Methods Used to Evaluate Pain Behaviors in Rodents

Promotive effect of skin precursor-derived Schwann cells on brachial plexus neurotomy and motor neuron damage repair through milieu-regulating secretome

Brachial plexus injury (BPI) with motor neurons (MNs) damage still remain poor recovery in preclinical research and clinical therapy, while cell-based therapy approaches emerged as novel strategies. Previous work of rat skin precursor-derived Schwann cells (SKP-SCs) provided substantial foundation for repairing peripheral nerve injury (PNI). Given that, our present work focused on exploring the repair efficacy and possible mechanisms of SKP-SCs implantation on rat BPI combined with neurorrhaphy post-neurotomy. Results indicated the significant locomotive and sensory function recovery, with improved morphological remodeling of regenerated nerves and angiogenesis, as well as amelioration of target muscles atrophy and motor endplate degeneration. Besides, MNs could restore from oxygen-glucose-deprivation (OGD) injury upon SKP-SCs-sourced secretome treatment, implying the underlying paracrine mechanisms. Moreover, rat cytokine array assay detected 67 cytokines from SKP-SC-secretome, and bioinformatic analyses of screened 32 cytokines presented multiple functional clusters covering diverse cell types, including inflammatory cells, Schwann cells, vascular endothelial cells (VECs), neurons, and SKP-SCs themselves, relating distinct biological processes to nerve regeneration. Especially, a panel of hypoxia-responsive cytokines (HRCK), can participate into multicellular biological process regulation for permissive regeneration milieu, which underscored the benefits of SKP-SCs and sourced secretome, facilitating the chorus of nerve regenerative microenvironment. Furthermore, platelet-derived growth factor-AA (PDGF-AA) and vascular endothelial growth factor-A (VEGF-A) were outstanding cytokines involved with nerve regenerative microenvironment regulating, with significantly elevated mRNA expression level in hypoxia-responsive SKP-SCs. Altogether, through recapitulating the implanted SKP-SCs and derived secretome as niche sensor and paracrine transmitters respectively, HRCK would be further excavated as molecular underpinning of the neural recuperative mechanizations for efficient cell therapy; meanwhile, the analysis paradigm in this study validated and anticipated the actions and mechanisms of SKP-SCs on traumatic BPI repair, and was beneficial to identify promising bioactive molecule cocktail and signaling targets for cell-free therapy strategy on neural repair and regeneration.

Repressing iron overload ameliorates central post-stroke pain via the Hdac2-Kv1.2 axis in a rat model of hemorrhagic stroke

JOURNAL/nrgr/04.03/01300535-202412000-00027/figure1/v/2024-04-08T165401Z/r/image-tiff Thalamic hemorrhage can lead to the development of central post-stroke pain. Changes in histone acetylation levels, which are regulated by histone deacetylases, affect the excitability of neurons surrounding the hemorrhagic area. However, the regulatory mechanism of histone deacetylases in central post-stroke pain remains unclear. Here, we show that iron overload leads to an increase in histone deacetylase 2 expression in damaged ventral posterolateral nucleus neurons. Inhibiting this increase restored histone H3 acetylation in the Kcna2 promoter region of the voltage-dependent potassium (Kv) channel subunit gene in a rat model of central post-stroke pain, thereby increasing Kcna2 expression and relieving central pain. However, in the absence of nerve injury, increasing histone deacetylase 2 expression decreased Kcna2 expression, decreased Kv current, increased the excitability of neurons in the ventral posterolateral nucleus area, and led to neuropathic pain symptoms. Moreover, treatment with the iron chelator deferiprone effectively reduced iron overload in the ventral posterolateral nucleus after intracerebral hemorrhage, reversed histone deacetylase 2 upregulation and Kv1.2 downregulation, and alleviated mechanical hypersensitivity in central post-stroke pain rats. These results suggest that histone deacetylase 2 upregulation and Kv1.2 downregulation, mediated by iron overload, are important factors in central post-stroke pain pathogenesis and could serve as new targets for central post-stroke pain treatment.

Modulation of endogenous opioid signaling by inhibitors of puromycin-sensitive aminopeptidase

The endogenous opioid system regulates pain through local release of neuropeptides and modulation of their action on opioid receptors. However, the effect of opioid peptides, the enkephalins, is short-lived due to their rapid hydrolysis by enkephalin-degrading enzymes. In turn, an innovative approach to the management of pain would be to increase the local concentration and prolong the stability of enkephalins by preventing their inactivation by neural enkephalinases such as puromycin-sensitive aminopeptidase (PSA). Our previous structure-activity relationship studies offered the S-diphenylmethyl cysteinyl derivative of puromycin (20) as a nanomolar inhibitor of PSA. This chemical class, however, suffered from undesirable metabolism to nephrotoxic puromycin aminonucleoside (PAN). To prevent such toxicity, we designed and synthesized 5'-chloro substituted derivatives. The compounds retained the PSA inhibitory potency of the corresponding 5'-hydroxy analogs and had improved selectivity toward PSA. In vivo treatment with the lead compound 19 caused significantly reduced pain response in antinociception assays, alone and in combination with Met-enkephalin. The analgesic effect was reversed by the opioid antagonist naloxone, suggesting the involvement of opioid receptors. Further, PSA inhibition by compound 19 in brain slices caused local increase in endogenous enkephalin levels, corroborating our rationale. Pharmacokinetic assessment of compound 19 showed desirable plasma stability and identified the cysteinyl sulfur as the principal site of metabolic liability. We gained additional insight into inhibitor-PSA interactions by molecular modeling, which underscored the importance of bulky aromatic amino acid in puromycin scaffold. The results of this study strongly support our rationale for the development of PSA inhibitors for effective pain management.

Gadolinium-based contrast agents aggravate mechanical and thermal hyperalgesia in a nitroglycerine-induced migraine model in male mice

In the diagnosis of migraine, which is a neurovascular disease, gadolinium-based contrast agents (GBCAs) are used to rule out more serious conditions. On the other hand, it remains unclear as a scientific gap whether GBCAs may trigger migraine-related pain. The aim of this study was to investigate the effect of GBCAs on mechanical and thermal pain behaviour in a nitroglycerin (NTG)-induced migraine model in mice. NTG (10 mg/kg) was administered intraperitoneally to adult (6-8weeks old) BALB/c mice 2 h before behavioral tests 5 times every other day on days 1st, 3rd, 5th and 9th to induce migraine model (N = 50). As GBCAs, gadobenate dimeglumine (linear-ionic), Gadodiamide (linear-nonionic), and gadobutrol (macrocyclic-nonionic) were delivered intravenously through the tail vein of mice for 5 days on test days. Mechanical pain threshold (plantar and facial withdrawal threshold) was evaluated by plantar von Frey and periorbital von Frey tests on days 1st, 5th, and 9th, and thermal pain threshold (latency) was evaluated by hot plate and cold plate tests on days 3rd and 7th. There was a statistically significant increase in mechanical and thermal hyperalgesia in NTG administered groups compared to the control group. Gadodiamide, gadobutrol and gadobenate dimeglumine administration significantly decreased latency, paw and facial withdrawal threshold (0.18 ± 0.05, 0.17 ± 0.07, 0.16 ± 0.09; 9th day values respectively) compared to NTG group (0.27 ± 0.05). The results of this in vivo study show that GBCAs produce effects that may trigger migraine attacks in migraine. It is recommended that these effects be further investigated and supported by further clinical studies.

Fenofibrate ameliorates nitroglycerin-induced migraine in rats: Role of CGRP/p-CREB/P2X3 and NGF/PKC/ASIC3 signaling pathways

Migraine, a debilitating neurological condition, significantly affects patients' quality of life. Fenofibrate, a peroxisome proliferator-activated receptor alpha (PPAR-α) agonist approved for managing dyslipidemia, has shown promise in treating neurological disorders. Therefore, this study aims to investigate the protective effects of fenofibrate against nitroglycerin (NTG)-induced chronic migraine in rats. Migraine was induced in rats by administering five intermittent doses of NTG (10 mg/kg, i. p.) on days 1, 3, 5, 7, and 9. Rats were treated with either topiramate (80 mg/kg/day, p. o.), a standard drug, or fenofibrate (100 mg/kg/day, p. o.) from day 1-10. Fenofibrate significantly improved mechanical and thermal hypersensitivity, photophobia, and head grooming compared to topiramate. These effects were associated with reduced serum levels of nitric oxide (NO), calcitonin gene-related peptide (CGRP), and pituitary adenylate cyclase-activating polypeptide (PACAP). Furthermore, fenofibrate down-regulated c-Fos expression in the medulla and medullary pro-inflammatory cytokine contents. Additionally, fenofibrate attenuated NTG-induced histopathological changes in the trigeminal ganglia and trigeminal nucleus caudalis. These effects were associated with the inhibition of CGRP/p-CREB/purinergic 2X receptor 3 (P2X3) and nerve growth factor (NGF)/protein kinase C (PKC)/acid-sensing ion channel 3 (ASIC3) signaling pathways. This study demonstrates that fenofibrate attenuated NTG-induced migraine-like signs in rats. These effects were partially mediated through the inhibition of CGRP/p-CREB/P2X3 and NGF/PKC/ASIC3 signaling pathways. The present study supports the idea that fenofibrate could be an effective candidate for treating migraine headache without significant adverse effects. Future studies should explore its clinical applicability.

