Objective To explore the functional mechanism of spinal cord fragile X mental retardation protein(FMRP)involved in neuropathic pain(NP)by using the sciatic nerve model of chronic compression injury(CCI).Methods First,to investigate the changes of spinal cord FMRP and β-catenin following the development of NP,this study compared the 50%mechanical withdrawal threshold(MWT)and thermal withdrawal latency(TWL)in CCI rats,as well as changes of FMRP and β-catenin in the spinal dorsal horn post-surgery,through random grouping.Immunofluorescence staining was performed on spinal cord tissue sections from CCI rats.Second,to further validate the alterations in pain behavior when the FMRP function was lost,we measured the 50%MWT,TWL,and FMRP and β-catenin in the spinal dorsal horn after FMRP knockdown in CCI rats.Finally,we measured the 50%MWT,TWL,and FMRP and β-catenin in the case of FMRP hyperfunction for validation.Results Compared with the baseline CCI group and the naive and sham groups after modeling,the CCI group after modeling showed decreases in 50%MWT and TWL(all P<0.001).After modeling,compared with the naive group and the sham group,the CCI group presented up-regulated expression of FMRP(P=0.027,P=0.022)and β-catenin(P<0.001,P=0.001)in the spinal dorsal horn.No co-localization of FMRP with astrocytes and microglia was observed in the spinal cord,while the co-localization with neurons was observed.Compared with the baseline,the CCI+FMRP knockdown group showed decreases in 50%MWT(P=0.015)and TWL(P=0.001)after modeling.After intrathecal injection of small interfering RNA(siRNA),the 50%MWT(P=0.020)and TWL(P=0.009)of the CCI+FMRP knockdown group were increased.Moreover,compared with the CCI group and the CCI+solvent group,the CCI+FMRP knockdown group showed increases in 50%MWT(both P<0.001)and TWL(P=0.005,P=0.006).After intrathecal injection of siRNA,the expression levels of FMRP(P=0.012,P=0.007)and β-catenin(both P<0.001)in the spinal dorsal horn of the CCI+FMRP knockdown group were lower than those of the CCI group and the CCI+solvent group.Compared with the baseline FMRP overexpression group and the naive and negative control groups after adeno-associated virus(AAV)injection,the FMRP overexpression group after AAV injection showed decreases in 50%MWT and TWL(all P<0.001).After AAV injection,compared with the naive group and the negative control group,the FMRP overexpression group demonstrated up-regulated expression of FMRP(both P<0.001)and β-catenin(P=0.006,P=0.008)in the spinal cord.Conclusions This study confirms that spinal cord FMRP and β-catenin are involved in NP induced by CCI.Spinal cord FMRP may be one of the potential therapeutic targets for NP.
Animals ; beta Catenin/metabolism* ; Neuralgia/metabolism* ; Fragile X Mental Retardation Protein/physiology* ; Spinal Cord/metabolism* ; Rats ; Rats, Sprague-Dawley ; Male

Central sensitization(CS) is an important factor in inducing neuropathic pain(NPP), and the association between signal transduction protein 1(Epac1) and piezoelectric type mechanosensitive ion channel component 2(Piezo2) is a new and significant pathway for initiating CS. This study whether the central analgesic effect of Maxiong Powder is achieved through the synchronized regulation of the Epac1-Piezo2 signaling pathway in the medial habenular nucleus(MHb) and interpeduncular nucleus(IPN) of the brain. Dynamic in vivo microdialysis, combined with high-performance liquid chromatography-fluorescence detection(HPLC-RFC), behavioral assessments, immunohistochemistry, Western blot, and quantitative reverse transcription PCR, were employed in rats with partial sciatic nerve injury(SNI) to investigate the distribution and expression of Epac1 and Piezo2 proteins and genes in the MHb and IPN regions, and the changes in the extracellular levels of glutamate(Glu), aspartic acid(Asp), and glycine(Gly). Compared with the sham group, rats in the SNI group showed significantly reduced analgesic activity, a significant increase in cold pain sensitivity scores, and elevated Glu levels in the MHb and IPN regions. Additionally, the number of Piezo2-positive cells in these regions, as well as the expression levels of Epac1 and Piezo2 proteins and genes, were significantly increased. Compared with the SNI group, after Maxiong Powder administration, the analgesic activity in rats significantly increased, and cold pain sensitivity scores were significantly reduced. Maxiong Powder also significantly decreased the Glu content in the MHb and IPN regions and the Gly content in the MHb region, while significantly increasing the Asp content in both regions. Furthermore, Maxiong Powder significantly reduced the number of Piezo2-positive cells and lowered the protein and gene expression levels of Epac1 and Piezo2 in both brain regions. The central analgesic effect of Maxiong Powder may be related to its inhibition of Glu and Gly release in the extracellular fluid of the MHb and IPN regions, the increase of Asp levels in these regions, and the regulation of the Epac1-Piezo2 pathway through the reduction of Epac1 and Piezo2 protein and gene expression. These results provide partial scientific evidence for the clinical analgesic efficacy of Maxiong Powder and offer new ideas and approaches for the clinical treatment of NPP.
