Injury-induced Neuropathic Pain In Rats Research Articles

Novel Pulsed-Ultrahigh-Frequency Spinal Cord Stimulation Inhibits Mechanical Hypersensitivity and Brain Neuronal Activity in Rats after Nerve Injury.

Spinal cord stimulation (SCS) is an important pain treatment modality. We hypothesized that a novel pulsed-ultrahigh-frequency SCS (pUHF-SCS) could safely and effectively inhibit spared nerve injury-induced neuropathic pain in rats. Epidural pUHF-SCS (± 3V, 2Hz pulses comprising 500 kHz biphasic sinewaves) was implanted at the thoracic vertebrae (T9-T11). Local field brain potentials following hind paw stimulation were recorded. Analgesia was evaluated by von-Frey-evoked allodynia and acetone-induced cold allodynia. The mechanical withdrawal threshold of the injured paw was 0.91 ± 0.28 g lower than that of the sham surgery (24.9 ± 1.2 g). Applying 5-, 10-, or 20-minute pUHF-SCS five times every two days significantly increased the paw withdrawal threshold to 13.3 ± 6.5, 18.5 ± 3.6, and 21.0 ± 2.8 g at 5 hours post-SCS, respectively (p = 0.0002, < 0.0001, and < 0.0001; n = 6/group), and to 6.1 ± 2.5, 8.2 ± 2.7, and 14.3 ± 5.9 g on the second day, respectively (p = 0.123, 0.013, and < 0.0001). Acetone-induced paw response numbers decreased from pre-SCS (41 ± 12) to 24 ± 12 and 28 ± 10 (p = 0.006 and 0.027; n = 9) at 1 and 5 hours post-three rounds of 20-minute pUHF-SCS, respectively. The areas under the curve from the C component of the evoked potentials at the left primary somatosensory and anterior cingulate cortices were significantly decreased from pre-SCS (101.3 ± 58.3 and 86.9 ± 25.5, respectively) to 39.7 ± 40.3 and 36.3 ± 20.7 (p = 0.021, and 0.003; n = 5) at 60 minutes post-SCS, respectively. The intensity thresholds for pUHF-SCS to induce brain and sciatic nerve activations were much higher than the therapeutic intensities and thresholds of conventional low-frequency SCS. pUHF-SCS inhibited neuropathic pain-related behavior and paw stimulation evoked brain activation through mechanisms distinct from low-frequency SCS.

Solasodine Containing Solanum torvum L. Fruit Extract Prevents Chronic Constriction Injury-Induced Neuropathic Pain in Rats: In Silico and In Vivo Evidence of TRPV1 Receptor and Cytokine Inhibition.

This study aimed to assess the efficacy of ethanolic extract of Solanum torvum L. fruit (EESTF) containing solasodine in treating chronic constriction injury (CCI)-induced neuropathic pain in rats. Three-dimensional (3D) simulation studies of solasodine binding were conducted on the TRPV1 receptor, IL-6, and TNF-α structures. For in vivo justification, an assessment of behavioral, biochemical, and histological changes was designed after a CCI-induced neuropathic pain model in rats. On days 7, 14, and 21, CCI significantly increased mechanical, thermal, and cold allodynia while producing a functional deficit. IL-6, TNF-α, TBARS, and MPO levels also increased. SOD levels of catalase and reduced glutathione levels also decreased. Administration of pregabalin (30 mg/kg, oral), solasodine (25 mg/kg, oral), and EESTF (100 and 300 mg/kg, oral) significantly reduced CCI-induced behavioral and biochemical changes (P < 0.05). The protective nature of EESTF was also confirmed by histological analysis. Capsaicin, a TRPV1 receptor agonist, abolished the antinociceptive effects of EESTF when used previously. From the observations of the docking studies, solasodine acted as an antagonist at TRPV1, whereas the docking scores of solasodine against TNF-α and IL-6 were reported to be -11.2 and -6.04 kcal/mol, respectively. The attenuating effect of EESTF might be related to its antagonistic effects on TRPV1, suppression of cytokines, and anti-inflammatory and antioxidant properties.

