This study was funded by the&#160;National Natural Science Foundation of China&#160;for Young Scholars (52207254 and 82301657) and the&#160;China Postdoctoral Science Fund (2022M711833).

The Institutional Animal Care and Use Committee approved all animal experiments&#160;and the studies were conducted in accordance with relevant animal welfare regulations.
1. Animals preparation
<ol>
	<li>Animals
	<ol>
		<li>Housing information: House male Sprague-Dawley rats (Postnatal 10-14 days, P10-P14) in a specific pathogen-free environment. 
		NOTE: Room conditions were maintained at 20 &#176;C &#177; 2 &#176;C, humidity: 50%-60%, with a 12-h light/ dark cycle. Animals had free access to food and water.</li>
		<li>Label the motor neurons retrogradely: Inject Fluoro-Gold (FG) into the bilateral tibialis anterior and gastrocnemius muscle (2% in sterile saline, 50 &#181;L per muscle) to retrogradely label the motor neurons 2 days before the sacrifice.</li>
	</ol>
	</li>
	<li>Solutions
	<ol>
		<li>Prepare cutting solution: Mix 120 mM Choline Chloride, 2.6 mM KCl, 26 mM NaHCO3, 1.25 mM NaH2PO4, 0.5 mM CaCl2, 7 mM MgCl2, 1.3 mM Ascorbic Acid, 15 mM Glucose. Pre-bubble the solution with 95% O2 and 5% CO2 (adjust to pH 7.4 with KOH) for 30 min before the dissection and slicing. Cool the solution with crushed ice.</li>
		<li>Prepare artificial cerebrospinal fluid (ACSF): Mix 126 mM NaCl, 3 mM KCl, 1.2 mM NaH2PO4; 1.3 mM MgCl2, 2.4 mM CaCl2, 26 mM NaHCO3, and 10 mM glucose. Pre-bubble the solution with 95% O2 and 5% CO2 for 30 min before the incubation.</li>
		<li>Prepare intracellular solution: Mix 126 mM K-Gluconate, 2 mM KCl, 2 mM MgCl2, 0.2 mM EGTA, 10 mM HEPES, 4 mM Na2ATP, 0.4 mM Na2GTP, 10 mM K-Phosphocreatine, and 0.5% Neurobiotin (pH 7.25 and 305 mOsm/Kg). Cool the solution with crushed ice.</li>
		<li>Prepare low-melting agarose gel: Dissolve 4 g of agarose in 100 mL of cutting solution, and use a magnetic stirring rotor to fully dissolve it. At 30 min before embedding, heat the low-melting-point agarose in the microwave oven with high power for 1 min, and then transfer it into a 39 &#176;C water bath to maintain the liquid state.</li>
	</ol>
	</li>
	<li>Instrument preparation
	<ol>
		<li>Place crushed ice on the perfusion tray (Supplementary Figure 1A) at 10 min prior to perfusion. Place the anatomical tray (Supplementary Figure 1B) and cutting tray (Supplementary Figure 1C) with a water band at -80 &#176;C overnight in advance.</li>
		<li>Place the incubation chamber with nylon mesh in the oven at 45 &#176;C overnight in advance.</li>
		<li>Use low-melting point agarose to prefabricate a 35&#176; slope and a 2 mm thick platform (Supplementary Figure 1D). After gel solidification, place them in the center of a 35-mm Petri dish to support the spinal cord in the next coming procedures.</li>
	</ol>
	</li>
	<li>Intracardial perfusion
	<ol>
		<li>Anesthetize the rats with 2.5% tribromoethanol (160 &#181;L/10 g) via intraperitoneal injection. Ensure the rats are fully anesthetized by verifying the lack of response to external stimuli, such as a gentle pinch of the toe.</li>
		<li>When the proper anesthetization is confirmed, place the rats supine and immobilize them in the Petri dish filled with silica gel.</li>
		<li>Cut a 5-mm longitudinal skin incision caudally to the xiphoid process, then fully expand the subcutaneous space. Cut a 2-cm longitudinal skin incision along the ventral midline to fully expose the outer chest wall, starting with the above-mentioned incision and ending with the top of the chest.</li>
		<li>Use toothed tweezers to lift the xiphoid (Supplementary Figure 2A), and then use fine scissors to cut the diaphragm. Cut the sternum along both sides of the xiphoid process to open the chest and expose the heart (Supplementary Figure 2B). 
		NOTE: Be careful to preserve the internal thoracic vessels on both sides; otherwise, it may cause massive bleeding.</li>
		<li>Use toothless tweezers to lift the left ventricle. Insert a 22 G needle into the left ventricular apex along the longitudinal axis of the left ventricle (Supplementary Figure 2C). Meanwhile, observe the rhythmic blood pulsation in the perfusion tube, or the needle may puncture into the right ventricle, which may lead to a poor perfusion effect. 
		NOTE: Toothed tweezer should not be used; otherwise it may cause extra blood leakage from the tweezer holding site.</li>
		<li>Use fine scissors to cut the right atrium (Supplementary Figure 2C), then manually inject 100 mL of ice-cold perfusing fluid at a rate of about 2 mL/s within 1 min. 
