Mechanical Paw Withdrawal Threshold Research Articles

Electroacupuncture alleviates paradoxical sleep deprivation-induced postoperative hyperalgesia via a7nAChR mediated BDNF/TrkB-KCC2 signaling pathway in the spinal cord

Perioperative Paradoxical sleep deprivation (PSD) is associated with postoperative hyperalgesia. However, the clinical therapeutic strategies for PSD-induced postoperative hyperalgesia are limited. Electroacupuncture (EA) has been used for attenuating many types of pain, including neuropathic pain and inflammatory pain, but its effect on PSD-induced postoperative hyperalgesia is still unclear, and its analgesia mechanism should be further explored. In this study, we designed to investigate the possible mechanism of PSD-induced postoperative hyperalgesia and the effect of EA on PSD-induced postoperative hyperalgesia, and whether the mechanism is related to the BDNF/TrkB signaling pathway mediated by α7nAChR in the spinal cord. The paw withdrawal thermal latency (PWTL) and paw withdrawal mechanical threshold (PWMT) of rats were used to detect PSD-induced hyperalgesia. The expression of α7nAChR, BDNF, TrkB and KCC2 in the spinal cord were evaluated by Western blot and immunofluorescence. The results showed that preoperative 24h PSD significantly decreased the PWTL and PWMT. The expression of α7nAChR and KCC2 significantly downregulated in the spinal cord of PSD-induced postoperative hyperalgesia rats, the opposite was observed for BDNF and TrkB expression. Moreover, intrathecal injection of alpha-bungarotoxin (α-BGT), a selective antagonist for α7nAChR, not only aggravated the pain hypersensitivity, but also demonstrated a further decrease of α7nAChR and KCC2 expression and a further increase of BDNF and TrkB expression. EA stimulation increased the PWTL and PWMT values of PSD-induced postoperative hyperalgesia rats, significantly upregulated α7nAChR and KCC2 expression, and significantly downregulated BDNF and TrkB expression. Moreover, intrathecal injection of α-BGT suppressed the analgesic effect of EA, inhibited the enhancement of α7nAChR and KCC2 expression and the reduction of BDNF and TrkB expression induced by EA. In conclusion, our study indicated that 24h PSD can cause postoperative hyperalgesia, and the mechanism may be related to the disorder of α7nAChR mediated BDNF/TrkB-KCC2 signaling pathway. EA can alleviate postoperative hyperalgesia induced by PSD, which may be related to its effect in activating α7nAChR, inhibiting the expression of BDNF/TrkB, and up-regulating the expression of KCC2 in the spinal cord.

Lentivirus-mediated RNA interference targeting HMGB1 modulates AQP1 to reduce pain induced by chronic compression of the dorsal root ganglia.

Neuropathic pain (NP) is a kind of chronic pain that has attracted much attention in clinical practice, characterized by high morbidity, complex mechanisms, and difficulties in clinical treatment, with which the activation of High mobility group box 1 (HMGB1) is closely related. The aim of this study was to investigate the effects of lentivirus-mediated RNA interference gene therapy targeting HMGB1 on neuropathic pain in rats with chronic dorsal root ganglion compression (CCD) and its specific mechanisms, so as to explore new pharmacological targets. Adult male Wistar rats were surgically subjected to chronic compression of the dorsal root ganglia (CCD). Behavioral tests were performed by calculating the paw withdrawal mechanical threshold (PWMT) and the thermal paw withdrawal latency (TPWL). Co-immunoprecipitation (CO-IP) was used to clarify protein interactions. Gene silencing was induced by injecting lentivirus expressing HMGB1 short hairpin RNA (shRNA) into rats. An LPS-inflammation-stimulated rat astrocyte model was established to validate the animal experiment results further. Western blot analysis and real-time quantitative PCR were used to detect pathway protein expression. After first establishing the rat CCD model, both PWMT and PTWL were significantly reduced in rats, indicating that the model construction was successful. After lentiviral silencing of HMGB1 expression, NP was significantly alleviated in CCD rats. CO-IP experiments showed a link between HMGB1 and AQP1; After silencing HMGB1 expression, the expression of AQP1 was significantly reduced, and HMGB1 was able to modulate the effect of AQP1 on NP. Further use of an inhibitor of the HMGB1 receptor showed that after inhibition of RAGE, AQP1 was significantly reduced; HMGB1 may regulate AQP1 through its receptor RAGE to affect NP. Silencing of HMGB1 resulted in a significant decrease in NF-κB, and HMGB1 affects the inflammatory pathways it mediates. After silencing AQP1, NF-κB also decreased significantly, indicating that AQP1 is an upstream regulator of NF-κB. Lentivirus-mediated RNA interference (RNAi) silencing targeting HMGB1 may play a key role in the development of neuropathic pain in rats by regulating AQP1 expression via RAGE and ultimately activating NF-κB.

