This work was supported by grants from the CIHR Neuromuscular Research Partnership (JNM &#x2013; 90959; to J.A.E.B).

Prior to using this model, investigators must have received approval for the surgical protocol from their institution&#39;s animal use governing body. The model is approved by the Research Ethics Board, Hamilton Health Sciences Corporation, McMaster University (AUP # 10-04-24) and is carried out in strict accordance with the recommendations of the Canadian Council on Animal Care.
1. Mouse Preparation
<ol>
	<li>Weigh the mouse. Induce anesthesia with 5% isoflurane or 2% halothane. The circuit used should ensure adequate scavenging of the anesthetic to protect the surgeon. &#160;After 2-3 min the animal&#39;s respiration will slow. Ensure the blink reflex is absent and pinch the &#160;interdigital spaces in the paw to confirm surgical anesthesia (i.e. no response by the mouse). Apply ophthalmic lubricant to the eye, to prevent drying of the cornea during surgery.</li>
	<li>Shave the lateral thigh and buttock from the sciatic notch to the knee and disinfect with proviodine. Shaving will keep the site of the incision hair free to ensure adequate visualization of the surgical field and to minimize interference with nerve dissection and transection. The sciatic notch, which is superior and posterior to the femur, can be identified by palpation.</li>
</ol>
2. Operative Procedure
<ol>
	<li>Reduce inhalational isoflurane to 2% (halothane 1%) and place the mouse on its side (side intended for surgery facing up), under an operating or dissecting microscope. Alternatively surgery can be performed with surgical loupes since 3.5X magnification is satisfactory for an adult (20-25 g) mouse.</li>
	<li>Don sterile gloves. Identify the sciatic notch by palpation. Using a scalpel, incise the skin of the lateral thigh from the sciatic notch to the knee (approximately 1 cm).</li>
	<li>Gently spread the skin. Identify the biceps femoris muscle, which is the flat superficial muscle of the lateral thigh immediately beneath the skin. Using fine scissors, split the biceps femoris muscle along the muscle fibers and hold open with a spring retractor to expose the sciatic nerve and its branches.</li>
	<li>Identify the sciatic nerve immediately deep to the biceps femoris muscle. It can be identified by its characteristic shiny white color and is approximately 0.8 mm in diameter. It runs from the sciatic notch to the knee, branching into the tibial, peroneal and sural nerves at the level of the popliteal fossa.</li>
	<li>Gently separate the tibial from the peroneal and sural nerve branches with ultrafine forceps and spring microdissecting scissors. The tibial nerve is the largest branch and is usually central. It&#39;s important not to crush the nerve while separating the branches. Holding the nerve just on the outer adventicial layer with the ultrafine forceps, and keeping the nerve slack (not taught), will avoid nerve crush and traction injury.</li>
	<li>For complete and lasting denervation, cut the tibial nerve with microdissecting scissors as distally as possible, carefully avoiding the popliteal vessels. Alternatively, for temporary denervation with expected complete reinnervation in 2-4 weeks, the tibial nerve can simply be crushed with ultrafine forceps for 15 sec instead of transected. (Peripheral nerves regrow following injury and will reinnervate target muscle.)</li>
	<li>If complete denervation is required, suture the end of the transected tibial nerve to the anterior surface of the biceps femoris muscle with 10-0 Nylon and re-approximate the biceps femoris with 5-0 Vicryl to prevent aberrant re-innervation of the gastrocnemius and soleus muscles.</li>
	<li>Close the skin with a running 5-0 Vicryl suture.</li>
</ol>
3. Post Operative Care
<ol>
	<li>Turn off the inhalational anesthetic but maintain the flow of oxygen. Administer buprinorphine (or substitute) analgesic subcutaneously.</li>
	<li>Transfer the mouse to a clean cage with no bedding while waking from anesthesia. Keep on a warming blanket within the cage and under direct observation until ambulating.</li>
	<li>Transfer and house in soft bottom cage (not wire) with ample soft bedding.</li>
	<li>Inspect the operative limb daily for condition of the surgical wound and the foot for the development of decubitus heel ulcers or evidence of chewing. Minor problems can be managed with topical antibiotics or antiseptics such as proviodine. Endpoint indicators requiring animal euthanasia are weight loss, evidence of poor self care (ruffled fur), and hunched posture. In addition, animals with major wound disruption or ulcers that do not heal in 1-2 weeks with topical antibiotics or appear to have pain should be sacrificed.</li>
</ol>
4. Denervated Gastrocnemius and Soleus Muscle Harvest
<ol>
	<li>At the post-operative time point desired, weigh the mouse and sacrifice with CO2 overdose.</li>
	<li>Shave the medial aspect of both the operative and contralateral control legs and clean with alcohol. Place the mouse under an operating or dissecting microscope, or alternatively use surgical viewing loupes for magnification.</li>
	<li>On the operative limb, incise the medial calf skin with a scalpel from the ankle to the knee and circumferentially around the ankle. Gently pull the skin with forceps off the muscle and proximally toward the thigh. This exposes all the muscles of the leg. Identify the gastrocnemius muscle, which is the calf muscle that runs from the knee to the ankle on the posterior aspect of the leg and lies immediately underneath the skin. Identify the distal insertion of the biceps femoris muscle, proximal to the gastrocnemius muscle on the medial aspect of the knee. At its distal insertion the biceps femoris appears thin and filmy and overlies the most proximal portion of the gastrocnemius. Using scissors and blunt end dissection, gently separate the distal insertion of the biceps femoris from the gastrocnemius muscle.</li>
	<li>At its distal insertion into the calcaneous, the gastrocnemius muscle tapers into the Achilles tendon. Identify the Achilles tendon, which appears white and sinewy. Hold the Achilles tendon with forceps, taking care not to hold or crush the gastrocnemius muscle, and divide the Achilles tendon from the calcaneus insertion using scissors.</li>
	<li>Still holding the tendon, gently lift the gastrocnemius muscle (pale red) off the deep soleus (deeper red), from the distal insertion towards its origin at the knee (the soleus can be harvested separately).</li>
	<li>Dissect the gastrocnemius off the leg by dividing the origin of the gastrocnemius from the medial and lateral femur chondyles using scissors. Very gentle traction on the muscle facilitates this process. Be careful not to crush the muscle.</li>
	<li>The soleus will now be plainly visible, immediately under the site of the gastrocnemius. Lift the soleus from its insertion on the Achilles tendon to its origin on the posterior calf. If the soleus is inadvertently raised with the gastrocnemius, gently separate it from the harvested specimen. The gastrocnemius (light red) and soleus (dark red) remain easily identifiable in the harvested specimen due to their color differences.</li>
	<li>Weigh the muscles separately on a precision scale.</li>
	<li>Split the muscles vertically, half for snap freezing in liquid nitrogen (for subsequent protein and/or RNA extraction), and half for histology (i.e. morphometric assessment, immunohistology) fixing either in 10% formalin, or frozen fixation in isopentane cooled with liquid nitrogen, as desired.</li>
	<li>Repeat from step 4.3 above on the control, un-operated, side to harvest control gastrocnemius and soleus muscles.</li>
</ol>

