Quantitative assessment of tactile allodynia in the rat paw

High-Fat Diet-Induced Blood-Brain Barrier Dysfunction: Impact on Allodynia and Motor Coordination in Rats

The associations among increased pain sensitivity, obesity, and systemic inflammation have not been described as related to BBB dysfunctions. To analyze the metabolic, behavioral, and inflammatory effects of a high-fat diet (HFD) and ultrastructural modifications in brain regions, we used an in vivo experimental model. Adult male Wistar rats were randomly assigned to one of two conditions, an ad libitum control group or an HFD (60%)-fed group, for eight weeks. At the end of the protocol, glucose and insulin tolerance tests were performed. Additionally, we analyzed the response to a normally innocuous mechanical stimulus and changes in motor coordination. At the end of the protocol, HFD-fed rats presented increased HOMA-IR and metabolic syndrome (MetS) prevalence. HFD-fed rats also developed an increased nociceptive response to mechanical stimuli and neurological injury, resulting in impaired motor function. Hypothalamus and cerebellum neurons from HFD-fed rats presented with nuclear swelling, an absence of nucleoli, and karyolysis. These results reveal that HFD consumption affects vital brain structures such as the cerebellum, hippocampus, and hypothalamus. This, in turn, could be producing neuronal damage, impairing cellular communication, and consequently altering motricity and pain sensitivity. Although direct evidence of a causal link between BBB dysfunction and sensory-motor changes was not observed, understanding the association uncovered in this study could lead to targeted therapeutic strategies.

The Effect of Spinal Cord Stimulation on Spinal Dorsal Horn Lipid Expression in Experimental Painful Diabetic Polyneuropathy: A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Imaging Study

OBJECTIVES

Diabetes-induced peripheral nerve fiber damage can cause painful diabetic polyneuropathy (PDPN), induced by central sensitization through proinflammatory processes in the spinal dorsal horn. Disturbances in spinal dorsal horn lipid metabolism play a major role in proinflammatory regulation. Conventional (Con)-spinal cord stimulation (SCS) is an alternative treatment for pain relief in PDPN, whereas differential target multiplexed (DTM)-SCS could be more effective than Con-SCS, specifically targeting the spinal inflammatory response. We hypothesize that Con- and DTM-SCS differentially affect lipid metabolism in the spinal cord of PDPN animals. To study pain relief mechanisms, we analyzed lipid expression in the spinal dorsal horn using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry imaging (MSI).

MATERIAL AND METHODS

Diabetes was induced through streptozotocin (STZ) injection in 28 rats, of which 12 developed PDPN. These and four nondiabetic animals (sham STZ) were implanted with a quadripolar lead and stimulated with Con-, DTM-, or Sham-SCS for 48 hours. Mechanical sensitivity was assessed using Von Frey filaments after 24 and 48 hours. After 48 hours of SCS, the spinal cord was collected, and lipids were analyzed using MALDI-TOF MSI.

RESULTS

STZ-induced hypersensitivity in the hind paws was reduced by Con- and DTM-SCS. PDPN induction decreased the expression of a glycosphingolipid in laminae 3 of the spinal dorsal horn. After 48 hours of Con- and DTM-SCS, expression levels of several lipids in the spinal dorsal horn decreased, including (HexCer 36:1;O, 40:1;O3), diacylglycerophosphocholines (PC 36:1, 38:6, 40:5), and diacylglycerophosphoserines (PS 36:4).

CONCLUSIONS

Both Con- and DTM-SCS provide pain relief and decrease spinal dorsal horn lipid expression of PDPN animals, highlighting the complex effects of SCS on the spinal cord physiology. STZ-induced PDPN has a limited effect on lipid expression in the spinal dorsal horn.

Effects of Electroacupuncture at Varied Frequencies on Analgesia and Mechanisms in Sciatic Nerve Cuffing-Induced Neuropathic Pain Mice

Addressing the intricate challenge of chronic neuropathic pain has significant implications for the physical and psychological well-being of patients, given its enduring nature. In contrast to opioids, electroacupuncture (EA) may potentially provide a safer and more efficacious therapeutic alternative. Our objective is to investigate the distinct analgesic effects and potential mechanisms of EA at frequencies of 2 Hz, 100 Hz, and 18 kHz in order to establish more precise frequency selection criteria for clinical interventions. Analgesic efficacy was evaluated through the measurement of mice's mechanical and thermal pain thresholds. Spinal cord inflammatory cytokines and neuropeptides were quantified via Quantitative Real-time PCR (qRT-PCR), Western blot, and immunofluorescence. Additionally, RNA sequencing (RNA-Seq) was conducted on the spinal cord from mice in the 18 kHz EA group for comprehensive transcriptomic analysis. The analgesic effect of EA on neuropathic pain in mice was frequency-dependent. Stimulation at 18 kHz provided superior and prolonged relief compared to 2 Hz and 100 Hz. Our research suggests that EA at frequencies of 2 Hz, 100 Hz, and 18 kHz significantly reduce the release of inflammatory cytokines. The analgesic effects of 2 Hz and 100 Hz stimulation are due to frequency-dependent regulation of opioid release in the spinal cord. Furthermore, 18 kHz stimulation has been shown to reduce spinal neuronal excitability by modulating the serotonergic pathway and downstream receptors in the spinal cord to alleviate neuropathic pain.

Small-molecule natural product sophoricoside reduces peripheral neuropathic pain via directly blocking of NaV1.6 in dorsal root ganglion nociceptive neurons

Peripheral neuropathic pain poses a significant global health challenge. Current drugs for peripheral neuropathic pain often fall short in efficacy or come with severe side effects, emphasizing the critical need for the development of highly effective and well-tolerated alternatives. Sophoricoside (SOP) is a nature product-derived isoflavone that possesses various pharmacological effects on inflammatory and neuropathy diseases. Here, in this study, analgesic effect was investigated by intrathecally administration of SOP/vehicle to spared nerve injury (SNI) or paclitaxel-induced peripheral neuropathic pain (PINP) rodent models, and mechanical allodynia was measured in Von Frey tests. Ipsilateral L4-L6 dorsal root ganglia (DRG) were used for protein expression. In silico molecular docking analysis was applied for assessing compound-target binding affinity. Primary cultured DRG neurons were utilized to investigate SOP's effect on veratridine-triggered nociceptor activities and its selective inhibition of voltage-gated sodium channels subtype 1.6 (NaV1.6). The results showed SOP treatment alleviated mechanical allodynia in SNI and PINP rodent models (paw withdrawal threshold after 1 h of injection: SNI-vehicle: 1.385 ± 0.338 g; SNI-SOP: 9.963 ± 2.029 g, P < 0.001; PINP-vehicle: 5.040 ± 0.985 g; PINP-SOP: 8.287 ± 3.812 g, P = 0.004). SOP presented effects on both inhibiting veratridine-triggered nociceptor activities (oscillatory population: vehicle: 39.9 ± 7.3%; SOP: 30.7 ± 9.8%, P = 0.021) and selectively blocking NaV1.6 in DRG sensory neurons. Molecular docking analysis indicated direct binding between SOP and NaV1.6, leading to its endocytosis in DRG Sensory Neurons. In conclusion, SOP alleviated nociceptive allodynia induced by peripheral nerve injury via selectively blocking of NaV1.6 in DRG nociceptive neurons. we highlight its potential as an analgesic and elucidate its mechanism involving NaV1.6 endocytosis. This research opens avenues for exploring the analgesic effects of SOP and its potential impact on neuropathic pain therapy.

Spinal lumbar Urocortin 3-expressing neurons are associated with both scratching and Compound 48/80-induced sensations

ABSTRACT

Urocortin 3 is a neuropeptide that belongs to the corticotropin-releasing hormone family and is involved in mechanosensation and stress regulation. In this study, we show that Urocortin 3 marks a population of excitatory neurons in the mouse spinal cord, divided into 2 nonoverlapping subpopulations expressing protein kinase C gamma or calretinin/calbindin 2, populations previously associated with mechanosensation. Electrophysiological experiments demonstrated that lumbar spinal Urocortin 3 neurons receive both glycinergic and GABAergic local tonic inhibition, and monosynaptic inputs from both Aβ and C fibers, which could be confirmed by retrograde trans-synaptic rabies tracing. Furthermore, fos analyses showed that subpopulations of lumbar Urocortin 3 neurons are activated by artificial scratching or Compound 48/80-induced sensations. Chemogenetic activation of lumbar Urocortin 3-Cre neurons evoked a targeted biting/licking behavior towards the corresponding dermatome and chemogenetic inhibition decreased Compound 48/80-induced behavior. Hence, spinal lumbar Urocortin 3 neurons represent a mechanically associated population with roles in both scratching and Compound 48/80-induced sensations.

Cannabinoid CB2 receptors enhance high-fat diet evoked peripheral neuroinflammation

It is known that the cannabinoid type 2 (CB2) receptor has an anti-inflammatory role. Therefore, animals without CB2 receptors show enhanced inflammation and pain in the model of chronic pain, e.g., neuropathic pain. We previously proposed the upregulated leptin signaling at the peripheral nerve as one of the underlying molecular mechanisms of pain exacerbation in nerve-injured CB2 knockouts, as they displayed robust upregulation of leptin receptors and leptin signaling in the peripheral nerve. Due to these past results, we hypothesized that CB2 receptor deficiency might also modify the peripheral neuroinflammation led by chronic exposure to a high-fat diet (HFD). Interestingly, CB2 knockout animals showed significant resistance to HFD-induced neuroinflammation. Namely, 5-week feeding of HFD induced substantial hypersensitivity in WT animals, while tactile sensitivity of HFD-fed CB2 knockouts remained intact. HFD-fed WT animals also displayed the robust upregulation of chemokine CXCR4 expression with increased macrophage infiltration, which was never observed in HFD-fed CB2 knockout mice. Moreover, 5-week HFD exposure led significant increase of CD11b+Ly6G-Ly6Chigh cells and a decrease of CD11b+Ly6G+Ly6Clow cells in the spleen of WT animals, which was also not found in either HFD-fed CB2 knockouts or standard diet-fed WT and CB2 animals. Together with past reports, these results suggest that CB2 receptors might have a double-sided regulatory role in the context of inflammation development or, more widely, immune system regulation. We propose that CB2 signaling is not always anti-inflammatory and could take a pro-inflammatory role depending on the cause of the inflammation.