Modulation of Brain-derived Neurotrophic Factor Expression by Physical Exercise in Reserpine-induced Pain-depression Dyad in Mice.

Pain accompanied by depressive symptoms is a common reason for seeking medical assistance, and many chronic pain patients experience comorbid depression. The brain-derived neurotrophic factor (BDNF) is a well-known neurotrophin expressed throughout the nervous system, playing a crucial role in neuronal growth and neuroplasticity. This study aimed to examine the effects of exercise on BDNF expression in the nervous system and reserpine (RSP)-induced pain-depression dyad. RSP (1 mg/kg) was subcutaneously administered once daily for three days in mice. The exercise was performed using a rota-rod tester for seven consecutive days following RSP administration. Pain responses were evaluated using von Frey filaments, and depression-like behaviors were assessed through forced swimming and open field tests. Immunofluorescence staining was performed to examine the changes in BDNF expression in the dorsal root ganglion (DRG), spinal cord, and hippocampus. Administration of RSP reduced mechanical paw withdrawal threshold, increased immobility time in the forced swimming test, and decreased movement in the open field test. The immunoreactivity of BDNF was increased in the DRG and spinal dorsal regions, and decreased in the hippocampus after RSP administration. Physical exercise significantly reduced the RSP-induced mechanical hypersensitivity and depression-like behaviors. In addition, exercise suppressed not only the increased expression of BDNF in the DRG and spinal dorsal regions but also the decreased expression of BDNF in the hippocampus induced by RSP administration. These findings suggest that repetitive exercise could serve as an effective and non-invasive treatment option for individuals experiencing both pain and depression by modulating BDNF expression.

Electroacupuncture alleviates neuropathic pain by regulating hippocampal SP/NK1R/ARRB1 pathway.

To observe the effect of electroacupuncture (EA) on pain, anxiety like behavior, and substance P(SP) /neurokinin-1 receptor (NK1R) /β -arrestin 1(ARRB1) pathway related protein expression in hippocampus of chronic constriction injury (CCI) rats, so as to explore its mechanisms underlying improvement of neuropathic pain. Twenty-seven male SD rats were randomly divided into sham operation, model and EA groups, with 9 rats in each group. The CCI model was established by ligature of the left sciatic nerve. On the 8th day following modeling, EA (2 Hz, 0.5-1.5 mA) was applied to the left "Huantiao" (GB34) and "Yanglingquan" (GB34) for 30 min, once every other day for 13 times. Mechanical paw withdrawal threshold (MWT), thermal paw withdrawal threshold (TWL) and difference of the weight distribution of the hind limbs were detected before operation and at the 5th, 9th, 17th, 25th and 33rd days after operation. Open field test was used to evaluate the anxiety-like behavior of rats. The content of SP in hippocampus was determined by ELISA. The protein expression of NK1R and ARRB1 in hippocampus was detected by Western blot. Compared with the sham operation group, the MWT and TWL of the left hind limb at the 5th, 9th, 17th, 25th and 33rd days after operation, the time of entering the central area and the total distance of movement, and the content of SP in the hippocampus were significantly decreased (P<0.001, P<0.01), while the difference of the weight distribution of the hind limbs at the 5th, 9th, 17th, 25th and 33rd days after operation and the protein expression of NK1R and ARRB1 were significantly increased (P<0.001, P<0.05) in the model group. After EA intervention, the MWT and TWL of the left hind limb, the time of entering the central area and the total moving distance, and the expression of SP in the hippocampus were significantly increased (P<0.01, P<0.001, P<0.05), while the difference in the weight distribution of the hind limbs was significantly reduced, and the expression of NK1R and ARRB1 protein in the hippocampus were significantly decreased (P<0.001, P<0.05) in the EA group. EA can effectively improve the pain and anxiety behaviors in CCI rats, and reverse the abnormal expression of SP, NK1R and ARRB1 proteins in the hippocampus, which may be related to its effects in regulating the SP/NK1R/ARRB1 pathway in the hippocampus.

Loss of ATP-Sensitive Potassium Channel Expression and Function in the Nervous System Decreases Opioid Sensitivity in a High-Fat Diet-Fed Mouse Model of Diet-Induced Obesity.

During diabetes progression, β-cell dysfunction due to loss of potassium channels sensitive to ATP, known as KATP channels, occurs contributing to hyperglycemia. The aim of this study is to investigate if KATP channel expression or activity in the nervous system was altered in a high-fatdiet-( HFD) fed mouse model of diet-induced obesity. Expression of two KATP channel subunits, Kcnj11 (Kir6.2) and Abcc8 (SUR1), were decreased in the peripheral and central nervous system in HFD mice, which is significantly correlated with mechanical paw withdrawal thresholds. HFD mice had decreased antinociception to systemic morphine compared to control diet (CON) mice, which was expected as KATP channels are downstream targets of opioid receptors. Mechanical hypersensitivity in HFD mice was exacerbated after systemic treatment with glyburide or nateglinide, KATP channel antagonists clinically used to control blood glucose levels. Upregulation of SUR1 and Kir6.2, through an adenovirus delivered intrathecally, increased morphine antinociception in HFD mice,. These data present a potential link between KATP channel function and neuropathy during early stages of diabetes. There is a need for increased knowledge in how diabetes affects structural and molecular changes in the nervous system, including ion channels, to lead to the progression of chronic pain and sensory issues.

