The study was funded (awarded to F-Q.Z.) by NIH (R01NS064288, R01NS085176, R01GM111514, R01EY027347), the Craig H. Neilsen Foundation and the BrightFocus Foundation.

All animal experiments were performed in accordance with the animal protocol approved by the Johns Hopkins Institutional Animal Care and Use Committee.
1. Materials and Reagents
<ol>
	<li>Animals
	<ol>
		<li>Use six-week-old female CF1 mice weighing 30&#8211;35 g for the experiments. 
		NOTE: The mice were group-housed (5 mice per cage) in individually ventilated sterilized cages with 1/4&#8221; corn cob bedding and 2&#8221; square nestlets for nesting. The cages were m...

<ol>
	<li>Saijilafu, , et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PI3K-GSK3+signalling+regulates+mammalian+axon+regeneration+by+inducing+the+expression+of+Smad1.">PI3K-GSK3 signalling regulates mammalian axon regeneration by inducing the expression of Smad1.</a> Nature Communications. 4, 2690 (2013).</li><li>Zhang, B. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Akt-independent+GSK3+inactivation+downstream+of+PI3K+signaling+regulates+mammalian+axon+regeneration.">Akt-independent GSK3 inactivation downstream of PI3K signaling regulates mammalian axon regeneration.</a> Biochemical and Biophysical Research Communications. 443 (2), 743-748 (2014).</li><li>Jiang, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MicroRNA-26a+supports+mammalian+axon+regeneration+in+vivo+by+suppressing+GSK3beta+expression.">MicroRNA-26a supports mammalian axon regeneration in vivo by suppressing GSK3beta expression.</a> Cell Death &amp; Disease. 6, 1865 (2015).</li><li>Krames, E. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+the+dorsal+root+ganglion+in+the+development+of+neuropathic+pain.">The role of the dorsal root ganglion in the development of neuropathic pain.</a> Pain Medicine. 15 (10), 1669-1685 (2014).</li><li>Salimzadeh, L., Jaberipour, M., Hosseini, A., Ghaderi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-viral+transfection+methods+optimized+for+gene+delivery+to+a+lung+cancer+cell+line.">Non-viral transfection methods optimized for gene delivery to a lung cancer cell line.</a> Avicenna Journal of Medical Biotechnology. 5 (2), 68-77 (2013).</li><li>Keeler, A. M., ElMallah, M. K., Flotte, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+Therapy+2017:+Progress+and+Future+Directions.">Gene Therapy 2017: Progress and Future Directions.</a> Clinical and Translational Science. 10 (4), 242-248 (2017).</li><li>Neumann, E., Schaeferridder, M., Wang, Y., Hofschneider, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene-Transfer+into+Mouse+Lyoma+Cells+by+Electroporation+in+High+Electric-Fields.">Gene-Transfer into Mouse Lyoma Cells by Electroporation in High Electric-Fields.</a> The EMBO Journal. 1 (7), 841-845 (1982).</li><li>Liu, C. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MicroRNA-138+and+SIRT1+form+a+mutual+negative+feedback+loop+to+regulate+mammalian+axon+regeneration.">MicroRNA-138 and SIRT1 form a mutual negative feedback loop to regulate mammalian axon regeneration.</a> Genes &amp; Development. 27 (13), 1473-1483 (2013).</li><li>Saito, T., Nakatsuji, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+gene+transfer+into+the+embryonic+mouse+brain+using+in+vivo+electroporation.">Efficient gene transfer into the embryonic mouse brain using in vivo electroporation.</a> Developmental Biology. 240 (1), 237-246 (2001).</li><li>Saijilafu, E. M., Hur, F. Q., Zhou, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+dissection+of+axon+regeneration+via+in+vivo+electroporation+of+adult+mouse+sensory+neurons.">Genetic dissection of axon regeneration via in vivo electroporation of adult mouse sensory neurons.</a> Nature Communications. 2, 543 (2011).</li><li>Pan, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shrinkage-mediated+imaging+of+entire+organs+and+organisms+using+uDISCO.">Shrinkage-mediated imaging of entire organs and organisms using uDISCO.</a> Nature Methods. 13, 859 (2016).</li><li>Rao, R. D., Bagaria, V. B., Cooley, B. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Posterolateral+intertransverse+lumbar+fusion+in+a+mouse+model:+surgical+anatomy+and+operative+technique.">Posterolateral intertransverse lumbar fusion in a mouse model: surgical anatomy and operative technique.</a> Spine Journal. 7 (1), 61-67 (2007).</li><li>Dommisse, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+blood+supply+of+the+spinal+cord.+A+critical+vascular+zone+in+spinal+surgery.">The blood supply of the spinal cord. A critical vascular zone in spinal surgery.</a> The Journal of Bone and Joint Surgery. British Volume. 56 (2), 225-235 (1974).</li><li>Sorensen, D. 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Several surgical steps require particular attention. The L4 and L5 DRGs (location of somas), which dominate the sciatic nerve, need to be correctly identified and injected with gene constructs. Otherwise, the GFP-labeling will be absent in sciatic nerve axons. The iliac crests can be viewed as useful anatomical landmarks to pinpoint L4 and L5 DRGs. In most mice, the facet joint between L5 and L6 vertebrae is proximate to iliac crests12. Alternatively, L3 DRG can be chosen instead of L5, especially...