ApoA-I binding protein (AIBP) regulates transient receptor potential vanilloid 1 (TRPV1) activity in rat dorsal root ganglion neurons by selective disruption of toll-like receptor 4 (TLR4)-lipid rafts

Toll-like receptor 4 (TLR4) and the transient receptor potential vanilloid subtype 1 (TRPV1) are both upregulated and play key roles in the induction and expression of paclitaxel-related chemotherapy-induced peripheral neuropathy (CIPN). Using Apolipoprotein A-I binding protein, non-specific cholesterol depletion, TLR4 mis-sense rats and a TLR4 inhibitor, we demonstrate that co-localization of TRPV1 with TLR4 to cholesterol-rich lipid membrane rafts in nociceptors is essential for its normal activation as well as for its exaggerated activation that underlies the development and expression of CIPN. The findings suggest that TLR4-lipid rafts may have an essential role in numerous neuroinflammatory and neuropathic pain conditions. This mechanism is also generalized to female rats for the first time.

Chimeras Derived from a P2Y14 Receptor Antagonist and UDP-Sugar Agonists for Potential Treatment of Inflammation

Tethered glycoconjugates of a naphthalene- and piperidine-containing antagonist of the P2Y14 receptor (PPTN) were synthesized, and their nM receptor binding affinity was determined using a fluorescent tracer in hP2Y14R-expressing whole CHO cells. The rationale for preparing mono- and disaccharide conjugates of the antagonists was to explore the receptor binding site, which we know recognizes a glucose moiety on the native agonist (UDP-glucose), as well as enhance aqueous solubility and pharmacokinetics, including kidney excretion to potentially counteract sterile inflammation. Glycoconjugates with varied linker length, including PEG chains, were compared in hP2Y14R binding, suggesting that an optimal affinity (IC50, nM) in the piperidine series was achieved for triazolyl N-linked glucose conjugates having one (8a, MRS4872, 3.21) or two (7a, MRS4865, 2.40) methylene spacers. In comparison of different carbohydrate conjugates lacking a piperidine moiety but containing triazole spacers, optimal hP2Y14R affinity (IC50, nM) was achieved with N-linked glycosides of fucose 10f (6.19) and lactose 10h (1.88), and C-linked glucose 11a (5.30). Selected compounds were examined in mouse models of conditions known to be ameliorated by P2Y14R antagonists. Two glycoconjugates that lacked a piperidine moiety, N-linked glucose derivative 10a and the isomeric C-linked glucose derivative 11a, were protective in a mouse model of allergic asthma. Piperidine-containing glucose conjugate 7a of intermediate linker length and corresponding glucuronide 7b (MRS4866) protected against neuropathic pain. Thus, glycoconjugation of a known antagonist scaffold has produced less hydrophobic P2Y14R antagonists having substantial in vitro and in vivo activity.

A RANKL-UCHL1-sCD13 negative feedback loop limits osteoclastogenesis in subchondral bone to prevent osteoarthritis progression

Abnormal subchondral bone remodeling plays a pivotal role in the progression of osteoarthritis (OA). Here, we analyzed subchondral bone samples from OA patients and observed a significant upregulation of ubiquitin carboxy-terminal hydrolase L1 (UCHL1) specifically in subchondral bone osteoclasts. Notably, we found a strong correlation between UCHL1 expression and osteoclast activity in the subchondral bone during OA progression in both human and murine models. Conditional UCHL1 deletion in osteoclast precursors exacerbated OA progression, while its overexpression, mediated by adeno-associated virus 9, alleviated this process in male mice. Mechanistically, RANKL stimulates UCHL1 expression in osteoclast precursors, subsequently stabilizing CD13, augmenting soluble CD13 (sCD13) release, and triggering an autocrine inhibitory effect on the MAPK pathway, thereby suppressing osteoclast formation. These findings unveil a previously unidentified negative feedback loop, RANKL-UCHL1-sCD13, that modulates osteoclast formation and presents a potential therapeutic target for OA.

Wnt5a/Ryk signaling contributes to bone cancer pain by sensitizing the peripheral nociceptors through JNK-mediated TRPV1 pathway in rats

ABSTRACT

Treating bone cancer pain (BCP) continues to be a clinical challenge, and the underlying mechanisms of BCP remain elusive. This study reports that Wnt5a/Ryk signaling in the dorsal root ganglion neurons is critical to the development of BCP. Tibia bone cavity tumor cell implantation produces spontaneous and evoked behaviorally expressed pain as well as ectopic sprouting and activity of Wnt5a/Ryk signaling in the neural soma and peripheral terminals and the tumor-affected bone tissues. Intraplantar, intratibial, or intrathecal injection of Wnt5a/Ryk signaling blockers significantly suppresses the painful symptoms. Peripheral injection of exogenous Wnt5a in naïve rats produces pain, and the dorsal root ganglion neurons become more sensitive to Wnt5a. Wnt5a/Ryk signaling activation increases intracellular calcium response and expression of transient receptors potential vanilloid type-1 and regulates capsaicin-induced intracellular calcium response. Blocking Ryk receptor activation suppresses Wnt5a-induced mechanical allodynia and thermal hyperalgesia. Wnt5a facilitation of transient receptors potential vanilloid type-1 sensitization is blocked by inhibiting c-Jun N-terminal kinase activation. These findings indicate a critical peripheral mechanism of Wnt5a/Ryk signaling underlying the pathogenesis of BCP and suggest that targeting Wnt5a/Ryk in the primary sensory neurons and the tumor-invasive area may be an effective approach for the prevention and treatment of BCP.

Cortical kappa opioid receptors integrate negative affect and sleep disturbance

Sleep disruption and negative affect are attendant features of many psychiatric and neurological conditions that are often co-morbid including major depressive disorder, generalized anxiety disorder and chronic pain. Whether there is a causal relationship between negative affect and sleep disruption remains unclear. We therefore asked if mechanisms promoting negative affect can disrupt sleep and whether inhibition of pathological negative affect can normalize disrupted sleep. Signaling at the kappa opioid receptor (KOR) elicits dysphoria in humans and aversive conditioning in animals. We tested the possibility that (a) increased KOR signaling in the anterior cingulate cortex (ACC), a brain region associated with negative emotions, would be sufficient to promote both aversiveness and sleep disruption and (b) inhibition of KOR signaling would normalize pathological negative affect and sleep disruption induced by chronic pain. Chemogenetic Gi-mediated inhibition of KOR-expressing ACC neurons produced conditioned place aversion (CPA) as well as sleep fragmentation in naïve mice. CRISPR/Cas9 editing of ACC KOR normalized both the negative affect and sleep disruption elicited by pathological chronic pain while maintaining the physiologically critical sensory features of pain. These findings suggest therapeutic utility of KOR antagonists for treatment of disease conditions that are associated with both negative affect and sleep disturbances.

The single-cell transcriptomic atlas iPain identifies senescence of nociceptors as a therapeutical target for chronic pain treatment

Chronic pain remains a significant medical challenge with complex underlying mechanisms, and an urgent need for new treatments. Our research built and utilized the iPain single-cell atlas to study chronic pain progression in dorsal root and trigeminal ganglia. We discovered that senescence of a small subset of pain-sensing neurons may be a driver of chronic pain. This mechanism was observed in animal models after nerve injury and in human patients diagnosed with chronic pain or diabetic painful neuropathy. Notably, treatment with senolytics, drugs that remove senescent cells, reversed pain symptoms in mice post-injury. These findings highlight the role of cellular senescence in chronic pain development, demonstrate the therapeutic potential of senolytic treatments, and underscore the value of the iPain atlas for future pain research.

Skin keratinocyte-derived SIRT1 and BDNF modulate mechanical allodynia in mouse models of diabetic neuropathy

Diabetic neuropathy is a debilitating disorder characterized by spontaneous and mechanical allodynia. The role of skin mechanoreceptors in the development of mechanical allodynia is unclear. We discovered that mice with diabetic neuropathy had decreased sirtuin 1 (SIRT1) deacetylase activity in foot skin, leading to reduced expression of brain-derived neurotrophic factor (BDNF) and subsequent loss of innervation in Meissner corpuscles, a mechanoreceptor expressing the BDNF receptor TrkB. When SIRT1 was depleted from skin, the mechanical allodynia worsened in diabetic neuropathy mice, likely due to retrograde degeneration of the Meissner-corpuscle innervating Aβ axons and aberrant formation of Meissner corpuscles which may have increased the mechanosensitivity. The same phenomenon was also noted in skin-keratinocyte specific BDNF knockout mice. Furthermore, overexpression of SIRT1 in skin induced Meissner corpuscle reinnervation and regeneration, resulting in significant improvement of diabetic mechanical allodynia. Overall, the findings suggested that skin-derived SIRT1 and BDNF function in the same pathway in skin sensory apparatus regeneration and highlighted the potential of developing topical SIRT1-activating compounds as a novel treatment for diabetic mechanical allodynia.