Exercise as a promising alternative for sciatic nerve injury pain relief: a meta-analysis.

The efficacy of drug therapies in managing neuropathic pain is constrained by their limited effectiveness and potential for adverse effects. In contrast, exercise has emerged as a promising alternative for pain relief. In this study, we conducted a systematic evaluation of the therapeutic impact of exercise on neuropathic pain resulting from sciatic nerve injury in rodent models. The PubMed, Embase, and Web of Science databases were retrieved before April 2024. A series of studies regarding the effect of treadmill, swimming, wheel and other exercises on neuropathic pain induced by sciatic nerve injury in rats and mice were collected. Using predefined inclusion criteria, two researchers independently performed literature screening, data extraction, and methodological quality assessment utilizing SYRCLE's risk of bias tool for animal studies. Statistical analysis was conducted using RevMan 5.3 and STATA 12.0 analysis software. A total of 12 relevant academic sources were included in the analysis of controlled animal studies, with 133 rodents in the exercise group and 135 rodents in the sedentary group. The meta-analysis revealed that exercise was associated with a significant increase in paw withdrawal mechanical threshold [Standard Mean Difference (SMD) = 0.84, 95% confidence interval (CI): 0.28-1.40, p = 0.003] and paw withdrawal thermal latency (SMD = 1.54, 95%CI: 0.93-2.15, p < 0.0001) in rats and mice with sciatic nerve injury. Subgroup analyses were conducted to evaluate the impact of exercise duration on heterogeneity. The results showed that postoperative exercise duration ≤3 weeks could significantly elevate paw withdrawal mechanical threshold (SMD = 1.04, 95% CI: 0.62-1.46, p < 0.00001). Postoperative exercise duration ≤4 weeks could significantly improve paw withdrawal thermal latency (SMD = 1.93, 95% CI:1.19-2.67, p < 0.00001). Exercise represents an effective method for improving mechanical and thermal hypersensitivity resulting from sciatic nerve injury in rodents. Factors such as pain models, the initiation of exercise, the type of exercise, and the species of rodent do not significantly impact the development of exercise-induced hypoalgesia. However, the duration of postoperative exercise plays a crucial role in the onset of exercise-induced hypoalgesia.

Hyperbaric Oxygen Attenuates Chronic Postsurgical Pain by Regulating the CD73/Adenosine/A1R Axis of the Spinal Cord in Rats

Chronic postsurgical pain (CPSP) affects postoperative rehabilitation and quality of life in patients, but its mechanisms are still poorly understood. Hyperbaric oxygen (HBO) attenuates neuropathic pain in animal and human studies, but its efficacy for CPSP treatment and its underlying mechanism have not been elucidated. This study aimed to investigate the analgesic effect of HBO in a CPSP rat model and the role of spinal cord adenosine circulation in HBO-induced analgesia. A skin/muscle incision and retraction (SMIR) rat model was used to mimic CPSP, and HBO treatment (2.5 atmospheric absolute, 60 minutes) was administered once daily for 5 consecutive days beginning 3 days after surgery. The role of spinal cord adenosine circulation in HBO-induced analgesia was investigated using β-methylene ADP (a CD73 inhibitor), 8-cyclopentyl-1,3-dipropylxanthine (an A1R antagonist), or an intrathecal injection of adenosine. The mechanical paw withdrawal threshold was determined at different timepoints before and after surgery. The spinal cord adenosine and adenosine triphosphate (ATP) contents were analyzed using high-performance liquid chromatography, and the spinal cord expression of adenosine-1 receptor (A1R), extracellular 5′-nucleotidase (CD73), and adenosine kinase (ADK) was examined by Western blotting and immunofluorescence staining. The results showed that the mechanical paw withdrawal threshold of the ipsilateral hind paw and the adenosine content decreased, and the spinal cord expression of A1R, CD73, and ADK and ATP content increased within 14 days after surgery. HBO treatment alleviated mechanical allodynia, reduced ATP content, and increased adenosine content by activating CD73 but downregulated the spinal cord expression of A1R, CD73, and ADK. Intrathecal adenosine alleviated mechanical allodynia after SMIR and downregulated the spinal cord expression of A1R and CD73, and intrathecal β-methylene ADP or 8-cyclopentyl-1,3-dipropylxanthine attenuated the analgesic effect of HBO treatment on SMIR-induced CPSP. PerspectiveSpinal cord adenosine is involved in the occurrence and development of CPSP, and HBO treatment alleviates CPSP by regulating adenosine production/metabolism in the spinal cord. Thus, HBO may be employed for the treatment of CPSP with favorable efficacy.

