Name: toluidine blue staining of resin-embedded sections for evaluation of peripheral nerve morphology
Uploaded: 2018-07-03T15:00:00
Description: Watch this Scientific Journal Video about Toluidine Blue Staining of Resin-Embedded Sections for Evaluation of Peripheral Nerve Morphology at JoVE.com

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 t...

<ol>
	<li>Zacchigna, S., Ruiz de Almodovar, C., Carmeliet, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Similarities+between+angiogenesis+and+neural+development:+What+small+animal+models+can+tell+us.">Similarities between angiogenesis and neural development: What small animal models can tell us.</a> Current Topics in Developmental Biology. 80, 1-55 (2008).</li><li>Grinsell, D., Keating, C. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peripheral+nerve+reconstruction+after+injury:+A+review+of+clinical+and+experimental+therapies.">Peripheral nerve reconstruction after injury: A review of clinical and experimental therapies.</a> BioMed Research International. 2014, 1-13 (2014).</li><li>Chen, M. B., Zhang, F., Lineaweaver, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Luminal+fillers+in+nerve+conduits+for+peripheral+nerve+repair.">Luminal fillers in nerve conduits for peripheral nerve repair.</a> Annals of Plastic Surgery. 57 (4), 462-471 (2006).</li><li>Scipio, F., Raimondo, S., Tos, P., Geuna, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+protocol+for+paraffin-embedded+myelin+sheath+staining+with+osmium+tetroxide+for+light+microscope+observation.">A simple protocol for paraffin-embedded myelin sheath staining with osmium tetroxide for light microscope observation.</a> Microscopy Research and Technique. 71, 497-502 (2008).</li><li>Raimondo, S., Fornaro, M., Di Scipio, F., Ronchi, G., Giacobini-Robecchi, M. G., Geuna, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+5:+Methods+and+protocols+in+peripheral+nerve+regeneration+experimental+research:+part+II-morphological+techniques.">Chapter 5: Methods and protocols in peripheral nerve regeneration experimental research: part II-morphological techniques.</a> International Review of Neurobioly. 87, 81-103 (2009).</li><li>Carriel, V., Garzon, I., Alaminos, M., Campos, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+myelin+sheath+and+collagen+reorganization+pattern+in+a+model+of+peripheral+nerve+regeneration+using+an+integrated+histochemical+approach.">Evaluation of myelin sheath and collagen reorganization pattern in a model of peripheral nerve regeneration using an integrated histochemical approach.</a> Histochemistry and Cell Biology. , 709-717 (2011).</li><li>Sridharan, G., Shankar, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toluidine+blue:+A+review+of+its+chemistry+and+clinical+utility.">Toluidine blue: A review of its chemistry and clinical utility.</a> Journal of Oral and Maxillofacial Pathology. 16, 251-255 (2012).</li><li>Epstein, J. B., Scully, C., Spinelli, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toluidine+blue+and+Lugol's+iodine+application+in+the+assessment+of+oral+malignant+disease+and+lesions+at+risk+of+malignancy.">Toluidine blue and Lugol's iodine application in the assessment of oral malignant disease and lesions at risk of malignancy.</a> Journal of Oral Pathology &amp; Medicine. 21, 160-163 (1992).</li><li>Carriel, V., Garzon, I., Alaminos, M., Cornelissen, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histological+assessment+in+peripheral+nerve+tissue+engineering.">Histological assessment in peripheral nerve tissue engineering.</a> Neural Regeneration Research. 9, 1657-1660 (2014).</li><li>Dykstra, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> A manual of applied techniques for biological electron microscopy. , 257 (1993).</li><li>Vleggeert-Lankamp, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+evaluation+methods+in+the+assessment+of+peripheral+nerve+regeneration+through+synthetic+conduits:+A+systematic+review.">The role of evaluation methods in the assessment of peripheral nerve regeneration through synthetic conduits: A systematic review.</a> Journal of Neurosurgery. 