This work was supported by funding from the National Natural Science Foundation of China (31671089 and 81701108) and Shaanxi Provincial Social Development Science and Technology Research Project (2016SF-250).

The current protocol followed the Guide for United States Public Health Service&#39;s Policy on the Humane Care and Use of Laboratory Animals, and the Committee on the Ethics of Animal Experiments of the Fourth Military Medical University approved the protocol.
1. Animals
<ol>
	<li>Divide 24 Sprague-Dawley rats (4-8 weeks old) into two groups. Produce complete Freund&#39;s adjuvant (CFA) model by intraplantar injection of 100 &#956;L of CFA in one group of 14 rats and another group of 10 rats by treatment with saline. 
	NOTE: All of the animals were acquired from the Animal Center of the Fourth Military Medical University. Adult male and female Sprague-Dawley rats (150-200 g) were used for all procedures, and rats were randomly assigned to cages. Two rats were housed per cage under a 12-/12-hour light/dark cycle at a constant temperature (25 &#177; 1 &#176;C) with free access to food and water.</li>
</ol>
2. In Vivo Single-fiber Recording
<ol>
	<li>Prepare and disinfect all surgical instruments (scalpel, tweezers, ophthalmic scissors, shearing scissors, glass separating needle, suture needle, bone rongeur) prior to surgery. Prepare 1 L or 2 L of normal Ringer&#8217;s extracellular solution (in mM: NaCl 124, KCl 3, MgSO4 1.3, CaCl2 2, NaHCO3 26, NaH2PO4 1.25, glucose 15; pH 7.4 and 305 mOsm). Store at 4 &#176;C until use.</li>
	<li>Anesthetize rats. On days 3 to 7 after CFA injection, use intraperitoneal injection of a mixed solution (1% chloralose and 17% urethane, 5 mL/kg body weight) to keep the animals in a stable aesthetic condition during the experiment. Apply supplementary injection of anesthetics, if necessary, after checking pupils and the response to pain stimulation. Monitor and maintain a&#160;body temperature near 37 &#176;C.</li>
	<li>Exposure of sciatic nerve trunk for recording
	<ol>
		<li>Cut open the skin and muscle on the dorsal part of the thigh. Perform a blunt dissection along femoral biceps. Carefully isolate the sciatic nerve trunk using ophthalmic scissors and a glass separation needle. Keep the tissue wet using Ringer&#39;s solution.</li>
		<li>Fix the animal on a homemade metal hoop (3 cm long, 2 mm wide metal hoop with an iron wire 1 mm in diameter) via sewing the skin into the slot around it. Pull the skin up slightly so as to establish a fluid bath.</li>
		<li>Expose 1 cm of sciatic nerve trunk at the proximal side. Place a small brown platform under the nerve trunk to enhance the contrast and observe the fine nerve trunk clearly. Heat liquid paraffin in a water bath to 37 &#176;C and drop it on the top of the nerve trunk to prevent drying of the surface of the fiber. Remove the pia mater spinalis and dura mater around the sciatic nerve.</li>
	</ol>
	</li>
	<li>Recording session
	<ol>
		<li>Select a platinum filament (29 &#956;m in diameter) as the recording electrode. Heat over for easier molding, and create a small hook at the very end. Attach the electrode to a micromanipulator to move the electrode as required.</li>
		<li>In the bath, place a reference electrode in adjacent subcutaneous tissue. Split the spinal dura and the pia mater. Separate the sciatic nerve into a single fiber (15-20 &#956;m in diameter) in the recording pool. Then, pick up a fine fascicle of axon and suspend the proximal end of the axon on the hook of the recording electrode under a stereoscope at 25x magnification. 
		NOTE: The just-dissected filaments tend to be thicker and require further separation until a single unit may be recorded.</li>
		<li>Identify the receptive field of a single nociceptive C-fiber using a mechanical stimulus (Von Frey hairs) and thermal stimulus (small cotton ball with 50-55 &#176;C water). Briefly, if the firing of nerve fiber respond to the mechanical stimuli and hot water, then consider it as a polymodal nociceptive C-fiber4. Next, insert two needle stimulus electrodes (2 mm interval) into the skin of the identified field for the delivery of electrical stimuli.</li>
		<li>Display the waveform of an action potential on oscilloscope and employ a computer A/D board with a signal sampling rate of 20 kHz to amplify and record the spikes.</li>
		<li>Collect data using data acquisition software (Table of Materials). Save data on a computer and analyze later with professional software (Table of Materials).</li>
	</ol>
	</li>
</ol>
3. Measurement of Conduction Failure
<ol>