		NOTE: When rats&#39; liver and paws turn pale, and no blood flows out from the right atrium, good perfusion can be achieved.</li>
	</ol>
	</li>
	<li>Spinal cord dissection (Figure 1)
	<ol>
		<li>Place the rat in the prone position, and cut the spine at the anterior superior iliac spine (about L4 vertebral level) and the curvature shifting point of the thoracic column (about T6 vertebral level), respectively (Figure 1A). Then, immediately place the isolated spine in the oxygenated ice-cold perfusing solution to wash off the residual blood and fat tissue; this procedure is beneficial for keeping the operative field clean in the subsequent procedures. 
		NOTE: The paraspinal muscles should be reserved, which is conducive for the subsequent fixation of the spine by using an insect pin.</li>
		<li>Immediately transfer the isolated spine to the anatomical tray (Figure 1B) with the dorsal side up and the rostral end close to the operator. Fill the anatomical tray with 50 mL of continuously oxygenated ice-cold cutting solution (Figure 1B).</li>
		<li>Use four insect pins to fix the spine by penetrating the paraspinal muscles (Figure 1B).</li>
		<li>Under the dissection microscope, cut the vertebral pedicles of both sides from the rostral end with the micro-scissor, which can be termed &#34;laminectomy&#34; (Figure 1C). Pay attention not to damage the spinal cord. Meanwhile, use the micro-toothed tweezers to lift the cut vertebral body.</li>
		<li>After the laminectomy, do not separate the spinal cord from the spinal canal immediately. Instead, use a micro-scissor to cut the dura mater along the dorsal midline, which is conducive for nutrient uptake between cells and oxygenated ACSF (Figure 1D). 
		NOTE: Never tear the dura mater. Only cutting the dura mater by micro-scissor is permitted; otherwise, the nerve root and the spinal parenchyma will be seriously damaged!</li>
		<li>Lift the rostral part of the spinal cord, then carefully cut the nerve root with about 1 mm reserved (Figure 1E). After separating the spinal cord from the vertebral canal, use 2 insect pins to fix the spinal cord with the ventral side up (Figure 1F).</li>
		<li>Use a micro-scissor to cut the dura mater along the ventral midline (Figure 1F). Cut off the redundant nerve roots with about 1 mm reserved. 
		NOTE: The nerve is much more tenacious than the spinal cord. If the reserved nerve root is too long (&#62;1 mm), the vibratome cannot cut off the nerve root, which may lead to a serious tear in the spinal parenchyma.</li>
		<li>Use a micro-scissor to separate the lumbar enlargement to a length of 6-7 mm (Figure 1G).</li>
	</ol>
	</li>
	<li>Embedding in the low-melting agarose
	<ol>
		<li>Place the lumbar enlargement on the 35 &#176;slope (Figure 1H) with the dorsal side up and caudal end down. Use an absorbent filter paper to remove abundant water on the tissue surface (Figure 1H).</li>
		<li>Slowly pour the molten agarose gel into the Petri dish containing the lumbar enlargement (Figure 1I). 
		NOTE: Do not pour too fast, or bubbles will accumulate in the gel.</li>
		<li>Place the above Petri dish in the ice-water mixture to cool the gel as soon as possible, which is conducive to maintaining the activity of cells.</li>
		<li>Trim the gel into a 15 mm x 10 mm x 10 mm cube and mount it on the specimen disc with superglue (Figure 1J).</li>
	</ol>
	</li>
	<li>Slicing
	<ol>
		<li>Place the specimen disc into the pre-frozen cutting tray, then pour the ice-cold cutting solution (Figure 1K). Continuously bubble with 95% CO2 and 5% O2 into the cutting tray.</li>
		<li>Set the vibratome parameters: thickness: 350 &#181;m; speed: 0.14-0.16&#160;mm/s, amplitude: 1.0&#160;mm, and vibration frequency: 85 Hz.</li>
		<li>Harvest 2-3 suitable slices per animal. Record 1-2 healthy FG+ motor neurons per slice, with a range of 5-6 cells per animal.</li>
	</ol>
	</li>
	<li>Incubation
	<ol>
		<li>Use cover slide tweezers to clip a slice (Figure 1L) and place it into the incubation chamber filled with continuously oxygenated ACSF. Place the incubation chamber in a water bath at 32 &#176;C for 30 min, and then continue to incubate it at room temperature (RT) for another 30 min prior to recording. 
		&#8203;NOTE: The above procedures, from anesthesia to obtaining the first slice, should be completed within 20-30 min to retain the viability of cells as much as possible. The motor neurons in each slice can maintain their viability for approximately 6-7 h.</li>
