Bone morphogenetic protein 4 derived from the cerebrospinal fluid in patients with postherpetic neuralgia induces allodynia via the crosstalk between microglia and astrocyte.

INTRODUCTION: During postherpetic neuralgia (PHN), the cerebral spinal fluid (CSF) possesses the capability to trigger glial activation and inflammation, yet the specific changes in its composition remain unclear. Recent findings from our research indicate elevations of central bone morphogenetic protein 4 (BMP4) during neuropathic pain (NP), serving as an independent modulator of glial cells. Herein, the aim of the present study is to test the CSF-BMP4 expressions and its role in the glial modulation in the process of PHN. METHODS: CSF samples were collected from both PHN patients and non-painful individuals (Control) to assess BMP4 and its antagonist Noggin levels. Besides, intrathecal administration of both CSF types was conducted in normal rats to evaluate the impact on pain behavior, glial activity, and inflammation.; Additionally, both Noggin and STAT3 antagonist-Stattic were employed to treat the PHN-CSF or exogenous BMP4 challenged cultured astrocytes to explore downstream signals. Finally, microglial depletion was performed prior to the PHN-CSF intervention so as to elucidate the microglia-astrocyte crosstalk. RESULTS: BMP4 levels were significantly higher in PHN-CSF compared to Control-CSF (P < 0.001), with a positive correlation with pain duration (P < 0.05, r = 0.502). Comparing with the Control-CSF producing moderate paw withdrawal threshold (PWT) decline and microglial activation, PHN-CSF further exacerbated allodynia and triggered both microglial and astrocytic activation (P < 0.05). Moreover, PHN-CSF rather than Control-CSF evoked microglial proliferation and pro-inflammatory transformation, reinforced iron storage, and activated astrocytes possibly through both SMAD159 and STAT3 signaling, which were all mitigated by the Noggin application (P < 0.05). Next, both Noggin and Stattic effectively attenuated BMP4-induced GFAP and IL-6 upregulation, as well as SMAD159 and STAT3 phosphorylation in the cultured astrocytes (P < 0.05). Finally, microglial depletion diminished PHN-CSF induced astrogliosis, inflammation and endogenous BMP4 expression (P < 0.05). CONCLUSION: Our study highlights the role of CSF-BMP4 elevation in glial activation and allodynia during PHN, suggesting a potential therapeutic avenue for future exploration.

Ferroptosis: a new regulatory mechanism in neuropathic pain.

Neuropathic pain (NP) is pain caused by damage to the somatosensory system. It is a common progressive neurodegenerative disease that usually presents with clinical features such as spontaneous pain, touch-evoked pain, nociceptive hyperalgesia, and sensory abnormalities. Due to the complexity of the mechanism, NP often persists. In addition to the traditionally recognized mechanisms of peripheral nerve damage and central sensitization, excessive iron accumulation, oxidative stress, neuronal inflammation, and lipid peroxidation damage are distinctive features of NP in pathophysiology. However, the mechanisms linking these pathological features to NP are not fully understood. The complexity of the pathogenesis of NP greatly limits the development of therapeutic approaches for NP. Ferroptosis is a novel form of cell death discovered in recent years, in which cell death is usually accompanied by massive iron accumulation and lipid peroxidation. Ferroptosis-inducing factors can affect glutathione peroxidase directly or indirectly through different pathways, leading to decreased antioxidant capacity and accumulation of lipid reactive oxygen species (ROS) in cells, ultimately leading to oxidative cell death. It has been shown that ferroptosis is closely related to the pathophysiological process of many neurological disorders such as NP. Possible mechanisms involved are changes in intracellular iron ion levels, alteration of glutamate excitability, and the onset of oxidative stress. However, the functional changes and specific molecular mechanisms of ferroptosis during this process still need to be further explored. How to intervene in the development of NP by regulating cellular ferroptosis has become a hot issue in etiological research and treatment. In this review, we systematically summarize the recent progress of ferroptosis research in NP, to provide a reference for further understanding of its pathogenesis and propose new targets for treatment.

Cannabis-Based Medicine for Neuropathic Pain and Spasticity-A Multicenter, Randomized, Double-Blinded, Placebo-Controlled Trial.

