Spinal Cord Stimulation In Rats Research Articles

Frequency-Dependent Neural Modulation of Dorsal Horn Neurons by Kilohertz Spinal Cord Stimulation in Rats.

Kilohertz high-frequency spinal cord stimulation (kHF-SCS) is a rapidly advancing neuromodulatory technique in the clinical management of chronic pain. However, the precise cellular mechanisms underlying kHF-SCS-induced paresthesia-free pain relief, as well as the neural responses within spinal pain circuits, remain largely unexplored. In this study, using a novel preparation, we investigated the impact of varying kilohertz frequency SCS on dorsal horn neuron activation. Employing calcium imaging on isolated spinal cord slices, we found that extracellular electric fields at kilohertz frequencies (1, 3, 5, 8, and 10 kHz) induce distinct patterns of activation in dorsal horn neurons. Notably, as the frequency of extracellular electric fields increased, there was a clear and significant monotonic escalation in neuronal activity. This phenomenon was observed not only in superficial dorsal horn neurons, but also in those located deeper within the dorsal horn. Our study demonstrates the unique patterns of dorsal horn neuron activation in response to varying kilohertz frequencies of extracellular electric fields, and we contribute to a deeper understanding of how kHF-SCS induces paresthesia-free pain relief. Furthermore, our study highlights the potential for kHF-SCS to modulate sensory information processing within spinal pain circuits. These insights pave the way for future research aimed at optimizing kHF-SCS parameters and refining its therapeutic applications in the clinical management of chronic pain.

Enhancing spinal cord stimulation-induced pain inhibition by augmenting endogenous adenosine signalling after nerve injury in rats

BackgroundThe mechanisms for spinal cord stimulation (SCS) to alleviate chronic pain are only partially known. We aimed to elucidate the roles of adenosine A1 and A3 receptors (A1R, A3R) in the inhibition of spinal nociceptive transmission by SCS, and further explored whether 2′-deoxycoformycin (dCF), an inhibitor of adenosine deaminase, can potentiate SCS-induced analgesia. MethodsWe used RNAscope and immunoblotting to examine the distributions of adora1 and adora3 expression, and levels of A1R and A3R proteins in the spinal cord of rats after tibial-spared nerve injury (SNI-t). Electrophysiology recording was conducted to examine how adenosine receptor antagonists, virus-mediated adora3 knockdown, and dCF affect SCS-induced inhibition of C-fibre-evoked spinal local field potential (C-LFP). ResultsAdora1 was predominantly expressed in neurones, whereas adora3 is highly expressed in microglial cells in the rat spinal cord. Spinal application of antagonists (100 μl) of A1R (8-cyclopentyl-1,3-dipropylxanthine [DPCPX], 50 μM) and A3R (MRS1523, 200 nM) augmented C-LFP in SNI-t rats (DPCPX: 1.39 [0.18] vs vehicle: 0.98 [0.05], P=0.046; MRS1523: 1.21 [0.07] vs vehicle: 0.91 [0.03], P=0.002). Both drugs also blocked inhibition of C-LFP by SCS. Conversely, dCF (0.1 mM) enhanced SCS-induced C-LFP inhibition (dCF: 0.60 [0.04] vs vehicle: 0.85 [0.02], P<0.001). In the behaviour study, dCF (100 nmol 15 μl−1, intrathecal) also enhanced inhibition of mechanical hypersensitivity by SCS in SNI-t rats. ConclusionsSpinal A1R and A3R signalling can exert tonic suppression and also contribute to SCS-induced inhibition of spinal nociceptive transmission after nerve injury. Inhibition of adenosine deaminase may represent a novel adjuvant pharmacotherapy to enhance SCS-induced analgesia.

ID: 208638 Evoked Compound Action Potentials and Closed-Loop Spinal Cord Stimulation in Neuropathic Rats: Feasibility Study

Evoked compound action potentials (ECAPs) identified during spinal cord stimulation (SCS) in humans have been observed to closely correlate with the activation of the stimulation-induced sensory perception perceived as paresthesia1. We recently demonstrated feasibility of recording ECAPs from the spinal cord in naïve rats using uniquely designed equipment2. Here, we extended our experiments to provide electrophysiological characteristics of the response of dorsal column axons to SCS based on ECAPs recording in rats with neuropathic pain. Moreover, we demonstrate the ability to deliver ECAP-controlled closed-loop SCS in neuropathic pain rats, which has been proven superior to open-loop stimulation in humans3,4.