Sevoflurane impedes neuropathic pain by maintaining endoplasmic reticulum stress and oxidative stress homeostasis through inhibiting the activation of the PLCγ/CaMKII/IP3R signaling pathway.

To investigate the effect of sevoflurane on neuropathic pain induced by chronic constriction injury (CCI) of sciatic nerve in mice, and to elucidate its mechanism by animal experiments. Thirty-two C57BL/6 mice were randomly divided into four groups: Sham group, Model group, Control group and Sevoflurane group. First, a mouse model of neuropathic pain was established. Then, the mice in each group were killed on Day 14 after operation to harvest the enlarged lumbosacral spinal cord. In contrast with the Model group, the Sevoflurane group displayed a significantly increased paw withdrawal mechanical threshold (PWMT) and significantly prolonged paw withdrawal thermal latency (PWTL) from Day 5 after operation. The morphological changes of lumbosacral spinal cord were observed by hematoxylin-eosin (HE) staining and transmission electron microscopy. Pathological results showed that sevoflurane reduced nuclear pyknosis in lumbosacral spinal cord tissue, with a large number of mitochondrial crista disappearance and mitochondrial swelling. The results of Western blotting showed that sevoflurane significantly decreased the protein expressions of phosphorylated phospholipase Cγ (p-PLCγ), phosphorylated calcium/calmodulin-dependent protein kinase II (p-CaMKII) and phosphorylated inositol 1,4,5-triphosphate receptor (p-IP3R), and reduced the protein expressions of endoplasmic reticulum (ER) stress proteins glucose-regulated protein 78 (GRP78) and GRP94, oxidative stress-related proteins P22 and P47 and inflammatory factors nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), interleukin-1 β (IL-1β), and tumor necrosis factor-α (TNF-α). Sevoflurane inhibits neuropathic pain by maintaining ER stress and oxidative stress homeostasis through inhibiting the activation of the PLCγ/CaMKII/IP3R signaling pathway.

Evaluation of the Therapeutic Potential of Amantadine in a Vincristine-Induced Peripheral Neuropathy Model in Rats.

This study aimed to evaluate the therapeutic potential of amantadine in a vincristine-induced peripheral neuropathy model in rats. Forty-eight male Wistar rats were used. The treated groups received oral amantadine at doses of 2, 5, 12, 25 and 50 mg/kg, with daily applications for 14 days. The mechanical paw withdrawal threshold was measured using a digital analgesimeter. Immunohistochemical analysis of IL-6, TNFα, MIP1α, IL-10, CX3CR1, CXCR4, SOD, CAT and GPx, and enzymatic activity analysis of CAT, SOD and GPx were performed, in addition to quantitative PCR of Grp78, Chop, Ho1, Perk, Bax, Bcl-xL, Casp 3, Casp 9, IL-6, IL-10, IL-18 and IL-1β. The results showed an increase in nociceptive thresholds in animals that received 25 mg/kg and 50 mg/kg amantadine. Immunohistochemistry showed a decrease in the immunostaining of IL-6, TNFα, MIP1α and CX3CR1, and an increase in IL-10. CAT and SOD showed an increase in both immunochemistry and enzymatic analysis. qPCR revealed a reduced expression of genes related to endoplasmic reticulum stress and regulation in the expression of immunological and apoptotic markers. Amantadine demonstrated antinociceptive, anti-inflammatory and antioxidant effects in the vincristine-induced peripheral neuropathy model in rats, suggesting that amantadine may be considered an alternative approach for the treatment of vincristine-induced peripheral neuropathic pain.

Intravenous application of human umbilical cord mesenchymal stem cells alleviate neuropathic pain by suppressing microglia activation in rats