	</ol>
	</li>
</ol>
2. Patch-clamp recording with SCS (Figure 2)
<ol>
	<li>Preparations
	<ol>
		<li>Perfuse the recording chamber with continuously bubbled ACSF at a rate of about 1-2 mL/min. Adjust the flow rate individually via the control panel on the peristaltic pump.</li>
		<li>Place a slice into the recording chamber. Use the U-shaped platinum wire with nylon threads to firmly stabilize the slice in place.</li>
		<li>Use an infrared differential interference contrast microscope (IR-DIC) to observe the slice. Under the 4x objective lens, confirm that the length of the dorsal root is about 1 mm. Find the area where the dorsal root enters the parenchyma, then move the central field of vision to this area.</li>
		<li>Connect the pulse generator with custom-made electrodes (Figure 2A).</li>
	</ol>
	</li>
	<li>SCS configuration
	<ol>
		<li>Place the anode of SCS near the dorsal midline via the micromanipulation system (Figure 2B).</li>
		<li>Place the cathode of SCS near the dorsal root entry zone (DREZ) via the micromanipulation system (Figure 2B).</li>
	</ol>
	</li>
	<li>Cell targeting and imaging
	<ol>
		<li>Use IR-DIC with a 10x objective lens roughly find the dorsolateral region of the motor column, where most motor neurons are located. Then, move the central field of vision to this area.</li>
		<li>Switch to a 60x objective lens to find a healthy neuron with a smooth and bright surface and invisible nuclei (Figure 2C,F).</li>
		<li>Slightly turn down the IR intensity and turn on the fluorescence light source. Switch the light filter to the wide band ultraviolet excitation filter (Figure 2D,G), to select an appropriate FG-positive (FG+) motor neuron (Figure 2E,H).</li>
		<li>Use suction electrodes to apply 1x motor threshold stimulation to the dorsal root. If an evoked action potential is detected in the motor neurons (Supplementary Figure 3), it confirms that the activity of the dorsal root is intact. If not, this slice should be discarded.</li>
	</ol>
	</li>
	<li>Patch-clamp recording
	<ol>
		<li>Fill the micropipette with the intracellular solution and insert it into the electrode holder. Use the micromanipulation system to lower the pipette into the ACSF bath. The pipette resistance ranges from 5-8 M&#937;.</li>
		<li>Apply a small amount of positive pressure to the pipette to blow away the dust and cell debris.
		<ol>
			<li>Lower the electrode to approach the cell. When the pipette touches the surface of FG+ neuron, a small indentation of the membrane becomes visible at the level of the tip. Release the positive pressure.</li>
			<li>Then, apply a small amount of negative pressure to the pipette using a syringe. This creates a small amount of suction that pulls the cell membrane into contact with the glass pipette. Always pay attention to the total resistance on the software interface until the resistance value increases to gigaohms (&#62;1 G&#937;). Then, the gigaseal is formed.</li>
		</ol>
		</li>
		<li>Clamp the membrane potential at -70 mV, then press the fast capacitance compensation button on the software interface of the amplifier. Gently apply a transiently negative pressure to rupture the cell membrane, then press the slow capacitance compensation button on the software interface of the amplifier. At this point, a good whole-cell configuration is obtained.</li>
		<li>Switch to current-clamp mode by clicking the IC button on the software interface, and record the resting membrane potential (RMP).</li>
		<li>Apply the SCS for 1-2 s with the amplitude of 1-10 mA, while the pulse width and frequency are fixed at 210 &#181;s and 40 Hz, respectively. Determine the motor threshold by slowly increasing the stimulation amplitude until the first AP is observed.</li>
		<li>Distinguish delayed and immediate firing motor neurons using a 5 s depolarizing current injection around rheobase in the current-clamp mode10,11,12. Immediate firing motor neurons: Low rheobase can induce immediate and repetitive firing with stable firing frequency; Delayed firing motor neurons: High rheobase can induce a delayed onset for repetitive firing with an accelerating firing rate (Figure 3).</li>
		<li>When SCS is turned off, continue to record the membrane potential for capturing the spontaneous APs firing.</li>
		<li>Perform voltage-clamp recordings voltage-clamp recordings for excitatory postsynaptic current (EPSC) when SCS is on and off. The stimulation parameter is 1x motor threshold, 210 &#181;s, 2 Hz.</li>
	</ol>
	</li>
</ol>