Piezo2 voltage-block regulates mechanical pain sensitivity

PIEZO2 is a trimeric mechanically-gated ion channel expressed by most sensory neurons in the dorsal root ganglia. Mechanosensitive PIEZO2 channels are also genetically required for normal touch sensation in both mice and humans. We previously showed that PIEZO2 channels are also strongly modulated by membrane voltage. Specifically, it is only at very positive voltages that all channels are available for opening by mechanical force. Conversely, most PIEZO2 channels are blocked at normal negative resting membrane potentials. The physiological function of this unusual biophysical property of PIEZO2 channels, however, remained unknown. We characterized the biophysical properties of three PIEZO2 ion channel mutations at an evolutionarily conserved arginine (R2756). Using genome engineering in mice we generated Piezo2R2756H/R2756H and Piezo2R2756K/R2756K knock-in mice to characterize the physiological consequences of altering PIEZO2 voltage sensitivity in vivo. We measured endogenous mechanosensitive currents in sensory neurons isolated from the dorsal root ganglia and characterized mechanoreceptor and nociceptor function using electrophysiology. Mice were also assessed behaviourally and morphologically. Mutations at the conserved Arginine (R2756) dramatically changed the biophysical properties of the channel relieving voltage block and lowering mechanical thresholds for channel activation. Piezo2R2756H/R2756H and Piezo2R2756K/R2756K knock-in mice that were homozygous for gain-of-function mutations were viable and were tested for sensory changes. Surprisingly, mechanosensitive currents in nociceptors, neurons that detect noxious mechanical stimuli, were substantially sensitized in Piezo2 knock-in mice, but mechanosensitive currents in most mechanoreceptors that underlie touch sensation were only mildly affected by the same mutations. Single-unit electrophysiological recordings from sensory neurons innervating the glabrous skin revealed that rapidly-adapting mechanoreceptors that innervate Meissner's corpuscles exhibited slightly decreased mechanical thresholds in Piezo2 knock-in mice. Consistent with measurements of mechanically activated currents in isolated sensory neurons essentially all cutaneous nociceptors, both fast conducting Aδ-mechanonociceptors and unmyelinated C-fibre nociceptors were substantially more sensitive to mechanical stimuli and indeed acquired receptor properties similar to ultrasensitive touch receptors in Piezo2 knock-in mice. Mechanical stimuli also induced enhanced ongoing activity in cutaneous nociceptors in Piezo2 knock-in mice and hyper-sensitive PIEZO2 channels were sufficient alone to drive ongoing activity, even in isolated nociceptive neurons. Consistently, Piezo2 knock-in mice showed substantial behavioural hypersensitivity to noxious mechanical stimuli. Our data indicate that ongoing activity and sensitization of nociceptors, phenomena commonly found in human chronic pain syndromes, can be driven by relieving the voltage-block of PIEZO2 ion channels. Indeed, membrane depolarization caused by multiple noxious stimuli may sensitize nociceptors by relieving voltage-block of PIEZO2 channels.

Effects of immunosuppression after limb fracture in mice on nociceptive, cognitive, and anxiety-related outcomes

Introduction

Chronic pain is a common and problematic consequence of injuries with few proven methods for prevention or treatment. In addition to pain, functional limitations and neuropsychiatric changes such as cognitive impairment and anxiety worsen outcomes.

Objectives

To determine whether inhibiting activation of the adaptive immune response after limb fracture would reduce pain, functional loss, memory changes, and anxiety.

Methods

These experiments used a murine tibial fracture/cast immobilization model that develops these adverse outcomes. Adaptive immunity was blocked using the immunosuppressant FK506 beginning at the time of fracture.

Results

The administration of FK506 reduced mechanical allodynia and hind limb unweighting for weeks after cast removal as well as nonevoked pain measures. Fracture was associated with working memory loss in the Y-maze assay in vehicle- but not FK506-treated mice. Object recognition memory was not improved with FK506 after fracture. Also, vehicle- but not FK506-treated mice developed an anxiety phenotype. Impaired running wheel performance after cast removal over the following 2 weeks was not improved with FK506 administration. In addition, FK506 treatment blocked Immunoglobulin M (IgM) accumulation in the skin of the fractured limbs, and hippocampal enhancement of matrix metalloproteinase-8 expression, a metalloproteinase associated with neuroplastic changes after injuries, was completely blocked.

Conclusion

Taken together, our results show that blocking the adaptive immune response after limb trauma reduces the severity of nociceptive and biological changes. The same treatment may reduce the adverse consequences of anxiety and memory deficits using some measures, but other measures of memory are not affected, and activity is not enhanced.

CARTp/GPR160 mediates behavioral hypersensitivities in mice through NOD2

ABSTRACT

Neuropathic pain is a debilitating chronic condition that remains difficult to treat. More efficacious and safer therapeutics are needed. A potential target for therapeutic intervention recently identified by our group is the G-protein coupled receptor 160 (GPR160) and the cocaine- and amphetamine-regulated transcript peptide (CARTp) as a ligand for GPR160. Intrathecal administration of CARTp in rodents causes GPR160-dependent behavioral hypersensitivities. However, the molecular and biochemical mechanisms underpinning GPR160/CARTp-induced behavioral hypersensitivities in the spinal cord remain poorly understood. Therefore, we performed an unbiased RNA transcriptomics screen of dorsal horn spinal cord (DH-SC) tissues harvested at the time of peak CARTp-induced hypersensitivities and identified nucleotide-binding oligomerization domain-containing protein 2 (Nod2) as a gene that is significantly upregulated. Nucleotide-binding oligomerization domain-containing protein 2 is a cytosolic pattern-recognition receptor involved in activating the immune system in response to bacterial pathogens. While NOD2 is well studied under pathogenic conditions, the role of NOD2-mediated responses in nonpathogenic settings is still not well characterized. Genetic and pharmacological approaches reveal that CARTp-induced behavioral hypersensitivities are driven by NOD2, with co-immunoprecipitation studies indicating an interaction between GPR160 and NOD2. Cocaine- and amphetamine-regulated transcript peptide-induced behavioral hypersensitivities are independent of receptor-interacting protein kinase 2 (RIPK2), a common adaptor protein to NOD2. Immunofluorescence studies found NOD2 co-expressed with endothelial cells rather than glial cells, implicating potential roles for CARTp/NOD2 signaling in these cells. While these findings are based only on studies with male mice, our results identify a novel pathway by which CARTp causes behavioral hypersensitivities in the DH-SC through NOD2 and highlights the importance of NOD2-mediated responses in nonpathogenic settings.

Hemoglobin α-derived peptides VD-hemopressin (α) and RVD-hemopressin (α) are involved in electroacupuncture inhibition of chronic pain

Introduction

Knee osteoarthritis (KOA) is a chronic degenerative bone metabolic disease that primarily affects older adults, leading to chronic pain and disability that affect patients' daily activities. Electroacupuncture (EA) is a commonly used method for the treatment of chronic pain in clinical practice. Previous studies indicate that the endocannabinoid system is involved in EA analgesia, but whether endocannabinopeptide VD-hemopressin (α) and RVD-hemopressin (α) derived from hemoglobin chains are involved in EA analgesia is unclear.

Methods

RNA-seq technology was used to screen which genes involved in EA analgesia. The expression of hemoglobin α chain and 26S proteasome were determined by Western blotting. The level of VD-hemopressin (α) and RVD-hemopressin (α) were measured by UPLC-MS/MS. Microinjection VD-Hemopressin (α), RVD-Hemopressin (α) and 26S proteasome inhibitor MG-132 into vlPAG, then observe mechanical and thermal pain thresholds.

Results

Therefore, we used RNA-seq to obtain differentially expressed genes Hba-a1 and Hba-a2 involved in EA analgesia in the periaqueductal gray (PAG), which were translated into the hemoglobin α chain. EA significantly increased the expression of the hemoglobin α chain and the level of hemopressin (α) and RVD-hemopressin (α). Microinjection of VD-hemopressin (α) and RVD-hemopressin (α) into the ventrolateral periaqueductal gray (vlPAG) mimicked the analgesic effect of EA, while CB1 receptor antagonist AM251 reversed this effect. EA significantly increased the expression of 26S proteasome in KOA mice. Microinjection of 26S proteasome inhibitor MG132 before EA prevented both the anti-allodynic effect and upregulation of the concentration of RVD-hemopressin (α) by EA treatment and upregulated the expression of the hemoglobin α chain.

Discussion

Our data suggest that EA upregulated the concentration of VD-hemopressin (α) and RVD-hemopressin (α) through enhancement of the hemoglobin α chain degradation by 26S proteasome in the PAG, then activated the CB1 receptor, thereby exerting inhibition of chronic pain in a mouse model of KOA. These results provide new insights into the EA analgesic mechanisms and reveal possible targets for EA treatment of chronic pain.

Effect of 28 days treatment of baricitinib on mechanical allodynia, osteopenia, and loss of nerve fibers in an experimental model of type-1 diabetes mellitus

BACKGROUND

Type-1 diabetes mellitus (T1DM) is associated with numerous health problems, including peripheral neuropathy, osteoporosis, and bone denervation, all of which diminish quality of life. However, there are relatively few therapies to treat these T1DM-related complications. Recent studies have shown that Janus kinase (JAK) inhibitors reverse aging- and rheumatoid arthritis-induced bone loss and reduce pain associated with peripheral nerve injuries, and rheumatoid arthritis. Thus, we assessed whether a JAK1/JAK2 inhibitor, baricitinib, ameliorates mechanical pain sensitivity (a measure of peripheral neuropathy), osteoporosis, and bone denervation in the femur of mice with T1DM.

METHODS

Female ICR mice (13 weeks old) received five daily administrations of streptozotocin (ip, 50 mg/kg) to induce T1DM. At thirty-one weeks of age, mice were treated with baricitinib (po; 40 mg/kg/bid; for 28 days) or vehicle. Mechanical sensitivity was evaluated at 30, 33, and 35 weeks of age on the plantar surface of the right hind paw. At the end of the treatment, mice were sacrificed, and lower extremities were harvested for microcomputed tomography and immunohistochemistry analyses.

RESULTS

Mice with T1DM exhibited greater blood glucose levels, hind paw mechanical hypersensitivity, trabecular bone loss, and decreased density of calcitonin gene-related peptide-positive and tyrosine hydroxylase-positive axons within the marrow of the femoral neck compared to control mice. Baricitinib treatment significantly reduced mechanical hypersensitivity and ameliorated sensory and sympathetic denervation at the femoral neck, but it did not reverse trabecular bone loss.

CONCLUSIONS

Our findings suggest that baricitinib may represent a new therapeutic alternative to treat T1DM-induced peripheral neuropathy and bone denervation.

Improved therapeutic index of the liposomal docetaxel-glutathione prepared by active click loading

The clinical usage of docetaxel (DTX) is severely hindered by the dose-limiting neutropenia and peripheral neurotoxicity of polysorbate 80-solubilized DTX injection, and there are no alternative formulations until now. In this study, we developed a new liposomal formulation of DTX to reduce its toxicities, accompanying with the greatly improved antitumor activity. The DTX was encapsulated into liposomes in the form of hydrophilic glutathione (GSH)-conjugated prodrugs using a click drug loading method, which achieved a high encapsulation efficiency (∼95 %) and loading capacity (∼30 % wt). The resulting liposomal DTX-GSH provided a sustained and efficient DTX release (∼50 % within 48 h) in plasma, resulting in a greatly improved antitumor activities as compared with that of polysorbate 80-solubilized DTX injection in the subcutaneous and orthotopic 4T1 breast tumor bearing mice. Even large tumors > 500 mm3 could be effectively inhibited and shrunk after the administration of liposomal DTX-GSH. More importantly, the liposomal DTX-GSH significantly decreased the neutropenia and peripheral neurotoxicity as compared with that of polysorbate 80-solubilized DTX injection at the equivalent dose. These data suggested that the liposomal DTX-GSH might become a superior alternative formulation to the commercial DTX injection.

