Mechanical hypersensitivity, sympathetic sprouting, and glial activation are attenuated by local injection of corticosteroid near the lumbar ganglion in a rat model of neuropathic pain

Dexamethasone attenuates neuropathic pain through spinal microglial expression of dynorphin A via the cAMP/PKA/p38 MAPK/CREB signaling pathway

This study aimed to elucidate the opioid mechanisms underlying dexamethasone-induced pain antihypersensitive effects in neuropathic rats. Dexamethasone (subcutaneous and intrathecal) and membrane-impermeable Dex-BSA (intrathecal) administration dose-dependently inhibited mechanical allodynia and thermal hyperalgesia in neuropathic rats. Dexamethasone and Dex-BSA treatments increased expression of dynorphin A in the spinal cords and primary cultured microglia. Dexamethasone specifically enhanced dynorphin A expression in microglia but not astrocytes or neurons. Intrathecal injection of the microglial metabolic inhibitor minocycline blocked dexamethasone-stimulated spinal dynorphin A expression; intrathecal minocycline, the glucocorticoid receptor antagonist Dex-21-mesylate, dynorphin A antiserum, and κ-opioid receptor antagonist GNTI completely blocked dexamethasone-induced mechanical antiallodynia and thermal antihyperalgesia. Additionally, dexamethasone elevated spinal intracellular cAMP levels, leading to enhanced phosphorylation of PKA, p38 MAPK and CREB. The specific adenylate cyclase inhibitor DDA, PKA inhibitor H89, p38 MAPK inhibitor SB203580 and CREB inhibitor KG-501 completely blocked dexamethasone-induced anti-neuropathic pain and increased microglial dynorphin A exprression. In conclusion, this study reveal that dexamethasone mitigateds neuropathic pain through upregulation of dynorphin A in spinal microglia, likely involving the membrane glucocorticoid receptor/cAMP/PKA/p38 MAPK/CREB signaling pathway.

The effectiveness of cervical transforaminal epidural steroid injections for the treatment of cervical radicular pain: A prospective cohort study reporting 12-month outcomes

Objectives

To evaluate the effectiveness of cervical transforaminal epidural steroid injection (CTFESI) for the treatment of unilateral cervical radicular pain.

Design

Single-group prospective cohort study.

Methods

Outcomes included ≥50% reductions in Numeric Rating Scale (NRS) for arm pain, ≥30% Neck Disability Index (NDI-5) improvement, health-related quality of life (EQ-5D), global improvement (PGIC), personal goal achievement (COMBI), Chronic Pain Sleep Index (CPSI), and healthcare utilization at one, three, six, and 12 months. Data analysis included descriptive statistics with the calculations of 95% confidence intervals (CIs), contingency table analysis, and multilevel logistic regression (LR) analysis, including a worst-case (WC) sensitivity analysis in which missing data were treated as treatment failure. Participants who were treated surgically were considered failures in the categorical analyses.

Results

33 consecutively enrolled participants (63.6% females, 51.2 ± 12.2 years of age, BMI 28.3 ± 4.5 kg/m2) were analyzed. Success rates for ≥50% reduction in NRS for arm pain at one, three, six and 12 months were 57.6% (95% CI 40.8-72.8%), 71.9% (95% CI 54.6-84.4%), 64.5% (95% CI 46.9-78.9%), and 64.5% (95% CI 46.9-78.9%). Success rates for ≥30% improvement in NDI-5 were 60.6% (95% CI 43.7-75.3%), 68.8% (95% CI 51.4-82.0%), 61.3% (95% CI 43.8-76.3%), and 71.0% (95% CI 53.4-83.9%). In WC analysis, success rates for ≥50% arm NRS and NDI-5 were 0-4.3% lower between 1 and 12 months. PGIC scores were at least "much improved" or "very much improved," in 48.4-65.6% of participants between 1 and 12 months. 6.1%, 6.1%, and 3.0% had one, two, or three repeat injections, respectively. 18.2% of participants underwent surgery by 12 months. Participants showed significant improvements in arm NRS and NDI-5 after treatment (p < 0.05), multilevel logistic regression models showed no significant decline in improvements across the follow-up time points (p > 0.05).

Conclusion

Statistically significant and clinically meaningful improvements in pain and disability were observed after CTFESI for up to 12 months in individuals with unilateral cervical radicular pain.

The Short-Term Outcome of Transforaminal Epidural Steroid Injection in Patients with Radicular Pain Due to Foraminal Stenosis from Lumbar Isthmic Spondylolisthesis

Purpose

In this study, we evaluated the therapeutic outcomes of transforaminal epidural steroid injection (TFESI) in managing chronic radicular pain due to foraminal stenosis. Furthermore, we evaluated its effectiveness according to isthmic spondylolisthesis (IS) severity.

Patients and Methods

We included 40 patients with radicular pain due to IS-derived foraminal stenosis in our study and treated them with TFESI. Two patients were lost during follow-up. Based on the lateral lumbar radiograph findings, we allocated the recruited patients with < 25% slippage by IS to Group 1 (n = 23) and those having 25-50% slippage to Group 2 (n = 15). The degree of pain was measured using a numeric rating scale (NRS) at pre-treatment and 1 and 2 months after TFESI.

Results

In 38 patients who completed the study, the NRS at pre-treatment was significantly reduced at the 1- and 2-month follow-ups. In the Group analysis, the NRS scores were significantly reduced after TFESI in both Groups 1 and 2, regardless of IS severity. However, the reduction in NRS scores 1 month after TFESI was significantly greater in Group 1 than in Group 2. Moreover, the rate of successful treatment outcomes was significantly higher (65.2%) in Group 1 than in Group 2 (26.7%).

Conclusion

After TFESI, chronic radicular pain was significantly reduced regardless of IS severity, and its effect persisted for at least 2 months. However, its effect was superior when the vertebra slippage by IS was less than 25% compared to patients with 25%-50%.

Immunohistochemical phenotype of sensory neurons associated with sympathetic plexuses in the trigeminal ganglia of adult nerve growth factor transgenic mice

Following peripheral nerve injury, postganglionic sympathetic axons sprout into the affected sensory ganglia and form perineuronal sympathetic plexuses with somata of sensory neurons. This sympathosensory coupling contributes to the onset and persistence of injury-induced chronic pain. We have documented the presence of similar sympathetic plexuses in the trigeminal ganglia of adult mice that ectopically overexpress nerve growth factor (NGF), in the absence of nerve injury. In this study, we sought to further define the phenotype(s) of these trigeminal sensory neurons having sympathetic plexuses in our transgenic mice. Using quantitative immunofluorescence staining analyses, we show that the invading sympathetic axons specifically target sensory somata immunopositive for several biomarkers: NGF high-affinity receptor tyrosine kinase A (trkA), calcitonin gene-related peptide (CGRP), neurofilament heavy chain (NFH), and P2X purinoceptor 3 (P2X3). Based on these phenotypic characteristics, the majority of the sensory somata surrounded by sympathetic plexuses are likely to be NGF-responsive nociceptors (i.e., trkA expressing) that are peptidergic (i.e., CGRP expressing), myelinated (i.e., NFH expressing), and ATP sensitive (i.e., P2X3 expressing). Our data also show that very few sympathetic plexuses surround sensory somata expressing other nociceptive (pain) biomarkers, including substance P and acid-sensing ion channel 3. No sympathetic plexuses are associated with sensory somata that display isolectin B4 binding. Though the cellular mechanisms that trigger the formation of sympathetic plexus (with and without nerve injury) remain unknown, our new observations yield an unexpected specificity with which invading sympathetic axons appear to target a precise subtype of nociceptors. This selectivity likely contributes to pain development and maintenance associated with sympathosensory coupling.

The effectiveness of intradiscal corticosteroid injection for the treatment of chronic discovertebral low back pain: a systematic review

OBJECTIVE

Determine the effectiveness of intradiscal corticosteroid injection (IDCI) for the treatment of discovertebral low back pain.

DESIGN

Systematic review.

POPULATION

Adults with chronic low back pain attributed to disc or vertebral end plate pain, as evidenced by positive provocation discography or Modic 1 or 2 changes on magnetic resonance imaging.

INTERVENTION

Fluoroscopically guided or computed tomography-guided IDCI.

COMPARISON

Sham/placebo procedure including intradiscal saline, anesthetic, discography alone, or other active treatment.

