The authors would like to thankthe Jenkins Microscopy Facility at the University of Wyoming for their help, and the members of the Bushman lab, Kelly Roballo, Hayden True, Wupu Osimanjiang and Subash Dhunghana, for assistance in animal care. This publication was made possible by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under Grant # 2P20GM103432.

Adult Sprague Dawley rats were used in this project and all procedures were approved by the University of Wyoming Institutional Animal Care and Use Committee.
1. Surgery and In Vivo Nerve Fixation
NOTE: Vendor information for all materials and equipment used in this protocol are listed in the Table of Materials.
NOTE: In vivo nerve fixation is used to preserve the tissue and reduce structural degradation that can occur between the time of death and collection of the nerves.&#160;In vivo tissue fixation is a standard practice for preparation of nervous system tissue for histology, where perfusion is often a precursor to this. The placement and size of peripheral nerves allowed for in situ fixation. We do not recommend collection and fixation of tissue after euthanasia due to the possibility of tissue degradation.
<ol>
	<li>Prepare the rat for general anesthesia by placing it in an induction chamber with 2-3% isoflurane, then place the anesthetized rat in the prone position on the top of a dissection mat and maintain at 1-2% of isoflurane via anesthetic nose cone.&#160;To ensure adequate depth of anesthesia, test animals for pedal withdrawal at the hind feet and check for the absence of palpebral reflexes at the eyes by touching the medial canthus of the eye. 
	NOTE: Intraperitoneal injection of ketamine is a commonly used alternative to inhaled isoflurane.</li>
	<li>To expose the sciatic nerve, shave the hair of the hind limb(s) and clean the shaved areas with 70% ethanol. With a scalpel or scissors, make a 2-3 cm incision in the skin along the hind limb from the knee up to the greater trochanter, where palpation of the femur using the sterile scalpel to ensure the proper location of the incision.&#160;The femur is located just proximal to the most accessible segment of the sciatic nerve. Even though this is a non-survival surgery, maintain sterile techniques.</li>
	<li>After making the skin incision, locate the plane between the biceps femoris muscle and the gluteus maximus muscle, and using microdissection scissors separate the underlying fascia and expose 2-3 cm of the underline sciatic nerve. To expose a clear section of the sciatic nerve, use a retractor to widen the gap between the two muscles (Figure 1A). With fine forceps and iris scissors, carefully separate the nerve from surrounding connective tissue, taking great care not to compress or cut the nerve.</li>
	<li>Add sufficient Trump&#8217;s fixative (4% formaldehyde, 1% glutaraldehyde in 1x PBS (phosphate buffered saline) with 1.16 g of NaH2PO4&#183;H2O per 100 mL) into the cavity containing the exposed nerve to cover the nerve and let sit for 10 min. If necessary, place gauze under the hind leg to improve the angle so that more fixative can be added into the cavity. Remove the fixative after 10 min&#160;and repeat this step two more times.</li>
	<li>Using a dissecting microscope, cut the nerve from both sides using fine dissection scissors, making sure not to stretch or pinch the sciatic nerve, and immediately put the nerve sections in 15 mL tubes containing Trump&#39;s fixative at 4 &#176;C for one week, changing the fixative every 48 h.</li>
	<li>Do not leave animals unattended during any part of the surgical procedure. After removal of the nerve, euthanize animals by cervical dislocation while under anesthesia.</li>
</ol>
2. Osmium Tetroxide Treatment and Resin Embedding
<ol>
	<li>Post fixation, carefully remove any remaining fat and connective tissues from the nerve and use a sharp scalpel to cut the nerve into segments approximately 5 mm in length (nerve segments can be separated and labeled in different tubes). Prepare fresh 2% osmium tetroxide diluted in Trump&#39;s fixative solution and keep in a glass tube. Immerse nerve segments in 2% osmium tetroxide for 2 h, which can be in plastic tubes for this short period of time. 
	NOTE: Some plastic tubes react with osmium tetroxide, causing a darkening of the solution, so prolonged storage of osmium tetroxide in plastic tubes is not recommended.</li>
	<li>Using an epoxy embedding medium kit, prepare the final embedding formula:
	<ol>
		<li>Mix the epoxy embedding medium with DDSA solution (dodecenylsuccinic anhydride; mixture A) and mix the epoxy embedding medium with NMA solution (methylnadic anhydride; mixture B). Let both mixtures A and B mix at least 20 min&#160;by stirring with a magnetic stirrer.</li>
		<li>Immediately before use, mix mixture A and B and add the accelerator DPM-30 (2,4,6-tris(dimethylaminomethyl)phenol) in the proportion of 1.5 to 2.0% of the total volume of the mixture. Note that the DPM-30 solution should be measured precisely to prevent the block from becoming dark in color and brittle. All resin chemicals are toxic; take extra care to prevent skin contact or inhalation.</li>
	</ol>
	</li>
	<li>Using 1.5 mL tubes, wash nerve segments with PBS and start the dehydration process by placing the nerve segments in different acetone/distilled water passages:&#160;30%, 60%, 90%, concentrations for 10 min each, then in 100% acetone 3 times for 10 min each.&#160; Note that ethanol can be used in the place of acetone.</li>
	<li>For resin infiltration, place the nerve segments in a mixture of 1 part of the final embedding mixture and 1 part 100% acetone for 30 min, then in a mixture of 2 parts of the final embedding mixture and 1 part 100% acetone for 30 min, and finally place the nerve segments in the final embedding mixture for 30 min.</li>
	<li>Put the nerve segments into silicone rubber embedding molds (we have used 106 mm length x 71 mm width x 7 mm depth; block size 11 mm length x 6 mm width x 3 mm depth). Gently add the resin on top of the nerves, making sure to cover the whole nerve segments and avoid making air bubbles. Leave the mold containing nerve segments with the resin to polymerize at 60 &#176;C overnight.</li>
</ol>
3. Sectioning by Ultramicrotome
<ol>
	<li>Prepare glass knives using a glass knife maker (Figure 1B) and make glass knives with boats(Figure 1C), which are used to collect nerve sections floating on the distilled water.</li>
	<li>Place resin embedded nerve blocks into the ultramicrotome holder with the trapezoidal side facing up. Using the ultramicrotome scope, trim any excess resin surrounding the nerve tissue, and make the block face a trapezoid shape and as close to the longitudinal surface of the nerve as possible using a single-edged blade, such as a razor blade. Do not penetrate the longitudinal surface of the nerve segment, which is recognizable by its dark staining by osmium tetroxide. 
	NOTE: Trimming of excess resin will reduce the area of resin to be sectioned and improve blade performance and cutting in subsequent steps.</li>
	<li>Using the ultramicrotome, make multiple cross sections sufficient to expose a uniform cross section surface of the nerve tissue using a plain glass knife. Once this is done, switch to a glass knife whose boat is filled with distilled water at room temperature and adjust the ultramicrotome to 1-2 &#956;m to cut thin sections.</li>
	<li>Transfer floating thin sections from the glass knife boat to a drop of deionized water on glass slide using metal loop (Figure 1D). Dry slides containing sections by passing several times over a flame for a few seconds, making sure not to overheat the sections. Stain dried sections immediately with toluidine blue or store at room temperature for several days before staining. 
	NOTE: Sections can also be dried using a plate warmer at 60 &#176;C for 15 min. A slow drying process makes the sections smooth.</li>
</ol>
4. Toluidine Blue Staining
<ol>
	<li>Prepare 1% solution of toluidine blue by dissolving 2 g of sodium borate in 100 mL of deionized water, then add 1 g of toluidine blue and stir until dissolved. Filter the solution using filter paper (pore size: 11 &#181;m) and keep the solution in an opaque bottle at room temperature for up to two weeks.</li>
	<li>Using a plastic pipette or micro pipettor, add a drop of toluidine blue solution on the top of the nerve sections and leave for 20-30 s.</li>
	<li>Rinse off all toluidine blue solution excess by gently dipping the slides into deionized water jar and repeat 3-4 times until sections are clear. Dry the slides at least 15 min at 60 &#176;C or overnight at room temperature and then cover the sections with a coverslip using regular mounting medium. Examine the mounted slides immediately or store at room temperature.</li>
	<li>Examine under a light microscope. A 100X oil immersion lens is recommended for detailed images used to calculate g-ratios.</li>
</ol>

