A continuous spinal cord stimulation model attenuates pain-related behavior in vivo following induction of a peripheral nerve injury

Implantable, Programmable, and Wireless Device for Electrical Stimulation of the Dorsal Root Ganglion in Freely-Moving Rats: A Proof of Concept Study

Objective

This was a proof of concept study, based on systematic reviews of the efficacy and safety of the dorsal root ganglion (DRG) stimulation. The main objective was to develop an implantable, programmable, and wireless device for electrical stimulation of DRG and a methodology that can be used in translational research, especially to understand the mechanism of neuromodulation and to test new treatment modalities in animal models of pain.

Methods

We developed and tested a stimulator that uses a battery-powered microelectronic circuit, to generate constant current square biphasic or monophasic pulsed waveform of variable amplitudes and duration. It is controlled by software and an external controller that allows radio frequency communication with the stimulator. The stimulator was implanted in Sprague–Dawley (SD) rats. The lead was positioned at the L5 DRG level, while the stimulator was placed in the skin pocket at the ipsilateral side. Forty-five animals were used and divided into six groups: spinal nerve ligation (SNL), chronic compression injury of the DRG (CCD), SNL + active DRG stimulation, intact control group, group with the implanted sham stimulator, and sham lead. Behavioral testing was performed on the day preceding surgery and three times postoperatively (1st, 3rd, and 7th day).

Results

In animals with SNL, neurostimulation reduced pain-related behavior, tested with pinprick hyperalgesia, pinprick withdrawal test, and cold test, while the leads per se did not cause DRG compression. The rats well tolerated the stimulator. It did not hinder animal movement, and it enabled the animals to be housed under regular conditions.

Conclusion

A proof-of-concept experiment with our stimulator verified the usability of the device. The stimulator enables a wide range of research applications from adjusting stimulation parameters for different pain conditions, studying new stimulation methods with different frequencies and waveforms to obtain knowledge about analgesic mechanisms of DRG stimulation.

Modulation of Glia-Mediated Processes by Spinal Cord Stimulation in Animal Models of Neuropathic Pain

Glial cells play an essential role in maintaining the proper functioning of the nervous system. They are more abundant than neurons in most neural tissues and provide metabolic and catabolic regulation, maintaining the homeostatic balance at the synapse. Chronic pain is generated and sustained by the disruption of glia-mediated processes in the central nervous system resulting in unbalanced neuron–glial interactions. Animal models of neuropathic pain have been used to demonstrate that changes in immune and neuroinflammatory processes occur in the course of pain chronification. Spinal cord stimulation (SCS) is an electrical neuromodulation therapy proven safe and effective for treating intractable chronic pain. Traditional SCS therapies were developed based on the gate control theory of pain and rely on stimulating large Aβ neurons to induce paresthesia in the painful dermatome intended to mask nociceptive input carried out by small sensory neurons. A paradigm shift was introduced with SCS treatments that do not require paresthesia to provide effective pain relief. Efforts to understand the mechanism of action of SCS have considered the role of glial cells and the effect of electrical parameters on neuron–glial interactions. Recent work has provided evidence that SCS affects expression levels of glia-related genes and proteins. This inspired the development of a differential target multiplexed programming (DTMP) approach using electrical signals that can rebalance neuroglial interactions by targeting neurons and glial cells differentially. Our group pioneered the utilization of transcriptomic and proteomic analyses to identify the mechanism of action by which SCS works, emphasizing the DTMP approach. This is an account of evidence demonstrating the effect of SCS on glia-mediated processes using neuropathic pain models, emphasizing studies that rely on the evaluation of large sets of genes and proteins. We show that SCS using a DTMP approach strongly affects the expression of neuron and glia-specific transcriptomes while modulating them toward expression levels of healthy animals. The ability of DTMP to modulate key genes and proteins involved in glia-mediated processes affected by pain toward levels found in uninjured animals demonstrates a shift in the neuron–glial environment promoting analgesia.

