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The transcription repressor REST in the dorsal root ganglion (DRG) is upregulated by peripheral nerve injury and promotes the development of chronic pain. However, the genes targeted by REST in neuropathic pain development remain unclear. The expression levels of four opioid receptor genes (Oprm1, Oprd1, Oprl1 and Oprk1) and the cannabinoid CB1 receptor (Cnr1) gene in the DRG regulate nociception. In this study, we determined the role of REST in controlling their expression in the DRG induced by spared nerve injury (SNI). SNI induced chronic pain hypersensitivity in wild-type mice and was accompanied by increased levels of Rest transcript and protein. Transcriptomic analyses of wild-type mouse DRGs suggested that SNI upregulates the expression of Rest transcripts and downregulates the transcripts of all four opioid receptor genes and the Cnr1 gene. Quantitative reverse transcription polymerase chain reaction analyses of these tissues validated these results. Analysis of publicly available bioinformatic data suggested that REST binds to the promoter regions of Oprm1 and Cnr1. Chromatin immunoprecipitation analyses indicated the presence of REST at these promoters. Full-length Rest conditional knockout in primary sensory neurons reduced SNI-induced pain hypersensitivity and rescued the SNI-induced reduction in the expression of Oprd1 and Cnr1 in mouse DRG. Our results suggest that nerve injury represses the transcription of at least the Oprd1 and Cnr1 genes via REST in primary sensory neurons and that REST is a potential therapeutic target for neuropathic pain. Thus, inhibiting REST activity could potentially reduce chronic neuropathic pain and augment opioid/cannabinoid analgesic actions by increasing the transcription of Oprd1 and Cnr1 genes in DRG neurons. [ABSTRACT FROM AUTHOR]

Injury to the peripheral nervous system disconnects targets to the central nervous system, disrupts signal transmission, and results in functional disability. Although surgical and therapeutic treatments improve nerve regeneration, it is generally hard to achieve fully functional recovery after severe peripheral nerve injury. A better understanding of pathological changes after peripheral nerve injury helps the development of promising treatments for nerve regeneration. Single-cell analyses of the peripheral nervous system under physiological and injury conditions define the diversity of cells in peripheral nerves and reveal cell-specific injury responses. Herein, we review recent findings on the single-cell transcriptome status in the dorsal root ganglia and peripheral nerves following peripheral nerve injury, identify the cell heterogeneity of peripheral nerves, and delineate changes in injured peripheral nerves, especially molecular changes in neurons, glial cells, and immune cells. Cell-cell interactions in peripheral nerves are also characterized based on ligand-receptor pairs from coordinated gene expressions. The understanding of cellular changes following peripheral nerve injury at a single-cell resolution offers a comprehensive and insightful view for the peripheral nerve repair process, provides an important basis for the exploration of the key regulators of neuronal growth and microenvironment reconstruction, and benefits the development of novel therapeutic drugs for the treatment of peripheral nerve injury. [ABSTRACT FROM AUTHOR]

Background: Dorsal root ganglion stimulation (DRG‐S) has emerged as a novel therapeutic approach for managing chronic neuropathic pain. Aims: This study aims to compare the effectiveness of 4–20 Hz DRG‐S through a retrospective analysis of a cohort of 28 patients with various neuropathic pain etiologies and pain locations. Materials and Methods: Patient responses to both stimulation frequencies were examined using the Numeric Rating Scale (NRS) and Patient Global Impression of Change (PGIC) assessments. Factors such as patient preference and satisfaction were also evaluated. Results: The results indicate that 4 Hz DRG‐S is not only as effective as 20 Hz stimulation but may also surpass it. Among the 28 patients, 26 assessed 4 Hz stimulation to be at least as effective as 20 Hz, with the majority (22 out of 26) considering 4 Hz stimulation superior. After trying 4 Hz stimulation, 24 out of 28 patients chose it over 20 Hz, while two patients opted for a combination of both settings. Only two patients reverted to their original 20 Hz stimulation program. A statistically significant pain reduction of 24% was observed when comparing the effects of 4 Hz versus 20 Hz. Discussion: The study highlights the broader applicability of low‐frequency DRG‐S, extending its benefits beyond the realm of low back pain. Patients with diverse pain etiologies and locations experienced comparable positive outcomes, suggesting that the advantages of low‐frequency stimulation are not confined to specific pain types or locations. Conclusion: This study emphasizes the potential of 4 Hz DRG‐S as a valuable alternative to the standard 20 Hz stimulation. Although the exact mechanisms require further investigation, the observed clinical benefits and patient preferences for low‐frequency stimulation suggest its viability across diverse pain indications and locations. Additional research is necessary to substantiate these findings and assess the durability and economic implications of low‐frequency DRG‐S. [ABSTRACT FROM AUTHOR]

Splicing is a posttranscriptional RNA processing mechanism that enhances genomic complexity by creating multiple isoforms from the same gene. We aimed to characterize the isoforms expressed in the human peripheral nervous system, with the goal of creating a resource to identify novel isoforms of functionally relevant genes associated with somatosensation and nociception. We used longread sequencing to document isoform expression in the human dorsal root ganglia from 3 organ donors and validated in silico by confirming expression in short-read sequencing from 3 independent organ donors. Nineteen thousand five hundred forty-seven isoforms of protein-coding genes were detected and validated. We identified 763 isoforms with at least one previously undescribed splice junction. Previously unannotated isoforms of multiple pain-associated genes, including ASIC3, MRGPRX1, and HNRNPK, were identified. In the novel isoforms of ASIC3, a region comprising approximately 35% of the 5’UTR was excised. By contrast, a novel splice junction was used in isoforms of MRGPRX1 to include an additional exon upstream of the start codon, consequently adding a region to the 5’UTR. Novel isoforms of HNRNPK were identified, which used previously unannotated splice sites to both excise exon 14 and include a sequence in the 3’ end of exon 13. This novel insertion is predicted to introduce a tyrosine phosphorylation site potentially phosphorylated by SRC. We also independently confirm a recently reported DRG-specific splicing event in WNK1 that gives insight into how painless peripheral neuropathy occurs when this gene is mutated. Our findings give a clear overview of mRNA isoform diversity in the human dorsal root ganglia obtained using long-read sequencing. [ABSTRACT FROM AUTHOR]

Nerve injury-induced changes in gene expression in the dorsal root ganglion (DRG) contribute to the genesis of neuropathic pain. SYNCRIP, an RNA-binding protein, is critical for the stabilisation of gene expression. Whether SYNCRIP participates in nerve injury-induced alterations in DRG gene expression and nociceptive hypersensitivity is unknown. The expression and distribution of SYNCRIP in mouse DRG after chronic constriction injury (CCI) of the unilateral sciatic nerve were assessed. Effect of microinjection of Syncrip small interfering RNA into the ipsilateral L3 and L4 DRGs on the CCI-induced upregulation of chemokine (C-C motif) receptor 2 (CCR2) and nociceptive hypersensitivity were examined. Additionally, effects of microinjection of adeno-associated virus 5 expressing full length Syncrip mRNA (AAV5- Syncrip) on basal DRG CCR2 expression and nociceptive thresholds were observed. SYNCRIP is expressed predominantly in DRG neurones, where it co-exists with CCR2. Levels of Syncrip mRNA and SYNCRIP protein in injured DRG increased time-dependently on days 3–14 after CCI. Blocking this increase through microinjection of Syncrip small interfering RNA into injured DRG attenuated CCI-induced upregulation of DRG CCR2 and development and maintenance of nociceptive hypersensitivities. Mimicking this increase through DRG microinjection of AAV5- Syncrip elevated CCR2 expression in microinjected DRGs, enhanced the responses to mechanical, heat, and cold stimuli, and induced ongoing pain in naive mice. Mechanistically, SYNCRIP bound to 3-UTR of Ccr2 mRNA and stabilised its expression in DRG neurones. SYNCRIP contributes to the induction and maintenance of neuropathic pain likely through stabilising expression of CCR2 in injured DRG. SYNCRIP may be a potential target for treating this disorder. [ABSTRACT FROM AUTHOR]

Injury to the peripheral nervous system disconnects targets to the central nervous system, disrupts signal transmission, and results in functional disability. Although surgical and therapeutic treatments improve nerve regeneration, it is generally hard to achieve fully functional recovery after severe peripheral nerve injury. A better understanding of pathological changes after peripheral nerve injury helps the development of promising treatments for nerve regeneration. Single-cell analyses of the peripheral nervous system under physiological and injury conditions define the diversity of cells in peripheral nerves and reveal cellspecific injury responses. Herein, we review recent findings on the single-cell transcriptome status in the dorsal root ganglia and peripheral nerves following peripheral nerve injury, identify the cell heterogeneity of peripheral nerves, and delineate changes in injured peripheral nerves, especially molecular changes in neurons, glial cells, and immune cells. Cell-cell interactions in peripheral nerves are also characterized based on ligand-receptor pairs from coordinated gene expressions. The understanding of cellular changes following peripheral nerve injury at a single-cell resolution offers a comprehensive and insightful view for the peripheral nerve repair process, provides an important basis for the exploration of the key regulators of neuronal growth and microenvironment reconstruction, and benefits the development of novel therapeutic drugs for the treatment of peripheral nerve injury. [ABSTRACT FROM AUTHOR]

