Propofol Alleviates Neuropathic Pain Induced by Chronic Contractile Injury by Regulating the Spinal glun2b-p38mapkepac1 Pathway.

BACKGROUND: Propofol acts as an intravenous anesthetic cure which is widely used as a therapy for the craniocerebral injury that comprised surgical anesthesia as well as the sedation done in the intensive care units. Propofol is one of the most commonly used and efficient anesthetics where the painful effects are followed by an injection of propofol. In many cases, patients experience pain followed by anxiety, boredom, fear, and even myocardial ischemia. OBJECTIVE: This study was performed to investigate the underlying mechanism of propofol and its effect on regulating spinal glun2b-p38mapkepac1 pathways in chronic contractile injury. Material and Methods. Contractile injury was performed by ligation around the nerve of the thigh region postanesthesia. Rats were divided into three groups to analyze the changes like mechanical allodynia by the paw withdrawal threshold and histopathological analysis for assessing cellular degradation. L4-L6 from the spinal dorsal horns were isolated and harvested for studying protein expression, by the method of western blotting and immunofluorescence analysis. RESULTS: The pain caused due to mechanical allodynia in the paw region was highest at 1 hour postinduction and lasted for three days postinjury. Pain was significantly less in the group receiving propofol when compared with the isoflurane group for the first two hours of injury. In the propofol group, EPAC1, GluN2B, and p38 MAP K were significantly lower. CONCLUSION: In the rat model of induced chronic contractile injury, postsurgery there was a suppression of the GluN2B-p38MAPK/EPAC1 signaling pathway in the propofol group. As the p38MAPK/EPAC pathway has a significant role in the postoperative hyperalgesia, thus our experiment suggests that propofol has analgesic effects.

Modulation of proteoglycan receptor regulates RhoA/CRMP2 pathways and promotes axonal myelination.

The function of the myelinating system is important because a defective myelin sheath results in various nervous disorders, including multiple sclerosis and peripheral neuropathies. The dorsal root entry zone (DREZ) is a transitional area between the central nervous system (CNS) and the peripheral nervous system (PNS) that is generated by two types of cells-oligodendrocytes and Schwann cells (SCs). It is well known that after injury the extracellular matrix, including the CSPG, impairs axonal myelination by activating protein tyrosine phosphatase-σ (PTPσ) in both cells. The Intracellular Sigma Peptide (ISP) is memetic of the PTPσ wedge region. It competitively binds to PTPσ and regulates the downstream signaling of RhoA. In the present study, we aimed to investigate whether the ISP increased myelination in vivo and in vitro. The in vitro assay was meant to further verify the in vivo mechanisms. We observed that ISP administration could increase axonal myelination both in vivo and in vitro. Furthermore, we provide evidence that, in oligodendrocytes and Schwann cells, the myelination-induced effects of ISP application entail an inverse expression of the RhoA/CRMP2 signaling pathway. Overall, our results indicate that the ISP modulation of PTPσ enhances axonal myelination via the RhoA/CRMP2 signaling pathways.

ATF3-Expressing Large-Diameter Sensory Afferents at Acute Stage as Bio-Signatures of Persistent Pain Associated with Lumbar Radiculopathy.

The mechanism of pain chronicity is largely unknown in lumbar radiculopathy (LR). The anatomical location of nerve injury is one of the important factors associated with pain chronicity of LR. Accumulating evidence has shown constriction distal to the dorsal root ganglion (DRG) caused more severe radiculopathy than constriction proximal to the DRG; thereby, the mechanism of pain chronicity in LR could be revealed by comparing the differences in pathological changes of DRGs between nerve constriction distal and proximal to the DRG. Here, we used 2 rat models of LR with nerve constriction distal or proximal to the DRG to probe how the different nerve injury sites could differentially affect pain chronicity and the pathological changes of DRG neuron subpopulations. As expected, rats with nerve constriction distal to the DRG showed more persistent pain behaviors than those with nerve constriction proximal to the DRG in 50% paw withdraw threshold, weight-bearing test, and acetone test. One day after the operation, distal and proximal nerve constriction showed differential pathological changes of DRG. The ratios of activating transcription factor3 (ATF3)-positive DRG neurons were significantly higher in rats with nerve constriction distal to DRG than those with nerve constriction proximal to DRG. In subpopulation analysis, the ratios of ATF3-immunoreactivity (IR) in neurofilament heavy chain (NFH)-positive DRG neurons significantly increased in distal nerve constriction compared to proximal nerve constriction; although, both distal and proximal nerve constriction presented increased ratios of ATF3-IR in calcitonin gene-related peptide (CGRP)-positive DRG neurons. Moreover, the nerve constriction proximal to DRG caused more hypoxia than did that distal to DRG. Together, ATF3 expression in NHF-positive DRG neurons at the acute stage is a potential bio-signature of persistent pain in rat models of LR.