Patients with multiple sclerosis (MS) and spinal cord injury (SCI) commonly sustain central neuropathic pain (NP) and spasticity. Despite a lack of consistent evidence, cannabis-based medicine (CBM) has been suggested as a supplement treatment. We aimed to investigate the effect of CBM on NP and spasticity in patients with MS or SCI. We performed a randomized, double-blinded, placebo-controlled trial in Denmark. Patients aged ≥18 years with NP (intensity >3, ≤9 on a numerical rating scale (NRS0-10) and/or spasticity (>3 on NRS0-10) were randomized to treatment consisting of either delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), a combination of THC&CBD in maximum doses of 22.5 mg, 45 mg and 22.5/45 mg per day, respectively, or placebo. A baseline registration was performed before randomization. Treatment duration was six weeks followed by a one-week phaseout. Primary endpoints were the intensity of patient-reported NP and/or spasticity. Between February 2019 and December 2021, 134 patients were randomized (MS n = 119, SCI n = 15), where 32 were assigned to THC, 31 to CBD, 31 to THC&CBD, and 40 to placebo. No significant difference was found for: mean pain intensity (THC 0.42 (-0.54-1.38), CBD 0.45 (-0.47-1.38) and THC&CBD 0.16 (-0.75-1.08)), mean spasticity intensity (THC 0.24 (-0.67-1.45), CBD 0.46 (-0.74-1.65), and THC&CBD 0.10 (-1.18-1.39), secondary outcomes (patient global impression of change and quality of life), or any tertiary outcomes. We aimed to include 448 patients in the trial; however, due to COVID-19 and recruitment challenges, fewer were included. Nevertheless, in this four-arm parallel trial, no effect was found between placebo and active treatment with THC or CBD alone or in combination on NP or spasticity in patients with either MS or SCI. The trial was registered with the EU Clinical Trials Register EudraCT (2018-002315-98).

Research trends and hotspots of neuropathic pain in neurodegenerative diseases: a bibliometric analysis.

Background: Neuropathic pain is caused by a neurological injury or disease and can have a significant impact on people's daily lives. Studies have shown that neuropathic pain is commonly associated with neurodegenerative diseases. In recent years, there has been a lot of literature on the relationship between neuropathic pain and neurodegenerative diseases. However, bibliometrics is rarely used in analyzing the general aspects of studies on neuropathic pain in neurodegenerative diseases. Methods: The bibliometric analysis software CiteSpace and VOSviewer were used to analyze the knowledge graph of 387 studies in the Science Citation Index Expanded of the Web of Science Core Collection Database. Results: We obtained 2,036 documents through the search, leaving 387 documents after culling. 387 documents were used for the data analysis. The data analysis showed that 330 papers related to neuropathic pain in neurodegenerative diseases were published from 2007-2022, accounting for 85.27% of all published literature. In terms of contributions to the scientific study of neuropathic pain, the United States is in the top tier, with the highest number of publications, citations, and H-indexes. Conclusion: The findings in our study may provide researchers with useful information about research trends, frontiers, and cooperative institutions. Multiple sclerosis, Parkinson's disease, and Alzheimer's disease are the three most studied neurodegenerative diseases. Among the pathological basis of neurodegenerative diseases, microglia-regulated neuroinflammation is a hot research topic. Deep brain stimulation and gamma knife radiosurgery are two popular treatments.

Transcriptomic and proteomic profiling of the anterior cingulate cortex in neuropathic pain model rats.