Pacinian corpuscle neurons are specialized low-threshold mechanoreceptors (LTMRs) that are tuned to detect high-frequency vibration (∼50–2,000 Hz); however, it is unclear how Pacinians and other LTMRs encode mechanical forces encountered during naturalistic behavior. Here, we developed methods to record LTMRs in awake, freely moving mice. We find that Pacinians, but not other LTMRs, encode subtle vibrations of surfaces encountered by the animal, including low-amplitude vibrations initiated over 2 m away. Strikingly, Pacinians are also highly active during a wide variety of natural behaviors, including walking, grooming, digging, and climbing. Pacinians in the hindlimb are sensitive enough to be activated by forelimb- or upper-body-dominant behaviors. Finally, we find that Pacinian LTMRs have diverse tuning and sensitivity. Our findings suggest a Pacinian population code for the representation of vibro-tactile features generated by self-initiated movements and low-amplitude environmental vibrations emanating from distant locations. • Recording of Pacinian neurons in awake, freely moving animals • Pacinian neurons are activated by self-generated movement • Pacinian neurons are activated by distant and subtle environmental vibrations • Diverse tuning results in activation by different behaviors and environments Turecek and Ginty record from mechanosensory neurons in awake, freely moving animals. They find that Pacinian neurons tuned to mechanical vibration can detect body movement and subtle environmental vibrations from great distances. Pacinian neurons also span a range of sensitivities, allowing them to encode a wide range of environmental stimuli. [ABSTRACT FROM AUTHOR]

Adenosine receptors are a family of purinergic G protein-coupled receptors that are widely distributed in bodily organs and in the peripheral and central nervous systems. Recently, antihyperalgesic actions have been suggested for the adenosine A3 receptor, and its agonists have been proposed as new neuropathic pain treatments. We hypothesized that these receptors may be expressed in nociceptive primary afferent neurons. However, RNA sequencing across species, eg, rat, mouse, dog, and human, suggests that dorsal root ganglion (DRG) expression of ADORA3 is inconsistent. In rat andmouse, Adora3 shows veryweak to no expression inDRG, whereas it iswell expressed in humanDRG.However, the cell types in humanDRGthat express ADORA3 have not been delineated. An examination of DRG cell types using in situ hybridization clearly detected ADORA3 transcripts in peripheral macrophages that are in close apposition to the neuronal perikarya but not in peripheral sensory neurons. By contrast, ADORA1 was found primarily in neurons, where it is broadly expressed at low levels. These results suggest that a more complex or indirect mechanism involving modulation of macrophage and/or microglial cells may underlie the potential analgesic action of adenosine A3 receptor agonism. [ABSTRACT FROM AUTHOR]

Introduction: Dorsal root ganglion pulsed radiofrequency (DRG-PRF) is frequently used for the treatment of chronic lumbar radicular pain with good outcomes in terms of pain management. Transforaminal epidural steroid injection (TFESI) is often administered immediately after DRG-PRF to increase the anti-inflammatory effects, but support for the synergic mechanism is lacking in the literature. The aim of this study was to investigate the potential role of TFESI immediately after DRG-PRF and its possible role on pain intensity and patient disability. Methods: A database of patients who underwent DRG-PRF with or without TFESI immediately after DRG-PRF was retrospectively analysed; propensity score matching was applied to the analysis to reduce possible bias. Pain intensity (numerical rating scale [NRS]) and Oswestry disability index (ODI) were recorded pre-operatively and at the 1- and 3-month follow-up in the two groups of patients. Results: A total of 252 patients were included in this retrospective analysis, 126 patients in the DRG-PRF + TFESI group and 126 patients in the DRG-PRF group after propensity score matching. Both groups displayed a significant reduction in pain intensity (NRS score reduction; p < 0.0001) and improvement in the ODI (p < 0.0001) from baseline at the 3-month follow-up. Interestingly, the use of TFESI after DRG-PRF was not associated with any clinical benefit as no difference in NRS and ODI was found between the two groups at the 1- and 3-month follow-ups. Conclusions: Our study revealed a significant pain reduction and disability improvement after DRG-PRF in patients with lumbar radicular pain. Interestingly, no positive role of TFESI immediately after DRG-PRF was observed. These findings suggest that DRG-PRF provides substantial pain relief, and no added benefit is obtained with subsequent steroid injection. Future prospective studies with expanded follow-up periods are needed to confirm these findings. [ABSTRACT FROM AUTHOR]

Objective: Neuropathic pain can be provoked by high mobility group box 1 (HMGB1) activation of toll-like receptor (TLR)4/nuclear factor (NF)-κB signaling in the dorsal root ganglion (DRG). Electroacupuncture (EA) has been reported to effectively alleviate neuropathic pain with few side effects, but its precise mechanism of action remains unknown. The aim of this study was to explore whether 2 Hz EA stimulation suppresses TLR4/NF-κB signaling in the DRG following spared nerve injury (SNI) in a rat model. Methods: In this experiment, SNI rats were given 2 Hz EA once every other day for a total of 21 days. Paw withdrawal threshold (PWT) was measured to assess SNI-induced mechanical hypersensitivity, and western blotting and immunofluorescence staining were used to determine the levels of pain-related signaling molecules and pro-inflammatory mediators in the DRG. Results: SNI up-regulated HMGB1, TLR4, myeloid differentiation factor-88 adaptor protein (MyD88) and NF-κB p65 protein expression in the DRG. In addition, immunofluorescence staining demonstrated that SNI induced higher levels of TLR4 and MyD88 in the DRG. We also demonstrated co-localization of TLR4 and MyD88 with both calcitonin gene-related peptide (CGRP) and isolectin GS-IB4 in the DRG of SNI rats, respectively. Meanwhile, 2 Hz EA stimulation effectively reversed the elevations of HMGB1, TLR4, MyD88 and NF-κB p65 induced by SNI in the DRG, which was coupled with amelioration of SNI-induced mechanical hypersensitivity. Conclusions: The results of this study suggested that inhibition of the TLR4/NF-κB signaling pathway in the DRG by 2 Hz EA might be exploited as a therapeutic option for neuropathic pain. [ABSTRACT FROM AUTHOR]

Background: IL-1β plays a critical role in the pathophysiology of neuroinflammation. The presence of cleaved IL-1β (cIL-1β) in the neurons of the dorsal root ganglion (DRG) implicates its function in biological signaling arising from the sensory neuron. This study was conducted to analyze the role of IL-1β in nociceptive transduction after tissue injury. Methods: A plantar incision was made in C57BL/6 mice, following which immunohistochemistry and RNA scope in situ hybridization were performed at various time points to analyze cIL-1β, caspase-1, and IL-1 receptor 1 (IL-1R1) expression in the DRG. The effect of intrathecal administration of a caspase-1 inhibitor or regional anesthesia using local anesthetics on cIL-1β expression and pain hypersensitivity was analyzed by immunohistochemistry and behavioral analysis. ERK phosphorylation was also analyzed to investigate the effect of IL-1β on the activity of spinal dorsal horn neurons. Results: cIL-1β expression was significantly increased in caspase-1-positive DRG neurons 5 min after the plantar incision. Intrathecal caspase-1 inhibitor treatment inhibited IL-1β cleavage and pain hypersensitivity after the plantar incision. IL-1R1 was also detected in the DRG neurons, although the majority of IL-1R1-expressing neurons lacked cIL-1β expression. Regional anesthesia using local anesthetics prevented cIL-1β processing. Plantar incision-induced phosphorylation of ERK was inhibited by the caspase-1 inhibitor. Conclusion: IL-1β in the DRG neuron undergoes rapid cleavage in response to tissue injury in an activity-dependent manner. Cleaved IL-1β causes injury-induced functional activation of sensory neurons and pain hypersensitivity. IL-1β in the primary afferent neurons is involved in physiological nociceptive signal transduction. [ABSTRACT FROM AUTHOR]

Glial cells of the peripheral nervous system (PNS) are one of the major focuses of modern neurobilogy. This review aims to summarize our own and literature data on the expression and distribution patterns of glial fibrillary acidic protein (GFAP) in PNS glial cells, specifically, in the enteric nervous system, dorsal root ganglia, and peripheral nerves. A comparative study of different PNS gliocyte populations shows that GFAP, a key intermediate filament protein, has different distribution patterns in these cells. Analysis of the literature demonstrates that although this protein is widely employed as a molecular marker of glial activation, there is still a lack of understanding of the exact mechanisms behind its involvement in glial reactivity. The described features of GFAP-expressing gliocytes in different parts of the PNS reveals a functional polymorphism of this protein. Its ability to be expressed in PNS gliocytes in response to injury requires further investigation. [ABSTRACT FROM AUTHOR]