Dermorphin [D-Arg2, Lys4] (1-4) Amide Alleviates Frostbite-Induced Pain by Regulating TRP Channel-Mediated Microglial Activation and Neuroinflammation

Cold injury or frostbite is a common medical condition that causes serious clinical complications including sensory abnormalities and chronic pain ultimately affecting overall well-being. Opioids are the first-choice drug for the treatment of frostbite-induced chronic pain; however, their notable side effects, including sedation, motor incoordination, respiratory depression, and drug addiction, present substantial obstacle to their clinical utility. To address this challenge, we have exploited peripheral mu-opioid receptors as potential target for the treatment of frostbite-induced chronic pain. In this study, we investigated the effect of dermorphin [D-Arg2, Lys4] (1-4) amide (DALDA), a peripheral mu-opioid receptor agonist, on frostbite injury and hypersensitivity induced by deep freeze magnet exposure in rats. Animals with frostbite injury displayed significant hypersensitivity to mechanical, thermal, and cold stimuli which was significant ameliorated on treatment with different doses of DALDA (1, 3, and 10 mg/kg) and ibuprofen (100 mg/kg). Further, molecular biology investigations unveiled heightened oxido-nitrosative stress, coupled with a notable upregulation in the expression of TRP channels (TRPA1, TRPV1, and TRPM8), glial cell activation, and neuroinflammation (TNF-α, IL-1β) in the sciatic nerve, dorsal root ganglion (DRG), and spinal cord of frostbite-injured rats. Treatment with DALDA leads to substantial reduction in TRP channels, microglial activation, and suppression of the inflammatory cascade in the ipsilateral L4-L5 DRG and spinal cord of rats. Overall, findings from the present study suggest that activation of peripheral mu-opioid receptors mitigates chronic pain in rats by modulating the expression of TRP channels and suppressing glial cell activation and neuroinflammation.

JWH-182: a safe and effective synthetic cannabinoid for chemotherapy-induced neuropathic pain in preclinical models

Chemotherapy-induced neuropathic pain (CINP), a condition with unmet treatment needs, affects over half of cancer patients treated with chemotherapeutics. Researchers have recently focused on the endocannabinoid system because of its critical role in regulating our bodies' most important functions, including pain. We used in vitro and in vivo methods to determine the toxicity profile of a synthetic cannabinoid, JWH-182, and whether it could be potentially effective for CINP alleviation. In vitro, we evaluated JWH-182 general toxicity, measuring fibroblast viability treated with various concentrations of compound, and its neuroprotection on dorsal root ganglion neurons treated with paclitaxel. In vivo, we performed an evaluation of acute and 28-day repeated dose toxicity in mice, with monitoring of health status and a complete histopathological examination. Finally, we evaluated the efficacy of JWH-182 on a CINP model in mice using specific pain assessment tests. JWH-182 has an acceptable toxicity profile, in both, in vitro and in vivo studies and it was able to significantly reduce pain perception in a CINP model in mice. However, the translation of these results to the clinic needs further investigation.

Comparison of nylon, vicryl, and fibrin glue for nerve grafting in rats

OBJECTIVES

For nerve injuries, not amendable to tensionless epineural coaptation of the nerve, autografts are the preferred treatment. Although absorbable sutures are not recommended for nerve repair, there is no evidence that non-absorbable sutures are superior to absorbable sutures. This study aims to assess the effectiveness of non-absorbable monofilament nylon sutures, absorbable monofilament vicryl sutures, and fibrin glue when used for nerve grafting.

METHODS

Lewis rats (N = 32) were subjected to a sciatic nerve transection and randomly assigned to a group: graft with Nylon, graft with Vicryl, graft with Fibrin Glue, or no graft. Motor function, sensory function, and thermal pain were assessed during a 12-week recovery period, and immunohistochemistry was used to assess macrophage response.

RESULTS

At 12 weeks, the Vicryl and Nylon groups had significantly larger ankle angles at to lift off, which is a measure of motor function, compared to injured controls (p < 0.05). Grafted rats displayed no difference in thermal response but hypersensitivity to mechanical stimuli compared to the uninjured hindlimb. The Nylon, Vicryl, and Fibrin Glue groups all had significantly less atrophy of the gastrocnemius muscle compared to injured controls (p < 0.0001). In the Fibrin Glue group, 3/9 grafts did not incorporate. The Nylon group had significantly less (p = 0.0004) axon growth surrounding the suture holes compared to the Vicryl group. There were no differences in the axon counts, motor neurons, or sensory neurons between all grafted rats.

CONCLUSIONS

These results demonstrate that vicryl sutures work just as well as nylon for nerve recovery after injury and grafting.

OBSERVE: guidelines for the refinement of rodent cancer models

Existing guidelines on the preparation (Planning Research and Experimental Procedures on Animals: Recommendations for Excellence (PREPARE)) and reporting (Animal Research: Reporting of In Vivo Experiments (ARRIVE)) of animal experiments do not provide a clear and standardized approach for refinement during in vivo cancer studies, resulting in the publication of generic methodological sections that poorly reflect the attempts made at accurately monitoring different pathologies. Compliance with the 3Rs guidelines has mainly focused on reduction and replacement; however, refinement has been harder to implement. The Oncology Best-practices: Signs, Endpoints and Refinements for in Vivo Experiments (OBSERVE) guidelines are the result of a European initiative supported by EurOPDX and INFRAFRONTIER, and aim to facilitate the refinement of studies using in vivo cancer models by offering robust and practical recommendations on approaches to research scientists and animal care staff. We listed cancer-specific clinical signs as a reference point and from there developed sets of guidelines for a wide variety of rodent models, including genetically engineered models and patient derived xenografts. In this Consensus Statement, we systematically and comprehensively address refinement and monitoring approaches during the design and execution of murine cancer studies. We elaborate on the appropriate preparation of tumor-initiating biologicals and the refinement of tumor-implantation methods. We describe the clinical signs to monitor associated with tumor growth, the appropriate follow-up of animals tailored to varying clinical signs and humane endpoints, and an overview of severity assessment in relation to clinical signs, implantation method and tumor characteristics. The guidelines provide oncology researchers clear and robust guidance for the refinement of in vivo cancer models.

Early signs of osteoarthritis in differing rat osteochondral defects

Preclinical models of osteochondral defects (OCDs) are fundamental test beds to evaluate treatment modalities before clinical translation. To increase the rigor and reproducibility of translational science for a robust "go or no-go," we evaluated disease progression and pain phenotypes within the whole joint for two OCD rat models with same defect size (1.5 x 0.8 mm) placed either in the trochlea or medial condyle of femur. Remarkably, we only found subtle transitory changes to gaits of rats with trochlear defect without any discernible effect to allodynia. At 8-weeks post-surgery, anatomical evaluations of joint showed early signs of osteoarthritis with EPIC-microCT. For the trochlear defect, cartilage attenuation was increased in trochlear, medial, and lateral compartments of the femur. For condylar defect, increased cartilage attenuation was isolated to the medial condyle of the femur. Further, the medial ossicle showed signs of deterioration as indicated with decreased bone mineral density and increased bone surface area to volume ratio. Thus, OCD in a weight-bearing region of the femur gave rise to more advanced osteoarthritis phenotype within a unilateral joint compartment. Subchondral bone remodeling was evident in both models without any indication of closure of the articular cartilage surface. We conclude that rat OCD, placed in the trochlear or condylar region of the femur, leads to differing severity of osteoarthritis progression. As found herein, repair of the defect with fibrous tissue and subchondral bone is insufficient to alleviate onset of osteoarthritis. Future therapies using rat OCD model should address joint osteoarthritis in addition to repair itself.

Synthesis, characterization, and biological study of new synthetic opioid hemorphin-4 peptides containing sterically restricted nonnatural amino acids

Some new hemorphin-4 analogs with structures of Xxx-Pro-Trp-Thr-NH2 and Tyr-Yyy-Trp-Thr-NH2, where Xxx is 2-amino-3-(4-hydroxy-2,6-dimethylphenyl)propanoic acid or 2-amino-3-(4-dibenzylamino-2,6-dimethylphenyl)propanoic acid, and Yyy is (2S,4S)-4-amino-pyrrolidine-2-carboxylic acid, were synthesized and characterized by electrochemical and spectral analyses. In vivo anticonvulsant and antinociceptive activities of peptide derivatives were studied after intracerebroventricular injection in mice. The therapeutic effects of the modified peptides on seizures and pain in mice were evaluated to provide valuable insights into the potential applications of the novel compounds. Electrochemical characterization showed that the compounds behave as weak protolytes and that they are in a soluble, stable molecular form at physiological pH values. The antioxidant activity of the peptides was evaluated with voltammetric analyses, which were confirmed by applying the 2,2-Diphenyl-1-picrylhydrazyl method. The compounds showed satisfactory results regarding their structural stability, reaching the desired centers for the manifestation of biological activity without hydrolysis processes at 37°C and physiological pH. Dm-H4 and H4-P1 exhibited 100% and 83% potency to suppress the psychomotor seizures in the 6-Hz test compared to 67% activity of H4. Notably, only the H4-P1 had efficacy in blocking the tonic component in the maximal electroshock test with a potency comparable to H4. All investigated peptides containing unnatural conformationally restricted amino acids showed antinociceptive effects. The analogs Db-H4 and H4-P1 showed the most pronounced and long-lasting effect in both experimental models of pain induced by thermal and chemical stimuli. Dm-H4 produced a dose-dependent thermal antinociception and H4-P2 inhibited only formalin-induced pain behavior.

Intramuscular Pulsed Radiofrequency Upregulates BNDF-TrKB Expression in the Spinal Cord in Rats as an Alternative Treatment for Complicated Pain

Two cases of complicated pain exist: posterior screw fixation and myofascial pain. Intramuscular pulsed radiofrequency (PRF) may be an alternative treatment for such patients. This is a two-stage animal study. In the first stage, two muscle groups and two nerve groups were subdivided into a high-temperature group with PRF at 58 °C and a regular temperature with PRF at 42 °C in rats. In the second stage, two nerve injury groups were subdivided into nerve injury with PRF 42 °C on the sciatic nerve and muscle. Blood and spinal cord samples were collected. In the first stage, the immunohistochemical analysis showed that PRF upregulated brain-derived neurotrophic factor (BDNF) in the spinal cord in both groups of rats. In the second stage, the immunohistochemical analysis showed significant BDNF and tropomyosin receptor kinase B (TrkB) expression within the spinal cord after PRF in muscles and nerves after nerve injury. The blood biomarkers showed a significant increase in BDNF levels. PRF in the muscle in rats could upregulate BDNF-TrkB in the spinal cord, similar to PRF on the sciatica nerve for pain relief in rats. PRF could be considered clinically for patients with complicated pain and this study also demonstrated the role of BDNF in pain modulation. The optimal temperature for PRF was 42 °C.