	<li>Deliver the repetitive electrical stimuli (0.8 ms duration, 1.5x threshold intensity) in different frequencies (2 Hz, 5 Hz, 10 Hz) to a C-fiber for 60 s4,8,9. Allow a 10 min interval for fiber to relax between stimuli. Calculate the ratio of the number of failures to the number of delivered repetitive stimulus pulses and multiply by 100% to obtain the degree of conduction failure.</li>
</ol>
4. Preparation of Iintact DRG Attached with Sciatic Nerve
<ol>
	<li>Prepare surgical tools and Ringer&#39;s extracellular solution as described in step 2.1.</li>
	<li>Separate the DRG with the attached sciatic nerve.
	<ol>
		<li>Anesthetize the rats as described in step 2.2 (On days 3 to 7 after CFA injection). Cut the hair on back and leg with shearing scissors, and sterilize the skin with tincture of iodine.</li>
		<li>For DRG exposure, first cut open the skin from the midline of the back at the L4 to L5 segment level. Remove muscles, the process of spine, vertebra board, and transverse process using a bone rongeur to expose the spinal cord and DRG body. Cover the exposed spinal cord and DRG with cottons infiltrated by normal Ringer&#39;s extracellular solution to maintain neural activity. Stop the bleeding and clear the blood in time.</li>
		<li>Expose the sciatic nerve from two directions: remove the L4 to S1 bone structure above the vertebral foramen using ophthalmic scissors to expose the spinal nerve connected to DRG which is at the proximal end of sciatic nerve. Cut open the skin to expose the sciatic nerve at the middle thigh. Separate and disconnect the sciatic nerve from the distal end of the nerve where it goes inside the muscle, and ligate the nerve trunk with surgical line at the end of the nerve prior to cutting.</li>
		<li>Separate the sciatic nerve from the underlying connective tissue using ophthalmic scissors via lifting of the nerve ligation point. Remove the dura from the spinal cord and separate the DRG from the underlying connective tissue via lifting the dorsal root&#160;until it reaches the adjacent part of the sciatic nerve. Thus, isolate the whole preparation of DRG with an attached sciatic nerve.</li>
	</ol>
	</li>
	<li>Clear the surface of the DRG.
	<ol>
		<li>Carefully remove the spinal dura on the surfaces of L4&#8722;L6 DRG using tweezers under a stereoscope at 4x magnification.</li>
		<li>Place the DRG with attached sciatic nerve in a glass tube containing 1 mL of mixed enzymes (0.2% proteinase and 0.32% collagenase) and digest in a 37 &#176;C water bath for 15 min (blow slightly with a plastic dropper at an interval of 5 min).</li>
		<li>Lift the end of the ligation&#160;line and move the preparation to a dish filled with a normal Ringer&#39;s extracellular solution to wash out the enzyme. Then transfer the digested DRG to a container (Figure 1A) filled with oxygenated Ringer&#39;s extracellular solution for recording.</li>
	</ol>
	</li>
	<li>Recording session
	<ol>
		<li>Prepare intracellular solution (in mM: potassium gluconate 120, KCl 18, MgCl2 2, ethylene glycol-bis(&#946;-aminoethyl ether)-N,N,N&#39;,N&#39;-tetraacetic acid [EGTA] 5, HEPES 10, Na2-ATP 5, Na-GTP 0.4, CaCl2 1; pH 7.2 and 300 mOsm). Keep at 0 &#176;C until use.</li>
		<li>Stabilize ganglia using a slice anchor and connect nerve end to a suction-stimulating electrode (Figure 1A). Visualize and select a DRG neuron with a water-immersion objective at 40x magnification.</li>
		<li>Pull an electrode (Table of Materials) and fill it with intracellular solution. Insert electrode on holder and apply positive pressure in the pipette with a final resistance of 4-7 M&#937;.</li>
		<li>Bring electrode close to the cell and touch it. Give a negative pressure in the pipette, once G&#937; seal is reached, set the membrane potential at about -60 mV and then establish whole-cell recording mode.</li>
		<li>Deliver repetitive stimuli&#160;of 5-50 Hz to the sciatic nerve through the suction electrode to screen for conduction failure. Measure the amplitude of afterhyperpolarization potential (AHP) from baseline to peak, and the 80% AHP duration. 
		NOTE: One-way analysis of variance (ANOVA; for more than two groups) or Student&#8217;s t-test (for only two groups) was used to analyze the data. Data are presented as means &#177; standard error of the mean (SEM). The statistical significant level was set at p &#60; 0.05.</li>
	</ol>
	</li>
	<li>Ending the Experiment
	<ol>
		<li>&#8203;When the experimental task is finished while the rats are still under anaesthetic situation, rats are humanely euthanized with a intracardiac injections of overdose pentobarbital sodium.&#160;</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