107 (6), 1168-1189 (2007).</li><li>Williams, P., Wendell-Smith, C. P., Finch, A., Stevens, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Further+uses+and+methods+of+processing+of+fresh+frozen+sections+of+peripheral+nerve.">Further uses and methods of processing of fresh frozen sections of peripheral nerve.</a> Journal of Cell Science. 3 (69), 99-105 (1964).</li><li>Castro, J., Negredo, P., Avenda&#241;o, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fiber+composition+of+the+rat+sciatic+nerve+and+its+modification+during+regeneration+through+a+sieve+electrode.">Fiber composition of the rat sciatic nerve and its modification during regeneration through a sieve electrode.</a> Brain research. , 65-77 (2008).</li><li>Raimondo, S., Fornaro, M., Di Scipio, F., Ronchi, G., Giacobini-Robecchi, M. G., Geuna, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+and+protocols+in+peripheral+nerve+regeneration+experimental+research:+Part+II-morphological+techniques.">Methods and protocols in peripheral nerve regeneration experimental research: Part II-morphological techniques.</a> International review of neurobiology. 87, 81-103 (2009).</li><li>Bozkurt, A., Lassner, F., O'Dey, D., Deumens, R., B&#246;cker, A., Schwendt, T., Janzen, C., Suschek, C. V., Tolba, R., Kobayashi, E., Sellhaus, 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+role+of+microstructured+and+interconnected+pore+channels+in+a+collagen-based+nerve+guide+on+axonal+regeneration+in+peripheral+nerves.">The role of microstructured and interconnected pore channels in a collagen-based nerve guide on axonal regeneration in peripheral nerves.</a> Biomaterials. 33 (5), 1363-1375 (2012).</li><li>Weis, J., Brandner, S., Lammens, M., Sommer, C., Vallat, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Processing+of+nerve+biopsies:+A+practical+guide+for+neuropathologists.">Processing of nerve biopsies: A practical guide for neuropathologists.</a> Clinical Neuropathology. 31 (1), 7-23 (2012).</li><li>Battiston, B., Tos, P., Geuna, S., Giacobini-Robecchi, M. G., Guglielmone, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nerve+repair+by+means+of+vein+filled+with+muscle+grafts.+II.+Morphological+analysis+of+regeneration.">Nerve repair by means of vein filled with muscle grafts. II. Morphological analysis of regeneration.</a> Microsurgery. 20 (1), 37-41 (2000).</li><li>Bhattacharyya, T. K., Thomas, 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=Comparison+of+staining+methods+for+resin-embedded+peripheral+nerve.">Comparison of staining methods for resin-embedded peripheral nerve.</a> Journal of Histotechnology. 27, 161-164 (2004).</li><li>Zbaeren, J., Zbaeren-Colbourn, D., Haeberli, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+immunohistochemistry+on+improved+glycol+methacrylate-resin+sections.">High-resolution immunohistochemistry on improved glycol methacrylate-resin sections.</a> Journal of Histotechnology. 30 (1), 27-33 (2007).</li><li>Alturkistani, H. A., Tashkandi, F. M., Mohammedsaleh, Z. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histological+stains:+A+literature+review+and+case+study.">Histological stains: A literature review and case study.</a> Global Journal of Health Science. 8 (3), 72-79 (2016).</li><li>Ezra, M., Bushman, J., Shreiber, D., Schachner, M., Kohn, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Porous+and+nonporous+nerve+conduits:+the+effects+of+a+hydrogel+luminal+filler+with+and+without+a+neurite-promoting+moiety.">Porous and nonporous nerve conduits: the effects of a hydrogel luminal filler with and without a neurite-promoting moiety.</a> Tissue Engineering Part A. (9-10), 818-826 (2016).</li><li>Bhatnagar, D., Bushman, J. S., Murthy, N. S., Merolli, A., Kaplan, H. M., Kohn, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fibrin+glue+as+a+stabilization+strategy+in+peripheral+nerve+repair+when+using+porous+nerve+guidance+conduits.">Fibrin glue as a stabilization strategy in peripheral nerve repair when using porous nerve guidance conduits.</a> Journal of Materials Science: Materials in Medicine. 28 (5), 79 (2017).</li></ol>