Amphiphilic NLC-Gel formulation loaded with Sebacoyl dinalbuphine ester and Nalbuphine for localized postoperative pain management

Opioids are powerful analgesics; however, their significant systemic adverse effects and the need for frequent administration restrict their use. Nalbuphine (NA) is a κ-agonist narcotic with limited adverse effects, but needs to be frequently administrated due to its short elimination half-life. Whereas sebacoyl dinalbuphine ester (SDE) is a NA prodrug, which can effectively prolong the analgesic effect, but lacks immediate pain relief. Therefore, in this study, a rapid and sustained local delivery formulation to introduce NA and SDE directly into surgical sites was developed. An amphiphilic nanostructured lipid carrier (NLC) poloxamer 407 (P407) gel (NLC-Gel) was developed to permit concurrent delivery of hydrophobic SDE from the NLC core and hydrophilic NA from P407, offering a dual rapid and prolonged analgesic effect. Benefiting from the thermal-sensitive characteristic of P407, the formulation can be injected in liquid phase and instantly transit into gel at wound site. NLC-Gel properties, including particle size, drug release, rheology, and stability, were assessed. In vivo evaluation using a rat spinal surgery model highlighted the effect of the formulation through pain behavior test and hematology analysis. NLC-Gels demonstrated an analgesic effect comparable with that of commercial intramuscular injected SDE formulation (IM SDE), with only 15 % of the drug dosage. The inclusion of supplemental NA in the exterior gel (PA12-Gel + NA) provided rapid drug onset owing to swift NA dispersion, addressing acute pain within hours along with prolonged analgesic effects. Our findings suggest that this amphiphilic formulation significantly enhanced postoperative pain management in terms of safety and efficacy.

Cannabinoid receptor 1 positive allosteric modulator ZCZ011 shows differential effects on behavior and the endocannabinoid system in HIV-1 Tat transgenic female and male mice

The cannabinoid receptor type 1 (CB1R) is a promising therapeutic target for various neurodegenerative diseases, including HIV-1-associated neurocognitive disorder (HAND). However, the therapeutic potential of CB1R by direct activation is limited due to its psychoactive side effects. Therefore, research has focused on indirectly activating the CB1R by utilizing positive allosteric modulators (PAMs). Studies have shown that CB1R PAMs (ZCZ011 and GAT211) are effective in mouse models of Huntington's disease and neuropathic pain, and hence, we assess the therapeutic potential of ZCZ011 in a well-established mouse model of neuroHIV. The current study investigates the effect of chronic ZCZ011 treatment (14 days) on various behavioral paradigms and the endocannabinoid system in HIV-1 Tat transgenic female and male mice. Chronic ZCZ011 treatment (10 mg/kg) did not alter body mass, locomotor activity, or anxiety-like behavior regardless of sex or genotype. However, differential effects were noted in hot plate latency, motor coordination, and recognition memory in female mice only, with ZCZ011 treatment increasing hot plate latency and improving motor coordination and recognition memory. Only minor effects or no alterations were seen in the endocannabinoid system and related lipids except in the cerebellum, where the effect of ZCZ011 was more pronounced in female mice. Moreover, AEA and PEA levels in the cerebellum were positively correlated with improved motor coordination in female mice. In summary, these findings indicate that chronic ZCZ011 treatment has differential effects on antinociception, motor coordination, and memory, based on sex and HIV-1 Tat expression, making CB1R PAMs potential treatment options for HAND without the psychoactive side effects.

Disrupted stress-induced analgesia in a neuropathic pain state is rescued by the endocannabinoid degradation inhibitor JZL195

Acute stress normally engages descending brain pathways to produce an antinociceptive response, known as stress-induced analgesia. Paradoxically, these descending pain modulatory pathways are also involved in the maintenance of the abnormal pain associated with chronic neuropathic pain. It remains unclear how stress-induced analgesia is affected by neuropathic pain states. We therefore examined the impact of a chronic constriction nerve-injury (CCI) model of neuropathic pain on restraint stress-induced analgesia in C57BL/6 mice. Thirty minutes of restraint stress produced analgesia in the hotplate thermal nociceptive assay that was less in CCI compared to control mice who underwent a sham-surgery. In sham but not CCI mice, stress-induced analgesia was reduced by the opioid receptor antagonist naltrexone. The cannabinoid CB1 receptor antagonist AM281 did not affect stress-induced analgesia in either sham or CCI mice. Low-dose pre-treatment with the dual fatty acid amide hydrolase and monoacylglycerol lipase inhibitor JZL195 increased stress-induced analgesia in CCI but not sham mice. The JZL195 enhancement of stress-induced analgesia in CCI mice was abolished by AM281 but was unaffected by naltrexone. These findings indicate that the acute opioid-mediated analgesic response to a psychological stressor is disrupted in a nerve-injury model of neuropathic pain. Importantly, this impairment of stress-induced analgesia was rescued by blockade of endocannabinoid breakdown via a cannabinoid CB1 receptor dependent mechanism. These findings suggest that subthreshold treatment with endocannabinoid degradation blockers could be used to alleviate the disruption of endogenous pain control systems in a neuropathic pain state.

Development of a novel three-dimensional injection guide for trigeminal ganglia

BACKGROUND

Trigeminal ganglion (TG) plays an important role in the process of orthodontic pain. It's necessary to design an accurate, precise and minimally invasive trigeminal ganglion injection guide plate to study TG.

METHODS

Micro-CT was used to obtain the Dicom format data, and three-dimensional (3D) software (mimics and magics23.03) was used to reconstruct 3D head models. Design and modifications of the TG injection guide plate were performed in Magic 23.03 software, and the guide plate was produced by a 3D stereolithography printer. X-ray, micro-CT, Evans blue, and virus transduction were used to demonstrate the accuracy of the guide-assisted injection. Pain levels were evaluated after using the injection guide by a bite force test and Von Frey test.

RESULTS

X-ray and micro-CT tests confirmed that the injection needle reached the bilateral trigeminal ganglia fossa. The Evans blue test and virus transduction proved that the injected drug could be accurately injected into the bilateral trigeminal ganglion and the lentivirus could be successfully transfected. The percentage of accurate injection was 10/10 (bilateral trigeminal ganglia). Orofacial pain induced by the trigeminal ganglion injection was mild and returned to baseline within seven days.

CONCLUSION

The injection guide described in this study is viable and reliable for the delivery of drugs and virus transduction into the trigeminal ganglia.

Ursolic acid inhibits NF-κB signaling and attenuates MMP-9/TIMP-1 in progressive osteoarthritis: a network pharmacology-based analysis

Osteoarthritis (OA) is a degenerative joint disease, characterized by infiltration of monocytes into the synovial joint which promotes inflammation, stiffness, joint swelling, cartilage degradation and further bone destruction. The leaves of Ocimum forskolei have been used for inflammation-related disease management in traditional medicine. Additionally, the downregulation of NF-κB and the MMP/TIMP-1 ratio has been shown to protect against OA. The LC-HR-MS metabolic analysis of Ocimum yielded 19 putative compounds, among which ursolic acid (UA) was detected. Ursolic acid possesses significant anti-inflammatory effects and has been reported to downregulate oxidative stress and inflammatory biomarkers. It was tested on rats in a model of intra-articular carrageenan injection to investigate its efficacy on osteoarthritis progression. The UA emulgel exerted chondroprotective, analgesic and local anaesthetic efficacies confirmed via histopathological investigation and radiographical imaging. A network pharmacology followed by molecular docking highlighted TNF-α, TGF-β and NF-κB as the top filtered genes. Quantitative real-time PCR analysis showed that UA significantly attenuated serum levels of TNF-α, IL-1β, NF-κB, MMP-9/TIMP-1 and elevated levels of TGF-β. Taken together, these results suggest that UA could serve as a functional food-derived phytochemical with a multi-targeted efficacy on progression of OA, regulating the immune and inflammatory responses, particularly, attenuating chondrocytes degeneration via suppression of NF-κB and MMP-9/TIMP-1. Accordingly, UA might be a promising alternative to conventional therapy for safe, easily applicable and effective management of OA.

Transplantation of dorsal root ganglia overexpressing the NaChBac sodium channel improves locomotion after complete SCI

Spinal cord injury (SCI) is a debilitating condition currently lacking treatment. Severe SCI causes the loss of most supraspinal inputs and neuronal activity caudal to the injury, which, coupled with the limited endogenous capacity for spontaneous regeneration, can lead to complete functional loss even in anatomically incomplete lesions. We hypothesized that transplantation of mature dorsal root ganglia (DRGs) genetically modified to express the NaChBac sodium channel could serve as a therapeutic option for functionally complete SCI. We found that NaChBac expression increased the intrinsic excitability of DRG neurons and promoted cell survival and neurotrophic factor secretion in vitro. Transplantation of NaChBac-expressing dissociated DRGs improved voluntary locomotion 7 weeks after injury compared to control groups. Animals transplanted with NaChBac-expressing DRGs also possessed higher tubulin-positive neuronal fiber and myelin preservation, although serotonergic descending fibers remained unaffected. We observed early preservation of the corticospinal tract 14 days after injury and transplantation, which was lost 7 weeks after injury. Nevertheless, transplantation of NaChBac-expressing DRGs increased the neuronal excitatory input by an increased number of VGLUT2 contacts immediately caudal to the injury. Our work suggests that the transplantation of NaChBac-expressing dissociated DRGs can rescue significant motor function, retaining an excitatory neuronal relay activity immediately caudal to injury.

