The authors thank members of the Valdez laboratory for intellectual input on experiments and comments on the manuscript.

All experiments were carried out under NIH guidelines and animal protocols approved by the Virginia Tech Institutional Animal Care and Use Committee.
1. Preparing Animals for Surgery
<ol>
	<li>Anesthetize mice with a mixture of ketamine (90 mg/kg) and xylazine (10 mg/kg) via subcutaneous inguinal injection with a sterile 1 ml insulin syringe. Carrier solution contains a mixture of 0.9% saline, 17.4 mg/ml ketamine, and 2.6 mg/ml xylazine. Place animals back in cages while waiting for medicati...

<ol>
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J., Alton, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+age+impairs+the+response+of+the+neuromuscular+junction+to+nerve+transection+and+repair:+An+experimental+study+in+rats.">How age impairs the response of the neuromuscular junction to nerve transection and repair: An experimental study in rats.</a> J Orthop Res. 27 (3), 385-393 (2009).</li><li>Balice-Gordon, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age-related+changes+in+neuromuscular+innervation.">Age-related changes in neuromuscular innervation.</a> Muscle Nerve Suppl. 5, S83-S87 (1997).</li><li>Valdez, G., Tapia, J. C., Lichtman, J. W., Fox, M. A., Sanes, J. 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W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+mechanisms+of+cellular+interactions+in+peripheral+nerve+regeneration.">Molecular mechanisms of cellular interactions in peripheral nerve regeneration.</a> Curr Opin Neurol. 14 (5), 635-639 (2001).</li><li>Gaudet, A. D., Popovich, P. G., Ramer, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wallerian+degeneration:+gaining+perspective+on+inflammatory+events+after+peripheral+nerve+injury.">Wallerian degeneration: gaining perspective on inflammatory events after peripheral nerve injury.</a> J Neuroinflammation. 8, 110 (2011).</li><li>Chen, P., Piao, X., Bonaldo, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+macrophages+in+Wallerian+degeneration+and+axonal+regeneration+after+peripheral+nerve+injury.">Role of macrophages in Wallerian degeneration and axonal regeneration after peripheral nerve injury.</a> Acta Neuropathol. 130 (5), 605-618 (2015).</li><li>Chen, Z. -. L., Yu, W. -. M., Strickland, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peripheral+regeneration.">Peripheral regeneration.</a> Annu Rev Neurosci. 30, 209-233 (2007).</li><li>Darabid, H., Perez-Gonzalez, A. P., Robitaille, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neuromuscular+synaptogenesis:+coordinating+partners+with+multiple+functions.">Neuromuscular synaptogenesis: coordinating partners with multiple functions.</a> Nat. Rev. Neurosci. 15 (11), 703-718 (2014).</li><li>Geuna, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+sciatic+nerve+injury+model+in+pre-clinical+research.">The sciatic nerve injury model in pre-clinical research.</a> J. Neurosci. Methods. 243, 39-46 (2015).</li><li>Batt, J. A. E., Bain, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tibial+nerve+transection+-+a+standardized+model+for+denervation-induced+skeletal+muscle+atrophy+in+mice.">Tibial nerve transection - a standardized model for denervation-induced skeletal muscle atrophy in mice.</a> J. Vis. Exp. (81), e50657 (2013).</li><li>Savastano, L. E., Laurito, S. R., Fitt, M. R., Rasmussen, J. A., Gonzalez Polo, V., Patterson, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sciatic+nerve+injury:+a+simple+and+subtle+model+for+investigating+many+aspects+of+nervous+system+damage+and+recovery.">Sciatic nerve injury: a simple and subtle model for investigating many aspects of nervous system damage and recovery.</a> J. Neurosci. Methods. 227, 166-180 (2014).</li><li>Kang, H., Lichtman, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Motor+axon+regeneration+and+muscle+reinnervation+in+young+adult+and+aged+animals.">Motor axon regeneration and muscle reinnervation in young adult and aged animals.</a> J Neurosci. 33 (50), 19480-19491 (2013).</li><li>Gage, G. J., Kipke, D. R., Shain, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole+animal+perfusion+fixation+for+rodents.">Whole animal perfusion fixation for rodents.</a> J. Vis. Exp. (65), e3564 (2012).</li><li>Feng, G., Mellor, R. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+Neuronal+Subsets+in+Transgenic+Mice+Expressing+Multiple+Spectral+Variants+of+GFP.">Imaging Neuronal Subsets in Transgenic Mice Expressing Multiple Spectral Variants of GFP.</a> Neuron. 28 (1), 41-51 (2000).</li><li>Sanes, J. R., Lichtman, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+the+vertebrate+neuromuscular+junction.">Development of the vertebrate neuromuscular junction.</a> Annu Rev Neurosci. 22, 389-442 (1999).</li><li>Bowen, D. C., Park, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+and+regulation+of+MuSK+at+the+neuromuscular+junction.">Localization and regulation of MuSK at the neuromuscular junction.</a> Dev Biol. 199 (2), 309-319 (1998).</li><li>Gay, S., Jublanc, E., Bonnieu, A., Bacou, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myostatin+deficiency+is+associated+with+an+increase+in+number+of+total+axons+and+motor+axons+innervating+mouse+tibialis+anterior+muscle.">Myostatin deficiency is associated with an increase in number of total axons and motor axons innervating mouse tibialis anterior muscle.</a> Muscle Nerve. 45 (5), 698-704 (2012).</li><li>Livak, K. J., Schmittgen, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+relative+gene+expression+data+using+real-time+quantitative+PCR+and+the+2(-Delta+Delta+C(T))+Method.">Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method.</a> Methods. 25 (4), 402-408 (2001).</li></ol>