Objective: To discuss the effect of cold exposure on nociception in the rats and its regulatory mechanism on transient receptor potential (TRP) ion channels in the sensory neurons, and to provide the basis for clarifying the biological mechanism of cold-sensitive pain. Methods: Sixteen female SD rats were divided into control group (n=8) and cold group (n=8). The rats in control group were exposed to the environment of (24±2) ℃, and the rats in cold group were exposed to low temperature (4 ℃±1 ℃) in an artificial intelligence climate chamber for 4 h daily, for one week. Von Frey filaments were used to detect the mechanical withdrawal threshold (MWT) of the rats in two groups； immunofluorescence staining was used to observe the expression levels of TRPA1, TRPM8, TRPV1, and TRPV4 in dorsal root ganglion (DRG) tissue of the rats in two groups, the expression levels of calcitonin gene-related peptide (CGRP) and substance P (SP) in DRG tissue of the rats in two groups, and the expression levels of TRPA1, TRPM8, TRPV1, and TRPV4 in synovial tissue of the rats in two groups. Results: Compared with control group, the MWT of the rats in cold group was significantly decreased (P< 0. 05), the expression levels of TRPA1 and TRPM8 in DRG tissue were significantly increased (P< 0. 05), the expression level of TRPV1 was significantly decreased (P<0. 05), there was no significant difference in the expression level of TRPV4 (P>0. 05), and the expression levels of CGRP and SP were significantly increased (P<0. 05). Compared with control group, the expression level of TRPA1 in synovial tissue of the rats in cold group was significantly increased (P<0. 05), while the expression levels of TRPM8, TRPV1, and TRPV4 were significantly decreased (P<0. 05). Conclusion: Short-term cold exposure can induce the hyperalgesia of the rats, and its mechanism may be associated with the changes in the expression of TRP ion channels in DRG and synovial tissues. TRPA1 sensory neurons play an important role in local joint cold pain. [ABSTRACT FROM AUTHOR]

Mechanosensitive ion channels, particularly Piezo channels, are widely expressed in various tissues. However, their role in immune cells remains underexplored. Therefore, this study aimed to investigate the functional role of Piezo1 in the human eosinophil cell line AML14.3D10. We detected Piezo1 mRNA expression, but not Piezo2 expression, in these cells, confirming the presence of the Piezo1 protein. Activation of Piezo1 with Yoda1, its specific agonist, resulted in a significant calcium influx, which was inhibited by the Piezo1-specific inhibitor Dooku1, as well as other nonspecific inhibitors (Ruthenium Red, Gd3+, and GsMTx-4). Further analysis revealed that Piezo1 activation modulated the expression and secretion of both pro-inflammatory and anti-inflammatory cytokines in AML14.3D10 cells. Notably, supernatants from Piezo1-activated AML14.3D10 cells enhanced capsaicin and ATP-induced calcium responses in the dorsal root ganglion neurons of mice. These findings elucidate the physiological role of Piezo1 in AML14.3D10 cells and suggest that factors secreted by these cells can modulate the activity of transient receptor potential 1 (TRPV1) and purinergic receptors, which are associated with pain and itch signaling. The results of this study significantly advance our understanding of the function of Piezo1 channels in the immune and sensory nervous systems. [ABSTRACT FROM AUTHOR]

Abstract The transcription repressor REST in the dorsal root ganglion (DRG) is upregulated by peripheral nerve injury and promotes the development of chronic pain. However, the genes targeted by REST in neuropathic pain development remain unclear. The expression levels of four opioid receptor genes (Oprm1, Oprd1, Oprl1 and Oprk1) and the cannabinoid CB1 receptor (Cnr1) gene in the DRG regulate nociception. In this study, we determined the role of REST in controlling their expression in the DRG induced by spared nerve injury (SNI). SNI induced chronic pain hypersensitivity in wild-type mice and was accompanied by increased levels of Rest transcript and protein. Transcriptomic analyses of wild-type mouse DRGs suggested that SNI upregulates the expression of Rest transcripts and downregulates the transcripts of all four opioid receptor genes and the Cnr1 gene. Quantitative reverse transcription polymerase chain reaction analyses of these tissues validated these results. Analysis of publicly available bioinformatic data suggested that REST binds to the promoter regions of Oprm1 and Cnr1. Chromatin immunoprecipitation analyses indicated the presence of REST at these promoters. Full-length Rest conditional knockout in primary sensory neurons reduced SNI-induced pain hypersensitivity and rescued the SNI-induced reduction in the expression of Oprd1 and Cnr1 in mouse DRG. Our results suggest that nerve injury represses the transcription of at least the Oprd1 and Cnr1 genes via REST in primary sensory neurons and that REST is a potential therapeutic target for neuropathic pain. Thus, inhibiting REST activity could potentially reduce chronic neuropathic pain and augment opioid/cannabinoid analgesic actions by increasing the transcription of Oprd1 and Cnr1 genes in DRG neurons.

Neuropathic pain is a common symptom of Guillain–Barré syndrome (GBS). The infiltration of macrophages in the dorsal root ganglion (DRG) contributed to neuropathic pain in nerve injury. The underlying mechanisms of neuropathic pain in patients with GBS remain unknown. Experimental autoimmune neuritis (EAN) is a useful mice model of GBS. Our study aimed to explore whether the infiltration of macrophages in DRG is associated with neuropathic pain of EAN.

First-line pharmacotherapy for peripheral neuropathic pain (NP) of diverse pathophysiology consists of antidepressants and gabapentinoids, but only a minority achieve sufficient analgesia with these drugs. Opioids are considered third-line analgesics in NP due to potential severe and unpredictable adverse effects in long-term use. Also, opioid tolerance and NP may have shared mechanisms, raising further concerns about opioid use in NP. We set out to further elucidate possible shared and separate mechanisms after chronic morphine treatment and oxaliplatin-induced and diabetic polyneuropathies, and to identify potential diagnostic markers and therapeutic targets. We analysed thermal nociceptive behaviour, the transcriptome of dorsal root ganglia (DRG) and the metabolome of cerebrospinal fluid (CSF) in these three conditions, in rats. Several genes were differentially expressed, most following oxaliplatin and least after chronic morphine treatment, compared with saline-treated rats. A few genes were differentially expressed in the DRGs in all three models (e.g. Csf3r and Fkbp5). Some, e.g. Alox15 and Slc12a5, were differentially expressed in both diabetic and oxaliplatin models. Other differentially expressed genes were associated with nociception, inflammation, and glial cells. The CSF metabolome was most significantly affected in the diabetic rats. Interestingly, we saw changes in nicotinamide metabolism, which has been associated with opioid addiction and withdrawal, in the CSF of morphine-tolerant rats. Our results offer new hypotheses for the pathophysiology and treatment of NP and opioid tolerance. In particular, the role of nicotinamide metabolism in opioid addiction deserves further study.

Background: Peripheral nerve injury is a challenging orthopedic issue in clinical management that often leads to limb dysfunction or even disability in severe cases. A thorough exploration of the repair process of peripheral nerve injury and the underlying mechanism contributes to formulate more effective therapeutic strategies. Methods: In the present study, we established a sciatic nerve transection injury model in Sprague-Dawley (SD) rats. A 12-week compensatory repair of sciatic nerve transection injury using a chitin cannula for small gap anastomosis was then performed via sleeve jointing the proximal common peroneal nerve to the distal tibial nerve and common peroneal nerve, with a 2 mm interval. Compensatory repair via small gap amplification was observed via gross observation of nerve specimen, osmic acid staining, and electrophysiological stimulation of sciatic nerve branches of the tibial and common peroneal nerve. Rat limbs were observed, and the functional recovery of effector muscles of the gastrocnemius and tibialis anterior muscles was assessed through weighing the muscle wet weight, Hematoxylin and Eosin (H&E) staining, and muscle strength detection. H&E staining, Masson staining, and toluidine blue staining were performed to observe the morphological changes of the dorsal root ganglion. Positive expressions of key proteins involved in the Phosphatase and tensin homologue deleted on chromosome ten (PTEN)-protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway, including PTEN, AKT, mTOR, Toll-like receptor 4 (TLR4), and Caspase9 in the dorsal root ganglion during compensatory repair of sciatic nerve after injury via small gap amplification, were detected by immunohistochemical staining. Results: It is found that the compensatory repair of sciatic nerve transection injury using a chitin cannula for small gap anastomosis via sleeve jointing effectively restored the continuity, number of myelinated nerve fibers, and nerve conduction velocity. It promoted toe abduction recovery, improved muscle fiber morphology and increased the wet weight and muscle strength of the gastrocnemius muscle and tibialis anterior muscle. Moreover, it increased the number of neurons and nerve fibers, and improved their morphology. Downregulated PTEN, TLR4, and Caspase9 in the dorsal root ganglia and upregulated AKT and mTOR were observed after small gap amplification than those of the transection injury group, which were closer to those of the control group. Conclusions: Compensatory repair of sciatic nerve transection injury using a chitin cannula for small gap anastomosis via sleeve jointing can restore the morphology and function of the sciatic nerve, effector muscles, and corresponding dorsal root ganglia by activating the PTEN-AKT/mTOR signaling pathway in the dorsal root ganglia. Our findings provide novel therapeutic targets for peripheral nerve injuries. [ABSTRACT FROM AUTHOR]