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The authors declare that they have no conflicts of interest.

Examinations of the morphological structures of peripheral nerve injury and regeneration are frequent subjects of study13. In this protocol, we describe the steps to obtain high quality images for histological data quantifications using rat sciatic nerve tissue embedded in resin blocks and stained with toluidine blue. This technique provides an image of nerve morphology in which the nerve regeneration can be quantified by measuring the number of axons, degree of myelination, presence of infiltrative fibrotic tissue, and the health nerves. While the images show sectioning and processing of uninjured nerves as samples, the same steps and materials are applicable to injured nerves and nerves regenerated with conduits or tissue grafts, provided that fixation of the tissue is adequate20,21. 
While all steps of the protocol are essential, some of these steps are more likely to lead to poor quality sections or images. Insufficient tissue dehydration may lead to holes in the nerve sections (Figure 5B). One possible explanation is the immiscibility of resin with water, and excess water in the tissue prevents resin from infiltrating the tissue. Therefore, allowing sufficient time and the use of absolute acetone is essential to ensure proper dehydration step. Although we used acetone in this protocol, ethanol can also be used. Many resins, however, are not reactive with ethanol, so the tissue must be treated with propylene oxide to serve as a transition between the ethanol dehydration and resin embedding.
Due to the thinness of the sections, transferring nerve sections from the glass knife to the glass slide should be done with great care (Figure 5C). 1-2 &#956;m sections are very fragile, and improper transfer of the section could cause the section to break. If the section is picked up in the central portion of the section with a needle, the section is prone to folding in on itself and often will be difficult to unfold when transferred to the slide. Different tools can be used for the transfer of the section to the glass slide, including needles and loops, and each should be tested for the specific user to determine which will yield the best transfer results. For our purposes, using a loop that could encompass the entire section greatly reduced the folding of sections when they were transferred from the glass knife to the microscope slide (Figure 1D).
In general, proper handling of the nerves is essential as compression of the nerves can cause cracks to occur in nerve sections (Figure 5A). Nerve tissue compression can happen during transfer of nerve segments in the processes of exposure in the animal, fixation, dehydration, and resin embedding. To avoid nerve tissue compression, nerve segments should be transferred by fine forceps and picked up on one end of the segment ideally by just the epineurial layer, so the entire nerve will not be affected. The presence of cracks and lines (knife marks) in the nerve sections may also occur due to dull or overused glass knives. To guarantee optimal sectioning, we recommend making fresh glass knives and changing the glass knife every 25-30 cuts, fewer if sectioning through nerve encased within a conduit.
Resins can be relatively expensive, are inadequate when longitudinal nerve sections are required, and can require expensive tools such as an ultramicrotome and a glass knife maker. Despite these limitations, toluidine blue staining of resin embedded peripheral nerve sections is still considered the gold standard for visualization of cross sections of peripheral nerve morphometry4,5. Longitudinal sections can also reveal important features of peripheral nerves, such as axonal continuity and nodes of Ranvier, but is most useful with immunohistochemistry. In such cases it is the general practice to differentially process two sections of the same nerve, one for toluidine blue cross sections and the other for longitudinal immunohistochemistry. Due to increased incidences of peripheral nerve trauma and injuries and the needs of a better way of assessing nerve morphological structures, this method can continue to be applied as an essential tool to gain histological data of nerve damage and regeneration.