ObjectiveNeuropathic pain has been considered as one of the most serious chronic pain subtypes and causes intolerable suffering to patients physically and mentally. This study aimed to verify the analgesic effect of intravenous administration of human umbilical cord mesenchymal stem cells (HUC-MSCs) upon rats with chronic constriction injury (CCI)-induced neuropathic pain and the concomitant mechanism via modulating microglia. Methods30 male SD rats were randomized divided into three groups (n = 10 per group): Sham + Saline group (S&S group), CCI + Saline group (C&S group) and CCI + HUC-MSCs group (C&U group). Rats were injected with either saline or HUC-MSCs via the caudal vein on the 7th day after modelling. The paw mechanical withdrawal threshold (PMWT) and thermal withdrawal latency (TWL) of the ligation side were measured before (day 0) and after (day 1, 3, 5, 7, 9, 11, 13, and 15) modelling. On day 15 after modelling, western-blotting and immunofluorescent staining were used to assess the expressive abundance of Iba-1 (a typical biomarker of activated microglia) in the ligation side of the spinal cord dorsal horn, and ultrastructural changes of the ligation of sciatic nerve were evaluated by transmission electron microscope (TEM). ResultsCompared with the S&S group, PMWT and TWL in the C&S group were significantly decreased on day 5 and then persisted to day 15 after modelling (C&S vs S&S, P < 0.05), while a significant amelioration of mechanical hyperalgesia (day 13, day 15) and thermal allodynia (day 9, day 11, day 15) was observed in the C&U group (C&U vs C&S, P < 0.05). Meanwhile, the expression of Iba-1 was significantly suppressed by systemic infusion of HUC-MSCs in the C&U group according to western-blotting and immunofluorescent staining analyses (P < 0.05). With the aid of TEM detection, we intuitively noticed the efficacious reconstruction of the laminate structure of the sciatic nerve ligation, elimination of mitochondrial swelling, and formation of new myelination were noted on day 15 after modelling in the C&U group. ConclusionsOverall, intravenous administration of HUC-MSCs systemically revealed an ameliorative effect upon CCI-induced neuropathic pain in SD rats by inhibiting microglia activation in the dorsal horn of the impaired spinal cord and alleviating sciatic nerve injury. Our findings supply new references for the further development of HUC-MSCs-based cytotherapy for neuropathic pain administration.

Glucose competition between endothelial cells in the blood-spinal cord barrier and infiltrating regulatory T cells is linked to sleep restriction-induced hyperalgesia

BackgroundSleep loss is a common public health problem that causes hyperalgesia, especially that after surgery, which reduces the quality of life seriously.MethodsThe 48-h sleep restriction (SR) mouse model was created using restriction chambers. In vivo imaging, transmission electron microscopy (TEM), immunofluorescence staining and Western blot were performed to detect the status of the blood-spinal cord barrier (BSCB). Paw withdrawal mechanical threshold (PWMT) was measured to track mouse pain behavior. The role of infiltrating regulatory T cells (Tregs) and endothelial cells (ECs) in mouse glycolysis and BSCB damage were analyzed using flow cytometry, Western blot, CCK-8 assay, colorimetric method and lactate administration.ResultsThe 48-h SR made mice in sleep disruption status and caused an acute damage to the BSCB, resulting in hyperalgesia and neuroinflammation in the spinal cord. In SR mice, the levels of glycolysis and glycolysis enzymes of ECs in the BSCB were found significantly decreased [CON group vs. SR group: CD31+Glut1+ cells: p < 0.001], which could cause dysfunction of ECs and this was confirmed in vitro. Increased numbers of infiltrating T cells [p < 0.0001] and Treg population [p < 0.05] were detected in the mouse spinal cord after 48-h SR. In the co-cultured system of ECs and Tregs in vitro, the competition of Tregs for glucose resulted in the glycolysis disorder of ECs [Glut1: p < 0.01, ENO1: p < 0.05, LDHα: p < 0.05; complete tubular structures formed: p < 0.0001; CCK8 assay: p < 0.001 on 24h, p < 0.0001 on 48h; glycolysis level: p < 0.0001]. An administration of sodium lactate partially rescued the function of ECs and relieved SR-induced hyperalgesia. Furthermore, the mTOR signaling pathway was excessively activated in ECs after SR in vivo and those under the inhibition of glycolysis or co-cultured with Tregs in vitro.ConclusionsAffected by glycolysis disorders of ECs due to glucose competition with infiltrating Tregs through regulating the mTOR signaling pathway, hyperalgesia induced by 48-h SR is attributed to neuroinflammation and damages to the barriers, which can be relieved by lactate supplementation.

Different genes involved in the amelioration of chronic neuropathic pain and comorbid anxiety by electroacupuncture with different intensities