Understanding Motor Neuron Responses to Spinal Cord Stimulation

<ol>
	<li>Rowald, A., 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=Activity-dependent+spinal+cord+neuromodulation+rapidly+restores+trunk+and+leg+motor+functions+after+complete+paralysis.">Activity-dependent spinal cord neuromodulation rapidly restores trunk and leg motor functions after complete paralysis.</a> Nature Medicine. 28 (2), 260-271 (2022).</li><li>Kathe, 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=The+neurons+that+restore+walking+after+paralysis.">The neurons that restore walking after paralysis.</a> Nature. 611 (7936), 540-547 (2022).</li><li>Smith, S. J., Buchanan, J., Osses, L. R., Charlton, M. P., Augustine, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+spatial+distribution+of+calcium+signals+in+squid+presynaptic+terminals.">The spatial distribution of calcium signals in squid presynaptic terminals.</a> The Journal of Physiology. 472, 573-593 (1993).</li><li>Augustine, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+transmitter+release+at+the+squid+giant+synapse+by+presynaptic+delayed+rectifier+potassium+current.">Regulation of transmitter release at the squid giant synapse by presynaptic delayed rectifier potassium current.</a> The Journal of Physiology. 431, 343-364 (1990).</li><li>Llin&#225;s, R., McGuinness, T. L., Leonard, C. S., Sugimori, M., Greengard, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intraterminal+injection+of+synapsin+I+or+calcium/calmodulin-dependent+protein+kinase+II+alters+neurotransmitter+release+at+the+squid+giant+synapse.">Intraterminal injection of synapsin I or calcium/calmodulin-dependent protein kinase II alters neurotransmitter release at the squid giant synapse.</a> Proceedings of the National Academy of Sciences of the United States of America. 82 (9), 3035-3039 (1985).</li><li>Formento, E., 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=Electrical+spinal+cord+stimulation+must+preserve+proprioception+to+enable+locomotion+in+humans+with+spinal+cord+injury.">Electrical spinal cord stimulation must preserve proprioception to enable locomotion in humans with spinal cord injury.</a> Nature Neuroscience. 21 (12), 1728-1741 (2018).</li><li>Hari, K., 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=GABA+facilitates+spike+propagation+through+branch+points+of+sensory+axons+in+the+spinal+cord.">GABA facilitates spike propagation through branch points of sensory axons in the spinal cord.</a> Nature Neuroscience. 25 (10), 1288-1299 (2022).</li><li>Sakmann, B., Neher, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patch+clamp+techniques+for+studying+ionic+channels+in+excitable+membranes.">Patch clamp techniques for studying ionic channels in excitable membranes.</a> Annual Review Of Physiology. 46, 455-472 (1984).</li><li>Leroy, F., Lamotte d'Incamps, 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+preparation+of+oblique+spinal+cord+slices+for+ventral+root+stimulation.">The preparation of oblique spinal cord slices for ventral root stimulation.</a> Journal of Visualized Experiments:JoVE. (116), e54525 (2016).</li><li>Sharples, S. A., Miles, G. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maturation+of+persistent+and+hyperpolarization-activated+inward+currents+shapes+the+differential+activation+of+motoneuron+subtypes+during+postnatal+development.">Maturation of persistent and hyperpolarization-activated inward currents shapes the differential activation of motoneuron subtypes during postnatal development.</a> Elife. 10, e71385 (2021).</li><li>Bhumbra, G. S., Beato, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recurrent+excitation+between+motoneurones+propagates+across+segments+and+is+purely+glutamatergic.">Recurrent excitation between motoneurones propagates across segments and is purely glutamatergic.</a> PLoS Biology. 16 (3), e2003586 (2018).</li><li>Leroy, F., Lamotte d'Incamps, B., Imhoff-Manuel, R. D., Zytnicki, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+intrinsic+hyperexcitability+does+not+contribute+to+motoneuron+degeneration+in+amyotrophic+lateral+sclerosis.">Early intrinsic hyperexcitability does not contribute to motoneuron degeneration in amyotrophic lateral sclerosis.</a> Elife. 3, 04046 (2014).</li><li>Tahir, R. A., Pabaney, A. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Therapeutic+hypothermia+and+ischemic+stroke:+A+literature+review.">Therapeutic hypothermia and ischemic stroke: A literature review.</a> Surgical Neurology International. 7, S381-S386 (2016).</li><li>Lu, 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=Management+of+intractable+pain+in+patients+with+implanted+spinal+cord+stimulation+devices+during+the+COVID-19+pandemic+using+a+remote+and+wireless+programming+system.">Management of intractable pain in patients with implanted spinal cord stimulation devices during the COVID-19 pandemic using a remote and wireless programming system.</a> Frontiers in Neuroscience. 14, 594696 (2020).