Background: Neuropathic pain (NP) takes a heavy toll on individual life quality, yet gaps in its molecular characterization persist and effective therapy is lacking. This study aimed to provide comprehensive knowledge by combining transcriptomic and proteomic data of molecular correlates of NP in the anterior cingulate cortex (ACC), a cortical hub responsible for affective pain processing. Methods: The NP model was established by spared nerve injury (SNI) in Sprague-Dawley rats. RNA sequencing and proteomic data from the ACC tissue isolated from sham and SNI rats 2 weeks after surgery were integrated to compare their gene and protein expression profiles. Bioinformatic analyses were performed to figure out the functions and signaling pathways of the differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) enriched in. Results: Transcriptomic analysis identified a total of 788 DEGs (with 49 genes upregulated) after SNI surgery, while proteomic analysis found 222 DEPs (with 89 proteins upregulated). While Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses of the DEGs suggested that most of the altered genes were involved in synaptic transmission and plasticity, bioinformatics analysis of the DEPs revealed novel critical pathways associated with autophagy, mitophagy, and peroxisome. Notably, we noticed functionally important NP-related changes in the protein that occurred in the absence of corresponding changes at the level of transcription. Venn diagram analysis of the transcriptomic and proteomic data identified 10 overlapping targets, among which only three genes (XK-related protein 4, NIPA-like domain-containing 3, and homeodomain-interacting protein kinase 3) showed concordance in the directions of change and strong correlations between mRNA and protein levels. Conclusion: The present study identified novel pathways in the ACC in addition to confirming previously reported mechanisms for NP etiology, and provided novel mechanistic insights for future research on NP treatment. These findings also imply that mRNA profiling alone fails to provide a complete landscape of molecular pain in the ACC. Therefore, explorations of changes at the level of protein are necessary to understand NP processes that are not transcriptionally modulated.

Exploring gene signatures and regulatory networks in a rat model of sciatica: implications and validation in neuropathic pain.

Background: Sciatica (neuropathic pain [NP]) is a common disease characterized by pain from radiation along the sciatic nerve. The aim of this study was to study the genes associated with chronic systolic injury of sciatic nerve (SCN-CCI) in rats by RNA-Seq technique, and to explore their potential as therapeutic targets. Methods: Sciatic nerve rat model was obtained by ligation of sciatic nerve and divided into two groups: SCN-CCI group and Sham group. Behavioral assessments were performed to evaluate pain sensitivity, following which their spinal cord dorsal horn were resected and RNA sequencing was conducted to identify differentially expressed genes (DEGs). Bioinformatics and functional enrichment analysis was performed to identify promising DEGs and their related biological processes and pathways associated with SCN-CCI. PPI network analysis and hub gene identification were conducted. QRT-PCR, western blot, ELISA, and immunofluorescence staining were performed on rat models to validate the expression of these hub genes and investigate related proteins and inflammatory markers. Results: The SCN-CCI rat model was successfully obtained, exhibiting increased pain sensitivity compared to the Sham group, as indicated by decreased mechanical allodynia thresholds, thermal latencies, and increased paw withdrawals. RNA-Seq analysis identified 117 DEGs in the SCN-CCI rat model, involved in various biological processes and pathways related to sciatica. PPI network analysis revealed hub genes, including Ly6g6e, which exhibited significant differential expression. QRT-PCR and Western blot analysis confirmed the expression patterns of these hub genes. Pain behavior assessment demonstrated reduced pain thresholds and increased paw flinching responses in the SCN-CCI group. Furthermore, the SCN-CCI group showed upregulated expression of Ly6g6e, increased protein levels of Ly6g6e, CGRP, and NGF, as well as elevated levels of IL-1ß, MCP-1, and IL-6, and microglial cell activation in the spinal dorsal horn. ELISA results confirmed the increased levels of IL-1ß, MCP-1, and IL-6 in the spinal dorsal horn. Conclusion: These comprehensive findings provide valuable insights into the SCN-CCI rat model, DEGs associated with sciatica, hub genes (Ly6g6e as promising targets), pain behavior changes and molecular alterations.

Sex Differences in CGRP Regulation and Function in the Amygdala in a Rat Model of Neuropathic Pain.

