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

Neuropathic pain, a debilitating condition caused by dysfunction of the somatosensory nervous system, remains difficult to treat due to limited understanding of its molecular mechanisms. Bioinformatics analysis identified cerebellin 2 (CBLN2) as highly enriched in human and murine proprioceptive and nociceptive neurons. We found that CBLN2 expression is persistently upregulated in dorsal root ganglia (DRG) following spinal nerve ligation (SNL) in mice. In addition, transcription factor SOX11 binds to 12 cis-regulatory elements within the Cbln2 promoter to enhance its transcription. SNL also induced SOX11 upregulation, with SOX11 and CBLN2 co-localized in nociceptive neurons. The siRNA-mediated knockdown of Sox11 or Cbln2 attenuated SNL-induced mechanical allodynia and thermal hyperalgesia. High-throughput sequencing of DRG following intrathecal injection of CBLN2 revealed widespread gene expression changes, including upregulation of numerous NF-κB downstream targets. Consistently, CBLN2 activated NF-κB signaling, and inhibition with pyrrolidine dithiocarbamate reduced CBLN2-induced pain hypersensitivity, proinflammatory cytokines and chemokines production, and neuronal hyperexcitability. Together, these findings identified the SOX11/CBLN2/NF-κB axis as a critical mediator of neuropathic pain and a promising target for therapeutic intervention.
Animals ; Neuralgia/metabolism* ; Ganglia, Spinal/metabolism* ; Up-Regulation ; Mice ; NF-kappa B/metabolism* ; SOXC Transcription Factors/genetics* ; Male ; Neuroinflammatory Diseases/metabolism* ; Mice, Inbred C57BL ; Nerve Tissue Proteins/genetics* ; Hyperalgesia/metabolism* ; Signal Transduction ; Spinal Nerves

Astrocytes in the spinal dorsal horn (SDH) exhibit diverse reactive phenotypes under neuropathic conditions, yet the mechanisms driving this diversity and its implications in chronic pain remain unclear. Here, we report that spared nerve injury (SNI) induces marked upregulation of both complement component 3 (C3⁺, A1-like) and S100 calcium-binding protein A10 (S100A10⁺, A2-like) astrocyte subpopulations in the SDH, with elevated microglial cytokines including interleukin-1α, tumor necrosis factor-α, and complement component 1q. Transcriptomic, immunohistochemical, and Western blot analyses reveal co-activation of multiple reactive astrocyte states over a unidirectional shift toward an A1-like phenotype. Fibroblast growth factor 8 (FGF8), a neuroprotective factor via FGFR3, mitigated microglia-induced C3⁺ astrocyte reactivity in vitro and suppressed spinal C3 expression and mechanical allodynia following intrathecal administration in SNI mice. These findings reveal a microglia-astrocyte signaling axis that promotes A1 reactivity and position FGF8 as a promising therapeutic candidate for neuropathic pain by modulating astrocyte heterogeneity.
Animals ; Astrocytes/drug effects* ; Neuralgia/pathology* ; Receptor, Fibroblast Growth Factor, Type 3/metabolism* ; Signal Transduction/physiology* ; Male ; Mice ; Microglia/drug effects* ; Fibroblast Growth Factor 8/pharmacology* ; Mice, Inbred C57BL ; Hyperalgesia/drug therapy* ; Spinal Cord/drug effects* ; Complement C3/metabolism* ; Spinal Cord Dorsal Horn/metabolism*

Neuropathic pain is frequently comorbidity with cognitive deficits. Neuralized1 (Neurl1)-mediated ubiquitination of CPEB3 in the hippocampus is critical in learning and memory. However, the role of Neurl1 in the cognitive impairment in neuropathic pain remains elusive. Herein, we found that lumbar 5 spinal nerve ligation (SNL) in male rat-induced neuropathic pain was followed by learning and memory deficits and LTP impairment in the hippocampus. The Neurl1 expression in the hippocampal CA1 was decreased after SNL. And this decrease paralleled the reduction of ubiquitinated-CPEB3 level and reduced production of GluA1 and GluA2. Overexpression of Neurl1 in the CA1 rescued cognitive deficits and LTP impairment, and reversed the reduction of ubiquitinated-CPEB3 level and the decrease of GluA1 and GluA2 production following SNL. Specific knockdown of Neurl1 or CPEB3 in bilateral hippocampal CA1 in naïve rats resulted in cognitive deficits and impairment of synaptic plasticity. The rescued cognitive function and synaptic plasticity by the treatment of overexpression of Neurl1 before SNL were counteracted by the knockdown of CPEB3 in the CA1. Collectively, the above results suggest that the downregulation of Neurl1 through reducing CPEB3 ubiquitination and, in turn, repressing GluA1 and GluA2 production and mediating synaptic plasticity impairment in hippocampal CA1 leads to the genesis of cognitive deficits in neuropathic pain.
Animals ; Male ; Neuralgia/metabolism* ; Rats ; Down-Regulation/physiology* ; Ubiquitination/physiology* ; Neuronal Plasticity/physiology* ; Rats, Sprague-Dawley ; CA1 Region, Hippocampal/metabolism* ; Cognitive Dysfunction/metabolism* ; RNA-Binding Proteins/metabolism* ; Receptors, AMPA/metabolism*

The prelimbic cortex (PL) plays a critical role in processing both the sensory and affective components of pain. However, the underlying molecular mechanisms remain poorly understood. In this study, we observed a reduction in hyperpolarization-activated cation current (I_h) in layer V pyramidal neurons of the contralateral PL in a mouse model of spared nerve injury (SNI). The expression of hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) channels was also decreased in the contralateral PL. Conversely, microinjection of fisetin, a partial agonist of HCN2, produced both analgesic and anxiolytic effects. Additionally, we found that cyclin-dependent kinase 5 (CDK5) was activated in the contralateral PL, where it formed a complex with HCN2 and phosphorylated its C-terminus. Knockdown of CDK5 restored HCN2 expression and alleviated both pain hypersensitivity and anxiety-like behaviors. Collectively, these results indicate that CDK5-mediated dysfunction of HCN2 in the PL underlies nerve injury-induced mechanical hypersensitivity and anxiety.
Animals ; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/metabolism* ; Hyperalgesia/metabolism* ; Cyclin-Dependent Kinase 5/metabolism* ; Neuralgia/metabolism* ; Male ; Anxiety/metabolism* ; Mice ; Potassium Channels/metabolism* ; Mice, Inbred C57BL ; Disease Models, Animal ; Pyramidal Cells/metabolism*

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

Endothelin-1 is a peptide derived from endothelial cells, consisting of 21 amino acid residues. In recent years, research has found that endothelin-1 not only plays a key role in vascular tone regulation but also participates in the occurrence and development of various types of pathological pain, including inflammatory pain, neuropathic pain, and cancer pain. Endothelin-1 binds to its receptors and activates multiple signaling pathways such as protein kinase C, calcium ion channels, and the phosphoinositide pathway, thereby influencing neuronal excitability and nociceptive information transmission. This article briefly reviews the current understanding of the mechanisms and potential roles of endothelin-1 in the development of pain, as well as commonly used endothelin-1 receptor antagonists, aiming to provide clues for better utilizing endothelin-1 and its receptors to alleviate and treat pathological pain.
Humans ; Endothelin-1/physiology* ; Pain/physiopathology* ; Signal Transduction/physiology* ; Animals ; Neuralgia/physiopathology* ; Cancer Pain/physiopathology* ; Endothelin Receptor Antagonists