ID: 202712 Loss of Conduction Fidelity in Dorsal Column Axons During Spinal Cord Stimulation With Conventional Frequencies

Epidural spinal cord stimulation (SCS) is an effective therapy for chronic pain, but there remains an opportunity to increase efficacy and response rates. Conventional paresthesia-producing SCS delivers pulse repetition frequencies < 200 Hz. SCS produces analgesia by activating large dorsal column axons which innervate inhibitory interneurons in the dorsal horn (Gate control theory). This understanding and contemporary research presume that dorsal column (DC) axons propagate faithfully every time a stimulation pulse is delivered. However, recent computational studies suggested that there may be a loss of conduction fidelity, or faithful propagation of an action potential for each stimulation pulse, depending on the stimulation frequency. We measured the response of single dorsal column axons to epidural SCS in healthy urethane-anesthetized Sprague-Dawley rats.

Electrically Evoked Compound Action Potentials in Spinal Cord Stimulation: Implications for Preclinical Research Models

ObjectivesThe study aimed to assess the feasibility of recording electrically evoked compound action potentials (ECAPs) from the rat spinal cord. To achieve this, we characterized electrophysiological responses of dorsal column (DC) axons from electrical stimulation and quantified the relationship between ECAP and motor thresholds (ECAPTs and MTs). Material and MethodsNaïve, anesthetized, and freely behaving rats were implanted with a custom-made epidural spinal cord stimulation (SCS) lead. Epidural stimulation and recordings were performed on the same lead using specifically designed equipment. ResultsThe ECAPs recorded from the rat spinal cord demonstrated the expected triphasic morphology. Using 20 μsec pulse duration and 2 Hz frequency rate, the current required in anesthetized rats to generate ECAPs was 0.13 ± 0.02 mA, while the average current required to observe MT was 1.49 ± 0.14 mA. In unanesthetized rats, the average current required to generate ECAPs was 0.09 ± 0.02 mA, while the average current required to observe MT was 0.27 ± 0.04 mA. Thus, there was a significant difference between the ECAPT and MT in both anesthetized and unanesthetized rats (MT was 13.39 ± 2.40 and 2.84 ± 0.33 times higher than ECAPT, respectively). Signal analysis revealed average conduction velocities (CVs) suggesting that predominantly large, myelinated fibers were activated. In addition, a morphometric evaluation of spinal cord slices indicated that the custom-made lead may preferentially activate DC axons. ConclusionsThis is the first evidence demonstrating the feasibility of recording ECAPs from the rat spinal cord, which may be more useful in determining parameters of SCS in preclinical SCS models than MTs. Thus, this approach may allow for the development of a novel model of SCS in rats with chronic pain that will translate better between animals and humans.

A flexible electrode array for determining regions of motor function activated by epidural spinal cord stimulation in rats with spinal cord injury.

Epidural stimulation of the spinal cord is a promising technique for the recovery of motor function after spinal cord injury. The key challenges within the reconstruction of motor function for paralyzed limbs are the precise control of sites and parameters of stimulation. To activate lower-limb muscles precisely by epidural spinal cord stimulation, we proposed a high-density, flexible electrode array. We determined the regions of motor function that were activated upon epidural stimulation of the spinal cord in a rat model with complete spinal cord, which was established by a transection method. For evaluating the effect of stimulation, the evoked potentials were recorded from bilateral lower-limb muscles, including the vastus lateralis, semitendinosus, tibialis anterior, and medial gastrocnemius. To determine the appropriate stimulation sites and parameters of the lower muscles, the stimulation characteristics were studied within the regions in which motor function was activated upon spinal cord stimulation. In the vastus lateralis and medial gastrocnemius, these regions were symmetrically located at the lateral site of L1 and the medial site of L2 vertebrae segment, respectively. The tibialis anterior and semitendinosus only responded to stimulation simultaneously with other muscles. The minimum and maximum stimulation threshold currents of the vastus lateralis were higher than those of the medial gastrocnemius. Our results demonstrate the ability to identify specific stimulation sites of lower muscles using a high-density and flexible array. They also provide a reference for selecting the appropriate conditions for implantable stimulation for animal models of spinal cord injury. This study was approved by the Animal Research Committee of Southeast University, China (approval No. 20190720001) on July 20, 2019.