Intrathecal gastrodin alleviates allodynia in a rat spinal nerve ligation model through NLRP3 inflammasome inhibition

BACKGROUND

Gastrodin (GAS), a main bioactive component of the herbal plant, Gastrodia elata Blume, has shown to have beneficial effects on neuroinflammatory diseases such as Alzheimer's disease in animal studies and migraine in clinical studies. Inflammasome is a multimeric protein complex having a core of pattern recognition receptor and has been implicated in the development of neuroinflammatory diseases. Gastrodin has shown to modulate the activation of nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome. This study investigated the effects of GAS on the intensity of mechanical allodynia and associated changes in NLRP3 inflammasome expression at the spinal level using L5/6 spinal nerve ligation model (SNL) in rats.

METHODS

Intrathecal (IT) catheter implantation and SNL were used for drug administration and pain model in male Sprague-Dawley rats. The effect of gastrodin or MCC950 (NLRP3 inflammasome inhibitor) on mechanical allodynia was measured by von Frey test. Changes in NLRP3 inflammasome components and interleukin-1β (IL-1β) and cellular expression were examined in the spinal cord and dorsal root ganglion.

RESULTS

The expression of NLRP3 inflammasome components was found mostly in the neurons in the spinal cord and dorsal root ganglion. The protein and mRNA levels of NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), caspase-1, and IL-1β were upregulated in SNL animals compared to Sham animals. IT administration of GAS significantly attenuated the expression of NLRP3 inflammasome and the intensity of SNL-induced mechanical allodynia. NLRP3 inflammasome inhibitor, MCC950, also attenuated the intensity of allodynia, but the effect is less strong and shorter than that of GAS.

CONCLUSIONS

Expression of NLRP3 inflammasome and IL-1β is greatly increased and mostly found in the neurons at the spinal level in SNL model, and IT gastrodin exerts a significant anti-allodynic effect in SNL model partly through suppressing the expression of NLRP3 inflammasome.

In vivo anti-inflammatory activity of BACCHARIN from BRAZILIAN green PROPOLIS

Baccharin is one of the major compounds found in Brazilian green propolis and its botanical source, Baccharis dracunculifolia. Considering the biological effects of propolis and B. dracunculifolia, this study aims to evaluate the analgesic and anti-inflammatory potential of baccharin. The neurodepressor potential was performed by the open field test, analgesia by mechanical stimulation with Dynamic Plantar Aesthesiometer, and by thermal stimulation with Hargreaves apparatus. In addition, the anti-inflammatory potential was achieved by the paw edema assay, histopathological evaluation, and NF-kB expression. Doses of 2.5, 5, and 10 mg/kg of baccharin were evaluated. After euthanasia, plantar tissue was collected and prepared for histology. As a result, analgesic activity was observed at a dose of 10 mg/kg of baccharin in thermal stimulation under an inflammatory process and anti-inflammatory potential at a dose of 5 mg/kg of baccharin from the second hour in the paw edema test. A decrease in cellular infiltrate and down-modulation of NF-kB, besides the reduction of edema in the histopathology was observed. There was no evidence of kidney and liver toxicity and neurodepressive potential at the doses tested. Thus, baccharin has a promising anti-inflammatory effect possibly associated with antiedematogenic activity by inhibiting mediators such as prostaglandins, inhibiting the migration of polymorphonuclear cells, and modulating NF-kB expression.

Binary classification model of machine learning detected altered gut integrity in controlled-cortical impact model of traumatic brain injury

Aim of the study: To examine the effect of controlled-cortical impact (CCI), a preclinical model of traumatic brain injury (TBI), on intestinal integrity using a binary classification model of machine learning (ML).Materials and methods: Adult, male C57BL/6 mice were subjected to CCI surgery using a stereotaxic impactor (Impact One™). The rotarod and hot-plate tests were performed to assess the neurological deficits.Results: Mice underwent CCI displayed a remarkable neurological deficit as noticed by decreased latency to fall and lesser paw withdrawal latency in rotarod and hot plate test, respectively. Animals were sacrificed 3 days post-injury (dpi). The colon sections were stained with hematoxylin and eosin (H&E) to integrate with machinery tool-based algorithms. Several stained colon images were captured to build a dataset for ML model to predict the impact of CCI vs sham procedure. The best results were obtained with VGG16 features with SVM RBF kernel and VGG16 features with stacked fully connected layers on top. We achieved a test accuracy of 84% and predicted the disrupted gut permeability and epithelium wall of colon in CCI group as compared to sham-operated mice.Conclusion: We suggest that ML may become an important tool in the development of preclinical TBI model and discovery of newer therapeutics.

Transspinal Focused Ultrasound Suppresses Spinal Reflexes in Healthy Rats

OBJECTIVES

Low-intensity, focused ultrasound (FUS) is an emerging noninvasive neuromodulation approach, with improved spatial and temporal resolution and penetration depth compared to other noninvasive electrical stimulation strategies. FUS has been used to modulate circuits in the brain and the peripheral nervous system, however, its potential to modulate spinal circuits is unclear. In this study, we assessed the effect of trans-spinal FUS (tsFUS) on spinal reflexes in healthy rats.

MATERIALS AND METHODS

tsFUS targeting different spinal segments was delivered for 1 minute, under anesthesia. Monosynaptic H-reflex of the sciatic nerve, polysynaptic flexor reflex of the sural nerve, and withdrawal reflex tested with a hot plate were measured before, during, and after tsFUS.

RESULTS

tsFUS reversibly suppresses the H-reflex in a spinal segment-, acoustic pressure- and pulse-repetition frequency (PRF)-dependent manner. tsFUS with high PRF augments the degree of homosynaptic depression of the H-reflex observed with paired stimuli. It suppresses the windup of components of the flexor reflex associated with slower, C-afferent, but not faster, A- afferent fibers. Finally, it increases the latency of the withdrawal reflex. tsFUS does not elicit neuronal loss in the spinal cord.

CONCLUSIONS

Our study provides evidence that tsFUS reversibly suppresses spinal reflexes and suggests that tsFUS could be a safe and effective strategy for spinal cord neuromodulation in disorders associated with hyperreflexia, including spasticity after spinal cord injury and painful syndromes.

SIRT1 mediates the excitability of spinal CaMKIIα-positive neurons and participates in neuropathic pain by controlling Nav1.3

AIMS

Neuropathic pain is a common chronic pain disorder, which is largely attributed to spinal central sensitization. Calcium/calmodulin-dependent protein kinase II alpha (CaMKIIα) activation in the spinal dorsal horn (SDH) is a major contributor to spinal sensitization. However, the exact way that CaMKIIα-positive (CaMKIIα+) neurons in the SDH induce neuropathic pain is still unclear. This study aimed to explore the role of spinal CaMKIIα+ neurons in neuropathic pain caused by chronic constriction injury (CCI) and investigate the potential epigenetic mechanisms involved in CaMKIIα+ neuron activation.

METHODS

CCI-induced neuropathic pain mice model, Sirt1loxP/loxP mice, and chemogenetic virus were used to investigate whether the activation of spinal CaMKIIα+ neurons is involved in neuropathic pain and its involved mechanism. Transcriptome sequence, western blotting, qRT-PCR, and immunofluorescence analysis were performed to assay the expression of related molecules and activation of neurons. Co-immunoprecipitation was used to observe the binding relationship of protein. Chromatin immunoprecipitation (ChIP)-PCR was applied to analyze the acetylation of histone H3 in the Scn3a promoter region.

RESULTS

The expression of sodium channel Nav1.3 was increased and the expression of SIRT1 was decreased in the spinal CaMKIIα+ neurons of CCI mice. CaMKIIα neurons became overactive after CCI, and inhibiting their activation relieved CCI-induced pain. Overexpression of SIRT1 reversed the increase of Nav1.3 and alleviated pain, while knockdown of SIRT1 or overexpression of Nav1.3 promoted CaMKIIα+ neuron activation and induced pain. By knocking down spinal SIRT1, the acetylation of histone H3 in the Scn3a (encoding Nav1.3) promoter region was increased, leading to an increased expression of Nav1.3.

CONCLUSION

The findings suggest that an aberrant reduction of spinal SIRT1 after nerve injury epigenetically increases Nav1.3, subsequently activating CaMKIIα+ neurons and causing neuropathic pain.

A novel animal model of tegafur-induced hand-foot syndrome

Hand-foot syndrome (HFS) is a common side effect of fluoropyrimidine anticancer drugs and often becomes a dose-limiting manifestation of toxicity once it occurs. The precise mechanism of HFS remains unclear, and effective measures to prevent or relieve it are currently limited. To investigate the pathogenesis of HFS and effective measures for treating or preventing it, establishment of animal models is crucial. Here, we gave male SD rats 170 mg/kg of tegafur (prodrug of 5-FU) daily for 35 days and evaluated their clinical and histopathological characteristics and pain-related behavioral tests. TUNEL-positive apoptotic cells and 5-FU concentrations in the plantar skin were also evaluated to investigate the mode of toxicity. Tegafur treatment induced hypersensitivity to mechanical pressure on the plantar surface beginning in Week 3, with decreased locomotor activity. Focal desquamation of the plantar skin was observed almost concomitantly and gradually worsened to palmar and plantar skin thickening with severe desquamation, cracks, or both. Histopathological lesions in the plantar skin at treatment end included desquamation and thickening, with epidermal cell swelling and spongiosis and focal inflammation in the dermis. The time-course of development and the characteristics of the tegafur-induced skin lesions were highly similar to those in human fluoropyrimidine-induced HFS, indicating that a HFS rat model was successfully established. Localized high concentrations of 5-FU in the palmar and plantar skin, with increased apoptosis, are likely involved in the mode of toxicity. Our model should clarify the pathogenesis of HFS, providing new insights into the best supportive care and prevention.

