Background Neuropathic pain (NP) caused by the injury or dysfunction of the nervous system is a chronic pain state accompanied by hyperalgesia, and the available clinical treatment is relatively scarce. Hyperalgesia mediated by pro‐inflammatory factors and chemokines plays an important role in the occurrence and maintenance of NP. Data treatment Therefore, we conducted a systematic literature review of experimental NP (PubMed Medline), in order to find the mechanism of inducing central sensitization and explore the intervention methods of hyperalgesia caused by real or simulated injury. Result In this review, we sorted out the activation pathways of microglia, astrocytes and neurons, and the process of crosstalk among them. It was found that in NP, the microglia P2X4 receptor is the key target, which can activate the mitogen‐activated protein kinase pathway inward and then activate astrocytes and outwardly activate neuronal tropomyosin receptor kinase B receptor to activate neurons. At the same time, activated neurons continue to maintain the activation of astrocytes and microglia through chemokines on CXCL13/CXCR5 and CX3CL1/CX3CR1. This crosstalk process is the key to maintaining NP. Conclusion We summarize the further research on crosstalk among neurons, microglia, and astrocytes in the central nervous system, elaborate the ways and connections of relevant crosstalk, and find potential crosstalk targets, which provides a reference for drug development and preclinical research.

Neuropathic pain (NP) is a common pain disease that seriously affects the quality of life and physical and mental health of patients. Daphnetin is extracted from the Daphne giraldii Nitsche and has the structure of 7,8-dihydroxy coumarin. As a natural product, daphnetin displays a wide range of pharmacological activities, such as analgesia and anti-inflammatory activities, but whether it is able to improve NP through anti-inflammatory effects is unknown. Therefore, this paper intends to investigate the mechanism of daphnetin in improving NP rats affected by the intrathecal injection of tumor necrosis factor-α (TNF-α) from the perspective of anti-inflammation. Our results showed that daphnetin significantly improved hyperalgesia in NP rats. Daphnetin inhibited the activation and polarization of glial cells and neurons in the spinal cord of NP rats and reduced the expression of mRNA and protein of inflammatory factors and chemokine pairs in the spinal cord. Daphnetin inhibited the polarization of human microglia cell 3 (HMC3) cells and human glioma cells (U251) cells toward M1 microglia and A1 astrocytes, respectively, and induced the conversion of M1 microglia and A1 astrocytes to M2 microglia and A2 astrocytes, respectively. In conclusion, daphnetin ameliorates NP by inhibiting the expression of inflammatory factors and chemokines and the polarization of glial cells in the spinal cord of NP rats. This study provides a theoretical basis for the treatment of NP with daphnetin to expand the clinical application of daphnetin.

Context Daphnetin is a natural product with anti-inflammatory, antioxidant, and neuroprotective properties. Reports have found that it has a strong analgesic effect; however, its analgesic mechanism is unknown. Objective We explored the effect and mechanism of daphnetin on neuropathic pain (NP). Materials and methods The rat model of NP was established by ligation of the sciatic nerve. Male Sprague-Dawley rats were divided into six groups: Control, Model, Sham, morphine (0.375 mg/kg), and daphnetin (0.0625 and 0.025 mg/kg). Rats were intrathecally injected with drugs or normal saline once daily for three days. Hyperalgesia was evaluated by mechanical withdrawal threshold (MWT) and thermal withdrawal threshold (TWT). Protein levels were detected using ELISA, immunofluorescence, and western blotting. Results Compared to the Model group, daphnetin improved TWT (46.70 °C vs. 42.20 °C) and MWT (45.60 g vs. 23.60 g), reduced the expression of interleukin-1β (0.99 ng/g vs. 1.42 ng/g), interleukin-6 (0.90 ng/g vs. 1.52 ng/g), and tumor necrosis factor-α (0.93 ng/g vs. 1.52 ng/g) in the sciatic nerve. Daphnetin decreased the expression of toll-like receptor 4 (TLR4) (0.47-fold), phosphorylated inhibitor of NF-κB (p-IKBα) (0.29-fold), nuclear factor kappaB (NF-κB) (0.48-fold), glial fibrillary acidic protein (GFAP) (0.42-fold), CXC chemokine ligand type 1 (CXCL1) (0.84-fold), CXC chemokine receptor type 2 (CXCR2) (0.78-fold) in the spinal cord. Discussion and conclusions Daphnetin alleviates NP by inhibiting inflammation and astrocyte activation in the spinal cord, providing theoretical support for the extensive clinical treatment of NP.

Background: Neuropathic pain is a common chronic pain caused by a lesion or diseases of somatosensory nervous system, which has a significant impact on the quality of life. It has been found that its underling pathological mechanism is related to inflammation. Daphnetin is a natural product with a variety of biological activities such as anti-inflammatory and analgesic. It has been shown to be effective in the treatment of chronic inflammatory pain, but its underlying mechanisms are not completely understood. We aimed to evaluate the effect and regulatory mechanism of daphnetin on neuropathic pain.Methods: The experimental animals were divided into 8 groups: control group, model group, sham group, positive group (0.0375mg/kg), DAPH group (0.0625mg/kg), DAPL group (0.025mg/kg), P2X4 blocker group (1mg/kg) and P38 blocker group (5mg/kg). After constructing the subdural drug delivery system in rats, the neuropathic pain model was established by chronic constrictive injury (CCI), and the pain sensitivity was evaluated by measuring mechanical withdrawal threshold (MWT) and thermal withdrawal threshold (TWT). The protein expression of inflammatory factors and related pathways was measured by Western Blot. The activation of microglia and neurons and the expression of target protein in spinal dorsal horn were measured by immunofluorescence staining.Results: Compared with the sham group, MWT and TWT decreased significantly in model group, and the expression of IL-1 β, IL-6 and TNF-α increased. After intrathecal injection of daphnetin, the MWT and TWT of rats were significantly increased, and the protein expression of IL-1 β, IL-6 and TNF- α was significantly decreased compared with the model group. Compared with sham group, the expression of P2X4, IRF8, IRF5, BDNF, p-P38 / P38, p-JNK / JNK and p-ERK1/2 / ERK1/2 in model group increased significantly. After intrathecal injection of daphnetin, the expression of the above proteins was significantly down-regulated compared with model group. Compared with sham group, microglia and neurons in the spinal dorsal horn of model group were activated, and the expression of P2X4 and P38 in microglia increased. After intrathecal injection of daphnetin, compared with the model group, the activation of microglia and neurons in the spinal dorsal horn decreased significantly, and the expression of P2X4 and P38 in microglia decreased. Importantly, daphnetin could not improve neuropathic pain in CCI rats under the action of P2X4 and P38 blocker.Conclusion: daphnetin can alleviate neuropathic pain in CCI model rats by interfering with P2X4-P38 MAPK pathway of microglia, suggesting that daphnetin is a potential drug for the treatment of neuropathic pain.