title: Induction of regional collateral sprouting following muscle denervation.
abstract: OBJECTIVE
  Anecdotal clinical findings suggest that denervated muscle may regain modest functional recovery via spontaneous collateral sprouts from intact adjacent nerve fibers. The current study evaluates the conditions needed for the denervated masseter muscle to induce axonal sprouting from the facial nerve. We hypothesize that epineurial injury is required to induce collateral sprouting toward a neighboring denervated muscle.
  
  
  METHODS
  Twelve thy1-yellow fluorescent protein-16 (thy1-YFP-16) transgenic mice whose axons express yellow fluorescent protein were allocated into six groups, with four degrees of facial nerve injury (intact, crush, transection, removed segment) with or without masseter denervation.
  
  
  METHODS
  Animals underwent serial in vivo imaging analyses under the fluorescent microscope weekly for 5 or 7 weeks and were subsequently perfused for analysis. Masseter muscle acetylcholine receptors (AChRs) were stained with Alexa Fluor 594 conjugated alpha-bungarotoxin, and whole mounts were imaged with confocal microscopy.
  
  
  RESULTS
  In groups with intact or crushed facial nerves, no evidence of collateral sprouting was demonstrated. Mice with transected facial nerve branches or removed segments demonstrated sprouting from the proximal stump into the denervated masseter. Staining of the AChRs confirmed that new neuromuscular junctions were established between the facial nerve and the denervated masseter.
  
  
  CONCLUSIONS
  This study suggests that epineurial injury is required to stimulate axonal sprouting into adjacent denervated muscle. Nerves with compromised epineurium may be useful in promoting neo-neurotization after muscle denervation.
authors: Departments of Plastic and Reconstructive Surgery, Washington University, Saint Louis, Missouri, USA.
authors: Jason W
authors: JW
authors: Koob
authors: Arash
authors: A
authors: Moradzadeh
authors: Alice
authors: A
authors: Tong
authors: Ayato
authors: A
authors: Hayashi
authors: Terence M
authors: TM
authors: Myckatyn
authors: Thomas H
authors: TH
authors: Tung
authors: Susan E
authors: SE
authors: Mackinnon
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D020220:Facial Nerve Injuries / Q000628:therapy; D008406:Masseter Muscle / Q000166:cytology / Q000294:innervation* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009121:Muscle Denervation; D009412:Nerve Fibers / Q000502:physiology; D009414:Nerve Growth Factors / Q000502:physiology; D019635:Neurosurgical Procedures / Q000379:methods; D010525:Peripheral Nerves / Q000502:physiology; D011950:Receptors, Cholinergic / Q000378:metabolism
chemical_list: D009414:Nerve Growth Factors; D011950:Receptors, Cholinergic