, mainly myosin heavy chain (MyHC) IIB fibers. In group B, fiber number and fiber type proportion s were normal. In group C, fiber number was subnormal. Diameters and propor tions of MyHC IIA and hybrid fibers were above normal. The proportion of My HC IIB fibers was subnormal. Immediate and delayed repair gave similar resu lts with respect to the parameters examined. Group D rats underwent severe atrophic and degenerative changes. Hybrid fibers prevailed. These data sugg est that spontaneous regeneration of the rat facial nerve is superior to re generation after surgical repair and that immediacy does not give better re sults than moderate delay with respect to surgical repair. Long delays are shown to be detrimental. (C) 2001 John Wiley & Sons, Inc.