Patch Clamp Analysis of Opioid-Induced Kir3 Currents in Mouse Peripheral Sensory Neurons Following Nerve Injury.

Patch clamp is an electrophysiological technique that allows to analyze the activity of ion channels in neurons. In this chapter, we provide a detailed description of patch clamp protocol to measure the effect of a µ-opioid receptor agonist on the activity of G protein-coupled inwardly rectifying potassium (GIRK or Kir3) channels. This is performed in peripheral sensory neurons isolated from dorsal root ganglia (DRG) of mice without or with a chronic constriction injury (CCI) of the sciatic nerve, which models neuropathic pain. We describe the induction of the CCI , isolation and culture of DRG neurons, performance of the patch clamp recordings, and identification of opioid-responding neurons.

Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury.

After a dorsal root crush injury, centrally-projecting sensory axons fail to regenerate across the dorsal root entry zone (DREZ) to extend into the spinal cord. We find that chemogenetic activation of adult dorsal root ganglion (DRG) neurons improves axon growth on an in vitro model of the inhibitory environment after injury. Moreover, repeated bouts of daily chemogenetic activation of adult DRG neurons for 12 weeks post-crush in vivo enhances axon regeneration across a chondroitinase-digested DREZ into spinal gray matter, where the regenerating axons form functional synapses and mediate behavioral recovery in a sensorimotor task. Neuronal activation-mediated axon extension is dependent upon changes in the status of tubulin post-translational modifications indicative of highly dynamic microtubules (as opposed to stable microtubules) within the distal axon, illuminating a novel mechanism underlying stimulation-mediated axon growth. We have identified an effective combinatory strategy to promote functionally-relevant axon regeneration of adult neurons into the CNS after injury.

A Ca2+-Dependent Switch Activates Axonal Casein Kinase 2α Translation and Drives G3BP1 Granule Disassembly for Axon Regeneration.

The main limitation on axon regeneration in the peripheral nervous system (PNS) is the slow rate of regrowth. We recently reported that nerve regeneration can be accelerated by axonal G3BP1 granule disassembly, releasing axonal mRNAs for local translation to support axon growth. Here, we show that G3BP1 phosphorylation by casein kinase 2α (CK2α) triggers G3BP1 granule disassembly in injured axons. CK2α activity is temporally and spatially regulated by local translation of Csnk2a1 mRNA in axons after injury, but this requires local translation of mTor mRNA and buffering of the elevated axonal Ca2+ that occurs after axotomy. CK2α's appearance in axons after PNS nerve injury correlates with disassembly of axonal G3BP1 granules as well as increased phospho-G3BP1 and axon growth, although depletion of Csnk2a1 mRNA from PNS axons decreases regeneration and increases G3BP1 granules. Phosphomimetic G3BP1 shows remarkably decreased RNA binding in dorsal root ganglion (DRG) neurons compared with wild-type and non-phosphorylatable G3BP1; combined with other studies, this suggests that CK2α-dependent G3BP1 phosphorylation on Ser 149 after axotomy releases axonal mRNAs for translation. Translation of axonal mRNAs encoding some injury-associated proteins is known to be increased with Ca2+ elevations, and using a dual fluorescence recovery after photobleaching (FRAP) reporter assay for axonal translation, we see that translational specificity switches from injury-associated protein mRNA translation to CK2α translation with endoplasmic reticulum (ER) Ca2+ release versus cytoplasmic Ca2+ chelation. Our results point to axoplasmic Ca2+ concentrations as a determinant for the temporal specificity of sequential translational activation of different axonal mRNAs as severed axons transition from injury to regenerative growth.

Pain modulation effect on motor cortex after optogenetic stimulation in shPKCγ knockdown dorsal root ganglion-compressed Sprague-Dawley rat model.