Peripheral nerves extend throughout the body, innervating target tissues with motor or sensory axons1. Peripheral nerve defects caused by medical disorders and trauma represent a major public health concern and have large economic impacts2,3. Despite the advances in assessing the outcomes of peripheral nerve injuries and understanding nerve regeneration, traditional methods such as nerve histology and staining techniques are essential tools to qualitatively and quantitatively assess nerve health as a terminal outcome measurement in animal models or excised human tissue. This is often paired with electrophysiological measurements of peripheral nerve function, where morphometry can reveal why functional nerve regeneration did or did not occur.
Toluidine blue staining of resin embedded semi-thin peripheral nerve sections is a specialized method for imaging myelinated nerve fibers, providing high quality and clear detailed images of nerve structures4,5,6. Toluidine blue is an acidophilic metachromatic stain, discovered by William Henry Perkin in 18567, and has been used in several medical applications8. Toluidine blue-stained peripheral nerve sections obtained from resin-embedded nerve segments allows for clear visualization of nerve structures. Visualization of myelin sheath structure can be enhanced by the use of osmium tetroxide post-fixation4,9. Osmium tetroxide is a toxic oxidant and lipid fixative agent that interacts with the double bonds in lipids, resulting in starkly defined lipid-rich myelin sheaths10. However, osmium tetroxide is toxic, expensive, requires a longer incubation of nerve segments, and is not always used.
Alternative methods of processing and staining have been developed for visualization of peripheral nerve morphology; Paraffin, cryogenic sectioning, and epoxy resin-embedded nerve sectioning followed by staining with toluidine blue or phenylenediamine solution has been used to quantify morphological changes of peripheral nerve regeneration 11,12. These methods each have their advantages and yield essential data on the number of axons, myelin thickness, axon diameter, and axon diameter to myelinated fiber diameter (g-ratio) 11,13,14,15.
The primary distinction of the resin-embedding in this protocol is that it facilitates obtaining 1-2 &#956;m thickness cross-sections due to the hardness of the resin while maintaining the histological qualities of the nerve. These thin sections, as opposed to the 4-5 &#956;m thickness sections obtained from paraffin embedding, provide peripheral nerve sections with higher resolution, allowing for a more accurate quantification of axon myelination, such as the g-ratio, that cannot be obtained from thicker sections16. While cryogenic sectioning can be used to obtain 1-2 &#181;m sections, it has been our experience that it is more difficult to obtain sections without numerous large cracks. Such cracked sections can cause inaccurate counting of the number of axons and aspects of myelination.
In addition to toluidine blue staining17, a silver staining method18 and Masson&#39;s trichrome staining4 can also be used to show nerve axons. However, using resin embedding of rat median nerve sections stained with either hematoxylin and eosin or Masson&#39;s trichrome showed faint myelin sheaths and unrecognized structures, whereas toluidine blue staining showed clear myelin sheath image and easily can be quantified4. Despite some limitations, toluidine blue staining of resin embedded peripheral nerves is a valuable technique that can be used when high resolution images of nerve morphology are required.
The primary disadvantage for resin embedding is that it is time-consuming and does not allow for immunostaining of the same tissue due to the difficulty of antigen retrieval when compared to paraffin and frozen embedded sections techniques. Thus, it is not generally possible to utilize the same tissue for immunostaining that is processed via resin-embedding for toluidine blue staining. Although not used here, if immunohistochemistry is desired in resin embedded sections, the use of glycol methacrylate embedding resins allows for immunohistochemistry to be performed on tissue sections, but it is relatively expensive19. This can be somewhat mitigated by cutting the peripheral nerve into separate segments, some for resin-embedding and others for immunostaining directly after fixation.
The process of toluidine blue staining of resin embedded peripheral nerves, as with most histopathological analysis, can be broken up into five stages, including fixation, dehydration, embedding, sectioning, and staining20. We aim here to provide a protocol and practical guideline for using resin embedded rat sciatic nerve sections stained with toluidine blue to acquire high quality images.