OUTCOMES

Reduction in chronic low back pain reported on a visual analog scale or numeric rating scale and reduction in disability reported by a validated scale such as the Oswestry Disability Index.

METHODS

Four reviewers independently assessed articles published before January 31, 2023, in Medline, Embase, CENTRAL, and CINAHL. The quality of evidence was evaluated with the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework. The risk of bias in randomized trials was evaluated with the Cochrane Risk of Bias tool (version 2).

RESULTS

Of the 7806 unique records screened, 6 randomized controlled trials featuring 603 total participants ultimately met the inclusion criteria. In multiple randomized controlled trials, IDCI was found to reduce pain and disability for 1-6 months in those with Modic 1 and 2 changes but not in those selected by provocation discography.

CONCLUSION

According to GRADE, there is low-quality evidence that IDCI reduces pain and disability for up to 6 months in individuals with chronic discovertebral low back pain as evidenced by Modic 1 and 2 changes but not in individuals selected by provocation discography.

STUDY REGISTRATION

PROSPERO (CRD42021287421).

Targeting dorsal root ganglia and primary sensory neurons for the treatment of chronic pain: an update

INTRODUCTION

Current treatments for chronic pain are inadequate. Here, we provide an update on the new therapeutic strategies that target dorsal root ganglia (DRGs) in the peripheral nervous system for a better and safer treatment of chronic pain.

AREAS COVERED

Despite the complex nature of chronic pain and its underlying mechanisms, we do know that changes in the plasticity and modality of neurons in DRGs play a pivotal role. DRG neurons are heterogenous and offer potential pain targets for different therapeutic interventions. We discuss the last advancements of these interventions, which include the use of systemic and local administrations, selective nerve drug delivery, and gene therapy. In particular, we provide updates and further details on the molecular characterization of primary sensory neurons, new analgesics entering the market, and future gene therapy approaches.

EXPERT OPINION

DRGs and primary sensory neurons are promising targets for chronic pain treatment due to their key role in pain signaling, unique anatomical location, and the potential for different targeted therapeutic interventions.

The Contribution of TSLP Activation to Hyperalgesia in Dorsal Root Ganglia Neurons of a Rat

Peripheral nerve injury involves divergent alterations within dorsal root ganglia (DRG) neurons sensitized by persistent inflammation. Thymic stromal lymphopoietin (TSLP) production is crucial in the development of chronic inflammatory responses. Herein, we investigate the changes of TSLP expression in rats’ DRG neurons between injured and uninjured sides in the same rat. Linalyl acetate (LA) was served as a TSLP inhibitor and given intraperitoneally. Rats were assigned to be group of chronic constriction injury (CCI) of the sciatic nerve and the group of CCI of the sciatic nerve administrated with LA. Over 14 days, the rats were measured for paw withdrawal thresholds. DRGs were collected to assess morphological changes via immunofluorescence study. After receiving CCI, the rats rapidly developed mechanical hyperalgesia. TSLP expression at DRG, on the ipsilateral injured side, was consistent with changes in pain behaviors. TSLP appeared in nerve fibers with both small diameters and large diameters. Additionally, TSLP was expressed mostly in transient receptor potential vanilloid-1 (TRPV1)-positive nociceptive neurons. Administration with LA can attenuate the pain behaviors and expression of TSLP in DRG neurons, and in apoptotic neurons at the injured side, but not in the contra-lateral uninjured side. Overall, these results imply that altered expressions of TSLP in nociceptive DRG neurons contributed to mechanical hyperalgesia in a CCI rat model.

Increased Expression of Thymic Stromal Lymphopoietin in Chronic Constriction Injury of Rat Nerve

Thymic stromal lymphopoietin (TSLP) is a well-known cytokine for T helper 2 inflammatory responses. A nerve injury activates the neuroinflammation cascade and neuron-glia interaction in dorsal root ganglions (DRG)s, leading to neuropathic pain. Therefore, this study was to investigate the role of TSLP after nerve injury. Male Sprague-Dawley rats were divided as an experimental group with chronic constriction injury (CCI) to the sciatic nerve and a control group. The mechanical pain threshold response was determined by calibration forceps. After assessment of mechanical allodynia, the ipsilateral spinal cord, DRG, sciatic nerve and skin were harvested. Immunofluorescence staining was performed to identify cell types with various markers. Western blot analyses were performed to evaluate protein expressions. Mechanical allodynia developed after CCI and persisted for the next 14 days. Astrocyte reactions occurred and continued until day 14, too. After CCI, DRG and the sciatic nerve also had significantly increased expressions of TSLP/TSLP-R/STAT5. The TSLPR was localized to sensory neuronal endings innervating the skin. This study is the first to demonstrate that the TSLP complex and the STAT5 pathway in nerve are potential therapeutic targets because of their roles in pain regulation after nerve injury.

Sensory Perception in Lumbosacral Radiculopathy with Radicular Pain: Feasibility Study of Multimodal Bedside-Suitable Somatosensory Testing

Background

Somatosensory testing could be useful in stratifying pain patients and improving pain treatment guidelines. Bedside-suitable techniques are searched for application in daily clinical practice. This study aimed to characterize chronic unilateral lumbosacral radiculopathy (LSR) patients with radicular pain using multimodal bedside-suitable somatosensory testing.

Materials and methods

We evaluated 50 chronic unilateral LSR patients with radicular pain (LSR group) and 24 controls (Control group). Sensory testing was performed using a battery of bedside sensory tests (10g monofilament, 200–400 mN brush, Lindblom rollers with controlled 25°C and 40°C temperature, and 40g neurological pin and investigator’s finger pressure). Participants had to rate their sensory perceptions on both legs at multiple test points within L3 to S2 dermatomes. Characteristics of the testing process and sensory disturbances were analyzed.

Results

LSR group showed sensory disturbances in 82% of patients. The Control group showed no sensory disturbances. Sensory testing took longer (p < 0.001) in the LSR group (29.3 ± 6.5 minutes per patient) than in the Control group (20.5 ± 5.2). Nine sensory phenotypes were detected in the LSR group according to individual sensory disturbances within 5 superficial tests.

Conclusions

The applied multimodal bedside-suitable somatosensory testing battery is suitable for sensory evaluation and characterization of LSR patients. Grouping of allied sensory phenotypes revealed some tendencies in pain intensity characteristics.

Satellite Glial Cells in Pain Research: A Targeted Viewpoint of Potential and Future Directions

Chronic pain is known to be caused by sensitization within the pain circuits. An imbalance occurs between excitatory and inhibitory transmission that enables this sensitization to form. In addition to neurons, the contribution of central glia, especially astrocytes and microglia, to the pathogenesis of pain induction and maintenance has been identified. This has led to the targeting of astrogliosis and microgliosis to restore the normal functions of astrocytes and microglia to help reverse chronic pain. Gliosis is broadly defined as a reactive response of glial cells in response to insults to the central nervous system (CNS). The role of glia in the peripheral nervous system (PNS) has been less investigated. Accumulating evidence, however, points to the contribution of satellite glial cells (SGCs) to chronic pain. Hence, understanding the potential role of these cells and their interaction with sensory neurons has become important for identifying the mechanisms underlying pain signaling. This would, in turn, provide future therapeutic options to target pain. Here, a viewpoint will be presented regarding potential future directions in pain research, with a focus on SGCs to trigger further research. Promising avenues and new directions include the potential use of cell lines, cell live imaging, computational analysis, 3D tissue prints and new markers, investigation of glia–glia and macrophage–glia interactions, the time course of glial activation under acute and chronic pathological pain compared with spontaneous pain, pharmacological and non-pharmacological responses of glia, and potential restoration of normal function of glia considering sex-related differences.