BackgroundWith its complex and prevalent symptoms, chronic neuropathic pain (CNP) is frequently combined with negative emotions. Electroacupuncture (EA) is a widely-used and effective treatment for CNP and pain-induced comorbid anxiety-like behaviors (PABs). Although different effects may result from EA with different intensities, the underlying mechanisms remain unclear. ObjectiveThe study aimed to investigate the effects of EA with different intensities on CNP and PABs and the underlying mechanisms, by exploring the different genes through RNASeq in the spinal cord dorsal horn (SCDH) and periaqueductal gray (PAG). MethodsA spared nerve injury (SNI) model was established using male C57BL/6 J mice, and treated with EA of different intensities (0.1 mA or 0.3 mA, both at 100 Hz). The von-Frey tests, open field tests and elevated plus maze tests were used to measure the mechanical paw withdrawal threshold (PWT) and PABs of the mice. The tissues of SCDH and PAG regions were extracted to identify the changes in gene expression, and biofunctional analysis of differentially expressed genes (DEGs) was further performed by RNA-seq analysis. The expression of key DEGs and corresponding proteins was assessed using quantitative real-time PCR (qPCR) and protein immunofluorescence detection, respectively. ResultsBoth 0.1 mA and 0.3 mA EA at 100 Hz alleviated PABs compared with the SNI group. Furthermore, 0.3 mA EA was effective in increasing PWT in SNI mice, whereas 0.1 mA EA was not. A total of 108 DEGs was identified in the SCDH, and 254 DEGs were identified in the PAG. Specifically, the expression of Tnr in SNI mice decreased after the treatment with 0.3 mA EA at 100 Hz, and the expression of Ptprb, Net1, Abcb1a and Adgrf5 in SNI mice decreased in the PAG after the treatment with 0.1 mA EA at 100 Hz. ConclusionThe effect of 0.3 mA EA on chronic pain may be related to the decrease of Tnr expression in SCDH, and the effect of 0.1 mA EA on PABs may be achieved by decreased expression of Ptprb and Net1 in PAG.

The Role of p38 Mitogen-Activated Protein Kinase-Mediated F-Actin in the Acupuncture-Induced Mitigation of Inflammatory Pain in Arthritic Rats.

The analgesic efficacy of acupuncture has been widely recognized. However, the mechanism by which manual acupuncture-generated mechanical stimuli translate into biological signals remains unclear. This study employed a CFA-induced inflammatory pain rat model. Acupuncture intervention was then performed following standardized procedures. Enzyme-linked immunosorbent assay (ELISA) assessed inflammatory cytokines levels, while immunofluorescence and qRT-PCR screened the level of p38 and F-actin expression in the ST36 acupoint area of rats. Results indicated increased inflammatory factors, including IL-1β and TNFα, with reduced paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) in CFA rats compared to unmodeled rats. After acupuncture intervention, the heightened expression level of F-actin and p38 mRNA and the phosphorylation of p38 in the acupoint area was observed alongside decreased inflammatory factors in diseased ankle joints. The application of lifting and thrusting manipulations further enhanced the effect of acupuncture, in which the molecular expression level of muscle and connective tissue increased most significantly, indicating that these two tissues play a major role in the transformation of acupuncture stimulation. Moreover, antagonizing p38 expression hindered acupuncture efficacy, supporting the hypothesis that p38 MAPK-mediated F-actin transduces mechanical signals generated by acupuncture and related manipulation into biological signals.

Sustained morphine exposure alters spinal NMDA receptor and astrocyte expression and exacerbates chronic pain behavior in female rats.

Sustained opioid use has long-term negative impacts on future pain experience, particularly in women. This study aimed to investigate the underlying spinal neurobiology of this clinical observation in an experimental model of joint pain. In this study, we tested the hypothesis that sustained opioid treatment exacerbates chronic pain responses and alters spinal cord dorsal horn astrogliosis and the expression of GluN2B-containing N-methyl-d-aspartate receptors in female rats. Subcutaneous morphine (3 mg/kg) or saline was administered twice daily for 1 week before inducing a model of joint knee pain (intra-articular injection of 2 mg of monosodium iodoacetate [MIA]) in adult female Sprague-Dawley rats, with pain-free controls receiving 50 µL of saline. Pain behavior (weight-bearing and mechanical paw withdrawal thresholds) was measured at baseline and at intervals thereafter. Twice-daily morphine/saline treatment was continued for up to 3 weeks after intra-articular injections, and spinal cord tissue was collected for Western blot analyses. Area under the curve analysis of weight-bearing asymmetry confirmed a significant exacerbation of pain behavior in the morphine/MIA group, compared with the saline/MIA group (F(3,18) = 46.3, P < 0.0001), despite comparable joint damage in both groups. Sustained morphine treatment was associated with significant elevations in dorsal horn expression of astrocytic glial fibrillary acidic protein (27 ± 5% increase) and neuronal GluN2B (80 ± 30% increase), but not microglial IBA1, irrespective of the model of joint pain. These data suggest that sustained morphine treatment in female rats drives spinal cord plasticity, including spinal astrogliosis and the expression of GluN2B-containing N-methyl-d-aspartate receptors, priming the dorsal horn to incoming sensory inputs and producing exacerbated pain responses.

Ciprofol alleviates remifentanil-induced hyperalgesia by regulating α2GABAARs, NR2B, and P-CaMKIIα levels in the spinal cord and hippocampus.