Objective To investigate the effect of sigma-1 receptor (sig-1R) inhibition on apoptosis in the dorsal root ganglion (DRG) of rats with sciatic nerve chronic constriction injury (CCI)-mediated neuropathic pain. Methods Rats undergoing intrathecal intubation were randomly divided into three groups with 12 in each: sham group, model group (CCI modeling one week after intrathecal intubation) and sig-1R inhibitor group (BD1047 group) that was injected intrathecally on the fourth, fifth, and sixth days after the CCI operation. The mechanical withdrawal threshold (MWT) of rats was detected on the day before surgery and then first, third, fifth and seventh days after surgery. The expression of sig-1R, Bcl-2 and Bax was detected by Western blot and immunofluorescence in DRG cell; TUNEL staining microscopy was used to observe the apoptosis of DRG cells. The changes of endoplasmic reticulum and mitochondria were observed by transmission electron microscopy of DRG cells. Results Compared with the sham group, the model group showed a decreased MWT at all time points after surgery, up-regulation of DRG cell apoptosis, up-regulation of sig-1R and Bax, down-regulation of Bcl-2, swelling of endoplasmic reticulum, disruption of mitochondrial membrane and reduction of mitochondrial cristae in the DRG cell endoplasmic reticulum after surgery(P＜0.05).BD1047 group showed elevated MWT at the fifth and seventh postoperative days, down-regulation of DRG cell apoptosis, down-regulated expression of sig-1R and Box, up-regulated expression of Bcl-2 and slightly damaged endoplasmic reticulum as well as mitochondria of DRG cells compared with model group(P＜0.05). Conclusions Inhibition of sig-1R up-regulates mechanical withdrawal threshold and reduces DRG cell apoptosis in CCI rats.

Xinchao Jiang,1,&ast; Yinyin Guo,2,&ast; Mei Fang,1 Xin Wang,3 Biao Zhang,4 Yi Song,1 Jianxue Qian1 1Department of Pain Medicine, Suzhou Hospital of Integrated Traditional Chinese and Western Medicine, Suzhou, Jiangsu, People’s Republic of China; 2Department of Oncology, Suzhou Hospital of Integrated Traditional Chinese and Western Medicine, Suzhou, Jiangsu, People’s Republic of China; 3Department of Nephrology, Suzhou Hospital of Integrated Traditional Chinese and Western Medicine, Suzhou, Jiangsu, People’s Republic of China; 4Department of Intensive Care, Suzhou Hospital of Integrated Traditional Chinese and Western Medicine, Suzhou, Jiangsu, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Jianxue Qian; Yi Song, Department of Pain Medicine, Suzhou Hospital of Integrated Traditional Chinese and Western Medicine, 39 Xiashatang Road, Wuzhong District, Suzhou, Jiangsu, People’s Republic of China, Tel/Fax +86 0512-69388313 ; +86 0512-69388412, Email szxqjx@126.com; 376063583@qq.comObjective: Knee osteoarthritis (KOA) is a chronic condition characterized by persistent pain that can lead to severe disability. In this study, we primarily investigated the analgesic effect of Huojing decoction on MIA-induced knee arthritis.Methods: The network pharmacology method was employed to acquire target information of Huojing decoction and KOA. MIA was intratibially injected to induce KOA pain in rats. Huojing decoction was then administered once daily via intragastric administration for 14 days. Pain level was assessed by paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). The levels of inflammatory cytokines were determined by ELISA and PCR. TRPV1 and CGRP were detected through immunohistochemistry. The protein expression of TrkA, MKK3/6 and p38 was assessed by Western blot.Results: Mechanical allodynia and thermal hyperalgesia were observed in KOA rats. The expression levels of inflammatory cytokines were significantly decreased after Huojing decoction infusion of KOA rats. TRPV1 and CGRP were reduced with treatment. Furthermore, the protein expressions of TrkA, MKK3/6 and p38 in the DRG of rats were significantly decreased.Conclusion: Our data suggested that Huojing decoction can alleviate inflammation in KOA pain rats. Additionally, it can inhibit the expression of TrKA, MKK3/6 and p38 signaling pathways, indicating its analgesic effect on KOA pain rats. Keywords: huojing decoction, analgesic effect, knee osteoarthritis, dorsal root ganglion, TrkA/MKK3/6/p38 pathway

Abstract Introduction Dorsal root ganglion pulsed radiofrequency (DRG-PRF) is frequently used for the treatment of chronic lumbar radicular pain with good outcomes in terms of pain management. Transforaminal epidural steroid injection (TFESI) is often administered immediately after DRG-PRF to increase the anti-inflammatory effects, but support for the synergic mechanism is lacking in the literature. The aim of this study was to investigate the potential role of TFESI immediately after DRG-PRF and its possible role on pain intensity and patient disability. Methods A database of patients who underwent DRG-PRF with or without TFESI immediately after DRG-PRF was retrospectively analysed; propensity score matching was applied to the analysis to reduce possible bias. Pain intensity (numerical rating scale [NRS]) and Oswestry disability index (ODI) were recorded pre-operatively and at the 1- and 3-month follow-up in the two groups of patients. Results A total of 252 patients were included in this retrospective analysis, 126 patients in the DRG-PRF + TFESI group and 126 patients in the DRG-PRF group after propensity score matching. Both groups displayed a significant reduction in pain intensity (NRS score reduction; p

Abstract The cell-adhesion molecule NEPH1 is required for maintaining the structural integrity and function of the glomerulus in the kidneys. In the nervous system of Drosophila and C. elegans, it is involved in synaptogenesis and axon branching, which are essential for establishing functional circuits. In the mammalian nervous system, the expression regulation and function of Neph1 has barely been explored. In this study, we provide a spatiotemporal characterization of Neph1 expression in mouse dorsal root ganglia (DRGs) and spinal cord. After the neurogenic phase, Neph1 is broadly expressed in the DRGs and in their putative targets at the dorsal horn of the spinal cord, comprising both GABAergic and glutamatergic neurons. Interestingly, we found that PRRXL1, a homeodomain transcription factor that is required for proper establishment of the DRG-spinal cord circuit, prevents a premature expression of Neph1 in the superficial laminae of the dorsal spinal cord at E14.5, but has no regulatory effect on the DRGs or on either structure at E16.5. By chromatin immunoprecipitation analysis of the dorsal spinal cord, we identified four PRRXL1-bound regions within the Neph1 introns, suggesting that PRRXL1 directly regulates Neph1 transcription. We also showed that Neph1 is required for branching, especially at distal neurites. Together, our work showed that Prrxl1 prevents the early expression of Neph1 in the superficial dorsal horn, suggesting that Neph1 might function as a downstream effector gene for proper assembly of the DRG-spinal nociceptive circuit.

Huaichang Wen,1,2,&ast; Yi Wang,2,&ast; Hao Cheng,2 Bin Wang,2 Xianwen Hu1 1Department of Anesthesiology, The Second Hospital of Anhui Medical University, Hefei, People’s Republic of China; 2Department of Anesthesiology, First Affiliated Hospital of Wannan Medical College, Wuhu, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Xianwen Hu, Department of Anesthesiology, The Second Hospital of Anhui Medical University, Hefei, 230032, People’s Republic of China, Email huxianwen0002@126.comBackground: The treatment of herpes zoster-related pain is challenging, and requires a variety of methods including pulse radio frequency modulation. Among them, single-time high-voltage long-term pulsed radiofrequency (HL-PRF) has been proved to be an effective treatment for subacute postherpetic neuralgia. However, it has the possibility of poor long-term curative effect and recurrence of neuralgia. In this study, we aim to identify the clinical efficacy and safety of twice repeated HL-PRF treatment in patients with subacute postherpetic neuralgia.Design: We conducted a retrospective analysis of subacute postherpetic neuralgia patients who underwent HL-PRF treatment.Setting: Pain Management Department of First Affiliated Hospital of Wannan Medical College.Patients: We enrolled all patients with subacute postherpetic neuralgia, who underwent HL-PRF treatment from January 2023 to October 2023.Measurements: The primary outcome variable was the visual Analog Scale (VAS) scores at 1, 4, 8, and 12 weeks after treatment. Secondary outcomes included Pittsburgh sleep quality index (PSQI), 36-item short-form health survey (SF-36) score, and total effective rate after treatment.Results: A total of 63 patients were included in the analysis. Among them, 33 patients received single-time HL-PRF treatment (Group S) and 30 patients received twice repeated HL-PRF treatment (Group T). Pain scores, PSQI scores, and SF-36 score were reduced in both groups after treatment (P < 0.001). Compared to group S, the VAS scores, PSQI scores, anxiety scores, and depression scores were significantly lower at 1, 4, 8, and 12 weeks in group T. (P < 0.001). The total efficiency rate at 12 weeks after treatment of group T was statistically higher than that of group S (60.6% vs 86.7%, P < 0.05).Conclusion: Twice repeated high-voltage long-duration PRF therapy demonstrates satisfactory efficacy in patients with subacute postherpetic neuralgia and is associated with no significant adverse reactions.Keywords: herpes zoster, subacute postherpetic neuralgia, CT-guided, pulsed radiofrequency therapy, dorsal root ganglion