Although recent studies have achieved calcium imaging of DRG neurons in vivo16, performing in vivo patch-clamp recording from individual DRG nociceptors remains extremely challenging. Therefore, an in vivo single-fiber approach for the pain field is of continuing importance. Single-fiber recording in the present protocol allow objective observation of conduction failure phenomena, and the combination of this technique with the ex vivo preparation developed in the current study allows examination o...

The normal transmission of information along nerve fibers guarantees the normal function of the nervous system. Abnormal functioning of the nervous system is also reflected in the electrical signal transmission of nerve fibers. For example, the degree of demyelination in central demyelination lesions can be classified via comparison of changes in nerve conduction velocity before and after intervention application1. It is difficult to intracellularly record nerve fibers, except in special preparations such as the squid giant axon2. Therefore, electrophysiological activity is only recordable via the extracellular recording of single fibers. As one of the classical electrophysiological methods, single-fiber recording has a longer history than other techniques. However, fewer electrophysiologists grasping this method despite its extensive application. Therefore, a detailed introduction of the standard protocol for single-fiber recording is needed for its appropriate application.
Although various patch-clamp techniques have dominated modern electrophysiological study, single-fiber recording still plays an irreplaceable role in recording the activities of nerve fibers, especially fibers transmitting peripheral sensation with their sensory cell body located in dorsal root ganglion (DRG). The advantage of using single-fiber recording here is that in vivo fiber recording provides a long observation time with the capacity to record responses to natural stimuli in preclinical models without disturbance of the intracellular environment3,4.
An increasing number of studies over the last two decades has examined complex functions along nerve fibers5, and conduction failure, which is defined as a state of unsuccessful nerve impulse transmission along the axon, was present in many different peripheral nerves6,7. The presence of conduction failure in our investigation served as an intrinsic self-inhibitory mechanism for the modulation of persistent nociceptive input along C-fibers8. This conduction failure was significantly attenuated under conditions of hyperalgesia4,9. Therefore, targeting the factors involved in conduction failure may represent a new treatment for neuropathic pain. To observe conduction failure, the firing pattern should be recorded and analyzed on the basis of sequentially discharged spikes based on single-fiber recording.
To thoroughly understand the mechanism of conduction failure, it is necessary to identify the transmission properties of the axon, or more precisely, the membrane properties of DRG neurons, based on their pseudo-unipolar anatomical properties. Many previous studies in this field have been performed on dissociated DRG neurons10,11, which may not be feasible for the investigation of conduction failure due to two obstacles. First, various mechanical and chemical methods are used in the dissociation process to free DRG neurons, which may result in unhealthy cells or alter the phenotype/properties of the neurons and confound the findings. Second, the attached peripheral nerves are basically removed, and conduction failure phenomena are not observable in these preparations. Therefore, a preparation of intact DRG neurons with an attached nerve has been improved to avoid the abovementioned obstacles.&#160;