</li><li>Yao, Q., 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=Wireless+epidural+electrical+stimulation+in+combination+with+serotonin+agonists+improves+intraspinal+metabolism+in+spinal+cord+injury+rats.">Wireless epidural electrical stimulation in combination with serotonin agonists improves intraspinal metabolism in spinal cord injury rats.</a> Neuromodulation. 24 (3), 416-426 (2021).</li><li>Arlotti, M., Rahman, A., Minhas, P., Bikson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Axon+terminal+polarization+induced+by+weak+uniform+dc+electric+fields:+a+modeling+study.">Axon terminal polarization induced by weak uniform dc electric fields: a modeling study.</a> 2012 Annual International Conference of the IEEE Engineering in Medicine and Biology Society. , 4575-4578 (2012).</li><li>Espino, 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=Na(V)1.1+is+essential+for+proprioceptive+signaling+and+motor+behaviors.">Na(V)1.1 is essential for proprioceptive signaling and motor behaviors.</a> Elife. 11, e79917 (2022).</li><li>Romer, S. H., Deardorff, A. S., Fyffe, R. E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+molecular+rheostat:+Kv2.1+currents+maintain+or+suppress+repetitive+firing+in+motoneurons.">A molecular rheostat: Kv2.1 currents maintain or suppress repetitive firing in motoneurons.</a> The Journal of Physiology. 597 (14), 3769-3786 (2019).</li><li>Yao, X., 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=Structures+of+the+R-type+human+Ca(v)2.3+channel+reveal+conformational+crosstalk+of+the+intracellular+segments.">Structures of the R-type human Ca(v)2.3 channel reveal conformational crosstalk of the intracellular segments.</a> Nature Communications. 13 (1), 7358 (2022).</li><li>Bandres, M. F., Gomes, J., McPherson, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+multimodal+neural+transmission+suggests+that+adult+spinal+networks+maintain+an+intrinsic+state+of+readiness+to+execute+sensorimotor+behaviors.">Spontaneous multimodal neural transmission suggests that adult spinal networks maintain an intrinsic state of readiness to execute sensorimotor behaviors.</a> Journal Of Neuroscience. 41 (38), 7978-7990 (2021).</li><li>Manuel, M., Heckman, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+intracellular+recording+of+a+lumbar+motoneuron+and+the+force+produced+by+its+motor+unit+in+the+adult+mouse+in+vivo.">Simultaneous intracellular recording of a lumbar motoneuron and the force produced by its motor unit in the adult mouse in vivo.</a> Journal of Visualized Experiments: JoVE. (70), e4312 (2012).</li><li>Luo, X., Wang, S., Rutkove, S. B., Sanchez, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonhomogeneous+volume+conduction+effects+affecting+needle+electromyography:+an+analytical+and+simulation+study.">Nonhomogeneous volume conduction effects affecting needle electromyography: an analytical and simulation study.</a> Physiological Measurement. 42 (11), (2021).</li><li>Barra, B., 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=Epidural+electrical+stimulation+of+the+cervical+dorsal+roots+restores+voluntary+upper+limb+control+in+paralyzed+monkeys.">Epidural electrical stimulation of the cervical dorsal roots restores voluntary upper limb control in paralyzed monkeys.</a> Nature Neuroscience. 25 (7), 924-934 (2022).</li><li>Powell, M. P., 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=Epidural+stimulation+of+the+cervical+spinal+cord+for+post-stroke+upper-limb+paresis.">Epidural stimulation of the cervical spinal cord for post-stroke upper-limb paresis.</a> Nature Medicine. 29 (3), 689-699 (2023).</li><li>Wenger, N., 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=Spatiotemporal+neuromodulation+therapies+engaging+muscle+synergies+improve+motor+control+after+spinal+cord+injury.">Spatiotemporal neuromodulation therapies engaging muscle synergies improve motor control after spinal cord injury.</a> Nature Medicine. 22 (2), 138-145 (2016).</li><li>&#214;zyurt, M. G., Ojeda-Alonso, J., Beato, M., Nascimento, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+longitudinal+lumbar+spinal+cord+preparations+to+study+sensory+and+recurrent+motor+microcircuits+of+juvenile+mice.">In vitro longitudinal lumbar spinal cord preparations to study sensory and recurrent motor microcircuits of juvenile mice.</a> Journal of Neurophysiology. 128 (3), 711-726 (2022).</li><li>Moraud, E. 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=Mechanisms+underlying+the+neuromodulation+of+spinal+circuits+for+correcting+gait+and+balance+deficits+after+spinal+cord+injury.">Mechanisms underlying the neuromodulation of spinal circuits for correcting gait and balance deficits after spinal cord injury.</a> Neuron. 89 (4), 814-828 (2016).</li><li>Capogrosso, 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=A+computational+model+for+epidural+electrical+stimulation+of+spinal+sensorimotor+circuits.">A computational model for epidural electrical stimulation of spinal sensorimotor circuits.</a> Journal of Neuroscience. 33 (49), 19326-19340 (2013).</li></ol>