Several studies have shown that propofol administration during surgery effectively attenuates remifentanil-induced hyperalgesia (RIH). Ciprofol, a novel intravenous sedative agent analogous to propofol, has not yet been proven efficacious in alleviating RIH. The present study aimed to investigate the effect of ciprofol on RIH and the possible mechanisms involved. The RIH model was established by an infusion of remifentanil (1 μg·kg-1·min-1) 60min in rats with incisional pain. Ciprofol (0.1, 0.25, and 0.4 mg·kg-1·min-1) was simultaneously infused to evaluate its effect on RIH. The antinociception of ciprofol was verified by measured paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL). γ-aminobutyric acid type A receptor α2 subunit (α2GABAAR), N-methyl-d-aspartate receptor NR2B subunit (NR2B), calcium/calmodulin-dependent protein kinase II α (CaMKIIα), and phosphorylated CaMKIIα (P-CaMKIIα) in the spinal cord and hippocampus of rats were assessed by western blotting and immunohistochemistry. The results showed that ciprofol dose-dependently increased PWMT and PWTL values in RIH rats. Moreover, ciprofol upregulated α2GABAAR and downregulated NR2B and P-CaMKIIα in the rat spinal cord and hippocampus. Ciprofol alleviates RIH effectively, and the anti-hyperalgesic mechanisms may involve increasing α2GABAAR levels and decreasing NR2B and P-CaMKIIα levels in the spinal cord and hippocampus.

Chronic restraint stress induces abnormal behaviors in pain sensitivity and cognitive function in mice: the role of Keap1/Nrf2 pathway

Stress is a series of physical and psychological responses to external and internal environmental stimuli. Growing studies have demonstrated the detrimental impacts of acute restraint stress (ARS) and chronic restraint stress (CRS) on animal behavior. However, the related pathogenesis and therapeutic mechanisms remain unclear. Hence, the present study aimed to examine whether unfolded protein response (UPR) and Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2 related factor 2 (Nrf2) pathway are associated with ARS- and CRS- induced abnormal behaviors of pain sensitivity and cognitive function. We here used four behavioral tests to evaluate pain sensitivity and cognitive function in ARS and CRS mice. CRS markedly decreased Paw Withdrawal Mechanical Threshold (PWMT) and Tail-flick Latency (TFL) scores, whereas ARS altered TFL but had no effect on PWMT scores. Additionally, CRS, but not ARS, significantly changed behaviors in nest building behavior and MWMT. Intriguingly, the expression of Keap1 and Nrf2 protein were decreased in the spinal cord and hippocampus in CRS mice, but not in ARS mice. Moreover, neither the ARS nor the CRS groups significantly differed from the control group in terms of endoplasmic reticulum stress (ERS). Taken together, this study demonstrated that CRS could induce abnormal pain sensitivity and cognitive function probably via Keap1/Nrf2 pathway in spinal cord and hippocampus. It is therefore likely that effective intervention of Keap1/Nrf2 pathway may contribute to preventing and treating hyperalgesia and cognitive dysfunction in CRS.

Xenon ameliorates chronic post-surgical pain by regulating mitophagy in microglia and rats mediated by PINK1/Parkin pathway.

Chronic post-surgical pain (CPSP) is one of the important causes of poor postoperative outcomes, the activation of microglia in the spinal cord is closely related to the generation, transmission and maintenance of CPSP. Xenon (Xe), an anesthetic gas, has been reported to be able to significantly reduce intraoperative analgesia and postoperative pain sensation at low doses. However, the mechanism of the regulatory effect of xenon on activated microglia after CPSP remains unclear. In this study, CPSP model rats were treated with 50% Xe inhalation for 1 h following skin/muscle incision and retraction (SMIR), once a day for 5 consecutive days, and then the painbehavioraltests (pain behavior indexes paw withdrawal mechanical threshold, PWMT and thermal withdrawal latency, TWL), microglial activation, oxidative stress-related indexes (malondialdehyde, MDA; superoxide dismutase, SOD; hydrogen peroxide, H2O2; and catalase, CAT), mitophagy and PINK1/Parkin pathway were examined. The present results showed that a single dose of Xe treatment in SMIR rat model could significantly improve PWMT and TWL in the short-term at a single treatment and long-term at multiple treatments. Xe treatment inhibited microglia activation and oxidative stress in the spinal dorsal horn of SMIR rats, as indicated by the decrease of Iba1 and MDA/H2O2 levels and the increase of SOD/CAT levels. Compared with the control group, Xe further increased the CPSP promoted Mito-Tracker (a mitochondrial marker) and LC3 (an autophagy marker) co-localization positive spots and PINK1/Parkin/ATG5/BECN1 (autophagy-related proteins) protein expression levels, and inhibited the Mito-SOX (a mitochondrial reactive oxygen species marker) positive signal, indicating that Xe promoted microglia mitophagy and inhibited oxidative stress in CPSP. Mechanistically, we verified that Xe promoted PINK1/Parkin signaling pathway activation. Xe plays a role in ameliorating chronic post-surgical pain by regulating the PINK1/Parkin pathway mediated microglial mitophagy and provide new ideas and targets for the prevention and treatment of CPSP.