<table border="0" cellpadding="0" cellspacing="0" style="width:605px;" width="605">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:43px;width:161px;">Instruments and software used in single fiber recording</td>
			<td style="width:148px;"></td>
			<td style="width:93px;"></td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Amplifier</td>
			<td style="width:148px;">Nihon kohden</td>
			<td style="width:93px;">MEZ-8201</td>
			<td style="width:203px;">Amplification of the electrophysiological signals</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:43px;width:161px;">Bioelectric amplifier monitor</td>
			<td style="width:148px;">ShangHai JiaLong Teaching instrument factory</td>
			<td style="width:93px;">SZF-1</td>
			<td style="width:203px;">Monitor firing process via sound which is transformed from physiological discharge signal</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Data acquisition and analysis system</td>
			<td style="width:148px;">CED</td>
			<td style="width:93px;">Spike-2</td>
			<td style="width:203px;">Software for data acquisition and analysis</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Electrode manipulator</td>
			<td style="width:148px;">Narishige</td>
			<td style="width:93px;">SM-21</td>
			<td style="width:203px;">Contro the movement of the electrode as required</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Hairspring tweezers</td>
			<td style="width:148px;">A.Dumont</td>
			<td style="width:93px;">5#</td>
			<td style="width:203px;">Separate the single fiber</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Isolator</td>
			<td style="width:148px;">Nihon kohden</td>
			<td style="width:93px;">SS-220J</td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="42">
			<td height="64" rowspan="2" style="height:64px;width:161px;">Memory oscilloscope</td>
			<td rowspan="2" style="width:148px;">Nihon kohden</td>
			<td rowspan="2" style="width:93px;">VC-9</td>
			<td style="width:203px;">Display recorded discharge during</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:203px;">experiment</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:161px;">Stereomicroscope</td>
			<td style="width:148px;">ZEISS</td>
			<td style="width:93px;">SV-11</td>
			<td style="width:203px;">Have clear observation when separate the local tissue and single fiber</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Stimulator</td>
			<td style="width:148px;">Nihon kohden</td>
			<td style="width:93px;">SEZ-7203</td>
			<td style="width:203px;">Delivery of the electrical stimuli</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Von Frey Hair</td>
			<td style="width:148px;">Stoelting accompany</td>
			<td style="width:93px;"></td>
			<td style="width:203px;">Delivery of the mechanical stimuli</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:161px;">Water bath</td>
			<td style="width:148px;">Scientz biotechnology Co., Ltd.</td>
			<td style="width:93px;">SC-15</td>
			<td style="width:203px;">Heating paroline to maintain at 37oC</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:161px;">Instruments and software used in patch clamp recording</td>
			<td style="width:148px;"></td>
			<td style="width:93px;"></td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="106">
			<td height="106" style="height:106px;width:161px;">Amplifier</td>
			<td style="width:148px;">Axon Instruments</td>
			<td style="width:93px;">Multiclamp 700B</td>
			<td style="width:203px;">Monitors the currents flowing through the recording electrode and also controls the stimuli by sending a signal to the electrode</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:161px;">Anti-vibration table</td>
			<td style="width:148px;">Optical Technology Co., Ltd.</td>
			<td style="width:93px;"></td>
			<td style="width:203px;">Isolates the recording system from vibrations induced by the environment</td>
		</tr>
		<tr height="127">
			<td height="127" style="height:127px;width:161px;">Camera</td>
			<td style="width:148px;">Olympus</td>
			<td style="width:93px;">TH4-200</td>
			<td style="width:203px;">See the neurons in bright field; the controlling software allows to take pictures and do live camera image to monitor the approach of the electrode to the cell</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Clampex</td>
			<td style="width:148px;">Axon</td>
			<td style="width:93px;">Clampex 9.2</td>
			<td style="width:203px;">Software for data acquisition and delivery of stimuli</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Clampfit</td>
			<td style="width:148px;">Axon</td>
			<td style="width:93px;">Clampfit 10.0</td>
			<td style="width:203px;">Software for data analysis</td>
		</tr>
		<tr height="66">
			<td height="66" style="height:66px;width:161px;">Electrode puller</td>
			<td style="width:148px;">Sutter</td>
			<td style="width:93px;">P-97</td>
			<td style="width:203px;">Prepare recording pipettes of about 2&#956;m diameter with resistance about 5 to 8 M&#937;</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Glass pipette</td>
			<td style="width:148px;">Sutter</td>
			<td style="width:93px;">BF 150-75-10</td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Micromanipulator</td>
			<td style="width:148px;">Sutter</td>
			<td style="width:93px;">MP225</td>
			<td style="width:203px;">Give a precise control of the microelectrode</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:161px;">Microscope</td>
			<td style="width:148px;">Olympus</td>
			<td style="width:93px;">BX51WI</td>
			<td style="width:203px;">Upright microcope equipped with epifluorescence for clearly observe the cells which would be patched</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Origin</td>
			<td style="width:148px;">Origin lab</td>
			<td style="width:93px;">Origin 8</td>
			<td style="width:203px;">Software for drawing picture</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Perfusion Pump</td>
			<td style="width:148px;">BaoDing LanGe Co., Ltd.</td>
			<td style="width:93px;">BT100-1J</td>
			<td style="width:203px;">Perfusion of DRG in whole-cell patch clamp</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Other instruments</td>
			<td style="width:148px;"></td>
			<td style="width:93px;"></td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Electronic balance</td>
			<td style="width:148px;">Sartorius</td>
			<td style="width:93px;">BS 124S</td>
			<td style="width:203px;">Weighing reagent</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">pH Modulator</td>
			<td style="width:148px;">Denver Instrument</td>
			<td style="width:93px;">UB7</td>
			<td style="width:203px;">Adjust pH to 7.4</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Solutions/perfusion/chemicals</td>
			<td style="width:148px;"></td>
			<td style="width:93px;"></td>
			<td style="width:203px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Calcium chloride</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">C5670</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:161px;">Chloralose</td>
			<td style="width:148px;">Shanghai Meryer Chemical Technology Co., Ltd.</td>
			<td style="width:93px;">M07752</td>
			<td style="width:203px;">Mixed solution for Anesthesia</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Collagenase</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">SLBQ1885V</td>
			<td style="width:203px;">Enzyme used for clearing the surface of DRG</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">D (+) Glucose</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">G7528</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Liquid Paraffin</td>
			<td style="width:148px;">TianJin HongYan Reagent Co., Ltd.</td>
			<td style="width:93px;"></td>
			<td style="width:203px;">Maintain fiber wetting</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Magnesium sulfate</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">M7506</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Potassium chloride</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">P3911</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Protease</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">62H0351</td>
			<td style="width:203px;">Enzyme used for clearing the surface of DRG</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Sodium bicarbonate</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">S5671</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Sodium chloride</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">S5886</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Sodium phosphate monobasic</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">S0751</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:161px;">Sucrose</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">S0389</td>
			<td style="width:203px;">Extracellular solution</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:161px;">Urethane</td>
			<td style="width:148px;">Sigma-Aldrich</td>
			<td style="width:93px;">U2500</td>
			<td style="width:203px;">Mixed solution for Anesthesia</td>
		</tr>
	</tbody>
</table>