Effects of Long-Term Endogenous Corticosteroid Exposure on Brain Volume and Glial Cells in the AdKO Mouse

Chronic exposure to high circulating levels of glucocorticoids has detrimental effects on health, including metabolic abnormalities, as exemplified in Cushing’s syndrome (CS). Magnetic resonance imaging (MRI) studies have found volumetric changes in gray and white matter of the brain in CS patients during the course of active disease, but also in remission. In order to explore this further, we performed MRI-based brain volumetric analyses in the AdKO mouse model for CS, which presents its key traits. AdKO mice had reduced relative volumes in several brain regions, including the corpus callosum and cortical areas. The medial amygdala, bed nucleus of the stria terminalis, and hypothalamus were increased in relative volume. Furthermore, we found a lower immunoreactivity of myelin basic protein (MBP, an oligodendrocyte marker) in several brain regions but a paradoxically increased MBP signal in the male cingulate cortex. We also observed a decrease in the expression of glial fibrillary acidic protein (GFAP, a marker for reactive astrocytes) and ionized calcium-binding adapter molecule 1 (IBA1, a marker for activated microglia) in the cingulate regions of the anterior corpus callosum and the hippocampus. We conclude that long-term hypercorticosteronemia induced brain region-specific changes that might include aberrant myelination and a degree of white matter damage, as both repair (GFAP) and immune (IBA1) responses are decreased. These findings suggest a cause for the changes observed in the brains of human patients and serve as a background for further exploration of their subcellular and molecular mechanisms.

Qualitative Sensory Testing in Outcome Prediction of Transforaminal Epidural Steroid Injection for Chronic Painful Unilateral Lumbosacral Radiculopathy: Prospective Observational Study

BACKGROUND

Transforaminal epidural steroid injection (TFESI) is widely practiced for the treatment of radicular pain. As its effectiveness is still subject to debate, a better patient selection for TFESI is necessary. We aimed to evaluate the potential of bedside-suitable qualitative sensory testing (QualST) to determine the early effectiveness of TFESI for the treatment of chronic lumbosacral radiculopathy (LSR)-related pain.

METHODS

Thirty-six patients with chronic painful unilateral LSR were evaluated in a prospective observational study using five standardized sensory tests (10 g monofilament, 200 to 400 mN brush, Lindblom rollers with controlled 25 and 40°C temperature, and 40 g neurological pin). Quality of sensory perceptions on the painful leg was compared to the non-painful leg and rated as normal sensitivity, hyposensitivity, or hypersensitivity. Pain and related characteristics were evaluated before TFESI, 1 week after and 4 weeks after intervention.

RESULTS

Seven sensory phenotypes were distinguished according to individual sets of sensory disturbances acquired with five sensory tests. Patients were grouped into four groups of allied phenotypes (normal sensitivity, hyposensitivity to 1 to 3 modalities, hyposensitivity to 4 to 5 modalities, and hypersensitivity). The whole study group showed significant improvement in most parameters of outcome measurements. Statistical analysis revealed some significant differences between sensory groups in patient-reported treatment effect scales after 4 weeks. We also detected significant differences between sensory groups in repeated measures after 1 and 4 weeks in some pain intensity characteristics and patient-reported treatment effect scales.

CONCLUSION

QualST might be clinically applicable for detecting patient subgroups that could differ in the early treatment results of radicular pain by TFESI.

The Outcome of Epidural Injections in Lumbar Radiculopathy Is Not Dependent on the Presence of Disc Herniation on Magnetic Resonance Imaging: Assessment of Short-Term and Long-Term Efficacy

OBJECTIVE

Lumbar radiculopathy is a condition with major physical, social, and economic consequences. Despite its favorable prognosis, the burden can be significant. In this study, we aimed to determine the value of magnetic resonance imaging (MRI) and the efficacy of transforaminal epidural injections (TEIs) in patients with lumbar radiculopathy secondary to lumbar disc herniation (LDH) and other causes (non-LDH).

METHODS

Patients with lumbar radiculopathy were reviewed for radiologic diagnosis based on MRI. For patients receiving TEI therapy, response after 6-8 weeks (short-term) and 16 weeks (long-term), number of injections, subsequent surgery, and patient outcome were evaluated. Treatment response was assessed by patient-reported symptom relief and numeric rating scale pain scores.

RESULTS

Overall, 66% of MRI examinations showed a clinically relevant LDH. A total of 486 of 1824 patients received TEI, of whom one third did not show LDH. Of patients, 70% reported a short-term effect with significant pain reduction and 44% reported a long-term effect. No significant differences were observed between the LDH and non-LDH groups. Of patients, 59% required multiple injections and reported similar efficacy compared with patients treated with a single injection.

CONCLUSIONS

A considerable part of MRI examinations in patients with lumbar radiculopathy do not show a clinically relevant LDH. Regardless of the radiologic diagnosis, most patients treated with TEI benefit in both the short-term and the long-term after a single-injection or multiple-injection regime. Subsequent injections are advisable if the effect from the first injection is unsatisfactory or wears off. MRI examination before TEI therapy may be redundant, which allows for expedition of this treatment.

Effects of low- and high-frequency electroacupuncture on protein expression and distribution of TRPV1 and P2X3 in rats with peripheral nerve injury

BACKGROUND

Whether electroacupuncture (EA) stimulation at different frequencies has a similar effect on spared nerve injury (SNI) as other neuropathic pain models, and how EA at different frequencies causes distinct analgesic effects on neuropathic pain is still not clear.

METHODS

Adult male Sprague-Dawley rats were randomly divided into sham SNI, SNI, 2 Hz, 100 Hz and sham EA groups. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were measured. EA was performed once a day on days 1 to 14 after SNI. The expressions of transient receptor potential cation subfamily V member 1 (TRPV1) and peripheral purinergic P2X receptor 3 (P2X3) were determined by western blotting and immunofluorescence. TRPV1 siRNA and P2X3 siRNA were administered by intrathecal injection. TRPV1 or P2X3 agonists were combined with EA.

RESULTS

There were significant decreases in PWT, but no changes in PWL in the 14 days after SNI. EA using 2- or 100-Hz stimulation similarly increased PWT at every time point. The cytosol protein expression of P2X3 in the L4-L6 dorsal root ganglia (DRG) increased, but the expression of TRPV1 decreased in the SNI model. Both these effects were ameliorated by EA, with 2-Hz stimulation having a stronger effect than 100-Hz stimulation. Blocking either TRPV1 or P2X3 specific siRNAs attenuated the decreased PWT induced by SNI. Administration of either a TRPV1 or P2X3 agonist inhibited EA analgesia.

CONCLUSION

2- and 100-Hz EA similarly induced analgesic effects in SNI. This effect was related to up-regulation and down-regulation, respectively, of cytosol protein expression of P2X3 and TRPV1 in L4-L6 DRG, with 2 Hz having a better effect than 100 Hz.

Metabolic Imaging of Pain Matrix Using 18 F Fluoro-deoxyglucose Positron Emission Tomography/Computed Tomography for Patients Undergoing L2 Dorsal Root Ganglion Stimulation for Low Back Pain

INTRODUCTION

Nociceptive signals from lumbar intervertebral discs ascend in the sympathetic chain via the L2 dorsal root ganglion (L2 DRG), a potential target for discogenic low back pain in neuromodulation. Positron Emission Tomography/Computed Tomography (PET-CT) measures functional changes in the brain metabolic activity, identified by the changes in the regional cerebral blood flow (rCBF) as determined by the changes of F-18 Fluoro-deoxyglucose (¹⁸ F FDG) tracer within brain tissues.

METHODS AND MATERIALS

Nine patients were recruited to explore the changes in PET-CT imaging at baseline and four-weeks post implantation of bilateral L2 DRG neurostimulation leads and implantable pulse generator (IPG). PET-CT scans were performed 30 min following an IV injection of 250±10% MBq of ¹⁸ F FDG tracer. Fifteen frames were acquired in 15 min. PET list-mode raw data were reconstructed and normalized appropriately to a brain anatomical atlas.

RESULTS

Nine patients were recruited to the study, where PET-CT imaging data for five patients were analyzed. The right and left insular cortex, primary and secondary somato-sensory cortices, prefrontal cortex, anterior cingulate cortex, thalamus, amygdala, hippocampus and the midline periaqueductal areas, were assessed for any changes in the metabolic activity. A total of 85 pain matrix regions were delineated SUV (standardized uptake value)_MAX , SUV _MEAN  ± SD, and SUV_PEAK were calculated for each of these regions of the brain and were compared pre- and post-L2 DRG stimulation. Sixty-one of the 85 matrices showed an increase in metabolic activity whereas 24 matrices showed a reduction in metabolic activity.

CONCLUSION

This is the first ever study reporting the changes in cerebral metabolic activity and multi-frame static brain ¹⁸ F FDG PET imaging after L2 DRG stimulation for discogenic low back pain. Predominantly an increased metabolic activity in nociceptive brain matrices are seen with an increased in F¹⁸ F FDG uptake following L2 DRG stimulation.