A novel synthetic oleanane triterpenoid, 2‐cyano‐3,12‐dioxoolean‐1,9‐dien‐28‐oic acid, regulates mechanical allodynia by rescuing neuronal cell death and glial cell activation in the spinal cord of resiniferatoxin‐treated rats

AbstractBackgroundTreating postherpetic neuralgia (PHN), which is characterized with a long‐lasting lancinating mechanical allodynia or hyperalgesia, is a big challenge as it is hard to achieve complete resolution. A synthetic triterpenoid, CDDO (2‐cyano‐3,12‐dioxoolean‐1,9‐dien‐28‐oic acid) can exert pleiotropic effects including anti‐inflammation and neuroprotective activities. Nevertheless, the antinociceptive effect of CDDO and its derivatives remains unknown. Resiniferatoxin (RTX) is easily feasible, and an RTX‐treated rodent model can mimic the PHN‐like symptoms. Therefore, RTX‐treated rats were used to serve as a PHN rats’ model in the study to elucidate whether a synthetic triterpenoid, CDDO, can improve mechanical allodynia in RTX‐treated rats.MethodsThe antinociceptive effects of CDDO were assessed by behavioral tests, western blotting, and immunohistochemistry. Paw withdrawal mechanical threshold was determined using calibrated forceps.ResultsAdministration of RTX led to mechanical allodynia, neuronal cell death, and glial cell activation in the spinal cord of RTX‐treated rats. A synthetic triterpenoid, CDDO, blocked RTX‐induced mechanical allodynia, rescued neuronal cell death, and inhibited glial cell activation in the spinal cord of RTX‐treated rats.ConclusionsOur study provides a novel result that a synthetic triterpenoid, CDDO, can interfere neuronal cell death and glial cell activation in the spinal cord of RTX‐treated rats. Hence, CDDO is an alternative therapeutic choice for PHN.

Octanol alleviates chronic constriction injury of sciatic nerve-induced peripheral neuropathy by regulating AKT/mTOR signaling.

Activation of gap junction channels can induce neuropathic pain. Octanol can limit the conductance of gap junctions containing connexin 43 proteins. Thus, this study focused on the roles of octanol in chronic constriction injury (CCI)-induced peripheral neuropathy in mice and its mechanisms of action. Male mice were assigned into control, sham, CCI, CCI + Octanol-20mg/kg, CCI + Octanol-40mg/kg and CCI + Octanol-80mg/kg groups. CCI was performed by applying three loose ligations to mouse sciatic nerve, and the mice with CCI was administered with 20mg/kg, 40mg/kg, or 80mg/kg octanol. The neuropathic pain development was examined by assessing thermal withdrawal latency, paw withdrawal mechanical threshold, and sciatic functional index. Histopathological changes were evaluated by hematoxylin and eosin staining. The phosphorylation of protein kinase B (Akt) and mammalian target of rapamycin (mTOR) was examined by western blotting. The expression of Akt and mTOR was also evaluated by immunofluorescence staining. Octanol alleviated the CCI-induced mechanical and thermal hyperalgesia and sciatic functional loss. Additionally, octanol relieved the CCI-induced abnormal histopathological changes. Mechanistically, octanol inactivated the Akt/mTOR pathway in the mice with CCI. In conclusion, octanol can alleviate CCI-induced peripheral neuropathic by regulating the Akt/mTOR pathway and might be a novel pharmacological intervention for neuropathic pain.

Effectiveness of Low Level Laser Therapy and Low Intensity Pulsed Ultrasound on Neuropathic Pain among the Experimentally Induced Peripheral Nerve Injury in Rat Model

Background: Peripheral nerve injury creates an impact on the inflammatory process, leading to an elevation inHypoxia-inducible factor-1 alpha levels, which contributes to the development and progression of neuropathicpain. An innovative approach to alleviating neuropathic pain involves targeting inflammation.Purpose: This study aims to compare the effect of Low-Level Laser Therapy (LLLT) and Low-Intensity PulsedUltrasound (LIPUS) on neuropathic pain among the experimentally induced peripheral nerve injury in rat model.Methods: Rats with induced sciatic nerve crush injury were randomly divided into three groups: control, LIPUStreatment, and LLLT treatment. Mechanical paw withdrawal threshold analysis was performed before the injuryand from POD 2nd, 7th, 14th, and 21st to assess effectiveness of the treatment.Result: Low-Level Laser Therapy (LLLT) group showing statistically greater improvement on POD 14 and 21compared to both the LIPUS group and the control group in terms of paw withdrawal threshold measurementsamong rats with crush-induced neuropathic pain (P &lt; 0.001).Conclusion: This study found that the use of LLLT has a beneficial effect in the management of neuropathic painand control of analgesia compared to LIPUS by inhibiting the upregulation of HIF-1α synthesis during ischemia,hypoxia, and inflammation. However further studies are recommended to analyze long term results in largersample to control neuropathic pain.