10-kHz Spinal Cord Stimulation for Chronic Postsurgical Pain: Results From a 12-Month Prospective, Multicenter Study

Background

Chronic postsurgical pain (CPSP) can be caused by peripheral nerve injury (PNI) resulting from surgical procedures and has a significant neuropathic component. This prospective, single‐arm study was conducted to document the effectiveness of 10‐kHz spinal cord stimulation (10‐kHz SCS) as a treatment for patients with CPSP.

Methods

Subjects with CPSP who were refractory to conventional medical interventions and reported pain scores of ≥5 cm on a 10‐cm VAS underwent trial stimulations lasting up to 14 days. Epidural leads were implanted at locations appropriate for the primary area of pain, and trials resulting in ≥40% pain relief were considered successful. Subjects with successful trials underwent implantation with a permanent 10‐kHz SCS system and were followed for 12 months after implantation.

Results

Of the 34 subjects who underwent trial stimulation, 1 was withdrawn early and 29 (87.9%) had a successful trial and received a permanent implant. After 12 months of treatment, the mean VAS score decreased by 6.5 cm, the response rate was 88.0% (22/25), and 18 subjects (62.1%) were remitters with VAS scores sustained at ≤3.0 cm. Scores for all components of the short‐form McGill Pain Questionnaire 2 were significantly reduced, including affective descriptors of pain. Pain catastrophizing and vigilance, patient function, physical and mental well‐being, and sleep quality all improved over the course of the study. No neurologic deficits reported in the study.

Conclusions

10‐kHz SCS is effective and tolerated in patients with CPSP, and further study of its clinical application in this population is warranted.

Suppression of Superficial Microglial Activation by Spinal Cord Stimulation Attenuates Neuropathic Pain Following Sciatic Nerve Injury in Rats

We evaluated the mechanisms underlying the spinal cord stimulation (SCS)-induced analgesic effect on neuropathic pain following spared nerve injury (SNI). On day 3 after SNI, SCS was performed for 6 h by using electrodes paraspinally placed on the L4-S1 spinal cord. The effects of SCS and intraperitoneal minocycline administration on plantar mechanical sensitivity, microglial activation, and neuronal excitability in the L4 dorsal horn were assessed on day 3 after SNI. The somatosensory cortical responses to electrical stimulation of the hind paw on day 3 following SNI were examined by using in vivo optical imaging with a voltage-sensitive dye. On day 3 after SNI, plantar mechanical hypersensitivity and enhanced microglial activation were suppressed by minocycline or SCS, and L4 dorsal horn nociceptive neuronal hyperexcitability was suppressed by SCS. In vivo optical imaging also revealed that electrical stimulation of the hind paw-activated areas in the somatosensory cortex was decreased by SCS. The present findings suggest that SCS could suppress plantar SNI-induced neuropathic pain via inhibition of microglial activation in the L4 dorsal horn, which is involved in spinal neuronal hyperexcitability. SCS is likely to be a potential alternative and complementary medicine therapy to alleviate neuropathic pain following nerve injury.

Proteomic Modulation in the Dorsal Spinal Cord Following Spinal Cord Stimulation Therapy in an In Vivo Neuropathic Pain Model

OBJECTIVES

Spinal cord stimulation (SCS) provides relief for patients suffering from chronic neuropathic pain although its mechanism may not be as dependent on electrical interference as classically considered. Recent evidence has been growing regarding molecular changes that are induced by SCS as being a key player in reversing the pain process. Here, we observed the effect of SCS on altering protein expression in spinal cord tissue using a proteomic analysis approach.

METHODS

A microlead was epidurally implanted following induction of an animal neuropathic pain model. After the model was established, stimulation was applied for 72 hours continuously followed by tissue collection and proteomic analysis via tandem mass spectroscopy. Identified proteins were run through online data bases for protein identification and classification of biological processes.

