Chronic Constriction Injury Of Sciatic Nerve Research Articles

Analgesic Activity of Synaptamide in a Rat Sciatic Nerve Chronic Constriction Injury Model

At present, there is a growing interest in the study of the neurotropic activity of polyunsaturated fatty acid ethanolamides (N-acylethanolamines). N-docosahexaenoylethanolamine (DHEA), or synaptamide, an endogenous metabolite of docosahexaenoic acid, is a promising compound with anti-inflammatory activity. The results of this study demonstrate that synaptamide, when administered subcutaneously (4 mg/kg/day, 35 days), promotes a decrease in cold allodynia and mechanical hyperalgesia in a rat sciatic nerve chronic constriction injury (CCI) model. After CCI, synaptamide treatment enhanced the remyelination process in the site of sciatic nerve injury (33.4 ± 1.1% in the CCI+Syn group, compared to 28.4 ± 0.9% in the CCI group). Further, synaptamide suppressed the CCI-induced increase in the activity of microglia (13.1 ± 0.5% in CCI+Syn, compared to 15.3 ± 0.7% in the CCI group) and the number of nitric oxide synthase-positive neurons (58,307 ± 5,206 cells/mm3 in CCI+Syn, compared to 80,288 ± 4,287 cells/mm3 in the CCI group) in the dorsal horns of the spinal cord, and also reduced the concentration of interleukin 1 beta in the spinal cord (169.3 ± 4 pg/mg of protein in CCI+Syn, compared to 236.9 ± 9.3 pg/mg of protein in CCI group) 35 days after surgery. Synaptamide treatment resulted in decrease of reactive astrogliosis in the spinal cord dorsal horns to 20.8 ± 1.3%, which occurred simultaneously with a decrease in the substance P (SP) level (9.8 ± 0.5%) compared to vehicle-treated animals (30.2 ± 2.2% and 13.4 ± 0.9% of astroglia and SP staining area, respectively). In addition, synaptamide increased superoxide dismutase activity up to 68.6 ± 0.8% (control 50.6 ± 0.9%) in astrocyte culture. Thus, synaptamide provides anti-inflammatory and neuroprotective effects in both peripheral and central nervous system after sciatic nerve injury.

Mechanisms Underlying the Selective Therapeutic Efficacy of Carbamazepine for Attenuation of Trigeminal Nerve Injury Pain.

Different peripheral nerve injuries cause neuropathic pain through distinct mechanisms. Even the site of injury may impact underlying mechanisms, as indicated by the clinical finding that the antiseizure drug carbamazepine (CBZ) relieves pain because of compression injuries of trigeminal but not somatic nerves. We leveraged this observation in the present study hypothesizing that because CBZ blocks voltage-gated sodium channels (VGSCs), its therapeutic selectivity reflects differences between trigeminal and somatic nerves with respect to injury-induced changes in VGSCs. CBZ diminished ongoing and evoked pain behavior in rats with chronic constriction injury (CCI) to the infraorbital nerve (ION) but had minimal effect in rats with sciatic nerve CCI. This difference in behavior was associated with a selective increase in the potency of CBZ-induced inhibition of compound action potentials in the ION, an effect mirrored in human trigeminal versus somatic nerves. The increase in potency was associated with a selective increase in the efficacy of the NaV1.1 channel blocker ICA-121431 and NaV1.1 protein in the ION, but no change in NaV1.1 mRNA in trigeminal ganglia. Importantly, local ICA-121431 administration reversed ION CCI-induced hypersensitivity. Our results suggest a novel therapeutic target for the treatment of trigeminal neuropathic pain.SIGNIFICANCE STATEMENT This study is based on evidence of differences in pain and its treatment depending on whether the pain is above (trigeminal) or below (somatic) the neck, as well as evidence that voltage-gated sodium channels (VGSCs) may contribute to these differences. The focus of the present study was on channels underlying action potential propagation in peripheral nerves. There were differences between somatic and trigeminal nerves in VGSC subtypes underlying action potential propagation both in the absence and presence of injury. Importantly, because the local block of NaV1.1 in the trigeminal nerve reverses nerve injury-induced mechanical hypersensitivity, the selective upregulation of NaV1.1 in trigeminal nerves suggests a novel therapeutic target for the treatment of pain associated with trigeminal nerve injury.