Spinal cord fMRI with MB-SWIFT for assessing epidural spinal cord stimulation in rats.

PurposeElectrical epidural spinal cord stimulation (SCS) is used as a treatment for chronic pain as well as to partially restore motor function after a spinal cord injury. Monitoring the spinal cord activity during SCS with fMRI could provide important and objective measures of integrative responses to treatment. Unfortunately, spinal cord fMRI is severely challenged by motion and susceptibility artifacts induced by the implanted electrode and bones. This pilot study introduces multi‐band sweep imaging with Fourier transformation (MB‐SWIFT) technique for spinal cord fMRI during SCS in rats. Given the close to zero acquisition delay and high bandwidth in 3 dimensions, MB‐SWIFT is demonstrated to be highly tolerant to motion and susceptibility‐induced artifacts and thus holds promise for fMRI during SCS.MethodsMB‐SWIFT with 0.78 × 0.78 × 1.50 mm3 spatial resolution and 3‐s temporal resolution was used at 9.4 Tesla in rats undergoing epidural SCS at different frequencies. Its performance was compared with spin echo EPI. The origin of the functional contrast was also explored using suppression bands.ResultsMB‐SWIFT was tolerant to electrode‐induced artifacts and respiratory motion, leading to substantially higher fMRI sensitivity than spin echo fMRI. Clear stimulation frequency‐dependent responses to SCS were detected in the rat spinal cord close to the stimulation site. The origin of MB‐SWIFT fMRI signals was consistent with dominant inflow effects.ConclusionfMRI of the rat spinal cord during SCS can be consistently achieved with MB‐SWIFT, thus providing a valuable experimental framework for assessing the effects of SCS on the central nervous system.

Modulation of Spinal Nociceptive Transmission by Sub-Sensory Threshold Spinal Cord Stimulation in Rats After Nerve Injury

High-frequency spinal cord stimulation (SCS) administered below the sensory threshold (subparesthetic) can inhibit pain, but the mechanisms remain obscure. We examined how different SCS paradigms applied at intensities below the threshold of Aβ-fiber activation (sub-sensory threshold) affect spinal nociceptive transmission in rats after an L5 spinal nerve ligation (SNL). Electrophysiology was used to record local field potential (LFP) at L4 spinal cord before, during, and 0-60 min after SCS in SNL rats. LFP was evoked by high-intensity paired-pulse test stimulation (5 mA, 0.2 msec, 400 msec interval) at the sciatic nerve. Epidural SCS was delivered through a miniature electrode placed at T13-L1 and L2-L3 spinal levels. Four patterns of SCS (200 Hz, 1 msec; 500 Hz, 0.5 msec; 1200 Hz; 0.2 msec; 10,000 Hz, 0.024 msec, 30 min, bipolar) were tested at 90% Aβ-threshold as a subthreshold intensity. As a positive control, traditional SCS (50 Hz, 0.2 msec) was tested at 100% Aβ-plateau as a suprathreshold intensity. Traditional suprathreshold SCS at T13-L1 level significantly reduced LFP to C-fiber inputs (C-LFP). Subthreshold SCS of 200 and 500 Hz, but not 1200 or 10,000 Hz, also reduced C-LFP, albeit to a lesser extent than did traditional SCS (n = 7-10/group). When SCS was applied at the L2-L3 level, only traditional SCS and subthreshold SCS of 200 Hz inhibited C-LFP (n = 8-10/group). Traditional suprathreshold SCS acutely inhibits spinal nociceptive transmission. Low-frequency subthreshold SCS with a long pulse width (200 Hz, 1 msec), but not higher-frequency SCS, also attenuates C-LFP.