Neuropathic pain can be generated by chronic compression of dorsal root ganglion (CCD). Stimulation of primary motor cortex can disrupt the nociceptive sensory signal at dorsal root ganglion level and reduce pain behaviors. But the mechanism behind it is still implicit. Protein kinase C gamma is known as an essential enzyme for the development of neuropathic pain, and specific inhibitor of protein kinase C gamma can disrupt the sensory signal and reduce pain behaviors. Optogenetic stimulation has been emerged as a new and promising conducive method for refractory neuropathic pain. The aim of this study was to provide evidence whether optical stimulation of primary motor cortex can modulate chronic neuropathic pain in CCD rat model. Animals were randomly divided into CCD group, sham group, and control group. Dorsal root ganglion-compressed neuropathic pain model was established in animals, and knocking down of protein kinase C gamma was also accomplished. Pain behavioral scores were significantly improved in the short hairpin Protein Kinase C gamma knockdown CCD animals during optic stimulation. Ventral posterolateral thalamic firing inhibition was also observed during light stimulation on motor cortex in CCD animal. We assessed alteration of pain behaviors in pre-light off, stimulation-light on, and post-light off state. In vivo extracellular recording of the ventral posterolateral thalamus, viral expression in the primary motor cortex, and protein kinase C gamma expression in dorsal root ganglion were investigated. So, optical cortico-thalamic inhibition by motor cortex stimulation can improve neuropathic pain behaviors in CCD animal, and knocking down of protein kinase C gamma plays a conducive role in the process. This study provides feasibility for in vivo optogenetic stimulation on primary motor cortex of dorsal root ganglion-initiated neuropathic pain.

Global transcriptome analysis of rat dorsal root ganglia to identify molecular pathways involved in incisional pain.

To develop non-opioid therapies for postoperative incisional pain, we must understand its underlying molecular mechanisms. In this study, we assessed global gene expression changes in dorsal root ganglia neurons in a model of incisional pain to identify pertinent molecular pathways. Male, Sprague-Dawley rats underwent infiltration of 1% capsaicin or vehicle into the plantar hind paw (n = 6-9/group) 30 min before plantar incision. Twenty-four hours after incision or sham (control) surgery, lumbar L4-L6 dorsal root ganglias were collected from rats pretreated with vehicle or capsaicin. RNA was isolated and sequenced by next generation sequencing. The genes were then annotated to functional networks using a knowledge-based database, Ingenuity Pathway Analysis. In rats pretreated with vehicle, plantar incision caused robust hyperalgesia, up-regulated 36 genes and downregulated 90 genes in dorsal root ganglias one day after plantar incision. Capsaicin pretreatment attenuated pain behaviors, caused localized denervation of the dermis and epidermis, and prevented the incision-induced changes in 99 of 126 genes. The pathway analyses showed altered gene networks related to increased pro-inflammatory and decreased anti-inflammatory responses in dorsal root ganglias. Insulin-like growth factor signaling was identified as one of the major gene networks involved in the development of incisional pain. Expression of insulin-like growth factor -2 and IGFBP6 in dorsal root ganglia were independently validated with quantitative real-time polymerase chain reaction. We discovered a distinct subset of dorsal root ganglia genes and three key signaling pathways that are altered 24 h after plantar incision but are unchanged when incision was made after capsaicin infiltration in the skin. Further exploration of molecular mechanisms of incisional pain may yield novel therapeutic targets.

Naked mole-rats lack cold sensitivity before and after nerve injury.

Neuropathic pain is a chronic disease state resulting from injury to the nervous system. This type of pain often responds poorly to standard treatments and occasionally may get worse instead of better over time. Patients who experience neuropathic pain report sensitivity to cold and mechanical stimuli. Since the nociceptive system of African naked mole-rats contains unique adaptations that result in insensitivity to some pain types, we investigated whether naked mole-rats may be resilient to sensitivity following nerve injury. Using the spared nerve injury model of neuropathic pain, we showed that sensitivity to mechanical stimuli developed similarly in mice and naked mole-rats. However, naked mole-rats lacked sensitivity to mild cold stimulation after nerve injury, while mice developed robust cold sensitivity. We pursued this response deficit by testing behavior to activators of transient receptor potential (TRP) receptors involved in detecting cold in naïve animals. Following mustard oil, a TRPA1 activator, naked mole-rats responded similarly to mice. Conversely, icilin, a TRPM8 agonist, did not evoke pain behavior in naked mole-rats when compared with mice. Finally, we used RNAscope to probe for TRPA1 and TRPM8 messenger RNA expression in dorsal root ganglia of both species. We found increased TRPA1 messenger RNA, but decreased TRPM8 punctae in naked mole-rats when compared with mice. Our findings likely reflect species differences due to evolutionary environmental responses that are not easily explained by differences in receptor expression between the species.