Interaction of auditory and pain pathways: Effects of stimulus intensity, hearing loss and opioid signaling

Moderate intensity sounds can reduce pain sensitivity (i.e., audio-analgesia) whereas intense sounds can induce aural pain, evidence of multisensory interaction between auditory and pain pathways. To explore auditory-pain pathway interactions, we used the tail-flick (TF) test to assess thermal tail-pain sensitivity by measuring the latency of a rat to remove its tail from 52 °C water. In Experiment 1, TF latencies were measured in ambient noise and broadband noise (BBN) presented from 80 to 120 dB SPL. TF latencies gradually increased from ambient to 90 dB SPL (audio-analgesia), but then declined. At 120 dB, TF latencies were significantly shorter than normal, evidence for audio-hyperalgesia near the aural threshold for pain. In Experiment II, the opioid pain pathway was modified by treating rats with a high dose of fentanyl known to induce post-treatment hyperalgesia. TF latencies in ambient noise were normal 10-days post-fentanyl. However, TF latencies became shorter than normal from 90 to 110 dB indicating that fentanyl pre-treatment had converted audio-analgesia to audio-hyperalgesia. In Experiment III, we tested the hypothesis that hearing loss could alter pain sensitivity by unilaterally exposing rats to an intense noise that induced a significant hearing loss. TF latencies in ambient noise gradually declined from 1- to 4-weeks post-exposure indicating that noise-induced hearing loss had increased pain sensitivity. Our results suggest that auditory and pain pathways interact in ways that depend on intensity, hearing loss and opioid pain signaling, results potentially relevant to pain hyperacusis.

Tumor-induced neurogenesis and immune evasion as targets of innovative anti-cancer therapies

Normal cells are hijacked by cancer cells forming together heterogeneous tumor masses immersed in aberrant communication circuits that facilitate tumor growth and dissemination. Besides the well characterized angiogenic effect of some tumor-derived factors; others, such as BDNF, recruit peripheral nerves and leukocytes. The neurogenic switch, activated by tumor-derived neurotrophins and extracellular vesicles, attracts adjacent peripheral fibers (autonomic/sensorial) and neural progenitor cells. Strikingly, tumor-associated nerve fibers can guide cancer cell dissemination. Moreover, IL-1β, CCL2, PGE2, among other chemotactic factors, attract natural immunosuppressive cells, including T regulatory (Tregs), myeloid-derived suppressor cells (MDSCs), and M2 macrophages, to the tumor microenvironment. These leukocytes further exacerbate the aberrant communication circuit releasing factors with neurogenic effect. Furthermore, cancer cells directly evade immune surveillance and the antitumoral actions of natural killer cells by activating immunosuppressive mechanisms elicited by heterophilic complexes, joining cancer and immune cells, formed by PD-L1/PD1 and CD80/CTLA-4 plasma membrane proteins. Altogether, nervous and immune cells, together with fibroblasts, endothelial, and bone-marrow-derived cells, promote tumor growth and enhance the metastatic properties of cancer cells. Inspired by the demonstrated, but restricted, power of anti-angiogenic and immune cell-based therapies, preclinical studies are focusing on strategies aimed to inhibit tumor-induced neurogenesis. Here we discuss the potential of anti-neurogenesis and, considering the interplay between nervous and immune systems, we also focus on anti-immunosuppression-based therapies. Small molecules, antibodies and immune cells are being considered as therapeutic agents, aimed to prevent cancer cell communication with neurons and leukocytes, targeting chemotactic and neurotransmitter signaling pathways linked to perineural invasion and metastasis.

The Delayed-Onset Mechanical Pain Behavior Induced by Infant Peripheral Nerve Injury Is Accompanied by Sympathetic Sprouting in the Dorsal Root Ganglion

Background

Sympathetic sprouting in the dorsal root ganglion (DRG) following nerve injuries had been proved to induce adult neuropathic pain. However, it is unclear whether the abnormal sprouting occurs in infant nerve injury.

Methods

L5 spinal nerve ligation (SNL) or sham surgery was performed on adult rats and 10-day-old pups, and mechanical thresholds and heat hyperalgesia were analyzed on 3, 7, 14, 28, and 56 postoperative days. Tyrosine hydroxylase-labeled sympathetic fibers were observed at each time point, and 2 neurotrophin receptors (p75NTR and TrkA) were identified to explore the mechanisms of sympathetic sprouting.

Results

Adult rats rapidly developed mechanical and heat hyperalgesia from postoperative day 3, with concurrent sympathetic sprouting in DRG. In contrast, the pup rats did not show a significantly lower mechanical threshold until postoperative day 28, at which time the sympathetic sprouting became evident in the DRG. No heat hyperalgesia was presented in pup rats at any time point. There was a late expression of glial p75NTR in DRG of pups from postoperative day 28, which was parallel to the occurrence of sympathetic sprouting. The expression of TrkA did not show such a postoperative syncing change.

Conclusion

The delayed-onset mechanical allodynia in the infant nerve lesion was accompanied with parallel sympathetic sprouting in DRG. The late parallel expression of glial p75NTR injury may play an essential role in this process, which provides novel insight into the treatment of delayed adolescent neuropathic pain.

Role of transforaminal epidural injections or selective nerve root blocks in the management of lumbar radicular syndrome - A narrative, evidence-based review

OBJECTIVE

Lumbar radicular Syndrome (LRS) is a common spinal pathology and is attributed to complex interplay of mechanical, inflammatory and immunological processes. Epidural injection of steroids has a significant therapeutic role in mitigating the inflammatory component of LRS. Trans-foraminal approach under image guidance enables a targeted drug delivery. The current narrative review discusses the various aspects related to lumbar trans-foraminal epidural injection of steroid (LTFIS).

METHODS

An elaborate search on PubMed, Google and Medline databases was made using keywords "lumbar selective nerve root block", "lumbar trans-foraminal epidural steroid injection", "selective nerve root block in lumbar disc prolapse", "trans-foraminal epidural steroid injection in lumbar prolapse", "selective nerve root block in lumbar radiculopathy", and "trans-foraminal epidural steroid injection in lumbar radiculopathy" The articles were selected based on specific inclusion criteria.

RESULTS

Our search identified 539 articles. All articles discussing alternate procedures, LTFIS in other pathologies, diagnostic roles of LTFIS, not pertaining to concerned questions, in non-English language and duplicate articles were excluded. Review articles, randomised controlled trials or level 1 studies were given preference. Overall, 108 articles were included. Being a focussed narrative review, further screening [Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) or Methodological Index for non-randomized studies (MINORS) criteria] was not performed to select articles. Based on the evidence, LTFIS is an effective and useful treatment modality. It is offered to patients with lumbar disc herniation (LDH) presenting with persistent, unilateral, radiculopathy after a course of conservative measures for around 6 weeks' duration. It has been reported to yield better results than caudal or inter-laminar epidural injections. The anti-inflammatory and nociceptive signal stabilization actions of steroids, as well as mechanical effects of washout of inflammatory mediators and neural lysis contribute to its efficacy. The three different approaches include sub-pedicular, retro-neural and retro-discal. The procedure is performed under image guidance using a water-soluble contrast under fluoroscopy. The four described radiculogram patterns include "arm", "arrow", "linear" and "splash". Computerised tomography, ultrasonography and magnetic resonance imaging are other modalities, which may be helpful in performing LTFIS. The use of particulate versus non-particulate steroids is controversial.

CONCLUSION

The overall success rate of SNRB is reported to be 76-88%. The majority of benefits are observed during immediate and early post-injection period. Clinical factors including duration and severity of symptoms, and radiological factors like presence of osteophytes, location, size and type of disc prolapse influence outcomes. The radiculogram "splash" pattern is associated with poor outcomes.