Burst and Tonic Spinal Cord Stimulation Both Activate Spinal GABAergic Mechanisms to Attenuate Pain in a Rat Model of Chronic Neuropathic Pain.

BackgroundExperimental and clinical studies have shown that tonic spinal cord stimulation (SCS) releases gamma‐aminobutyric acid (GABA) in the spinal dorsal horn. Recently, it was suggested that burst SCS does not act via spinal GABAergic mechanisms. Therefore, we studied spinal GABA release during burst and tonic SCS, both anatomically and pharmacologically, in a well‐established chronic neuropathic pain model.MethodsAnimals underwent partial sciatic nerve ligation (PSNL). Quantitative immunohistochemical (IHC) analysis of intracellular GABA levels in the lumbar L4 to L6 dorsal spinal cord was performed after 60 minutes of burst, tonic, or sham SCS in rats that had undergone PSNL (n = 16). In a second pharmacological experiment, the effects of intrathecal administration of the GABAA antagonist bicuculline (5 μg) and the GABAB antagonist phaclofen (5 μg) were assessed. Paw withdrawal thresholds to von Frey filaments of rats that had undergone PSNL (n = 20) were tested during 60 minutes of burst and tonic SCS 30 minutes after intrathecal administration of the drugs.ResultsQuantitative IHC analysis of GABA immunoreactivity in spinal dorsal horn sections of animals that had received burst SCS (n = 5) showed significantly lower intracellular GABA levels when compared to sham SCS sections (n = 4; P = 0.0201) and tonic SCS sections (n = 7; P = 0.0077). Intrathecal application of the GABAA antagonist bicuculline (5 μg; n = 10) or the GABAB antagonist phaclofen (5 μg; n = 10) resulted in ablation of the analgesic effect for both burst SCS and tonic SCS.ConclusionsIn conclusion, our anatomical and pharmacological data demonstrate that, in this well‐established chronic neuropathic animal model, the analgesic effects of both burst SCS and tonic SCS are mediated via spinal GABAergic mechanisms.

The Impact of Electrical Charge Delivery on Inhibition of Mechanical Hypersensitivity in Nerve-Injured Rats by Sub-Sensory Threshold Spinal Cord Stimulation

Spinal cord stimulation (SCS) represents an important neurostimulation therapy for pain. A new ultra-high frequency (10,000 Hz) SCS paradigm has shown improved pain relief without eliciting paresthesia. We aim to determine whether sub-sensory threshold SCS of lower frequencies also can inhibit mechanical hypersensitivity in nerve-injured rats and examine how electric charge delivery of stimulation may affect pain inhibition by different patterns of subthreshold SCS. We used a custom-made quadripolar electrode (Medtronic Inc., Minneapolis, MN, USA) to provide bipolar SCS epidurally at the T10 to T12 vertebral level. According to previous findings, SCS was tested at 40% of the motor threshold, which is considered to be a sub-sensory threshold intensity in rats. Paw withdrawal thresholds to punctate mechanical stimulation were measured before and after SCS in rats that received an L5 spinal nerve ligation. Both 10,000 Hz (10 kHz, 0.024 msec) and lower frequencies (200 Hz, 1 msec; 500 Hz, 0.5 msec; 1200 Hz; 0.2 msec) of subthreshold SCS (120 min) attenuated mechanical hypersensitivity, as indicated by increased paw withdrawal thresholds after stimulation in spinal nerve ligation rats. Pain inhibition from different patterns of subthreshold SCS was not governed by individual stimulation parameters. However, correlation analysis suggests that pain inhibition from 10 kHz subthreshold SCS in individual animals was positively correlated with the electric charges delivered per second (electrical dose). Inhibition of neuropathic mechanical hypersensitivity can be achieved with low-frequency subthreshold SCS by optimizing the electric charge delivery, which may affect the effect of SCS in individual animals.