Injuries in the nervous system caused by neural trauma or various neurodegenerative diseases usually result in defects in motor, sensory and cognitive functions. Recently, much effort has been devoted to regenerative potency re-establishment in adult neurons to restore the physiological functionsof injured neurons1,2,3. Sensory neurons in the DRG are a cluster of nerve cells that convey different sensory stimuli, such as pain, temperature, touch, or body posture, to the brain. Each of these neurons is pseudo-unipolar and contains a single axon that bifurcates with one branch extending toward the periphery and the other branch heading toward the spinal cord4. The adult sensory neurons in DRGs are among a few mature mammalian neurons known to regenerate their axons actively after injury. Hence, injuries of sensory axons have been extensively employed as a crucial model to study the mechanisms of axonal regeneration in vivo.
In vivo gene transfection techniques, which are usually less time-consuming to set up and more flexible than using transgenic animals, have been playing essential roles in studying the functions of genes and signaling pathways in the nervous system. The main techniques can be categorized into two approaches: instrument-based and virus-based5. Viral-based in vivo gene delivery in adult neurons can provide precise spatiotemporal manipulation of gene expression6. However, labor-intensive processes are involved in viral-based methods, such as the production and purification of viral particles containing the desired gene. In addition, many viral vectors could activate the immune system of the host, which may interfere with the data acquisition, data analysis and possibly mislead the interpretation of experimental results. Electroporation, a typical instrument-based transfection approach, uses an electrical pulse to increase the permeability of cell and nuclear membranes transiently, which favors the influx of gene vectors or small RNA oligos from space outside of the cells7. In vitro electroporation is widely recognized as a transient but highly efficient strategy for manipulating targeted gene expression in many cell types. Although in vivo electroporation only leads to transient gene expression with low transfecting efficiency compared to viral vectors, it has various advantages over viral approaches. For instance, it can be applied to almost all tissues and cells7,8,9. In addition, either plasmids encoding genes-of-interest or small RNA oligos (e.g., siRNAs, microRNAs) against certain transcripts can be injected into the target tissue directly and then electrically pulsed, which make the procedure less labor- and time- consuming. Moreover, transfecting multiple plasmids and RNA oligos simultaneously with single electroporation is possible.
We have established an in vivo electroporation approach to manipulate gene expression in adult mouse sensory neurons and successfully applied and validated such approach in numerous pioneer studies1,2,3,8,10. Here, we present a detailed protocol to facilitate the usage of this approach for future studies of mammalian axon regeneration.