Abnormal Reinnervation of Denervated Areas Following Nerve Injury Facilitates Neuropathic Pain.

An injury to peripheral nerves leads to skin denervation, which often is followed by increased pain sensitivity of the denervated areas and the development of neuropathic pain. Changes in innervation patterns during the reinnervation process of the denervated skin could contribute to the development of neuropathic pain. Here, we examined the changes in the innervation pattern during reinnervation and correlated them with the symptoms of neuropathic pain. Using a multispectral labeling technique-PainBow, which we developed, we characterized dorsal root ganglion (DRG) neurons innervating distinct areas of the rats' paw. We then used spared nerve injury, causing partial denervation of the paw, and examined the changes in innervation patterns of the denervated areas during the development of allodynia and hyperalgesia. We found that, differently from normal conditions, during the development of neuropathic pain, these areas were mainly innervated by large, non-nociceptive neurons. Moreover, we found that the development of neuropathic pain is correlated with an overall decrease in the number of DRG neurons innervating these areas. Importantly, treatment with ouabain facilitated reinnervation and alleviated neuropathic pain. Our results suggest that local changes in peripheral innervation following denervation contribute to neuropathic pain development. The reversal of these changes decreases neuropathic pain.

Optical Modulation on the Nucleus Accumbens Core in the Alleviation of Neuropathic Pain in Chronic Dorsal Root Ganglion Compression Rat Model.

OBJECTIVE: The role of the nucleus accumbens (NAc) in chronic neuropathic pain has been suggested, but the role of the NAc in dorsal root ganglion (DRG) neuropathic pain remains unclear. The objective of this study was to determine whether optogenetic stimulation of the NAc influences DRG compression-induced neuropathic pain. MATERIALS AND METHODS: We established sham or DRG lesions in female Sprague-Dawley rats by L4-5 DRG root compression, and the animals received unilateral injections of optogenetic virus in the NAc core. We employed reflexive pain tests to assess the alterations between the groups at the light on/off states. To determine thalamic firing, we performed single-unit in vivo extracellular recording. For statistical analysis, we used one- or two-way repeated-measures analysis of variance. RESULTS: Compared to sham-operated rats, chronic compressed DRG rats showed elevated behavioral sensitivity and sustained neuronal hyperexcitability in the thalamus. NAc optic stimulation improved pain behaviors and lowered thalamic discharge from ventral posterolateral thalamic nuclei. CONCLUSIONS: The NAc core impacts the reward and motivational aspects of chronic neuropathic pain influenced by limbic behaviors to thalamic discharge. Increased thalamic firing activity may result in chronic compressed DRG-induced neuropathic pain, and optogenetic neuromodulation of the NAc can ease chronic pain and thalamic discharge.

Perineural application of resiniferatoxin on uninjured L3 and L4 nerves completely alleviates thermal and mechanical hypersensitivity following L5 nerve injury in rats.

Fifth lumbar (L5) nerve injury in rats causes neuropathic pain manifested with thermal and mechanical hypersensitivity in the ipsilateral hind paw. This study aimed to determine whether the elimination of unmyelinated primary afferents of the adjacent uninjured nerves (L3 and L4) would alleviate peripheral neuropathic pain. Different concentrations of capsaicin or its analog, resiniferatoxin (RTX), were applied perineurally on either the left L4 or L3 and L4 nerves in Wistar rats whose left L5 nerves were ligated and cut. The application of both capsaicin and RTX on the L4 nerve significantly reduced both thermal and mechanical hypersensitivity. However, only the application of RTX on both L3 and L4 nerves completely alleviated all neuropathic manifestations. Interestingly, responses to thermal and mechanical stimuli were preserved, despite RTX application on uninjured L3, L4, and L5 nerves, which supply the plantar skin in rats. Perineural application of RTX caused downregulation of TRPV1, CGRP, and IB4 binding and upregulation of VIP in the corresponding dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. In comparison, VGLUT1 and NPY immunoreactivities were not altered. RTX application did not cause degenerative or ultrastructural changes in the treated nerves and corresponding DRGs. The results demonstrate that RTX induces neuroplasticity, rather than structural changes in primary afferents, that are responsible for alleviating hypersensitivity and chronic pain. Furthermore, this study suggests that treating uninjured adjacent spinal nerves may be used to manage chronic neuropathic pain following peripheral nerve injury.