Enzyme scaffolding for metabolic engineering endeavors

Spinal cord stimulation (SCS) represents an important neurostimulation therapy for pain. A new ultra-high frequency (10,000 Hz) SCS paradigm has shown improved pain relief without eliciting paresthesia. We aim to determine whether sub-sensory threshold SCS of lower frequencies also can inhibit mechanical hypersensitivity in nerve-injured rats and examine how electric charge delivery of stimulation may affect pain inhibition by different patterns of subthreshold SCS.Materials and Methods: We used a custom-made quadripolar electrode (Medtronic Inc., Minneapolis, MN, USA) to provide bipolar SCS epidurally at the T10 to T12 vertebral level. According to previous findings, SCS was tested at 40% of the motor threshold, which is considered to be a sub-sensory threshold intensity in rats. Paw withdrawal thresholds to punctate mechanical stimulation were measured before and after SCS in rats that received an L5 spinal nerve ligation.Results: Both 10,000 Hz (10 kHz, 0.024 msec) and lower frequencies (200 Hz, 1 msec; 500 Hz, 0.5 msec; 1200 Hz; 0.2 msec) of subthreshold SCS (120 min) attenuated mechanical hypersensitivity, as indicated by increased paw withdrawal thresholds after stimulation in spinal nerve ligation rats. Pain inhibition from different patterns of subthreshold SCS was not governed by individual stimulation parameters. However, correlation analysis suggests that pain inhibition from 10 kHz subthreshold SCS in individual animals was positively correlated with the electric charges delivered per second (electrical dose).Conclusions: Inhibition of neuropathic mechanical hypersensitivity can be achieved with low-frequency subthreshold SCS by optimizing the electric charge delivery, which may affect the effect of SCS in individual animals.

Applying Multichannel Optogenetic System for Epidural Spinal Cord Stimulation in Rats.

This study reports on the technique of applying multichannel optogenetic system to spinal cord stimulation in rats. Epidural spinal cord stimulation has been shown to reactivate spinalized hind limb motion; however, the stimulating parameters and detailed mechanism remain unclear. In order to utilize the high spatial resolution and cell type selectivity of optogenetics for studying the mechanism behind epidural spinal cord stimulation, a multichannel optical fiber bundle was designed, composed of 720 optical fibers of 200 $\mu $m diameter arranged in a 48$\times $ textbf15 matrix cover the vertebral columns of rats from level T13 to L2. The stimulating location was controlled by changing the direction of projection of a laser diode, and the appropriate projecting angle to obtain the maximum optical power output of each fiber was determined by a hill-climbing algorithm. A spinal cord window was developed to fit the head of the optical fiber bundle onto the dorsal part of rat spinal cord. Preliminary test in a rat revealed different stimulating area distribution of the optogenetically induced tibialis anterior (TA) and medial gastrocnemius (MG) muscle reactions and demonstrated the capability of the system for in-vivo study.

Effects of endogenous nitric oxide on adrenergic nerve-mediated vasoconstriction and calcitonin gene-related peptide-containing nerve-mediated vasodilation in pithed rats

Vascular adrenergic nerves mainly regulate the tone of blood vessels. Calcitonin gene-related peptide-containing (CGRPergic) vasodilator nerves also participate in the regulation of vascular tone. Furthermore, there are nitric oxide (NO)-containing (nitrergic) nerves, which include NO in blood vessels as vasodilator nerves, but it remains unclear whether nitrergic nerves participate in vascular regulation. The present study investigated the role of nitrergic nerves in vascular responses to spinal cord stimulation (SCS) and vasoactive agents in pithed rats. Wistar rats were anesthetized and pithed, and vasopressor responses to SCS and injections of norepinephrine were observed. To evaluate vasorelaxant responses, the BP was increased by a continuous infusion of methoxamine with hexamethonium to block autonomic outflow. After the elevated BP stabilized, SCS and injections of acetylcholine (ACh), sodium nitroprusside (SNP), and CGRP were intravenously administered. We then evaluated the effects of the NO synthase (NOS) inhibitor, N-ω-nitro-L-arginine methylester hydrochloride (L-NAME), on these vascular responses. Pressor responses to SCS and norepinephrine in pithed rats were enhanced by L-NAME, while the combined infusion of L-NAME and L-arginine had no effect on these responses. L-NAME infusion significantly increased the release of norepinephrine evoked by SCS. In pithed rats with artificially increased BP and L-NAME infusion, depressor response to ACh (except for 0.05nmol/kg) was suppressed and SNP (only 2nmol/kg) was enhanced. However, depressor responses to SCS and CGRP were similar to control responses. The present results suggest endogenous NO regulates vascular tone through endothelium function and inhibition of adrenergic neurotransmission, but not through CGRPergic nerves.