<table border="0" cellpadding="0" cellspacing="0" style="width:1039px;" width="1037">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="26">
			<td height="26" style="height:27px;width:335px;">ECM 830 Square wave electroporation system</td>
			<td style="width:232px;">BTX Harvard Apparatus</td>
			<td style="width:121px;">45-0052</td>
			<td style="width:351px;">For in vivo electroporation</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:27px;width:335px;">Tweezertrodes electrodes</td>
			<td style="width:232px;">BTX Harvard Apparatus</td>
			<td style="width:121px;">45-0524</td>
			<td>For in vivo electroporation, 1 mm flat</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Picospritzer III</td>
			<td style="width:232px;">Parker Instrumentation</td>
			<td style="width:121px;">1096</td>
			<td>Intracellular Microinjection Dispense Systems</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Glass Capillary Puller</td>
			<td style="width:232px;">NARISHIGE</td>
			<td>PC-10</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Borosilicate Glass Capillaries</td>
			<td>World Precision Instruments, Inc.</td>
			<td style="width:121px;">1902328</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Stereo Dissection Microscope</td>
			<td style="width:232px;">Leica</td>
			<td style="width:121px;">M80</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Microsurgery Rongeur</td>
			<td style="width:232px;">F.S.T</td>
			<td style="width:121px;">16221-14</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Microsurgery Forceps</td>
			<td style="width:232px;">FST by DUMONT, Switzerland</td>
			<td style="width:121px;">11255-20</td>
			<td>Only for sciatic nerve crush</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Glass Capillary</td>
			<td style="width:232px;">World Precision Instruments, Inc.</td>
			<td style="width:121px;">TW100-4</td>
			<td>10 cm, standard wall</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Tape</td>
			<td style="width:232px;">Fisherbrand</td>
			<td style="width:121px;">15-901-30</td>
			<td>For fixing the mouse on the corkboard</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2, 2, 2-Tribromoethanol (Avertin)</td>
			<td style="width:232px;">Sigma-Aldrich</td>
			<td style="width:121px;">T48402</td>
			<td>Avertin stock solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2-methyl-2-butanol</td>
			<td style="width:232px;">Sigma-Aldrich</td>
			<td style="width:121px;">152463</td>
			<td>Avertin stock solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">siRNA Fluorescent Universal Negative Control #1</td>
			<td style="width:232px;">Sigma-Aldrich</td>
			<td style="width:121px;">SIC003</td>
			<td>Non-target siRNA with fluorescence</td>
		</tr>
		<tr height="28">
			<td height="28" style="height:28px;width:335px;">microRNA Mimic Transfection Control with Dy547</td>
			<td style="width:232px;">Dharmacon</td>
			<td style="width:121px;">CP-004500-01-05</td>
			<td>Non-target microRNA with fluorescence</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Plasmids preparation kit</td>
			<td style="width:232px;">Invitrogen Purelink</td>
			<td style="width:121px;">K210016</td>
			<td>GFP-coding plasmid preparation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Fast Green Dye</td>
			<td style="width:232px;">Millipore-Sigma</td>
			<td style="width:121px;">F7252</td>
			<td>For better visualization of the DRG outline during injection</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Ketamine</td>
			<td style="width:232px;">Putney, Inc</td>
			<td style="width:121px;">NDC 26637-731-51</td>
			<td>Anesthesia induction</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Xylazine</td>
			<td style="width:232px;">AnaSed</td>
			<td style="width:121px;">NDC 59399-110-20</td>
			<td>Anesthesia induction</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:335px;">Acetaminophen</td>
			<td style="width:232px;">McNeil Consumer Healthcare</td>
			<td style="width:121px;">NDC 50580-449-36</td>
			<td>Post-surgical pain relief</td>
		</tr>
	</tbody>
</table>

investigating mammalian axon regeneration: in vivo electroporation of adult mouse dorsal root ganglion

Electroporation is an essential non-viral gene transfection approach to introduce DNA plasmids or small RNA molecules into cells. A sensory neuron in the dorsal root ganglion (DRGs) extends a single axon with two branches. One branch goes to the peripheral nerve (peripheral branch), and the other branch enters the spinal cord through the dorsal root (central branch). After the neural injury, the peripheral branch regenerates robustly whereas the central branch does not regenerate. Due to the high regenerative capacity, sensory axon regeneration has been widely used as a model system to study mammalian axon regeneration in both the peripheral nervous system (PNS) and the central nervous system (CNS). Here, we describe a previously established approach protocol to manipulate gene expression in mature sensory neurons in vivo via electroporation. Based on transfection with plasmids or small RNA oligos (siRNAs or microRNAs), the approach allows for both loss- and gain-of-function experiments to study the roles of genes-of-interests or microRNAs in regulation of axon regeneration in vivo. In addition, the manipulation of gene expression in vivo can be controlled both spatially and temporally within a relatively short time course. This model system provides a unique tool to investigate the molecular mechanisms by which mammalian axon regeneration is regulated in vivo.

To quantify the cytotoxicity of the current protocol and to validate that transfection rate of in vivo DRG electroporation is high enough, we injected and electroporated fluorescently-tagged microRNA or siRNA into L4 and L5 DRGs. The detached DRGs were processed through cryo-sectioning and immunohistochemistry (Figure 1A-B). When estimating the cell survival rate after injection and electroporation, the intact DRGs from L4 and L5 wer...