The amygdala has emerged as a key player in the emotional response to pain and pain modulation. The lateral and capsular regions of the central nucleus of the amygdala (CeA) represent the "nociceptive amygdala" due to their high content of neurons that process pain-related information. These CeA divisions are the targets of the spino-parabrachio-amygdaloid pain pathway, which is the predominant source of calcitonin gene-related peptide (CGRP) within the amygdala. Changes in lateral and capsular CeA neurons have previously been observed in pain models, and synaptic plasticity in these areas has been linked to pain-related behavior. CGRP has been demonstrated to play an important role in peripheral and spinal mechanisms, and in pain-related amygdala plasticity in male rats in an acute arthritis pain model. However, the role of CGRP in chronic neuropathic pain-related amygdala function and behaviors remains to be determined for both male and female rats. Here we tested the hypothesis that the CGRP1 receptor is involved in neuropathic pain-related amygdala activity, and that blockade of this receptor can inhibit neuropathic pain behaviors in both sexes. CGRP mRNA expression levels in the CeA of male rats were upregulated at the acute stage of the spinal nerve ligation (SNL) model of neuropathic pain, whereas female rats had significantly higher CGRP and CGRP receptor component expression at the chronic stage. A CGRP1 receptor antagonist (CGRP 8-37) administered into the CeA in chronic neuropathic rats reduced mechanical hypersensitivity (von Frey and paw compression tests) in both sexes but showed female-predominant effects on emotional-affective responses (ultrasonic vocalizations) and anxiety-like behaviors (open field test). CGRP 8-37 inhibited the activity of CeA output neurons assessed with calcium imaging in brain slices from chronic neuropathic pain rats. Together, these findings may suggest that CGRP1 receptors in the CeA are involved in neuropathic pain-related amygdala activity and contribute to sensory aspects in both sexes but to emotional-affective pain responses predominantly in females. The sexually dimorphic function of CGRP in the amygdala would make CGRP1 receptors a potential therapeutic target for neuropathic pain relief, particularly in females in chronic pain conditions.

Electroacupuncture attenuates spared nerve injury-induced neuropathic pain possibly by promoting the progression of AMPK/mTOR-mediated autophagy in spinal microglia.

Background: Neuropathic pain (NP) is a syndrome that arises from central or peripheral nerve injury, which manifests primarily as hyperalgesia, spontaneous pain, and allodynia. The recent trend has exhibited a shift towards the development of therapies for managing NP. Activation of autophagy is involved in the function of the glial cells, which may be implicated further to attenuate pain. Methods: In this study, the analgesic effects of electroacupuncture (EA) were evaluated among NP rats developed using spared nerve injury (SNI). Acupuncture treatment or EA was carried out after 7 days of SNI at two acupoints, i.e., the Zusanli (ST36) and Huantiao (GB30). Results: The application of EA was found to attenuate mechanical hyperalgesia. The marker protein for microglial cells (CD11b) alone, without either the astrocyte marker or neuronal marker, was co-expressed with the autophagy indicator p62, as illustrated with immunofluorescence staining. Western blotting demonstrated that the expression levels of p62, Beclin-1, and LC3-II/LC3-I were elevated in the spinal cords of rats in the SNI group compared to the control levels. EA treatment resulted in reduced expression of p62, while the expressions of Beclin-1 and LC3-II/LC3-I were increased. The electron microscopy results indicated that EA could induce autophagy progression in the microglia of the spinal dorsal horn in SNI rats. Furthermore, we explored the causal relationship between EA-induced inhibition of NP and increased autophagic levels in microglia using the AMPK inhibitor compound C, and found that the mechanism of EA-induced analgesia may contribute to the promotion of AMPK/mTOR-mediated autophagy in spinal microglia. Conclusions: Our work showed that the analgesic impact of EA is partly related to AMPK/mTOR pathway activation and autophagy induction in microglial cells, providing a potential therapeutic target for NP.

Electroacupuncture alleviates neuropathic pain caused by spared nerve injury by promoting AMPK/mTOR-mediated autophagy in dorsal root ganglion macrophage.

Background: Dorsal root ganglia (DRG) plays an important role in mediating the peripheral sensation transduction through the primary afferent neurons in pain research. Neuropathic pain (NP) is a syndrome of hyperalgesia, spontaneous pain and allodynia caused by central or peripheral nerve injury. Recent trends of study are turning towards the development of therapies for the management of NP. Activation of autophagy in glial cells in the spinal cord has been reported to be associated with attenuation of NP, but the autophagic process in DRG is rarely studied. Methods: The analgesic effect of electroacupuncture (EA) was evaluated in NP-induced rats developed using spared nerve injury (SNI). Acupuncture or EA was performed after 7 days of SNI at Zusanli (ST36) and Huantiao (GB30) acupoints. Then, the activation status of autophagy process in DRGs of rats treated with SNI and EA were investigated, and the possible mechanism of the analgesic effect of EA were explored. Results: Application of EA has been found to reduce mechanical hyperalgesia. Autophagy indicator p62 was colocalized with the marker proteins for macrophages (CD11b), but not with NeuN (marker protein for neurons) or GFAP (marker protein for satellite glial cells), as shown by immunofluorescence. Western blots results indicate that the expression levels of p62, Beclin-1 and LC3-II in the L4-L6 DRG of rats in the SNI group were increased, compared with that in the control group. EA treatment resulted in decreased expression of p62 and increased expression of Beclin-1 and LC3-II/LC3-I. Furthermore, we explored the causal relationship between EA-induced suppression of NP and increased levels of autophagy in DRG using electron microscopy and the AMPK (AMP-activated protein kinase) inhibitor compound C. Conclusions: SNI achieved a significant upregulation of autophagy levels in DRG macrophages. Furthermore, EA attenuated NP, which may contribute to the promotion of AMPK/mTOR (mammalian target of rapamycin)-mediated autophagy in DRG macrophages. Therefore, this strategy provides a new target for therapeutic intervention of NP.