RESULTS

A significant improvement in mechanical sensitivity was observed following 48 hours of SCS therapy. Proteomic analysis identified 5840 proteins, of which 155 were significantly affected by SCS. Gene ontology data bases indicated that a significant number of proteins were associated to stress response, oxidation/reduction, or extracellular matrix pathways. Additionally, many of the proteins identified also play a role in neuron-glial interactions and are involved in nociception.

CONCLUSIONS

The development of an injury unbalances the proteome of the local neural tissue, neurons, and glial cells, and shifts the proteomic profile to a pain producing state. This study demonstrates the reversal of the injury-induced proteomic state by applying conventional SCS therapy. Additional studies looking at variations in electrical parameters are needed to optimize SCS.

Changes in Dorsal Root Ganglion Gene Expression in Response to Spinal Cord Stimulation

BACKGROUND AND OBJECTIVES

Spinal cord stimulation (SCS) has been shown to influence pain-related genes in the spinal cord directly under the stimulating electrodes. There is limited information regarding changes occurring at the dorsal root ganglion (DRG). This study evaluates gene expression in the DRG in response to SCS therapy.

METHODS

Rats were randomized into experimental or control groups (n = 6 per group). Experimental animals underwent spared-nerve injury, implantation of lead, and continuous SCS (72 hours). Behavioral assessment for mechanical hyperalgesia was conducted to compare responses after injury and treatment. Ipsilateral DRG tissue was collected, and gene expression quantified for interleukin 1b (IL-1b), interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), GABA B receptor 1 (GABAbr1), substance P (subP), Integrin alpha M (ITGAM), sodium/potassium ATP-ase (Na/K ATPase), fos proto-oncogene (cFOS), serotonin receptor 3A (5HT3r), galanin (Gal), vasoactive intestinal peptide (VIP), neuropeptide Y (NpY), glial fibrillary acidic protein (GFAP), and brain derived neurotropic factor (BDNF) via quantitative polymerase chain reaction. Statistical significance was established using analysis of variance (ANOVA), independent t tests, and Pearson correlation tests.

RESULTS

Expression of IL-1b and IL-6 was reversed following SCS therapy relative to the increase caused by the injury model. Both GABAbr1 and Na/K ATPase were significantly up-regulated upon implantation of the lead, and SCS therapy reversed their expression to within control levels. Pearson correlation analyses reveal that GABAbr1 and Na/K ATPase expression was dependent on the stimulating current intensity.

CONCLUSIONS

Spinal cord stimulation modulates expression of key pain-related genes in the DRG. Specifically, SCS led to reversal of IL-1b and IL-6 expression induced by injury. Interleukin 6 expression was still significantly larger than in sham animals, which may correlate to residual sensitivity following continuous SCS treatment. In addition, expression of GABAbr1 and Na/K ATPase was down-regulated to within control levels following SCS and correlates with applied current.

Sub-paresthesia spinal cord stimulation reverses thermal hyperalgesia and modulates low frequency EEG in a rat model of neuropathic pain

Paresthesia, a common feature of epidural spinal cord stimulation (SCS) for pain management, presents a challenge to the double-blind study design. Although sub-paresthesia SCS has been shown to be effective in alleviating pain, empirical criteria for sub-paresthesia SCS have not been established and its basic mechanisms of action at supraspinal levels are unknown. We tested our hypothesis that sub-paresthesia SCS attenuates behavioral signs of neuropathic pain in a rat model, and modulates pain-related theta (4–8 Hz) power of the electroencephalogram (EEG), a previously validated correlate of spontaneous pain in rodent models. Results show that sub-paresthesia SCS attenuates thermal hyperalgesia and power amplitude in the 3–4 Hz range, consistent with clinical data showing significant yet modest analgesic effects of sub-paresthesia SCS in humans. Therefore, we present evidence for anti-nociceptive effects of sub-paresthesia SCS in a rat model of neuropathic pain and further validate EEG theta power as a reliable ‘biosignature’ of spontaneous pain.