Evidence that increased cholecystokinin (CCK) in the periaqueductal gray (PAG) facilitates changes in Resident–Intruder social interactions triggered by peripheral nerve injury

Individual differences in the effects of a chronic neuropathic injury on social behaviours characterize both the human experience and pre-clinical animal models. The impacts of these changes to the well-being of the individual are often underappreciated. Earlier work from our laboratory using GeneChip® microarrays identified increased cholecystokinin (CCK) gene expression in the periaqueductal gray (PAG) of rats that showed persistent changes in social interactions during a Resident-Intruder encounter following sciatic nerve chronic constriction injury (CCI). In this study, we confirmed these gene regulation patterns using RT-PCR and identified the anatomical location of the CCK-mRNA as well as the translated CCK peptides in the midbrains of rats with a CCI. We found that rats with persistent CCI-induced changes in social behaviours had increased CCK-mRNA in neurons of the ventrolateral PAG and dorsal raphe nuclei, as well as increased CCK-8 peptide expression in terminal boutons located in the lateral and ventrolateral PAG. The functional significance of these changes was explored by microinjecting small volumes of CCK-8 into the PAG of uninjured rats and observing their Resident-Intruder social interactions. Disturbances to social interactions identical to those observed in CCI rats were evoked when injection sites were located in the rostral lateral and ventrolateral PAG. We suggest that CCI-induced changes in CCK expression in these PAG regions contributes to the disruptions to social behaviours experienced by a subset of individuals with neuropathic injury.

Escalating morphine dosage fails to elicit conditioned analgesia in a preclinical chronic neuropathic pain model.

Many people with chronic pain escalate their opioid dosage to counteract tolerance effects. A treatment regimen consisting of placebos admixed with opioids has been suggested as a possible therapeutic option that could reduce the harm of long-term opioid use. However, the analgesic efficacy of such a regimen requires further investigation before widespread adoption. We have recently reported that a 4-day pharmacological conditioning procedure, which paired morphine (6 mg/kg) with contextual cues, elicited placebo analgesia in subpopulations of male (35%) and female (25%) rats with sciatic nerve chronic constriction injury (CCI). Here, we investigated how an escalating morphine dosage during conditioning affects the incidence and strength of placebo analgesia. Forty-four male, Sprague-Dawley rats received CCI. Thirty-eight (86%) rats developed strong cold allodynia by day 6 post-surgery, as measured by hind paw withdrawal (HPW) behaviour on a 5°C cold plate (120 s). In this experiment, pharmacological conditioning consisted of an escalating morphine dose over 4 days (8/9/10/12 mg/kg). This dosing regimen produced strong reductions in HPW behaviour and counteracted the effects of morphine tolerance during conditioning. However, none of the rats given the placebo treatment (n = 12) demonstrated reductions in HPW behaviour when morphine was substituted for saline (i.e. placebo analgesia), but instead showed a strong behavioural response (rearing). These results demonstrate that a high, escalating dose of morphine failed to produce conditioned placebo analgesia in rats with CCI. It is possible that admixing placebos with opioids may be similarly ineffective in chronic pain patients when the opioids regimen is high or escalating.

Gelsemium effect against nerve injury-induced mechanical allodynia and hyperalgesia