Inhibition effect of choline and parecoxib sodium on chronic constriction nerve injury-induced neuropathic pain in rats

PurposeThe simultaneous use of drugs with different mechanisms of analgesic action is a strategy for achieving effective pain control while minimizing dose-related side effects. Choline was described to potentiate the analgesic action of parecoxib sodium at small doses in several inflammatory pain models. However, these findings are still very limited, and more associated data are required to confirm the effectiveness of the combined choline and parecoxib sodium therapy against inflammatory pain.MethodsAdult rats were randomly divided into 9 groups (N = 6/group). The sham surgery group received an intraperitoneal (i.p.) injection of saline. Rats with chronic constriction injury (CCI) of the sciatic nerve received saline, choline (cho, 6, 12 and 24 mg/kg), parecoxib sodium (pare, 3, 6, and 12 mg/kg), or a combination of choline 6 mg/kg and parecoxib sodium 3 mg/kg. Mechanical and heat pain thresholds were measured at 30 min after drug treatment at Days 3, 5, 7, 10, and 14 after CCI. Another 30 rats were divided into 5 groups (N = 6/group): the sham, CCI + saline, CCI + cho-6 mg/kg, CCI + pare-3 mg/kg, and CCI + cho-6 mg/kg + pare-3 mg/kg groups. After repeated drug treatment for 7 days, five rats were randomly selected from each group, and the lumbar dorsal root ganglia (DRGs) (L4–6) were harvested for western blot analysis.ResultsCholine significantly attenuated mechanical and heat hypersensitivity in CCI rats at 12 and 24 mg/kg doses (P < 0.05) but was not effective at the 6 mg/kg dose. Parecoxib sodium exerted significant pain inhibitory effects at the 6 and 12 mg/kg doses (P < 0.05) but not at the 3 mg/kg dose. Combining a low dose of choline (6 mg/kg) and parecoxib sodium (3 mg/kg) produced significant pain inhibition in CCI rats and reduced the expression of high mobility group protein 1 (HMGB1) and nuclear factor-kappa Bp65 (NF-κBp65) in L4–6 DRGs.Conclusion1. In a rat model of chronic neuropathic pain (CCI), at a certain dose, choline or parecoxib sodium can alleviate mechanical pain and thermal hyperalgesia caused by CCI. 2. The combination of choline and parecoxib sodium in nonanalgesic doses can effectively relieve neuropathic pain, and its mechanism may be related to the inhibition of the high mobility group protein 1 (HMGB1)/Toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) pathway.

Betaine Attenuates Chronic Constriction Injury-Induced Neuropathic Pain in Rats by Inhibiting KIF17-Mediated Nociception.

Kinesin superfamily proteins transport a diverse range of cargo, including excitatory receptors to the dendrite and axon of a neuron via retrograde and anterograde fashions along microtubules, causing central sensitization and neuropathic pain. In this study, we have performed in silico molecular dynamics simulation to delineate the dynamic interaction of betaine with KIF17, a kinesin protein, known to be involved in neuropathic pain. The results from the molecular dynamics study suggest that the betaine-KIF17 complex is stabilized through hydrogen bonding, polar interactions, and water bridges. Findings from in vivo studies suggest a significant increase in pain hypersensitivity, oxido-nitrosative stress, and KIF17 overexpression in the sciatic nerve, dorsal root ganglion (DRG), and spinal cord of nerve-injured rats, which was significantly attenuated on treatment with betaine. Betaine treatment also restored the increased NR2B expressions and levels of proinflammatory cytokines and neuropeptides in the DRG and spinal cord of nerve-injured rats. Findings from the current study suggest that betaine attenuates neuropathic pain in rats by inhibiting KIF17-NR2B-mediated neuroinflammatory signaling.

The Antinociceptive Potential of Camellia japonica Leaf Extract, (-)-Epicatechin, and Rutin against Chronic Constriction Injury-Induced Neuropathic Pain in Rats.

Neuropathic pain is caused by a lesion or disease of the somatosensory nervous system. Currently, prescribed treatments are still unsatisfactory or have limited effectiveness. Camellia japonica leaves are known to have antioxidant and anti-inflammatory properties.; however, their antinociceptive efficacy has not yet been explored. We examined the antinociceptive efficacy and underlying mechanism of C. japonica leaf extract (CJE) in chronic constriction injury (CCI)-induced neuropathic pain models. To test the antinociceptive activity of CJE, three types of allodynia were evaluated: punctate allodynia using von Frey filaments, dynamic allodynia using a paintbrush and cotton swab, and cold allodynia using a cold plate test. CCI rats developed neuropathic pain representing increases in the three types of allodynia and spontaneous pain. In addition, CCI rats showed high phosphorylation levels of mitogen-activated protein kinases (MAPKs), transcription factors, and nociceptive mediators in dorsal root ganglion (DRG). The ionized calcium-binding adapter molecule 1 levels and neuroinflammation also increased following CCI surgery in the spinal cord. CJE and its active components have potential antinociceptive effects against CCI-induced neuropathic pain that might be mediated by MAPK activation in the DRG and microglial activation in the spinal cord. These findings suggest that CJE, (−)-epicatechin, and rutin could be novel candidates for neuropathic pain management.

