Neuropeptide Y Y2 Receptors in Sensory Neurons Tonically Suppress Nociception and Itch but Facilitate Postsurgical and Neuropathic Pain Hypersensitivity.

BACKGROUND: Neuropeptide Y (NPY) Y2 receptor (Y2) antagonist BIIE0246 can both inhibit and facilitate nociception. The authors hypothesized that Y2 function depends on inflammation or nerve injury status. METHODS: The authors implemented a battery of behavioral tests in mice of both sexes that received (1) no injury; (2) an incision model of postoperative pain; (3) a spared nerve injury model of neuropathic pain; and (4) a latent sensitization model of chronic postsurgical pain. In addition to Y2 gene expression assays, spinal Y2 G-protein coupling was studied with guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPγS) binding assays. RESULTS: The authors report that intrathecal BIIE0246 increased mechanical and cold hypersensitivity, produced behavioral signs of spontaneous nociception and itch, and produced conditioned place aversion and preference in normal, uninjured mice. BIIE0246 did not change heat hypersensitivity or motor coordination. Conditional (sensory neuron-specific) Y2 deletion prevented BIIE0246-induced mechanical and cold hypersensitivity, nocifensive behaviors, and aversion. Both conditional deletion and pharmacologic blockade of Y2 reduced mechanical and thermal hypersensitivity after incision or nerve injury. SNI did not change the sensitivity of Y2 G-protein coupling with the Y2 agonist peptide YY (3-36) (PYY3-36), but increased the population of Y2 that effectively coupled G-proteins. Intrathecal PYY3-36 failed to reduce spared nerve injury- or incision-induced hypersensitivity in C57BL/6N mice. Incision did not change Npy2r gene expression in dorsal root ganglion. CONCLUSIONS: The authors conclude that Y2 at central terminals of primary afferent neurons provides tonic inhibition of mechanical and cold nociception and itch. This switches to the promotion of mechanical and thermal hyperalgesia in models of acute and chronic postsurgical and neuropathic pain, perhaps due to an increase in the population of Y2 that effectively couples to G-proteins. These results support the development of Y2 antagonists for the treatment of chronic postsurgical and neuropathic pain.

The association between changes in clinical pain severity and IL-6 reactivity among patients undergoing total knee Arthroplasty: The moderating role of change in insomnia.

Knee osteoarthritis (KOA) is linked to an enhanced release of interleukin-6 (IL-6). Increased levels of IL-6 are associated with greater pain and insomnia. While total knee arthroplasty (TKA) typically results in the reduction of pain, for a subgroup of patients, pain does not improve. Understanding patients' propensity to upregulate IL-6 may provide insight into variation in the clinical success of TKA for improving pain, and insomnia may play an important modulatory role. We investigated the association between pre- and post-surgical changes in clinical pain and IL-6 reactivity, and whether change in insomnia moderated this association. Patients (n = 39) with KOA came in-person before and 3-months after TKA. At both visits, patients completed validated measures of clinical pain and insomnia, as well as underwent quantitative sensory testing (QST). Blood samples were collected to analyze IL-expression both before and after QST procedures to assess changes in IL-6 in response to QST (IL-6 reactivity). Patients were categorized into two groups based on change in clinical pain from pre- to post-surgery: 1) pain decreased > 2 points (pain improved) and 2) pain did not decrease > 2 points (pain did not improve). Based on this definition, 49 % of patients had improved pain at 3-months. Among patients with improved pain, IL-6 reactivity significantly decreased from pre- to post-surgery, whereas there was no significant change in IL-6 reactivity among those whose pain did not improve. There was also a significant interaction between pain status and change in insomnia, such that among patients whose insomnia decreased over time, improved pain was significantly associated with a reduction in IL-6 reactivity. However, among patients whose insomnia increased over time, pain status and change in IL-6 reactivity were not significantly associated. Our findings suggest that the resolution of clinical pain after TKA may be associated with discernible alterations in pro-inflammatory responses that can be measured under controlled laboratory conditions, and this association may be moderated by perioperative changes in insomnia. Randomized controlled trials which carefully characterize the phenotypic features of patients are needed to understand how and for whom behavioral interventions may be beneficial in modulating inflammation, pain, and insomnia.