Background Gelsemium dilutions are prescribed for their anxiolytic and its analgesic effects. Investigations using alkaloids isolated from Gelsemium support the hypothesis of Gelsemium-induced analgesia. Aims We evaluated the antinociceptive effect of Gelsemium dilutions 3, 5 and 9C in neuropathic models. Methodology To investigate the potential effect of Gelsemium dilutions 3, 5 and 9C to prevent or to correct sciatic nerve chronic constriction (CCI) injury, we used the von-Frey hair behavioral test. CCI-induced neuropathic pain in rats represents characteristic painful behaviors like hyperalgesia and allodynia, thus validating its suitability for the evaluation of anti-neuropathic drugs. To test the corrective effect, Gelsemium 3, 5 or 9 C or placebo were administered from Day 14 after sciatic nerve ligation, i.e., when neuropathic symptoms were observed. In the preventive strategy, Gelsemium dilutions and placebo began immediately after the sciatic nerve ligation (D0). Results and discussion We observed that in placebo groups, the mechanical-sensitivity thresholds remained unchanged all treatment days whereas Gelsemium dilutions 3C and 5C exerted a strong or moderate antinociceptive effect, respectively. In CCI-rats, the contralateral paw of placebo-treated animals did not respond to 4g non-noxious stimulation but the ipsilateral responses increased progressively (0%-D0, 52%-D14, 72%-D21 and 88%-D28), confirming the occurrence of allodynia. Gelsemium dilution 3C corrective and preventive treatments efficiently reduced the allodynic responses (72-to-38%-D21 and 88-to-22%-D28). Gelsemium 5C also exhibited significant anti-allodynic action while Gelsemium 9C was ineffective. Similarly, one week treatment with Gelsemium 3 or 5C efficiently reduced 15g or 26g-evoked hyperalgesia and the beneficial action improved after 2 weeks. Chronic therapies with current analgesics induce several side-effects. Conclusion The present work, suggest that Gelsemium dilutions devoid of toxicity and used as anxiolytic in humans induced analgesia, opens interesting/alternative perspectives for long-term management of pain without undesirable effects.

PDTC ameliorates neuropathic pain by inhibiting microglial activation via blockage of the TNFα-CX3CR1 pathway.

Previous studies have suggested that pyrrolidine dithiocarbamate (PDTC), a nuclear factor κB (NF-κB) inhibitor, plays a role in deterring nerve injury-induced neuropathic pain (NP). The activation of NF-κB pathway may contribute to spinal microglial activation, CX3CR1 and tumor necrosis factor-alpha (TNF-a) up-regulation. The aim of this study was to clarify whether PDTC could inhibit the development of neuropathic pain via decreasing TNF-a-induced CX3CR1 up-regulation. Sprague-Dawley rats were randomly divided into sham group and NP group. Rats in each group were treated with intrathecal infusion of PDTC (100 or 1000 pmol/d) or saline. The sciatic nerve chronic constriction injury (CCI) model was used to induce NP in rats. Mechanical stimuli and radiant heat were used to evaluate mechanical allodynia and thermal hyperalgesia. Spinal microglial marker OX42 and TNF-a were detected by immunohistochemistry. In vitro BV-2 microglia activation was induced by TNF-a incubation, and the levels of CX3CR1 were assessed by western blot and reverse transcription- polymerase chain reaction. Pain behavior and immunohistochemistry results showed that intrathecal infusion of PDTC at 100 or 1000 pmol/d prevented the development of mechanical and thermal hyperalgesia, spinal microglial activation and TNF-a expression induced by sciatic nerve CCI in rats. In vitro experiment results showed that PDTC inhibited the TNF-a-induced CX3CR1 up-regulation in BV-2 microglial cells. In conclusion, intrathecal infusion of PDTC could attenuate the pain-related behaviors induced by sciatic nerve CCI through suppressing the spinal microglia activation and TNF-a up-regulation in rats. The NF-κB activation might be responsible for TNF-a-induced CX3CR1 up-regulation in microglia.

Preventive and therapeutic effects of JM-20 on paclitaxel-evoked painful peripheral neuropathy in rats