The movement information modulated by SCS is finally converged to the motor neurons. Therefore, taking the motor neurons as the research target may simplify the study design and reveal the neuromodulation mechanism of SCS more directly. To simultaneously record diverse stimulus characteristics and cellular responses, a patch-clamp is a good method to study the electrophysiological characteristics at a single-cell scale. However, there are still some difficulties, including how to maintain cell viability, how to quickly s...

Spinal cord stimulation (SCS) can effectively restore locomotor function after spinal cord injury (SCI). Andreas Rowald et al. reported that SCS enables lower limb locomotor and trunk function within a single day1. Exploring the biological mechanism of SCS for locomotor recovery is a critical and trending research field for developing a more precise SCS strategy. For example, Gr&#233;goire Courtine&#39;s team demonstrated that excitatory Vsx2 interneuron and Hoxa10 neurons in the spinal cord are the key neurons to response to SCS, and cell-specific neuromodulation is feasible to restore the rat walking ability after SCI2. However, few studies focus on the electrical mechanism of SCS at a single-cell scale. Although it is well-known that the suprathreshold direct current stimulus can elicit the action potentials (APs) in the classic squid experiment3,4,5, how the pulsed alternating electrical stimulation, such as SCS, affects the motor signal generation is still unclear.
Given the complexity of intraspinal neural circuits, appropriate selection for cell population is important for investigating the electrical mechanism of SCS. Although SCS restores motor function by activating the proprioceptive pathway6, the motor neurons are the final unit to execute the motor command, derived from integrating proprioception information afferent input7. Therefore, directly studying the electrical characteristics of motor neurons with SCS can help us understand the underlying logic of spinal motor modulation.
As we know, patch-clamp is the golden-standard method for cellularly electrophysiological recording with extremely high spatiotemporal resolution8. Therefore, this study describes a method using a patch clamp to study the electrical responses of motor neurons to SCS. Compared with the brain patch-clamp9, the spinal cord patch-clamp is more difficult due to the following reasons: (1) The spinal cord is protected by the vertebral canal with tiny volume, which requires very fine micromanipulation and rigorous ice-cold maintenance to obtain better cell viability. (2) Because the spinal cord is too slender to be secured on the cutting tray, it should be immersed in low-melting point agarose and trimmed after solidification.
Hence, this method provides technical details in dissecting the spinal cord and maintaining the cell viability at the same time so as to smoothly study the electrical mechanism of SCS on motor neurons and avoid unnecessary trials and mistakes.

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		<tr>
			<td>Adenosine 5&#8217;-triphosphate magnesium salt</td>
			<td>Sigma</td>
			<td>A9187</td>
			<td></td>
		</tr>
		<tr>
			<td>Ascorbic Acid</td>
			<td>Sigma</td>
			<td>A4034</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2&#183;2H2O</td>
			<td>Sigma</td>
			<td>C5080</td>
			<td></td>
		</tr>
		<tr>
			<td>Choline Chloride</td>
			<td>Sigma</td>
			<td>C7527</td>
			<td></td>
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		<tr>
			<td>Cover slide tweezers</td>
			<td>VETUS</td>
			<td>36A-SA</td>
			<td>Clip a slice</td>
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		<tr>
			<td>D-Glucose</td>
			<td>Sigma</td>
			<td>G8270</td>
			<td></td>
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		<tr>
			<td>EGTA</td>
			<td>Sigma</td>
			<td>E4378</td>
			<td></td>
		</tr>
		<tr>
			<td>Fine scissors</td>
			<td>RWD Life Science</td>
			<td>S12006-10</td>
			<td>Cut the diaphragm</td>
		</tr>
		<tr>
			<td>Fluorescence Light Source</td>
			<td>Olympus&#160;</td>
			<td>U-HGLGPS</td>
			<td></td>
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		<tr>
			<td>Fluoro-Gold</td>
			<td>Fluorochrome</td>
			<td>Fluorochrome</td>
			<td>Label the motor neuron</td>
		</tr>
		<tr>
			<td>Guanosine 5&#8242;-triphosphate sodium salt hydrate</td>
			<td>Sigma</td>
			<td>G8877</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma</td>
			<td>H3375</td>
			<td></td>
		</tr>
		<tr>
			<td>infrared CCD camera</td>
			<td>Dage-MTI</td>
			<td>IR-1000E</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma</td>
			<td>P5405</td>
			<td></td>
		</tr>
		<tr>
			<td>K-gluconate</td>
			<td>Sigma</td>
			<td>P1847</td>
			<td></td>
		</tr>
		<tr>
			<td>Low melting point agarose</td>
			<td>Sigma</td>
			<td>A9414</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4&#183;7H2O</td>
			<td>Sigma</td>
			<td>M2773</td>
			<td></td>
		</tr>
		<tr>
			<td>Micromanipulator&#160;</td>
			<td>Sutter Instrument&#160;</td>
			<td>MP-200</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipette puller</td>
			<td>Sutter instrument</td>
			<td>P1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro-scissors&#160;</td>
			<td>Jinzhong</td>
			<td>wa1020</td>
			<td>Laminectomy</td>
		</tr>
		<tr>
			<td>Microscope for anatomy</td>
			<td>Olympus&#160;</td>
			<td>SZX10</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope for ecletrophysiology</td>
			<td>Olympus&#160;</td>
			<td>BX51WI</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro-toothed tweezers</td>
			<td>RWD Life Science</td>
			<td>F11008-09</td>
			<td>Lift the cut vertebral body</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma</td>
			<td>S5886</td>
			<td></td>
		</tr>
		<tr>
			<td>NaH2PO4</td>
			<td>Sigma</td>
			<td>S8282</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Sigma</td>
			<td>V900182</td>
			<td></td>
		</tr>
		<tr>
			<td>Na-Phosphocreatine</td>
			<td>Sigma</td>
			<td>P7936</td>
			<td></td>
		</tr>
		<tr>
			<td>Objective lens for ecletrophysiology</td>
			<td>Olympus&#160;</td>
			<td>LUMPLFLN60XW</td>
			<td>working distance 2 mm&#160;</td>
		</tr>
		<tr>
			<td>Osmometer&#160;</td>
			<td>Advanced&#160;</td>
			<td>FISKE 210</td>
			<td></td>
		</tr>
		<tr>
			<td>Patch-clamp amplifier&#160;</td>
			<td>Axon&#160;</td>
			<td>Multiclamp 700B</td>
			<td></td>
		</tr>
		<tr>
			<td>Patch-clamp digitizer</td>
			<td>Axon&#160;</td>
			<td>Digidata 1550B</td>
			<td></td>
		</tr>
		<tr>
			<td>pH meter&#160;</td>
			<td>Mettler Toledo&#160;</td>
			<td>FE28</td>
			<td></td>
		</tr>
		<tr>
			<td>Slice Anchor</td>
			<td>Multichannel system</td>
			<td>SHD-27H</td>
			<td></td>
		</tr>
		<tr>
			<td>Spinal cord stimulatior</td>
			<td>PINS</td>
			<td>T901</td>
			<td></td>
		</tr>
		<tr>
			<td>Toothed tweezer</td>
			<td>RWD Life Science</td>
			<td>F13030-10</td>
			<td>Lift the xiphoid</td>
		</tr>
		<tr>
			<td>Vibratome</td>
			<td>Leica</td>
			<td>VT1200S</td>
			<td></td>
		</tr>
		<tr>
			<td>Wide band ultraviolet excitation filter</td>
			<td>Olympus&#160;</td>
			<td>U-MF2</td>
			<td></td>
		</tr>
	</tbody>
</table>