Additive antinociceptive action of intrathecal anandamide reuptake inhibitor and morphine in the management of post-incisional pain in rats.

Spinal opioids have mixed efficacy and their adverse effects force treatment cessation of postoperative pain. Consequently, there is an ongoing search for new therapeutic strategies. Here, we evaluated the analgesic efficacy of intrathecal UCM707, an anandamide reuptake inhibitor, and morphine combination. Firstly, we assessed the effects of morphine (1, 5 and 10 µg), UCM707 (75 µg) and its combination in the hot plate. Then, morphine + UCM707 at sub-effective doses was evaluated in a rat post-incisional pain model. In addition, µ-, CB1r-, CB2r- and TRPV1-antagonists were pre-administered before the combination. Activation of µ-opioid and CB1r, and Cnr1, Cnr2, Oprm1 and TRPV1 expressions were evaluated in the lumbar sacra and periaqueductal grey by [35 S]-GTPγS binding autoradiography and qPCR studies. In the hot plate, morphine (1 µg) and UCM707 (75 µg) induced a more robust analgesic effect than each drug alone. Morphine plus UCM707 did not modify µ-opioid nor CB1 receptor function in the PAG or LS. Cnr1 and TRPV1 expression increased in the lumbar sacra (LS). Morphine plus UCM707 significantly reduced post-incisional pain at 1 and 4 days after surgery. Cnr1, Cnr2 and TRPV1 expressions increased in the LS. Blockade of µ-opioid receptor reduced combination effects on days 1 and 4. CB1r- and CB2r-antagonism reduced morphine + UCM707 effects on days 1 and 4, respectively. CB1r and TRPV1-antagonism improved their antinociceptive effects on day 4. These results revealed a synergistic/additive analgesic effect of UCM707 and morphine combination controlling postincisional pain. CB1r, CB2r and TRPV1 contribute differently as central sensitization occurs.

Pronociceptive role of spinal Cav2.3 (R-type) calcium channels in a mouse model of postoperative pain.

BACKGROUND: More than 80% of patients may experience acute pain after a surgical procedure, and this is often refractory to pharmacological intervention. The identification of new targets to treat postoperative pain is necessary. There is an association of polymorphisms in the Cav2.3 gene with postoperative pain and opioid consumption. Our study aimed to identify Cav2.3 as a potential target to treat postoperative pain and to reduce opioid-related side effects. EXPERIMENTAL APPROACH: A plantar incision model was established in adult male and female C57BL/6 mice. Cav2.3 expression was detected by qPCR and suppressed by siRNA treatment. The antinociceptive efficacy and safety of a Cav2.3 blocker-alone or together with morphine-was also assessed after surgery. KEY RESULTS: Paw incision in female and male mice caused acute nociception and increased Cav2.3 mRNA expression in the spinal cord but not in the incised tissue. Intrathecal treatment with siRNA against Cav2.3, but not with a scrambled siRNA, prevented the development of surgery-induced nociception in both male and female mice, with female mice experiencing long-lasting effects. High doses of i.t. SNX-482, a Cav2.3 channel blocker, or morphine injected alone, reversed postoperative nociception but also induced side effects. A combination of lower doses of morphine and SNX-482 mediated a long-lasting reversal of postsurgical pain in female and male mice. CONCLUSION: Our results demonstrate that Cav2.3 has a pronociceptive role in the induction of postoperative pain, indicating that it is a potential target for the development of therapeutic approaches for the treatment of postoperative pain.

Effects of White Noise on Pain Scores and Salivary Cortisol Levels in Surgical Neonates: A Randomized Controlled Trial.

BACKGROUND: Neonates experience varying intensities of pain after surgery. While white noise has been used for postoperative pain relief in infants, its effects on neonates after surgery need further exploration. PURPOSE: This study aimed to evaluate the effects of white noise on pain scores and salivary cortisol levels in surgical neonates. METHODS: In this randomized controlled trial, 64 neonates scheduled for surgery were recruited and assigned by block randomization into 2 groups. The intervention group listened to white noise at 50 dB, while the control group listened to white noise at 0 dB, for 30 minutes 6 times for 48 hours postoperatively. Pain scores, measured by the COMFORTneo Scale, and salivary cortisol levels were compared. RESULTS: Although pain scores decreased after surgery in all subjects, no statistically significant difference was observed between the 2 groups (P = .937). There was a significant difference between pre- and postintervention pain scores in the intervention group only (P = .006). Salivary cortisol levels decreased after intervention in the intervention group, but there was no significant difference between pre- and postintervention levels in the 2 groups (P = .716). IMPLICATIONS FOR PRACTICE: Given the reduction in pain scores and salivary cortisol concentrations after white noise intervention, white noise shows potential as an adjunctive soothing measure for neonates after surgery. IMPLICATIONS FOR RESEARCH: Future studies are needed to confirm the efficacy and utility of white noise intervention in clinical settings.