Context: JM-20 is a hybrid synthetic molecule, which is based on a multimodal drug design paradigm for cerebrovascular disease. In addition to its neuroprotective effects, JM-20 also decreased sciatic nerve chronic constriction injury (CCI)-induced mechanical hypersensitivity in rats. JM-20 has a strong mitoprotective ability, and its effects could be in correspondence with the mitotoxicity hypothesis for paclitaxel-induced painful peripheral neuropathy. Aims: To evaluate the efficacy of the JM-20 to reduce neuropathic pain manifestations induced by the administration of paclitaxel in rats. Methods: In this study was implemented a rat model of painful peripheral neuropathy, produced by the chemotherapeutic agent paclitaxel, to determine whether JM-20 (10 mg/kg, p.o) could prevent the development of neuropathic pain during the exposure to paclitaxel. As well as to determine whether JM-20 (20 mg/kg, p.o) could reverse the established neuropathic pain. Mechanical behavioral assessment using von Frey filaments applied to the hind paws was applied before, during, and after treatments for 35 days. Results: Giving JM-20 during the exposure to paclitaxel significantly reduced the severity of mechanical allodynia and mechanical hyperalgesia. Moreover, JM-20 significantly reduced both established neuropathic pain manifestations. There was no evidence of tolerance to the effect during three days of dosing, and a long-term effect was observed after JM-20 discontinuation. Conclusions: JM-20 may be clinically relevant for both the prevention and treatment of paclitaxel-induced painful peripheral neuropathy.

Partial high frequency nerve block decreases neuropathic signaling following chronic sciatic nerve constriction injury

Objective. High frequency (HF) block can quickly and reversibly stop nerve conduction. We hypothesized HF block at the sciatic nerve would minimize nociception by preventing neuropathic signals from reaching the central nervous system. Approach. Lewis rats were implanted with a constriction cuff and a distal cuff electrode around their right sciatic nerve. Tactile sensitivity was evaluated using the 50% paw withdrawal threshold (PWT) determined using Chaplan’s method for von Frey monofilaments. Over the course of 49 d, the 50% PWT was measured (1) before HF block, (2) during HF block (50 kHz, 3 V pp), and (3) after HF block. Gait was observed and scored before and during block. At end point, HF block efficacy was directly evaluated using additional cuff electrodes to elicit and record compound neural action potentials across the HF blocking cuff. Main results. At days 7 and 14 d post-operation, tactile sensitivity was significantly lower during HF block compared to before and after block (p< 0.005). Additionally, an increase in gait disability was not visually observed during HF block. Significance. HF block can reduce tactile sensitivity in a limb with a neuropthic injury in a rapidly reversible fashion.

Alpha lipoic acid attenuated neuropathic pain induced by chronic constriction Injury of sciatic nerve in rats

BackgroundChronic neuropathic pain syndrome is associated with impaired quality of life and is poorly manageable. Alpha lipoic acid (ALA) is a powerful antioxidant and showed its effectiveness on diabetic neuropathy and other acute peripheral nerve injuries but it was not evaluated in the chronic neuropathic pain, chronic constriction injury (CCI) in rat model by using duloxetine (DLX) as standard.MethodologyThe main objective of the study was to expedite ALA effect on chronic peripheral neuropathy induced by CCI of sciatic nerve in rats. In this study, male Wister rats were randomly divided into six groups (n = 8) including, normal saline, sham operated, surgery control, DLX 30mg/kg treated, ALA treated 25mg/kg, and ALA+DLX. The CCI of sciatic nerve was conducted on all animals except normal saline group and studied for 21 days (i.e. 14 days treatment period & 7 days treatment free period) by using different behavioral, biochemical and, histopathology studies.ResultsALA showed minor but significant decrease of thermal hyperalgesia, cold allodynia, malondialdehyde (MDA), total protein, lipid peroxidation, and nitric oxide levels and significant increase of motor coordination, glutathione level and decreased axonal degeneration significantly. These effects sustained even during treatment free period. ALA enhanced the effect of DLX when given in combination by showing sustained effect. In conclusion, ALA acted as potent antioxidant may be this activity is responsible for the potent neuroprotective effect.ConclusionHence, ALA attenuated the nueroinflammation mediated by chronic peripheral neuropathy. Further studies are warranted with ALA to develop as a clinically relevant therapeutic agent for the treatment of neuropathic pain.