Watch this Scientific Journal Video about Investigating Mammalian Axon Regeneration: In Vivo Electroporation of Adult Mouse Dorsal Root Ganglion at JoVE.com

Investigating Mammalian Axon Regeneration: In Vivo Electroporation of Adult Mouse Dorsal Root Ganglion

Electroporation is an effective approach to deliver genes of interests into cells. By applying this approach in vivo on the neurons of adult mouse dorsal root ganglion (DRG), we describe a model to study axon regeneration in vivo.

Investigating Mammalian Axon Regeneration: In Vivo Electroporation of Adult Mouse Dorsal Root Ganglion

Electroporation is an essential non-viral gene transfection approach to introduce DNA plasmids or small RNA molecules into cells. A sensory neuron in the ...

This method provides an in-vivo gene transfection technique to manipulate gene expression in adult mouse sensory neurons for future studies of mammalian exo-regeneration. The main advantage of this technique is that it's less labor and time consuming, and can both overexpress and knock down the target genes simultaneously and separately. To begin this procedure, mark both sides of the iliac crest of an anesthetized mouse with a fine marker.Draw a line connecting two points of the iliac crest to facilitate the identification of L5 DRGs positions. Then, make a three centimeter incision along the midline of the lower back with micro scissors. Afterward, detach the paraspinous muscles, such as the musculus multifidus and the musculus longissimus lumborum, from the L3 to S1 spinous processes, and expose the fascia joint of the L4-5 and L5-6.Next, use a micro rongeur to remove the fascia joints of the L4-5 and L5-6. Subsequently, remove the left neural arch of L4 and L5, to expose the dorsal side of the DRGs. For DRG injection, load the DNA plasmids or RNA oligos into the glass capillary pipette.Then, insert the tip of the capillary glass pipette, carefully, into the DRG, and gradually inject one microliter solution of DNA plasmids or RNA oligos using the intracellular micro injection dispense system. For electroporation, pinch the target DRG with the electrodes gently, and apply five square electric pulses with the electroporation system. Subsequently, close the muscle, then the skin layers with nylon sutures.Two or three days after the DRG electroporation, anesthetize the mouse intraperitoneally, tape its limbs on the cork board, and make a one centimeter incision 0.5 centimeters to the left side along the midline. Next, cut the muscles, such as gluteus maximus muscle and piriformis muscle, longitudinally. Then, expose the segment of the sciatic nerve between the greater sciatic foramen, and the sciatic notch.Crush the nerve with microsurgery forceps for 12 seconds, and mark the crush site with a nylon epineural suture. Afterward, close the muscle and skin layers with nylon suture. After profusion, separate the DRGs together with the nerve roots and sciatic nerve, carefully, with micro scissors and micro forceps under the dissection microscope.Then, transfer the sciatic nerve directly in 4%PFA overnight at four degrees celsius. To image and measure the fluorescence labeled sensory axons under the dissection microscope, strip off the attached tissue and membrane on the fixed sciatic nerve with micro scissors and micro forceps, carefully. Then, wash the nerve with PVS three times.Next, place the sciatic nerve on a slide and keep it straight. Add 80 microliters of anti-fade solution around the nerve, then lay a cover slip on it. Flatten the whole mounted tissue with pressure.Afterward, place the flattened tissue under the inverted epifluorescence microscope, equipped with an accessory for mosaic acquisition and image processing. When measuring the length of regenerated axons, trace all identifiable fluorescently labeled axons in the sciatic nerve from the crush site to the distal axon ends. When applying the current, in-vivo electroporation method to study axonal regeneration, the sciatic nerve was flattened and imaged.Every regenerated axon with distinctive trajectory and recognizable distal axon end, can be traced from the crush site indicated by the suture knot. The white arrowhead, arrow, and star, indicate three distinctive axon ends, all of which extend from the crush site. Additionally, the DRGs were electroporated with EGFP plasmids, and the spinal cord was harvested.The EGFP labeled, dorsal column axons, in the spinal cord, were imaged and identified in both the longitudinal and sagittal projecting images. Here is a detailed view of axons in the dorsal column, and here is a detailed view of axons in the the dorsal root entry zone. This image shows the sagittal projection of the EGFP labeled axons within the dorsal column.Alternatively, the confocal images can be processed with microscopy visualization software to reconstruct a 3D image. While attempting this procedure, it's important to remember to position the L4 and the L5 DRGs correctly, and to make a knot on the dural membrane without impaling the sciatic nerve, while labeling the crush site with a suture knot. After its development, this technique pave the way for researchers in the field of axon regeneration to explore genes that are required for PNS, natural axon regeneration, or genes that can further promote regeneration in adult mouse in-vivo.