Intra-articular injection of triamcinolone acetonide releasing biomaterial microspheres inhibits pain and inflammation in an acute arthritis model

Inflammation of the synovium and joint capsule is a main driver of pain in an osteoarthritic (OA) joint. Triamcinolone acetonide (TAA) is a classical corticosteroid that reduces synovitis and alleviates pain, albeit transiently. Biomaterial-based local TAA release may prolong the suppression of pain without the need for multiple injections. Polylactic-co-glycolic acid (PLGA) formulations of TAA prolong OA pain relief to a limited extent. A novel polyesteramide (PEA) microsphere platform allows for extended release in the OA joint for over 3 months. To evaluate their effect on pain and inflammation, TAA-loaded microspheres were intra-articularly delivered to the knee joint in a rat model of acute arthritis induced by intra-articular injection of streptococcal cell wall peptidoglycan-polysaccharide (PGPS) and subsequent flare-ups by intravenous PGPS injections. PEA-loaded microspheres were benchmarked with TAA-loaded PLGA microspheres and bolus TAA injection. TAA treatments were injected intra-articularly before the first induced flare-up. TAA-loaded PEA and PLGA microspheres reduced joint swelling and signs of pain-like behavior over the entire study period, as assessed by weight bearing and referred mechanical hypersensitivity, whereas bolus suspension was effective for a shorter time period. TAA-loaded PEA microspheres reduced lameness to a greater extent than TAA-loaded PLGA microspheres. In conclusion, a single intra-articular injection of TAA-loaded PEA microspheres reduced joint swelling and induced longer pain relief compared to bolus injection. Hence relief of inflammation and pain by PEA-based delivery of TAA may prove to be effective and durable.

The Effectiveness of Lumbar Transforaminal Injection of Steroid for the Treatment of Radicular Pain: A Comprehensive Review of the Published Data

Objective

To determine the effectiveness of lumbar transforaminal injection of steroid for the treatment of radicular pain.

Design

Comprehensive systematic review.

Outcome Measures

The primary outcome of interest was the proportion of individuals with reduction of pain by ≥50%. Additional outcomes of interest were a more-than-two-point reduction in pain score, patient satisfaction, functional improvement, decreased use of pain medication, and avoidance of spinal surgery.

Results

For patients with disc herniations, using the criterion of ≥50% reduction in pain, success rates across included studies (range) were 63% (58–68%) at one month, 74% (68–80%) at three months, 64% (59–69%) at six months, and 64% (57–71%) at one year. For patients with lumbar spinal stenosis, success rates across included studies (range) were 49% (43–55%) at one month, 48% (35–61%) at three months, 43% (33–53%) at six months, and 59% (45–73%) at one year, but there was a lack of corroboration from appropriately controlled studies.

Conclusions

There is strong evidence that lumbar transforaminal injection of steroids is an effective treatment for radicular pain due to disc herniation. There is a lack of high-quality evidence demonstrating their effectiveness for the treatment of radicular pain due to spinal stenosis, though small studies suggest a possible benefit. Lumbar transforaminal injection of nonparticulate steroids is as effective as injections with particulate steroids.

Intra-articular injection of triamcinolone acetonide releasing biomaterial microspheres inhibits pain and inflammation in an acute arthritis model

Inflammation of the synovium and joint capsule is a main driver of pain in an osteoarthritic (OA) joint. Triamcinolone acetonide (TAA) is a classical corticosteroid that reduces synovitis and alleviates pain, albeit transiently. Biomaterial-based local TAA release may prolong the suppression of pain without the need for multiple injections. Polylactic-co-glycolic acid (PLGA) formulations of TAA prolong OA pain relief to a limited extent. A novel polyesteramide (PEA) microsphere platform allows for extended release in the OA joint for over 3 months. To evaluate their effect on pain and inflammation, TAA-loaded microspheres were intra-articularly delivered to the knee joint in a rat model of acute arthritis induced by intra-articular injection of streptococcal cell wall peptidoglycan-polysaccharide (PGPS) and subsequent flare-ups by intravenous PGPS injections. PEA-loaded microspheres were benchmarked with TAA-loaded PLGA microspheres and bolus TAA injection. TAA treatments were injected intra-articularly before the first induced flare-up. TAA-loaded PEA and PLGA microspheres reduced joint swelling and signs of pain-like behavior over the entire study period, as assessed by weight bearing and referred mechanical hypersensitivity, whereas bolus suspension was effective for a shorter time period. TAA-loaded PEA microspheres reduced lameness to a greater extent than TAA-loaded PLGA microspheres. In conclusion, a single intra-articular injection of TAA-loaded PEA microspheres reduced joint swelling and induced longer pain relief compared to bolus injection. Hence relief of inflammation and pain by PEA-based delivery of TAA may prove to be effective and durable.

Rapid and Efficient Differentiation of Rodent Neural Stem Cells into Oligodendrocyte Progenitor Cells

Oligodendrocyte progenitor cells (OPCs) may have beneficial effects in cell replacement therapy of neurodegenerative disease owing to their unique capability to differentiate into myelinogenic oligodendrocytes (OLs) in response to extrinsic signals. Therefore, it is of significance to establish an effective differentiation methodology to generate highly pure OPCs and OLs from some easily accessible stem cell sources. To achieve this goal, in this study, we present a rapid and efficient protocol for oligodendroglial lineage differentiation from mouse neural stem cells (NSCs), rat NSCs, or mouse embryonic stem cell-derived neuroepithelial stem cells. In a defined culture medium containing Smoothened Agonist, basic fibroblast growth factor, and platelet-derived growth factor-AA, OPCs could be generated from the above stem cells over a time course of 4–6 days, achieving a cell purity as high as ∼90%. In particular, these derived OPCs showed high expandability and could further differentiate into myelin basic protein-positive OLs within 3 days or alternatively into glial fibrillary acidic protein-positive astrocytes within 7 days. Furthermore, transplantation of rodent NSC-derived OPCs into injured spinal cord indicated that it is a feasible strategy to treat spinal cord injury. Our results suggest a differentiation strategy for robust production of OPCs and OLs from rodent stem cells, which could provide an abundant OPC source for spinal cord injury.

Advances in Pain Management: Palliative Care Applications

One of the most important goals of palliative medicine and hospice care is pain relief. Although great strides have been made in veterinary analgesia, severe pain, especially at home, is still difficult to control. Pain control in the context of palliative medicine and hospice care is far more advanced in human medicine. Many modalities used in chronically or terminally ill humans might be adapted to animals to better manage severe pain. This article discusses drugs and procedures used to control pain in humans that are relatively nascent or unavailable in veterinary medicine and deserve further attention.

Analgesic effects of TLR4/NF-κB signaling pathway inhibition on chronic neuropathic pain in rats following chronic constriction injury of the sciatic nerve

OBJECTIVE

Chronic neuropathic pain (CNP) is attributed to a lesion or disease of the somatosensory system, may be derived from the peripheral and central system. Recent study revealed that spinal cord stimulation attenuated CNP by inhibiting TLR4/NF-κB signaling pathway. The present study focuses on the potential analgesic effects of TLR4/NF-κB signaling pathway on CNP in a rat model of chronic constriction injury (CCI).

METHODS

We successfully established the rat model of CCI by Bennett method, and then inhibited the TLR4/NF-κB signaling pathway in rat models. Next, we measured the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) 0D, 2D, 6D, 8D and 12D after operation respectively. MTS510 100 mg/kg, an inhibitor of TLR4, was intrathecal injected into rats after 6D, 8D and 12D after operation. The experiment lasted for 12 days, and then the rats were sacrificed to collect the spinal cord tissues. Protein and mRNA expression levels of toll-like receptor 4 (TLR4), nuclear factor-kappaB (NF-κB), glial cell line-derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP) and nerve growth factor (NGF) were detected by western blot analysis and RT-qPCR, respectively. Immunohistochemistry was performed to detect GDNF, GFAP and NGF expression.

RESULTS

With the prolongation of MTS510 treatment time, MWT and TWL were increased and finally, the MWT and TWL were close to the baseline level. The levels of TLR4, NF-κB, GDNF, and GFAP as well as NGF increased in rats treated with CCI + Immunoglobulin G1 (IgG1) or CCI + MTS510, suggesting the model establishment was successful. Besides, with the prolongation of MTS510 treatment time, the protein level and mRNA expression of NF-kB, GDNF, GFAP and NGF decreased in rats treated with CCI + IgG1 or CCI + MTS510. Moreover, the GDNF, GFAP and NGF expression in spinal cord tissue in rats treated with CCI + IgG1 or CCI + MTS510 increased obviously, while the GDNF, GFAP and NGF expression decreased in spinal cord tissue in rats treated with CCI + IgG1 or CCI + MTS510 after MTS510 treatment.