Approximately 36%-55% of patients with chronic low back pain (LBP) have neuropathic pain syndrome. Prescription of adjuvant analgesics or antidepressants is effective in reducing pain but requires special attention. A female patient, 57 y, presented with complaints of LBP for 5-7 days. Pain was spread bilateral in the hips-groin, as well as to the fingers and soles (NRS 6-8, PainDETECT 35). She had history of falls 10 y ago, but still worked for 5 hours daily. She had allodynia, dysesthesia, hyperalgesia, and L4-5 and L5-S1 hypesthesia. Magnetic resonance imaging (MRI) showed postero-central and lateral bulged L4-5 and L5-S1 discs. Radiofrequency ablation (RFA) 70o of superior hypogastric ganglion for 90 sec, and pulsed radiofrequency (PRF) 42o of dorsal root ganglion (DRG) L4-5, L5-S1 bilaterally for 2 min reduced nociceptive pain (NRS 2-3) and neuropathic pain (PainDETECT 12). Post-surgical medication included levofloxacin, gabapentin, paracetamol, amitriptyline and Vitamin B12. The sympathetic ganglia supply the anterior segments of the lumbar vertebrae and the anterior longitudinal ligament, often overlooked as a cause of pain. The management of LBP patient depends upon the etiology, whether associated to structural abnormalities or nerve dysfunction. [ABSTRACT FROM AUTHOR]

Objective To investigate the effect of sigma-1 receptor (sig-1R) inhibition on apoptosis in the dorsal root ganglion (DRG) of rats with sciatic nerve chronic constriction injury (CCI)-mediated neuropathic pain. Methods Rats undergoing intrathecal intubation were randomly divided into three groups with 12 in each: sham group, model group (CCI modeling one week after intrathecal intubation) and sig-1R inhibitor group (BD1047 group) that was injected intrathecally on the fourth, fifth, and sixth days after the CCI operation. The mechanical withdrawal threshold (MWT) of rats was detected on the day before surgery and then first, third, fifth and seventh days after surgery. The expression of sig-1R, Bcl-2 and Bax was detected by Western blot and immunofluorescence in DRG cell; TUNEL staining microscopy was used to observe the apoptosis of DRG cells. The changes of endoplasmic reticulum and mitochondria were observed by transmission electron microscopy of DRG cells. Results Compared with the sham group, the model group showed a decreased MWT at all time points after surgery, up-regulation of DRG cell apoptosis, up-regulation of sig-1R and Bax, down-regulation of Bcl-2, swelling of endoplasmic reticulum, disruption of mitochondrial membrane and reduction of mitochondrial cristae in the DRG cell endoplasmic reticulum after surgery (P<0.05). BD1047 group showed elevated MWT at the fifth and seventh postoperative days, down-regulation of DRG cell apoptosis, down-regulated expression of sig-1R and Box, upregulated expression of Bcl-2 and slightly damaged endoplasmic reticulum as well as mitochondria of DRG cells compared with model group (P<0.05). Conclusions Inhibition of sig-1R up-regulates mechanical withdrawal threshold and reduces DRG cell apoptosis in CCI rats. [ABSTRACT FROM AUTHOR]

Aim: This study aims to investigate the potential neuroprotective effects of fibroblast growth factor-21 (FGF21) on dorsal root ganglion (DRG) neurons under high glucose (HG) conditions, mimicking diabetic neuropathy. Specifically, we hypothesize that FGF21 enhances cell viability and reduces glucose-induced neuronal death via the activation of the phosphatidyl-inositol-3-kinase (PI3K)/AKT signaling pathway. Materials and Methods: DRG neurons were cultured from 1-day-old to 2-day-old Wistar rats and exposed to HG concentrations to simulate diabetic conditions. Various concentrations of FGF21 were administered to the DRG neurons. Cell viability was assessed using the MTT assay (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide), a widely used enzymatic method for determining cellular metabolic activity. The involvement of the PI3K/AKT signaling pathway in mediating the effects of FGF21 was also examined through biochemical assays and pathway inhibitors. Results: Administration of FGF21 to DRG neurons exposed to HG conditions significantly protected cell viability and reduced glucose-induced neuronal death (p<0.05). The protective effects of FGF21 were found to be dose-dependent, with higher concentrations showing more pronounced benefits. Furthermore, the activation of the PI3K/AKT signaling pathway was confirmed to play a crucial role in the neuroprotective mechanism of FGF21, as inhibition of this pathway attenuated the protective effects. Conclusion: This study demonstrates for the first time that FGF21 has a neuroprotective effect on DRG neuron survival in a diabetic neuropathy model. By activating the PI3K/AKT signaling pathway, FGF21 helps maintain cell viability and reduces glucoserelated neuronal death. These findings provide a promising basis for the development of new therapeutic strategies for the treatment of diabetic neuropathy, leveraging the neuroprotective properties of FGF21. [ABSTRACT FROM AUTHOR]

Acute and chronic itch are prevalent and incapacitating, yet the neural mechanisms underlying both acute and chronic itch are just starting to be unraveled. Activated transcription factor 4 (ATF4) belongs to the ATF/CREB transcription factor family and primarily participates in the regulation of gene transcription. Our previous study has demonstrated that ATF4 is expressed in sensory neurons. Nevertheless, the role of ATF4 in itch sensation remains poorly understood. Here, we demonstrate that ATF4 plays a significant role in regulating itch sensation. The absence of ATF4 in dorsal root ganglion (DRG) neurons enhances the itch sensitivity of mice. Overexpression of ATF4 in sensory neurons significantly alleviates the acute and chronic pruritus in mice. Furthermore, ATF4 interacts with the transient receptor potential cation channel subfamily V member 4 (TRPV4) and inhibits its function without altering the expression or membrane trafficking of TRPV4 in sensory neurons. In addition, interference with ATF4 increases the itch sensitivity in nonhuman primates and enhances TRPV4 currents in nonhuman primates DRG neurons; ATF4 and TRPV4 also co-expresses in human sensory neurons. Our data demonstrate that ATF4 controls pruritus by regulating TRPV4 signaling through a nontranscriptional mechanism and identifies a potential new strategy for the treatment of pathological pruritus. [ABSTRACT FROM AUTHOR]

Herpes zoster (HZ), resulting from the reactivation of the varicella‐zoster virus, is a significant disease. This study aimed to explore the factors influencing sensory neuron involvement in HZ at different locations and its association with postherpetic neuralgia (PHN). A total of 3143 cases were retrieved from an electronic medical record system, including 2676 cases of HZ and 467 cases of PHN. Gender, age, site of onset, past surgical history, and comorbidities were analyzed using a multifactorial logistic regression model. The results revealed correlations between age, gender, comorbidities (diabetes, coronary heart disease, percutaneous coronary intervention [PCI]), and sensory neuron involvement in HZ. Specifically, older age, female gender, and comorbid conditions such as diabetes/coronary heart disease were associated with sacral dorsal root ganglion (DRG) involvement, while PCI history was associated with lumbar DRG involvement. Additionally, sensory neuron involvement at different locations by HZ was linked to PHN. Furthermore, independent risk factors for PHN included thoracic DRG involvement, older age, and comorbidities (diabetes, surgical history, malignancy). It is crucial to prevent damage to the DRG, especially in individuals with comorbidities, through activities avoidance and active treatment, to minimize the occurrence of PHN. [ABSTRACT FROM AUTHOR]