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L., Chamberlain, D., Fahnestock, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+functional+recovery+of+denervated+skeletal+muscle+after+temporary+sensory+nerve+innervation.">Improved functional recovery of denervated skeletal muscle after temporary sensory nerve innervation.</a> Neuroscience. , 103-503 (2001).</li><li>Batt, J., Bain, J., Goncalves, J., Michalski, B., Plant, P., Fahnestock, M., Woodgett, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+gene+expression+profiling+of+short+and+long+term+denervated+muscle.">Differential gene expression profiling of short and long term denervated muscle.</a> FASEB J. 20, 115-117 (2006).</li><li>Sher, J., Cardasis, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skeletal+muscle+fiber+types+in+the+adult+mouse.">Skeletal muscle fiber types in the adult mouse.</a> Acta Neurol. 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P., Holmes, M., Bain, J., Fahnestock, M., de Bruin, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+muscle+stimulation+after+immediate+nerve+repair+reduces+muscle+atrophy+without+affecting+reinnervation.">Electrical muscle stimulation after immediate nerve repair reduces muscle atrophy without affecting reinnervation.</a> Muscle Nerve. 48, 219-225 (2013).</li><li>Sterne, G. D., Coulton, G. R., Brown, R. A., Green, C. J., Terenghi, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neurotrophin-3-enhanced+nerve+regeneration+selectively+improves+recovery+of+muscle+fibers+expressing+myosin+heavy+chains+2b.">Neurotrophin-3-enhanced nerve regeneration selectively improves recovery of muscle fibers expressing myosin heavy chains 2b.</a> J. Cell Biol. 139, 709-715 (1997).</li><li>Plant, P. J., North, M. L., Ward, A., Ward, M., Khanna, N., Correa, J., Scott, J. A., Batt, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypertrophic+airway+smooth+muscle+mass+correlates+with+increased+airway+responsiveness+in+a+murine+model+of+asthma.">Hypertrophic airway smooth muscle mass correlates with increased airway responsiveness in a murine model of asthma.</a> Am. J. Respir. Cell Mol. Biol. 46, 532-540 (2012).</li><li>Bain, J. R., Mackinnon, S. E., Hunter, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+evaluation+of+complete+sciatic,+peroneal,+and+posterior+tibial+nerve+lesions+in+the+rat.">Functional evaluation of complete sciatic, peroneal, and posterior tibial nerve lesions in the rat.</a> Plast. Reconstr. Surg. 83, 129-138 (1989).</li><li>Hare, G. M., Evans, P. J., Mackinnon, S. E., Best, T. J., Midha, R., Szalai, J. P., Hunter, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Walking+track+analysis:+utilization+of+individual+footprint+parameters.">Walking track analysis: utilization of individual footprint parameters.</a> Ann. Plast. Surg. 30, 147-153 (1993).</li><li>McLean, J., Batt, J., Doering, L. C., Rotin, D., 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=Enhanced+rate+of+nerve+regeneration+and+directional+errors+after+sciatic+nerve+injury+in+receptor+protein+tyrosine+phosphatase+sigma+knock-out+mice.">Enhanced rate of nerve regeneration and directional errors after sciatic nerve injury in receptor protein tyrosine phosphatase sigma knock-out mice.</a> J. Neurosci. 22, 5481-5491 (2002).</li><li>Richner, M., Bjerrum, O. J., Nykjaer, A., Vaegter, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+spared+nerve+injury+(SNI)+model+of+induced+mechanical+allodynia+in+mice.">The spared nerve injury (SNI) model of induced mechanical allodynia in mice.</a> J. Vis. Exp. (54), e3092 (2011).</li><li>Rogoz, K., Lagerstrom, M. C., Dufour, S., Kullander, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=VGLUT2-dependent+glutamatergic+transmission+in+primary+afferents+is+required+for+intact+nociception+in+both+acute+and+persistent+pain+modalities.">VGLUT2-dependent glutamatergic transmission in primary afferents is required for intact nociception in both acute and persistent pain modalities.</a> Pain. 153, 1525-1536 (2012).</li><li>Thornell, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sarcopenic+obesity:+satellite+cells+in+the+aging+muscle.">Sarcopenic obesity: satellite cells in the aging muscle.</a> Curr. Opin. Clin. Nutr. Metab. Care. 14, 22-27 (2011).</li></ol>

No conflicts of interest are declared.