The method presented in this manuscript provides unique opportunities to identify mechanisms involved in repairing neuromuscular junctions (NMJ). This method involves crushing the common fibular nerve as it passes over the gastrocnemius tendon near the knee. We show that after only 5 sec of nerve compression with a forceps, complete degeneration is noted by 4 days after injury. In young adult mice, alpha-motor axons begin to reinnervate previous synaptic sites in the extensor digitorum longus muscle (EDL) at 7 days post-...

In young adult and healthy animals, the neuromuscular junction (NMJ) is a highly stable connection between the presynapse, the nerve ending of an &#945;-motor axon, and the postsynapse, the specialized region of an extrafusal muscle fiber where nicotinic acetylcholine receptors (AChRs) selectively aggregate1. The nearly perfect apposition of the pre- and post-synaptic apparatuses is necessary for proper neurotransmission, survival of &#945;-motor neurons and muscle fibers and motor function. Unfortunately, the function of the NMJ is adversely affected by aging, diseases such as amyotrophic lateral sclerosis (ALS), autoimmune diseases and injury to muscles and peripheral nerves2-5. These insults often result in degeneration of presynaptic nerve endings, leaving muscles denervated and significantly altering motor skills. For this reason, the identification of molecules that function to maintain and repair the NMJ has become a priority. Because peripheral nerves regenerate and reinnervate targets, peripheral nerve injury models have been used to identify molecular changes associated with regenerating NMJs. 
Peripheral nerve injury models often involve either completely cutting or crushing specific nerve branches6. Following a cut, the endoneurial tube has to be reformed, delaying axonal regeneration and reinnervation of target cells and tissues. The severity of this type of injury also causes axons to meander away from their original path, resulting in their failure to reach original targets. This is in contrast to nerves injured via crush where the endoneurium remains contiguous, providing a path for efficient and proper regrowth of regenerating axons. It also allows axons to find and reinnervate their original muscle fiber partners. Irrespective of injury model, there are a number of cellular and molecular changes that must occur for axons to regenerate and reinnervate targets. After an injury, the nerve segment proximal to the target is broken down and removed via a process termed Wallerian Degeneration7. This process involves reprogramming and de-differentiation of Schwann cells into non-myelinating cells that secrete regenerative factors, clear myelin, and recruit macrophages to the site of injury8. Macrophages in turn complete the clearance of myelin and axonal debris, which would otherwise impede growth of the regenerating axon9. In parallel, motor and sensory neurons activate mechanisms needed to promote regeneration of their severed axons. Once the regenerating axon reaches the target, it must transform from a growth cone to a nerve ending capable of properly transmitting (for motor axons) or receiving (for sensory axons) information10. In this regard, alpha-motor axons undergo a series of well-orchestrated changes that culminate in their growth cone differentiating into a fully functional presynaptic nerve ending that nearly perfectly opposes the post-synaptic site on the target muscle fiber11. 
The sciatic, tibial and accessory nerves have been the primary choices for studying axonal and NMJ regeneration12-14. However, there are a number of drawbacks when using these models to examine cellular and molecular changes associated with regenerating NMJs between animals and under different conditions. Firstly, the sciatic nerve supplies the majority of the muscles of the hind limb, with injury significantly limiting both movement and sensation. It is therefore not possible to use this method to study the impact of exercise alone or in combination with other factors. Additionally, the sciatic nerve is a rather thick structure and thus requires a large amount of compressive force to fully injure all axons. This in turn may result in complete transection of the more superficial axons while leaving the endoneurial tube of deeper lying axons intact, introducing significant variability in the rate and fidelity of regeneration among these axons. Complete transection of this nerve is even less desirable given that many axons will fail to reconnect with the same muscle fibers. Complicating matters, the sciatic nerve possesses intrinsic anatomic variability, both in the number and site of origin of its terminal nerve branches. It is therefore very difficult to lesion the same site. While the tibial nerve is smaller and more amenable to crush injuries, there is also no readily available landmark to serve as a lesion site for this nerve branch. 