Effect of cGMP-activated aquaporin 1 on TRPV4 in rats with allodynia induced by chronic compression of the dorsal root ganglion.

BACKGROUND: The aim of this study was to investigate the effects of aquaporin 1 (AQP1) knockdown on allodynia in rats with chronic compression of the dorsal root ganglia (DRG) and the role of TRPV4 in these effects. METHODS: Adult male Wistar rats were subjected to chronic compression of the dorsal root ganglia (CCD) via surgery. Behavioral tests were performed to calculate the paw withdrawal mechanical threshold (PWMT). Gene silence was induced by injecting rats with lentivirus expressing AQP1 short hairpin RNA (shRNA, Lv-shAQP1). Western blot analyses were performed to examine AQP1 and TRPV4 protein expression. The concentration of cyclic guanosine monophosphate (cGMP) was determined via enzyme-linked immunosorbent assay. RESULTS: AQP1 protein levels in DRG neurons were significantly increased in CCD rats and were accompanied by a decrease in the PWMT. Lentivirus-mediated RNA interference of AQP1 decreased AQP1 protein expression in CCD rats and normalized their PWMT, but not in rats infected with lentivirus-expressing negative control short hairpin RNA. Furthermore, AQP1 was identified as a cGMP-gated channel. cGMP concentration was upregulated in CCD rats. This effect was attenuated by treatment with a cGMP inhibitor. Additionally, the cGMP inhibitor decreased the mechanical allodynia and AQP1 protein expression in CCD rats. Finally, levels of TRPV4 expression were upregulated in DRG neurons and the L4/L5 spinal cord following surgery, and these effects were reversed by treatment with Lv-shAQP1 or a cGMP inhibitor. CONCLUSION: AQP1 plays a vital role in CCD-induced allodynia as Lv-shAQP1 significantly reduced the allodynia in CCD rats by inhibiting TRPV4 expression.

Epigenomic signatures underpin the axonal regenerative ability of dorsal root ganglia sensory neurons.

Axonal injury results in regenerative success or failure, depending on whether the axon lies in the peripheral or the CNS, respectively. The present study addresses whether epigenetic signatures in dorsal root ganglia discriminate between regenerative and non-regenerative axonal injury. Chromatin immunoprecipitation for the histone 3 (H3) post-translational modifications H3K9ac, H3K27ac and H3K27me3; an assay for transposase-accessible chromatin; and RNA sequencing were performed in dorsal root ganglia after sciatic nerve or dorsal column axotomy. Distinct histone acetylation and chromatin accessibility signatures correlated with gene expression after peripheral, but not central, axonal injury. DNA-footprinting analyses revealed new transcriptional regulators associated with regenerative ability. Machine-learning algorithms inferred the direction of most of the gene expression changes. Neuronal conditional deletion of the chromatin remodeler CCCTC-binding factor impaired nerve regeneration, implicating chromatin organization in the regenerative competence. Altogether, the present study offers the first epigenomic map providing insight into the transcriptional response to injury and the differential regenerative ability of sensory neurons.

Interleukin-1 Receptor Associated Kinase 1 Mediates the Maintenance of Neuropathic Pain after Chronic Constriction Injury in Rats.