The tibial nerve transection model of denervation-induced skeletal muscle atrophy is a commonly employed and well validated model in rats. We have adapted this model for use in mice, which allows the investigator to take advantage of the existence of genetically engineered mice and study the process of muscle atrophy in vivo in the absence of proteins crucial to the regulation of muscle mass7,8. The gastrocnemius and soleus muscles, both denervated in this model, can be easily and rapidly dissected with minimal handling, thus providing excellent quality mRNA and protein for subsequent molecular analyses. Similarly, because of the size of the muscles, they can be split, providing tissue from the same animal for concomitant histologic and morphometric analyses. If hindlimb functional assessment is required, walking track analysis can be serially performed. The feet are dipped in ink and the mouse is walked through a enclosure with paper on the bottom. Characteristics of the prints can be reliably measured and scored to indicate the extent of neuromuscular disability and gait compromise, since footprint characteristics reflect the functional muscle groups13,14. While originally developed and validated in rat13, walking track analysis can also be performed in mice15.
Tibial nerve transection is generally extremely well tolerated by the mice. Only a single dose of analgesic is necessary in the immediate postoperative period. With the use of proper sterile technique, soft tissue infection is rare. While tibial nerve transection does induce sensory paraesthesia on the plantar aspect of the foot, in our experience C57black6 and knockout or transgenic mice derived on this line do not tend to auto-mutilate. However, the mice must be inspected daily for signs of auto-mutilation, heel pressure ulcers, as well as point of care endpoints. While we have negligible mortality with the model, we find that approximately 2-5% of mice must be euthanized due to self-mediated injury to, or pressure ulcers developing on, the operated hind limb. The use of soft bedding post-operatively is crucial to ensure the animal&#39;s comfort and helps to prevent the development of pressure ulcers on the operated side. Sciatic nerve ligation as well as the SNI model of ligation (where the tibial and common peroneal branches of the sciatic are ligated, but the sural is left intact) serve as models of neuropathic pain16,17. Thus, allodynia and thermal hyperalgesia could occur in the foot in our model as well, but we have not seen overt pain behavior in the mice with normal daily activity on soft bedding.
The tibial nerve of only one hindlimb is transected and since the mice weight bear almost equally on both hindlimbs, the musculature from the contralateral un-operated limb can be used as an internal control within each animal7-10. This is not necessarily the case in the sciatic transection model, where more significant abnormalities of gait can induce a hypertrophic response in the contralateral limb muscle. In the tibial nerve transection model, we typically use the gastrocnemius and soleus muscle from the un-operated limb as our control muscle7,8. If the investigator chooses to use separate animals from which to harvest control muscle, then sham surgery should be performed. Sham surgery would consist of the administration of anesthesia, splitting of the skin to expose the tibial nerve, but no transection. Skin would simply be closed following nerve exposure.
In some peripheral nerve transection models, errant reinnervation from the proximal stump to the target muscle contaminates the planned denervation. In this model, securing the proximal end of the transected tibial nerve to the superficial surface of the biceps femoris muscle, thus closing the muscle interface, inhibits the errant reinnervation. As such, it is a critical and essential step in the model. Errant reinnervation is rare in this model.
Similarly, careful handling of the nerve during surgery is essential. The sural and peroneal nerve branches must be gently separated from the tibial nerve prior to tibial transection, and not crushed or stretched in the process. Rough handling of these nerves will compromise their function, partially denervating other hindlimb musculature. If this occurs the animal&#39;s gait will be differentially influenced compared to those mice undergoing sole tibial nerve transection, and the variable muscle loading may contaminate the experimental results. Similarly, care must be taken when dissecting the denervated musculature. Muscle should be handled by the tendon, and not grasped directly to avoid crush artifact that will affect histology, muscle fiber morphometric analyses and possibly gene expression.
We typically employ this model in mice 20-24 g (2-3 months of age), as the animal is mature and the sciatic and tibial nerves are both of adequate size to be easily handled. The surgery can be performed on younger, smaller animals if desired, but the limiting factor here will be the prowess of the operating surgeon. This may be an issue if the investigator is interested in studying the satellite cell response in denervated muscle. The satellite cell regenerative potential diminishes in older, compared to younger, animals18 and therefore younger animals may be required in the experimental design, presenting a technical challenge for a less experienced operator.
The tibial nerve transection model can be adapted from simply a model of denervation-induced muscle atrophy, to one of delayed muscle reinnervation (&#62;4 weeks), if desired and if experienced surgical operators are available1,3. Following a period of denervation specified by the investigator, the mouse can be reoperated and the peroneal nerve mobilized to reinnervate the denervated musculature. The distal stump of the transected tibial nerve is identified, trimmed and the peroneal nerve is mobilized at its distal end and microsurgically repaired to the tibial nerve stump. The peroneal nerve will grow at a rate of approximately 1 mm/day into the tibial nerve stump to reinnervate the gastrocnemius and soleus muscles. The tibial nerve transection model provides an advantage over the sciatic nerve transection model in that a nerve graft is not necessary in the reinnervation procedure2 because of the availability of the peroneal nerve. However, it should be noted that nerve reanastomoses requires the precision of a skilled and experienced operator.
In summary, here we demonstrate the tibial nerve transection model in mice, as an easy, robust, well validated and reproducible model of denervation-induced skeletal muscle atrophy.