<table border="0" cellpadding="0" cellspacing="0" width="1092">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Dulbecco&#39;s Phosphate Buffer Saline</td>
			<td style="width:216px;">Gibco</td>
			<td style="width:137px;">14200-075</td>
			<td style="width:384px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Glutaraldehyde Solution</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">G6257</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Paraformaldehyde</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">P6148</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Sodium Phosphate Monobasic Monohydrate</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">S9638</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Toluidine Blue O</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">T3260</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Sodium Tetraborate Decahydrate</td>
			<td style="width:216px;">Acros Organics</td>
			<td style="width:137px;">205950010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Isoflurane</td>
			<td style="width:216px;">Piramal</td>
			<td style="width:137px;">NDC 66794-013-25</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Epoxy Embedding Medium Kit</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">45359</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Sodium Hydroxide Solution</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">72068</td>
			<td>To adjust Trump&#39;s fixative pH</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Acetone</td>
			<td style="width:216px;">Fisher Chemical</td>
			<td style="width:137px;">170942</td>
			<td></td>
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			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">75632</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">VWR Micro Slides, Superfrost Plus</td>
			<td style="width:216px;">VWR</td>
			<td style="width:137px;">48311-703</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Microscope Cover Glass</td>
			<td style="width:216px;">Fisher Scientific</td>
			<td>12545102</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Pelco Embedding Cast</td>
			<td style="width:216px;">Fisher Scientific</td>
			<td>NC9671811</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Glass Knife Maker</td>
			<td style="width:216px;">RMC Products</td>
			<td style="width:137px;">GKM-2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Ultramicrotome</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:355px;">15 mL Conical Tube</td>
			<td style="width:216px;">Falcon</td>
			<td>ISO 9001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Eppendorf 1.5 mL microcentrifuge tubes</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td>T9661</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">4 mL Glass Vial</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td>854190</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:355px;">Razor Blades</td>
			<td style="width:216px;">VWR</td>
			<td style="width:137px;">55411-050</td>
			<td>For trimming resin block</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:355px;">Perfect Loop</td>
			<td style="width:216px;">Electron Microscopy Sciences</td>
			<td style="width:137px;">70944</td>
			<td>For picking up thin resin sections</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:355px;">Ultra Glass Knife Strips 6.4 mm x 25 mm x 400 mm</td>
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			<td style="width:137px;">71012</td>
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		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">100 Watt Oven</td>
			<td style="width:216px;">Millipore&#160;</td>
			<td style="width:137px;">6350115</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Whatman Filter Paper</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td>WHA10010155</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">3 mL plastic pipette</td>
			<td style="width:216px;">Sigma-Aldrich</td>
			<td style="width:137px;">Z331740</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Micro-surgical Kit</td>
			<td style="width:216px;">World precision instruments</td>
			<td style="width:137px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:355px;">Olympus fluorescence microscope</td>
			<td style="width:216px;"></td>
			<td style="width:137px;"></td>
			<td>Dual CCD Color and Monochrome Camera, DP80</td>
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toluidine blue staining of resin-embedded sections for evaluation of peripheral nerve morphology

Peripheral nerves extend throughout the body, innervating target tissues with motor or sensory axons. Due to widespread distribution, peripheral nerves are frequently damaged because of trauma or disease. As methods and strategies have been developed to assess peripheral nerve injury in animal models, function and regeneration, analyzing the morphometry of the peripheral nerve has become an essential terminal outcome measurement. Toluidine blue staining of nerve cross sections obtained from resin embedded nerve sections is a reproducible method for qualitative and quantitative assessments of peripheral nerves, enabling visualization of morphology number of axons and degree of myelination. This technique, as with many other histological methods, can be difficult to learn and master using standard written protocols. The intent of this publication is therefore to accentuate written protocols for toluidine blue staining of peripheral nerves with videography of the method, using sciatic nerves harvested from rats. In this protocol, we describe in vivo peripheral nerve fixation and collection of the tissue, and post-fixation with 2% osmium tetroxide, embedding of nerves in epoxy resin, and ultramicrotome sectioning of nerves to 1-2&#956;m thickness. Nerve sections then transferred to a glass slide and stained with toluidine blue, after which they are quantitatively and qualitatively assessed. Examples of the most common problems are shown, as well as steps for mitigating these issues.