Aloin attenuates chronic constriction injury-induced neuropathic pain in rats by inhibiting inflammatory cytokines and oxidative stress

Objective: To investigate the effect of aloin against chronic constriction injury (CCI)-induced neuropathic pain in rats. Methods: Rats were randomly divided into 7 groups: Group I (normal control), Group II (sham-operated), Group III (CCI control) and Group IV, V, VI, and VII, which underwent CCI surgery and then were administered with aloin (5 mg/kg, p.o.; 25 mg/kg, p.o.; 125 mg/kg, p.o.) and gabapentin (50 mg/kg, p.o.), respectively for 14 days. Peripheral neuropathy was induced by silk ligatures (4-0) loosely placed around the sciatic nerve. Nociceptive thresholds against mechanical stimuli (Von-Frey filaments) and thermal stimuli (12 °C and 40 °C) were measured at mid-plantar paw region ipsilateral to the compressed nerve on day-3, 7, 11, and 14. The concentration of cytokines including tumor necrosis factor-α (TNF-α), interleukin-6, and interleukin-1β was estimated at day-7. At day 14, motor nerve conduction velocity was determined under urethane anesthesia (1.25 g/kg). Oxidative stress parameters (malondiadehyde, glutathione, catalase, and superoxide dismutase) were estimated in sciatic nerve homogenates at day 14. Representative nerve samples were processed for histological investigations. Results: Aloin significantly reduced CCI-induced mechanical and thermal allodynia. It also improved motor nerve conduction velocity and decreased oxidative stress in nerve tissues. In addition, it decreased pro-inflammatory cytokine levels and restored the histoarchitecture of compressed sciatic nerve. Conclusions: Aloin mitigates CCI-induced neuropathic pain in rats by inhibiting oxidative stress and pro-inflammatory cytokines in the afflicted sciatic nerve.

Thymus algeriensis and Thymus fontanesii exert neuroprotective effect against chronic constriction injury-induced neuropathic pain in rats

We have previously demonstrated that the Thymus algeriensis and Thymus fontanesii extracts have powerful anti-inflammatory, antipyretic, and analgesic effects against acute pain models. We profiled their chemical composition and found many phenolic acids, flavonoids, and phenolic diterpenes. In this work, we investigated their antioxidant properties on HaCaT cells exposed to UVA-induced oxidative stress and examined their effects against chronic neuropathic pain and the underlying mechanisms. Through a rat chronic constriction injury (CCI) model, we induced chronic neuropathic pain by placing 4 loose ligatures around the right sciatic nerve for 14 days. Thermal and mechanical hyperalgesia in addition to cold and dynamic allodynia were tested on the day before surgery and on the 7th and 14th post-surgery days. Key markers of the nitrosative and oxidative stresses, in addition to markers of inflammation, were measured at day 14 post surgery. Histopathological examination and immunostaining of both synaptophysin and caspase-3 of sciatic nerve and brain stem were also performed. Results of this study showed that T. algeriensis extract suppresses UVA oxidative stress in HaCaT cells via activation of the Nrf-2 pathway. Both extracts attenuated hyperalgesia and allodynia at 7- and 14-days post-surgery with more prominent effects at day 14 of surgery. Their protective effects against neuropathic pain were mediated by inhibiting NOX-1, iNOS, by increasing the enzyme activity of catalase, and inhibition of inflammatory mediators, NF-κB, TNF-α, lipoxygenase, COX-2 enzymes, and PGE2. Furthermore, they improved deleterious structural changes of the brainstem and sciatic nerve. They also attenuated the increased caspase-3 and synaptophysin. The data indicate that both extracts have neuroprotective effects against chronic constriction injury-induced neuropathic pain. The observed protective effects are partially mediated through attenuation of oxidative and nitrosative stress and suppression of both neuroinflammation and neuronal apoptosis, suggesting substantial activities of both extracts in amelioration of painful peripheral neuropathy.