Skeletal muscle denervation, due to traumatic peripheral nerve injury, disease or pharmacologic intervention, results in the immediate loss of muscle voluntary contractile function. Muscle concomitantly begins to atrophy and this atrophy is reversible if timely, good-quality reinnervation occurs1,2. In the absence of reinnervation, myofiber atrophy progresses, and irreversible biologic changes in the muscle occur with muscle fibrosis and myofiber death. Here we demonstrate the tibial nerve transection model, a model of denervation-induced skeletal muscle atrophy and fibrosis, in mice. This model enables scientists to study the physiologic, cellular and molecular biologic mechanisms that underlie muscle atrophy in vivo in the gastrocnemius and soleus muscles. While historically used predominantly in rats, more recent application of this model to knockout and transgenic mouse lines specifically, allows investigators to assess the role of their particular protein(s) of interest in the induction, development and maintenance, or alternatively the resolution of, muscle atrophy and fibrosis in vivo.
The tibial nerve is a mixed motor-sensory peripheral nerve in the rodent hindlimb, and is one of the three terminal branches of the sciatic nerve. Transection of the tibial nerve denervates the gastrocnemius, soleus and plantaris muscles (and the three small deep flexor muscles of the foot including tibialis posterior, flexor digitorum longus and flexor hallicus longus), and is a well standardized and validated model in rats3,4. The gastrocnemius and soleus muscles can be easily dissected at serial time points post tibial nerve transection, fixed and processed for assessment of muscle histology and muscle fiber morphometrics, or flash frozen for extraction of muscle RNA and protein for the purpose of studying, for example, the cellular signaling networks regulating muscle atrophy. The gastrocnemius muscle is a mixed fiber type muscle (type I and type II, although predominantly type II) and the soleus muscle is composed of a large proportion of type I fibers, thereby providing both fast and slow twitch muscle for assessment5,6. The tibial nerve transection model is suitable for studying the process of denervation-induced muscle atrophy in both the short term (days)7 and long term (weeks to months)4,8.
In contrast to the sciatic nerve transection model (a second model of denervation-induced muscle atrophy commonly used in rodents), tibial nerve transection induces less morbidity in the animal, making it a more attractive model. Transection of the sciatic nerve denervates all the muscles of the leg (below the knee) and foot, impairing the animal&#39;s ability to ambulate2, whereas transection of the tibial nerve leaves the peroneal and sural nerve branches of the sciatic nerve intact, thus preserving their target muscles and sensory territories. The mouse is unable to plantar flex or invert the foot, but is able to ambulate easily and the weight bears equally on both hind limbs, thereby significantly diminishing the morbidity of the model. Gait analysis studies evaluating walking patterns have been performed in rats following tibial and sciatic nerve injuries and demonstrate that footprint and weight bearing is better preserved with tibial injury9,10. In addition, in the tibial nerve transection model, the peroneal nerve can be mobilized at a later time point and transferred as a source of delayed reinnervation, if the study design requires3. In contrast, delayed reinnervation in the sciatic nerve transection model necessitates the use of a nerve graft to the sciatic nerve deficit, very significantly increasing the technical difficulty of the model and limiting its use to skilled surgeons.
While the tibial nerve transection model requires familiarity of the operator with sterile operative technique in animal surgery, both the tibial nerve and calf muscles it innervates are easily accessible and identifiable for manipulation, so that individuals who are not surgeons, or highly experienced with animal surgery, can readily master this model.

<table border="1">
	<tbody>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Reagents and Materials</td>
		</tr>
		<tr>
			<td>10-0 Nylon suture</td>
			<td>Ethicon</td>
			<td>2850G</td>
			<td></td>
		</tr>
		<tr>
			<td>5-0 Vicryl suture</td>
			<td>Ethicon</td>
			<td>J553G</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>Equipment</td>
		</tr>
		<tr>
			<td>Spring microdissecting scissors</td>
			<td>Fine Surgical Tools</td>
			<td>15021-15</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra fine forceps</td>
			<td>Fine Surgical Tools</td>
			<td>11370-40</td>
			<td></td>
		</tr>
		<tr>
			<td>Non locking micro needle holder (driver)</td>
			<td>Fine Surgical Tools</td>
			<td>12076-12</td>
			<td></td>
		</tr>
		<tr>
			<td>Spring retractor</td>
			<td>Fine Surgical Tools</td>
			<td>17000-02</td>
			<td></td>
		</tr>
	</tbody>
</table>

tibial nerve transection - a standardized model for denervation-induced skeletal muscle atrophy in mice

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of denervation-induced skeletal muscle atrophy in rodents. Although originally developed and used extensively in the rat due to its larger size, the tibial nerve in mice is big enough that it can be easily manipulated with either crush or transection, leaving the peroneal and sural nerve branches of the sciatic nerve intact and thereby preserving their target muscles. Thus, this model offers the advantages of inducing less morbidity and impediment of ambulation than the sciatic nerve transection model and also allows investigators to study the physiologic, cellular and molecular biologic mechanisms regulating the process of muscle atrophy in genetically engineered mice. The tibial nerve supplies the gastrocnemius, soleus and plantaris muscles, so its transection permits the study of denervated skeletal muscle composed of fast twitch type II fibers and/or slow twitch type I fibers. Here we demonstrate the tibial nerve transection model in the C57Black6 mouse. We assess the atrophy of the gastrocnemius muscle, as a representative muscle, at 1, 2, and 4 weeks post-denervation by measuring muscle weights and fiber type specific cross-sectional area on paraffin-embedded histologic sections immunostained for fast twitch myosin.