The cell-adhesion molecule NEPH1 is required for maintaining the structural integrity and function of the glomerulus in the kidneys. In the nervous system of Drosophila and C. elegans, it is involved in synaptogenesis and axon branching, which are essential for establishing functional circuits. In the mammalian nervous system, the expression regulation and function of Neph1 has barely been explored. In this study, we provide a spatiotemporal characterization of Neph1 expression in mouse dorsal root ganglia (DRGs) and spinal cord. After the neurogenic phase, Neph1 is broadly expressed in the DRGs and in their putative targets at the dorsal horn of the spinal cord, comprising both GABAergic and glutamatergic neurons. Interestingly, we found that PRRXL1, a homeodomain transcription factor that is required for proper establishment of the DRG-spinal cord circuit, prevents a premature expression of Neph1 in the superficial laminae of the dorsal spinal cord at E14.5, but has no regulatory effect on the DRGs or on either structure at E16.5. By chromatin immunoprecipitation analysis of the dorsal spinal cord, we identified four PRRXL1-bound regions within the Neph1 introns, suggesting that PRRXL1 directly regulates Neph1 transcription. We also showed that Neph1 is required for branching, especially at distal neurites. Together, our work showed that Prrxl1 prevents the early expression of Neph1 in the superficial dorsal horn, suggesting that Neph1 might function as a downstream effector gene for proper assembly of the DRG-spinal nociceptive circuit. [ABSTRACT FROM AUTHOR]

Background: Central nervous system (CNS) disorders, such as stroke, often lead to spasticity, which result in limb deformities and significant reduction in quality of life. Spasticity arises from disruptions in the normal functioning of cortical and descending inhibitory pathways in the brainstem, leading to abnormal muscle contractions. Contralateral seventh cervical nerve cross transfer (CC7) surgery has been proven to effectively reduce spasticity, but the specific mechanism for its effectiveness is unclear. Methods: This study aimed to investigate the changes in the dorsal root ganglia (DRG) following CC7 surgery. A comprehensive anatomical analysis was conducted through cadaveric study and magnetic resonance imaging (MRI) study, to accurately measure the regional anatomy of the C7 DRG. DRG perfusion changes were quantitatively assessed by comparing pre‐ and postoperative dynamic contrast‐enhanced (DCE) MRI. Results: In CC7 surgery, the C7 nerve root on the affected side is cut close to the DRG (3.6 ± 1.0 mm), while the C7 nerve root on the healthy side is cut further away from the DRG (65.0 ± 10.0 mm). MRI studies revealed that after C7 proximal neurotomy on the affected side, there was an increase in DRG volume, vascular permeability, and perfusion; after C7 distal neurotomy on the healthy side, there was a decrease in DRG volume, with no significant changes in vascular permeability and perfusion. Conclusion: This study provides preliminary insights into the mechanisms of spasticity reduction following CC7 surgery, indicating that changes in the DRG, such as increased vascular permeability and perfusion, could disrupt abnormal spinal γ‐circuits. The resulting high‐perfusion state of DRG, possibly due to heightened neuronal activity and metabolic demands, necessitating further research to verify this hypothesis. [ABSTRACT FROM AUTHOR]

Neuropathic pain can occur during the prediabetic stage, even in the absence of hyperglycemia. The presence of prediabetic neuropathic pain (PDNP) poses challenges to the management of individuals with prediabetes. However, the mechanisms underlying this pain remain unclear. This study aims to investigate the underlying mechanism and identify potential therapeutic targets of PDNP. A prediabetic animal model induced by a high‐energy diet exhibits both mechanical allodynia and thermal hyperalgesia. Furthermore, hyperexcitability and decreased potassium currents are observed in the dorsal root ganglion (DRG) neurons of these rats. TREK1 and TREK2 channels, which belong to the two‐pore‐domain K+ channel (K2P) family and play an important role in controlling cellular excitability, are downregulated in DRG neurons. Moreover, this alteration is modulated by Sortilin, a molecular partner that modulates the expression of TREK1. The overexpression of Sortilin negatively affects the expression of TREK1 and TREK2, leading to increased neuronal excitability in the DRG and enhanced peripheral pain sensitivity in rats. Moreover, the downregulation of Sortilin or activation of TREK1 and TREK2 channels by genetic or pharmacological approaches can alleviate PDNP. Therefore, targeting the Sortilin‐mediated TREK1/2 pathway may provide a therapeutic approach for ameliorating PDNP. [ABSTRACT FROM AUTHOR]

This study investigated the ERK pathway of the peripheral nervous system and discovered a gender-specific pattern of ERK activation in the dorsal root ganglion of an acid-induced chronic widespread muscular pain model. We employed a twice acid-induced chronic musculoskeletal pain model in rats to evaluate mechanical pain behavior in both male and female groups. We further conducted protein analysis of dissected dorsal root ganglions from both genders. Both male and female rats exhibited a similar pain behavior trend, with females demonstrating a lower pain threshold. Protein analysis of the dorsal root ganglion (DRG) showed a significant increase in phosphorylated ERK after the second acid injection in all groups. However, phosphorylation of ERK was observed in the dorsal root ganglion, with higher levels in the male ipsilateral group compared to the female group. Moreover, there was a no difference between the left and right sides in males, whereas the significant difference was observed in females. In conclusions, the administration of acid injections induced painful behavior in rats, and concurrent with this, a significant upregulation of pERK was observed in the dorsal root ganglia, with a greater magnitude of increase in males than females, and in the contralateral side compared to the ipsilateral side. Our findings shed light on the peripheral mechanisms underlying chronic pain disorders and offer potential avenues for therapeutic intervention. [ABSTRACT FROM AUTHOR]

Evidence from previous studies supports the concept that spinal cord injury (SCI)-induced neuropathic pain (NP) has its neural roots in the peripheral nervous system. There is uncertainty about how and to which degree mechanoreceptors contribute. Sensorimotor activation-based interventions (eg, treadmill training) have been shown to reduce NP after experimental SCI, suggesting transmission of pain-alleviating signals through mechanoreceptors. The aim of the present study was to understand the contribution of mechanoreceptors with respect to mechanical allodynia in a moderate mouse contusion SCI model. After genetic ablation of tropomyosin receptor kinase B expressing mechanoreceptors before SCI, mechanical allodynia was reduced. The identical genetic ablation after SCI did not yield any change in pain behavior. Peptidergic nociceptor sprouting into lamina III/IV below injury level as a consequence of SCI was not altered by either mechanoreceptor ablation. However, skin-nerve preparations of contusion SCI mice 7 days after injury yielded hyperexcitability in nociceptors, not in mechanoreceptors, which makes a substantial direct contribution of mechanoreceptors to NP maintenance unlikely. Complementing animal data, quantitative sensory testing in human SCI subjects indicated reduced mechanical pain thresholds, whereas the mechanical detection threshold was not altered. Taken together, early mechanoreceptor ablation modulates pain behavior, most likely through indirect mechanisms. Hyperexcitable nociceptors seem to be the main drivers of SCI-induced NP. Future studies need to focus on injury-derived factors triggering early-onset nociceptor hyperexcitability, which could serve as targets for more effective therapeutic interventions. [ABSTRACT FROM AUTHOR]

Background: Pulsed radiofrequency (PRF) of the lumbar dorsal root ganglion (DRG) has been widely used as a method to relieve lumbar radicular pain (LRP). However, the value of PRF application in LRP patients remains uncertain. This systematic review aimed to compare the effects of PRF of lumbar DRG and LEI in patients with LRP. Methods: A literature search was performed using well‐known databases for articles published up to May 2023. We included randomized controlled trials (RCTs) that evaluated the effects of PRF compared to LEI with or without steroids. We screened articles, extracted data, and assessed risk of bias in duplicate. The pain scores and Oswestry Disability Index (ODI) scores at 1, 3, and 6 months after procedures were obtained. A random‐effects meta‐analysis model was applied for outcomes. We evaluated evidence certainty for each outcome using the GRADE scoring system. This review was registered in the PROSPERO (ID: CRD42021253628). Results: A total of 10 RCTs were included and data of 613 patients were retrieved. We assessed the overall quality of the evidence as very low to moderate. PRF showed no difference in pain scores at 1 (mean difference [MD] −0.80, 95% confidence interval [CI] –1.59 to 0.00, low certainty) and 6 months (MD –2.37, 95% CI –4.79 to 0.05, very low certainty), and significantly improved pain scores at 3 months (MD –1.31, 95% CI –2.29 to −0.33, low certainty). There was no significant difference in ODI score at any interval (very low to low certainty). In the subgroup who underwent a diagnostic block, did not use steroids, and PRF duration greater than 360 s, PRF significantly reduced pain scores at 3 months after procedures. Conclusions: We found low quality of the evidence supporting adjuvant PRF to the lumbar DRG has a greater analgesic effect at 3 months after procedures in patients with LRP than LEI. We identified no convincing evidence to show that this treatment improves function. High‐quality evidence is lacking, and data were largely derived from short‐term effects. Given these limitations, high‐quality trials with data on long‐term effects are needed. [ABSTRACT FROM AUTHOR]