CONCLUSIONS

Collectively, this study defines the role of TLR4 and NF-κB, and inhibition of TLR4/NF-κB signaling pathway might contribute to the alleviation of CNP and improvement of MWT and TWL in a rat model of CCI. Additionally, the results obtained from the study provided a promising basis that could aid as an experimental basis for the potential treatment of TLR4/NF-κB signaling pathway.

Chronic orofacial pain animal models - progress and challenges

INTRODUCTION

Chronic orofacial pain is one of the most common pain conditions experienced by adults. Animal models are often selected as the most useful scientific methodology to explore the pathophysiology of the disorders that cause this disabling pain to facilitate the development of new treatments. The creation of new models or the improvement of existing ones is essential for finding new ways to approach the complex neurobiology of this type of pain. Areas covered: The authors describe and discuss a variety of animal models used in chronic orofacial pain (COFP). Furthermore, they examine in detail the mechanisms of action involved in orofacial neuropathic pain and orofacial inflammatory pain. Expert opinion: The use of animal models has several advantages in chronic orofacial pain drug discovery. Choosing an animal model that most closely represents the human disease helps to increase the chances of finding effective new therapies and is key to the successful translation of preclinical research to clinical practice. Models using genetically modified animals seem promising but have not yet been fully developed for use in chronic orofacial pain research. Although animal models have provided significant advances in the pharmacological treatment of orofacial pain, several barriers still need to be overcome for better treatment options.

The Neuromodulation Appropriateness Consensus Committee on Best Practices for Dorsal Root Ganglion Stimulation

INTRODUCTION

The Neuromodulation Appropriateness Consensus Committee (NACC) is dedicated to improving the safety and efficacy of neuromodulation and thus improving the lives of patients undergoing neuromodulation therapies. With continued innovations in neuromodulation comes the need for evolving reviews of best practices. Dorsal root ganglion (DRG) stimulation has significantly improved the treatment of complex regional pain syndrome (CRPS), among other conditions. Through funding and organizational leadership by the International Neuromodulation Society (INS), the NACC reconvened to develop the best practices consensus document for the selection, implantation and use of DRG stimulation for the treatment of chronic pain syndromes.

METHODS

The NACC performed a comprehensive literature search of articles about DRG published from 1995 through June, 2017. A total of 2538 article abstracts were then reviewed, and selected articles graded for strength of evidence based on scoring criteria established by the US Preventive Services Task Force. Graded evidence was considered along with clinical experience to create the best practices consensus and recommendations.

RESULTS

The NACC achieved consensus based on peer-reviewed literature and experience to create consensus points to improve patient selection, guide surgical methods, improve post-operative care, and make recommendations for management of patients treated with DRG stimulation.

CONCLUSION

The NACC recommendations are intended to improve patient care in the use of this evolving therapy for chronic pain. Clinicians who choose to follow these recommendations may improve outcomes.

Percutaneous dorsal root ganglion block for treating lumbar compression fracture-related pain

BACKGROUND

The pain of acute compression fracture in the lumbar spine may be refractory to conservative treatment, and surgery is not an optimal choice for the elderly or infirm individuals. Moreover, even vertebroplasty can cause many side effects such as chemical leak, adjacent segment instability, and residual pain. Percutaneous dorsal root ganglion block (PDRGB) possibly is an alternative therapeutic option. In this study, we evaluated the efficacy of pain relief and the rate of adjacent level compression fracture in patients with acute compression fracture of the lumbar spine.

METHODS

We retrospectively reviewed 40 patients with lumbar compression fracture from 2013 to 2015. The patients were treated with navigation-assisted CT-guided PDRGB with steroid at the pathological level and at the adjacent level above and below. Therapeutic response was evaluated using the Numerical Rating Scale (NRS); and an optimal, acceptable, and unfavorable outcome were analyzed.

RESULTS

Among the 40 patients treated, initial pain relief on the first day was dramatic, and the average NRS did not change significantly up to the first-year follow-up. The highest percentage of a good outcome, at 90% (37.5% with an optimal outcome, 52.5% with an acceptable outcome), was reported at 1 week postoperatively. The percentage of optimal outcomes increased even at the 1-year follow-up. No adjacent compression fracture was found in the group treated with PDRGB alone at the 1-year follow-up.

CONCLUSIONS

PDRGB is a simple, safe, and minimally invasive procedure that showed immediate and prolonged improvement of pain in lumbar osteoporotic compression fracture patients who failed conservative treatment or had residual pain after vertebroplasty. However, continuous medication for osteoporosis was still required.

Effect of Interlaminar Epidural Steroid Injection in Patients with Central Cervical Spinal Stenosis

OBJECTIVE

To investigate the effect of interlaminar epidural steroid injection (ESI) for management of central cervical spinal stenosis-induced posterior neck pain.

METHODS

This retrospective study recruited 45 patients with posterior neck pain caused by central cervical spinal stenosis. For the ESI procedure, a 21-gauge Touhy needle was inserted into the epidural space between C7 and T1, and 20 mg (40 mg/mL) of dexamethasone with 4 mL of normal saline was injected. The effect of the procedure was evaluated using a numerical rating scale at 1, 2, and 3 months after the procedure. Successful pain relief was defined as reduction in numerical rating scale score of ≥50% compared with before treatment. At 3 months after treatment, patient satisfaction levels were examined; patients who reported very good (score = 7) or good results (score = 6) were considered to be satisfied with the procedure.

RESULTS

Posterior neck pain was significantly reduced at follow-up evaluation 1, 2, and 3 months after ESI (P < 0.001, repeated measures 1-factor analysis). At 3 months after the procedure, 58% of the patients achieved a successful response (≥50% pain reduction), and 56% were satisfied with treatment results.

CONCLUSIONS

Cervical interlaminar ESI appears to be a good treatment method for managing chronic posterior neck pain induced by central cervical spinal stenosis, especially when pain is refractory to oral medication.

Targeting dorsal root ganglia and primary sensory neurons for the treatment of chronic pain

INTRODUCTION

Currently the treatment of chronic pain is inadequate and compromised by debilitating central nervous system side effects. Here we discuss new therapeutic strategies that target dorsal root ganglia (DRGs) in the peripheral nervous system for a better and safer treatment of chronic pain. Areas covered: The DRGs contain the cell bodies of primary sensory neurons including nociceptive neurons. After painful injuries, primary sensory neurons demonstrate maladaptive molecular changes in DRG cell bodies and in their axons. These changes result in hypersensitivity and hyperexcitability of sensory neurons (peripheral sensitization) and are crucial for the onset and maintenance of chronic pain. We discuss the following new strategies to target DRGs and primary sensory neurons as a means of alleviating chronic pain and minimizing side effects: inhibition of sensory neuron-expressing ion channels such as TRPA1, TRPV1, and Nav1.7, selective blockade of C- and Aβ-afferent fibers, gene therapy, and implantation of bone marrow stem cells. Expert opinion: These peripheral pharmacological treatments, as well as gene and cell therapies, aimed at DRG tissues and primary sensory neurons can offer better and safer treatments for inflammatory, neuropathic, cancer, and other chronic pain states.

Analgesic Effect of Dexamethasone after Arthroscopic Knee Surgery: A Randomized Controlled Trial

Background. Dexamethasone is sometimes used as a coanalgesic because of its anti-inflammatory properties. Objective. To evaluate opioid use, postoperative pain intensity, and side effects after a single dose of dexamethasone in patients undergoing arthroscopic knee surgery. Methods. In this randomized controlled study patients were randomized to receive either 10 mg of intravenous dexamethasone (DM group) or 0.9% normal saline (NS group) during the intraoperative period. Primary outcomes were pain intensity and total morphine and codeine use after surgery. Results. Seventy-eight patients were included in the study. The DM group showed statistically significant higher pain intensity at the fourth postoperative hour (DM: 3.96/10, standard deviation [SD] 0.54; NS: 2.46/10, SD 0.45; p = 0.036). No statistically significant difference in total opioid use (morphine plus codeine) was identified with 15.9 (SD 1.97) codeine tablets used in DM group and 20 (SD 2.14) in NS group (p = 0.25). Discussion. Pain intensity tended to decrease in both groups suggesting morphine as the main source of analgesia. Conclusions. Intravenous dexamethasone during the intraoperative period has no clinical impact on postoperative pain intensity during the first 48 h after arthroscopic knee surgery. This trial is registered with R000020892.