Tibial nerve transection denervates the gastrocnemius, soleus and plantaris muscles of the calf. Here we assess the development of atrophy in the gastrocnemius muscle, as a representative muscle. Gastrocnemius muscle was harvested from 2-3 months old C57Black 6 mice (Jackson Laboratories) denervated for 1, 2, or 4 weeks. Muscle weights progressively decrease (Figure 1), as does the cross-sectional area of type II fast twitch muscle fibers (Figure 2), over time. The gastrocnemius is a mixed fiber type muscle (type I&#160;and type II), but denervation induces a fiber type switch from type I to type II fibers11, and as a result an adequate number of type I fibers may not be available for measurement and robust statistical analysis.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/50657/50657fig1highres.jpg" src="/files/ftp_upload/50657/50657fig1.jpg" /> 
Figure 1. Denervated gastrocnemius muscle demonstrates progressive atrophy. C57Black 6 mice underwent transection of the right tibial nerve. Gastrocnemius muscle was harvested from the denervated (right) and contralateral control (left) hindlimbs at 1, 2, or 4 weeks following nerve transection. Gastrocnemius muscles were weighed, and the weight of the denervated muscle is expressed as a ratio of the contralateral control innervated muscle. Denervation induces a progressive loss of muscle mass.
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/50657/50657fig2highres.jpg" src="/files/ftp_upload/50657/50657fig2.jpg" /> 
Figure 2. Denervated gastrocnemius muscle demonstrates progressive decrease in myofiber cross section area (A) Denervated and control gastrocnemius muscles were formalin fixed, cut on cross section at the muscle mid-section and immunostained for anti-skeletal muscle myosin, fast twitch isoform (My-32, Sigma, 1:500 dilution) followed by biotinylated secondary antibody and streptavidin-HRP/DAB as described7. Hematoxylin was used as a counterstain. Fast twitch type II fibers stain brown and slow twitch type I fibers stain light purple. The cross-sectional area (CSA) of the fibers was measured using ImageJ software (Bethesda, NIH) as described7,12. The fast twitch type II fibers demonstrate progressive atrophy. Too few type I fibers are present in denervated gastrocnemius to permit a statistically valid evaluation of fiber size. (n = 6 to 9 mice/group. A minimum of 200 myofibers were measured per muscle by a reviewer blinded to operative phenotype. Data are presented as the mean +/- SD. Scale bar equals 100 &#956;m). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/50657/50657fig1large.jpg" target="_blank"> Click here to view larger figure</a>.

Watch this Scientific Journal Video about Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice at JoVE.com

Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of skeletal muscle atrophy. The model surgical protocol is described and demonstrated in C57Black6 mice. &#160;

The tibial nerve transection model is a well-tolerated, validated, and reproducible model of denervation-induced skeletal muscle atrophy in rodents. ...

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24.3K Views.  St Michaels Hospital. The tibial nerve transection model is a well-tolerated, validated, and reproducible model of skeletal muscle atrophy. The model surgical protocol is described and demonstrated in C57Black6 mice.  

Video: Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice

Myo-mechanical Analysis of Isolated Skeletal Muscle

To assess the in vivo effects of therapeutic interventions for the treatment of muscle disease 1,2,3, quantitative methods are needed that measure force generation and fatigability in treated muscle. We describe a detailed approach to evaluating myo-mechanical properties in freshly explanted hindlimb muscle from the mouse. We describe the atraumatic harvest of mouse extensor digitorum longus muscle, mounting the muscle in a muscle strip myograph (Model 820MS; Danish Myo Technology), and the measurement of maximal twitch and tetanic tension, contraction time, and half-relaxation time, using a square pulse stimulator (Model S48; Grass Technologies). Using these measurements, we demonstrate the calculation of specific twitch and tetanic tension normalized to muscle cross-sectional area, the twitch-to-tetanic tension ratio, the force-frequency relationship curve and the low frequency fatigue curve 4. This analysis provides a method for quantitative comparison between therapeutic interventions in mouse models of muscle disease 1,2,3,5, as well as comparison of the effects of genetic modification on muscle function 6,7,8,9.

To assess the in vivo effects of therapeutic interventions for muscle disease, methods are needed to quantitate force generation and fatigability in treated muscle. We detail an approach to evaluating myo-mechanical properties in explanted mouse hindlimb muscle. This analysis provides a robust approach to quantitating the effects of genetic modification on muscle function, as well as comparison of therapies in mouse models of muscle disease.

To assess the in vivo effects of therapeutic interventions for the treatment of muscle disease 1,2,3, quantitative methods are needed that measure force ...

The Spared Nerve Injury (SNI) Model of Induced Mechanical Allodynia in Mice

Peripheral neuropathic pain is a severe chronic pain condition which may result from trauma to sensory nerves in the peripheral nervous system. The spared nerve injury (SNI) model induces symptoms of neuropathic pain such as mechanical allodynia i.e. pain due to tactile stimuli that do not normally provoke a painful response [1]. 
The SNI mouse model involves ligation of two of the three branches of the sciatic nerve (the tibial nerve and the common peroneal nerve), while the sural nerve is left intact [2]. The lesion results in marked hypersensitivity in the lateral area of the paw, which is innervated by the spared sural nerve. The non-operated side of the mouse can be used as a control. The advantages of the SNI model are the robustness of the response and that it doesn&#x2019;t require expert microsurgical skills.
The threshold for mechanical pain response is determined by testing with von Frey filaments of increasing bending force, which are repetitively pressed against the lateral area of the paw [3], [4]. A positive pain reaction is defined as sudden paw withdrawal, flinching and/or paw licking induced by the filament. A positive response in three out of five repetitive stimuli is defined as the pain threshold. 
As demonstrated in the video protocol, C57BL/6 mice experience profound allodynia as early as the day following surgery and maintain this for several weeks.