Chlorogenic acid co-administration alleviates cisplatin-induced peripheral neuropathy in rats

BACKGROUND

Chemotherapy-induced peripheral neuropathy (CIPN) is still an unresolved problem in cisplatin (CIS) use.

OBJECTIVES

This study investigates possible anti-neuropathic effect of chlorogenic acid (CGA) against CIS-induced CIPN in rats while also investigating the contribution of nitric oxide (NO) to this phenomenon.

METHODS

Initially, CGA (250-1000 μM) was tested by MTT assay on primary DRG neurons. Subsequently, CIPN was induced in Sprague-Dawley rats by 3 mg/kg intraperitoneal injections of CIS once/week for 5 weeks. CGA (100 mg/kg) was co-administered with CIS, both alone and in combination with l-arginine (LARG) or l-nitro-arginine-methyl-ester (LNAME), to elucidate the contribution of nitrergic system to anti-neuropathic effects. Mechanical allodynia, thermal hyperalgesia, and cold plate tests were performed to test CIPN. Rotarod, footprint analysis, and activitymeter were used to evaluate motor coordination and performance. Tumor necrosis factor alpha (TNF-α) was measured as a marker of inflammation. Histological evaluations of DRG and sciatic nerves (SNs) were performed utilizing toluidine blue staining. Two-way analysis of variance and Kruskal-Wallis following Tukey's test were used as statistical analysis.

RESULTS

Higher concentration of CGA (1000 μM) exhibited protective effect against in vitro neurotoxicity. Neither LARG nor LNAME exerted significant change in this effect. Co-administration of CGA alleviated histological abnormalities and neuropathic effects induced by CIS. Ameliorative effect of CGA was not changed in mechanical allodynia but attenuated in cold allodynia, and motor activity/coordination tests by LARG and LNAME. Neuropathic effects of CIS remained unchanged with LARG and LNAME in behavioral experiments.

CONCLUSION

The study identified CGA as candidate agent in mitigating CIPN. NO seems to play a modulatory role in this effect.

Local anesthetic delivery systems for the management of postoperative pain

Postoperative pain (POP) is a major clinical challenge. Local anesthetics (LAs), including amide-type LAs, ester-type LAs, and other potential ion-channel blockers, are emerging as drugs for POP management because of their effectiveness and affordability. However, LAs typically exhibit short durations of action and prolonging the duration by increasing their dosage or concentration may increase the risk of motor block or systemic local anesthetic toxicity. In addition, techniques using LAs, such as intrathecal infusion, require professional operation and are prone to catheter displacement, dislodgement, infection, and nerve damage. With the development of materials science and nanotechnology, various LAs delivery systems have been developed to compensate for these disadvantages. Numerous delivery systems have been designed to continuously release a safe dose in a single administration to ensure minimal systemic toxicity and prolong pain relief. LAs delivery systems can also be designed to control the duration and intensity of analgesia according to changes in the external trigger conditions, achieve on-demand analgesia, and significantly improve pain relief and patient satisfaction. In this review, we summarize POP pathways, animal models and methods for POP testing, and highlight LAs delivery systems for POP management. STATEMENT OF SIGNIFICANCE: Postoperative pain (POP) is a major clinical challenge. Local anesthetics (LAs) are emerging as drugs for POP management because of their effectiveness and affordability. However, they exhibit short durations and toxicity. Various LAs delivery systems have been developed to compensate for these disadvantages. They have been designed to continuously release a safe dose in a single administration to ensure minimal toxicity and prolong pain relief. LAs delivery systems can also be designed to control the duration and intensity of analgesia to achieve on-demand analgesia, and significantly improve pain relief and patient satisfaction. In this paper, we summarize POP pathways, animal models, and methods for POP testing and highlight LAs delivery systems for POP management.

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.

Schwann cell TRPA1 elicits reserpine-induced fibromyalgia pain in mice

BACKGROUND AND PURPOSE

Fibromyalgia is a complex clinical disorder with an unknown aetiology, characterized by generalized pain and co-morbid symptoms such as anxiety and depression. An imbalance of oxidants and antioxidants is proposed to play a pivotal role in the pathogenesis of fibromyalgia symptoms. However, the precise mechanisms by which oxidative stress contributes to fibromyalgia-induced pain remain unclear. The transient receptor potential ankyrin 1 (TRPA1) channel, known as both a pain sensor and an oxidative stress sensor, has been implicated in various painful conditions.

EXPERIMENTAL APPROACH

The feed-forward mechanism that implicates reactive oxygen species (ROS) driven by TRPA1 was investigated in a reserpine-induced fibromyalgia model in C57BL/6J mice employing pharmacological interventions and genetic approaches.

KEY RESULTS

Reserpine-treated mice developed pain-like behaviours (mechanical/cold hypersensitivity) and early anxiety-depressive-like disorders, accompanied by increased levels of oxidative stress markers in the sciatic nerve tissues. These effects were not observed upon pharmacological blockade or global genetic deletion of the TRPA1 channel and macrophage depletion. Furthermore, we demonstrated that selective silencing of TRPA1 in Schwann cells reduced reserpine-induced neuroinflammation (NADPH oxidase 1-dependent ROS generation and macrophage increase in the sciatic nerve) and attenuated fibromyalgia-like behaviours.

CONCLUSION AND IMPLICATIONS

Activated Schwann cells expressing TRPA1 promote an intracellular pathway culminating in the release of ROS and recruitment of macrophages in the mouse sciatic nerve. These cellular and molecular events sustain mechanical and cold hypersensitivity in the reserpine-evoked fibromyalgia model. Targeting TRPA1 channels on Schwann cells could offer a novel therapeutic approach for managing fibromyalgia-related behaviours.

The Effect of Pregabalin on Microglia Differentiation in Rat with Neuropathic pain: A Preliminary Study

This study investigated the effects of pregabalin on microglial differentiation in rats with neuropathic pain (NP) induced by sciatic nerve ligation and transection. After confirming NP, the rats were randomly allocated to either a pregabalin or control group. The pregabalin group received intraperitoneal injections of 10 mg/kg pregabalin, while the control group received an equivalent volume of normal saline following surgery. On postoperative day 28, neuronal damage, microglial activity, and microglial differentiation were assessed. The pregabalin group exhibited significantly less neuronal damage compared to the control group, along with a significant decrease in activated microglial expression in both the brain and spinal cord. Pregabalin treatment also significantly altered the microglial phenotype expression, with a decrease in the M1 phenotype percentage and an increase in the M2 phenotype percentage in both the brain (M1 phenotype: 43.52 ± 12.16% and 18.00 ± 8.57% in the control and pregabalin groups, respectively; difference: 27.26 [15.18-42.10], p = 0.002; M2 phenotype: 16.88 ± 6.47% and 39.63 ± 5.82% in the control and pregabalin groups, respectively; difference 22.04 [17.17-32.70], p < 0.001) and the spinal cord ipsilateral to nerve injury (M1 phenotype: 44.35 ± 12.12% and 13.78 ± 5.39% in the control and pregabalin groups, respectively; difference 30.46 [21.73-44.45], p < 0.001; M2 phenotype: 7.64 ± 3.91% and 33.66 ± 7.95% in the control and pregabalin groups, respectively; difference 27.41 [21.21-36.30], p < 0.001). Overall, pregabalin treatment significantly decreased the microglial M1 phenotype while increasing the microglial M2 phenotype in NP rats.

Dietary fiber may benefit chondrocyte activity maintenance

The understanding of the link between the gut-bone axis is growing yearly, but the mechanisms involved are not yet clear. Our study analyzed the role of Sestrin2 (SESN2)pathway in the gut-bone axis. We established an osteoarthritis (OA) model in Sprague-Dawley (SD) rats using the anterior cruciate ligament transection (ACLT) procedure, followed by a dietary intervention with varying levels of dietary fiber content for 8 weeks. By 16S rRNA sequencing of the gut microbiota, we found that high dietary fiber (HDF) intake could significantly increase the Bacillota-dominant gut microbiota. Meanwhile, enzyme linked immunosorbent assay (ELISA) and histological analysis showed that intervention with HDF could reduce the degree of bone and joint lesions and inflammation. We hypothesize that HDF increased the dominant flora of Bacillota, up-regulated the expression of SESN2 in knee joint, and reduced gut permeability, thereby reducing systemic inflammatory response and the degree of bone and joint lesions. Therefore, the present study confirms that changes in gut microbiota induced by increased dietary fiber intake delayed the onset of OA by promoting up-regulation of SESN2 expression at the knee joint to maintain chondrocyte activity and reduce synovial inflammation.

Pharmacological potential of 4-dimethylamino chalcone against acute and neuropathic pain in mice

OBJECTIVES

This work investigated the acute antinociceptive effect of a synthetic chalcone, 4-dimethylamino chalcone (DMAC), as well as its effects on vincristine-induced peripheral neuropathy (VIPN) in mice.

METHODS

The inhibitory activity of myeloperoxidase was assessed by measuring HOCl formation. Formalin and hot plate tests were used to study the acute antinociceptive effect of DMAC. VIPN was induced through the administration of vincristine sulphate (0.1 mg/kg, i.p., 14 days). Then, DMSO, DMAC (10 or 30 mg/kg; i.p.), or pregabalin (10 mg/kg, i.p.) were administered for 14 consecutive days. Thermal hyperalgesia and mechanical allodynia were evaluated before and after VIPN induction and on days 1, 3, 7, and 14 of treatment. Neurodegeneration and neuroinflammation were assessed through immunohistochemistry for NF200, iNOS, and arginase-1 within the sciatic nerve.

KEY FINDINGS

DMAC inhibited myeloperoxidase activity in vitro and presented an acute antinociceptive effect in both formalin and hot plate tests, with the involvement of muscarinic and opioid receptors. Treatment with 30 mg/kg of DMAC significantly attenuated thermal hyperalgesia and mechanical allodynia and prevented macrophage proinflammatory polarisation in VIPN mice.

CONCLUSIONS

Our results show that DMAC, acting through different mechanisms, effectively attenuates VIPN.