Novel Scorpion Toxin ω-Buthitoxin-Hf1a Selectively Inhibits Calcium Influx via CaV3.3 and CaV3.2 and Alleviates Allodynia in a Mouse Model of Acute Postsurgical Pain.

Venom peptides have evolved to target a wide range of membrane proteins through diverse mechanisms of action and structures, providing promising therapeutic leads for diseases, including pain, epilepsy, and cancer, as well as unique probes of ion channel structure-function. In this work, a high-throughput FLIPR window current screening assay on T-type CaV3.2 guided the isolation of a novel peptide named ω-Buthitoxin-Hf1a from scorpion Hottentotta franzwerneri crude venom. At only 10 amino acid residues with one disulfide bond, it is not only the smallest venom peptide known to target T-type CaVs but also the smallest structured scorpion venom peptide yet discovered. Synthetic Hf1a peptides were prepared with C-terminal amidation (Hf1a-NH2) or a free C-terminus (Hf1a-OH). Electrophysiological characterization revealed Hf1a-NH2 to be a concentration-dependent partial inhibitor of CaV3.2 (IC50 = 1.18 µM) and CaV3.3 (IC50 = 0.49 µM) depolarized currents but was ineffective at CaV3.1. Hf1a-OH did not show activity against any of the three T-type subtypes. Additionally, neither form showed activity against N-type CaV2.2 or L-type calcium channels. The three-dimensional structure of Hf1a-NH2 was determined using NMR spectroscopy and used in docking studies to predict its binding site at CaV3.2 and CaV3.3. As both CaV3.2 and CaV3.3 have been implicated in peripheral pain signaling, the analgesic potential of Hf1a-NH2 was explored in vivo in a mouse model of incision-induced acute post-surgical pain. Consistent with this role, Hf1a-NH2 produced antiallodynia in both mechanical and thermal pain.

Euchromatin histone-lysine N-methyltransferase 2 regulates the expression of potassium-sodium-activated channel subfamily T member 1 in primary sensory neurons and contributes to remifentanil-induced pain sensitivity.

Intraoperative remifentanil administration has been linked to increased postoperative pain sensitivity. Recent studies have identified the involvement of euchromatic histone-lysine N-methyltransferase 2 (Ehmt2/G9a) in neuropathic pain associated with the transcriptional silencing of many potassium ion channel genes. This study investigates whether G9a regulates the potassium sodium-activated channel subfamily T member 1 (Slo2.2) in remifentanil-induced post-incisional hyperalgesia (RIH) in rodents. We performed remifentanil infusion (1 µg·kg-1·min-1 for 60 min) followed by plantar incision to induce RIH in rodents. Our results showed that RIH was accompanied by increased G9a and H3K9me2 production and decreased Slo2.2 expression 48 h postoperatively. Deletion of G9a rescued Slo2.2 expression in DRG and reduced RIH intensity. Slo2.2 overexpression also reversed this hyperalgesia phenotype. G9a overexpression decreased Slo2.2-mediated leak current and increased excitability in the small-diameter DRG neurons and laminal II small-diameter neurons in the spinal dorsal horn, which was implicated in peripheral and central sensitization. These results suggest that G9a contributes to the development of RIH by epigenetically silencing Slo2.2 in DRG neurons, leading to decreased central sensitization in the spinal cord. The findings may have implications for the development of novel therapeutic targets for the treatment of postoperative pain.

Local Magnesium Sulfate Administration Ameliorates Nociception, Peripheral Inflammation, and Spinal Sensitization in a Rat Model of Incisional Pain.