The Spared Nerve Injury SNI Model of Induced Mechanical Allodynia in Mice

The Spared Nerve Injury animal model is described here as a mouse model of peripheral neuropathic pain following partial denervation of the sciatic nerve by lesioning the tibial and common peroneal nerve branches, leaving the remaining sural nerve intact. Behavioral modification resulting from mechanical allodynia is quantified by von Frey filaments.

Peripheral neuropathic pain is a severe chronic pain condition which may result from trauma to sensory nerves in the peripheral nervous system. The spared ...

Skeletal Muscle Gender Dimorphism from Proteomics

Gross contraction in skeletal muscle is primarily determined by a relatively small number of contractile proteins, however this tissue is also remarkably adaptable to environmental factors1 such as hypertrophy by resistance exercise and atrophy by disuse. It thereby exhibits remodeling and adaptations to stressors (heat, ischemia, heavy metals, etc.)2,3. Damage can occur to muscle by a muscle exerting force while lengthening, the so-called eccentric contraction4. The contractile proteins can be damaged in such exertions and need to be repaired, degraded and/or resynthesized; these functions are not part of the contractile proteins, but of other much less abundant proteins in the cell. To determine what subset of proteins is involved in the amelioration of this type of damage, a global proteome must be established prior to exercise5 and then followed subsequent to the exercise to determine the differential protein expression and thereby highlight candidate proteins in the adaptations to damage and its repair. Furthermore, most studies of skeletal muscle have been conducted on the male of the species and hence may not be representative of female muscle. 
In this article we present a method for extracting proteins reproducibly from male and female muscles, and separating them by two-dimensional gel electrophoresis followed by high resolution digital imaging6. This provides a protocol for spots (and subsequently identified proteins) that show a statistically significant (p &lt; 0.05) two-fold increase or decrease, appear or disappear from the control state. These are then excised, digested with trypsin and separated by high-pressure liquid chromatography coupled to a mass spectrometer (LC/MS) for protein identification (LC/MS/MS)5. This methodology (Figure 1) can be used on many tissues with little to no modification (liver, brain, heart etc.).

A straight-forward set of methods to isolate and determine the identity of the most abundant proteins expressed in skeletal muscle. About 800 spots are discerned on a two-dimensional gel from 10 mg muscle; this allows for the determination of gender-specific protein expression. These methods will give equivalent results in most tissues.

Gross contraction in skeletal muscle is primarily determined by a relatively small number of contractile proteins, however this tissue is also remarkably ...

The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice

Neuropathic pain arises as a consequence of a lesion or a disease affecting the somatosensory system. This syndrome results from maladaptive changes in injured sensory neurons and along the entire nociceptive pathway within the central nervous system. It is usually chronic and challenging to treat. In order to study neuropathic pain and its treatments, different models have been developed in rodents. These models derive from known etiologies, thus reproducing peripheral nerve injuries, central injuries, and metabolic-, infectious- or chemotherapy-related neuropathies. Murine models of peripheral nerve injury often target the sciatic nerve which is easy to access and allows nociceptive tests on the hind paw. These models rely on a compression and/or a section. Here, the detailed surgery procedure for the &#34;cuff model&#34; of neuropathic pain in mice is described. In this model, a cuff of PE-20 polyethylene tubing of standardized length (2 mm) is unilaterally implanted around the main branch of the sciatic nerve. It induces a long-lasting mechanical allodynia, i.e., a nociceptive response to a normally non-nociceptive stimulus that can be evaluated by using von Frey filaments. Besides the detailed surgery and testing procedures, the interest of this model for the study of neuropathic pain mechanism, for the study of neuropathic pain sensory and anxiodepressive aspects, and for the study of neuropathic pain treatments are also discussed.

Neuropathic pain is a consequence of a lesion or disease affecting the somatosensory system. The &#8220;cuff model&#8221; of neuropathic pain in mice consists of the implantation of a polyethylene cuff around the main branch of the sciatic nerve. Mechanical allodynia is tested using von Frey filaments.

Neuropathic pain arises as a consequence of a lesion or a disease affecting the somatosensory system. This syndrome results from maladaptive changes in ...

Human Skeletal Muscle Biopsy Procedures Using the Modified Bergstr&#246;m Technique

The percutaneous biopsy technique enables researchers and clinicians to collect skeletal muscle tissue samples. The technique is safe and highly effective. This video describes the percutaneous biopsy technique using a modified Bergstr&#246;m needle to obtain skeletal muscle tissue samples from the vastus lateralis of human subjects. The Bergstr&#246;m needle consists of an outer cannula with a small opening (&#8216;window&#8217;) at the side of the tip and an inner trocar with a cutting blade at the distal end. Under local anesthesia and aseptic conditions, the needle is advanced into the skeletal muscle through an incision in the skin, subcutaneous tissue, and fascia. Next, suction is applied to the inner trocar, the outer trocar is pulled back, skeletal muscle tissue is drawn into the window of the outer cannula by the suction, and the inner trocar is rapidly closed, thus cutting or clipping the skeletal muscle tissue sample. The needle is rotated 90&#176;&#160;and another cut is made. This process may be repeated three more times. This multiple cutting technique typically produces a sample of 100-200 mg or more in healthy subjects and can be done immediately before, during, and after a bout of exercise or other intervention. Following post-biopsy dressing of the incision site, subjects typically resume their activities of daily living right away and can fully participate in vigorous physical activity within 48-72 hr. Subjects should avoid heavy resistance exercise for 48 hr to reduce the risk of herniation of the muscle through the incision in the fascia.