Clinical relevance of chronic neuropathic pain phenotypes in mice: A comprehensive behavioral analysis

Despite a large number of preclinical studies performed each year, the safe and effective therapeutic interventions for chronic pain are scant. Therefore, it appears that pre-clinical modeling requires a systematically organized behavioral test paradigm to quantify the response of animals for a specific pain state. The present study, therefore, conceptualized a test battery to evaluate the behavioral changes in mice following neuropathic pain. We employed sciatic nerve chronic constriction injury (CCI) in C57BL/6 J mice to model chronic pain state. Mice were monitored for thermal hyperalgesia and grip strength for 30 days. Subsequently, mice underwent a behavioral test battery consisting of the nociceptive threshold, the affective and cognitive functions and motor coordination, and strength. Our results showed that CCI mice are insensitive to thermal stimuli. However, nerve-injured mice showed significant changes in neuromuscular coordination, basal anxiety, and hedonic state. Such impaired neuromuscular coordination is indicative of disability rather than the actual pain phenotype. While using the digital gait analysis, our study revealed rationales for the insensitivity of CCI mice to thermal stimuli. Our results suggest that the predictive validity of the CCI model necessitates a comprehensive behavioral test battery to select the clinically relevant and measurable phenotype to quantify chronic neuropathic pain.

Epigenetic modification of BDNF mediates neuropathic pain via miR-30a-3p/EP300 axis in CCI rats

Recent investigation of microRNAs on chronic pain has developed a breakthrough in neuropathic pain management. In the present study, decreased expression of miR-30a-3p was reported using qRT-PCR analysis and loss of miR-30a-3p promoted neuropathic pain progression in sciatic nerve chronic constrictive injury rats through determining the pain threshold. We predicted miR-30a-3p could target E-cadherin transcriptional activator (EP300) via bioinformatics analysis. Meanwhile, we found that brain-derived neurotrophic factor (BDNF) is involved in neuropathic pain. Here, we exhibited that EP300 epigenetically up-regulated BDNF via enhancing acetylated histone H3 and H4 on the promoter. For another, miR-30a-3p was able to modify the level of BDNF and acetylated histone H3 and H4. Loss of miR-30a-3p enhanced EP300 and BDNF colocalization in CCI rats. Subsequently, it was shown that increased EP300 induced neuropathic pain by an enhancement of neuronal BDNF level in vivo. To sum up, it was revealed that epigenetic modification of BDNF promoted neuropathic pain via EP300 induced by miR-30a-3p in CCI rats.

N-Docosahexaenoylethanolamine Attenuates Neuroinflammation and Improves Hippocampal Neurogenesis in Rats with Sciatic Nerve Chronic Constriction Injury.

Chronic neuropathic pain is a condition that causes both sensory disturbances and a variety of functional disorders, indicating the involvement of various brain structures in pain pathogenesis. One of the factors underlying chronic neuropathic pain is neuroinflammation, which is accompanied by microglial activation and pro-inflammatory factor release. N-docosahexaenoylethanolamine (DHEA, synaptamide) is an endocannabinoid-like metabolite synthesized endogenously from docosahexaenoic acid. Synaptamide exhibits anti-inflammatory activity and improves neurite outgrowth, neurogenesis, and synaptogenesis within the hippocampus. This study aims to evaluate the effects of synaptamide obtained by the chemical modification of DHA, extracted from the Far Eastern raw material Berryteuthis magister on neuroinflammatory response and hippocampal neurogenesis changes during neuropathic pain. The study of microglial protein and cytokine concentrations was performed using immunohistochemistry and ELISA. The brain lipid analysis was performed using the liquid chromatography-mass spectrometry technique. Behavioral experiments showed that synaptamide prevented neuropathic pain-associated sensory and behavioral changes, such as thermal allodynia, impaired locomotor activity, working and long-term memory, and increased anxiety. Synaptamide attenuated microglial activation, release of proinflammatory cytokines, and decrease in hippocampal neurogenesis. Lipid analysis revealed changes in the brain N-acylethanolamines composition and plasmalogen concentration after synaptamide administration. In conclusion, we show here that synaptamide may have potential for use in preventing or treating neuropathic cognitive pain and emotional effects.

Antinociceptive effects of lead acetate in sciatic nerve chronic constriction injury model of peripheral neuropathy in male Wistar rats.