Acetaminophen effects upon formalin-evoked flinching, postformalin, and postincisional allodynia and conditioned place preference

Introduction

We explored in mice, the analgesic, tolerance, dependency, and rewarding effects of systemic acetaminophen (APAP).

Methods

Studies employed adult mice (C57Bl6). (1) Intraplantar formalin flinching + post formalin allodynia. Mice were given intraperitoneal APAP in a DMSO (5%)/Tween 80 (5%) or a water-based formulation before formalin flinching on day 1 and tactile thresholds assessed before and after APAP at day 12. (2) Paw incision. At 24 hours and 8 days after hind paw incision in male mice, effects of intraperitoneal APAP on tactile allodynia were assessed. (3) Repeated delivery. Mice received daily (4 days) analgesic doses of APAP or vehicle and tested upon formalin flinching on day 5. (4) Conditioned place preference. For 3 consecutive days, vehicle was given in the morning in either of 2 chambers and in each afternoon, an analgesic dose of morphine or APAP in the other chamber. On days 5 and 10, animals were allowed to select a "preferred" chamber.

Results

Formalin in male mice resulted in biphasic flinching and an enduring postformalin tactile allodynia. Acetaminophen dose dependently decreased phase 2 flinching, and reversed allodynia was observed postflinching. At a comparable APAP dose, female mice showed similarly reduced phase 2 flinching. Incision allodynia was transiently reversed by APAP. Repeated APAP delivery showed no loss of effect after sequential injections or signs of withdrawal. Morphine, but not APAP or vehicle, resulted in robust place preference.

Conclusions

APAP decreased flinching and allodynia observed following formalin and paw incision and an absence of tolerance, dependence, or rewarding properties.

Downregulation of chloride voltage-gated channel 7 contributes to hyperalgesia following spared nerve injury

Alterations in anion balance potential, along with the involvement of cation-chloride cotransporters, play pivotal roles in the development of hyperalgesia after peripheral nerve injury. Chloride voltage-gated channel seven (CLCN7) is the predominant member of the CLC protein family. Investigations on CLCN7 have focused primarily on its involvement in osteosclerosis and lysosomal storage disorders; nevertheless, its contribution to neuropathic pain has not been determined. In this investigation, we noted high expression of CLCN7 in neurons situated within the spinal dorsal horns and dorsal root ganglions (DRGs). Immunofluorescence analysis revealed that CLCN7 was predominantly distributed among IB4-positive and CGRP-positive neurons. Furthermore, the expression of CLCN7 was observed to be mainly reduced in neurons within the spinal dorsal horns and in small- and medium-sized neurons located in the DRGs of spared nerve injury mice. Knockdown of CLCN7 via siRNA in the DRGs resulted in increased mechanical and thermal hyperalgesia in naïve mice. Furthermore, the excitability of cultured DRG neurons in vitro was augmented upon treatment with CLCN7 siRNA. These findings suggested that CLCN7 downregulation following SNI was crucial for the manifestation of mechanical and thermal hyperalgesia, highlighting potential targeting strategies for treating neuropathic pain.

Sigma-1 receptor targeting inhibits connexin 43 based intercellular communication in chronic neuropathic pain

BACKGROUND AND OBJECTIVE

Neuropathic pain is a chronic condition characterized by aberrant signaling within the somatosensory system, affecting millions of people worldwide with limited treatment options. Herein, we aim at investigating the potential of a sigma-1 receptor (σ1R) antagonist in managing neuropathic pain.

METHODS

A Chronic Constriction Injury (CCI) model was used to induce neuropathic pain. The potential of (+)-MR200 was evaluated following daily subcutaneous injections of the compound. Its mechanism of action was confirmed by administration of a well-known σ1R agonist, PRE084.

RESULTS

(+)-MR200 demonstrated efficacy in protecting neurons from damage and alleviating pain hypersensitivity in CCI model. Our results suggest that (+)-MR200 reduced the activation of astrocytes and microglia, cells known to contribute to the neuroinflammatory process, suggesting that (+)-MR200 may not only address pain symptoms but also tackle the underlying cellular mechanism involved. Furthermore, (+)-MR200 treatment normalized levels of the gap junction (GJ)-forming protein connexin 43 (Cx43), suggesting a reduction in harmful intercellular communication that could fuel the chronicity of pain.

CONCLUSIONS

This approach could offer a neuroprotective strategy for managing neuropathic pain, addressing both pain symptoms and cellular processes driving the condition. Understanding the dynamics of σ1R expression and function in neuropathic pain is crucial for clinical intervention.

STING recognition of viral dsDNA by nociceptors mediates pain in mice

Pain is often one of the initial indicators of a viral infection, yet our understanding of how viruses induce pain is limited. Immune cells typically recognize viral nucleic acids, which activate viral receptors and signaling, leading to immunity. Interestingly, these viral receptors and signals are also present in nociceptors and are associated with pain. Here, we investigate the response of nociceptors to nucleic acids during viral infections, specifically focusing on the role of the viral signal, Stimulator of Interferon Genes (STING). Our research shows that cytosolic double-stranded DNA (dsDNA) from viruses, like herpes simplex virus 1 (HSV-1), triggers pain responses through STING expression in nociceptors. In addition, STING agonists alone can elicit pain responses. Notably, these responses involve the direct activation of STING in nociceptors through TRPV1. We also provided a proof-of-concept showing that STING and TRPV1 significantly contribute to the mechanical hypersensitivity induced by HSV-1 infection. These findings suggest that STING could be a potential therapeutic target for relieving pain during viral infections.

The effect of female breast surface area on skin stiffness and tactile sensitivity at rest and following exercise in the heat

Female development includes significant morphological changes across the breast. Yet, whether differences in breast surface area (BrSA) modify breast skin stiffness and tactile sensitivity at rest and after exercise in the heat remain unclear. We investigated the relationship between BrSA and skin stiffness and tactile sensitivity in 20 young to middle-aged women (27 ± 8 years of age) of varying breast sizes (BrSA range: 147-502 cm2) at rest and after a submaximal run in a warm climatic chamber (32 C ${\mathrm{C}}$  ± 0 . 6 C ; ${\mathrm{0}}{\mathrm{.6C;}}$ 53% ± 1.7% relative humidity). Skin stiffness above and below the nipple and tactile sensitivity from the nipple down were measured. Associations between BrSA and both skin stiffness and tactile sensitivity at rest were determined via correlation analyses. Effects of exercise and test site were assessed by a two-way ANOVA. Skin stiffness was positively correlated with BrSA 3 cm above the areola edge (r = 0.61, P = 0.005) and at the superior areola border (r = 0.54, P = 0.016), but not below the nipple (P > 0.05). The area 3 cm below the areola was also significantly stiffer than all other test sites (P < 0.043). Tactile sensitivity did not vary with BrSA (P > 0.09), but it varied across the breast (i.e., the area 3 cm below the areola was more sensitive than the inferior areola edge; P = 0.018). Skin stiffness and tactile sensitivity across the breast decreased after exercise by ∼37% (P < 0.001) and ∼45% (P = 0.008), respectively. These findings expand our fundamental understanding of the mechanosensory properties of the female breast, and they could help to inform sportswear innovation to better meet the support needs of women of different breast sizes at rest and following exercise.

Comparison of Morphine and Endomorphin Analog ZH853 for Tolerance and Immunomodulation in a Rat Model of Neuropathic Pain

µ-Opioid receptor agonists, the gold standard for analgesia, come with significant side effects when used chronically. Tolerance, defined as the decrease in analgesic activity after repeated use, remains a vital therapeutic obstacle as it increases the likelihood of dose escalation and potentially lethal side effects like respiratory depression. Previous experiments have shown that the endomorphin-1 analog, ZH853, is a specific µ-opioid receptor agonist with reduced side effects like tolerance and glial activation following chronic central administration in pain-naive animals. Here, we investigated the effects of chronic, peripheral administration of µ-opioid receptor agonists following neuropathic injury. Though µ-opioids are effective at reducing neuropathic pain, they are not recommended for first-line treatment due to negative side effects. Compared with chronic morphine, chronic ZH853 treatment led to decreased tolerance and reduced glial activation. Following twice-daily intravenous injections, morphine was less potent and had a shorter duration of antinociception compared with ZH853. Chronic morphine, but not chronic ZH853, elevated markers of activation/inflammation of astrocytes (glial fibrillary acidic protein), microglia (ionized calcium-binding adapter molecule 1), the proinflammatory cytokine tumor necrosis factor-α, and phosphorylated mitogen-activated protein (MAP) kinase p38 (pp38). By contrast, chronic ZH853 reduced ionized calcium-binding adapter molecule 1 and tumor necrosis factor-α relative to both morphine and vehicle, suggesting anti-inflammatory properties with respect to these markers. Glial fibrillary acidic protein and pp38 were not significantly different from vehicle but were significantly lower than morphine. This study demonstrates the effectiveness of chronic ZH853 for providing analgesia in a neuropathic pain state with reduced tolerance compared with morphine, potentially due to reductions in spinal glial activation. PERSPECTIVE: Neuropathic pain is generally undertreated and resistant to medication, and side-effects limit opioid treatment. Here, we show that, compared with an equiantinociceptive dose of morphine, chronic intravenous administration of endomorphin analog ZH853 led to prolonged antiallodynia, reduced tolerance, and inhibition of spinal cord neuroinflammation in male spared nerve-injured rats.