investigating-mammalian-axon-regeneration-vivo-electroporation-adult

Research

JoVE Journal

Neuroscience

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural connectivity form during development. In mice, retinofugal projections are arranged in a topographic manner and form eye-specific layers in the Lateral Geniculate Nucleus (dLGN) of the thalamus and the Superior Colliculus (SC). The development of these precise patterns of retinofugal projections has typically been studied by labeling populations of RGCs with fluorescent dyes and tracers, such as horseradish peroxidase1-4. However, these methods are too coarse to provide insight into developmental changes in individual RGC axonal arbor morphology that are the basis of retinotopic map formation. They also do not allow for the genetic manipulation of RGCs.
Recently, electroporation has become an effective method for providing precise spatial and temporal control for delivery of charged molecules into the retina5-11. Current retinal electroporation protocols do not allow for genetic manipulation and tracing of retinofugal projections of a single or small cluster of RGCs in postnatal mice. It has been argued that postnatal in vivo electroporation is not a viable method for transfecting RGCs since the labeling efficiency is extremely low and hence requires targeting at embryonic ages when RGC progenitors are undergoing differentiation and proliferation6. 
In this video we describe an in vivo electroporation protocol for targeted delivery of genes, shRNA, and fluorescent dextrans to murine RGCs postnatally. This technique provides a cost effective, fast and relatively easy platform for efficient screening of candidate genes involved in several aspects of neural development including axon retraction, branching, lamination, regeneration and synapse formation at various stages of circuit development. In summary we describe here a valuable tool which will provide further insights into the molecular mechanisms underlying sensory map development.

Transfection of Mouse Retinal Ganglion Cells by in vivo Electroporation

We demonstrate an in vivo electroporation protocol for transfecting single or small clusters of retinal ganglion cells (RGCs) and other retinal cell types in postnatal mice over a wide range of ages. The ability to label and genetically manipulate postnatal RGCs in vivo is a powerful tool for developmental studies.

The targeting and refinement of RGC projections to the midbrain is a popular and powerful model system for studying how precise patterns of neural ...

Genetic Study of Axon Regeneration with Cultured Adult Dorsal Root Ganglion Neurons

It is well known that mature neurons in the central nervous system (CNS) cannot regenerate their axons after injuries due to diminished intrinsic ability to support axon growth and a hostile environment in the mature CNS1,2. In contrast, mature neurons in the peripheral nervous system (PNS) regenerate readily after injuries3. Adult dorsal root ganglion (DRG) neurons are well known to regenerate robustly after peripheral nerve injuries. Each DRG neuron grows one axon from the cell soma, which branches into two axonal branches: a peripheral branch innervating peripheral targets and a central branch extending into the spinal cord. Injury of the DRG peripheral axons results in substantial axon regeneration, whereas central axons in the spinal cord regenerate poorly after the injury. However, if the peripheral axonal injury occurs prior to the spinal cord injury (a process called the conditioning lesion), regeneration of central axons is greatly improved4. Moreover, the central axons of DRG neurons share the same hostile environment as descending corticospinal axons in the spinal cord. Together, it is hypothesized that the molecular mechanisms controlling axon regeneration of adult DRG neurons can be harnessed to enhance CNS axon regeneration. As a result, adult DRG neurons are now widely used as a model system to study regenerative axon growth5-7.
Here we describe a method of adult DRG neuron culture that can be used for genetic study of axon regeneration in vitro. In this model adult DRG neurons are genetically manipulated via electroporation-mediated gene transfection6,8. By transfecting neurons with DNA plasmid or si/shRNA, this approach enables both gain- and loss-of-function experiments to investigate the role of any gene-of-interest in axon growth from adult DRG neurons. When neurons are transfected with si/shRNA, the targeted endogenous protein is usually depleted after 3-4 days in culture, during which time robust axon growth has already occurred, making the loss-of-function studies less effective. To solve this problem, the method described here includes a re-suspension and re-plating step after transfection, which allows axons to re-grow from neurons in the absence of the targeted protein. Finally, we provide an example of using this in vitro model to study the role of an axon regeneration-associated gene, c-Jun, in mediating axon growth from adult DRG neurons9.

An in vitro model for genetic study of axon regeneration using cultured adult mouse dorsal root ganglion neurons is described. The method includes a re-suspension/re-plating step to allow axon re-growth from neurons undergoing genetic manipulation. This approach is especially useful for loss-of-function studies of axon regeneration using RNAi-based protein knockdown.