Glutamate functions as the major excitatory neurotransmitter for primary sensory neurons and has a crucial role in sensitizing peripheral nociceptor terminals producing sensitization. Glutaminase (GLS) is the synthetic enzyme that converts glutamine to glutamate. GLS-immunoreactivity (-ir) and enzyme activity are elevated in dorsal root ganglion (DRG) neuronal cell bodies during chronic peripheral inflammation, but the mechanism for this GLS elevation is yet to be fully characterized. It has been well established that, after nerve growth factor (NGF) binds to its high-affinity receptor tropomyosin receptor kinase A (TrkA), a retrograde signaling endosome is formed. This endosome contains the late endosomal marker Rab7GTPase and is retrogradely transported via axons to the cell soma located in the DRG. This complex is responsible for regulating the transcription of several critical nociceptive genes. Here, we show that this retrograde NGF signaling mediates the expression of GLS in DRG neurons during the process of peripheral inflammation. We disrupted the normal NGF/TrkA signaling in adjuvant-induced arthritic (AIA) Sprague Dawley rats by the pharmacological inhibition of TrkA or blockade of Rab7GTPase, which significantly attenuated the expression of GLS in DRG cell bodies. The results indicate that NGF/TrkA signaling is crucial for the production of glutamate and has a vital role in the development of neurogenic inflammation. In addition, our pain behavioral data suggest that Rab7GTPase can be a potential target for attenuating peripheral inflammatory pain. [ABSTRACT FROM AUTHOR]

KLS-13019 was reported previously to reverse paclitaxel-induced mechanical allodynia in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN). Recent studies demonstrated that paclitaxel-induced increases in inflammatory markers (GPR55, NLRP3, and IL-1β) of dorsal root ganglion (DRG) cultures were shown to be reversed by KLS-13019 treatment. The mechanism of action for KLS-13019-mediated reversal of paclitaxel-induced neuroinflammation now has been explored using GPR55 siRNA. Pre-treatment of DRG cultures with GPR55 siRNA produced a 21% decrease of immunoreactive (IR) area for GPR55 in cell bodies and a 59% decrease in neuritic IR area, as determined by high-content imaging. Using a 24-h reversal treatment paradigm, paclitaxel-induced increases in the inflammatory markers were reversed back to control levels after KLS-3019 treatment. Decreases in these inflammatory markers produced by KLS-13019 were significantly attenuated by GPR55 siRNA co-treatment, with mean IR area responses being attenuated by 56% in neurites and 53% in cell bodies. These data indicate that the percentage decreases in siRNA-mediated attenuation of KLS-13019-related efficacy on the inflammatory markers were similar to the percentage knockdown observed for neuritic GPR55 IR area. Similar studies conducted with cannabidiol (CBD), the parent compound of KLS-13019, produced low efficacy (25%) reversal of all inflammatory markers that were poorly attenuated (29%) by GPR55 siRNA. CBD was shown previously to be ineffective in reversing paclitaxel-induced mechanical allodynia. The present studies indicated significant differences between the anti-inflammatory properties of KLS-13019 and CBD which may play a role in their observed differences in the reversibility of mechanical allodynia in a mouse model of CIPN. [ABSTRACT FROM AUTHOR]

Abstract Hindlimb ischaemia–reperfusion (IR) is among the most prominent pathophysiological conditions observed in peripheral artery disease (PAD). An exaggerated arterial blood pressure (BP) response during exercise is associated with an elevated risk of cardiovascular events in individuals with PAD. However, the precise mechanisms leading to this exaggerated BP response are poorly elucidated. The P2X3 signalling pathway, which plays a key role in modifying the exercise pressor reflex (EPR), is the focus of the present study. We determined the regulatory role of P2X3 on the EPR in a rat model of hindlimb IR. In vivo and in vitro approaches were used to determine the expression and functions of P2X3 in muscle afferent nerves and EPR in IR rats. We found that in IR rats there was (1) upregulation of P2X3 protein expression in the L4–6 dorsal root ganglia (DRG); (2) amplified P2X currents in isolated isolectin B4 (IB4)‐positive muscle DRG neurons; and (3) amplification of the P2X‐mediated BP response. We further verified that both A‐317491 and siRNA knockdown of P2X3 significantly decreased the activity of P2X currents in isolated muscle DRG neurons. Moreover, inhibition of muscle afferents’ P2X3 receptor using A‐317491 was observed to alleviate the exaggerated BP response induced by static muscle contraction and P2X‐induced BP response by α,β‐methylene ATP injection. P2X3 signalling pathway activity is amplified in muscle afferent DRG neurons in regulating the EPR following hindlimb IR.

Abstract Background The channel-forming protein Pannexin1 (Panx1) has been implicated in both human studies and animal models of chronic pain, but the underlying mechanisms remain incompletely understood. Methods Wild-type (WT, n = 24), global Panx1 KO (n = 24), neuron-specific Panx1 KO (n = 20), and glia-specific Panx1 KO (n = 20) mice were used in this study at Albert Einstein College of Medicine. The von Frey test was used to quantify pain sensitivity in these mice following complete Freund’s adjuvant (CFA) injection (7, 14, and 21 d). The qRT-PCR was employed to measure mRNA levels of Panx1, Panx2, Panx3, Cx43, Calhm1, and β-catenin. Laser scanning confocal microscopy imaging, Sholl analysis, and electrophysiology were utilized to evaluate the impact of Panx1 on neuronal excitability and morphology in Neuro2a and dorsal root ganglion neurons (DRGNs) in which Panx1 expression or function was manipulated. Ethidium bromide (EtBr) dye uptake assay and calcium imaging were employed to investigate the role of Panx1 in adenosine triphosphate (ATP) sensitivity. β-galactosidase (β-gal) staining was applied to determine the relative cellular expression levels of Panx1 in trigeminal ganglia (TG) and DRG of transgenic mice. Results Global or neuron-specific Panx1 deletion markedly decreased pain thresholds after CFA stimuli (7, 14, and 21 d; P

Xinyong Chen,1,2,&ast; Zhe Chen,3,&ast; Gongchang Ma,2 Jianjun Sha,2 Shan Zhao,2 Zuoqing Liu,2 Nong Chen,2 Huilin Yang1 1Department of Orthopedics, The First Affiliated Hospital of Soochow University, Suzhou, 215000, People’s Republic of China; 2Department of Orthopedics, Qingpu Branch of Zhongshan Hospital Affiliated to Fudan University, Shanghai, 200025, People’s Republic of China; 3Department of Orthopedics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, 200025, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Nong Chen, Department of Orthopedics, Qingpu Branch of Zhongshan Hospital Affiliated to Fudan University, Shanghai, 200025, People’s Republic of China, Email chennong1975@126.com Huilin Yang, Department of Orthopedics, The First Affiliated Hospital of Soochow University, Suzhou, 215000, People’s Republic of China, Email orthdoctor@126.comBackground: Dorsal root ganglia (DRGs) contain sensory neurons that innervate intervertebral discs (IVDs) and may play a critical role in mediating low-back pain (LBP), but the potential pathophysiological mechanism needs to be clarified.Methods: A discogenic LBP model in rats was established by penetration of a lumbar IVD. The severity of LBP was evaluated through behavioral analysis, and the gene and protein expression levels of pro-algesic peptide substance P (SP) and calcitonin gene–related peptide (CGRP) in DRGs were quantified. The level of reactive oxygen species (ROS) in bilateral lumbar DRGs was also quantified using dihydroethidium staining. Subsequently, hydrogen peroxide solution or N-acetyl-L-cysteine was injected into DRGs to evaluate the change in LBP, and gene and protein expression levels of transient receptor potential vanilloid-1 (TRPV1) in DRGs were analyzed. Finally, an inhibitor or activator of TRPV1 was injected into DRGs to observe the change in LBP.Results: The rats had remarkable LBP after disc puncture, manifesting as mechanical and cold allodynia and increased expression of the pro-algesic peptides SP and CGRP in DRGs. Furthermore, there was significant overexpression of ROS in bilateral lumbar DRGs, while manipulation of the level of ROS in DRGs attenuated or aggravated LBP in rats. In addition, excessive ROS in DRGs stimulated upregulation of TRPV1 in DRGs. Finally, activation or inhibition of TRPV1 in DRGs resulted in a significant increase or decrease of discogenic LBP, respectively, suggesting that ROS-induced TRPV1 has a strong correlation with discogenic LBP.Conclusion: Increased ROS in DRGs play a primary pathological role in puncture-induced discogenic LBP, and excessive ROS–induced upregulation of TRPV1 in DRGs may be the underlying pathophysiological mechanism to cause nerve sensitization and discogenic LBP. Therapeutic targeting of ROS or TRPV1 in DRGs may provide a promising method for the treatment of discogenic LBP.Keywords: lower back pain, reactive oxygen species, dorsal root ganglion, transient receptor potential vanilloid-1, substance p, calcitonin gene related peptide, intervertebral disc