Downregulation of long noncoding RNA DLEU1 attenuates hypersensitivity in chronic constriction injury-induced neuropathic pain in rats by targeting miR-133a-3p/SRPK1 axis

BackgroundNeuropathic pain belongs to chronic pain and is caused by the primary dysfunction of the somatosensory nervous system. Long noncoding RNAs (lncRNAs) have been reported to regulate neuronal functions and play significant roles in neuropathic pain. DLEU1 has been indicated to have close relationship with neuropathic pain. Therefore, our study focused on the significant role of DLEU1 in neuropathic pain rat models.MethodsWe first constructed a chronic constrictive injury (CCI) rat model. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were employed to evaluate hypersensitivity in neuropathic pain. RT-qPCR was performed to analyze the expression of target genes. Enzyme-linked immunosorbent assay (ELISA) was conducted to detect the concentrations of interleukin‐6 (IL-6), tumor necrosis factor‐α (TNF-α) and IL-1β. The underlying mechanisms of DLEU1 were investigated using western blot and luciferase reporter assays.ResultsOur findings showed that DLEU1 was upregulated in CCI rats. DLEU1 knockdown reduced the concentrations of IL‐6, IL‐1β and TNF‐α in CCI rats, suggesting that neuroinflammation was inhibited by DLEU1 knockdown. Besides, knockdown of DLEU1 inhibited neuropathic pain behaviors. Moreover, it was confirmed that DLEU1 bound with miR-133a-3p and negatively regulated its expression. SRPK1 was the downstream target of miR-133a-3p. DLEU1 competitively bound with miR-133a-3p to upregulate SRPK1. Finally, rescue assays revealed that SRPK1 overexpression rescued the suppressive effects of silenced DLEU1 on hypersensitivity in neuropathic pain and inflammation of spinal cord in CCI rats.ConclusionDLEU1 regulated inflammation of the spinal cord and mediated hypersensitivity in neuropathic pain in CCI rats by binding with miR-133a-3p to upregulate SRPK1 expression.

SNHG16 aggravates chronic constriction injury-induced neuropathic pain in rats via binding with miR-124-3p and miR-141-3p to upregulate JAG1

Neuropathic pain is caused by damage to the nervous system. Increasing studies have confirmed that jagged 1 (JAG1) plays a significant role in nervous system diseases. However, the regulatory mechanisms of JAG1 in neuropathic pain remain vague. In this study, a chronic constriction injury (CCI) rat model was performed. JAG1 was found to be upregulated in CCI rats. The recombinant lentiviruses containing sh-JAG1 were injected to the CCI rats for knockdown of JAG1 in rats. JAG1 knockdown improved the mechanical allodynia and thermal hyperalgesia in CCI rats, and decreased the concentrations and mRNA expression of inflammatory cytokines (IL‐6, TNF-α and IL-1β) in spinal cord dorsal horn of CCI rats, suggesting that JAG1 knockdown attenuated neuropathic pain. In addition, we explored for the upstream mechanism of JAG1. Through RNA pull down assay and luciferase reporter assay, we confirmed that miR-124-3p and miR-141-3p bound with JAG1. Long non-coding RNA (lncRNA) small nucleolar RNA host gene 6 (SNHG16) was verified to be the upstream molecule of miR-124-3p and miR-141-3p to negatively regulate miR-124-3p and miR-141-3p. SNHG16 positively regulated JAG1 expression through competitively binding with miR-124-3p and miR-141-3p. Moreover, SNHG16 was found to be upregulated in CCI rats. SNHG16 knockdown improved the mechanical allodynia and thermal hyperalgesia as well as reduced the concentrations and mRNA expression of inflammatory cytokines in CCI rats. Finally, SNHG16 was confirmed to aggravate neuropathic pain in CCI rats via upregulating JAG1. In conclusion, this study verified that SNHG16 aggravated neuropathic pain in CCI rats via binding with miR-124-3p and miR-141-3p to upregulate JAG1, which may provide new insights into the development of gene therapy for neuropathic pain.

MiR-216a-5p alleviates chronic constriction injury-induced neuropathic pain in rats by targeting KDM3A and inactivating Wnt/β-catenin signaling pathway

Neuropathic pain is a devastating disease and exists tolerance to current available analgesics. MicroRNAs were reported to be involved in the regulation of neuropathic pain, but the biological role of miR-216a-5p in neuropathic pain remains unclear. In this study, we constructed a CCI rat model of neuropathic pain. Our results showed that the expression of miR-216a-5p was downregulated in CCI rats, and mechanical allodynia and thermal hyperalgesia in CCI rats were improved by miR-216a-5p overexpression, suggesting that miR-216a-5p overexpression alleviated neuropathic pain. Moreover, ELISA showed that miR-216a-5p overexpression inhibited concentration and mRNA expression of IL‐6, TNF-α and IL‐1β as well as suppressed microglial infiltration, indicating that miR-216a-5p overexpression inhibited neuroinflammation. Besides, we found that miR-216a-5p upregulation inactivated the Wnt/β-catenin signaling pathway. Furthermore, KDM3A was the downstream target of miR-216a-5p and KDM3A knockdown attenuated neuropathic pain. Finally, through rescue assay, we found that KDM3A countervailed miR-216a-5p mediated regulation of neuropathic pain via the Wnt/β-catenin signaling pathway. To sum up, our study confirmed that miR-216a-5p alleviated neuropathic pain in rats by targeting KDM3A and inactivating the Wnt/β-catenin signaling pathway, which may open a new and useful way for treatment of neuropathic pain.