OBJECTIVE: Postoperative pain remains one of the most common complaints after surgery, and appropriate treatments are limited. METHODS: We therefore investigated the effect of the anti-nociceptive properties of magnesium sulfate (MgSO4), an N-methyl-D-aspartate (NMDA) receptor antagonist, on incision-induced postoperative pain and peripheral and central nervous system inflammation. RESULTS: We found that local MgSO4 administration dose-dependently increases paw withdrawal latency, indicating reduced peripheral postoperative pain. Furthermore, MgSO4 inhibited the expression of interleukin-1ß (IL-1ß) and inducible nitric oxide synthase (iNOS) and phosphorylation of the NMDA receptor NR1 subunit in injured paw tissue and significantly attenuated microglial and astrocytic activation in the ipsilateral lumbar spinal cord dorsal horn. CONCLUSION: Locally administered MgSO4 has potential for development as an adjunctive therapy for preventing central nociceptive sensitization.

The alterations in nerve growth factor concentration in plasma and synovial fluid before and after total knee arthroplasty.

Total knee arthroplasty (TKA) is an effective procedure for pain relief; however, the emergence of postsurgical pain remains a concern. In this study, we investigated the production of nerve growth factor (NGF) and mediators that affect NGF production and their function in the synovial fluid and plasma after TKA. This study included 19 patients (20 knees) who had rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and knee osteoarthritis (OA) who underwent TKA, categorized into OA and non-OA groups. The levels of NGF, inflammatory cytokines, and lipid mediators were analyzed before and after surgery. The intraoperative synovial fluid NGF concentration was more than seven times higher in the non-OA group than in the OA group. The intra-articular NGF levels increased significantly by more than threefold postoperatively in the OA group but not in the non-OA group. Moreover, the levels of inflammatory cytokines and lipid mediators were increased in the synovial fluid of both groups. The intra-articular cytokines or NGF concentrations positively correlated with postoperative pain. Targeted NGF control has the potential to alleviate postsurgical pain in TKA, especially in patients with OA, emphasizing the importance of understanding NGF dynamics under different knee conditions.

CXCL13/CXCR5 promote chronic postsurgical pain and astrocyte activation in rats by targeting NLRP3.

Chronic postsurgical pain (CPSP) with high incidence negatively impacts the quality of life. X-C motif chemokine 13 (CXCL13) has been associated with postsurgery inflammation and exacerbates neuropathic pain in patients with CPSP. This study was aimed to illustrate the relationship between CXCL13 and nod-like receptor protein-3 (NLRP3), which is also involved in CPSP. A CPSP model was constructed by skin/muscle incision and retraction (SMIR) in right medial thigh, and the rats were divided into three groups: Sham, SMIR, and SMIR + anti-CXCL13 (intrathecally injected with anti-CXCL13 antibody). Then, the paw withdrawal threshold (PWT) score of rats was recorded. Primary rat astrocytes were isolated and treated with recombinant protein CXCL13 with or without NLRP3 inhibitor INF39. The expressions of CXCL13, CXCR5, IL-1ß, IL-18, GFAP, NLRP3, and Caspase-1 p20 were detected by real-time quantitative reverse transcription PCR, western blot, ELISA, immunocytochemistry, and immunofluorescence analyses. The anti-CXCL13 antibody alleviated SMIR-induced decreased PWT and increased expression of GFAP, CXCL13, CXCR5, NLRP3, and Caspase-1 p20 in spinal cord tissues. The production of IL-1ß, IL-18, and expression of CXCL13, CXCR5, GFAP, NLRP3, and Caspase-1 p20 were increased in recombinant protein CXCL13-treated primary rat astrocytes in a dose-dependent manner. Treatment with NLRP3 inhibitor INF39 inhibited the function of recombinant protein CXCL13 in primary rat astrocytes. The CXCL13/CXCR5 signaling could promote neuropathic pain, astrocytes activation, and NLRP3 inflammasome activation in CPSP model rats by targeting NLRP3. NLRP3 may be a potential target for the management of CPSP.

Microglial exosome miR-124-3p in hippocampus alleviates cognitive impairment induced by postoperative pain in elderly mice.