Spinal Cord Stimulation Modulates Gene Expression in the Spinal Cord of an Animal Model of Peripheral Nerve Injury

BACKGROUND AND OBJECTIVES

Previously, we found that application of pulsed radiofrequency to a peripheral nerve injury induces changes in key genes regulating nociception concurrent with alleviation of paw sensitivity in an animal model. In the current study, we evaluated such genes after applying spinal cord stimulation (SCS) therapy.

METHODS

Male Sprague-Dawley rats (n = 6 per group) were randomized into test and control groups. The spared nerve injury model was used to simulate a neuropathic pain state. A 4-contact microelectrode was implanted at the L1 vertebral level and SCS was applied continuously for 72 hours. Mechanical hyperalgesia was tested. Spinal cord tissues were collected and analyzed using real-time polymerase chain reaction to quantify levels of IL1β, GABAbr1, subP, Na/K ATPase, cFos, 5HT3ra, TNFα, Gal, VIP, NpY, IL6, GFAP, ITGAM, and BDNF.

RESULTS

Paw withdrawal thresholds significantly decreased in spared nerve injury animals and stimulation attenuated sensitivity within 24 hours (P = 0.049), remaining significant through 72 hours (P = 0.003). Nerve injury caused up-regulation of TNFα, GFAP, ITGAM, and cFOS as well as down-regulation of Na/K ATPase. Spinal cord stimulation therapy modulated the expression of 5HT3ra, cFOS, and GABAbr1. Strong inverse relationships in gene expression relative to the amount of applied current were observed for GABAbr1 (R = -0.65) and Na/K ATPase (R = -0.58), and a positive linear correlations between 5HT3r (R = 0.80) and VIP (R = 0.50) were observed.

CONCLUSIONS

Continuously applied SCS modulates expression of key genes involved in the regulation of neuronal membrane potential.

The preparation of rat's acellular spinal cord scaffold and co-culture with rat's spinal cord neuron in vitro

STUDY DESIGN

The rat's acellular spinal cord scaffold (ASCS) and spinal cord neurons were prepared in vitro to explore their biocompatibility.

OBJECTIVES

The preparation of ASCS and co-culture with neuron may lay a foundation for clinical treatment of spinal cord injury (SCI).

SETTING

Tianjin Medical University General Hospital, ChinaMethods:ASCS was prepared by chemical extraction method. Hematoxylin and eosin (H&E), myelin staining and scanning electron microscope were used to observe the surface structure of ASCS. Spinal cord neurons of rat were separated in vitro, and then co-cultured with prepared ASCS in virto.

RESULTS

The prepared ASCS showed mesh structure with small holes of different sizes. H&E staining showed that cell components were all removed. The ASCS possessed fine three-dimensional network porous structure. DNA components were not found in the ASCS by DNA agarose gel electrophoresis. The cultured cells express neuron-specific enolase (NSE) antigen with long axons. H&E staining showed that the neurons adhered to the pore structures of ASCS, and the cell growth was fine. The survival rate of co-cultured cells was (97.53±1.52%) by MTT detection. Immunohistochemical staining showed that neurons on the scaffold expressed NSE and NeuN antigen. Cells were arranged closely, and the channel structures of ASCS were fully filled with neurons. The cells accumulated in the channel and grew well in good state.

CONCLUSION

The structure of ASCS remained intact, and the neurons were closely arranged in the scaffolds. These results may lay a solid foundation for clinical treatment of SCI when considering glial scar replacement by biomaterials.

Genomics of the Effect of Spinal Cord Stimulation on an Animal Model of Neuropathic Pain

BACKGROUND

Few studies have evaluated single-gene changes modulated by spinal cord stimulation (SCS), providing a narrow understanding of molecular changes. Genomics allows for a robust analysis of holistic gene changes in response to stimulation.