Analgesic properties of intrathecal glucocorticoids in three well established preclinical pain models

BACKGROUND AND AIMS

Glucocorticoids, a group of anti-inflammatory agents, are frequently administered in pain medicine. Of interest is the reported activity after intrathecal delivery in patients with neuropathic pain syndromes such as postherpetic neuralgia, though its efficacy is controversial. After the publication of two randomized clinical trials in postherpetic neuralgia patients treated with similar intrathecal methylprednisolone acetate (MPA) dosing regimes with conflicting results; one showing significant pain reduction (Kotani N, Kushikata T, Hashimoto H, Kimura F, Muraoka M, Yodono M, Asai M, Matsuki A: Intrathecal methylprednisolone for intractable postherpetic neuralgia. N Engl J Med 2000;23: 1514-9), the other increased pain sensations (Rijsdijk M, van Wijck AJ, Meulenhoff PC, Kavelaars A, van der Tweel I, Kalkman CJ: No beneficial effect of intrathecal methylprednisolone acetate in postherpetic neuralgia patients. Eur J Pain 2013;38: 175-200), we decided additional research was warranted. Present study sought to determine effects of intrathecally delivered methylprednisolone on pain-like behaviour and pain-associated markers in three well established rodent pain models: (1) intraplantar carrageenan, (2) intraplantar formalin, and (3) ligation of L5/L6 spinal nerves (SNL model).

METHODS

Male rats with intrathecal catheters were examined for (1) tactile allodynia after unilateral hindpaw intraplantar carrageenan injection (2%), (2) flinching and subsequent long term tactile allodynia after unilateral hindpaw intraplantar formalin injection (2.5%) or (3) tactile allodynia after unilateral ligation of the L5 and L6 spinal nerves. Rats were treated with the maximum tolerable intrathecal dose of the soluble methylprednisolone sodium succinate (MP) or the particulate methylprednisolone acetate (MPA). Dorsal root ganglia and spinal cords were harvested for immunohistochemistry to assess markers of neuronal damage (ATF3) and glial activation (GFAP, Iba1).

RESULTS

During dose finding, severe generalized allodynia was observed with high intrathecal doses of both MPA and MP in naive rats. MPA had no effect upon tactile allodynia after carrageenan. MP and MPA did not reverse tactile allodynia in the SNL model, and did not reduce flinching in the formalin model. MP and MPA prevented the delayed (7-day) tactile allodynia otherwise observed in the formalin-injected paw. Systemic MP or perineural MP or MPA did not reduce pain-like behaviour in the SNL model. No reduction of neuronal injury (ATF3) in the dorsal root ganglion or astrocyte activation (GFAP) in the spinal dorsal horn with intrathecal MP or MPA was observed. There was a decrease in microglial activation (Iba1) in the spinal dorsal horn with MPA after SNL.

CONCLUSION

Severe generalized allodynia was observed after high intrathecal doses of MP and MPA in naive rats. No acute analgesic effects with intrathecal glucocorticoids were observed in three well established pain models. Only a late antiallodynic effect was present in the formalin model, 7 days after formalin injection and drug treatment.

IMPLICATIONS

Our results do not support use of intrathecal methylprednisolone in the treatment of pain.

Progress in Sympathetically Mediated Pathological Pain

Aim of review

Many chronic pain conditions remain difficult to treat, presenting a high burden to society. Conditions such as complex regional pain syndrome may be maintained or exacerbated by sympathetic activity. Understanding the interactions between sympathetic nervous system and sensory system will help to improve the effective management of pathological pain including intractable neuropathic pain and persistent inflammatory pain.

Method

We first described the discovery of abnormal connections between sympathetic and sensory neurons. Subsequently, the functional roles of sympathetic sprouting in altered neuronal excitability and increased pain sensitivity were discussed. The mechanisms of the sympathetic sprouting were focusing on its relationship with neurotrophins, local inflammation, and abnormal spontaneous activity. Finally, we discussed clinical implications and conflicting findings in the laboratory and clinical research with respect to the interaction between sympathetic system and sensory system.

Recent findings

The findings that sprouting of sympathetic fibers into the sensory ganglia (dorsal root ganglion) after peripheral nerve injury, offers a possible explanation of the sympathetic involvement in pain. It is also suggested that releases of adenosine triphosphate (ATP), in addition to norepinephrine, from sympathetic nerve endings play important roles in sympathetic-mediated pain. New evidence indicates the importance of sympathetic innervation in local inflammatory responses.

Summary

Hopefully, this review will reinvigorate the study of sympathetic-sensory interactions in chronic pain conditions, and help to better understand how sympathetic system contributes to this serious clinical problem.

Nerve block for the treatment of headaches and cranial neuralgias - a practical approach

BACKGROUND

Several studies have presented evidence that blocking peripheral nerves is effective for the treatment of some headaches and cranial neuralgias, resulting in reduction of the frequency, intensity, and duration of pain.

OBJECTIVES

In this article we describe the role of nerve block in the treatment of headaches and cranial neuralgias, and the experience of a tertiary headache center regarding this issue. We also report the anatomical landmarks, techniques, materials used, contraindications, and side effects of peripheral nerve block, as well as the mechanisms of action of lidocaine and dexamethasone.

CONCLUSIONS

The nerve block can be used in primary (migraine, cluster headache, and nummular headache) and secondary headaches (cervicogenic headache and headache attributed to craniotomy), as well in cranial neuralgias (trigeminal neuropathies, glossopharyngeal and occipital neuralgias). In some of them this procedure is necessary for both diagnosis and treatment, while in others it is an adjuvant treatment. The block of the greater occipital nerve with an anesthetic and corticosteroid compound has proved to be effective in the treatment of cluster headache. Regarding the treatment of other headaches and cranial neuralgias, controlled studies are still necessary to clarify the real role of peripheral nerve block.

The effects of locally injected triamcinolone on entrapment neuropathy in a rat chronic constriction injury model

PURPOSE

Patients with idiopathic carpal tunnel syndrome are commonly treated by steroid injections into the carpal tunnel. We administered triamcinolone (Tr) to chronic constriction injury model rats. We hypothesized that Tr administration would have both favorable behavioral effects and quantifiable immunohistological effects on compressed nerves.

METHODS

Thirty-six male Wister rats were used. For rats to be treated with Tr, we loosely ligated their right sciatic nerves at 4 sites. Sham rats had their nerves exposed without ligation. On postoperative day 7, we reexposed their ligated nerves, after which we delivered either 0.1 mg of Tr (0.1-mg group), 0.5 mg of Tr (0.5-mg group), or normal saline (saline group) around the nerve fibers at the injured sites. Gait was analyzed, and allodynia was assessed with von Frey hairs, before surgery and on postoperative days 3, 7, 10, 14, and 21. The right sciatic nerve was resected and stained using hematoxylin-eosin, and the fourth and fifth lumbar dorsal root ganglia (DRG) were removed and assessed by immunohistochemistry for calcitonin gene-related peptide (CGRP) and activating transcription factor 3 (ATF3) on postoperative day 21. In addition, interleukin-1β (IL-1β) in sciatic nerve was quantified using enzyme-linked immunosorbent assays.

RESULTS

Mechanical allodynia was significantly decreased in the 0.5-mg group compared with the saline group. In hematoxylin-eosin sections, the extent of inflammation-induced edema between the nerve fibers and infiltration of inflammatory cells was significantly reduced in the 0.5-mg group compared with the saline group. IL-1β levels at the sciatic nerve in the 0.5-mg group were significantly lower than those in the saline group.

CONCLUSIONS

Tr-treated chronic constriction injury rats exhibited significant alleviation of sensory disturbance, edema, inflammation, and pain-related peptide upregulation. These phenomena suggest the validity of Tr administration as a treatment affecting the nerve itself.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic I.

Peripheral nervous system origin of phantom limb pain

Nearly all amputees continue to feel their missing limb as if it still existed, and many experience chronic phantom limb pain (PLP). What is the origin of these sensations? There is currently a broad consensus among investigators that PLP is a top-down phenomenon, triggered by loss of sensory input and caused by maladaptive cortical plasticity. We tested the alternative hypothesis that PLP is primarily a bottom-up process, due not to the loss of input but rather to exaggerated input, generated ectopically in axotomized primary afferent neurons in the dorsal root ganglia (DRGs) that used to innervate the limb. In 31 amputees, the local anesthetic lidocaine was applied intrathecally and/or to the DRG surface (intraforaminal epidural block). This rapidly and reversibly extinguished PLP and also nonpainful phantom limb sensation (npPLS). Control injections were ineffective. For intraforaminal block, the effect was topographically appropriate. The suppression of PLP and npPLS could also be demonstrated using dilute lidocaine concentrations that are sufficient to suppress DRG ectopia but not to block the propagation of impulses generated further distally in the nerve. PLP is driven primarily by activity generated within the DRG. We recommend the DRG as a target for treatment of PLP and perhaps also other types of regional neuropathic pain.