Cognitive impairment induced by postoperative pain severely deteriorates the rehabilitation outcomes in elderly patients. The present study focused on the relationship between microglial exosome miR-124-3p in hippocampus and cognitive impairment induced by postoperative pain. Cognitive impairment model induced by postoperative pain was constructed by intramedullary nail fixation after tibial fracture. Morphine intraperitoneally was carried out for postoperative analgesia. Morris water maze tests were carried out to evaluate the cognitive impairment, while mRNA levels of neurotrophic factors (BDNF, NG) and neurodegenerative biomarker (VILIP-1) in hippocampus were tested by q-PCR. Transmission electron microscope was used to observe the axon degeneration in hippocampus. The levels of pro-inflammatory factors (TNF-α, IL-1ß, IL-6), the levels of anti-inflammatory factors (Ym, Arg-1, IL-10) and microglia proliferation marker cyclin D1 in hippocampus were measured to evaluate microglia polarization. Bioinformatics analysis was conducted to identify key exosomes while BV-2 microglia overexpressing exosome miR-124-3p was constructed to observe microglia polarization in vitro experiments. Exogenous miR-124-3p-loaded exosomes were injected into hippocampus in vivo. Postoperative pain induced by intramedullary fixation after tibial fracture was confirmed by decreased mechanical and thermal pain thresholds. Postoperative pain induced cognitive impairment, promoted axon demyelination, decreased BDNF, NG and increased VILIP-1 expressions in hippocampus. Postoperative pain also increased pro-inflammatory factors, cyclin D1 and decreased anti-inflammatory factors in hippocampus. However, these changes were all reversed by morphine analgesia. Bioinformatics analysis identified the critical role of exosome miR-124-3p in cognitive impairment, which was confirmed to be down-regulated in hippocampus of postoperative pain mice. BV-2 microglia overexpressing exosome miR-124-3p showed decreased pro-inflammatory factors, cyclin D1 and increased anti-inflammatory factors. In vivo, stereotactic injection of exogenous miR-124-3p into hippocampus decreased pro-inflammatory factors, cyclin D1 and increased anti-inflammatory factors. The cognitive impairment, axon demyelination, decreased BDNF, NG and increased VILIP-1 expressions in hippocampus were all alleviated by exogenous exosome miR-124-3p. Microglial exosome miR-124-3p in hippocampus alleviates cognitive impairment induced by postoperative pain through microglia polarization in elderly mice.

SIRT2 overexpression decreases remifentanil-stimulated post-surgical hyperalgesia via microglia.

Remifentanil (Remi)-induced hyperalgesia is a serious but common postoperative clinical problem. Sirtuin 2 (SIRT2) is essential in the pathogenetic mechanisms of several neurological disorders. However, whether SIRT2 contributes to the modulation of Remi-induced postsurgical hyperalgesia (POH) is unknown. Here, we investigated the regulatory potential of SIRT2 in Remi-stimulated POH. A rat Remi-stimulated POH model was built by infusing Remi in the surgical incision. Mechanical allodynia and thermal hyperalgesia were separately assessed by paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) measurements. SIRT2 and binding adaptor molecule 1 (Iba1) protein expressions and localization in spinal cord samples were detected by western blot and immunofluorescence. The results revealed SIRT2 downregulation in the spinal cord of rats with Remi-stimulated POH. Intrathecal administration of the overexpression plasmid harboring SIRT2 remarkably relieved mechanical allodynia, along with thermal hyperalgesia in the model animals. Iba1 amounts were increased upon intraoperative incision or Remi infusion, and this effect was more pronounced upon combining both treatments. Furthermore, SIRT2 overexpression suppressed microglia activation in the spinal cord of model animals, and starkly relieved incision- and/or Remi-associated pronociceptive processes as well as spinal microglia activation. SIRT2 elevation relieved Remi-associated POH, likely by suppressing spinal microglia activation. Thus, SIRT2 could be a potent target for treating neuropathic pain.

Dehydrocorydaline alleviates sleep deprivation-induced persistent postoperative pain in adolescent mice through inhibiting microglial P2Y12 receptor expression in the spinal cord.