the ex vivo preparation of spinal cord slice for the whole-cell patch-clamp recording in motor neurons during spinal cord stimulation

Spinal cord stimulation (SCS) can effectively restore locomotor function after spinal cord injury (SCI). Because the motor neurons are the final unit to execute sensorimotor behaviors, directly studying the electrical responses of motor neurons with SCS can help us understand the underlying logic of spinal motor modulation. To simultaneously record diverse stimulus characteristics and cellular responses, a patch-clamp is a good method to study the electrophysiological characteristics at a single-cell scale. However, there are still some complex difficulties in achieving this goal, including maintaining cell viability, quickly separating the spinal cord from the bony structure, and using the SCS to successfully induce action potentials. Here, we present a detailed protocol using patch-clamp to study the electrical responses of motor neurons to SCS with high spatiotemporal resolution, which can help researcher improve their skills in separating the spinal cord and maintaining the cell viability at the same time to smoothly study the electrical mechanism of SCS on motor neuron and avoid unnecessary trial and mistake.

Author Spotlight: Advancing Spinal Cord Stimulation - Exploring the Cellular Responses of Motor Neurons Through Patch-Clamp Electrophysiology 

The Ex vivo Preparation of Spinal Cord Slice for the Whole-Cell Patch-Clamp Recording in Motor Neurons During Spinal Cord Stimulation

Spinal cord stimulation can help patients resolve most motion functions after injury. Most neurons are to execute sensory mode behaviors. Studying the electric response of most neurons can aid in understanding the underlying logic of spinal load neuromodulation.A patch clamp is the golden standard method for cellular electrophysiological recordings with the extremely high spatial temporal resolution. Therefore, this study describes a method using a patch clamp to simultaneously record the aortas stimulus characteristics and cellular responses of motor neurons at a single-cell scale. Compared with the brain patch clamp, the spinal cord patch clamp is more difficult, because the spinal cord is well protected by the vertebral canal with tiny volume.Therefore, this protocol provides technical details in quickly micro dissecting the spinal cord and reverse maintenance to obtain better cell viability. Patch clamp allows a unique understanding of the synaptic transmissions and the understanding of action potentials, coding pattern activities by the spinal cord stimulation.

Thanks to the rigorous low-temperature maintenance during the fine operation (Supplementary Figure 1, Supplementary Figure 2,&#160;and Figure 1), the cell viability was good enough to perform subsequent electrophysiological recordings. To simulate the clinical scenario as much as possible, we used micromanipulation to place the SCS cathode and anode near the dorsal midline and DREZ, respectively (Figure 2), which could initiate neural signal in ...