Animals ; Neuralgia/genetics* ; Rats ; Signal Transduction/drug effects* ; Male ; Rats, Sprague-Dawley ; Guanine Nucleotide Exchange Factors/genetics* ; Drugs, Chinese Herbal/administration & dosage* ; Habenula/drug effects* ; Ion Channels/genetics* ; Humans

BACKGROUND: Postherpetic neuralgia (PHN) is the most common complication of herpes zoster infection and affects patients' quality of life. Acupuncture therapy is regarded as a competitive method of treatment for analgesia. OBJECTIVE: To summarize evidence from systematic reviews (SRs) and evaluate the effectiveness and safety of different acupuncture therapies for treating PHN. METHODS: Eight electronic databases were searched from their inception to August 5, 2022, including 4 international electronic databases (PubMed, EMBASE, the Cochrane Library, and Web of Science) and 4 Chinese databases (Chinese Biomedical Database, China National Knowledge Infrastructure, VIP Database and Wanfang Database). Methodological quality was assessed by A Measurement Tool to Assess Systematic Reviews 2 (AMSTAR 2). The Risk of Bias in Systematic Review (ROBIS) tool was used to assess the risk of bias in SRs. Evidence level was assessed by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. RESULTS: Totally, 7 SRs were included, including 128 studies and 9,792 patients. In AMSTAR 2, most of the SRs were of low or critically low levels since they had more than 1 critical deficiency. In ROBIS, 1 SR (14.29%) was rated as high risk, and the other 6 (85.71%) were rated as low risk. In the GRADE system, 9 outcomes (28.13%) were valued as high level, 5 (15.63%) as moderate level, 1 (3.13%) as low, and 17 (53.13%) as very low. In the effectiveness of acupuncture therapy, the group "moxibustion vs. original medical treatment" [mean difference (MD)=-1.44, 95% confidence interval (CI): -1.80 to -1.08, I²=99%, P<0.00001] was of the highest heterogeneity and the group "bloodletting vs. original medical treatment" (MD=-2.80, 95% CI: -3.14 to -2.46, I²=0, P<0.00001) was of the lowest heterogeneity. Six SRs have reported the safety of their studies and no serious events were shown in the treatment and control groups. CONCLUSIONS Acupuncture therapy seems to be effective in treating PHN. Despite the evidence that suggested the advantages of acupuncture therapy in relieving pain and promoting efficacy and safety, the methodological quality was quite low. Further studies should pay more attention to the quality of original studies and evidence for SRs to confirm these findings. (PROSPERO registration No. CRD42022344790).