Extrasynaptic δGABAA receptors mediate resistance to migraine-like phenotype in rats

BACKGROUND

GABA, a key inhibitory neurotransmitter, has synaptic and extrasynaptic receptors on the postsynaptic neuron. Background GABA, which spills over from the synaptic cleft, acts on extrasynaptic delta subunit containing GABAA receptors. The role of extrasynaptic GABAergic input in migraine is unknown. We investigated the susceptibility to valid migraine-provoking substances with clinically relevant behavioral readouts in Genetic Absence Epilepsy of Rats Strasbourg (GAERS), in which the GABAergic tonus was altered. Subsequently, we screened relevant GABAergic mechanisms in Wistar rats by pharmacological means to identify the mechanisms.

METHODS

Wistar and GAERS rats were administered nitroglycerin (10 mg/kg) or levcromakalim (1 mg/kg). Mechanical allodynia and photophobia were assessed using von Frey monofilaments and a dark-light box. Effects of GAT-1 blocker tiagabine (5 mg/kg), GABAB receptor agonist baclofen (2 mg/kg), synaptic GABAA receptor agonist diazepam (1 mg/kg), extrasynaptic GABAA receptor agonists gaboxadol (4 mg/kg), and muscimol (0.75 mg/kg), T-type calcium channel blocker ethosuximide (100 mg/kg) or synaptic GABAA receptor antagonist flumazenil (15 mg/kg) on levcromakalim-induced migraine phenotype were screened.

RESULTS

Unlike Wistar rats, GAERS exhibited no reduction in mechanical pain thresholds or light aversion following nitroglycerin or levcromakalim injection. Ethosuximide did not reverse the resistant phenotype in GAERS, excluding the role of T-type calcium channel dysfunction in this phenomenon. Tiagabine prevented levcromakalim-induced mechanical allodynia in Wistar rats, suggesting a key role in enhanced GABA spillover. Baclofen did not alleviate mechanical allodynia. Diazepam failed to mitigate levcromakalim-induced migraine phenotype. Additionally, the resistant phenotype in GAERS was not affected by flumazenil. Extrasynaptic GABAA receptor agonists gaboxadol and muscimol inhibited periorbital allodynia in Wistar rats.

CONCLUSION

Our study introduced a rat strain resistant to migraine-provoking agents and signified a critical involvement of extrasynaptic δGABAergic receptors. Extrasynaptic δ GABAA receptors, by mediating constant background inhibition on the excitability of neurons, stand as a novel drug target with a therapeutic potential in migraine.

No Evidence of Sensory Neuropathy in a Traditional Mouse Model of Idiopathic Parkinson's Disease

Parkinson's disease (PD) is the second-most common neurodegenerative disorder worldwide and is diagnosed based on motor impairments. Non-motor symptoms are also well-recognised in this disorder, and peripheral neuropathy is a frequent but poorly appreciated non-motor sign. Studying how central and peripheral sensory systems are affected can contribute to the development of targeted therapies and deepen our understanding of the pathophysiology of PD. Although the cause of sporadic PD is unknown, chronic exposure to the pesticide rotenone in humans increases the risk of developing the disease. Here, we aimed to investigate whether peripheral neuropathy is present in a traditional model of PD. Mice receiving intrastriatal rotenone showed greatly reduced dopamine terminals in the striatum and a reduction in tyrosine hydroxylase-positive neurons in the Substantia nigra pars compacta and developed progressive motor impairments in hindlimb stepping and rotarod but no change in spontaneous activity. Interestingly, repeated testing using gold-standard protocols showed no change in gut motility, a well-known non-motor symptom of PD. Importantly, we did not observe any change in heat, cold, or touch sensitivity, again based upon repeated testing with well-validated protocols that were statistically well powered. Therefore, this traditional model fails to replicate PD, and our data again reiterate the importance of the periphery to the disorder.

Implication of system xc- in neuroinflammation during the onset and maintenance of neuropathic pain

BACKGROUND

Despite the high prevalence of neuropathic pain, treating this neurological disease remains challenging, given the limited efficacy and numerous side effects associated with current therapies. The complexity in patient management is largely attributed to an incomplete understanding of the underlying pathological mechanisms. Central sensitization, that refers to the adaptation of the central nervous system to persistent inflammation and heightened excitatory transmission within pain pathways, stands as a significant contributor to persistent pain. Considering the role of the cystine/glutamate exchanger (also designated as system xc-) in modulating glutamate transmission and in supporting neuroinflammatory responses, we investigated the contribution of this exchanger in the development of neuropathic pain.

METHODS

We examined the implication of system xc- by evaluating changes in the expression/activity of this exchanger in the dorsal spinal cord of mice after unilateral partial sciatic nerve ligation. In this surgical model of neuropathic pain, we also examined the consequence of the genetic suppression of system xc- (using mice lacking the system xc- specific subunit xCT) or its pharmacological manipulation (using the pharmacological inhibitor sulfasalazine) on the pain-associated behavioral responses. Finally, we assessed the glial activation and the inflammatory response in the spinal cord by measuring mRNA and protein levels of GFAP and selected M1 and M2 microglial markers.

RESULTS

The sciatic nerve lesion was found to upregulate system xc- at the spinal level. The genetic deletion of xCT attenuated both the amplitude and the duration of the pain sensitization after nerve surgery, as evidenced by reduced responses to mechanical and thermal stimuli, and this was accompanied by reduced glial activation. Consistently, pharmacological inhibition of system xc- had an analgesic effect in lesioned mice.

CONCLUSION

Together, these observations provide evidence for a role of system xc- in the biochemical processes underlying central sensitization. We propose that the reduced hypersensitivity observed in the transgenic mice lacking xCT or in sulfasalazine-treated mice is mediated by a reduced gliosis in the lumbar spinal cord and/or a shift in microglial M1/M2 polarization towards an anti-inflammatory phenotype in the absence of system xc-. These findings suggest that drugs targeting system xc- could contribute to prevent or reduce neuropathic pain.

Rosmarinic acid Ameliorates neuronal regeneration in the bridging silicone rubber conduits of the sciatic nerve in taxol-treated rats

Background and aim

Taxol modulates local inflammatory conditions in peripheral nerves, which may impair their regeneration and recovery when injured. This study aimed to determine the effects of rosmarinic acid (RA, a polyphenol constituent of many culinary herbs) on the regeneration of the sciatic nerves in the bridging conduits.

Experimental procedure

In the cell study, RA decreased nuclear factor (NF)-κB activity induced by taxol in a dose dependency. In the animal model, taxol-treated rats were divided into 3 groups (n = 10/group): taxol (2 mg/kg body weight for 4 times) and taxol + RA (3 times/week for 4 weeks at 20 and 40 mg/kg body weight) groups. Macrophage infiltration, calcitonin gene-related peptide (CGRP) expression levels, neuronal connectivity, animal behavior, and neuronal electrophysiology were evaluated.

Results and conclusion

At the end of 4 weeks, macrophage density, CGRP expression level, and axon number significantly increased in the RA group compared with the taxol group. The RA administration unaffected heat, cold plate licking latencies, and motor coordination. Moreover, the 40 mg/kg RA group had significantly larger nerve conduction velocity and less latency compared to the taxol group. This study suggested that RA could ameliorate local inflammatory conditions to augment the recovery of regenerating nerves by accelerating their regrowth and improving electrophysiological function in taxol-treated peripheral nerve injury repaired with the silicone rubber conduit.

Behavior, antioxidant, and metabolomics effects of Allium tuncelianum

Allium species are consumed extensively as folkloric medicine and dietary elements, but limited studies have been conducted on them. In this study, the effects of an ethanol-water extract obtained from the underground bulb of Allium tuncelianum (Kollmann) Özhatay, B. Mathew & Şiraneci (AT) on the behavioral, antioxidant, and metabolite parameters in rats were evaluated. AT was administered orally once a day at doses of 100 and 400 mg/kg to male Wistar albino rats for 10 consecutive days. The elevated plus maze, rotarod, and hotplate tests were used to examine anxiety-like behaviors, locomotor activities, and pain perception in the rats, respectively. Additionally, untargeted metabolomic analyses were performed on plasma samples and AT extracts using two orthogonal analytical platforms. The phenolic components, mainly fumaric acid, malic acid, vanillic acid, quercetin-3-arabinoside, hydrocinnamic acid, and gallocatechin, were determined in the extract. In addition, arbutin, salicylic acid, trehalose, and nicotinic acid were analyzed in the extract for the first time. The AT extract did not decrease the catalase, glutathione peroxidase, or superoxide dismutase levels; however, diazepam decreased some of those parameters significantly in the brain, liver, and kidney. Although both the AT and diazepam treatments resulted in an increase in anxiolytic-like effects compared to the control group, no significant differences were observed (p > .05). In the metabolomic analysis, significant changes were observed in the rats treated with AT and diazepam, and they caused significant changes in some metabolic pathways, including amino acid and fatty acid metabolism, compared to the control.

Tonic excitation by astrocytic GABA causes neuropathic pain by augmenting neuronal activity and glucose metabolism

Neuropathic pain is a debilitating condition caused by the hyperexcitability of spinal dorsal horn neurons and is often characterized by allodynia. Although neuron-independent mechanisms of hyperexcitability have been investigated, the contribution of astrocyte-neuron interactions remains unclear. Here, we show evidence of reactive astrocytes and their excessive GABA release in the spinal dorsal horn, which paradoxically leads to the tonic excitation of neighboring neurons in a neuropathic pain model. Using multiple electrophysiological methods, we demonstrated that neuronal hyperexcitability is attributed to both increased astrocytic GABA synthesis via monoamine oxidase B (MAOB) and the depolarized reversal potential of GABA-mediated currents (EGABA) via the downregulation of the neuronal K+/Cl- cotransporter KCC2. Furthermore, longitudinal 2-deoxy-2-[18F]-fluoro-D-glucose microPET imaging demonstrated increased regional glucose metabolism in the ipsilateral dorsal horn, reflecting neuronal hyperexcitability. Importantly, inhibiting MAOB restored the entire astrocytic GABA-mediated cascade and abrogated the increased glucose metabolism and mechanical allodynia. Overall, astrocytic GABA-mediated tonic excitation is critical for neuronal hyperexcitability, leading to mechanical allodynia and neuropathic pain.