The toxicological effects of lead and its compounds have overshadowed its possible health beneficial effects. Currently, the success rate for treating neuropathic pain has been very low. This study investigated the antinociceptive effects of orally administered low dose lead acetate in sciatic nerve ligated Wistar rats. Thirty Wistar rats randomly divided into five groups were used for this study. Chronic constriction injury (CCI) was used to induce neuropathic pain in Wistar rats. Allodynic and hyperalgesic signs were investigated using von Frey filaments and hotplate, respectively. Morris water maze test was used to assess the memory functions of the rats. The study revealed that oral administration of low-dose lead acetate significantly (p < 0.05) increased pain thresholds of ligated rats. CCI enhanced memory function in Wistar rats which was significantly decreased following lead acetate administration. The findings suggest that lead acetate possesses antinociceptive effects in peripherally induced neuropathic pain model in Wistar rats.

SIRT1 Mediates Neuropathic Pain Induced by Sciatic Nerve Chronic Constrictive Injury in the VTA-NAc Pathway.

Background Mounting evidence has shown that sirtuin 1 (SIRT1), a class III histone deacetylase, alleviated several types of neuropathic pain in the spinal cord and dorsal root ganglion and regulated some aberrant behaviors in the ventral tegmental area (VTA) and the nucleus accumbens (NAc). Methods In this context, the effect of SIRT1 on neuropathic pain in the VTA-NAc pathway was investigated in the model of chronic constrictive injury (CCI). Results SIRT1 was localized in the VTA neurons in naive mice. The expression of SIRT1 was decreased in the contralateral VTA of CCI mice. After microinjection of SRT1720 (an activator of SIRT1) in the contralateral VTA of CCI mice, the established thermal hyperalgesia was attenuated. However, it was further exacerbated by EX-527 (an inhibitor of SIRT1). The elevated level of acetyl-histone 3 was reduced by SRT1720 but further elevated by EX-527 in the contralateral VTA of CCI mice. The increased expression of Fos in both VTA and NAc was downregulated by SRT1720 but further upregulated by EX-527 in CCI mice. Conclusions The discovery of the effect of SIRT1 on neuropathic pain in the VTA represents an important step forward in understanding the analgesic mechanisms of the VTA-NAc pathway.

Renin-angiotensin system blockade modulates both the peripheral and central components of neuropathic pain in rats: Role of calcitonin gene-related peptide, substance P and nitric oxide.

Nonetheless, renin-angiotensin-aldosterone system (RAAS) blockers attenuate neuropathic pain (NP), the exact molecular mechanisms of this effect are not completely understood. The study aimed to investigate the role of calcitonin gene-related peptide (CGRP), substance P (SP) and nitric oxide (NO), which are all involved in pain modulation, in the analgesic effect of different RAAS blockers in NP both on the peripheral and on the central levels. NP was induced by sciatic nerve chronic constriction injury (CCI, 14days) in rats, that were given either centrally (telmisartan and ramipril) or peripherally (losartan and enalapril) acting angiotensin-converting enzyme inhibitors (ACE-Is) or angiotensin receptor blockers (ARBs). Behavioural assessment was performed, and CGRP, SP and NO levels were detected in the injured sciatic nerve and the brainstem at the end of experiment. CCI rats showed increased spontaneous pain response and foot deformity along with elevated CGRP, SP and NO levels. ARBs and ACE-Is treatment improved pain behaviour and reduced SP and NO levels. However, sciatic CGRP was increased with different interventions and brainstem CGRP was only elevated in the losartan group. These findings suggest an intermediary role of CGRP, SP and NO in RAAS blockers analgesic effect in NP.

MMP-9 regulates CX3CL1/CX3CR1 in the early phase of neuropathic pain in chronic sciatic nerve constriction injury (CCI) rats.