It is well known that mature neurons in the central nervous system (CNS) cannot regenerate their axons after injuries due to diminished intrinsic ability ...

In Vitro Modeling of Cancerous Neural Invasion: The Dorsal Root Ganglion Model

One way that solid tumors disseminate is through neural invasion. This route is well-known in cancers of the head and neck, prostate, and pancreas. These neurotropic cancer cells have a unique ability to migrate unidirectionally along nerves towards the central nervous system (CNS). The dorsal root ganglia (DRG)/cancer cell model is a three dimensional (3D) in vitro model frequently used for studying the interaction between neural stroma and cancer cells. In this model, mouse or human cancer cell lines are grown in ECM adjacent to preparations of freshly dissociated cultured DRG. In this article, the DRG isolation protocol from mice, and implantation in petri dishes for co-culturing with pancreatic cancer cells are demonstrated. Five days after implantation, the cancer cells made contact with the DRG neurites. Later, these cells formed bridgeheads to facilitate more extensive polarized, neurotropic migration of cancer cells.

In Vitro Modeling of Cancerous Neural Invasion: The Dorsal Root Ganglion Model

This video article shows the use of the dorsal root ganglia (DRG)/cancer cell model in pancreatic ductal adenocarcinoma.

One way that solid tumors disseminate is through neural invasion. This route is well-known in cancers of the head and neck, prostate, and pancreas. These ...

An Approach to Enhance Alignment and Myelination of Dorsal Root Ganglion Neurons

Axon regeneration is a chaotic process due largely to unorganized axon alignment. Therefore, in order for a sufficient number of regenerated axons to bridge the lesion site, properly organized axonal alignment is required. Since demyelination after nerve injury strongly impairs the conductive capacity of surviving axons, remyelination is critical for successful functioning of regenerated nerves. Previously, we demonstrated that mesenchymal stem cells (MSCs) aligned on a pre-stretch induced anisotropic surface because the cells can sense a larger effective stiffness in the stretched direction than in the perpendicular direction. We also showed that an anisotropic surface arising from a mechanical pre-stretched surface similarly affects alignment, as well as growth and myelination of axons. Here, we provide a detailed protocol for preparing a pre-stretched anisotropic surface, the isolation and culture of dorsal root ganglion (DRG) neurons on a pre-stretched surface, and show the myelination behavior of a co-culture of DRG neurons with Schwann cells (SCs) on a pre-stretched surface.

This protocol describes the isolation of dorsal root ganglion (DRG) neurons isolated from rats and the culture of DRG neurons on a static pre-stretched cell culture system to enhance axon alignment, with subsequent co-culture of Schwann Cells (SCs) to promote myelination.

Axon regeneration is a chaotic process due largely to unorganized axon alignment. Therefore, in order for a sufficient number of regenerated axons to ...

Dorsal Root Ganglion Injection and Dorsal Root Crush Injury as a Model for Sensory Axon Regeneration

Achieving axon regeneration after nervous system injury is a challenging task. As different parts of the central nervous system (CNS) differ from each other anatomically, it is important to identify an appropriate model to use for the study of axon regeneration. By using a suitable model, we can formulate a specific treatment based on the severity of injury, the neuronal cell type of interest, and the desired spinal tract for assessing regeneration. Within the sensory pathway, DRG neurons are responsible for relaying sensory information from the periphery to the CNS. We present here a protocol that uses a DRG injection with a viral vector and a concurrent dorsal root crush injury in the lower cervical spinal cord of an adult rat as a model to study sensory axon regeneration. As demonstrated using a control virus, AAV5-GFP, we show the effectiveness of a direct DRG injection in transducing DRG neurons and tracing sensory axons into the spinal cord. We also show the effectiveness of the dorsal root crush injury in denervating the forepaw as an injury model for evaluating axon regeneration. Despite the requirement for specialized training to perform this invasive surgical procedure, the protocol is flexible, and potential users can modify many parts to accommodate their experimental requirements. Importantly, it can serve as a foundation for those in search of a suitable animal model for their studies. We believe that this article will help new users to learn the procedure in a very efficient and effective manner.

This protocol presents the use of a dorsal root ganglion (DRG) injection with a viral vector and a concurrent dorsal root crush injury in an adult rat as a model to study sensory axon regeneration. This model is suitable for investigating the use of gene therapy to promote sensory axon regeneration.

Achieving axon regeneration after nervous system injury is a challenging task. As different parts of the central nervous system (CNS) differ from each ...