Humans ; Neuralgia, Postherpetic/therapy* ; Acupuncture Therapy/methods* ; Systematic Reviews as Topic

OBJECTIVE: To illustrate the role of dehydrocorydaline (DHC) in chronic constriction injury (CCI)-induced neuropathic pain and the underlying mechanism. METHODS: C57BL/6J mice were randomly divided into 3 groups by using a random number table, including sham group (sham operation), CCI group [intrathecal injection of 10% dimethyl sulfoxide (DMSO)], and CCI+DHC group (intrathecal injection of DHC), 8 mice in each group. A CCI mouse model was conducted to induce neuropathic pain through ligating the right common sciatic nerve. On day 14 after CCI modeling or sham operation, mice were intrathecal injected with 5 µL of 10% DMSO or 10 mg/kg DHC (5 µL) into the 5th to 6th lumbar intervertebral space (L5-L6). Pregnant ICR mice were sacrificed for isolating primary spinal neurons on day 14 of embryo development for in vitro experiment. Pain behaviors were evaluated by measuring the paw withdrawal mechanical threshold (PWMT) of mice. Immunofluorescence was used to observe the activation of astrocytes and microglia in mouse spinal cord. Protein expressions of inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), phosphorylation of N-methyl-D-aspartate receptor subunit 2B (p-NR2B), and NR2B in the spinal cord or primary spinal neurons were detected by Western blot. RESULTS: In CCI-induced neuropathic pain model, mice presented significantly decreased PWMT, activation of glial cells, overexpressions of iNOS, TNF-α, IL-6, and higher p-NR2B/NR2B ratio in the spinal cord (P<0.05 or P<0.01), which were all reversed by a single intrathecal injection of DHC (P<0.05 or P<0.01). The p-NR2B/NR2B ratio in primary spinal neurons were also inhibited after DHC treatment (P<0.05). CONCLUSION An intrathecal injection of DHC relieved CCI-induced neuropathic pain in mice by inhibiting the neuroinflammation and neuron hyperactivity.
Animals ; Neuralgia/etiology* ; Mice, Inbred C57BL ; Analgesics/pharmacology* ; Neuroinflammatory Diseases/pathology* ; Constriction ; Male ; Receptors, N-Methyl-D-Aspartate/metabolism* ; Nitric Oxide Synthase Type II/metabolism* ; Mice, Inbred ICR ; Microglia/pathology* ; Spinal Cord/drug effects* ; Female ; Mice ; Tumor Necrosis Factor-alpha/metabolism* ; Disease Models, Animal ; Constriction, Pathologic/complications* ; Interleukin-6/metabolism* ; Astrocytes/metabolism* ; Chronic Disease ; Neurons/metabolism*

OBJECTIVES: Neuropathic pain (NP) is one of the most common forms of chronic pain, yet current treatment options are limited in effectiveness. Peripheral nerve injury activates spinal microglia, altering their inflammatory response and phagocytic functions, which contributes to the progression of NP. Most current research on NP focuses on microglial inflammation, with relatively little attention to their phagocytic function. Early growth response factor 2 (EGR2) has been shown to regulate microglial phagocytosis, but its specific role in NP remains unclear. This study aims to investigate how EGR2 modulates microglial phagocytosis and its involvement in NP, with the goal of identifying potential therapeutic targets. METHODS: Adult male Sprague-Dawley (SD) rats were used to establish a chronic constriction injury (CCI) model of the sciatic nerve. Pain behaviors were assessed on days 1, 3, 7, 10, and 14 post-surgery to confirm successful model induction. The temporal and spatial expression of EGR2 in the spinal cord was examined using real-time quantitative PCR (RT-qPCR), Western blotting, and immunofluorescence staining. Adeno-associated virus (AAV) was used to overexpress EGR2 in the spinal cord, and behavioral assessments were performed to evaluate the effects of EGR2 modulation of NP. CCI and lipopolysaccharide (LPS) models were established in animals and microglial cell lines, respectively, and changes in phagocytic activity were measured using RT-qPCR and fluorescent latex bead uptake assays. After confirming the involvement of microglial phagocytosis in NP, AAV was used to overexpress EGR2 in both in vivo and in vitro models, and phagocytic activity was further evaluated. Finally, eukaryotic transcriptome sequencing was conducted to screen differentially expressed mRNAs, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses to identify potential downstream effectors of EGR2. RESULTS: The CCI model successfully induced NP. Following CCI, EGR2 expression in the spinal cord was upregulated in parallel with NP development. Overexpression of EGR2 via spinal AAV injection enhanced microglial phagocytic activity and increased pain hypersensitivity in rats. Both animal and cellular models showed that CCI or LPS stimulation enhanced microglial phagocytosis, which was further amplified by EGR2 overexpression. Transcriptomic analysis of spinal cord tissues from CCI rats overexpressing EGR2 revealed upregulation of numerous genes associated with microglial phagocytosis and pain regulation. Among them, Lag3 emerged as a potential downstream target of EGR2. CONCLUSIONS EGR2 contributes to the maintenance of NP by enhancing microglial phagocytosis in the spinal dorsal horn.