The accessory nerve branch (part of cranial nerve XI) that supplies the sternocleidomastoid muscle has also been used to study regeneration of NMJs15. This nerve is particularly attractive because NMJs in the sternocleidomastoid muscle can be more readily imaged in live animals compared to NMJs in other muscles. But similar to the sciatic and tibial nerves, there is no specific landmark that can be used to injure this nerve in the same location, limiting it as a model for comparing regeneration of NMJs among individual animals of an experimental cohort. An inconsistent lesion site introduces variability in the rates of NMJ reinnervation. Due to these shortcomings, the procedure presented here utilizes the injury of a different peripheral nerve branch to examine regenerating NMJs. 
The common fibular nerve, also called the common peroneal nerve, contains many features that make it a reliable nerve to examine regeneration of NMJs between animals and across different treatments. The common fibular nerve has a predictable anatomic course as it runs over the tendon of the lateral head of the gastrocnemius muscle in the knee, the intersection serving as a stable landmark for lesions. The nerve is accessed through a small and minimally invasive incision near but anatomically segregated from the muscles of interest. The findings presented here demonstrate that regenerating motor axons begin to reform NMJs in the extensor digitorum longus (EDL) muscle 8 days after crushing the fibular nerve in 70 days old young adult female mice. Importantly, the pattern and rate of reinnervation is consistent among animals of the same age and sex and therefore provide a reliable injury model that will significantly hasten our understanding of the cellular and molecular changes required to maintain and repair NMJs.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Ketamine</td>
			<td>VetOne&#160;</td>
			<td>501072&#160;</td>
		</tr>
		<tr>
			<td>Xylazine</td>
			<td>Lloyd Inc.&#160;</td>
			<td>003437&#160;</td>
		</tr>
		<tr>
			<td>Buprenorphine </td>
			<td>&#160;Zoopharm</td>
			<td>1Z-73000-150910&#160;</td>
		</tr>
		<tr>
			<td>Nair</td>
			<td>Nair</td>
			<td></td>
		</tr>
		<tr>
			<td>Kim-wipes</td>
			<td>Kimtech</td>
			<td>34155</td>
		</tr>
		<tr>
			<td>Electric Razor </td>
			<td>Braintree Scientific</td>
			<td>CLP-64800</td>
		</tr>
		<tr>
			<td>80% EtOH/H20</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>10% Proviodine</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1 mL Insulin Syringe</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Spring Scissors</td>
			<td>Vannas</td>
			<td>91500-09</td>
		</tr>
		<tr>
			<td>No. 15 scalpel</td>
			<td>Braintree Scientific</td>
			<td>SSS 15</td>
		</tr>
		<tr>
			<td>#5 Forceps</td>
			<td>Dumont</td>
			<td>11252-00</td>
		</tr>
		<tr>
			<td>6-0 silk suture on reverse cutting needle</td>
			<td>&#160;Suture Express</td>
			<td>752B&#160;</td>
		</tr>
		<tr>
			<td>Rodent Heating Pad</td>
			<td>Braintree Scientific</td>
			<td>AP-R-18.5</td>
		</tr>
		<tr>
			<td>Alexa 555 conjugated alpha-BTX </td>
			<td>Molecular Probes</td>
			<td>B35451</td>
		</tr>
		<tr>
			<td>Vectashield</td>
			<td>Vector Labs</td>
			<td>H-1000</td>
		</tr>
		<tr>
			<td>Olympus Stereo Zoom Microscope</td>
			<td>Olympus</td>
			<td>562037192</td>
		</tr>
		<tr>
			<td>Zeiss 700 Confocal Microscope</td>
			<td>Zeiss</td>
			<td></td>
		</tr>
		<tr>
			<td>Variable-flow peristaltic perfusion pump</td>
			<td>Fisher Scientific</td>
			<td>13-876-3</td>
		</tr>
		<tr>
			<td>Aurum Total RNA Mini Kit</td>
			<td>Bio-Rad</td>
			<td>7326820</td>
		</tr>
		<tr>
			<td>Bio-Rad iScript RT Supermix</td>
			<td>Bio-Rad</td>
			<td>1708840</td>
		</tr>
		<tr>
			<td>SsoFast Evagreen Supermix</td>
			<td>Bio-Rad</td>
			<td>1725200</td>
		</tr>
		<tr>
			<td>Bio-Rad CFX96</td>
			<td>Bio-Rad</td>
			<td>1855196</td>
		</tr>
		<tr>
			<td>Puralube vet ointment</td>
			<td>Puralube</td>
			<td>1621</td>
		</tr>
		<tr>
			<td>Synaptotagmin-2 antibody</td>
			<td>Antibodies-Online</td>
			<td>ABIN401605</td>
		</tr>
		<tr>
			<td>Neurofilament antibody</td>
			<td>Antibodies-Online</td>
			<td>ABIN2475842</td>
		</tr>
	</tbody>
</table>