Neuropathic pain (NP) has complicated pathogenesis as it mainly involves a lesion or dysfunction of the somatosensory nervous system and its clinical treatment remains challenging. Chronic constriction injury (CCI) model is a widely used neuropathic pain model and involved in mechanisms including both nerve inflammatory and injury. Cytokines and their receptors play essential roles in the occurrence and persistence of neuropathic pain, but the underlying mechanisms have not well been understood. Therefore, Interleukin-1 receptor-associated kinase 1 (IRAK1) is chosen to explore the possible mechanisms of NP. In the present study, IRAK1 was found to persistently increase in the dorsal root ganglion (DRG) and spinal cord (SC) during CCI detected by western blot. The staining further confirmed that IRAK1 was mainly co-located in the DRG astrocytes or SC neurons, but less in the DRG microglia or SC astrocytes. Moreover, the region of increased IRAK1 expression was observed in superficial laminae of the spinal dorsal horn, which was the nociceptive neuronal expression domain, suggesting that IRAK1 may mediated CCI-induced pain by nociceptive primary afferent. In addition, intrathecal injection of Toll-like receptor 4 (TLR4) inhibitor or IRAK1 siRNA decreased the expression of IRAK1 accompanied with the alleviation of CCI-induced neuropathic pain. The upregulation of p-NF-κB expression was reversed by IRAK1 siRNA in SC, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. Taking together, targeting IRAK1 may be a potential treatment for chronic neuropathic pain.

Dorsal Root Entry Zone Lesion for Neuropathic Pain Due to Thoracolumbar Spine Fracture: Long-Term Result.

OBJECTIVE: To retrospectively evaluate long-term efficacy and safety of dorsal root entry zone (DREZ) lesion for treatment of neuropathic pain within the lower extremities and perineal region after thoracolumbar spine fracture. METHODS: Forty-two patients were treated with posterior laminectomy under general anesthesia. The DREZ regions of the spinal cord segments were ablated under a microscope. Data regarding pain relief, pain variation over time, and postoperative complications were collected. The relationship between injured spinal column segment, spinal cord, nerve root, and pain territory were analyzed retrospectively. RESULTS: Spinal column injury segments were located between T12 and L4. Pain territories were distributed between the T11 and S5 dermatomes with varying ranges, at an average of 2-6 segments higher than the spinal cord injury segments. Pain relief rate was 100% in 21 patients (50.0%) and was over 50% in 14 patients (33.3%). Eighteen patients (42.9%) developed temporary tingling in the upper edge of the spinal cord lesion segment after surgery. Of the 4 patients with unilateral lower extremity pain, 2 developed postoperative persistent pain in the contralateral lower extremity. CONCLUSIONS: For patients with neuropathic pain of the lower extremities and/or the perineal region after thoracolumbar spine fracture, pain within the lower extremities was mostly because of nerve root injury. Pain in the perineal region caused by L1 fracture was attributed to spinal cord injury segmental pain. Nerve root injury pain had a good prognosis after DREZ lesion; the effect of DREZ lesion for spinal cord injury segmental pain may be uncertain.

Role of NaV1.6 and NaVß4 Sodium Channel Subunits in a Rat Model of Low Back Pain Induced by Compression of the Dorsal Root Ganglia.

Low back pain is a common cause of chronic pain and disability. It is modeled in rodents by chronically compressing the lumbar dorsal root ganglia (DRG) with small metal rods, resulting in ipsilateral mechanical and cold hypersensitivity, and hyperexcitability of sensory neurons. Sodium channels are implicated in this hyperexcitability, but the responsible isoforms are unknown. In this study, we used siRNA-mediated knockdown of the pore-forming NaV1.6 and regulatory NaVß4 sodium channel isoforms that have been previously implicated in a different model of low back pain caused by locally inflaming the L5 DRG. Knockdown of either subunit markedly reduced spontaneous pain and mechanical and cold hypersensitivity induced by DRG compression, and reduced spontaneous activity and hyperexcitability of sensory neurons with action potentials <1.5 msec (predominately cells with myelinated axons, based on conduction velocities measured in a subset of cells) 4 days after DRG compression. These results were similar to those previously obtained in the DRG inflammation model and some neuropathic pain models, in which sensory neurons other than nociceptors seem to play key roles. The cytokine profiles induced by DRG compression and DRG inflammation were also very similar, with upregulation of several type 1 pro-inflammatory cytokines and downregulation of type 2 anti-inflammatory cytokines. Surprisingly, the cytokine profile was largely unaffected by NaVß4 knockdown in either model. The NaV1.6 channel, and the NaVß4 subunit that can regulate NaV1.6 to enhance repetitive firing, play key roles in both models of low back pain; targeting the abnormal spontaneous activity they generate may have therapeutic value.

Treatment of neuropathic pain after peripheral nerve and brachial plexus traumatic injury.