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 infiltrati...

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.

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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 myeli...

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 ...

This method could help answer key questions in the fields of peripheral nerve injury and regeneration such as what is the morphometry of a peripheral nerve, how many axons are present, what is the state of myelination, and is there fibrotic tissue present? The main advantage of this technique is that it allows for high-resolution visualization of nerve features. Begin by placing an anesthetized rat in the prone position on the top of a dissection mat.Place a nose cone to maintain anesthesia with 1-2%isoflurane. To ensure adequate depth of anesthesia test the animals for pedal withdrawal and palpebral reflexes of the hind feet. Once an appropriate depth of anesthesia is achieved, shave the hair of the hind limbs and sterilize the shaved areas with 70%ethanol.Palpate the femur to identify the proper location for the incision. The femur is located just proximal to the most accessible segment of the sciatic nerve. After making a two to three centimeter incision in the skin along the hind limb from the knee up to the greater trochanter locate the plane between the biceps femoris muscle and the gluteus maximus muscle.Then use microdissection scissors to separate the underlying fascia and expose two to three centimeters of the underlying sciatic nerve. Use a retractor to widen the gap between the two muscles. With fine forceps and iris scissors carefully separate the nerve from the surrounding connective tissue, taking great care not to compress or cut the nerve.Next, cover the exposed nerve with Trump's Fixative and let sit for 10 minutes. 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 minutes and repeat this step two more times.Under the dissecting microscope cut the sciatic nerve from both sides using fine dissection scissors, making sure not to stretch or pinch the nerve. Immediately put the nerve sections in 15 mL tubes containing Trump's Fixative and fix at four degrees Celsius for one week, changing the fixative every 48 hours. 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 five millimeters in length.Nerve segments can be separated into different labeled tubes. Immerse nerve segments in freshly prepared 2%osmium tetroxide for two hours. Using an epoxy embedding kit, prepare the final embedding mixture.Mix the epoxy embedding medium with DDSA solution and mix the epoxy embedding medium with NMA solution. Mix both solutions for at least 20 minutes with a magnetic stirrer. Immediately before use, combine the accelerator DPM to solution B and then combine this with solution A such that the accelerator's final proportion is between one point five and 2%of the total volume.Transfer the nerve segments to one point five milliliter tubes and after washing with PBS, start the dehydration process by the replacing the PBS with increasing concentrations of acetone and distilled water for 10 minutes each then in 100%acetone three times for 10 minutes each. One critical step is the tissue dehydration. Water and resin will not interact, so any water remaining in the tissue will not be infiltrated by the resin leaving holes in the section devoid of histological qualities.For resin infiltration, first place the nerve segments in a one-to-one mix of embedding mixture and 100%acetone for 30 minutes. After 30 minutes, transfer the segments to a two-to-one mix of embedding mixture and 100%acetone for 30 minutes. Place the nerve segements in silicone rubber embedding molds and gently add the resin on top of nerves, making sure to cover the whole nerve segment while avoiding air bubbles.Leave the resin to polymerize at 60 degrees Celsius overnight. Place a resin block with embedded nerve into the ultramicrotome holder with the trapezoidal side facing up. While viewing through the ultramicrotome scope, use a single-edged blade to trim excess resin surrounding the nerve tissue.Do not penetrate the longitudinal surface of the nerve segment which is recognizable by its dark staining by osmium tetroxide. With a plain glass knife on the ultramicrotome make multiple cross sections to expose a uniform cross-section surface of the nerve. Once this is done, switch to a glass knife with the boat filled with distilled water at room temperature and adjust the ultramicrotome to one to two microns to cut thin sections.Use a metal loop to transfer floating thin sections from the glass knife boat to a drop of deionized water on a glass slide. Another critical step is during the transfer of thin section from the glass knife to slide. These thin sections are very fragile and can break or fold.After sectioning, dry the sections on the slides by passing a slide over a flame several times, making sure not to overheat the sections. Slides can be stored at room temperature for several days if not immediately staining with toluidine blue. To stain the nerve sections, use a plastic pipette or micropipetter to add a drop of toluidine blue solution on the top of the nerve sections.After 20 to 30 seconds, rinse off all toluidine blue solution excess by gently dipping the slides into a jar of deionized water, repeating three to four times until sections are clear. Dry the slides for at least 15 minutes at 60 degrees Celsius or overnight at room temperature. After drying, add regular mounting medium and cover the sections with a coverslip.Finally, examine the mounted sections under a light microscope. A 100X oil immersion lens is recommended for detailed images to calculate g-ratios. Sciatic nerve sections embedded in resin medium and stained with toluidine blue showed clear images with optimal resolution at increasing magnification from 10X to 20X, 40X, and 60X.This method preserves nerve structure and allows for high-resolution, high-magnification imaging which facilitates the measurement of several parameters such as the g-ratio, which is the ratio of axon diameter, indicated by the arrow labeled B, to the total fiber diameter, labeled A.A variety of factors can lead to less than optimal peripheral nerve sections, including the presence of cracks in the section due to improper handling of the nerve. Holes can also occur in the section due to insufficient dehydration. Another possible error in the procedure is folding of the sections, which can be remedied by using inoculating loops for section transfer onto the glass slide.Following this procedure other methods like axon quantification can be performed to answer additional questions like what's the degree of regeneration in a regenerative nerve? After watching this video you should have a good understanding of how to obtain one to two micron peripheral nerve sections to assess nerve morphometry.