the fibular nerve injury method: a reliable assay to identify and test factors that repair neuromuscular junctions

The neuromuscular junction (NMJ) undergoes deleterious structural and functional changes as a result of aging, injury and disease. Thus, it is imperative to understand the cellular and molecular changes involved in maintaining and repairing NMJs. For this purpose, we have developed a method to reliably and consistently examine regenerating NMJs in mice. This nerve injury method involves crushing the common fibular nerve as it passes over the lateral head of the gastrocnemius muscle tendon near the knee. Using 70 day old female mice, we demonstrate that motor axons begin to reinnervate previous postsynaptic targets within 7 days post-crush. They completely reoccupy their previous synaptic areas by 12 days. To determine the reliability of this injury method, we compared reinnervation rates between individual 70 day old female mice. We found that the number of reinnervated postsynaptic sites was similar between mice at 7, 9, and 12 days post-crush. To determine if this injury assay can also be used to compare molecular changes in muscles, we examined levels of the gamma-subunit of the muscle nicotinic receptor (gamma-AChR) and the muscle-specific kinase (MuSK). The gamma-AChR subunit and MuSK to are highly upregulated following denervation and return to normal levels following reinnervation of NMJs. We found a close relationship between transcript levels for these genes and innervation status of muscles. We believe that this method will accelerate our understanding of the cellular and molecular changes involved in repairing the NMJ and other synapses.

The common fibular nerve, also called the common peroneal nerve, arises from the sciatic nerve above the popliteal fossa, where it swings around the head of the fibula to the anterior aspect of the leg (Figure 1A). There it branches into the superficial and deep fibular nerves, together supplying the dorsiflexors of the foot and toes (anterior tibialis, extensor digitorum longus and brevis, and extensor halluces longus muscles), and the everters of the foot (peroneus musc...

Watch this Scientific Journal Video about The Fibular Nerve Injury Method: A Reliable Assay to Identify and Test Factors That Repair Neuromuscular Junctions at JoVE.com

The Fibular Nerve Injury Method: A Reliable Assay to Identify and Test Factors That Repair Neuromuscular Junctions

We have developed a nerve injury method to reliably examine muscle reinnervation, and thus regeneration of neuromuscular junctions in mice. This technique involves injuring the common fibular nerve via a simple and highly reproducible surgery. Muscle reinnervation in then assessed by whole-mounting the extensor digitorum longus muscle.

The neuromuscular junction (NMJ) undergoes deleterious structural and functional changes as a result of aging, injury and disease. Thus, it is imperative ...