Intrathecal administration of MCRT produced potent antinociception in chronic inflammatory pain models via μ-δ heterodimer with limited side effects

An important goal in the opioid field is to discover effective analgesic drugs with minimal side effects. MCRT demonstrated potent antinociceptive effects with limited side effects, making it a promising candidate. However, its pharmacological properties and how it minimizes side effects remain unknown. Various mouse pain and opioid side effect models were used to evaluate the antinociceptive properties and safety at the spinal level. The targets of MCRT were identified through cAMP measurement, isolated tissue assays, and pharmacological experiments. Immunofluorescence was employed to visualize protein expression. MCRT displayed distinct antinociceptive effects between acute and chronic inflammatory pain models due to its multifunctional properties at the μ opioid receptor (MOR), µ-δ heterodimer (MDOR), and neuropeptide FF receptor 2 (NPFFR2). Activation of NPFFR2 reduced MOR-mediated antinociception, leading to bell-shaped response curves in acute pain models. However, activation of MDOR produced more effective antinociception in chronic inflammatory pain models. MCRT showed limited tolerance and opioid-induced hyperalgesia in both acute and chronic pain models and did not develop cross-tolerance to morphine. Additionally, MCRT did not exhibit addictive properties, gastrointestinal inhibition, and effects on motor coordination. Mechanistically, peripheral chronic inflammation or repeated administration of morphine and MCRT induced an increase in MDOR in the spinal cord. Chronic administration of MCRT had no apparent effect on microglial activation in the spinal cord. These findings suggest that MCRT is a versatile compound that provides potent antinociception with minimal opioid-related side effects. MDOR could be a promising target for managing chronic inflammatory pain and addressing the opioid crisis.

SrHPO4-coated Mg alloy implant attenuates postoperative pain by suppressing osteoclast-induced sensory innervation in osteoporotic fractures

Osteoporotic fractures have become a common public health problem and are usually accompanied by chronic pain. Mg and Mg-based alloys are considered the next-generation orthopedic implants for their excellent osteogenic inductivity, biocompatibility, and biodegradability. However, Mg-based alloy can initiate aberrant activation of osteoclasts and modulate sensory innervation into bone callus resulting in postoperative pain at the sequential stage of osteoporotic fracture healing. Its mechanism is going to be investigated. Strontium hydrogen phosphate (SrHPO4) coating to delay the Mg-based alloy degradation, can reduce the osteoclast formation and inhibit the growth of sensory nerves into bone callus, dorsal root ganglion hyperexcitability, and pain hypersensitivity at the early stage. Liquid chromatography-mass spectrometry (LC-MS) metabolomics analysis of bone marrow-derived macrophages (BMMs) treated with SrHPO4-coated Mg alloy extracts shows the potential effect of increased metabolite levels of AICAR (an activator of the AMPK pathway). We demonstrate a possible modulated secretion of AICAR and osteoclast differentiation from BMMs, which inhibits sensory innervation and postoperative pain through the AMPK/mTORc1/S6K pathway. Importantly, supplementing with AICAR in Mg-activated osteoclasts attenuates postoperative pain. These results suggest that Mg-induced postoperative pain is related to the osteoclastogenesis and sensory innervation at the early stage in the osteoporotic fractures and the SrHPO4 coating on Mg-based alloys can reduce the pain by upregulating AICAR secretion from BMMs or preosteoclasts.

Deconstruction the feedforward inhibition changes in the layer III of anterior cingulate cortex after peripheral nerve injury

The anterior cingulate cortex (ACC) is one of the critical brain areas for processing noxious information. Previous studies showed that peripheral nerve injury induced broad changes in the ACC, contributing to pain hypersensitivity. The neurons in layer 3 (L3) of the ACC receive the inputs from the mediodorsal thalamus (MD) and form the feedforward inhibition (FFI) microcircuits. The effects of peripheral nerve injury on the MD-driven FFI in L3 of ACC are unknown. In our study, we record the enhanced excitatory synaptic transmissions from the MD to L3 of the ACC in mice with common peroneal nerve ligation, affecting FFI. Chemogenetically activating the MD-to-ACC projections induces pain sensitivity and place aversion in naive mice. Furthermore, chemogenetically inactivating MD-to-ACC projections decreases pain sensitivity and promotes place preference in nerve-injured mice. Our results indicate that the peripheral nerve injury changes the MD-to-ACC projections, contributing to pain hypersensitivity and aversion.

MicroRNA-6954-3p Downregulation Contributes to Orofacial Neuropathic Pain in Mice Via Targeting Voltage-Gated Sodium Channel β2 Subunit Protein

The voltage-gated sodium channel β2 subunit protein (SCN2B) plays a crucial role in neuropathic pain. However, the role and mechanisms of SCN2B in orofacial neuropathic pain are still unclear. This study aimed to investigate the upstream regulatory mechanisms of SCN2B in the trigeminal ganglion (TG) underlying orofacial neuropathic pain. Chronic constriction injury of the infraorbital nerve (CCI-ION) of mice was performed to establish the model of orofacial neuropathic pain. Von Frey filament test was performed to detect the head withdrawal threshold (HWT) of mice. Quantitative reverse transcription-polymerase chain, western blotting (WB), fluorescence in situ hybridization, and immunofluorescence (IF) staining were used to detect the expression and distribution of SCN2B and miR-6954-3p in the TG of mice. A luciferase activity assay was carried out to prove the binding between SCN2B messenger ribonucleic acid (mRNA) and miR-6954-3p. After the CCI-ION surgery, the levels of Scn2b mRNA and protein significantly increased and miR-6954-3p decreased in the TG of mice with decreasing HWT. IF staining revealed that SCN2B was expressed specifically in the TG neurons. Silencing SCN2B in the TG of CCI-ION mice significantly increased the HWT. Importantly, the 3'-untranslated region of Scn2b mRNA was proved to bind with miR-6954-3p. Fluorescence in situ hybridization and IF staining demonstrated that miR-6954-3p was expressed in TG neurons and co-expressed with SCN2B. Furthermore, intraganglionic injection of miR-6954-3p agomir into the TG of CCI-ION mice resulted in the downregulation of SCN2B and increased the HWT. These findings suggest that the downregulation of miR-6954-3p in the TG promotes orofacial neuropathic pain by promoting SCN2B expression following trigeminal nerve injury. PERSPECTIVE: This study points to the important role of SCN2B in orofacial neuropathic pain. Furthermore, miR-6954-3p is proven to regulate the expression of SCN2B by binding to the 3'-untranslated region of Scn2b mRNA. These findings indicate that SCN2B and miR-6954-3p are potential therapeutic targets for the treatment of orofacial neuropathic pain.

Artemisia pallens W. Attenuates Inflammation and Oxidative Stress in Freund's Complete Adjuvant-Induced Rheumatoid Arthritis in Wistar Rats

Rheumatoid arthritis (RA) is an autoimmune disease that causes distinctive inflammatory symptoms and affects over 21 million people worldwide. RA is characterized by severe discomfort, swelling, and degradation of the bone and cartilage, further impairing joint function. The current study investigates the antiarthritic effect of a methanolic extract of Artemisia pallens (methanolic extract of A. pallens, MEAP), an aromatic herb. Artemisinin content (% per dry weight of the plant) was estimated using a UV Vis spectrophotometer. In the present study, animals were divided into six groups (n = 6). The control group (group I) was injected with 0.25% of carboxymethyl cellulose. The arthritic control group (group II) was treated with Freund's complete adjuvant (by injecting 0.1 mL). Prednisolone (10 mg/kg), a lower dose of MEAP (100 mg/kg), a medium dose of MEAP (200 mg/kg), and a higher dose of MEAP (400 mg/kg) were orally delivered to groups III, IV, V, and VI, respectively. Freund's complete adjuvant was administered into the sub-plantar portion of the left-hind paw in all the groups except vehicle control to induce rheumatoid arthritis. Weight variation; joint diameter; paw volume; thermal and mechanical hyperalgesia; hematological, biochemical, and oxidative stress parameters; radiology; and a histopathological assessment of the synovial joint were observed in order to evaluate the antiarthritic effect of the methanolic extract of A. pallens. In this study, the estimated content of artemisinin was found to be 0.28% (per dry weight of the plant), which was in good agreement with the reported value. MEAP (200 and 400 mg/kg) caused a significant reduction in increased paw volume and joint diameter in arthritic rats while significantly increasing body weight and the mechanical threshold of thermal algesia. Moreover, complete blood counts and serum enzyme levels improved significantly. Radiological analysis showed a reduction in soft tissue swelling and small erosions. A histopathological examination of the cells revealed reduced cell infiltration and the erosion of joint cartilage in MEAP-administered arthritic rats. The present research suggests that the antiarthritic activity of the methanolic extract of A. pallens wall is promising, as evidenced by the findings explored in our rat model.

Fecal Microbiota Transplantation-Mediated Rebalancing of the Gut-Brain Axis Alleviates Cisplatin-Induced Neuropathic Pain

Chemotherapy-induced neuropathic pain (CINP) presents a significant challenge in cancer treatment, necessitating novel therapeutic approaches. The intricate relationship between CINP and the gut-brain axis indicates a crucial role for the gut microbiota in pain modulation during cancer therapy. In this study, we investigated the effect of gut microbiota and their modulation on CINP in rats. Cisplatin administration (20 mg/kg, ip) disrupted the integrity of the blood-spinal cord barrier, as evidenced by reduced expression of tight junction proteins occludin and claudin-5 and increased leakage of pro-inflammatory cytokines into the spinal cord. Fecal microbiota transplantation (FMT, 0.5 mL of P.O.) from healthy rats over 21 days restored barrier integrity, as confirmed by Evan's blue assay. FMT intervention halted the progression of cisplatin-induced pain, demonstrated through a battery of pain assays assessing mechanical, thermal, and cold allodynia alongside hyperalgesia measurements. Additionally, FMT treatment reduced oxidative stress and modulated neuro-inflammatory markers, resulting in a rebalanced cytokine profile with decreased levels of neuro-inflammatory cytokines (IL-6 and TNFα) and increased expression of the anti-inflammatory cytokine IL-10. Gut microbiota-mediated IL-1β/NF-κB signaling emerged as a critical factor in leukocyte recruitment and microglial activation, highlighting the gut-brain axis as a key regulatory nexus in managing cisplatin-induced neuropathic pain. These findings underscore the therapeutic potential of targeting gut microbiota modulation as a promising strategy for alleviating CINP and improving the well-being of cancer patients undergoing chemotherapy.