Anthocyanin Derived from Purple Sweet Potato Water Extracts Ameliorated Oxidative Stress, Inflammation, Mechanical Allodynia, and Cold Allodynia among Chronic Constriction Injury-Induced Neuropathic Pain in Rats

BACKGROUND: Nerve injury leads to multiple events, including oxidative stress, inflammation, and glial cells activation, which all bring about the neuropathic pain condition. Any alternative novel treatment modalities from natural products are thus highly anticipated, given the account that current treatments for neuropathic pain have not generated any satisfactory efficacy.&#x0D; AIM: This study aims to address the pleiotropic effects of water extracts from the purple sweet potato (PSP) (Ipomoea batatas L.) as an antioxidant, anti-inflammatory, and anti-nociceptive agent to alleviate neuropathic pain behavior.&#x0D; METHODS: This is a randomized post-test control group design using chronic constriction injury (CCI) rat models. Thirty-two Wistar rats (34 survived until the end of study period) fulfilling the eligible criteria were randomized into either treatment or control group. Treatment group received water extracts of PSP containing 400 mg/kg of body weight/d of anthocyanin for 28 days. Antioxidant activity was evaluated from malondialdehyde (MDA) levels, anti-inflammatory activity was evaluated from prostaglandin E2 (PGE2) levels. Neuropathic pain was assessed from the animal’s behavioral responses toward mechanical and cold allodynia.&#x0D; RESULTS: The results showed that mean MDA levels of treatment group were significantly lower than control group (0.291 ± 0.046 μmol vs. 0.394 ± 0.057 μmol; p &lt; 0.001). Furthermore, treatment group’s PGE2 levels were also significantly lower than control’s (0.342 ± 0.096 ng/mL vs. 0.431 ± 0.061 ng/mL; p = 0.004). In addition, neuropathic pain behavior comprising mechanical and cold allodynia were significantly milder among treatment group than in the control group during the observation period (p &lt; 0.05).&#x0D; CONCLUSION: PSP water extracts had been shown to ameliorate oxidative stress, as well as exerted anti-inflammatory and anti-nociceptive effects and was able to suppress neuropathic pain behavior in Wistar rats with peripheral nerve injury.

Early high-frequency spinal cord stimulation treatment inhibited the activation of spinal mitogen-activated protein kinases and ameliorated spared nerve injury-induced neuropathic pain in rats

BackgroundNeuromodulation therapies offer a treatment option that has minimal side effects and is relatively safe and potentially reversible. Spinal cord stimulation (SCS) has been used to treat various pain conditions for many decades. High-frequency SCS (HFSCS) involves the application of a single waveform at 10,000 Hz at a subthreshold level, therefore providing pain relief without any paresthesia. MethodsWe tested whether early HFSCS treatment attenuated spared nerve injury (SNI)-induced neuropathic pain. The phosphorylation profile of mitogen-activated protein kinases (MAPKs), i.e., extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and p38, was evaluated to elucidate the potential underlying mechanism. ResultsSNI of rat unilateral sciatic nerves induced mechanical hyperalgesia in the ipsilateral hind paws. Rats were assigned to SCS sessions with HFSCS (frequency 10 kHz; pulse width 30 μs; pulse shape of charge-balanced, current controlled; delivered continuously for 72 h), or sham stimulation immediately after SNI. Tissue samples were examined at 1, 3, 7, and 14 days after SNI. Behavioral studies showed that HFSCS applied to the T10/T11 spinal cord significantly attenuated SNI-induced mechanical hyperalgesia compared with the sham stimulation group. Moreover, western blotting revealed a significant attenuation of the activation of ERK1, ERK2, JNK1, and p38 in the dorsal root ganglia and the spinal dorsal horn. ConclusionApplication of HFSCS provides an effective treatment for SNI-induced persistent mechanical hyperalgesia by attenuating ERK, JNK, and p38 activation in the dorsal root ganglia and the spinal dorsal horn.

Suppressive Effects of Bee Venom-Derived Phospholipase A2 on Mechanical Allodynia in a Rat Model of Neuropathic Pain.