Resin embedded peripheral nerve sections stained with toluidine blue allow for accurate histological data quantifications. An overview of the procedure is shown in (Figure 2). Sciatic nerves sections embedded in resin medium and stained with toluidine blue showed clear images with optimal resolution (Figures 3). Nerve damage can cause many changes in nerve morphological structures, for example, changes in nerve fiber, axon diameter, and myelin sheath thickness. This method can preserve nerve structure in its natural form, which facilitates the measurement of several parameters such as the ratio of axon diameter to the total fiber diameter (the g-ratio; Figure 4). A variety of factors can lead to less than optimal peripheral nerve sections including the presence of cracks (Figure 5A) in the section due to improper handling of the nerve. Holes can also occur in the section (Figure 5B) due to insufficient dehydration. Another possible error in the procedure is folding of the sections (Figure 5C), which can be remedied by using inoculating loops for section transfer onto the glass slide.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58031/58031fig1.jpg" /> 
Figure 1: Surgery and sectioning. (A) Rat sciatic nerve during in vivo fixation. (B) Glass knife maker (C) Glass knives with boat. (D)Metal loops used to transfer floated thin sections from the glass knives to a drop of deionized water on glass slide. <a href="https://www.jove.com/files/ftp_upload/58031/58031fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58031/58031fig2.jpg" /> 
Figure 2: Schematic of the method used in this protocol. (A) Adult Sprague Dawley rat is anesthetized, followed by in vivo nerve fixation (B) and nerve collection (C). The next step is post-fixation with 2% osmium tetroxide (D) and resin embedding (E). Resin embedded nerve sections are then trimmed (F) and sectioned (G) using an ultramicrotome. Finally, nerve sections on glass slide are stained with toluidine blue (H). <a href="https://www.jove.com/files/ftp_upload/58031/58031fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58031/58031fig3.jpg" /> 
Figure 3: Transverse section of a rat sciatic nerve stained with toluidine blue. Shows sections under different magnifications (10X, 20X, 40X, and 60X) of clear image with optimal resolution. <a href="https://www.jove.com/files/ftp_upload/58031/58031fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58031/58031fig4.jpg" /> 
Figure 4: Transverse section of a rat sciatic nerve stained with toluidine blue. This high-resolution image (100X) can be used to measure the ratio of axon diameter to the total fiber diameter (the g-ratio). <a href="https://www.jove.com/files/ftp_upload/58031/58031fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/58031/58031fig5.jpg" /> 
Figure 5: Transverse sections of a rat sciatic nerve stained with toluidine blue under different magnifications. Shown aresome of the problems that may be encountered during performance of this protocol. (A) and (B). The presence of cracks and holes inside the nerve section caused by improper handling of the section and insufficient dehydration of the tissue, respectively. (C). Folding of the sections, which may happen during transferring the sections from the glass knives to the slide. <a href="https://www.jove.com/files/ftp_upload/58031/58031fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Toluidine Blue Staining of Resin-Embedded Sections for Evaluation of Peripheral Nerve Morphology at JoVE.com

Toluidine Blue Staining of Resin-Embedded Sections for Evaluation of Peripheral Nerve Morphology

Here we present a protocol to visualize fine structures of peripheral nerves by obtaining and staining 1-2 &#181;m sections with toluidine blue

Peripheral nerves extend throughout the body, innervating target tissues with motor or sensory axons. Due to widespread distribution, peripheral nerves ...

toluidine-blue-staining-resin-embedded-sections-for-evaluation

Nanyang Technological University

Research

JoVE Journal

Neuroscience

18.7K Views.  University of Wyoming. Here we present a protocol to visualize fine structures of peripheral nerves by obtaining and staining 1-2 µm sections with toluidine blue

Video: Toluidine Blue Staining of Resin-Embedded Sections for Evaluation of Peripheral Nerve Morphology

Laser Capture Microdissection of Drosophila Peripheral Neurons

The dendritic arborization (da) neurons of the Drosophila peripheral nervous system (PNS) provide an excellent model system in which to investigate the molecular mechanisms underlying class-specific dendrite morphogenesis1,2. To facilitate molecular analyses of class-specific da neuron development, it is vital to obtain these cells in a pure population. Although a range of different cell, and tissue-specific RNA isolation techniques exist for Drosophila cells, including magnetic bead based cell purification3,4, Fluorescent Activated Cell Sorting (FACS)5-8, and RNA binding protein based strategies9, none of these methods can be readily utilized for isolating single or multiple class-specific Drosophila da neurons with a high degree of spatial precision. Laser Capture Microdissection (LCM) has emerged as an extremely powerful tool that can be used to isolate specific cell types from tissue sections with a high degree of spatial resolution and accuracy. RNA obtained from isolated cells can then be used for analyses including qRT-PCR and microarray expression profiling within a given cell type10-16. To date, LCM has not been widely applied in the analysis of Drosophila tissues and cells17,18, including da neurons at the third instar larval stage of development. 
Here we present our optimized protocol for isolation of Drosophila da neurons using the infrared (IR) class of LCM. This method allows for the capture of single, class-specific or multiple da neurons with high specificity and spatial resolution. Age-matched third instar larvae expressing a UAS-mCD8::GFP19 transgene under the control of either the class IV da neuron specific ppk-GAL420 driver or the pan-da neuron specific 21-7-GAL421 driver were used for these experiments. RNA obtained from the isolated da neurons is of very high quality and can be directly used for downstream applications, including qRT-PCR or microarray analyses. Furthermore, this LCM protocol can be readily adapted to capture other Drosophila cell types a various stages of development dependent upon the cell type specific, GAL4-driven expression pattern of GFP.

Laser Capture Microdissection of Drosophila Peripheral Neurons

In this video-article we present a method for isolating single or multiple Drosophila da neurons from third instar larvae using the infrared capture (IR) class of Laser Capture Microdissection (LCM). RNA obtained from the isolated neurons can be readily used for downstream applications including qRT-PCR or microarray analyses.

The dendritic arborization (da) neurons of the Drosophila peripheral nervous system (PNS) provide an excellent model system in which to investigate the ...