During adolescence, a second period of central nervous system (CNS) plasticity that follows the fetal period, which involves sleep deprivation (SD), becomes apparent. SD during adolescence may result in abnormal development of neural circuits, causing imbalance in neuronal excitation and inhibition, which not only results in pain, but increases the chances of developing emotion disorders in adulthood, such as anxiety and depression. The quantity of surgeries during adolescence is also consistently on the rise, yet the impact and underlying mechanism of preoperative SD on postoperative pain remain unexplored. This study demonstrates that preoperative SD induces upregulation of the P2Y12 receptor, which is exclusively expressed on spinal microglia, and phosphorylation of its downstream signaling pathway p38Mitogen-activated protein/Nuclear transcription factor-κB (p38MAPK/NF-κB)in spinal microglia, thereby promoting microglia activation and microglial transformation into the proinflammatory M1 phenotype, resulting in increased expression of proinflammatory cytokines that exacerbate persisting postoperative incisional pain in adolescent mice. Both intrathecal minocycline (a microglia activation inhibitor) and MRS2395 (a P2Y12 receptor blocker) effectively suppressed microglial activation and proinflammatory cytokine expression. Interestingly, supplementation with dehydrocorydaline (DHC), an extract of Rhizoma Corydalis, inhibited the P2Y12/p38MAPK/NF-κB signaling pathway, microglia activation, and expression of pro-inflammatory cytokines in the model mice. Taken together, the results indicate that the P2Y12 receptor and microglial activation are important factors in persistent postoperative pain caused by preoperative SD in adolescent mice and that DHC has analgesic effects by acting on these targets.

NETO2-GluK2 interaction contributes to postoperative pain hypersensitivity through inducing PKCγ activation and synaptic incorporation of AMPA receptor GluR1 subunits in rat dorsal horn.

Important roles in the initiation and maintenance of postoperative pain are played by the functional control of kainate (KA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors in the rat dorsal horn (DH). However, the mechanisms underpinning the cross-talk between spinal KA and AMPA receptors in postoperative pain are poorly understood. We hypothesized that after the rat's plantar incision, the synaptic incorporation of AMPA receptor GluR1 subunits in the DH ipsilateral to the incision would increase due to the interaction between GluK2 and neuropilin tolloid-like 2 (NETO2). Our findings showed that incision stimuli caused severe pain responses, as measured by cumulative pain scores. GluK2-NETO2 but not GluK2-NETO1interaction was upregulated in ipsilateral dorsal horn neurons (DHNs) at 6 h post-incision. At 6 h post-incision, NETO2 small interfering ribonucleic acid (siRNA) intrathecal pretreatment increased mechanical withdrawal thresholds to von Freys and decreased ipsilateral paw cumulative pain scores. Further, PKCγactivation and synaptic abundance of GluK2 and GluR1 subunits in the ipsilateral DH were decreased by intrathecal pretreatment with NETO2 siRNA at 6 h post-incision. In conclusion, our findings imply that GluK2-NETO2 interaction could trigger PKCγactivation and the synaptic incorporation of AMPA receptor GluR1 subunits in rat DHs, which in turn led to the enhanced pain hypersensitivity after surgery. It sheds light on the interplay between KA and AMPA receptors in DHNs, which is thought to contribute to postoperative pain.

STING-IFN-I pathway relieves incision induced acute postoperative pain via inhibiting the neuroinflammation in dorsal root ganglion of rats.

BACKGROUND: The purpose of this study was to study the effect of STING-IFN-I pathway on incision induced postoperative pain in rats and its possible mechanisms. METHODS: The pain thresholds were evaluated by measuring the mechanical withdrawal threshold and the thermal withdrawal latency. The satellite glial cell and macrophage of DRG were analyzed. The expression of STING, IFN-a, P-P65, iNOS, TNF-α, IL-1ß and IL-6 in DRG was evaluated. RESULTS: The activation of STING-IFN-I pathway can reduce the mechanical hyperalgesia, thermal hyperalgesia, down-regulate the expression of P-P65, iNOS, TNF-α, IL-1ß and IL-6, and inhibit the activation of satellite glial cell and macrophage in DRG. CONCLUSIONS: The activation of STING-IFN-I pathway can alleviate incision induced acute postoperative pain by inhibiting the activation of satellite glial cell and macrophage, which reducing the corresponding neuroinflammation in DRG.

Role of magnesium-L-Threonate in alleviating skin/muscle incision and retraction induced mechanical allodynia and anxiodepressive-like behaviors in male rats.