To observe the effects of MMP-9 (matrix metalloproteases-9) on the mechanical allodynia and thermal hyperalgesia and the expression of CX3CL1 (CX3C chemokine ligand 1) protein in the spinal dorsal root ganglion (DRG) in rats with chronic sciatic nerve constriction injury (CCI). A total of 84 male SD rats were randomly divided into seven groups, namely the normal group , the sham operation group , the model group , the CCI + MMP-9 group, the CCI + TIMP-1 group , the CCI + siRNA group, and the CCI + MM-siRNA group. The CCI model was prepared 5 days after implantation of intrathecal catheter. The rat paw mechanical withdrawal threshold (PWMT) and paw thermal withdrawal latency (PWTL) were measured 1 day before CCI surgery and 1, 2, 3 and 5 days after CCI respectively. Western blot (WB) was used to detect the expressions of the MMP-9 and the CX3CL1 protein in the L5 DRG of the spinal cord 1 day after CCI operation. (I) Behavioral assessment of hyperalgesia: compared with the Sham group, the PWMT and PWTL of the CCI group were significantly reduced at each time point after CCI surgery; compared with the CCI group, the PWMT and PWTL of the CCI + MMP-9 group decreased 1 day after CCI; for the PWMT and PWTL of the CCI + TIMP-1 group and CCI + siRNA group, PWMT and PWTL increased 1 day after CCI; (II) The expressions of MMP-9 and CX3CL1 protein in the DRG of the spinal cord: compared with Sham group, the expressions of MMP-9 and CX3CL1 protein in the DRG of the CCI group increased significantly 1 day after CCI surgery; compared with the CCI group, the expressions increased in the CCI + MMP-9 group 1 day after CCI . However, the expressions of MMP-9 and CX3CL1 in the CCI + TIMP-1 group and CCI + siRNA group were reduced on the first postoperative day. The mechanism of MMP-9 participating in the early phase of neuropathic pain (NP) in CCI rats is related to the upregulation of CX3CL1.

A critical role for miR‑135a‑5p‑mediated regulation of SLC24A2 in neuropathic pain

Neuropathic pain (NP) is a refractory and long‑lasting disease caused mostly by peripheral nerve injury. Currently, the mechanism of NP is yet to be elucidated. Intracellular calcium homeostasis is critical for some physiological functions, including the occurrence of NP. NCKX2, encoded by the solute carrier family4 member2 (SLC24A2) gene, is an important K+‑dependent Na+‑Ca2+ exchanger that mediates Ca2+ extrusion. The role of NCKX2 in the development of NP is unknown. For this purpose, a sciatic nerve chronic constriction injury(CCI) model was established and it was revealed that the expression levels of SLC24A2 and its encoded protein NCKX2 were both downregulated in the posterior horn of the spinal cord. Overexpression of SLC24A2 reduced both mechanical and thermal hyperalgesia and decreased the expression of inflammatory cytokines [interleukin(IL)‑1β, IL‑6 and tumor necrosis factor‑α] in CCI rats. Using bioinformatics analyses, luciferase reporter assays, and a series of behavioral tests, it was demonstrated that the decrease in SLC24A2 after CCI treatment was directly regulated by increased microRNA (miR)‑135a‑5p in the spinal cord. Moreover, the effects of miR‑135a‑5p on NP were SLC24A2‑dependent. In conclusion, the present results highlighted the suppressive role of NCKX2 in NP, which is mainly regulated by miR‑135a‑5p and mediates the release of inflammatory cytokines in the dorsal horn of the spinal cord. These findings deepen our understanding of the development of NP and provide novel candidates for NPtreatment.

Disability-specific genes GRIN1, GRIN2 and CNR1 show injury-dependent protein expression in the lumbar spinal cord of CCI rats