B cells drive neuropathic pain-related behaviors in mice through IgG-Fc gamma receptor signaling

Neuroimmune interactions are essential for the development of neuropathic pain, yet the contributions of distinct immune cell populations have not been fully unraveled. Here, we demonstrate the critical role of B cells in promoting mechanical hypersensitivity (allodynia) after peripheral nerve injury in male and female mice. Depletion of B cells with a single injection of anti-CD20 monoclonal antibody at the time of injury prevented the development of allodynia. B cell-deficient (muMT) mice were similarly spared from allodynia. Nerve injury was associated with increased immunoglobulin G (IgG) accumulation in ipsilateral lumbar dorsal root ganglia (DRGs) and dorsal spinal cords. IgG was colocalized with sensory neurons and macrophages in DRGs and microglia in spinal cords. IgG also accumulated in DRG samples from human donors with chronic pain, colocalizing with a marker for macrophages and satellite glia. RNA sequencing revealed a B cell population in naive mouse and human DRGs. A B cell transcriptional signature was enriched in DRGs from human donors with neuropathic pain. Passive transfer of IgG from injured mice induced allodynia in injured muMT recipient mice. The pronociceptive effects of IgG are likely mediated through immune complexes interacting with Fc gamma receptors (FcγRs) expressed by sensory neurons, microglia, and macrophages, given that both mechanical allodynia and hyperexcitability of dissociated DRG neurons were abolished in nerve-injured FcγR-deficient mice. Consistently, the pronociceptive effects of IgG passive transfer were lost in FcγR-deficient mice. These data reveal that a B cell-IgG-FcγR axis is required for the development of neuropathic pain in mice.

Artichoke leaf hydroethanolic extract reduces neuropathic pain in a rat model of chronic constriction injury via attenuating the sciatic nerve oxidative stress

Neuropathic pain, a nerve damage consequence, presents symptoms such as dysesthesia, hyperalgesia, and allodynia. This study aimed to evaluate the alleviating potential of artichoke leaf extract in neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in male rats. The hydroethanolic extract of artichoke leaf was administered via gavage at doses of 200, 400, and 800 mg/kg for 21 days. Behavioural tests were conducted on days 1, 4, 7, 14, and 21 post-surgeries. Only the dose of 800 mg/kg significantly reduced thermal hyperalgesia and allodynia from day 14 and mechanical allodynia from day 7, and the other doses did not affect behaviours. Biochemical analysis showed that artichoke extract decreased lipid peroxidation and restored antioxidant enzyme activities (SOD and GPx) in the sciatic nerve tissue. In conclusion, artichoke leaf extract administration diminishes neuropathic pain-related behaviours by enhancing antioxidant capacity and reducing oxidative stress in the rats' sciatic nerve.

Sex-dependent effects of the targeted NGF mutation (R100E) on pain behavior, joint inflammation, and bone erosion in mice

ABSTRACT

Nerve growth factor (NGF)-R100E is a mutated form of human recombinant NGF that reduces the binding of NGF to its p75NTR receptor while retaining its affinity toward the TrkA receptor. Here, we used human wild type NGF and NGF-R100E knock-in mice to investigate the effects of this NGF mutation on inflammation-induced pain-related behaviors and bone loss. The hNGF-R100E mutation did not alter the nerve fiber density in the sciatic nerve, ankle joint synovium, and skin of naïve mice. Withdrawal responses to mechanical, thermal, and cold stimuli before and after joint inflammation induced by intra-articular injection of complete Freund adjuvant (CFA) were similar between human recombinant nerve growth factor-wild type and hNGF-R100E male and female mice while weight bearing and gait analysis revealed significant differences. Intriguingly, hNGF-R100E male and female mice showed only mild changes, indicating lower degrees of deep joint-related pain compared to their wild type counterparts. Furthermore, micro-CT analysis demonstrated that hNGF-R100E female mice, but not males, were protected from CFA-induced bone loss, and mRNA analysis showed a different gene regulation indicating a sex-dependent relationship between NGF, inflammation, and bone loss. In conclusion, our study reveals that the hNGF-R100E mutation renders mice insensitive to inflammation-induced impact on joint loading and gait while preserving the development of the peripheral nociceptive neurons and sensitivity to punctate stimulation of the skin. Notably, the mutation uncovers a sex-dependent relationship between NGF and inflammation-induced bone loss. These findings offer valuable insights into NGF as a target for pain management and the interplay between NGF and bone architecture.

Electroacupuncture Relieves Neuropathic Pain via Adenosine 3 Receptor Activation in the Spinal Cord Dorsal Horn of Mice

Neuropathic pain (NPP) is a devastating and unbearable painful condition. As prevailing treatment strategies have failed to mitigate its complications, there remains a demand for effective therapies. Electroacupuncture (EA) has proved a potent remedial strategy in NPP management in humans and mammals. However, past studies have investigated the underlying mechanism of the analgesic effects of EA on NPP, focusing primarily on adenosine receptors in peripheral tissues. Herein, we elucidate the role of the adenosine (Adora-3) signaling pathway in mediating pain relief through EA in the central nervous system, which is obscure in the literature and needs exploration. Specific pathogen-free (SPF) male adult mice (C57BL/6 J) were utilized to investigate the effect of EA on adenosine metabolism (CD73, ADA) and its receptor activation (Adora-3), as potential mechanisms to mitigate NPP in the central nervous system. NPP was induced via spared nerve injury (SNI). EA treatment was administered seven times post-SNI surgery, and lumber (L4-L6) spinal cord was collected to determine the molecular expression of mRNA and protein levels. In the spinal cord of mice, following EA application, the expression results revealed that EA upregulated (p < 0.05) Adora-3 and CD73 by inhibiting ADA expression. In addition, EA triggered the release of adenosine (ADO), which modulated the nociceptive responses and enhanced neuronal activation. Meanwhile, the interplay between ADO levels and EA-induced antinociception, using an Adora-3 agonist and antagonist, showed that the Adora-3 agonist IB-MECA significantly increased (p < 0.05) nociceptive thresholds and expression levels. In contrast, the antagonist MRS1523 exacerbated neuropathic pain. Furthermore, an upregulated effect of EA on Adora-3 expression was inferred when the Adora-3 antagonist was administered, and the EA treatment increased the fluorescent intensity of Adora-3 in the spinal cord. Taken together, EA effectively modulates NPP by regulating the Adora-3 signaling pathway under induced pain conditions. These findings enhance our understanding of NPP management and offer potential avenues for innovative therapeutic interventions.

Orally administered Cannabigerol (CBG) in rats: Cannabimimetic actions, anxiety-like behavior, and inflammation-induced pain

Cannabigerol (CBG) is a phytocannabinoid found in cannabis that is promoted for medical use and other health benefits, but current empirical data on the behavioral effects of CBG are lacking. The purpose of this study was to evaluate the effects of a wide dose range of orally administered CBG on outcomes related to its potential cannabimimetic effects (cannabinoid tetrad), as well as effects on anxiety-like behavior, inflammation and related pain hypersensitivity. In a series of experiments, male and female Sprague Dawley rats received oral CBG (per os [p.o.]) or vehicle prior to testing of effects on 1) the cannabinoid tetrad (30-600 mg/kg, p.o.): assessments of locomotor activity, body temperature, antinociception (tail flick test), and catalepsy (bar test); 2) acoustic startle response (ASR) test of anxiety-like behavior (30-300 mg/kg, p.o.); 3) carrageenan-induced inflammation (paw edema), hyperalgesia (Hargreaves test), and allodynia (von Frey test) tests (10-60 mg/kg, p.o.). Positive control groups were administered THC (0-30 mg/kg, p.o.) for the cannabinoid tetrad assay, the benzodiazepine lorazepam (0-3 mg/kg, intraperitoneal [i.p.]) for the ASR test, or the opioid analgesic morphine (0-10 mg/kg, i.p.) for the carrageenan-induced inflammation and pain hypersensitivity tests. CBG did not produce cannabimimetic actions in the tetrad, but increased locomotor activity at the highest doses (300-600 mg/kg). THC produced typical dose-related cannabimimetic effects. CBG did not produce anxiolytic effects in the ASR test, while groups pretreated with lorazepam showed reductions in ASR. Finally, pretreatment with CBG prior to an intraplantar injection of carrageenan did not prevent the induction of an acute inflammatory state (i.e., increased paw edema and associated hyperalgesia and allodynia). In contrast, morphine alleviated hyperalgesia and allodynia induced by intraplantar carrageenan but did not affect the development of paw edema. In sum, these data do not support the use of oral CBG for anxiety or inflammatory pain.

Exploration of the mechanism underlying the therapeutic effect of electroacupuncture at chengshan acupoint on post-hemorrhoidectomy anal pain: Insights from the mAChRs/IP3-Ca2+-CaM signaling pathway

OBJECTIVE

In the context of postoperative anal pain, understanding the intricate mechanisms and effective interventions is paramount. This study investigates the role of Muscarinic Acetylcholine Receptors (mAChRs) and the IP3-Ca2+-CaM signaling pathway in a rat model of postoperative anal pain, exploring the potential analgesic effects of electroacupuncture.

METHODS

Comprehensive approaches involving mechanical sensitivity assays, Western blotting, immunohistochemistry, and intracellular calcium concentration measurement were used.

RESULTS

The authors found elevated mAChRs expression in the postoperative pain model. Antagonizing mAChRs reduced pain sensitivity and attenuated the IP3-Ca2+-CaM pathway. Remarkably, electroacupuncture treatment further mitigated pain, potentially by suppressing this signaling cascade.

INTERPRETATION

These findings reveal a novel connection between mAChRs and the IP3-Ca2+-CaM pathway in postoperative anal pain and suggest electroacupuncture as a promising avenue for pain relief through these mechanisms, offering insights into innovative strategies for postoperative pain management.

Ablation of the Integrin CD11b Mac-1 Limits Deleterious Responses to Traumatic Spinal Cord Injury and Improves Functional Recovery in Mice

Spinal cord injury (SCI) triggers microglial/monocytes activation with distinct pro-inflammatory or inflammation-resolving phenotypes, which potentiate tissue damage or facilitate functional repair, respectively. The major integrin Mac-1 (CD11b/CD18), a heterodimer consisting of CD11b and CD18 chains, is expressed in multiple immune cells of the myeloid lineage. Here, we examined the effects of CD11b gene ablation in neuroinflammation and functional outcomes after SCI. qPCR analysis of C57BL/6 female mice showed upregulation of CD11b mRNA starting from 1 d after injury, which persisted up to 28 d. CD11b knockout (KO) mice and their wildtype littermates were subjected to moderate SCI. At 1 d post-injury, qPCR showed increased expression of genes involved with inflammation-resolving processes in CD11b KO mice. Flow cytometry analysis of CD45intLy6C-CX3CR1+ microglia, CD45hiLy6C+Ly6G- monocytes, and CD45hiLy6C+Ly6G+ neutrophils revealed significantly reduced cell counts as well as reactive oxygen species (ROS) production in CD11b KO mice at d3 post-injury. Further examination with NanoString and RNA-seq showed upregulation of pro-inflammatory genes, but downregulation of the ROS pathway. Importantly, CD11b KO mice exhibited significantly improved locomotor function, reduced cutaneous mechanical/thermal hypersensitivity, and limited tissue damage at 8 weeks post-injury. Collectively, our data suggest an important role for CD11b in regulating tissue inflammation and functional outcome following SCI.