Spinal sensory projection neuron responses to spinal cord stimulation are mediated by circuits beyond gate control.

Spinal cord stimulation (SCS) is a therapy used to treat intractable pain with a putative mechanism of action based on the Gate Control Theory. We hypothesized that sensory projection neuron responses to SCS would follow a single stereotyped response curve as a function of SCS frequency, as predicted by the Gate Control circuit. We recorded the responses of antidromically identified sensory projection neurons in the lumbar spinal cord during 1- to 150-Hz SCS in both healthy rats and neuropathic rats following chronic constriction injury (CCI). The relationship between SCS frequency and projection neuron activity predicted by the Gate Control circuit accounted for a subset of neuronal responses to SCS but could not account for the full range of observed responses. Heterogeneous responses were classifiable into three additional groups and were reproduced using computational models of spinal microcircuits representing other interactions between nociceptive and nonnociceptive sensory inputs. Intrathecal administration of bicuculline, a GABAA receptor antagonist, increased spontaneous and evoked activity in projection neurons, enhanced excitatory responses to SCS, and reduced inhibitory responses to SCS, suggesting that GABAA neurotransmission plays a broad role in regulating projection neuron activity. These in vivo and computational results challenge the Gate Control Theory as the only mechanism underlying SCS and refine our understanding of the effects of SCS on spinal sensory neurons within the framework of contemporary understanding of dorsal horn circuitry.

Mechanism of mitigation of neuropathic pain by spinal cord stimulation in rats: the relationship with HMGB1/TLR4/NF-κB signaling pathway in the spinal cord

Objective To investigate the relationship between the mechanism of mitigation of neuropathic pain by spinal cord stimulation (SCS) and high mobility group protein box-1 (HMGB1)/Toll-like receptor 4 (TLR4)/NF-κB signaling pathway in the spinal cord of rats.Methods Forty-eight male Sprague-Dawley rats,aged 8 weeks,weighing 250-300 g,were randomly divided into 4 groups (n =12 each) using a random number table:sham operation group (S group),chronic constrictive injury (CCI) group,sham SCS group (S-SCS group),and SCS group.Neuropathic pain was induced by CCI in the animals anesthetized with intraperitoneal chloral hydrate.The sciatic nerve was exposed and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 silk thread.Electrodes were placed into the epidural space at 5 days after CCI in S-SCS and SCS groups,and in addition SCS was performed at 12-14 days after CCI in SCS group.Paw withdrawal threshold to mechanical stimulation (MWT) were measured at 1 day before operation and 1,4,7,14 days after CCI.After measurement of pain threshold at day 14 after CCI,the animals were sacrificed and the lumbar segments (L4-6) of the spinal cord were obtained for determination of mRNA expression of HMGB1,TLR4,and NF-κB p65 (in the nuclear protein,by real-time fluorescent quantitative PCR),protein expression of TLR4 and NF-κBp65 (by Western blot),and protein expression of HMGB1 (by immunohistochemistry).Results Compared with S group,MWT was significantly decreased after CCI,the mRNA and protein expression of HMGB1 and TLR4 was up-regulated,and the expression of NF-κB p65in the nuclear protein and mRNA was up-regulated in CCI,S-SCS and SCS groups.Compared with CCI group,MWT was significantly increased after spinal cord stimulation,the mRNA and protein expression of HMGB1 and TLR4 was down-regulated,and the expression of NF-κB p65 in the nuclear protein and mRNA was down-regulated in SCS group.Conclusion The mechanism by which SCS mitigates neuropathic pain may be related to inhibition of HMGB1/TLR4/NF-κB signaling pathway in the spinal cord of rats. Key words: Electric stimulation; Neuralgia; Spinal cord; High mobility group proteins; Toll-like receptor 4; NF-kappaB

Simulation of injury potential compensation by direct current stimulation in rat spinal cord.