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

Research

JoVE Journal

Neuroscience

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 ...

Dorsal Root Ganglia Neurons and Differentiated Adipose-derived Stem Cells: An In Vitro Co-culture Model to Study Peripheral Nerve Regeneration

Dorsal root ganglia (DRG) neurons, located in the intervertebral foramina of the spinal column, can be used to create an in vitro system facilitating the study of nerve regeneration and myelination. The glial cells of the peripheral nervous system, Schwann cells (SC), are key facilitators of these processes; it is therefore crucial that the interactions of these cellular components are studied together. Direct contact between DRG neurons and glial cells provides additional stimuli sensed by specific membrane receptors, further improving the neuronal response. SC release growth factors and proteins in the culture medium, which enhance neuron survival and stimulate neurite sprouting and extension. However, SC require long proliferation time to be used for tissue engineering applications and the sacrifice of an healthy nerve for their sourcing. Adipose-derived stem cells (ASC) differentiated into SC phenotype are a valid alternative to SC for the set-up of a co-culture model with DRG neurons to study nerve regeneration. The present work presents a detailed and reproducible step-by-step protocol to harvest both DRG neurons and ASC from adult rats; to differentiate ASC towards a SC phenotype; and combines the two cell types in a direct co-culture system to investigate the interplay between neurons and SC in the peripheral nervous system. This tool has great potential in the optimization of tissue-engineered constructs for peripheral nerve repair.

Dorsal Root Ganglia Neurons and Differentiated Adipose-derived Stem Cells: An In Vitro Co-culture Model to Study Peripheral Nerve Regeneration

Dorsal root ganglia (DRG) are structures containing the sensory neurons of the peripheral nervous system. When dissociated, they can be co-cultured with SC-like adipose-derived stem cells (ASC), providing a valuable model to study in vitro nerve regeneration and myelination, mimicking the in vivo environment at the injury site.

Dorsal root ganglia (DRG) neurons, located in the intervertebral foramina of the spinal column, can be used to create an in vitro system facilitating the ...

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 ...

Analyzing Dendritic Morphology in Columns and Layers

In many regions of the central nervous systems, such as the fly optic lobes and the vertebrate cortex, synaptic circuits are organized in layers and columns to facilitate brain wiring during development and information processing in developed animals. Postsynaptic neurons elaborate dendrites in type-specific patterns in specific layers to synapse with appropriate presynaptic terminals. The fly medulla neuropil is composed of 10 layers and about 750 columns; each column is innervated by dendrites of over 38 types of medulla neurons, which match with the axonal terminals of some 7 types of afferents in a type-specific fashion. This report details the procedures to image and analyze dendrites of medulla neurons. The workflow includes three sections: (i) the dual-view imaging section combines two confocal image stacks collected at orthogonal orientations into a high-resolution 3D image of dendrites; (ii) the dendrite tracing and registration section traces dendritic arbors in 3D and registers dendritic traces to the reference column array; (iii) the dendritic analysis section analyzes dendritic patterns with respect to columns and layers, including layer-specific termination and planar projection direction of dendritic arbors, and derives estimates of dendritic branching and termination frequencies. The protocols utilize custom plugins built on the open-source MIPAV (Medical Imaging Processing, Analysis, and Visualization) platform and custom toolboxes in the matrix laboratory language. Together, these protocols provide a complete workflow to analyze the dendritic routing of Drosophila medulla neurons in layers and columns, to identify cell types, and to determine defects in mutants.

Here, we show how to analyze dendritic routing of Drosophila medulla neurons in columns and layers. The workflow includes a dual-view imaging technique to improve the image quality and computational tools for tracing, registering dendritic arbors to the reference column array and for analyzing the dendritic structures in 3D space.

In many regions of the central nervous systems, such as the fly optic lobes and the vertebrate cortex, synaptic circuits are organized in layers and ...

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. ...