Screening key genes related to neuropathic pain-induced depression through an integrative bioinformatics analysis.

Background: Neuropathic pain (NP) is often accompanied by sleep disorders, anxiety, depression and other complications, and the pathogenesis is still unclear. Some drugs can relieve patients' pain, but the overall effect is not good. We screened for the key genes related to NP-induced depression based on bioinformatics. Methods: The dataset of GSE92718 was obtained from the Gene Expression Omnibus database, data mining was conducted based on R language, the genes modules were screened by weighted correlation network analysis, Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were performed, a protein-protein interaction (PPI) network was constructed in the STRING database, and hub genes were screened according to degree value. Results: Seven modules were obtained and built to identify the relationships between the NP-induced depression and the modules, weighted gene co-expression network analysis (WGCNA) was used to identify gene modules closely related to the experimental group. The GO annotations of depression-related genes mainly enriched in protein polyubiquitination, regulation of chromosome organization, mitochondrial matrix, mitochondrial protein-containing complex, etc. KEGG enrichment analysis results were: Alzheimer's disease, Huntington's disease, ribosome, thermogenesis, prion disease, non-alcoholic fatty liver disease, diabetic cardiomyopathy, oxidative phosphorylation, retrograde endocannabinoid signaling, 2-oxocarboxylic acid metabolism. PPI network analysis showed that Polr2f, Rps13, Mrpl2, Mrpl40, Mrpl34, and Ndufs8 were more highly expressed in NP-induced depression. Functional analysis of key genes showed that these genes were related to mitochondrial translation termination, respiratory chain complex I, mitochondrial, mRNA Splicing (minor pathway), and of rRNA processing in the nucleolus and cytosol (major pathway). Conclusions: The key genes of depression induced by NP are Polr2f, Rps13, Mrpl2, Mrpl40, Mrpl34, and Ndufs8.

Effect of intrathecal injection of miRNA-138 on neuropathic pain in rats undergoing partial sciatic nerve ligation and its underlying mechanism.

BACKGROUND: microRNA-138 (miRNA-138) might have a promising therapeutic effect in the Neuropathic pain (NP). We aim to investigate the effects of miRNA-138 on NP and explore its underlying mechanism. METHODS: we performed a partial sciatic nerve ligation (pSNL) surgery in rats to induce pain and inflammation. Rats were administrated by intrathecal injection of lentiviral (LV)-mediated miRNA-138. Mechanical withdrawal threshold (MWT) and paw withdrawal thermal latency (PWTL) were measured to evaluate the pain degree. The expression levels of miRNA-138, toll-like receptor 4 (TLR4), tumor necrosis factor-alpha (TNF-α), interleukin-ß (IL-ß), and IL-6 in the spinal cord were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Western blotting was performed to measure the expressions of macrophage inflammatory protein-1 alpha (MIP-1α) and C-C chemokine receptor type 1 (CCR1). Next, the mechanism of miRNA-138 on NP was investigated by intrathecal injection of CCR1 inhibitor or MIP-1α neutralizing antibody. Inflammatory factors, MWT, and PWTL were also measured on day 7. RESULTS: Intrathecal injection of miRNA138 significantly reduced MWT and PWTL. qRT-PCR showed that miRNA138 mimic group significantly reduced the level of TLR4, TNF-α, Il-ß, and IL-6 on day 7. Western blotting showed that the protein expressions of MIP-1α and CCR1 in pSNL + miRNA138 mimic group were significantly decreased on day 7. In addition, the miRNA138 inhibitor inversely increased MWT, PWTL and inflammatory cytokines. Further, the effect of miRNA138 inhibitor all were significantly reversed by CCR1 inhibitor or MIP-1α neutralizing antibody. CONCLUSIONS: Intrathecal injection of miRNA-138 can remarkably alleviate NP in rats with a pSNL, which may be achieved by suppressing the TLR4 and MIP-1α/CCR1 signaling pathways.