Injury potential, a significant index of spinal cord injury (SCI), is generated by the movement of extracellular ions. It can be compensated through applied direct current (DC) stimulation, which prevents the influx of the free calcium, and eventually reduces the development of secondary injury. Therefore, the compensation of injury potential is beneficial to the repairing of the function of spinal cord. The compensation effect can be evaluated by whether the magnitudes of longitudinal electric fields (EFs) are compensated to zero. However, there have been no established criteria to determine the distribution and shape of stimulating electrodes. In this study, in order to optimize the stimulating electrodes, a finite element model (FEM) of rat spinal cord was developed, and the EFs changes induced by electrodes of different sizes, shapes and locations after SCI were calculated. All the designed configurations of electrodes were able to compensate injury potential, but the resultant compensation effects vary. Pin and disc electrodes produced uneven EFs, while ring electrodes produced uniformly distributed EFs. Moreover, large ring electrodes can compensate the longitudinal EFs almost to zero with relatively low current density (0.55 μA/mm(2)) applied. These results provide a basis for the determination of electrical stimulation parameters in the compensation of injury potential.

Decreased intracellular GABA levels contribute to spinal cord stimulation-induced analgesia in rats suffering from painful peripheral neuropathy: The role of KCC2 and GABA A receptor-mediated inhibition

Elevated spinal extracellular γ-aminobutyric acid (GABA) levels have been described during spinal cord stimulation (SCS)-induced analgesia in experimental chronic peripheral neuropathy. Interestingly, these increased GABA levels strongly exceeded the time frame of SCS-induced analgesia. In line with the former, pharmacologically-enhanced extracellular GABA levels by GABA B receptor agonists in combination with SCS in non-responders to SCS solely could convert these non-responders into responders. However, similar treatment with GABA A receptor agonists and SCS is known to be less efficient. Since K + Cl − cotransporter 2 (KCC2) functionality strongly determines proper GABA A receptor-mediated inhibition, both decreased numbers of GABA A receptors as well as reduced KCC2 protein expression might play a pivotal role in this loss of GABA A receptor-mediated inhibition in non-responders. Here, we explored the mechanisms underlying both changes in extracellular GABA levels and impaired GABA A receptor-mediated inhibition after 30 min of SCS in rats suffering from partial sciatic nerve ligation (PSNL). Immediately after cessation of SCS, a decreased spinal intracellular dorsal horn GABA-immunoreactivity was observed in responders when compared to non-responders or sham SCS rats. One hour later however, GABA-immunoreactivity was already increased to similar levels as those observed in non-responder or sham SCS rats. These changes did not coincide with alterations in the number of GABA-immunoreactive cells. C-Fos/GABA double-fluorescence clearly confirmed a SCS-induced activation of GABA-immunoreactive cells in responders immediately after SCS. Differences in spinal dorsal horn GABA A receptor-immunoreactivity and KCC2 protein levels were absent between all SCS groups. However, KCC2 protein levels were significantly decreased compared to sham PSNL animals. In conclusion, reduced intracellular GABA levels are only present during the time frame of SCS in responders and strongly point to a SCS-mediated on/off GABAergic release mechanism. Furthermore, a KCC2-dependent impaired GABA A receptor-mediated inhibition seems to be present both in responders and non-responders to SCS due to similar KCC2 and GABA A receptor levels.

A fully implanted programmable stimulator based on wireless communication for epidural spinal cord stimulation in rats

Clinical research indicates that the epidural spinal cord stimulation (ESCS) has shown potential in promoting locomotor recovery in patients with incomplete spinal cord injury (ISCI). This paper presents the development of a fully implantable voltage-regulated stimulator with bi-directional wireless communication for investigating underlying neural mechanisms of ESCS facilitating motor function improvement. The stimulation system consists of a computer, an external controller, an implantable pulse generator (IPG), a magnet, the extension leads and a stimulation electrode. The telemetry transmission between the IPG and the external controller is achieved by a commercially available transceiver chip with 2.4GHz carrier band. The magnet is used to activate the IPG only when necessary to minimize the power consumption. The encapsulated IPG measures 33mm×24mm×8mm, with a total mass of ∼12.6g. Feasibility experiments are conducted in three Sprague-Dawley rats to validate the function of the stimulator, and to investigate the relationship between lumbar-sacral ESCS and hindlimb electromyography (EMG) responses. The results show that the stimulation system provides an effective tool for investigation of ESCS application in motor function recovery in small animals.