Organotypic Slice Culture of GFP-expressing Mouse Embryos for Real-time Imaging of Peripheral Nerve Outgrowth

For many purposes, the cultivation of mouse embryos ex vivo as organotypic slices is desirable. For example, we employ a transgenic mouse line (tauGFP) in which the enhanced version of the green fluorescent protein (EGFP) is exclusively expressed in all neurons of the developing central and peripheral nervous system1, allowing the possibility to both film the innervation of the forelimb and to manipulate this process with pharmacological and genetic techniques2. The most critical parameter in the successful cultivation of such slice cultures is the method by which the slices are prepared. After extensive testing of a variety of methods, we have found that a vibratome is the best possible device to slice the embryos such that they routinely result in a culture that demonstrates viability over a period of several days, and most importantly, develops in an age-specific manner. For mid-gestation embryos, this includes the normal outgrowth of spinal nerves from the spinal cord and the dorsal root ganglia to their targets in the periphery and the proper determination of skeletal and muscle tissue. 
In this work, we present a method for processing whole embryos of embryonic day (E) E10 to E12 into 300 - 400 micrometer slices for cultivation in a standard tissue culture incubator, which can be studied for up to two days after slice preparation. Critical for the success of this approach is the use of a vibratome to slice each agarose-embedded embryo. This is followed by the cultivation of the slices upon Millicell culture membrane inserts placed upon a small volume of medium, resulting in an interface culture technique. One litter with an average of 7 embryos routinely produces at least 14 slices (2-3 slices of the forelimb region per embryo), which varies slightly due to the age of the embryos as well as to the thickness of the slices. About 80% of the cultured slices show nerve outgrowth, which can be measured througout the culturing period2. Representative results using the tauGFP mouse line are demonstrated.

We present a method to prepare organotypic slices of mid-gestation mouse embryos for the cultivation and time-lapse imaging of peripheral nerve outgrowth.

For many purposes, the cultivation of mouse embryos ex vivo as organotypic slices is desirable. For example, we employ a transgenic mouse line (tauGFP) in ...

Immunohistochemical Analysis in the Rat Central Nervous System and Peripheral Lymph Node Tissue Sections

Immunohistochemistry (IHC) provides highly specific, reliable and attractive protein visualization. Correct performance and interpretation of an IHC-based multicolor labeling is challenging, especially when utilized for assessing interrelations between target proteins in the tissue with a high fat content such as the central nervous system (CNS).
Our protocol represents a refinement of the standard immunolabeling technique particularly adjusted for detection of both structural and soluble proteins in the rat CNS and peripheral lymph nodes (LN) affected by neuroinflammation. Nonetheless, with or without further modifications, our protocol could likely be used for detection of other related protein targets, even in other organs and species than here presented.

We here present an optimized, detailed protocol for double immunostaining in formalin-fixed, paraffin-embedded rat central nervous system (CNS) and peripheral lymph node (LN) tissue sections.

Immunohistochemistry (IHC) provides highly specific, reliable and attractive protein visualization. Correct performance and interpretation of an IHC-based ...

Transplantation of Olfactory Ensheathing Cells to Evaluate Functional Recovery after Peripheral Nerve Injury

Olfactory ensheathing cells (OECs) are neural crest cells which allow growth and regrowth of the primary olfactory neurons. Indeed, the primary olfactory system is characterized by its ability to give rise to new neurons even in adult animals. This particular ability is partly due to the presence of OECs which create a favorable microenvironment for neurogenesis. This property of OECs has been used for cellular transplantation such as in spinal cord injury models. Although the peripheral nervous system has a greater capacity to regenerate after nerve injury than the central nervous system, complete sections induce misrouting during axonal regrowth in particular after facial of laryngeal nerve transection. Specifically, full sectioning of the recurrent laryngeal nerve (RLN) induces aberrant axonal regrowth resulting in synkinesis of the vocal cords. In this specific model, we showed that OECs transplantation efficiently increases axonal regrowth.
OECs are constituted of several subpopulations present in both the olfactory mucosa (OM-OECs) and the olfactory bulbs (OB-OECs). We present here a model of cellular transplantation based on the use of these different subpopulations of OECs in a RLN injury model. Using this paradigm, primary cultures of OB-OECs and OM-OECs were transplanted in Matrigel after section and anastomosis of the RLN. Two months after surgery, we evaluated transplanted animals by complementary analyses based on videolaryngoscopy, electromyography (EMG), and histological studies. First, videolaryngoscopy allowed us to evaluate laryngeal functions, in particular muscular cocontractions phenomena. Then, EMG analyses demonstrated richness and synchronization of muscular activities. Finally, histological studies based on toluidine blue staining allowed the quantification of the number and profile of myelinated fibers.
All together, we describe here how to isolate, culture, identify and transplant OECs from OM and OB after RLN section-anastomosis and how to evaluate and analyze the efficiency of these transplanted cells on axonal regrowth and laryngeal functions.

Olfactory ensheathing cells (OECs) are neural crest cells which allow growth of the primary olfactory neurons. This specific property can be used for cellular transplantation. We present here a model of cellular transplantation based on the use of OECs in a laryngeal nerve injury model.

Olfactory ensheathing cells (OECs) are neural crest cells which allow growth and regrowth of the primary olfactory neurons. Indeed, the primary olfactory ...