Behavioral and pharmacological characterization of planarian nociception

Introduction

Pain mostly arises because specialized cells called nociceptors detect harmful or potentially harmful stimuli. In lower animals with less convoluted nervous system, these responses are believed to be purely nociceptive. Amongst invertebrate animal models, planarians are becoming popular in a wide range of pharmacological and behavioral studies beyond the field of regeneration. Recent publications led the way on pain studies by focusing on nociceptive behaviors such as the 'scrunching' gait displayed under various noxious stimuli, as opposed to the 'gliding' gait planarians usually adopt in normal conditions.

Methods

In this study, we adapted commonly used nociceptive tests to further explore nociception in planarians of the species Girardia dorotocephala. By using behavioral analysis in open fields and place preferences, we managed to set up chemical, thermal and mechanical nociceptive tests. We also adapted RNA interference protocols and explored the effects of knocking down TRPA1 ion channels, one of the main effectors of chemically and thermally-induced nociceptive responses in vertebrates.

Results

Consequently, we demonstrated the reliability of the scrunching gait in this planarian species, which they displayed in a dose-dependent manner when exposed to the irritant AITC. We also showed that suppressing the expression of TRPA1 ion channels completely suppressed the scrunching gait, demonstrating the involvement of TRPA1 nociceptors in this nociceptive reaction. Besides, we also explored the effects of two common analgesics that both displayed strong antinociceptive properties. First, morphine reduced the chemically-induced nociceptive scrunching gaits by more than 20% and shifted the E C 50 of the dose-response curve by approximately 10 μM. Secondly, the NSAID meloxicam drastically reduced chemically-induced scrunching by up to 60% and reduced heat avoidance in place preference tests.

Discussion

Thus, we managed to characterize both behavioral and pharmacological aspects of G. dorotocephala's nociception, further developing the use of planarians as a replacement model in pain studies and more globally the study of invertebrate nociception.

Surgical restabilization reduces the progression of post-traumatic osteoarthritis initiated by ACL rupture in mice

OBJECTIVE

People who sustain joint injuries such as anterior cruciate ligament (ACL) rupture often develop post-traumatic osteoarthritis (PTOA). In human patients, ACL injuries are often treated with ACL reconstruction. However, it is still unclear how effective joint restabilization is for reducing the progression of PTOA. The goal of this study was to determine how surgical restabilization of a mouse knee joint following non-invasive ACL injury affects PTOA progression.

DESIGN

In this study, 187 mice were subjected to non-invasive ACL injury or no injury. After injury, mice underwent restabilization surgery, sham surgery, or no surgery. Mice were then euthanized on day 14 or day 49 after injury/surgery. Functional analyses were performed at multiple time points to assess voluntary movement, gait, and pain. Knees were analyzed ex vivo with micro-computed tomography, RT-PCR, and whole-joint histology to assess articular cartilage degeneration, synovitis, and osteophyte formation.

RESULTS

Both ACL injury and surgery resulted in loss of epiphyseal trabecular bone (-27-32%) and reduced voluntary movement at early time points. Joint restabilization successfully lowered OA score (-78% relative to injured at day 14, p < 0.0001), and synovitis scores (-37% relative to injured at day 14, p = 0.042), and diminished the formation of chondrophytes/osteophytes (-97% relative to injured at day 14, p < 0.001, -78% at day 49, p < 0.001).

CONCLUSIONS

This study confirmed that surgical knee restabilization was effective at reducing articular cartilage degeneration and diminishing chondrophyte/osteophyte formation after ACL injury in mice, suggesting that these processes are largely driven by joint instability in this mouse model. However, restabilization was not able to mitigate the early inflammatory response and the loss of epiphyseal trabecular bone, indicating that these processes are independent of joint instability.

The Analgesic Potential of Litsea Species: A Systematic Review

Various plant species from the Litsea genus have been claimed to be beneficial for pain relief. The PRISMA approach was adopted to identify studies that reported analgesic properties of plants from the Litsea genus. Out of 450 records returned, 19 primary studies revealed the analgesic potential of nine Litsea species including (1) Litsea cubeba, (2) Litsea elliptibacea, (3) Litsea japonica, (4) Litsea glutinosa, (5) Litsea glaucescens, (6) Litsea guatemalensis, (7) Litsea lancifolia, (8) Litsea liyuyingi and (9) Litsea monopetala. Six of the species, 1, 3, 4, 7, 8 and 9, demonstrated peripheral antinociceptive properties as they inhibited acetic-acid-induced writhing in animal models. Species 1, 3, 4, 8 and 9 further showed effects via the central analgesic route at the spinal level by increasing the latencies of heat stimulated-nocifensive responses in the tail flick assay. The hot plate assay also revealed the efficacies of 4 and 9 at the supraspinal level. Species 6 was reported to ameliorate hyperalgesia induced via partial sciatic nerve ligation (PSNL). The antinociceptive effects of 1 and 3 were attributed to the regulatory effects of their bioactive compounds on inflammatory mediators. As for 2 and 5, their analgesic effect may be a result of their activity with the 5-hydroxytryptamine 1A receptor (5-HT1AR) which disrupted the pain-stimulating actions of 5-HT. Antinociceptive activities were documented for various major compounds of the Litsea plants. Overall, the findings suggested Litsea species as good sources of antinociceptive compounds that can be further developed to complement or substitute prescription drugs for pain management.

A Comprehensive Description of the Anatomy and Histochemistry of Psychotria capillacea (Müll. Arg.) Standl. and an Investigation into Its Anti-Inflammatory Effects in Mice and Role in Scopolamine-Induced Memory Impairment

Species of the genus Psychotria are used in popular medicine for pain, inflammatory symptoms, and mental disorders. Psychotria capillacea (Müll. Arg.) Standl. (Rubiaceae) is commonly known as coffee and some scientific studies have demonstrated its therapeutic potential. The goal of this study was to investigate the anti-inflammatory and neuroprotective effects, and acetylcholinesterase (AChE) inhibitory activity of a methanolic extract obtained from leaves of P. capillacea (MEPC), as well as the micromorphology and histochemistry of the leaves and stems of this plant. In addition, the MEPC was analyzed by UHPLC-MS/MS and the alkaloidal fraction (AF) obtained from the MEPC was tested in a mouse model of inflammation. MEPC contained three indole alkaloids, one sesquiterpene (megastigmane-type) and two terpene lactones. MEPC (3, 30 and 100 mg/kg) and AF (3 and 30 mg/kg) were evaluated in inflammation models and significantly inhibited edema at 2 h and 4 h, mechanical hyperalgesia after 4 h and the response to cold 3 h and 4 h after carrageenan injection. Scopolamine significantly increased the escape latency, and reduced the swimming time and number of crossings in the target quadrant and distance, while MEPC (3, 30 and 100 mg/kg), due to its neuroprotective actions, reversed these effects. AChE activity was significantly decreased in the cerebral cortex (52 ± 3%) and hippocampus (60 ± 3%), after MEPC administration. Moreover, micromorphological and histochemical information was presented, to aid in species identification and quality control of P. capillacea. The results of this study demonstrated that P. capillacea is an anti-inflammatory and antihyperalgesic agent that can treat acute disease and enhance memory functions in mouse models.

The Dorsal Column Nuclei Scale Mechanical Sensitivity in Naive and Neuropathic Pain States

Tactile perception relies on reliable transmission and modulation of low-threshold information as it travels from the periphery to the brain. During pathological conditions, tactile stimuli can aberrantly engage nociceptive pathways leading to the perception of touch as pain, known as mechanical allodynia. Two main drivers of peripheral tactile information, low-threshold mechanoreceptors (LTMRs) and postsynaptic dorsal column neurons (PSDCs), terminate in the brainstem dorsal column nuclei (DCN). Activity within the DRG, spinal cord, and DCN have all been implicated in mediating allodynia, yet the DCN remains understudied at the cellular, circuit, and functional levels compared to the other two. Here, we show that the gracile nucleus (Gr) of the DCN mediates tactile sensitivity for low-threshold stimuli and contributes to mechanical allodynia during neuropathic pain in mice. We found that the Gr contains local inhibitory interneurons in addition to thalamus-projecting neurons, which are differentially innervated by primary afferents and spinal inputs. Functional manipulations of these distinct Gr neuronal populations resulted in bidirectional changes to tactile sensitivity, but did not affect noxious mechanical or thermal sensitivity. During neuropathic pain, silencing Gr projection neurons or activating Gr inhibitory neurons was able to reduce tactile hypersensitivity, and enhancing inhibition was able to ameliorate paw withdrawal signatures of neuropathic pain, like shaking. Collectively, these results suggest that the Gr plays a specific role in mediating hypersensitivity to low-threshold, innocuous mechanical stimuli during neuropathic pain, and that Gr activity contributes to affective, pain-associated phenotypes of mechanical allodynia. Therefore, these brainstem circuits work in tandem with traditional spinal circuits underlying allodynia, resulting in enhanced signaling of tactile stimuli in the brain during neuropathic pain.