Watch this Scientific Journal Video about Advancing Spinal Cord Stimulation - Exploring the Cellular Responses of Motor Neurons Through Patch-Clamp Electrophysiology at JoVE.com

This protocol describes a method using a patch-clamp to study the electrical responses of motor neurons to spinal cord stimulation (SCS) with high spatiotemporal resolution, which can help researchers improve their skills in separating the spinal cord and maintaining cell viability simultaneously.

Spinal cord stimulation (SCS) can effectively restore locomotor function after spinal cord injury (SCI). Because the motor neurons are the final unit to ...

the-ex-vivo-preparation-spinal-cord-slice-for-whole-cell-patch-clamp

Research

JoVE Journal

Neuroscience

Spinal Cord Dissection for the Whole-Cell Patch-Clamp Recording in Motor Neurons

After exposing the heart of an anesthetized rat, cut the right atrium using fine scissors and inject 100 milliliters of chilled perfusing fluid at approximately two milliliters per second within one minute. Position the rat in the prone position. Cut the spine at the anterior superior iliac spine and the curvature shifting point of the thoracic column.Immediately place the isolated spine into the oxygenated ice cold perfusing solution to wash off residual blood and fat tissue. Then transfer the isolated spine to the anatomical tray with its dorsal side up and the rostral end near the operator. Fill the tray with 50 milliliters of continuously oxygenated ice cold cutting solution.Under a dissection microscope, cut the vertebral pedicles on both sides from the rostral end using micro scissors. Next, delicately sever the dura mater along its dorsal midline with micro scissors. Lift the rostral part of the spinal cord carefully and cut the nerve root, leaving about one millimeter reserved.After the spinal cord has been separated from the vertebral canal, secure it with the ventral side facing up using two insect pins. Trim any excessive nerve roots, leaving about one millimeter intact. Then separate the lumbar enlargement to a length of six to seven millimeters using a micro scissor.

Preparation of Spinal Cord Slice for the Whole-Cell Patch-Clamp Recording in Motor Neurons

After dissecting the spinal cord and separating the lumbar enlargement, place the lumbar enlargement on a 35 degree slope with the dorsal side up and the caudal side down. Absorb any excess water on the tissue surface using an absorbent filter paper. Carefully pour the molten agarose gel into the Petri dish containing the lumbar enlargement.Position the Petri dish in the ice water mixture to ensure rapid gel cooling. Shape the gel into a cube of 15 by 10 by 10 millimeters, and mount it onto the specimen disc using super glue. Adjust the vibratome settings to a thickness of 350 micrometers, a speed of 0.14 to 0.16 millimeters per second, an amplitude of one millimeter, and a vibration frequency of 85 hertz.Now, use the cover slide tweezers to clip a slice and place it into the incubation chamber, filled with continuously oxygenated artificial cerebrospinal fluid.

Patch-Clamp Recording to Study the Electrical Responses of Motor Neurons to Spinal Cord Stimulation

To begin, place the prepared spinal cord slice in the recording chamber. Then place the anode of the micro-manipulation system near the dorsal midline in the cathode close to the dorsal root entry zone for proper spinal cord stimulator positioning. Now switch to a 60X objective lens to identify a healthy neuron having a smooth and bright surface without visible nuclei.Slightly decrease the infrared intensity, turn on the fluorescent light source, and adjust the light filter to the wideband ultraviolet excitation option. Now, select an appropriate Fluoro-Gold-positive motor neuron and gradually lower the electrode until it is near the neuron. As the pipette contacts its surface, look for a small membrane indentation at the tip level and release the previously-applied positive pressure.Then apply negative pressure to the pipette using a syringe and wait until the resistance value rises to gigaohms on the software interface. Clamp the membrane potential at minus 70 millivolts. Press the fast capacitance compensation button on the amplifier's software interface, then apply a brief negative pressure to rupture the cell membrane and press the slow capacitance compensation button on the amplifier's software interface.Apply the spinal cord stimulation for one to two seconds keeping the amplitude between one and 10 milliamperes. Determine the motor threshold by gradually increasing the stimulation amplitude until the first action potential is observed. Distinguish delayed and immediate firing motor neurons using a five-second depolarizing current injection around rheobase in the current clamp mode.After turning off the spinal cord stimulation, continue recording the membrane potentials to capture the spontaneous action potentials firing. When the amplitude of spinal cord stimulation was raised, the membrane potential was increased, and the action potentials were triggered every 10 to 20 pulses. After the spinal cord stimulation was turned off, the neuron fired a series of spontaneous action potentials for a short period of time.Then, the resting membrane potential returned to minus 65 millivolts.

1.4K Views.  Tsinghua University.  This protocol describes a method using a patch-clamp to study the electrical responses of motor neurons to spinal cord stimulation (SCS) with high spatiotemporal resolution, which can help researchers improve their skills in separating the spinal cord and maintaining cell viability simultaneously.

Understanding Motor Neuron Responses to Spinal Cord Stimulation

Summary