Visualizing the Effects of a Positive Early Experience, Tactile Stimulation, on Dendritic Morphology and Synaptic Connectivity with Golgi-Cox Staining

To generate longer-term changes in behavior, experiences must be producing stable changes in neuronal morphology and synaptic connectivity. Tactile stimulation is a positive early experience that mimics maternal licking and grooming in the rat. Exposing rat pups to this positive experience can be completed easily and cost-effectively by using highly accessible materials such as a household duster. Using a cross-litter design, pups are either stroked or left undisturbed, for 15 min, three times per day throughout the perinatal period. To measure the neuroplastic changes related to this positive early experience, Golgi-Cox staining of brain tissue is utilized. Owing to the fact that Golgi-Cox impregnation stains a discrete number of neurons rather than all of the cells, staining of the rodent brain with Golgi-Cox solution permits the visualization of entire neuronal elements, including the cell body, dendrites, axons, and dendritic spines. The staining procedure is carried out over several days and requires that the researcher pay close attention to detail. However, once staining is completed, the entire brain has been impregnated and can be preserved indefinitely for ongoing analysis. Therefore, Golgi-Cox staining is a valuable resource for studying experience-dependent plasticity.

This paper describes the procedures for tactile stimulation of rat pups and subsequent Golgi-Cox staining of neuronal morphology. Tactile stimulation is a positive experience that is administered in the perinatal period by stroking pups with a household duster. Golgi-cox staining is a reliable procedure permitting the visualization of entire neurons.

To generate longer-term changes in behavior, experiences must be producing stable changes in neuronal morphology and synaptic connectivity. Tactile ...

The Indirect Neuron-astrocyte Coculture Assay: An In Vitro Set-up for the Detailed Investigation of Neuron-glia Interactions

Proper neuronal development and function is the prerequisite of the developing and the adult brain. However, the mechanisms underlying the highly controlled formation and maintenance of complex neuronal networks are not completely understood thus far. The open questions concerning neurons in health and disease are diverse and reaching from understanding the basic development to investigating human related pathologies, e.g.,&#160;Alzheimer&#39;s disease and&#160;Schizophrenia. The most detailed analysis of neurons can be performed in vitro. However, neurons are demanding cells and need the additional support of astrocytes for their long-term survival. This cellular heterogeneity is in conflict with the aim to dissect the analysis of neurons and astrocytes. We present here a cell-culture assay that allows for the long-term cocultivation of pure primary neurons and astrocytes, which share the same chemically defined medium, while being physically separated. In this setup, the cultures survive for up to four weeks and the assay is suitable for a diversity of investigations concerning neuron-glia interaction.

The Indirect Neuron-astrocyte Coculture Assay: An In Vitro Set-up for the Detailed Investigation of Neuron-glia Interactions

This protocol describes the indirect neuron-astrocyte coculture for compartmentalized analysis of neuron-glia interactions.

Proper neuronal development and function is the prerequisite of the developing and the adult brain. However, the mechanisms underlying the highly ...

Targeting Alpha Synuclein Aggregates in Cutaneous Peripheral Nerve Fibers by Free-floating Immunofluorescence Assay

To date, for most neurodegenerative diseases only a post-mortem histopathological definitive diagnosis is available. For Parkinson&#39;s disease (PD), the diagnosis still relies only on clinical signs of motor involvement that appear later on in the disease course, when most of the dopaminergic neurons are already lost. Hence, there is a strong need for a biomarker that can identify patients at the beginning of disease or at the risk of developing it. Over the last few years, skin biopsy has proved to be an excellent research and diagnostic tool for peripheral nerve diseases such as small fiber neuropathy. Interestingly, a small fiber neuropathy and alpha synuclein (&#945;Syn) neural deposits have been shown by skin biopsy in PD patients. Indeed, skin biopsy has the great advantage of being an easily accessible, minimally invasive and painless procedure that allows the analysis of peripheral nervous tissue prone to the pathology. Moreover, the possibility of repeating the skin biopsy in the course of the follow-up of the same patient allows studying the longitudinal correlation with the disease progression. We set up a standardized reliable protocol to investigate the presence of &#945;Syn aggregates in skin nerve fibers of the PD patient. This protocol involves few short fixation steps, a cryotome sectioning and then a free-floating immunofluorescence double-staining with two specific antibodies: anti Protein Gene Product 9.5 (PGP9.5) to mark the cutaneous nerve fibers and anti 5G4 for detecting &#945;Syn aggregates. It is a versatile, sensitive and easy to perform protocol that can also be applied for targeting other proteins of interest in skin nerves. The ability to mark &#945;Syn aggregates is another step forward to the use of skin biopsy as a tool for establishing a pre-mortem histopathological diagnosis of PD.

Here, we present a protocol for a free-floating indirect immunofluorescence assay on skin biopsy sections that allows for the identification of disease specific conformation variants of alpha synuclein involved in Parkinson disease and multiple proteins of the peripheral nervous system.

To date, for most neurodegenerative diseases only a post-mortem histopathological definitive diagnosis is available. For Parkinson&#39;s disease (PD), the ...

