AAHS ASPN ASRM - 2013 Annual Meeting - American Association ...

Induction of Regional Collateral Sprouting Following Muscle Denervation
Institution where the work was prepared: Washington University School of Medicine, St. Louis, MO, USA
Arash Moradzadeh, MD; JW Koob, BA; Alice Tong; Ayato Hayashi, MD; Terence M. Myckatyn, MD; Thomas H. Tung, MD; Susan E. Mackinnon, MD; Washington University
School of Medicine
BACKGROUND:
Controversy exists regarding the ability of collateral sprouting to occur in the absence of epineurotomy in cases of end-to-side neurorrhaphy. In addition, published
works report that collateral sprouting can be induced directly by denervated muscle. The current study evaluates the necessary conditions for the denervated
masseter muscle to induce collateral axonal sprouting from branches of the facial nerve. We hypothesize that the chemotactic stimuli from denervated
muscle tissue will not induce collateral sprouting from nerves with intact epineurium.
METHODS:
Transgenic mice expressing yellow fluorescent protein (YFP) under the control of neuron-specific elements from the thy1 gene were used to characterize the
nature and extent of collateral sprouting through live imaging analysis. These mice were randomly allocated into “immediate” and “predegenerated” masseter
muscle groups with subgroups undergoing varying degrees of injury to the marginal and buccal branches of the facial nerve: no injury, facial nerve crush, transection,
or removal of a nerve segment. Mice were imaged weekly following injury to the facial nerve for a period of six weeks. At the endpoint, animals were
perfused, acetylcholine receptors in the masseter muscle were stained with Alexa Fluor 488 alpha–bungarotoxin and muscle whole mounts were evaluated
under confocal microscopy.
RESULTS:
There was no evidence of collateral sprouting from axons in mice with intact or crushed facial nerve branches. Mice with transected branches of the facial
nerve, or removed segments, demonstrated sprouting from the proximal nerve stump into the denervated masseter. Staining of the acetylcholine receptors confirmed
that new neuromuscular junctions were established between the sprouting axons from the facial nerve branches and the denervated masseter.
CONCLUSION:
While further analysis is required to investigate the extent and nature of these neuromuscular junctions, this study provides evidence that denervated muscle
does not provide sufficient stimulus to induce collateral sprouting from nerves with intact epineurium. Nerves with compromised epineurium may be useful in
promoting neo-neurotization following muscle denervation when there is no possibility for nerve regeneration.
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