Animals ; Microglia/metabolism* ; Phagocytosis/physiology* ; Rats, Sprague-Dawley ; Neuralgia/physiopathology* ; Early Growth Response Protein 2/metabolism* ; Male ; Rats ; Spinal Cord/metabolism* ; Sciatic Nerve/injuries*

OBJECTIVES: Pain sensitization, as a core feature of neuropathic pain (NP), is closely associated with inflammatory imbalance within the central nervous system. To investigate the effects of intrathecal injection of noggin (NOG) on mechanical hypersensitivity, microglial (MG) activation and polarization, and iron metabolism in a spinal nerve ligation (SNL)-induced rat model of NP, and to explore the role of signal transducer and activator of transcription 3 (STAT3) in MG phenotypic transformation. METHODS: Sixty-six Sprague-Dawley (SD) rats were randomly divided into 3 groups: Sham, SNL, and SNL+NOG. Paw withdrawal threshold (PWT) was assessed using von Frey filaments. Western blotting and real-time polymerase chain reaction (RT-PCR) were used to detect spinal cord expression of MG activation marker CD11b, STAT3, phosphorylated STAT3 (p-STAT3), M1 polarization markers [CD86, CD32, interleukin (IL)-1β], tumor necrosis factor-alpha (TNF-α), and CC chemokine receptor 2 (CCR2), M2 markers [CD204, CD163, CX3C chemokine receptor 1 (CX3CR1), IL-10, and arginase-1 (ARG-1)], and iron metabolism-related proteins including ferroportin (FPN, gene: SLC40A1), hepcidin (gene: HAMP), transferrin receptor (gene: TFRC), and divalent metal transporter 1 (DMT-1, gene: SLC11A2). p-STAT3 localization in MGs was visualized via immunofluorescence. In vitro, primary MGs were divided into Control, bone morphogenetic protein-4 (BMP4), and BMP4+Stattic (STAT3 inhibitor) groups to examine the effects of STAT3 inhibition on MG activation, polarization, and iron regulation. RESULTS: In vivo, compared with the Sham group, the SNL and SNL+NOG groups exhibited significantly decreased PWT (P<0.05), elevated spinal CD11b and p-STAT3 protein levels (all P<0.05), increased M1 markers (CD86, CD32, IL-1β, TNF-α, and CCR2) (all P<0.05), and decreased M2 markers (CD204 protein; mRNA of CD204, ARG-1) (all P<0.05). Hepcidin protein and mRNA levels of HAMP, SLC11A2, and TFRC were significantly elevated, while FPN protein and SLC40A1 mRNA were reduced (all P<0.05). Compared to SNL alone, the SNL+NOG group showed increased PWT, decreased CD11b, p-STAT3, and M1 marker expression (except TNF-α), increased M2 marker expression, reduced hepcidin and HAMP levels, and increased FPN and SLC40A1 expression (all P<0.05). In vitro, BMP4 treatment increased CD11b, STAT3, p-STAT3, CD86, and hepcidin levels, while reducing CD204 and FPN (all P<0.05). Inhibition STAT3 with Stattic reversed these changes (all P<0.05). CONCLUSIONS NOG alleviates SNL-induced NP by antagonizing the STAT3 signaling pathway, thereby rebalancing microglial polarization and restoring iron metabolism.