Bipolar spinal cord stimulation attenuates mechanical hypersensitivity at an intensity that activates a small portion of A-fiber afferents in spinal nerve-injured rats

Spinal cord stimulation (SCS) is used clinically to treat neuropathic pain states, but the precise mechanism by which it attenuates neuropathic pain remains to be established. The profile of afferent fiber activation during SCS and how it may correlate with the efficacy of SCS-induced analgesia are unclear. After subjecting rats to an L5 spinal nerve ligation (SNL), we implanted a miniature quadripolar electrode similar to that used clinically. Our goal was to determine the population and number of afferent fibers retrogradely activated by SCS in SNL rats by recording the antidromic compound action potential (AP) at the sciatic nerve after examining the ability of bipolar epidural SCS to alleviate mechanical hypersensitivity in this model. Notably, we compared the profiles of afferent fiber activation to SCS between SNL rats that exhibited good SCS-induced analgesia (responders) and those that did not (nonresponders). Additionally, we examined how different contact configurations affect the motor threshold (MoT) and compound AP threshold. Results showed that three consecutive days of SCS treatment (50 Hz, 0.2 ms, 30 min, 80–90% of MoT), but not sham stimulation, gradually alleviated mechanical hypersensitivity in SNL rats. The MoT obtained in the animal behavioral study was significantly less than the Aα/β-threshold of the compound AP determined during electrophysiological recording, suggesting that SCS could attenuate mechanical hypersensitivity with a stimulus intensity that recruits only a small fraction of the A-fiber population in SNL rats. Although both the MoT and compound AP threshold were similar between responders and nonresponders, the size of the compound AP waveform at higher stimulation intensities was larger in the responders, indicating a more efficient activation of the dorsal column structure in responders.

Modulation of neuronal activity in dorsal column nuclei by upper cervical spinal cord stimulation in rats

Clinical human and animal studies show that upper cervical spinal cord stimulation (cSCS) has beneficial effects in treatment of some cerebral disorders, including those due to deficient cerebral circulation. However, the underlying mechanisms and neural pathways activated by cSCS using clinical parameters remain unclear. We have shown that a cSCS-induced increase in cerebral blood flow is mediated via rostral spinal dorsal column fibers implying that the dorsal column nuclei (DCN) are involved. The aim of this study was to examine how cSCS modulated neuronal activity of DCN. A spring-loaded unipolar ball electrode was placed on the left dorsal column at cervical (C2) spinal cord in pentobarbital anesthetized, ventilated and paralyzed male rats. Stimulation with frequencies of 1, 10, 20, 50 Hz (0.2 ms, 10 s) and an intensity of 90% of motor threshold was applied. Extracellular potentials of single neurons in DCN were recorded and examined for effects of cSCS. In total, 109 neurons in DCN were isolated and tested for effects of cSCS. Out of these, 56 neurons were recorded from the cuneate nucleus and 53 from the gracile nucleus. Mechanical somatic stimuli altered activity of 87/109 (83.2%) examined neurons. Of the neurons receiving somatic input, 62 were classified as low-threshold and 25 as wide dynamic range. The cSCS at 1 Hz changed the activity of 96/109 (88.1%) of the neurons. Neuronal responses to cSCS exhibited multiple patterns of excitation and/or inhibition: excitation (E, n=21), inhibition (I, n=19), E–I ( n=37), I–E ( n=8) and E–I–E ( n=11). Furthermore, cSCS with high-frequency (50 Hz) altered the activity of 92.7% (51/55) of tested neurons, including 30 E, 24 I, and 2 I–E responses to cSCS. These data suggested that cSCS significantly modulates neuronal activity in DCN. These nuclei might serve as a neural relay for cSCS-induced effects on cerebral dysfunction and diseases.