Peripheral nerve and brachial plexus injuries typically cause severe impairment in the affected limb. The incidence of neuropathic pain is high, reaching up to 95% of cases, especially if cervical root avulsion has occurred. Neuropathic pain results from damage to the somatosensory system, and its progression towards chronicity depends upon disruptions affecting both the peripheral and central nervous system. Managing these painful conditions is complex and must be accomplished by a multidisciplinary team, starting with first-line pharmacological therapies like tricyclic antidepressants and calcium channel ligands, combined physical and occupational therapy, transcutaneous electrical stimulation and psychological support. For patients refractory to the initial measures, several neurosurgical options are available, including nerve decompression or reconstruction and ablative/modulatory procedures.

Tabebuia aurea decreases hyperalgesia and neuronal injury induced by snake venom.

ETHNOPHARMACOLOGICAL RELEVANCE: Tabebuia aurea (Silva Manso) Benth. & Hook. f. ex S. Moore is used as anti-inflammatory, analgesic and antiophidic in traditional medicine, though its pharmacological proprieties are still underexplored. In the bothropic envenoming, pain is a key symptom drove by an intense local inflammatory and neurotoxic event. The antivenom serum therapy is still the main treatment despite its poor local effects against pain and tissue injury. Furthermore, it is limited to ambulatorial niches, giving space for the search of new and more inclusive pharmacological approaches. AIM OF THE STUDY: evaluation of Tabebuia aurea hydroethanolic extract (HEETa) in hyperalgesia and neuronal injury induced by Bothrops mattogrossensis venom (VBm). MATERIALS AND METHODS: Stem barks from Tabebuia aurea were extracted with ethanol and water (7:3, v/v) to yield the extract HEETa. Then, HEETa was analyzed by LC-DAD-MS and its constituents were identified. Snake venoms were extracted from adult specimens of Bothrops mattogrossensis, lyophilized and kept at -20 °C until use. Male Swiss mice, weighting 20-25 g, were used to hyperalgesia (electronic von Frey), motor impairment (Rotarod test) and tissue injury evaluation (histopatology and ATF-3 immunohistochemistry). Therefore, three experimental groups were formed: VBm (1 pg, 1 ng, 0.3 µg, 1 µg, 3 and 6 µg/paw), HEETa orally (180, 540, 720, 810 or 1080 mg/kg; 10 mL/kg, 30 min prior VBm inoculation) and VBm neutralized (VBm: HEETa, 1:100 parts, respectively). In all set of experiments a control (saline group) was used. First, we made a dose-time-response course curve of VBm's induced hyperalgesia. Next, VBm maximum hyperalgesic dose was employed to perform HEETa orally dose-time-response course curve and analyses of VBm neutralized. Paw tissues for histopathology and DRGs were collected from animals inoculated with VBm maximum dose and treated with HEETa antihyperalgesic effective dose or neutralized VBm. Paws were extract two or 72 h after VBm inoculation and DRGs, in the maximum expected time expression of ATF-3 (72 h). RESULTS: From HEETa extract, glycosylated iridoids were identified, such as catalpol, minecoside, verminoside and specioside. VBm induced a time and dose dependent hyperalgesia with its highest effect seen with 3 µg/paw, 2 h after venom inoculation. HEETa effective dose (720 mg/kg) decreased significantly VBm induced hyperalgesia (3 µg/paw) with no motor impairment and signs of acute toxicity. HEETa antihyperalgesic action starts 1.5 h after VBm inoculation and lasted up until 2 h after VBm. Hyperalgesia wasn't reduced by VBm: HEETa neutralization. Histopathology revealed a large hemorragic field 2 h after VBm inoculation and an intense inflammatory infiltrate of polymorphonuclear cells at 72 h. Both HEETa orally and VBm: HEETa groups had a reduced inflammation at 72 h after VBm. Also, the venom significantly induced ATF-3 expression (35.37 ±â€¯3.25%) compared with saline group (4.18 ±â€¯0.68%) which was reduced in HEETa orally (25.87 ±â€¯2.57%) and VBm: HEETa (19.84 ±â€¯2.15%) groups. CONCLUSION: HEETa reduced the hyperalgesia and neuronal injury induced by VBm. These effects could be related to iridoid glycosides detected in HEETa and their intrinsic reported mechanism.