Animals ; Neuralgia/drug therapy* ; Rats, Sprague-Dawley ; Microglia/cytology* ; STAT3 Transcription Factor/metabolism* ; Rats ; Iron/metabolism* ; Male ; Signal Transduction/drug effects* ; Carrier Proteins/therapeutic use* ; Homeostasis/drug effects* ; Spinal Cord/metabolism*

OBJECTIVES: To explore the therapeutic effect of LuoFuShan Rheumatism Plaster (LFS) on neuropathic pain (NP) and its molecular mechanism. METHODS: Mouse models of sciatic nerve chronic constriction injury (CCI) were treated with low, medium, and high doses (2.2, 4.4, and 8.8 cm², respectively) of LFS by topical application for 14 consecutive days. The therapeutic effects were assessed by evaluating the mechanical withdrawal threshold (MWT), paw withdrawal latency (PWL), plasma IL-6 and TNF-α levels, and histopathology of the sciatic nerve. Network pharmacology and molecular docking were used to identify the key targets and signaling pathways. The key targets were verified by RT-qPCR and immunohistochemistry. The biosafety of LFS was evaluated by measuring the organ indices and damage indicators of the heart, liver, and kidneys. RESULTS: Compared with the CCI group, LFS dose-dependently increased MWT and PWL, reduced plasma IL-6 and TNF-α levels, and alleviated sciatic nerve inflammation in the mouse models. Network pharmacology identified 378 bioactive compounds targeting 279 NP-associated genes enriched in TLR and TNF signaling. Molecular docking showed that quercetin and ursolic acid in LFS could stably bind to TLR4 and TNF‑α. In the mouse models of sciatic nerve CCI, LFS significantly downregulated the mRNA expression levels of Tlr4 and Tnf-α in the spinal cord in a dose-dependent manner and lowered the protein expressions of TLR4 and TNF-α in the sciatic nerve. LFS treatment did not cause significant changes in the organ indices or damage indicators of the heart, liver and kidneys as compared with those in the CCI model group and sham-operated group. CONCLUSIONS LFS alleviates NP in mice by suppression of TLR4/TNF-α-mediated neuroinflammation with a good safety profile.
Animals ; Toll-Like Receptor 4/metabolism* ; Neuralgia/metabolism* ; Mice ; Signal Transduction/drug effects* ; Tumor Necrosis Factor-alpha/metabolism* ; Drugs, Chinese Herbal/pharmacology* ; Sciatic Nerve/injuries* ; Male ; Molecular Docking Simulation ; Disease Models, Animal ; Interleukin-6

Neuropathic pain, often featuring allodynia, imposes significant physical and psychological burdens on patients, with limited treatments due to unclear central mechanisms. Addressing this challenge remains a crucial unsolved issue in pain medicine. Our previous study, using protein kinase C gamma (PKCγ)-tdTomato mice, highlights the spinal feedforward inhibitory circuit involving PKCγ neurons in gating neuropathic allodynia. However, the regulatory mechanisms governing this circuit necessitate further elucidation. We used diverse transgenic mice and advanced techniques to uncover the regulatory role of the descending serotonin (5-HT) facilitation system on spinal PKCγ neurons. Our findings revealed that 5-HT neurons from the rostral ventromedial medulla hyperpolarize spinal inhibitory interneurons via 5-HT_2C receptors, disinhibiting the feedforward inhibitory circuit involving PKCγ neurons and exacerbating allodynia. Inhibiting spinal 5-HT_2C receptors restored the feedforward inhibitory circuit, effectively preventing neuropathic allodynia. These insights offer promising therapeutic targets for neuropathic allodynia management, emphasizing the potential of spinal 5-HT_2C receptors as a novel avenue for intervention.