The purpose of this video is to present the modified Bergstr&#246;m skeletal muscle biopsy technique on human subjects.

The percutaneous biopsy technique enables researchers and clinicians to collect skeletal muscle tissue samples. The technique is safe and highly ...

A Simple Critical-sized Femoral Defect Model in Mice

While bone has a remarkable capacity for regeneration, serious bone trauma often results in damage that does not properly heal. In fact, one tenth of all limb bone fractures fail to heal completely due to the extent of the trauma, disease, or age of the patient. Our ability to improve bone regenerative strategies is critically dependent on the ability to mimic serious bone trauma in test animals, but the generation and stabilization of large bone lesions is technically challenging. In most cases, serious long bone trauma is mimicked experimentally by establishing a defect that will not naturally heal. This is achieved by complete removal of a bone segment that is larger than 1.5 times the diameter of the bone cross-section. The bone is then stabilized with a metal implant to maintain proper orientation of the fracture edges and allow for mobility. 
Due to their small size and the fragility of their long bones, establishment of such lesions in mice are beyond the capabilities of most research groups. As such, long bone defect models are confined to rats and larger animals. Nevertheless, mice afford significant research advantages in that they can be genetically modified and bred as immune-compromised strains that do not reject human cells and tissue.
Herein, we demonstrate a technique that facilitates the generation of a segmental defect in mouse femora using standard laboratory and veterinary equipment. With practice, fabrication of the fixation device and surgical implantation is feasible for the majority of trained veterinarians and animal research personnel. Using example data, we also provide methodologies for the quantitative analysis of bone healing for the model.

Animal models are frequently employed to mimic serious bone injury in biomedical research. Due to their small size, establishment of stabilized bone lesions in mice are beyond the capabilities of most research groups. Herein, we describe a simple method for establishing and analyzing experimental femoral defects in mice.

While bone has a remarkable capacity for regeneration, serious bone trauma often results in damage that does not properly heal. In fact, one tenth of all ...

Facial Nerve Axotomy in Mice: A Model to Study Motoneuron Response to Injury

The goal of this surgical protocol is to expose the facial nerve, which innervates the facial musculature, at its exit from the stylomastoid foramen and either cut or crush it to induce peripheral nerve injury. Advantages of this surgery are its simplicity, high reproducibility, and the lack of effect on vital functions or mobility from the subsequent facial paralysis, thus resulting in a relatively mild surgical outcome compared to other nerve injury models. A major advantage of using a cranial nerve injury model is that the motoneurons reside in a relatively homogenous population in the facial motor nucleus in the pons, simplifying the study of the motoneuron cell bodies. Because of the symmetrical nature of facial nerve innervation and the lack of crosstalk between the facial motor nuclei, the operation can be performed unilaterally with the unaxotomized side serving as a paired internal control. A variety of analyses can be performed postoperatively to assess the physiologic response, details of which are beyond the scope of this article. For example, recovery of muscle function can serve as a behavioral marker for reinnervation, or the motoneurons can be quantified to measure cell survival. Additionally, the motoneurons can be accurately captured using laser microdissection for molecular analysis. Because the facial nerve axotomy is minimally invasive and well tolerated, it can be utilized on a wide variety of genetically modified mice. Also, this surgery model can be used to analyze the effectiveness of peripheral nerve injury treatments. Facial nerve injury provides a means for investigating not only motoneurons, but also the responses of the central and peripheral glial microenvironment, immune system, and target musculature. The facial nerve injury model is a widely accepted peripheral nerve injury model that serves as a powerful tool for studying nerve injury and regeneration.

We present a surgical protocol detailing how to perform a cut or crush axotomy on the facial nerve in the mouse. The facial nerve axotomy can be employed to study the physiological response to nerve injury and test therapeutic techniques.

The goal of this surgical protocol is to expose the facial nerve, which innervates the facial musculature, at its exit from the stylomastoid foramen and ...

Ultrasound Based Assessment of Coronary Artery Flow and Coronary Flow Reserve Using the Pressure Overload Model in Mice

Transthoracic Doppler echocardiography (TTDE) is a clinically useful, noninvasive tool for studying coronary artery flow velocity and coronary flow reserve (CFR) in humans. Reduced CFR is accompanied by marked intramyocardial and pericoronary fibrosis and is used as an indication of the severity of dysfunction. This study explores, step-by-step, the real-time changes measured in the coronary flow velocity, CFR and systolic to diastolic peak velocity (S/D) ratio in the setting of an aortic banding model in mice. By using a Doppler transthoracic imaging technique that yields reproducible and reliable data, the method assesses changes in flow in the septal coronary artery (SCA), for a period of over two weeks in mice, that previously either underwent aortic banding or thoracotomy. 
During imaging, hyperemia in all mice was induced by isoflurane, an anesthetic that increased coronary flow velocity when compared with resting flow. All images were acquired by a single imager. Two ratios, (1) CFR, the ratio between hyperemic and baseline flow velocities, and (2) systolic (S) to diastolic (D) flow were determined, using a proprietary software and by two independent observers. Importantly, the observed changes in coronary flow preceded LV dysfunction as evidenced by normal LV mass and fractional shortening (FS). 
The method was benchmarked against the current gold standard of coronary assessment, histopathology. The latter technique showed clear pathologic changes in the coronary artery in the form of peri-coronary fibrosis that correlated to the flow changes as assessed by echocardiography. 
The study underscores the value of using a non-invasive technique to monitor coronary circulation in mouse hearts. The method minimizes redundant use of research animals and demonstrates that advanced ultrasound-based indices, such as CFR and S/D ratios, can serve as viable diagnostic tools in a variety of investigational protocols including drug studies and the study of genetically modified strains.