The overall goal of this peripheral nerve injury method is to reliably examine regenerating neuromuscular junctions in mice. This method will help us identify the molecular, cellular, and functional changes associated with regenerating neuromuscular junctions. The main advantage of this procedure is that the rate of neuromuscular junction regeneration can be reliably compared between experimental groups largely in the absence of myogenic changes.Demonstrating the procedure will be William Dalkin, a medical student in my laboratory. Before beginning the procedure, use 80%ethanol to clean the surgical site, board, and instruments, followed by disinfection with Povidone-iodine. Next, place the mouse on the surgical board and confirm a lack of response to toe pinch.Align the limbs within the restraints with the target hind limb in an anatomically natural position and the knee joints slightly extended without internal or external rotation. Then, transfer the animal under a surgical microscope and adjust the board until the bony knee joint and the ridge between the tibialis anterior and the gastrocnemius muscles are visible through the objective. Using a scalpel and forceps, make an approximately three centimeter incision through the skin, perpendicular to the underlying course of the common fibular nerve.Continue the incision through the superficial fascia exposing the biceps femoris and the vastus lateralis muscles, followed by a one to two centimeter incision through the connecting deep fascia to separate the muscles. Next, use mechanical retractors to recede the biceps femoris muscle caudally to reveal the common fibular nerve. Trace the nerve proximally until its intersection with the tendon of the lateral head of the gastrocnemius muscle is found.Then, use a fine forceps to grasp the nerve aligning the tips parallel to the lateral border of the gastrocnemius tendon and apply steady, concentrated pressure for five seconds to crush the common fibular nerve. Holding the forceps perpendicular to the fiber, grasp the tissue with the area just behind the tip of the forceps, and apply firm, but gentle pressure for a clean, linear crush of the nerve along the border of the tendon. Visually inspect the nerve through the surgical microscope to confirm a complete crush of the tissue.The nerve will appear translucent at the site of injury. If mice expressing fluorescence proteins in the peripheral axons are used, the fluorescence will disappear from the site of injury. If the nerve has been sufficiently damaged, remove the retractors and realign the muscles in the their anatomic positions.Then, use 6-0 silk sutures to close the incision site with one to three simple interrupted sutures and place the mouse on a heating pad in a clean cage with monitoring until it is fully recovered. Compressing the nerve for five seconds using a fine forceps results in the disappearance of YFP from the injury site. The epineurium remains contiguous, serving as a conduit for the precise regeneration of axons to their original targets.In 70 day old female mice, the nerve injury is sufficient to cause degeneration of all axonal segments distal from the neuronal soma, at four days post-crush. By seven days post-crush, the nerve endings are actively reoccupying the vacated post-synaptic sites. On day 12, the nerve endings continue to differentiate into pre-synaptic sites and the neuromuscular junctions are fully reinervated.There is little variability among mice denervated for the same length of time, demonstrating that fibular nerve crushing can be used as an assay to compare the reinervation of muscles between animals of the same age and sex. As expected, a number of changes occur in the alpha motor axons as they reinervate muscle fibers. The axonal growth cones expand and branch out as they contact post-synaptic sites, growing over specific regions of the post-synapse, and culminating in the near complete juxtaposition of the axonal endings, with the post-synaptic sites.As demonstrated by quantitative PCR, neuromuscular junction associated genes increase following denervation and decrease as the neuromuscular junctions are reinervated. Once mastered, this technique can be completed in 15 minutes if it is performed properly. While attempting this procedure, it's important to remember to take your time, visualize all of the structures, and double-check that a full crush has been obtained.Following this procedure, other methods like QPCR can be performed to answer additional questions about what genes are being up or down-regulated. After its development, this technique paved the way for researchers in the field of neurobiology to explore synaptic regenerations in mice. After watching this video, you should have a good understanding of how to perform a fibular nerve crush to examine the rates of neuromuscular junction reinervation in mice.

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15.4K visualizações.  Virginia Tech. The overall goal of this peripheral nerve injury method is to reliably examine regenerating neuromuscular junctions in mice. This method will help us identify the molecular, cellular, and functional changes associated with regenerating neuromuscular junctions. The main advantage of this procedure is that the rate of neuromuscular junction regeneration can be reliably compared between experimental groups largely in the absence of myogenic changes.Demonstrating the procedure will be Will...