Animals ; Neuralgia/physiopathology* ; Protein Kinase C/metabolism* ; Receptor, Serotonin, 5-HT2C/metabolism* ; Hyperalgesia/physiopathology* ; Mice, Transgenic ; Mice ; Spinal Cord/metabolism* ; Serotonin/metabolism* ; Male ; Neurons/metabolism* ; Mice, Inbred C57BL

Patients suffering from nerve injury often experience exacerbated pain responses and complain of memory deficits. The dorsal hippocampus (dHPC), a well-defined region responsible for learning and memory, displays maladaptive plasticity upon injury, which is assumed to underlie pain hypersensitivity and cognitive deficits. However, much attention has thus far been paid to intracellular mechanisms of plasticity rather than extracellular alterations that might trigger and facilitate intracellular changes. Emerging evidence has shown that nerve injury alters the microarchitecture of the extracellular matrix (ECM) and decreases ECM rigidity in the dHPC. Despite this, it remains elusive which element of the ECM in the dHPC is affected and how it contributes to neuropathic pain and comorbid cognitive deficits. Laminin, a key element of the ECM, consists of α-, β-, and γ-chains and has been implicated in several pathophysiological processes. Here, we showed that peripheral nerve injury downregulates laminin β1 (LAMB1) in the dHPC. Silencing of hippocampal LAMB1 exacerbates pain sensitivity and induces cognitive dysfunction. Further mechanistic analysis revealed that loss of hippocampal LAMB1 causes dysregulated Src/NR2A signaling cascades via interaction with integrin β1, leading to decreased Ca²⁺ levels in pyramidal neurons, which in turn orchestrates structural and functional plasticity and eventually results in exaggerated pain responses and cognitive deficits. In this study, we shed new light on the functional capability of hippocampal ECM LAMB1 in the modulation of neuropathic pain and comorbid cognitive deficits, and reveal a mechanism that conveys extracellular alterations to intracellular plasticity. Moreover, we identified hippocampal LAMB1/integrin β1 signaling as a potential therapeutic target for the treatment of neuropathic pain and related memory loss.
Animals ; Laminin/genetics* ; Hippocampus/metabolism* ; Neuralgia/metabolism* ; Cognitive Dysfunction/etiology* ; Male ; Peripheral Nerve Injuries/metabolism* ; Extracellular Matrix/metabolism* ; Integrin beta1/metabolism* ; Pyramidal Cells/metabolism* ; Signal Transduction

Neuropathic pain is a chronic condition caused by damage or dysfunction in the nervous system. While the spleen may influence neuropathic pain, its role has been poorly understood. This study demonstrates that the spleen plays a crucial role in regulating neuropathic pain through the bed nucleus of the stria terminalis (BNST) - paraventricular nucleus of the hypothalamus (PVN) neural circuit in a chronic constriction injury (CCI) mouse model. Splenectomy, splenic denervation, or splenic sympathectomy significantly increased the mechanical withdrawal threshold (MWT) and reduced macrophage infiltration in the dorsal root ganglia (DRG) of CCI mice. Pseudorabies virus injections into the spleen revealed connections to the BNST and PVN in the brain. Chemogenetic inhibition of the BNST-PVN circuit increased macrophage infiltration in the DRG and decreased the MWT; these effects were reversed by splenectomy, splenic denervation, or sympathectomy. These findings underscore the critical role of the spleen, regulated by the BNST-PVN circuit, in neuropathic pain.
Animals ; Neuralgia/pathology* ; Septal Nuclei/physiopathology* ; Male ; Spleen/physiopathology* ; Paraventricular Hypothalamic Nucleus/physiopathology* ; Mice, Inbred C57BL ; Splenectomy ; Mice ; Neural Pathways/physiopathology* ; Disease Models, Animal ; Ganglia, Spinal/physiopathology* ; Sympathectomy ; Macrophages