Meihui Li,1,2 Haiyan Zheng,3 Jae Chul Koh,4 Ghee Young Choe,5,6 Eun Joo Choi,1,2 Francis Sahngun Nahm,1,2 Pyung Bok Lee1,2 1Department of Anesthesiology and Pain Medicine, Seoul National University College of Medicine, Seoul, Korea; 2Department of Anesthesiology and Pain Medicine, Seoul National University Bundang Hospital, Seongnam, Korea; 3Department of Anesthesiology, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, People’s Republic of China; 4Department of Anesthesiology and Pain Medicine, Korea University College of Medicine, Seoul, Korea; 5Department of Pathology, Seoul National University Bundang Hospital, Seongnam, Korea; 6Department of Pathology, Seoul National University College of Medicine, Seoul, KoreaCorrespondence: Pyung Bok Lee, Email painfree@snu.ac.krObjective: To create a deep learning (DL) model that can accurately detect and classify three distinct types of rat dorsal root ganglion neurons: normal, segmental chromatolysis, and central chromatolysis. The DL model has the potential to improve the efficiency and precision of neuron classification in research related to spinal injuries and diseases.Methods: H&E slide images were divided into an internal training set (80%) and a test set (20%). The training dataset was labeled by two pathologists using pre-defined grades. Using this dataset, a two-component DL model was developed with the first component being a convolutional neural network (CNN) that was trained to detect the region of interest (ROI) and the second component being another CNN used for classification.Results: A total of 240 lumbar dorsal root ganglion (DRG) pathology slide images from rats were analyzed. The internal testing results showed an accuracy of 93.13%, and the external dataset testing demonstrated an accuracy of 93.44%.Conclusion: The DL model demonstrated a level of agreement comparable to that of pathologists in detecting and classifying normal and segmental chromatolysis neurons, although its agreement was slightly lower for central chromatolysis neurons. Significance: DL in improving the accuracy and efficiency of pathological analysis suggests that it may have a role in enhancing medical decision-making.Keywords: deep learning, dorsal root ganglion, chromatolysis, automated detection and spinal stenosis

ABSTRACTSexual dimorphism has been reported in multiple pre-clinical and clinical studies on pain. Previous investigations have suggested that in at least some states, rodent dorsal root ganglion (DRG) neurons display differential sex-dependent regulation and expression patterns of various proteins involved in the pain pathway. Our goal in this study was to determine whether sexual dimorphism in the biophysical properties of voltage-gated sodium (Nav) currents contributes to these observations in rodents. We recently developed a novel method that enables high-throughput, unbiased, and automated functional analysis of native rodent sensory neurons from naïve WT mice profiled simultaneously under uniform experimental conditions. In our previous study, we performed all experiments in neurons that were obtained from mixed populations of adult males or females, which were combined into single (combined male/female) data sets. Here, we have re-analyzed the same previously published data and segregated the cells based on sex. Although the number of cells in our previously published data sets were uneven for some comparisons, our results do not show sex-dependent differences in the biophysical properties of Nav currents in these native DRG neurons.

Sensory neurons cooperate with barrier tissues and resident immune cells to form a significant aspect of defensive strategies in concert with the immune system. This assembly of neuroimmune cellular units is exemplified across evolution from early metazoans to mammalian life. As such, sensory neurons possess the capability to detect pathogenic infiltrates at barrier surfaces. This capacity relies on mechanisms that unleash specific cell signaling, trafficking and defensive reflexes. These pathways exploit mechanisms to amplify and enhance the alerting response should pathogenic infiltration seep into other tissue compartments and/or systemic circulation. Here we explore two hypotheses: 1) that sensory neurons' potential cellular signaling pathways require the interaction of pathogen recognition receptors and ion channels specific to sensory neurons and; 2) mechanisms which amplify these sensing pathways require activation of multiple sensory neuron sites. Where possible, we provide references to other apt reviews which provide the reader more detail on specific aspects of the perspectives provided here.

Cancer patients undergoing treatment with antineoplastic drugs often experience chemotherapy-induced neuropathic pain (CINP), and the therapeutic options for managing CINP are limited. Here, we show that systemic paclitaxel administration upregulates the expression of neurotrophin-3 (Nt3) mRNA and NT3 protein in the neurons of dorsal root ganglia (DRG), but not in the spinal cord. Blocking NT3 upregulation attenuates paclitaxel-induced mechanical, heat, and cold nociceptive hypersensitivities and spontaneous pain without altering acute pain and locomotor activity in male and female mice. Conversely, mimicking this increase produces enhanced responses to mechanical, heat, and cold stimuli and spontaneous pain in naive male and female mice. Mechanistically, NT3 triggers tropomyosin receptor kinase C (TrkC) activation and participates in the paclitaxel-induced increases of C–C chemokine ligand 2 (Ccl2) mRNA and CCL2 protein in the DRG. Given that CCL2 is an endogenous initiator of CINP and that Nt3 mRNA co-expresses with TrkC and Ccl2 mRNAs in DRG neurons, NT3 likely contributes to CINP through TrkC-mediated activation of the Ccl2 gene in DRG neurons. NT3 may be thus a potential target for CINP treatment. Synopsis: Neurotrophin-3 (NT3) activates tropomyosin receptor kinase C (TrkC) to elevate C–C chemokine ligand 2 (CCL2) in dorsal root ganglion neurons contributing to paclitaxel-induced neuropathic pain. NT3 expression is increased in DRG neurons after systemic paclitaxel injection. Blocking this increase inhibits paclitaxel-induced nociceptive hypersensitivity. The inhibitory effect is mediated by preventing NT3-triggered TrkC activation and subsequent CCL2 production in DRG neurons. Neurotrophin-3 (NT3) activates tropomyosin receptor kinase C (TrkC) to elevate C-C chemokine ligand 2 (CCL2) in dorsal root ganglion neurons contributing to paclitaxel-induced neuropathic pain. [ABSTRACT FROM AUTHOR]

Although the molecular mechanisms of chronic pain have been extensively studied, a global picture of alternatively spliced genes and events in the peripheral and central nervous systems of chronic pain is poorly understood. The current study analyzed the changing pattern of alternative splicing (AS) in mouse brain, dorsal root ganglion, and spinal cord tissue under inflammatory and neuropathic pain. In total, we identified 6495 differentially alternatively spliced (DAS) genes. The molecular functions of shared DAS genes between these two models are mainly enriched in calcium signaling pathways, synapse organization, axon regeneration, and neurodegeneration disease. Additionally, we identified 509 DAS in differentially expressed genes (DEGs) shared by these two models, accounting for a small proportion of total DEGs. Our findings supported the hypothesis that the AS has an independent regulation pattern different from transcriptional regulation. Taken together, these findings indicate that AS is one of the important molecular mechanisms of chronic pain in mammals. This study presents a global description of AS profile changes in the full path of neuropathic and inflammatory pain models, providing new insights into the underlying mechanisms of chronic pain and guiding genomic clinical diagnosis methods and rational medication. [ABSTRACT FROM AUTHOR]

BACKGROUND: Heart failure is associated with a high rate of mortality and morbidity, and ventricular remodeling invariably precedes heart failure. Ventricular remodeling is fundamentally driven by mechanotransduction that is regulated by both the nervous system and the immune system. However, it remains unknown which key molecular factors govern the neuro/immune/cardio axis that underlies mechanotransduction during ventricular remodeling. Here, we investigated whether the mechanosensitive Piezo cation channel–mediated neurogenic inflammatory cascade underlies ventricular remodeling–related mechanotransduction. METHODS: By ligating the left coronary artery of rats to establish an in vivo model of chronic myocardial infarction (MI), lentivirus-mediated thoracic dorsal root ganglion (TDRG)–specific Piezo1 knockdown rats and adeno-associated virus–PHP.S—mediated TDRG neuron–specific Piezo1 knockout mice were used to investigate whether Piezo1 in the TDRG plays a functional role during ventricular remodeling. Subsequently, neutralizing antibody–mediated TDRG IL-6 (interleukin-6) inhibition rats and adeno-associated virus–PHP.S—mediated TDRG neuron–specific IL-6 knockdown mice were used to determine the mechanism underlying neurogenic inflammation. Primary TDRG neurons were used to evaluate Piezo1 function in vitro. RESULTS: Expression of Piezo1 and IL-6 was increased, and these factors were functionally activated in TDRG neurons at 4 weeks after MI. Both knockdown of TDRG-specific Piezo1 and deletion of TDRG neuron–specific Piezo1 lessened the severity of ventricular remodeling at 4 weeks after MI and decreased the level of IL-6 in the TDRG or heart. Furthermore, inhibition of TDRG IL-6 or knockdown of TDRG neuron–specific IL-6 also ameliorated ventricular remodeling and suppressed the IL-6 cascade in the heart, whereas the Piezo1 level in the TDRG was not affected. In addition, enhanced Piezo1 function, as reflected by abundant calcium influx induced by Yoda1 (a selective agonist of Piezo1), led to increased release of IL-6 from TDRG neurons in mice 4 weeks after MI. CONCLUSIONS: Our findings point to a critical role for Piezo1 in ventricular remodeling at 4 weeks after MI and reveal a neurogenic inflammatory cascade as a previously unknown facet of the neuronal immune signaling axis underlying mechanotransduction. [ABSTRACT FROM AUTHOR]