Chronic postsurgical pain (CPSP) and its emotional comorbidities poses health burden to patients who have received the surgical treatment. However, its underlying mechanism remains unclear. Emerging studies indicate that magnesium deficiency is associated with neurological diseases, and magnesium supplement confers protection under these disease conditions. In this study, we examined the role and mechanism of magnesium deficiency in the pathology of surgery-induced allodynia and negative emotion using a rat model of skin/muscle incision and retraction (SMIR) and investigated the therapeutic effects of magnesium supplementation by oral magnesium-L-Threonate (L-TAMS) in SMIR-injured rats. In the SMIR model, rats developed mechanical allodynia and anxiodepressive-like behaviors. Further, SMIR caused microglia and astrocyte activation and enhanced expression of pro-inflammatory cytokine (TNF-α, IL-1ß and IL-6) in the anterior cingulate cortex (ACC). Importantly, magnesium ion (Mg2+) levels decreased in the serum and cerebrospinal fluid (CSF) of SMIR-injured rats, which exhibited high correlation with pain and emotion behavioral phenotypes in these rats. Repeated oral administration of L-TAMS increased serum and CSF levels of Mg2+ in SMIR-injured rats. Notably, L-TAMS administration reversed SMIR-induced mechanical allodynia and anxiodepressive-like behaviors but did not affect pain and emotional behaviors in sham rats. Moreover, L-TAMS administration suppressed SMIR-caused glial activation and proinflammatory cytokine expression in the ACC but had no such effect in sham rats. Together, our study demonstrates the contributing role of magnesium deficiency in the pathology of surgery-induced chronic pain and negative emotion. Moreover, we suggest that L-TAMS might be a novel approach to treat CPSP and its emotional comorbidities.

Hydrogen attenuates postoperative pain through Trx1/ASK1/MMP9 signaling pathway.

BACKGROUND: Postoperative pain is a serious clinical problem with a poorly understood mechanism, and lacks effective treatment. Hydrogen (H2) can reduce neuroinflammation; therefore, we hypothesize that H2 may alleviate postoperative pain, and aimed to investigate the underlying mechanism. METHODS: Mice were used to establish a postoperative pain model using plantar incision surgery. Mechanical allodynia was measured using the von Frey test. Cell signaling was assayed using gelatin zymography, western blotting, immunohistochemistry, and immunofluorescence staining. Animals or BV-2 cells were received with/without ASK1 and Trx1 inhibitors to investigate the effects of H2 on microglia. RESULTS: Plantar incision surgery increased MMP-9 activity and ASK1 phosphorylation in the spinal cord of mice. MMP-9 knockout and the ASK1 inhibitor, NQDI-1, attenuated postoperative pain. H2 increased the expression of Trx1 in the spinal cord and in BV-2 cells. H2 treatment mimicked NQDI1 in decreasing the phosphorylation of ASK1, p38 and JNK. It also reduced MMP-9 activity, downregulated pro-IL-1ß maturation and IBA-1 expression in the spinal cord of mice, and ameliorated postoperative pain. The protective effects of H2 were abolished by the Trx1 inhibitor, PX12. In vitro, in BV-2 cells, H2 also mimicked NQDI1 in inhibiting the phosphorylation of ASK1, p38, and JNK, and also reduced MMP-9 activity and decreased IBA-1 expression induced by LPS. The Trx1 inhibitor, PX12, abolished the protective effects of H2 in BV-2 cells. CONCLUSIONS: For the first time, the results of our study confirm that H2 can be used as a therapeutic agent to alleviate postoperative pain through the Trx1/ASK1/MMP9 signaling pathway. MMP-9 and ASK1 may be the target molecules for relieving postoperative pain.

Sestrin2 prevents neonatal incision pain and re-incision enhanced hyperalgesia in adult rats.