METHODS

Rats were randomized into six groups to determine the effect of continuous SCS in uninjured and spared-nerve injury (SNI) animals. After behavioral assessment, tissues from the dorsal quadrant of the spinal cord (SC) and dorsal root ganglion (DRG) underwent full-genome microarray analyses. Weighted Gene Correlation Network Analysis (WGCNA), and Gene Ontology (GO) analysis identified similar expression patterns, molecular functions and biological processes for significant genes.

RESULTS

Microarray analyses reported 20,985 gene probes in SC and 19,104 in DRG. WGCNA sorted 7449 SC and 4275 DRG gene probes into 29 and 9 modules, respectively. WGCNA provided significant modules from paired comparisons of experimental groups. GO analyses reported significant biological processes influenced by injury, as well as the presence of an electric field. The genes Tlr2, Cxcl16, and Cd68 were used to further validate the microarray based on significant response to SCS in SNI animals. They were up-regulated in the SC while both Tlr2 and Cd68 were up-regulated in the DRG.

CONCLUSIONS

The process described provides highly significant interconnected genes and pathways responsive to injury and/or electric field in the SC and DRG. Genes in the SC respond significantly to the SCS in both injured and uninjured animals, while those in the DRG significantly responded to injury, and SCS in injured animals.

Anti-nociceptive, anti-hyperalgesic and anti-arthritic activity of amides and extract obtained from Piper amalago in rodents

ETHNOPHARMACOLOGICAL RELEVANCE

Piper amalago (Piperaceae) has been used in folk medicine as an analgesic. This study aimed to evaluate the pharmacological effects of extract and pure amides obtained from P. amalago on pain to provide a pharmacological basis for their use in traditional medicine.

AIM OF THE STUDY

This study evaluated the anti-nociceptive, anti-hyperalgesic, anti-arthritic and anti-depressive activities of the ethanolic extract of P. amalago (EEPA) and the amides N-[7-(3',4'-methylenedioxyphenyl)-2(Z),4(Z)-heptadienoyl] pyrrolidine (1) and N-[7-(3',4'-methylenedioxyphenyl)-2(E),4(E)-heptadienoyl] pyrrolidine (2) obtained from P. amalago in animal models.

MATERIALS AND METHODS

Mice treated daily with EEPA (100mg/kg, p.o.) were assayed for 20 days for knee edema (micrometer measurement), mechanical hyperalgesia (analgesiometer analysis), heat sensitivity and immobility (forced swim test) in the Complete Freund's Adjuvant (CFA) model. Cold (acetone test) and mechanical hyperalgesia (electronic von Frey analysis) responses were evaluated for 15 days in rats treated with oral EEPA (100mg/kg) in the spared nerve injury (SNI) model. Meanwhile, mice were evaluated for carrageenan-induced edema and mechanical hyperalgesia and for nociception using the formalin model after a single administration of EEPA (100mg/kg) or amides 1 and 2 (1mg/kg).

RESULTS

Amides (1) and (2) were detected and isolated from the EEPA. The EEPA inhibited mechanical hyperalgesia, knee edema, and heat hyperalgesia, but not depressive-like behavior, induced by the intraplantar injection of CFA. When evaluated in the SNI model, the EEPA inhibited mechanical and cold hyperalgesia. The EEPA, 1 and 2 prevented the mechanical hyperalgesia induced by carrageenan and the anti-nociceptive effects in both phases of formalin nociception. The EEPA did not induce alterations in the open field test.

CONCLUSION

The EEPA was effective for inhibition of pain and arthritic parameters but was not effective against depressive-like behavior; additionally, it did not alter locomotor activity. The amides obtained seemed to be the active component(s) present in the EEPA because they proved to be anti-nociceptive and anti-hyperalgesic in models of acute pain. Considering that few drugs are currently available for the treatment of chronic pain, especially neuropathic pain, the present results may have clinical relevance and open new possibilities for the development of new anti-hyperalgesic and anti-arthritic agents from P. amalago.