3D Kinematic Analysis for the Functional Evaluation in the Rat Model of Sciatic Nerve Crush Injury

Compared to the Sciatic Functional Index (SFI), kinematic analysis is a more reliable and sensitive method for performing functional evaluations of sciatic nerve injury rodent models. In this protocol, we describe a novel kinematic analysis method that uses a three-dimensional (3D) motion capture apparatus for functional evaluations using a rat sciatic nerve crush injury model. First, the rat is familiarized with treadmill walking. Markers are then attached to the designated bone landmarks and the rat is made to walk on the treadmill at the desired speed. Meanwhile, the posterior limb movements of the rat are recorded using four cameras. Depending on the software used, marker tracings are created using both automatic and manual modes and the desired data are produced after subtle adjustments. This method of kinematic analysis, which uses a 3D motion capture apparatus, offers numerous advantages, including superior precision and accuracy. Many more parameters can be investigated during the comprehensive functional evaluations. This method has several shortcomings that require consideration: The system is expensive, can be complicated to operate, and may produce data deviations due to skin shifting. Nevertheless, kinematic analysis using a 3D motion capture apparatus is useful for performing functional anterior and posterior limb evaluations. In the future, this method may become increasingly useful for generating accurate assessments of various traumas and diseases.

We introduce a kinematic analysis method that uses a three-dimensional motion capture apparatus containing four cameras and data processing software for performing functional evaluations during fundamental research involving rodent models.

Compared to the Sciatic Functional Index (SFI), kinematic analysis is a more reliable and sensitive method for performing functional evaluations of ...

Preparation of Peripheral Nerve Stimulation Electrodes for Chronic Implantation in Rats

Peripheral nerve cuff electrodes have long been used in the neurosciences and related fields for stimulation of, for example, vagus or sciatic nerves. Several recent studies have demonstrated the effectiveness of chronic VNS in enhancing central nervous system plasticity to improve motor rehabilitation, extinction learning, and sensory discrimination. Construction of chronically implantable devices for use in such studies is challenging due to rats&#8217; small size, and typical protocols require extensive training of personnel and time-consuming microfabrication methods. Alternatively, commercially available implantable cuff electrodes can be purchased at a significantly higher cost. In this protocol, we present a simple, low-cost method for construction of small, chronically implantable peripheral nerve cuff electrodes for use in rats. We validate the short and long-term reliability of our cuff electrodes by demonstrating that VNS in ketamine/xylazine anesthetized rats produces decreases in breathing rate consistent with activation of the Hering-Breuer reflex, both at the time of implantation and up to 10 weeks after device implantation. We further demonstrate the suitability of the cuff electrodes for use in chronic stimulation studies by pairing VNS with skilled lever press performance to induce motor cortical map plasticity.

Existing approaches for constructing chronically implantable peripheral nerve cuff electrodes for use in small rodents often require specialized equipment and/or highly trained personnel. In this protocol we demonstrate a simple, low-cost approach for fabricating chronically implantable cuff electrodes, and demonstrate their effectiveness for vagus nerve stimulation (VNS) in rats.

Peripheral nerve cuff electrodes have long been used in the neurosciences and related fields for stimulation of, for example, vagus or sciatic nerves. ...

Automated Gait Analysis to Assess Functional Recovery in Rodents with Peripheral Nerve or Spinal Cord Contusion Injury

Peripheral and central nerve injuries are mostly studied in rodents, especially rats, given the fact that these animal models are both cost-effective and a lot of comparative data has been published in the literature. This includes a multitude of assessment methods to study functional recovery following nerve injury and repair. Besides evaluation of nerve regeneration by means of histology, electrophysiology, and other in vivo and in vitro assessment techniques, functional recovery is the most important criterion to determine the degree of neural regeneration. Automated gait analysis allows recording of a vast quantity of gait-related parameters such as Paw Print Area and Paw Swing Speed as well as measures of inter-limb coordination. Additionally, the method provides digital data of the rats&#8217; paws after neuronal damage and during nerve regeneration, adding to our understanding of how peripheral and central nervous injuries affect their locomotor behavior. Besides the predominantly used sciatic nerve injury model, other models of peripheral nerve injury such as the femoral nerve can be studied by means of this method. In addition to injuries of the peripheral nervous systems, lesions of the central nervous system, e.g., spinal cord contusion can be evaluated. Valid and reproducible data assessment is strongly dependent on meticulous adjustment of the hard- and software settings prior to data acquisition. Additionally, proper training of the experimental animals is of crucial importance. This work aims to illustrate the use of computerized automated gait analysis to assess functional recovery in different animal models of peripheral nerve injury as well as spinal cord contusion injury. It also emphasizes the method&#8217;s limitations, e.g., evaluation of nerve regeneration in rats with sciatic nerve neurotmesis due to limited functional recovery. Therefore, this protocol is thought to help researchers interested in peripheral and central nervous injuries to assess functional recovery in rodent models.

Automated gait analysis is a feasible tool to evaluate functional recovery in rodent models of peripheral nerve injury and spinal cord contusion injury. While it requires only one setup to assess locomotor function in various experimental models, meticulous hard- and soft-ware adjustment and training of the animals is highly important.

Peripheral and central nerve injuries are mostly studied in rodents, especially rats, given the fact that these animal models are both cost-effective and ...