The effects of glucocorticoids on neuropathic pain: a review with emphasis on intrathecal methylprednisolone acetate delivery

Methylprednisolone acetate (MPA) has a long history of use in the treatment of sciatic pain and other neuropathic pain syndromes. In several of these syndromes, MPA is administered in the epidural space. On a limited basis, MPA has also been injected intrathecally in patients suffering from postherpetic neuralgia and complex regional pain syndrome. The reports on efficacy of intrathecal administration of MPA in neuropathic pain patients are contradictory, and safety is debated. In this review, we broadly consider mechanisms whereby glucocorticoids exert their action on spinal cascades relevant to the pain arising after nerve injury and inflammation. We then focus on the characteristics of the actions of MPA in pharmacokinetics, efficacy, and safety when administered in the intrathecal space.

Glia and pain: is chronic pain a gliopathy?

Activation of glial cells and neuro-glial interactions are emerging as key mechanisms underlying chronic pain. Accumulating evidence has implicated 3 types of glial cells in the development and maintenance of chronic pain: microglia and astrocytes of the central nervous system (CNS), and satellite glial cells of the dorsal root and trigeminal ganglia. Painful syndromes are associated with different glial activation states: (1) glial reaction (ie, upregulation of glial markers such as IBA1 and glial fibrillary acidic protein (GFAP) and/or morphological changes, including hypertrophy, proliferation, and modifications of glial networks); (2) phosphorylation of mitogen-activated protein kinase signaling pathways; (3) upregulation of adenosine triphosphate and chemokine receptors and hemichannels and downregulation of glutamate transporters; and (4) synthesis and release of glial mediators (eg, cytokines, chemokines, growth factors, and proteases) to the extracellular space. Although widely detected in chronic pain resulting from nerve trauma, inflammation, cancer, and chemotherapy in rodents, and more recently, human immunodeficiency virus-associated neuropathy in human beings, glial reaction (activation state 1) is not thought to mediate pain sensitivity directly. Instead, activation states 2 to 4 have been demonstrated to enhance pain sensitivity via a number of synergistic neuro-glial interactions. Glial mediators have been shown to powerfully modulate excitatory and inhibitory synaptic transmission at presynaptic, postsynaptic, and extrasynaptic sites. Glial activation also occurs in acute pain conditions, and acute opioid treatment activates peripheral glia to mask opioid analgesia. Thus, chronic pain could be a result of "gliopathy," that is, dysregulation of glial functions in the central and peripheral nervous system. In this review, we provide an update on recent advances and discuss remaining questions.

Abnormal activation of complement C3 in the spinal dorsal horn is closely associated with progression of neuropathic pain

The aim of the present study was to investigate the role of complement activation in the pathogenesis of neuropathic pain (NPP) induced by peripheral nerve injury. We modified a classical chronic constriction injury (CCI) model (mCCI), and verified its reliability in rats. Furthermore, reverse transcription-PCR and immunohistochemistry were conducted to investigate complement activation in the spinal dorsal horn and the effect of a complement inhibitor, cobra venom factor (CVF), on the behavior of the mCCI model rats. We found that rats in the mCCI group presented a better general condition, without signs of autophagy of the toes. Moreover, mCCI induced a significant increase (+40%) in the expression of component 3 (C3) mRNA in the spinal dorsal horn, which was associated with hyperalgesia. Correlation analysis showed a negative correlation between the mechanical pain threshold and the expression of C3 in the spinal cord. Administration of CVF reduced the occurrence of hyperalgesia in mCCI rats and nearly reversed the hyperalgesia. In addition, the mCCI rats exhibited significantly less spinal superoxide dismutase activity and significantly greater levels of maleic dialdehyde compared to the sham-operated rats. Transmission electron micrographs revealed mitochondrial swelling, cell membrane damage, and cristae fragmentation in the neurons of the spinal dorsal horn 14 days after mCCI. Mitochondrial swelling was attenuated in mCCI rats receiving CVF. The findings demonstrated that abnormal complement activation occurred in the dorsal horn of the spinal cord in rats with NPP, and C3 in the spinal dorsal horn could play an important role in the cascade reaction of complements that are involved in the development of hyperalgesia.

Surgically induced neuropathic pain: understanding the perioperative process

Nerve damage takes place during surgery. As a consequence, significant numbers (10%-40%) of patients experience chronic neuropathic pain termed surgically induced neuropathic pain (SNPP). The initiating surgery and nerve damage set off a cascade of events that includes both pain and an inflammatory response, resulting in "peripheral and central sensitization," with the latter resulting from repeated barrages of neural activity from nociceptors. In affected patients, these initial events produce chemical, structural, and functional changes in the peripheral and central nervous systems (CNS). The maladaptive changes in damaged nerves lead to peripheral manifestations of the neuropathic state-allodynia, sensory loss, shooting pains, etc, that can manifest long after the effects of the surgical injury have resolved. The CNS manifestations that occur are termed "centralization of pain" and affect sensory, emotional, and other (eg, cognitive) systems as well as contributing to some of the manifestations of the chronic pain syndrome (eg, depression). Currently there are no objective measures of nociception and pain in the perioperative period. As such, intermittent or continuous pain may take place during and after surgery. New technologies including direct measures of specific brain function of nociception and new insights into preoperative evaluation of patients including genetic predisposition, appear to provide initial opportunities for decreasing the burden of SNPP, until treatments with high efficacy and low adverse effects that either prevent or treat pain are discovered.

Microarray analysis of rat sensory ganglia after local inflammation implicates novel cytokines in pain

Inflammation plays a role in neuropathic pain conditions as well as in pain induced solely by an inflammatory stimulus. Robust mechanical hyperalgesia and allodynia can be induced by locally inflaming the L5 dorsal root ganglion (DRG) in rat. This model allows investigation of the contribution of inflammation per se to chronic pain conditions. Most previous microarray studies of DRG gene expression have investigated neuropathic pain models. To examine the role of inflammation, we used microarray methods to examine gene expression 3 days after local inflammation of the L5 DRG in rat. We observed significant regulation in a large number of genes (23% of observed transcripts), and examined 221 (3%) with a fold-change of 1.5-fold or more in more detail. Immune-related genes were the largest category in this group and included members of the complement system as well as several pro-inflammatory cytokines. However, these upregulated cytokines had no prior links to peripheral pain in the literature other than through microarray studies, though most had previously described roles in CNS (especially neuroinflammatory conditions) as well as in immune responses. To confirm an association to pain, qPCR studies examined these cytokines at a later time (day 14), as well as in two different versions of the spinal nerve ligation pain model including a version without any foreign immunogenic material (suture). Cxcl11, Cxcl13, and Cxcl14 were found to be significantly upregulated in all these conditions, while Cxcl9, Cxcl10, and Cxcl16 were upregulated in at least two of these conditions.

Identification and characterization of triamcinolone acetonide, a microglial-activation inhibitor

Recent studies show that necrotic neuronal cells (NNC) activate microglia, thereby leading to neuronal cell death. This suggests that chemicals that inhibit microglia activation may be used as neuroprotective drugs. In this context, we screened a chemical library for inhibitors of microglia activation. Using a screening system based on a nitrite assay, we isolated two chemicals that inhibit nitric oxide (NO) release from activated microglia: triamcinolone acetonide (TA) and amcinonide. The half-maximal inhibitory concentrations (IC50) of TA and amcinonide for NO release inhibition were 1.78 nM and 3.38 nM, respectively. These chemicals also inhibited NNC-induced expression of the proinflammatory genes iNOS, TNF-α, and IL-1β in glial cells. A study based on a luciferase assay revealed that TA attenuated NNC-induced microglia activation by blocking the NF-κB signaling pathway. In addition, TA protected cortical neurons in coculture with microglia from LPS/IFN-γ-induced neuronal cell death. In conclusion, TA may inhibit microglia activation and may protect neuronal cells from death induced by microglial activation.