Bee venom (BV) has a long history of being used in traditional Korean medicine to relieve pain. Here, we investigated the effect of BV-derived phospholipase A2 (bvPLA2), a major component of BV, on peripheral nerve injury-induced neuropathic pain in rats. Spinal nerve ligation (SNL) was performed in Sprague Dawley rats to induce neuropathic pain, and paw withdrawal thresholds were measured using von Frey test. Mechanical allodynia, the representative symptom of neuropathic pain, was manifested following SNL and persisted for several weeks. The repetitive bvPLA2 treatment (0.2 mg/kg/day, i.p.) for two days significantly relieved the SNL-induced mechanical allodynia. The antiallodynic effect of bvPLA2 was blocked by spinal pretreatment with α1-adrenergic antagonist prazosin (30 μg, i.t.) but not with α2-adrenergic antagonist idazoxan (50 μg, i.t.). Also, the spinal application of α1-adrenergic agonist phenylephrine (50 μg, i.t.) reduced mechanical allodynia. These results indicate that bvPLA2 could relieve nerve injury-induced neuropathic mechanical allodynia through the activation of spinal α1-adrenergic receptors.

Investigating the possible pain attenuating mechanisms of pregabalin in chronic constriction injury-induced neuropathic pain in rats

Aim of the study: The current study was aimed to investigate the neuropathic pain attenuating mechanism of pregabalin using chronic constriction injury (CCI) model in rats.Material and Methods: The sciatic nerve was ligated by placing four loose ligatures around it to induce neuropathic pain. The pain development in terms of cold allodynia, mechanical hyperalgesia, and heat hyperalgesia was assessed on the 7th and 14th day after surgery, using acetone drop, pinprick, and hot plate tests. On the 14th day after the injury, pain parameters were assessed 30 minutes after administration of pregabalin (30 mg/kg) and sodium nitroprusside (5 mg/kg) in CCI-subjected rats.Results: CCI led to induction of neuropathic pain, which was more prominent on 14th day in comparison to 7th day. A single administration of pregabalin and sodium nitroprusside on 14th day, markedly reduced pain parameters and increased serum nitrite levels. Pretreatment with L-NAME abolished neuropathic pain attenuating effects of pregabalin suggesting that pregabalin may increase the levels of nitric oxide to mitigate neuropathic pain. Pretreatment with naloxone significantly abrogated pain attenuating effects of pregabalin and sodium nitroprusside in CCI-subjected rats suggesting that pregabalin and nitric oxide-mediated analgesic action are mediated through release of endogenous opioids. Moreover, naloxone failed to modulate pregabalin-induced increase in nitric oxide levels suggesting that the opioid system does not control the nitric oxide levels, and opioids may be downstream modulators of nitric oxide.Conclusion: Pregabalin may increase the release of nitric oxide, which may increase the release of endogenous opioids to attenuate neuropathic pain in CCI subjected rats.

Suppression of MALAT1 ameliorates chronic constriction injury-induced neuropathic pain in rats via modulating miR-206 and ZEB2.

Long noncoding RNAs (lncRNAs) are involved in multiple nervous system diseases, including neuropathic pain. Previous studies have demonstrated that lncRNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been identified as a diagnostic biomarker in many diseases. Nevertheless, the function of MALAT1 in neuropathic pain progression is still unclear. Here, we established a chronic constriction injury (CCI) rat model. We found that MALAT1 was remarkably upregulated in CCI rats. In addition, neuropathic pain behaviors such as mechanical and thermal hyperalgesia were reduced by the inhibition of MALAT1. Meanwhile, the loss of MALAT1 was able to depress the neuroinflammation process via the inhibition of COX-2, interleukin-1β, and interleukin-6. A previous study has indicated that miR-206 upregulation can restrain the CCI-induced neuropathic pain. Furthermore, we exhibited that miR-206 was significantly downregulated and silence of MALAT1 restrained its expression in CCI rats. For another, ZEB2 was a target of miR-206 and it was shown that ZEB2 was elevated in CCI rats in a time-dependent manner. Overexpression of miR-206 obviously suppressed ZEB2 levels in rat microglial cells. Subsequently, it was demonstrated that upregulation of miR-206 rescued the neuropathic pain triggered by ZEB2 overexpression in vivo through neuroinflammation inhibition. Overall, we indicated that suppression of MALAT1 ameliorated neuropathic pain progression via miR-206/ZEB2 axis.