Laminotomy for Lumbar Dorsal Root Ganglion Access and Injection in Swine

Dorsal root ganglia (DRG) are anatomically well defined structures that contain all primary sensory neurons below the head. This fact makes DRG attractive targets for injection of novel therapeutics aimed at treating chronic pain. In small animal models, laminectomy has been used to facilitate DRG injection because it involves surgical removal of the vertebral bone surrounding each DRG. We demonstrate a technique for intraganglionic injection of lumbar DRG in a large animal species, namely, swine. Laminotomy is performed to allow direct access to DRG using standard neurosurgical techniques, instruments, and materials. Compared with more extensive bone removal via laminectomy, we implement laminotomy to conserve spinal anatomy while achieving sufficient DRG access. Intraoperative progress of DRG injection is monitored using a non-toxic dye. Following euthanasia on post-operative day 21, the success of injection is determined by histology for intraganglionic distribution of 4&#39;,6-diamidino-2-phenylindole (DAPI). We inject a biologically inactive solution to demonstrate the protocol. This method could be applied in future preclinical studies to target therapeutic solutions to DRG. Our methodology should facilitate testing the translatability of intraganglionic small animal paradigms in a large animal species. Additionally, this protocol may serve as a key resource for those planning preclinical studies of DRG injection in swine.

We describe a method for laminotomy in swine that provides access to lumbar dorsal root ganglia (DRG) for intraganglionic injection. Injection progress is monitored intraoperatively and histologically confirmed up to 21 days after surgery. This protocol could be used for future preclinical studies involving DRG injection.

Dorsal root ganglia (DRG) are anatomically well defined structures that contain all primary sensory neurons below the head. This fact makes DRG attractive ...

Analysis of Immune Cells in Single Sciatic Nerves and Dorsal Root Ganglion from a Single Mouse Using Flow Cytometry

Nerve-resident immune cells in the peripheral nervous system (PNS) are essential to maintaining neuronal integrity in a healthy nerve. The immune cells of the PNS are affected by injury and disease, affecting the nerve function and the capacity for regeneration. Neuronal immune cells are commonly analyzed by immunofluorescence (IF). While IF is essential for determining the location of the immune cells in the nerve, IF is only semi-quantitative and the method is limited to the number of markers that can be analyzed simultaneously and the degree of surface expression. In this study, flow cytometry was used for quantitative analysis of leukocyte infiltration into sciatic nerves or dorsal root ganglions (DRGs) of individual mice. Single cell analysis was performed using DAPI and several proteins were analyzed simultaneously for either surface or intracellular expression. Both sciatic nerves from one mouse that were treated according to this protocol generated &#8805; 30,000 single nucleated events. The proportion of leukocytes in the sciatic nerves, determined by expression of CD45, was approximately 5% of total cell content in the sciatic nerve and approximately 5-10% in the DRG. Although this protocol focuses primarily on the immune cell population within the PNS, the flexibility of flow cytometry to measure a number of markers simultaneously means that the other cells populations present within the nerve, such as Schwann cells, pericytes, fibroblasts, and endothelial cells, can also be analyzed using this method. This method therefore provides a new means for studying systemic effects on the PNS, such as neurotoxicology and genetic models of neuropathy or in chronic diseases, such as diabetes.

Quantitative analysis of cell content within the murine sciatic nerve is difficult due to the scarcity of the tissue. This protocol describes a method for tissue digestion and preparation that provides sufficient cells for flow cytometry analysis of immune cell populations from nerves of individual mice.

Nerve-resident immune cells in the peripheral nervous system (PNS) are essential to maintaining neuronal integrity in a healthy nerve. The immune cells of ...

Rapid Isolation of Dorsal Root Ganglion Macrophages

There are growing interests to study the molecular and cellular interactions among immune cells and sensory neurons in the dorsal root ganglia after peripheral nerve injury. Peripheral monocytic cells, including macrophages, are known to respond to a tissue injury through phagocytosis, antigen presentation, and cytokine release. Emerging evidence has implicated the contribution of dorsal root ganglia macrophages to neuropathic pain development and axonal repair in the context of nerve injury. Rapidly phenotyping (or &#8220;rapid isolation of&#8221;) the response of dorsal root ganglia macrophages in the context of nerve injury is desired to identify the unknown neuroimmune factors. Here we demonstrate how our lab rapidly and effectively isolates macrophages from the dorsal root ganglia using an enzyme-free mechanical dissociation protocol. The samples are kept on ice throughout to limit cellular stress. This protocol is far less time consuming compared to the standard enzymatic protocol and has been routinely used for our Fluorescence-activated Cell Sorting analysis.