The sensory changes triggered by peripheral nerve injury result from functional changes in both neurons and glia in the dorsal horn of the spinal cord. Whether the disrupted affective-motivational states often comorbid with injury-evoked changes in sensation are driven directly by these functional changes is a question only recently investigated. Using a combination of GeneChip microarrays and RT-PCR techniques we identified differences in mRNA expression unique to rats with sustained changes to their social behaviour following sciatic nerve chronic constriction injury (CCI). Amongst these changes were the mRNAs encoding several of the NMDA subunits and the CB1 receptor. However, as protein translation is not a necessary consequence of the upregulation or downregulation of genes we decided to evaluate the functional significance of our initial observations using immunohistochemical detection of their translated protein products to determine their location and abundance in the lumbar spinal cord. Spinal cord tissue from rats with (‘Affected’), and without (‘Unaffected’) changes in social behaviour after CCI was compared with tissue from uninjured controls. The expression of NMDA-1 (NR1) subunit, NMDA-2D subunit, Cannabinoid Receptor 1 (CB1), Glucocorticoid Receptor (GR) and Glial Fibrillary Acidic Protein (GFAP) immunoreactivities was quantified for these rats and revealed that nerve injury increased the expression of NMDA-2D, CB1 and GFAP immunoreactivity compared to uninjured controls. However, these changes were not specific to rats whose social behaviours were ‘Affected’ or ‘Unaffected’ by the nerve injury. Our data thus suggest that the development and expression of changes in social behaviour seen in a proportion of rats following CCI are unlikely to be directly related to the spinal changes in NMDA-2D, CB1 and GFAP expression induced by the nerve injury.

Mechanisms Involved in Angiotensin Receptor Blockade Superiority over ACE‐inhibition in Attenuating Neuropathic Pain Induced in Rats

Although, the beneficial role of angiotensin‐converting enzyme inhibitors (ACEi) or AT1 receptor blockers (ARBs) in attenuating Neuropathic pain (NP) was previously reported, the exact underlying mechanisms as well as superiority of using central versus peripheral acting Renin angiotensin aldosterone system (RAAS) drugs in NP is not yet explored. We investigated the effect of 14 days treatment of centrally (telmisartan and ramipril) or peripherally (losartan and enalapril) ARBs and ACEi, respectively in attenuating peripheral NP induced by sciatic nerve chronic constriction injury (CCI) in rats compared to pregabalin, the standard treatment for NP. Behavioral changes, inflammatory markers (nuclear factor‐kappa B (NFкβ), tumor necrosis factor (TNF)‐α release, Cyclooxygenase‐2 (COX‐2), prostaglandin E2 (PGE2) and bradykinin), oxidative stress markers (NADPH oxidase and catalase), signal transducer and activator of transcription 3 (STAT‐3) activation, levels of phosphorylated P38 mitogen activated protein kinase (P38 MAPK), angiotensin converting enzyme (ACE), AT1 receptor (AT1R) and AT2 receptor (AT2R) as well as histopathological picture were assessed in brain stem and sciatic nerve. CCI resulted in an obvious painful behavior along with increased levels of inflammatory and oxidative stress markers, STAT3 activity as well as the levels of phosphorylated P38 MAPK, ACE, AT1R and AT2R and worsened histopathological picture in both the brainstem and sciatic nerve. Treatment of CCI rats with ARBs resulted in improving in animal behavior and all measured parameters and were more effective compared to ACE inhibitors. Centrally acting ARBs or ACEi were not superior compared to their peripherally acting drugs of the same category. These findings suggest ARBs (central or peripheral) as an effective treatment modality for NP.

Transcribed ultraconserved noncoding RNA uc.153 is a new player in neuropathic pain.

Transcribed ultraconserved regions are a novel class of long noncoding RNAs and are completely conserved in humans, rats, and mice. Transcribed ultraconserved regions have been implicated in diverse biological processes; however, very little is currently known about their role in pain modulation. Here, we found that the level of the spinal transcribed ultraconserved region uc.153 was significantly increased in a mouse model of sciatic nerve chronic constriction injury (CCI)-induced chronic neuropathic pain. The knockdown of spinal uc.153 prevented and reversed chronic constriction injury-induced pain behaviours and spinal neuronal sensitization. By contrast, the overexpression of spinal uc.153 produced pain behaviours and neuronal sensitization in naive mice. Moreover, we found that uc.153 participates in the regulation of neuropathic pain by negatively modulating the processing of pre-miR-182-5p. Collectively, our findings reveal an important role for uc.153 in pain modulation and provide a novel drug target for neuropathic pain therapy.