use of in vivo single-fiber recording and intact dorsal root ganglion with attached sciatic nerve to examine the mechanism of conduction failure

Single-fiber recording has been a classical and effective electrophysiological technique over the last few decades because of its specific application for nerve fibers in the central and peripheral nervous systems. This method is particularly applicable to dorsal root ganglia (DRG), which are primary sensory neurons that exhibit a pseudo-unipolar structure of nervous processes. The patterns and features of the action potentials passed along axons are recordable in these neurons. The present study uses in vivo single-fiber recordings to observe the conduction failure of sciatic nerves in complete Freund&#8217;s adjuvant (CFA)-treated rats. As the underlying mechanism cannot be studied using in vivo single-fiber recordings, patch-clamp-recordings of DRG neurons are performed on preparations of intact DRG with the attached sciatic nerve. These recordings reveal a positive correlation between conduction failure and the rising slope of the after-hyperpolarization potential (AHP) of DRG neurons in CFA-treated animals. The protocol for in vivo single fiber-recordings allows the classification of nerve fibers via the measurement of conduction velocity and monitoring of abnormal conditions in nerve fibers in certain diseases. Intact DRG with attached peripheral nerve allows observation of the activity of DRG neurons in most physiological conditions. Conclusively, single-fiber recording combined with electrophysiological recording of intact DRGs is an effective method to examine the role of conduction failure during the analgesic process.

The outcome of the single-fiber recording protocol depends on the quality of the fiber dissection. The animal for in vivo experiments must be in a good situation to keep the nerve trunk healthy for easy dissection (see advice in the discussion section). A drug application bath is needed in many cases for drug delivery on fibers. Figure 1 illustrates how the in vivo single-fiber recording was operated (Figure 1A) and presents one classical recording from the sciatic nerve of ...

Watch this Scientific Journal Video about Use of In Vivo Single-fiber Recording and Intact Dorsal Root Ganglion with Attached Sciatic Nerve to Examine the Mechanism of Conduction Failure at JoVE.com

Use of In Vivo Single-fiber Recording and Intact Dorsal Root Ganglion with Attached Sciatic Nerve to Examine the Mechanism of Conduction Failure

Single-fiber recording is an effective electrophysiological technique that is applicable to the central and peripheral nervous systems. Along with the preparation of intact DRG with the attached sciatic nerve, the mechanism of conduction failure is examined. Both protocols improve the understanding of the peripheral nervous system&#39;s relationship with pain.