Role of spinal dopamine D2 receptors in analgesic effect of duloxetine in rats with neuropathic pain

Objective To evaluate the involvement of spinal dopamine D2 receptors in the analgesic effect of duloxetine in neuropathic pain rat models. Methods Experiment I, twenty-four male SD rats, weighting 200-250 g, were randomly divided into 4 groups (n=6), respectively receiving intraperitoneal injection of dimethyl sulfoxide (DMSO) (group DS), 3 mg/kg duloxetine (group D1), 10 mg/kg duloxetine (group D2), and 30 mg/kg duloxetine (group D3). These treatments started 7 days after spinal L5 nerve ligation, and the mechanical withdraw threshold (MWT) was determined at 7 time points: before spinal nerve ligation (SNL) surgery (T0), before duloxetine injection (T1), and 15 min (T2), 30 min (T3), 60 min (T4), 120 min (T5), 180 min (T6) after duloxetine injection. Experiment Ⅱ, twenty-four male SD rats, weighting 200-250 g, were subjected to intrathecal catheters insertion, and were randomly divided into 4 groups (n=6). In group DS, DMSO (group DS+DS) or 30 μg sulpride (group Sul+DS) was administered intrathecally 15 min before DMSO intraperitoneal injection. In group Dul, DMSO (group DS+Dul) or 30 μg sulpride (group Sul+Dul) was administered intrathecally 15 min before 30 mg/kg duloxetine intraperitoneal injection. Mechanical paw withdraw threshold was determined before and after duloxetine or DMSO injection. Experiment Ⅲ, twelve male SD rats, weighting 200-250 g, were randomly divided into 2 groups (n=6), respectively receiving intraperitoneal injection of DMSO (group N) and 10 mg/kg duloxetine (group D). Then, the concentrations of dopamine in the spinal cord were measured with microdialysis before and after injection of duloxetine or DMSO injection. Results Compared with group DS, the MWT was significantly increased in group D3 at T2-T6 (P<0.05). Compared with group DS+Dul, the MWT was dramatically decreased in group Sul+Dul at T2-T6 (P<0.05). Compared with group N, the concentrations of dopamine in the spinal cord was dramatically increased in group D at T8-T13 (P<0.05). Conclusions Duloxetine relieved spinal nerve injury-induced neuropathic pain in rats, which may be related to the enhancement of dopamine release and activation of D2 receptors in the spinal cord dorsal horn. Key words: Neuropathic pain; Duloxetine; Spinal cord dorsal horn; Dopamine D2 receptors

Overexpression of miR-206 ameliorates chronic constriction injury-induced neuropathic pain in rats via the MEK/ERK pathway by targeting brain-derived neurotrophic factor

Neuropathic pain is chronic pain caused by lesions or diseases of the somatosensory system and existing tolerance to currently available analgesics. MicroRNAs (miRNAs) have been widely studied in the development of neuropathic pain and neuro-inflammation resulting from nerve injury. However, the precise mechanism of miRNAs involved in neuropathic pain remains largely unknown. In the present study, we investigated the vital roles of miR-206 and its putative target gene, brain-derived neurotrophic factor (BDNF), in neuropathic pain in the rat model of chronic constriction injury (CCI). The levels of miR-206 were down-regulated in the dorsal root ganglion (DRG) of rats following CCI, while the expressions of BDNF mRNA and protein were up-regulated in vivo. MiR-206 mimics attenuated mechanical allodynia and thermal hyperalgesia in a time-dependent manner in CCI rats. The changes were most significant at 7days. And, the levels of TNF-α, IL-1β, and IL-6 were decreased by miR-206 mimics. A direct interaction between miR-206 and the 3'-UTR of BDNF was verified by a dual-luciferase reporter assay. MiR-206 mimics inhibited the expression levels of BDNF mRNA and protein. Moreover, miR-206 mimics suppressed the activation of the MEK/ERK pathway in the DRG of CCI rats. Overexpression of BDNF abrogated the effects of miR-206 inhibition on neuropathic pain, neuro-inflammation and the MEK/ERK pathway. Treatment with U0126, an ERK inhibitor, exerted the same effect as treatment with miR-206 mimics. These results demonstrate that miR-206 alleviates neuropathic pain development via targeting of BDNF, and negatively mediates the MEK/ERK pathway, suggesting that miR-206 may act as a potential target for the treatment of neuropathic pain.

Ameliorative potential of Alstonia scholaris (Linn.) R. Br. against chronic constriction injury-induced neuropathic pain in rats