Deleting PTEN, but not SOCS3 or myelin inhibitors, robustly boosts BRAF-elicited intraspinal regeneration of peripheral sensory axons

Primary sensory axons fail to regenerate into the spinal cord following dorsal root injury leading to permanent sensory deficits. Re-entry is prevented at the dorsal root entry zone (DREZ), the CNS-PNS interface. Current approaches for promoting DR regeneration across the DREZ have had some success, but sustained, long-distance regeneration, particularly of large-diameter myelinated axons, still remains a formidable challenge. We have previously shown that induced expression of constitutively active B-RAF (kaBRAF) enhanced the regenerative competence of injured DRG neurons in adult mice. In this study, we investigated whether robust intraspinal regeneration can be achieved after a cervical DR injury by selective expression of kaBRAF alone or in combination with deletion of the myelin-associated inhibitors or neuron-intrinsic growth suppressors (PTEN or SOCS3). We found that kaBRAF promoted some axon regeneration across the DREZ but did not produce significant functional recovery by two months. Supplementary deletion of Nogo, MAG, and OMgp only modestly improved kaBRAF-induced regeneration. Deletion of PTEN or SOCS3 individually or in combination failed to promote any growth across the DREZ. In marked contrast, simultaneous deletion of PTEN, but not SOCS3, dramatically enhanced kaBRAF-mediated regeneration enabling many more axons to penetrate the DREZ and grow deep into the spinal cord. This study shows that dual activation of BRAF-MEK-ERK and PI3K-Akt-mTOR signaling is an effective strategy to stimulate robust intraspinal DR regeneration.

Glucose attenuates the long-term adverse neurodevelopment effect of neonate pain stimulus via CRF/GR in rats

BACKGROUND

Neonates undergo numerous painful procedures throughout their hospitalization. Repeated procedural pain may cause adverse long-term effects. Glucose as a non-pharmacological analgesia, is used for neonate pain management. In this study, potential mechanism of attenuate pain induced by glucose in neurodevelopment effect of neonate pain stimulus was investigated.

METHODS

Neonatal rats to perform a repetitive injury model and glucose intervention model in the postnatal day 0-7(P0-7). Pain thresholds were measured by von Frey test weekly. The puberty behavioral outcome, tissue loss and protein expression in hippocampus were analyzed.

RESULTS

Oral administration of glucose after repeated pain stimulation can maintain the hippocampal structure in, and reduce the expressions of corticotropin releasing factor (CFR) and glucocorticoid receptor (GR), therefore, resulted in long-term threshold of pain and cognitive improvement.

CONCLUSION

Exposure to neonatal repeated procedural pain causes persistent mechanical hypersensitivity and the dysfunction of spatial memory retention at puberty. In addition, glucose can relieve these adverse effects, possibly via decreasing CRF/GR levels to change the hypothalamus-pituitary-adrenal (HPA) axis.

Oral application of magnesium-L-threonate alleviates radicular pain by inhibiting neuro-inflammation dependent central sensitization of rats

BACKGROUND

We have reported neuro-inflammation is involved in radicular pain by enhancing the efficiency of pain synaptic transmission in spinal level. Recently, peers' studies have confirmed that magnesium deficiency leads to neuro-inflammation, thus contributes to memory and emotional deficits and pain hypersensitivity in antineoplastic agents treated rats. In this study, we explore the effect of oral application of magnesium-L-threonate (L-TAMS) in radicular pain induced by lumbar disc herniation (LDH) of rats and the possible mechanisms.

METHODS

Rat model of LDH was induced by autologous nucleus pulposus (NP) implantation. Mechanical and thermal pain thresholds were assessed by von Frey filaments and hotplate test respectively. L-TAMS was applied from drinking water at dosage of 604 mg/kg/day from 2 day before NP implantation and until the end of the experiment. Free Mg2+ content in serum and cerebrospinal fluid (CSF) was measured by calmagite chromometry. Synaptic transmission efficiency was determined by C-fiber evoked field potentials recorded by electrophysiologic recording in vivo. The activation of microglia in spinal dorsal horn was displayed by immunofluorescence staining and western blotting. The expressions of pro-inflammatory cytokines and glutamic N-methyl-D-aspartate receptor (NMDAR) subunits (NR2A, NR2B) were assessed by western blotting and enzyme-linked immunosorbent assay (ELISA) respectively.

RESULTS

NP implantation induced mechanical allodynia and thermal hyperalgesia, accompanied by decreased Mg2+ concentration in serum and CSF which were both obscured by oral application of L-TAMS. L-TAMS inhibited spinal microglia activation and pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) expression of rats with NP. L-TAMS decreased C-fiber evoked potentials and NR2B protein level in rats with NP, which were rescued by extra intrathecal delivery of TNF-α or IL-6 or IL-1β.

CONCLUSIONS

Oral application of L-TAMS alleviates radicular pain by inhibiting neuro-inflammation dependent central sensitization of rats.

Is chronic pain caused by central sensitization? A review and critical point of view

Chronic pain causes disability and loss of health worldwide. Yet, a mechanistic explanation for it is still missing. Frequently, neural phenomena, and among them, Central Sensitization (CS), is presented as causing chronic pain. This narrative review explores the evidence substantiating the relationship between CS and chronic pain: four expert researchers were divided in two independent teams that reviewed the available evidence. Three criteria were established for a study to demonstrate a causal relationship: (1) confirm presence of CS, (2) study chronic pain, and (3) test sufficiency or necessity of CS over chronic pain symptoms. No study met those criteria, failing to demonstrate that CS can cause chronic pain. Also, no evidence reporting the occurrence of CS in humans was found. Worryingly, pain assessments are often confounded with CS measures in the literature, omitting that the latter is a neurophysiological and not a perceptual phenomenon. Future research should avoid this misconception to directly interrogate what is the causal contribution of CS to chronic pain to better comprehend this problematic condition.

Further evidence that peritraumatic 17β-estradiol levels influence chronic posttraumatic pain outcomes in women, data from both humans and animals

ABSTRACT

Chronic posttraumatic pain (CPTP) is common after traumatic stress exposure (TSE) and disproportionately burdens women. We previously showed across 3 independent longitudinal cohort studies that, in women, increased peritraumatic 17β-estradiol (E2) levels were associated with substantially lower CPTP over 1 year. Here, we assessed this relationship in a fourth longitudinal cohort and also assessed the relationship between E2 and CPTP at additional time points post-TSE. Furthermore, we used a well-validated animal model of TSE to determine whether exogenous E2 administration protects against mechanical hypersensitivity. Using nested samples and data from the Advancing Understanding of RecOvery afteR traumA study (n = 543 samples, 389 participants), an emergency department-based prospective study of TSE survivors, we assessed the relationship between circulating E2 levels and CPTP in women and men using multivariate repeated-measures mixed modeling. Male and ovariectomized female Sprague Dawley rats were exposed to TSE and administered E2 either immediately after or 3 days post-TSE. Consistent with previous results, we observed an inverse relationship between peritraumatic E2 and longitudinal CPTP in women only (β = -0.137, P = 0.033). In animals, E2 protected against mechanical hypersensitivity in female ovariectomized rats only if administered immediately post-TSE. In conclusion, peritraumatic E2 levels, but not those at post-TSE time points, predict CPTP in women TSE survivors. Administration of E2 immediately post TSE protects against mechanical hypersensitivity in female rats. Together with previous findings, these data indicate that increased peritraumatic E2 levels in women have protective effects against CPTP development and suggest that immediate post-TSE E2 administration in women could be a promising therapeutic strategy for reducing risk of CPTP.

Improving Functional Muscle Regeneration in Volumetric Muscle Loss Injuries by Shifting the Balance of Inflammatory and Pro-Resolving Lipid Mediators

Severe tissue loss resulting from extremity trauma, such as volumetric muscle loss (VML), poses significant clinical challenges for both general and military populations. VML disrupts the endogenous tissue repair mechanisms, resulting in acute and unresolved chronic inflammation and immune cell presence, impaired muscle healing, scar tissue formation, persistent pain, and permanent functional deficits. The aberrant healing response is preceded by acute inflammation and immune cell infiltration which does not resolve. We analyzed the biosynthesis of inflammatory and specialized pro-resolving lipid mediators (SPMs) after VML injury in two different models; muscle with critical-sized defects had a decreased capacity to biosynthesize SPMs, leading to dysregulated and persistent inflammation. We developed a modular poly(ethylene glycol)-maleimide hydrogel platform to locally release a stable isomer of Resolvin D1 (AT-RvD1) and promote endogenous pathways of inflammation resolution in the two muscle models. The local delivery of AT-RvD1 enhanced muscle regeneration, improved muscle function, and reduced pain sensitivity after VML by promoting molecular and cellular resolution of inflammation. These findings provide new insights into the pathogenesis of VML and establish a pro-resolving hydrogel therapeutic as a promising strategy for promoting functional muscle regeneration after traumatic injury.

Pregnancy ameliorates neuropathic pain through suppression of microglia and upregulation of the δ-opioid receptor in the anterior cingulate cortex in late-pregnant mice

PURPOSE

Pregnancy-induced analgesia develops in late pregnancy, but its mechanisms are unclear. The anterior cingulate cortex (ACC) plays a key role in the pathogenesis of neuropathic pain. The authors hypothesized that pregnancy-induced analgesia ameliorates neuropathic pain by suppressing activation of microglia and the expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and by upregulating opioid receptors in the ACC in late-pregnant mice.

METHODS

Neuropathic pain was induced in non-pregnant (NP) or pregnant (P) C57BL/6JJmsSlc female mice by partial sciatic nerve ligation (PSNL). The nociceptive response was evaluated by mechanical allodynia and activation of microglia in the ACC was evaluated by immunohistochemistry. The expressions of phosphorylated AMPA receptors and opioid receptors in the ACC were evaluated by immunoblotting.