Single-fiber recording has been a classical and effective electrophysiological technique over the last few decades because of its specific application for ...

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8.7K Views.  Fourth Military Medical University. Single-fiber recording is an effective electrophysiological technique that is applicable to the central and peripheral nervous systems. Along with the preparation of intact DRG with the attached sciatic nerve, the mechanism of conduction failure is examined. Both protocols improve the understanding of the peripheral nervous system's relationship with pain.

Video: Use of In Vivo Single-fiber Recording and Intact Dorsal Root Ganglion with Attached Sciatic Nerve to Examine the Mechanism of Conduction Failure

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 ...

Measuring Spinal Presynaptic Inhibition in Mice By Dorsal Root Potential Recording In Vivo

Presynaptic inhibition is one of the most powerful inhibitory mechanisms in the spinal cord. The underlying physiological mechanism is a depolarization of primary afferent fibers mediated by GABAergic axo-axonal synapses (primary afferent depolarization). The strength of primary afferent depolarization can be measured by recording of volume-conducted potentials at the dorsal root (dorsal root potentials, DRP). Pathological changes of presynaptic inhibition are crucial in the abnormal central processing of certain pain conditions and in some disorders of motor hyperexcitability. Here, we describe a method of recording DRP in vivo in mice. The preparation of spinal cord dorsal roots in the anesthetized animal and the recording procedure using suction electrodes are explained. This method allows measuring GABAergic DRP and thereby estimating spinal presynaptic inhibition in the living mouse. In combination with transgenic mouse models, DRP recording may serve as a powerful tool to investigate disease-associated spinal pathophysiology. In vivo recording has several advantages compared to ex vivo isolated spinal cord preparations, e.g. the possibility of simultaneous recording or manipulation of supraspinal networks and induction of DRP by stimulation of peripheral nerves.

Measuring Spinal Presynaptic Inhibition in Mice By Dorsal Root Potential Recording In Vivo

GABAergic presynaptic inhibition is a powerful inhibitory mechanism in the spinal cord important for motor and sensory signal integration in spinal cord networks. Underlying primary afferent depolarization can be measured by recording of dorsal root potentials (DRP). Here we demonstrate a method of in vivo recording of DRP in mice.

Presynaptic inhibition is one of the most powerful inhibitory mechanisms in the spinal cord. The underlying physiological mechanism is a depolarization of ...

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 ...

In Vivo Gene Transfer to Schwann Cells in the Rodent Sciatic Nerve by Electroporation

The formation of the myelin sheath by Schwann cells (SCs) is essential for rapid conduction of nerve impulses along axons in the peripheral nervous system. SC-selective genetic manipulation in living animals is a powerful technique for studying the molecular and cellular mechanisms of SC myelination and demyelination in vivo. While knockout/knockin and transgenic mice are powerful tools for studying SC biology, these methods are costly and time consuming. Viral vector-mediated transgene introduction into the sciatic nerve is a simpler and less laborious method. However, viral methods have limitations, such as toxicity, transgene size constraints, and infectivity restricted to certain developmental stages. Here, we describe a new method that allows selective transfection of myelinating SCs in the rodent sciatic nerve using electroporation. By applying electric pulses to the sciatic nerve at the site of plasmid DNA injection, genes of interest can be easily silenced or overexpressed in SCs in both neonatal and more mature animals. Furthermore, this in vivo electroporation method allows for highly efficient simultaneous expression of multiple transgenes. Our novel technique should enable researchers to efficiently manipulate SC gene expression, and facilitate studies on SC development and function.

In Vivo Gene Transfer to Schwann Cells in the Rodent Sciatic Nerve by Electroporation

Here, we present an in vivo technique for gene transfer to Schwann cells (SCs) in the rodent sciatic nerve. This simple technique is useful for investigating signaling mechanisms involved in the development and maintenance of myelinating SCs.

The formation of the myelin sheath by Schwann cells (SCs) is essential for rapid conduction of nerve impulses along axons in the peripheral nervous ...

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 ...

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.

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.

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

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 ...