BackgroundAlstonia scholaris commonly known as ‘Saptaparni’ is an Indian traditional medicinal plant used in Ayurveda. It is commonly used to treat various disorders like asthma, bronchitis, diarrhea, dysentery and malaria. In folklore medicine the milky juice of the plant is applied on wounds and ulcers to treat pain, ear ache and also in rheumatic pains.AimThe present study was designed to investigate the potential of A. scholaris R. Br. in chronic constriction injury of sciatic nerve (CCI) induced neuropathic pain in rats.MethodsPeripheral neuropathy was induced by chronic constriction injury of sciatic nerve. The behavioral parameters like mechanical and thermal hyperalgesia and cold allodynia were assessed on the 14th day. Tissue parameters like total protein, thiobarbituric acid reactive substances, reduced glutathione, myeloperoxidase, total calcium and TNF-α were assessed to check biochemical changes. Chloroform and methanol extract of A. scholaris leaves (100 and 200 mg/kg) and pregabalin (10 mg/kg, as positive control) were administered orally for 14 consecutive days starting from the day of surgery.ResultsCCI resulted in significant development of mechanical hyperalgesia, heat hyperalgesia and cold allodynia along with alteration in the biochemical changes. Administration of methanol extract at 200 mg/kg significantly attenuated the CCI induced change in nociceptive threshold and biochemical changes which was comparable to that of pregabalin. The high-performance liquid chromatography (HPLC) of the bioactive methanol extract revealed the presence of different types of flavonoids such as gallic acid, catechin, epicatechin, ellagic acid and kaempferol, in which kaempferol was observed to be in higher concentration.ConclusionMethanol extract (200 mg/kg) of A. scholaris showed the ameliorative effect in CCI induced neuropathic pain which may be due to the presence of kaempferol and attributed to its anti-oxidative and anti-inflammatory properties.

Intrathecal Administration of Tempol Reduces Chronic Constriction Injury-Induced Neuropathic Pain in Rats by Increasing SOD Activity and Inhibiting NGF Expression.

We investigate the antinociceptive effect of intrathecal and intraperitoneal tempol administration in a rat model of chronic constriction injury (CCI)-induced neuropathic pain and explore the underlying antinociceptive mechanisms of tempol. Rats were randomly assigned to four groups (n=8 per group): sham group, CCI group, Tem1 group (intrathecal injection of tempol), and Tem2 group (intraperitoneal injection of tempol). Neuropathic pain was induced by CCI of the sciatic nerve. Tempol was intrathecally or intraperitoneally administered daily for 7days beginning on postoperative day one. The mechanical withdrawal threshold and thermal withdrawal latency were tested on preoperative day 3 and postoperative days 1, 3, 5, 7, 10, 14, and 21. Structural changes were examined by hematoxylin and eosin staining, toluidine blue staining, and electron microscopy. Malondialdehyde (MDA) and superoxide dismutase (SOD) levels were determined using the thiobarbituric acid and nitroblue tetrazolium methods, respectively. Nerve growth factor (NGF) expression levels were determined by immunohistochemistry and Western blot. Intrathecal, but not intraperitoneal, injection of tempol produced a persistent antinociceptive effect. Intraperitoneal injection of tempol did not result in high enough concentration of tempol in the cerebrospinal fluid. Intrathecal, but not intraperitoneal, injection of tempol inhibited CCI-induced structural damage in the spinal cord reduced MDA levels, and increased SOD activities in the spinal cord. Furthermore, intrathecal, but not intraperitoneal, injection of tempol further downregulated the expression of NGF in the spinal cord following CCI, and this effect was blocked by p38MAPK inhibitor. Intrathecal injection of tempol produces antinociceptive effects and reduces CCI-induced structural damage in the spinal cord by increasing SOD activities and downregulating the expression of NGF via the p38MAPK pathway. Intraperitoneal administration of tempol does not exhibit antinociceptive effects.

Ameliorative potential of Ocimum sanctum in chronic constriction injury-induced neuropathic pain in rats.

The present study was designed to investigate the ameliorative potential of Ocimum sanctum and its saponin rich fraction in chronic constriction injury-induced neuropathic pain in rats. The chronic constriction injury was induced by placing four loose ligatures around the sciatic nerve, proximal to its trifurcation. The mechanical hyperalgesia, cold allodynia, paw heat hyperalgesia and cold tail hyperalgesia were assessed by performing the pinprick, acetone, hot plate and cold tail immersion tests, respectively. Biochemically, the tissue thio-barbituric acid reactive species, super-oxide anion content (markers of oxidative stress) and total calcium levels were measured. Chronic constriction injury was associated with the development of mechanical hyperalgesia, cold allodynia, heat and cold hyperalgesia along with an increase in oxidative stress and calcium levels. However, administration of Ocimum sanctum (100 and 200 mg/kg p.o.) and its saponin rich fraction (100 and 200 mg/kg p.o.) for 14 days significantly attenuated chronic constriction injury-induced neuropathic pain as well as decrease the oxidative stress and calcium levels. It may be concluded that saponin rich fraction of Ocimum sanctum has ameliorative potential in attenuating painful neuropathic state, which may be attributed to a decrease in oxidative stress and calcium levels.