BACKGROUND: Improving the methods for recognizing pain is important for infants admitted to the neonatal intensive care unit. Sestrin2 is a novel stress-inducible protein with a neuroprotective role that functions as a molecular mediator of hormesis. Nevertheless, the role of sestrin2 in the pain process is still unclear. The following study examined the role of sestrin2 on mechanical hypersensitivity after pups incision, as well as enhanced pain hyperalgesia after adulthood re-incision in rats. METHODS: The experiment was divided into two parts: (1) studying the effect of sestrin2 in the neonatal incision; (2) studying the priming effect in adulthood re-incision. An animal model was established in seven-day-old rat pups with a right hind paw incision. Pups were intrathecally administrated rh-sestrin2 (exogenous sestrin2). Paw withdrawal threshold testing was performed to assay mechanical allodynia; tissue was analyzed in ex vivo using Western blot and immunofluorescence. SB203580 was further used to inhibit microglial function and evaluate the sex-dependent effect in adulthood. RESULTS: Sestrin2 expression increased transitorily in the spinal dorsal horn in pups after incision. Administration of rh-sestrin2 improved pups' mechanical hypersensitivity by regulating the AMPK/ERK pathway and alleviated re-incision-induced enhanced hyperalgesia in male and female adult rats. After administration of SB203580 in pups, the mechanical hyperalgesia following re-incision in adult rats was prevented in males but not females; however, the protective effect of SB203580 in males was counteracted by silencing sestrin2. CONCLUSIONS: These data suggest that sestrin2 prevents neonatal incision pain and re-incision enhanced hyperalgesia in adult rats. Moreover, microglia inhibition affects enhanced hyperalgesia only in adult males, which may be regulated through the sestrin2 mechanism. To sum up, these sestrin2 data may be a potential common molecular target for treating re-incision hyperalgesia in different sexes.

Pretreatment of the ROS Inhibitor Phenyl-N-tert-butylnitrone Alleviates Sleep Deprivation-Induced Hyperalgesia by Suppressing Microglia Activation and NLRP3 Inflammasome Activity in the Spinal Dorsal Cord.

Sleep deprivation, a common perioperative period health problem, causes ocular discomfort and affects postsurgical pain. However, the mechanism of sleep deprivation-induced increased pain sensitivity is elusive. This study aims to explore the role of ROS in sleep deprivation (SD)-induced hyperalgesia and the underlying mechanism. A 48-h continuous SD was performed prior to the hind paw incision pain modeling in mice. We measured ROS levels, microglial activation, DNA damage and protein levels of iNOS, NLRP3, p-P65 and P65 in mouse spinal dorsal cord. The involvement of ROS in SD-induced prolongation of postsurgical pain was further confirmed by intrathecal injection of ROS inhibitor, phenyl-N-tert-butylnitrone (PBN). Pretreatment of 48-h SD in mice significantly prolonged postsurgical pain recovery, manifesting as lowered paw withdrawal mechanical threshold and paw withdrawal thermal latency. It caused ROS increase and upregulation of iNOS on both Day 1 and 7 in mouse spinal dorsal cord. In addition, upregulation of NLRP3 and p-P65, microglial activation and DNA damage were observed in mice pretreated with 48-h SD prior to the incision. Notably, intrathecal injection of PBN significantly reversed the harmful effects of SD on postsurgical pain recovery, hyperalgesia, microglial activation and DNA damage via the NF-κB signaling pathway. Collectively, ROS increase is responsible for SD-induced hyperalgesia through activating microglial, triggering DNA damage and enhancing NLRP3 inflammasome activity in the spinal dorsal cord.

Thalamocortical circuits drive remifentanil-induced postoperative hyperalgesia.

Remifentanil-induced hyperalgesia (RIH) is a severe but common postoperative clinical problem with elusive underlying neural mechanisms. Here, we discovered that glutamatergic neurons in the thalamic ventral posterolateral nucleus (VPLGlu) exhibited significantly elevated burst firing accompanied by upregulation of Cav3.1 T-type calcium channel expression and function in RIH model mice. In addition, we identified a glutamatergic neuronal thalamocortical circuit in the VPL projecting to hindlimb primary somatosensory cortex glutamatergic neurons (S1HLGlu) that mediated RIH. In vivo calcium imaging and multi-tetrode recordings revealed heightened S1HLGlu neuronal activity during RIH. Moreover, preoperative suppression of Cav3.1-dependent burst firing in VPLGlu neurons or chemogenetic inhibition of VPLGlu neuronal terminals in the S1HL abolished the increased S1HLGlu neuronal excitability while alleviating RIH. Our findings suggest that remifentanil induces postoperative hyperalgesia by upregulating T-type calcium channel-dependent burst firing in VPLGlu neurons to activate S1HLGlu neurons, thus revealing an ion channel-mediated neural circuit basis for RIH that can guide analgesic development.