Neuroinflammation in HIV-Related Neuropathic Pain.

In the management of human immunodeficiency virus (HIV) infection around the world, chronic complications are becoming a new problem along with the prolonged life expectancy. Chronic pain is widespread in HIV infected patients and even affects those with a low viral load undergoing long-term treatment with antiviral drugs, negatively influencing the adherence to disease management and quality of life. A large proportion of chronic pain is neuropathic pain, which defined as chronic pain caused by nervous system lesions or diseases, presenting a series of nervous system symptoms including both positive and negative signs. Injury caused by HIV protein, central and peripheral sensitization, and side effects of antiretroviral therapy lead to neuroinflammation, which is regarded as a maladaptive mechanism originally serving to promote regeneration and healing, constituting the main mechanism of HIV-related neuropathic pain. Gp120, as HIV envelope protein, has been found to be the major toxin that induces neuropathic pain. Particularly, the microglia, releasing numerous pro-inflammatory substances (such as TNFα, IL-1ß, and IL-6), not only sensitize the neurons but also are the center part of the crosstalk bridging the astrocytes and oligodendrocytes together forming the central sensitization during HIV infection, which is not discussed detailly in recent reviews. In the meantime, some NRTIs and PIs exacerbate the neuroinflammation response. In this review, we highlight the importance of clarifying the mechanism of HIV-related neuropathic pain, and discuss about the limitation of the related studies as future research directions.

Screening of disease-related biomarkers related to neuropathic pain (NP) after spinal cord injury (SCI).

BACKGROUND: Based on the molecular expression level, this paper compares lncRNA and mRNA expressions respectively in peripheral blood samples of the patients after SCI with NP and without NP, and screens disease-related biomarkers related to NP after SCI in peripheral blood samples of patients. METHOD: The expression spectrum of 25 human peripheral blood samples (12 samples of refractory NP patients after SCI) was downloaded and data were normalized. Screening of GO annotations significantly associated with significant differentially expressed mRNAs and significant involvement of the KEGG pathway. The WGCNA algorithm was used to screen for modules and RNAs that were significantly associated with disease characterization. A co-expression network was constructed to extract the genes involved in the disease pathway from the co-expression network, construct a network of SCI pain-related pathways, and screen important disease-related biomarkers. Quantitative real-time PCR was used to detect the mRNA expression of hub genes. RESULTS: Data were normalized and re-annotated by detection of platform information, resulting in a total of 289 lncRNA and 18197 mRNAs. Screening resulted in 338 significant differentially expressed RNAs that met the threshold requirements. Differentially expressed RNAs were significantly enriched with the brown and magenta modules. Six KEGG signaling pathways were screened in the co-expression network, and three KEGG pathways with direct neuropathic pain were identified. The expression levels of E2F1, MAX, MITF, CTNNA1, and ADORA2B in the disease group were all significantly upregulated (p < 0.01). Compared with the normal group, the expression of OXTR was upregulated. CONCLUSION: We speculate that there are 7 genes and 2 lncRNAs directly involved in the pain pathway: E2F1, MAX, MITF, CTNNA1, ADORA2B, GRIK3, OXTR, LINC01119, and LINC02447. These molecules may be important for NP after SCI.

Regulation of Pain Genes-Capsaicin vs Resiniferatoxin: Reassessment of Transcriptomic Data.