The nociceptive activity of peripheral sensory neurons is modulated by the neuronal membrane proteasome

Proteasomes are critical for peripheral nervous system (PNS) function. Here, we investigate mammalian PNS proteasomes and reveal the presence of the neuronal membrane proteasome (NMP). We show that specific inhibition of the NMP on distal nerve fibers innervating the mouse hind paw leads to reduction in mechanical and pain sensitivity. Through investigating PNS NMPs, we demonstrate their presence on the somata and proximal and distal axons of a subset of dorsal root ganglion (DRG) neurons. Single-cell RNA sequencing experiments reveal that the NMP-expressing DRGs are primarily MrgprA3+ and Cysltr2+. NMP inhibition in DRG cultures leads to cell-autonomous and non-cell-autonomous changes in Ca2+ signaling induced by KCl depolarization, αβ-meATP, or the pruritogen histamine. Taken together, these data support a model whereby NMPs are expressed on a subset of somatosensory DRGs to modulate signaling between neurons of distinct sensory modalities and indicate the NMP as a potential target for controlling pain.

Quantitative Sensory Testing in Spinal Cord Stimulation: A Narrative Review

OBJECTIVES

Quantitative sensory testing (QST) has been used for decades to study sensory abnormalities in multiple conditions in which the somatosensory system is compromised, including pain. It is commonly used in pharmacologic studies on chronic pain but less so in conjunction with neuromodulation. This review aims to assess the utility of QST in spinal cord stimulation (SCS) protocols.

MATERIALS AND METHODS

For this narrative review, we searched PubMed for records of studies in which sensory testing has been performed as part of a clinical study on SCS from 1975 onward until October 2023. We focused on studies in which QST has been used to explore the effect of SCS on neuropathic, neuropathic-like, or mixed pain.

RESULTS

Our search identified 22 useful studies, all small and exploratory, using heterogeneous methods. Four studies used the full battery of validated German Research Network on Neuropathic Pain QST. There is emerging evidence that assessment dynamic mechanical allodynia (eight studies), and mechanical/thermal temporal summation of pain (eight studies) may have a role in quantifying the response to various SCS waveforms. There also were sporadic reports of improvement of sensory deficits in a proportion of patients with neuropathic pain that warrant further study.

CONCLUSIONS

We recommend the adoption of QST into future clinical research protocols, using either the full QST protocol or a less time-demanding short-form QST.

Peripheral direct current reduces naturally evoked nociceptive activity at the spinal cord in rodent models of pain

Objective.Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation typically inhibit pain pathways indirectly and are not suitable for all types of chronic pain. Direct current (DC) stimulation is a recently developed technology which affects small-diameter fibres more strongly than pulsatile stimulation. Since nociceptors are predominantly small-diameter Aδand C fibres, we investigated if this property could be applied to preferentially reduce nociceptive signalling.Approach.We applied a DC waveform to the sciatic nerve in rats of both sexes and recorded multi-unit spinal activity evoked at the hindpaw using various natural stimuli corresponding to different sensory modalities rather than broad-spectrum electrical stimulus. To determine if DC neuromodulation is effective across different types of chronic pain, tests were performed in models of neuropathic and inflammatory pain.Main results.We found that in both pain models tested, DC application reduced responses evoked by noxious stimuli, as well as tactile-evoked responses which we suggest may be involved in allodynia. Different spinal activity of different modalities were reduced in naïve animals compared to the pain models, indicating that physiological changes such as those mediated by disease states could play a larger role than previously thought in determining neuromodulation outcomes.Significance.Our findings support the continued development of DC neuromodulation as a method for reduction of nociceptive signalling, and suggests that it may be effective at treating a broader range of aberrant pain conditions than existing devices.

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

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

Current understanding of the molecular mechanisms of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common off-target adverse effects caused by various chemotherapeutic agents, such as cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib. CIPN is characterized by a substantial loss of primary afferent sensory axonal fibers leading to sensory disturbances in patients. An estimated of 19-85% of patients developed CIPN during the course of chemotherapy. The lack of preventive measures and limited treatment options often require a dose reduction or even early termination of life-saving chemotherapy, impacting treatment efficacy and patient survival. In this Review, we summarized the current understanding on the pathogenesis of CIPN. One prominent change induced by chemotherapeutic agents involves the disruption of neuronal cytoskeletal architecture and axonal transport dynamics largely influenced by the interference of microtubule stability in peripheral neurons. Due to an ineffective blood-nerve barrier in our peripheral nervous system, exposure to some chemotherapeutic agents causes mitochondrial swelling in peripheral nerves, which lead to the opening of mitochondrial permeability transition pore and cytochrome c release resulting in degeneration of primary afferent sensory fibers. The exacerbated nociceptive signaling and pain transmission in CIPN patients is often linked the increased neuronal excitability largely due to the elevated expression of various ion channels in the dorsal root ganglion neurons. Another important contributing factor of CIPN is the neuroinflammation caused by an increased infiltration of immune cells and production of inflammatory cytokines. In the central nervous system, chemotherapeutic agents also induce neuronal hyperexcitability in the spinal dorsal horn and anterior cingulate cortex leading to the development of central sensitization that causes CIPN. Emerging evidence suggests that the change in the composition and diversity of gut microbiota (dysbiosis) could have direct impact on the development and progression of CIPN. Collectively, all these aspects contribute to the pathogenesis of CIPN. Recent advances in RNA-sequencing offer solid platform for in silico drug screening which enable the identification of novel therapeutic agents or repurpose existing drugs to alleviate CIPN, holding immense promises for enhancing the quality of life for cancer patients who undergo chemotherapy and improve their overall treatment outcomes.

Selective modification of ascending spinal outputs in acute and neuropathic pain states

Pain hypersensitivity arises from the plasticity of peripheral and spinal somatosensory neurons, which modifies nociceptive input to the brain and alters pain perception. We utilized chronic calcium imaging of spinal dorsal horn neurons to determine how the representation of somatosensory stimuli in the anterolateral tract, the principal pathway transmitting nociceptive signals to the brain, changes between distinct pain states. In healthy conditions, we identify stable, narrowly tuned outputs selective for cooling or warming, and a neuronal ensemble activated by intense/noxious thermal and mechanical stimuli. Induction of an acute peripheral sensitization with capsaicin selectively and transiently retunes nociceptive output neurons to encode low-intensity stimuli. In contrast, peripheral nerve injury-induced neuropathic pain results in a persistent suppression of innocuous spinal outputs coupled with activation of a normally silent population of high-threshold neurons. These results demonstrate the differential modulation of specific spinal outputs to the brain during nociceptive and neuropathic pain states.

Danggui Sini decoction alleviates oxaliplatin-induced peripheral neuropathy by regulating gut microbiota and potentially relieving neuroinflammation related metabolic disorder

BACKGROUND

Danggui Sini decoction (DSD), a traditional Chinese medicine formula, has the function of nourishing blood, warming meridians, and unblocking collaterals. Our clinical and animal studies had shown that DSD can effectively protect against oxaliplatin (OXA)-induced peripheral neuropathy (OIPN), but the detailed mechanisms remain uncertain. Multiple studies have confirmed that gut microbiota plays a crucial role in the development of OIPN. In this study, the potential mechanism of protective effect of DSD against OIPN by regulating gut microbiota was investigated.

METHODS

The neuroprotective effects of DSD against OIPN were examined on a rat model of OIPN by determining mechanical allodynia, biological features of dorsal root ganglia (DRG) as well as proinflammatory indicators. Gut microbiota dysbiosis was characterized using 16S rDNA gene sequencing and metabolism disorders were evaluated using untargeted and targeted metabolomics. Moreover the gut microbiota mediated mechanisms were validated by antibiotic intervention and fecal microbiota transplantation.

RESULTS

DSD treatment significantly alleviated OIPN symptoms by relieving mechanical allodynia, preserving DRG integrity and reducing proinflammatory indicators lipopolysaccharide (LPS), IL-6 and TNF-α. Besides, DSD restored OXA induced intestinal barrier disruption, gut microbiota dysbiosis as well as systemic metabolic disorders. Correlation analysis revealed that DSD increased bacterial genera such as Faecalibaculum, Allobaculum, Dubosiella and Rhodospirillales_unclassified were closely associated with neuroinflammation related metabolites, including positively with short-chain fatty acids (SCFAs) and sphingomyelin (d18:1/16:0), and negatively with pi-methylimidazoleacetic acid, L-glutamine and homovanillic acid. Meanwhile, antibiotic intervention apparently relieved OIPN symptoms. Furthermore, fecal microbiota transplantation further confirmed the mediated effects of gut microbiota.

CONCLUSION

DSD alleviates OIPN by regulating gut microbiota and potentially relieving neuroinflammation related metabolic disorder.

Modulation of endogenous opioid signaling by inhibitors of puromycin sensitive aminopeptidase

The endogenous opioid system regulates pain through local release of neuropeptides and modulation of their action on opioid receptors. However, the effect of opioid peptides, the enkephalins, is short-lived due to their rapid hydrolysis by enkephalin-degrading enzymes. In turn, an innovative approach to the management of pain would be to increase the local concentration and prolong the stability of enkephalins by preventing their inactivation by neural enkephalinases such as puromycin sensitive aminopeptidase (PSA). Our previous structure-activity relationship studies offered the S-diphenylmethyl cysteinyl derivative of puromycin (20) as a nanomolar inhibitor of PSA. This chemical class, however, suffered from undesirable metabolism to nephrotoxic puromycin aminonucleoside (PAN). To prevent such toxicity, we designed and synthesized 5'-chloro substituted derivatives. The compounds retained the PSA inhibitory potency of the corresponding 5'-hydroxy analogs and had improved selectivity toward PSA. In vivo treatment with the lead compound 19 caused significantly reduced pain response in antinociception assays, alone and in combination with Met-enkephalin. The analgesic effect was reversed by the opioid antagonist naloxone, suggesting the involvement of opioid receptors. Further, PSA inhibition by compound 19 in brain slices caused local increase in endogenous enkephalin levels, corroborating our rationale. Pharmacokinetic assessment of compound 19 showed desirable plasma stability and identified the cysteinyl sulfur as the principal site of metabolic liability. We gained additional insight into inhibitor-PSA interactions by molecular modeling, which underscored the importance of bulky aromatic amino acid in puromycin scaffold. The results of this study strongly support our rationale for the development of PSA inhibitors for effective pain management.