RESULTS

In von Frey reflex tests, NP-PSNL-treated mice showed a lower 50% paw-withdrawal threshold than NP-Naïve mice on experimental day 9. No difference in 50% paw-withdrawal threshold was found among the NP-Naïve, NP-Sham, P-Sham, and P-PSNL-treated mice. The number of microglia in the ACC was significantly increased in NP-PSNL-treated mice compared to NP-Sham mice. Immunoblotting showed significantly increased expression of phosphorylated AMPA receptor subunit GluR1 at Ser831 in NP-PSNL-treated mice compared to NP-Sham mice. Immunoblotting also showed significantly increased δ-opioid receptor in the ACC in P-Sham and P-PSNL-treated mice compared to NP-Sham mice.

CONCLUSION

Pregnancy-induced analgesia ameliorated neuropathic pain by suppressing activation of microglia and the expression of phosphorylated AMPA receptor subunit GluR1 at Ser831, and by upregulation of the δ-opioid receptor in the ACC in late-pregnant mice.

Analgesic Effect of Human Placenta Hydrolysate on CFA-Induced Inflammatory Pain in Mice

To evaluate the efficacy of human placenta hydrolysate (HPH) in a mice model of CFA-induced inflammatory pain. TNF-α, IL-1β, and IL-6 are key pro-inflammatory cytokine factors for relieving inflammatory pain. Therefore, this study investigates whether HPH suppresses CFA-induced pain and attenuates the inflammatory process by regulating cytokines. In addition, the relationship between neuropathic pain and HPH was established by staining GFAP and Iba-1 in mice spinal cord tissues. This study was conducted for a total of day 28, and inflammatory pain was induced in mice by injecting CFA into the right paw at day 0 and day 14, respectively. 100 μL of 20% glucose and polydeoxyribonucleotide (PDRN) and 100, 200, and 300 μL of HPH were administered intraperitoneally twice a week. In the CFA-induced group, cold and mechanical allodynia and pro-inflammatory cytokine factors in the spinal cord and plantar tissue were significantly increased. The five groups of drugs evenly reduced pain and gene expression of inflammatory factors, and particularly excellent effects were confirmed in the HPH 200 and 300 groups. Meanwhile, the expression of GFAP and Iba-1 in the spinal cord was increased by CFA administration but decreased by HPH administration, which was confirmed to suppress damage to peripheral ganglia. The present study suggests that HPH attenuates CFA-induced inflammatory pain through inhibition of pro-inflammatory cytokine factors and protection of peripheral nerves.

Sex differences in functional and structural alterations of hippocampus region in chronic pain: a DTI and resting-state fMRI study

Introduction

It is well known that there are significant differences in the prevalence of chronic pain between males and females. Human and animal imaging studies have shown that chronic pain profoundly alters the structure and function of brain regions. However, there is limited research on the sex-specific mechanisms underlying the brain plasticity and adaptive changes associated with chronic pain. In this article, we conducted a multimodal study to evaluate how nerve injury-induced chronic pain affects the brain.

Methods

Male and female Sprague-Dawley (SD) rats with spared nerve injury (SNI) model underwent resting-state functional magnetic resonance imaging (rs-fMRI) (male sham group: n = 18; male SNI group: n = 18; female sham group: n = 20; female SNI group: n = 18) and magnetic resonance diffusion tensor imaging (DTI) (male sham group: n = 23; male SNI group: n = 21; female sham group: n = 20; female SNI group: n = 21) scanning. ICA method, Fractional amplitude of low-frequency fluctuations (fALFF), immunofluorescence staining, and graph theory analysis was utilized to extract the rs-fMRI changes of brain regions of each group.

Results

Using SNI model, which promotes long-lasting mechanical allodynia, we found that neuropathic pain deeply modified the intrinsic organization of the brain functional network in male and female rats (main effect of operation: F = 298.449, P < 0.001). 64 independent components (ICs) in the brain were divided and assigned to 16 systems. In male rats, we observed significant alterations in the microstructure of the hippocampal cornu ammonis 1 and cornu ammonis 2 (CA1/CA2) region, as indicated by increased mean diffusivity (MD) (CA1_L: P = 0.02; CA1_R: P = 0.031; CA2_L: P = 0.035; CA2_R: P = 0.015) and radial diffusivity (RD) (CA1_L: P = 0.028; CA1_R: P = 0.033; CA2_L: P = 0.037; CA2_R: P = 0.038) values, along with enhanced activating transcription factor 3 (ATF3) expression. Conversely, in female rats, we found significant increases in the fractional amplitude of low frequency fluctuations (fALFF) value within the hippocampal dentate gyrus (DG) (F = 5.419, P = 0.023), accompanied by elevated c-Fos signal (F = 6.269, P = 0.031). Furthermore, graph theory analysis revealed notable differences in the small-world network of the hippocampal system in female rats, characterized by reduced small-world attributes and increased inter-nodal transmission efficiency.

Discussion

Our study indicates sex differences in structural and functional alterations in the hippocampal system in rats under chronic pain conditions. The results suggest that the hippocampus system plays an important role in the different mechanisms of chronic pain in different sexes. These findings provide reliable insights to explore the complex mechanisms underlying sex differences in chronic pain.

Liquiritin ameliorates painful diabetic neuropathy in SD rats by inhibiting NLRP3-MMP-9-mediated reversal of aquaporin-4 polarity in the glymphatic system

Background

Despite advancements in diabetes treatment, the management of Painful Diabetic Neuropathy (PDN) remains challenging. Our previous research indicated a significant correlation between the expression and distribution of Aquaporin-4 (AQP4) in the spinal glymphatic system and PDN. However, the potential role and mechanism of liquiritin in PDN treatment remain uncertain.

Methods

This study established a rat model of PDN using a combination of low-dose Streptozotocin (STZ) and a high-fat, high-sugar diet. Rats were treated with liquiritin and MCC950 (an NLRP3 inhibitor). We monitored fasting blood glucose, body weight, and mechanical allodynia periodically. The glymphatic system's clearance function was evaluated using Magnetic Resonance Imaging (MRI), and changes in proteins including NLRP3, MMP-9, and AQP4 were detected through immunofluorescence and Western blot techniques.

Results

The rats with painful diabetic neuropathy (PDN) demonstrated several physiological changes, including heightened mechanical allodynia, compromised clearance function within the spinal glymphatic system, altered distribution of AQP4, increased count of activated astrocytes, elevated expression levels of NLRP3 and MMP-9, and decreased expression of AQP4. However, following treatment with liquiritin and MCC950, these rats exhibited notable improvements.

Conclusion

Liquiritin may promote the restoration of AQP4 polarity by inhibiting NLRP3 and MMP-9, thereby enhancing the clearance functions of the spinal cord glymphatic system in PDN rats, alleviating the progression of PDN.

Self-Healing Hydrogel Resulting from the Noncovalent Interaction between Ropivacaine and Low-Molecular-Weight Gelator Sodium Deoxycholate Achieves Stable and Endurable Local Analgesia in Vivo

Regional analgesia based on the local anesthetic ropivacaine plays a crucial role in postoperative pain management and recovery; however, the short duration of analgesia limits its clinical potential. Various drug delivery systems such as microparticles and lipid carriers have been used to prolong the analgesic effect, yet most of them are prone to abrupt release from the site of administration or have poor analgesic effects of less than 48 h, which fail to meet the needs of postoperative analgesia. In this study, a low-molecular-weight gelator sodium deoxycholate-based hydrogel loaded with ropivacaine (DC-ROP gel) was designed for long-acting analgesia. The noncovalent interaction between ropivacaine and sodium deoxycholate helps to improve the stability and sustained release performance of the gel. This internal drug-binding hydrogel also avoids experiencing the burst release effect commonly seen in polymer hydrogels previously reported for the slow release of local anesthetics. DC-ROP gel exhibited the dual advantages of self-healing after compression and long-term controlled release. In mice with inflammatory pain, DC-ROP gel achieved peripheral nerve block for more than 1 week after a single injection. Histological and blood biochemical analyses confirmed that the DC-ROP gel did not produce systemic toxicity, and cytotoxicity experiments demonstrated that the DC-ROP gel resulted in low irritation. These results suggest that DC-ROP gel provides a promising strategy for local anesthetics in long-term postoperative pain management, broadening the potential of bile salt-based low-molecular-weight hydrogels for drug delivery.

Glial activation in pain and emotional processing regions in the nitroglycerin mouse model of chronic migraine

OBJECTIVE

Our aim was to survey astrocyte and microglial activation across four brain regions in a mouse model of chronic migraine.

BACKGROUND

Chronic migraine is a leading cause of disability, with higher rates in females. The role of central nervous system neurons and glia in migraine pathophysiology is not fully elucidated. Preclinical studies have shown abnormal glial activation in the trigeminal nucleus caudalis of male rodents. No current reports have investigated glial activation in both sexes in other important brain regions involved with the nociceptive and emotional processing of pain.

METHODS

The mouse nitroglycerin model of migraine was used, and nitroglycerin (10 mg/kg) or vehicle was administered every other day for 9 days. Prior to injections on days 1, 5, and 9, cephalic allodynia was determined by periorbital von Frey hair testing. Immunofluorescent staining of astrocyte marker, glial fibrillary protein (GFAP), and microglial marker, ionized calcium binding adaptor molecule 1 (Iba1), in male and female trigeminal nucleus caudalis, periaqueductal gray, somatosensory cortex, and nucleus accumbens was completed.

RESULTS

Behavioral testing demonstrated increased cephalic allodynia in nitroglycerin- versus vehicle-treated mice. An increase in the percent area covered by GFAP+ cells in the trigeminal nucleus caudalis and nucleus accumbens, but not the periaqueductal gray or somatosensory cortex, was observed in response to nitroglycerin. No significant differences were observed for Iba1 staining across brain regions. We did not detect significant sex differences in GFAP or Iba1 quantification.

CONCLUSIONS

Immunohistochemical analysis suggests that, at the time point tested, immunoreactivity of GFAP+ astrocytes, but not Iba1+ microglia, changes in response to chronic migraine-associated pain. Additionally, there do not appear to be significant differences between males and females in GFAP+ or Iba1+ cells across the four brain regions analyzed.