Coronary flow reserve (CFR) is useful for assessment of myocardial oxygen demand and evaluation of cardiovascular risk. This study establishes a step-by-step transthoracic Doppler echocardiographic (TTDE) method for longitudinal monitoring of the changes in CFR, as measured from coronary artery in mice, under the experimental pressure overload of aortic banding.

Transthoracic Doppler echocardiography (TTDE) is a clinically useful, noninvasive tool for studying coronary artery flow velocity and coronary flow ...

Human Vastus Lateralis Skeletal Muscle Biopsy Using the Weil-Blakesley Conchotome

Percutaneous muscle biopsy using the Weil-Blakesley conchotome is well established in both clinical and research practice. It is a safe, effective and well tolerated technique. The Weil-Blakesley conchotome has a sharp biting tip with a 4 - 6 mm wide hollow. It is inserted through a 5 - 10 mm skin incision and can be maneuvered for controlled tissue penetration. The tip is opened and closed within the tissue and then rotated through 90 -180&#176; to cut the muscle. The amount of muscle obtained following repeated sampling can vary from 20 mg to 290 mg which can be processed for both histology and molecular studies. The wound needs to be kept dry and vigorous physical activity kept to a minimum for approximately 72 hr although normal levels of activity can restart immediately following the procedure. This procedure is safe and effective when close attention is paid to the selection of subjects, full asepsis and post procedure care. &#160;Both right and left vastus lateralis are suitable for biopsy dependent on participant preference.

Human Vastus Lateralis Skeletal Muscle Biopsy Using the Weil-Blakesley Conchotome

This video demonstrates the technique of percutaneous muscle biopsy of the human vastus lateralis using the Weil-Blakesley conchotome.

Percutaneous muscle biopsy using the Weil-Blakesley conchotome is well established in both clinical and research practice. It is a safe, effective and ...

Surgical Angiogenesis in Porcine Tibial Allotransplantation: A New Large Animal Bone Vascularized Composite Allotransplantation Model

Segmental bone loss resulting from trauma, infection malignancy and congenital anomaly remains a major reconstructive challenge. Current therapeutic options have significant risk of failure and substantial morbidity.
Use of bone vascularized composite allotransplantation (VCA) would offer both a close match of resected bone size and shape and the healing and remodeling potential of living bone. At present, life-long drug immunosuppression (IS) is required. Organ toxicity, opportunistic infection and neoplasm risks are of concern to treat such non-lethal indications.
We have previously demonstrated that bone and joint VCA viability may be maintained in rats and rabbits without the need of long-term-immunosuppression by implantation of recipient derived vessels within the VCA. It generates an autogenous, neoangiogenic circulation with measurable flow and active bone remodeling, requiring only 2 weeks of IS. As small animals differ from man substantially in anatomy, bone physiology and immunology, we have developed a porcine bone VCA model to evaluate this technique before clinical application is undertaken. Miniature swine are currently widely used for allotransplantation research, given their immunologic, anatomic, physiologic and size similarities to man. Here, we describe a new porcine orthotopic tibial bone VCA model to test the role of autogenous surgical angiogenesis to maintain VCA viability.
The model reconstructs segmental tibial bone defects using size- and shape-matched allogeneic tibial bone segments, transplanted across a major swine leukocyte antigen (SLA) mismatch in Yucatan miniature swine. Nutrient vessel repair and implantation of recipient derived autogenous vessels into the medullary canal of allogeneic tibial bone segments is performed in combination with simultaneous short-term IS. This permits a neoangiogenic autogenous circulation to develop from the implanted tissue, maintaining flow through the allogeneic nutrient vessels for a short time. Once established, the new autogenous circulation maintains bone viability following cessation of drug therapy and subsequent nutrient vessel thrombosis.

Currently any kind of vascularized composite allotransplantation depends on long-term-immunosuppression, difficult to support for non-life-critical indications. We present a new porcine tibial VCA model that can be used to study bone VCA and demonstrate the use of surgical angiogenesis to maintain bone viability without the need of long-term immune-modulation.

Segmental bone loss resulting from trauma, infection malignancy and congenital anomaly remains a major reconstructive challenge. Current therapeutic ...

Tibial Nerve Transection - A Standardized Model for Denervation-induced Skeletal Muscle Atrophy in Mice

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Myo-mechanical Analysis of Isolated Skeletal Muscle

The Spared Nerve Injury (SNI) Model of Induced Mechanical Allodynia in Mice

Skeletal Muscle Gender Dimorphism from Proteomics

The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice

Human Skeletal Muscle Biopsy Procedures Using the Modified Bergström Technique

A Simple Critical-sized Femoral Defect Model in Mice

Facial Nerve Axotomy in Mice: A Model to Study Motoneuron Response to Injury

Ultrasound Based Assessment of Coronary Artery Flow and Coronary Flow Reserve Using the Pressure Overload Model in Mice

Human Vastus Lateralis Skeletal Muscle Biopsy Using the Weil-Blakesley Conchotome

Surgical Angiogenesis in Porcine Tibial Allotransplantation: A New Large Animal Bone Vascularized Composite Allotransplantation Model