Emerging evidence has shown a strong association between neuropathic pain and chronic diseases. In recent years, the treatment of neuropathic pain has attracted more attention. Natural products, such as capsaicin and resiniferatoxin, have been well utilized to treat this disease. In this study, we aim to compare the regulatory effects of capsaicin and resiniferatoxin on pain-related genes as well as on genes with no direct association with pain. Public transcriptomic and microarray data on gene expression in the dorsal root ganglia and genes associated with TRPV1 (+) neurons were obtained from the GEO database and then analyzed. Differentially expressed genes were selected for further functional analysis, including pathway enrichment, protein-protein interaction, and regulatory network analysis. Pain-associated genes were extracted with the reference of two pain gene databases and the effects of these two natural drugs on the pain-associated genes were measured. The results of our research indicate that as compared to capsaicin, resiniferatoxin (RTX) regulates more non pain-associated genes and has a negative impact on beneficial genes (off-targets) which are supposed to alleviate nociception and hypersensitivity by themselves. So, based on this study, we may conclude that capsaicin may be less potent when compared to RTX, but it will elicit considerably less adverse effects too. Thereby confirming that capsaicin could be used for the efficient alleviation of neuropathic pain with possibly fewer side effects.

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

BACKGROUND: 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). METHODS: 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. RESULTS: (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. CONCLUSIONS: The mechanism of MMP-9 participating in the early phase of neuropathic pain (NP) in CCI rats is related to the upregulation of CX3CL1.

Naprapathy attenuates neuropathic pain after brachial plexus injury.

BACKGROUND: This study was to explore the potential mechanism of naprapathy in treating neuropathic pain (NP) after brachial plexus injury (BPI). METHODS: Totally 72 rats were randomly divided into normal group, model control group, and naprapathy group (n=24 per group). A right upper-limb chronic NP model was established, and naprapathy was administered at C5-T1 Jiaji Points on 4th day after modeling. Naprapathy was performed for 15 min once daily with a frequency of 60 per minute. The treatment was applied for altogether 28 days. Cold pain threshold and mechanical pain threshold were measured 1 day before modeling, 3 days after modeling, and 7, 14, 21 and 28 days after naprapathy; 7, 14, 21 and 28 days after naprapathy, rats were killed and the ß-endorphin expression and γ-aminobutyric acid (GABA) content were detected in the thalamus. RESULTS: After 14-day treatment, there was significant difference of mechanical pain threshold between the naprapathy group and the normal group (P<0.05); after treatment for 21 and 28 days, there was no significant difference between the naprapathy group and the normal group (P>0.05); after 28-day naprapathy, there was significant difference of ß-EP expression between the normal group and the naprapathy group (P<0.05), while the difference between model control group and naprapathy group was statistically significant (P<0.05). After 14-day treatment, there was significant difference of GABA content between the model control group and the naprapathy group (P<0.05). After 28-day treatment, significant difference was also found between the model control group and the naprapathy group (P<0.05). CONCLUSIONS: After naprapathy, chronic NP is attenuated in rats with BPI, which might be ascribed to the upregulation of ß-endorphin and GABA.

Receptor for activated C kinase 1 mediates the chronic constriction injury-induced neuropathic pain in the rats' peripheral and central nervous system.

Peripheral and central sensitization has been reported as significant features in the course of the occurrence and development of neuropathic pain (NP). Receptor for activated C kinase 1 (RACK1), a scaffold protein, participated in fundamental cellular activities and various neuronal functions. Peripheral and central sensitization are a state that the morphology of neuronal cell bodies as well as the corresponding function change, whether this process can be regulated by RACK1 is still unknown. In this study, the biological effects and mechanisms of RACK1 contributes to the pathogenesis of chronic constriction injury (CCI)-induced neuropathic pain were investigated. By western blot and staining, we found that RACK1 protein changed in dorsal root ganglion (DRG) neurons and spinal cord (SC) neurons except glial cells after CCI. Especially, RACK1 was co-located with IB4-, CGRP-positive neurons, suggesting it was related to integrate nociceptive information from the primary aff ;erents in DRG. The successful establishment of CCI models also directly led to mechanical allodynia and heat hyperalgesia, which could be reversed by intrathecal injection of RACK1 siRNA. Furthermore, intrathecal injection of RACK1 siRNA reduced the expression of RACK1 and accompanying spinal c-fos, which is the transcription factor and marker of neuronal activation. These results suggested that targeting RACK1 be a sensible approach for treating NP.