Here we present a mechanical dissociation protocol to rapidly isolate macrophages from the dorsal root ganglion for phenotyping and functional analysis.

There are growing interests to study the molecular and cellular interactions among immune cells and sensory neurons in the dorsal root ganglia after ...

In Situ Visualization of Axon Growth and Growth Cone Dynamics in Acute Ex Vivo Embryonic Brain Slice Cultures

During neuronal development, axons navigate the cortical environment to reach their final destinations and establish synaptic connections. Growth cones -the sensory structures located at the distal tips of developing axons- execute this process. Studying the structure and dynamics of the growth cone is crucial to understanding axonal development and the interactions with the surrounding central nervous system (CNS) that enable it to form neural circuits. This is essential when devising methods to reintegrate axons into neural circuits following injury in fundamental research and pre-clinical contexts. Thus far, the general understanding of growth cone dynamics is primarily founded on studies of neurons cultured in two dimensions (2D). Although undoubtedly fundamental to the current knowledge of growth cone structural dynamics and response to stimuli, 2D studies misrepresent the physiological three-dimensional (3D) environment encountered by neuronal growth cones in intact CNS tissue. More recently, collagen gels were employed to overcome some of these limitations, enabling the investigation of neuronal development in 3D. However, both synthetic 2D and 3D environments lack signaling cues within CNS tissue, which direct the extension and pathfinding of developing axons. This protocol provides a method for studying axons and growth cones using organotypic brain slices, where developing axons encounter physiologically relevant physical and chemical cues. By combining fine-tuned in utero and ex utero electroporation to sparsely deliver fluorescent reporters along with super-resolution microscopy, this protocol presents a methodological pipeline for the visualization of axon and growth cone dynamics in situ. Furthermore, a detailed toolkit description of the analysis of long-term and live-cell imaging data is included.

In Situ Visualization of Axon Growth and Growth Cone Dynamics in Acute Ex Vivo Embryonic Brain Slice Cultures

This protocol demonstrates a straightforward and robust method to study in situ axon growth and growth cone dynamics. It describes how to prepare ex vivo physiologically relevant acute brain slices and provides a user-friendly analysis pipeline.

During neuronal development, axons navigate the cortical environment to reach their final destinations and establish synaptic connections. Growth cones ...

In Vitro Myelination of Peripheral Axons in a Coculture of Rat Dorsal Root Ganglion Explants and Schwann Cells

The process of myelination is essential to enable rapid and sufficient signal transduction in the nervous system. In the peripheral nervous system, neurons and Schwann cells engage in a complex interaction to control the myelination of axons. Disturbances of this interaction and breakdown of the myelin sheath are hallmarks of inflammatory neuropathies and occur secondarily in neurodegenerative disorders. Here, we present a coculture model of dorsal root ganglion explants and Schwann cells, which develops a robust myelination of peripheral axons to investigate the process of myelination in the peripheral nervous system, study axon-Schwann cell interactions, and evaluate the potential effects of therapeutic agents on each cell type separately. Methodologically, dorsal root ganglions of embryonic rats (E13.5) were harvested, dissociated from their surrounding tissue, and cultured as whole explants for 3 days. Schwann cells were isolated from 3-week-old adult rats, and sciatic nerves were enzymatically digested. The resulting Schwann cells were purified by magnetic-activated cell sorting and cultured under neuregulin and forskolin-enriched conditions. After 3 days of dorsal root ganglion explant culture, 30,000 Schwann cells were added to one dorsal root ganglion explant in a medium containing ascorbic acid. The first signs of myelination were detected on day 10 of coculture, through scattered signals for myelin basic protein in immunocytochemical staining. From day 14 onward, myelin sheaths were formed and propagated along the axons. Myelination can be quantified by myelin basic protein staining as a ratio of the myelination area and axon area, to account for the differences in axonal density. This model provides experimental opportunities to study various aspects of peripheral myelination in vitro, which is crucial for understanding the pathology of and possible treatment opportunities for demyelination and neurodegeneration in inflammatory and neurodegenerative diseases of the peripheral nervous system.

In the coculture system of dorsal root ganglia and Schwann cells, myelination of the peripheral nervous system can be studied. This model provides experimental opportunities to observe and quantify peripheral myelination and to study the effects of compounds of interest on the myelin sheath.

The process of myelination is essential to enable rapid and sufficient signal transduction in the nervous system. In the peripheral nervous system, ...