Sex-specific post-inflammatory dysbiosis mediates chronic visceral pain in colitis.

BACKGROUND: Despite achieving endoscopic remission, over 20% of inflammatory bowel disease (IBD) patients experience chronic abdominal pain. Visceral pain and the microbiome exhibit sex-dependent interactions, while visceral pain in IBD shows a sex bias. Our aim was to evaluate whether post-inflammatory microbial perturbations contribute to visceral hypersensitivity in a sex-dependent manner. METHODS: Males, cycling females, ovariectomized, and sham-operated females were given dextran sodium sulfate to induce colitis and allowed to recover. Germ-free recipients received sex-appropriate and cross-sex fecal microbial transplants (FMT) from post-inflammatory donor mice. Visceral sensitivity was assessed by recording visceromotor responses to colorectal distention. The composition of the microbiota was evaluated via 16S rRNA gene V4 amplicon sequencing, while the metabolome was assessed using targeted (short chain fatty acids - SCFA) and semi-targeted mass spectrometry. RESULTS: Post-inflammatory cycling females developed visceral hyperalgesia when compared to males. This effect was reversed by ovariectomy. Both post-inflammatory males and females exhibited increased SCFA-producing species, but only males had elevated fecal SCFA content. FMT from post-inflammatory females transferred visceral hyperalgesia to both males and females, while FMT from post-inflammatory males could only transfer visceral hyperalgesia to males. CONCLUSIONS: Female sex, hormonal status as well as the gut microbiota play a role in pain modulation. Our data highlight the importance of considering biological sex in the evaluation of visceral pain.

Blockade of Piezo2 Pathway Attenuates Inflammatory and Neuropathic Pain in the Orofacial Area.

Although previous studies suggest that Piezo2 regulates chronic pain in the orofacial area, few studies have reported the direct evidence of Piezo2's involvement in inflammatory and neuropathic pain in the orofacial region. In this study, we used male Sprague Dawley rats to investigate the role of the Piezo2 pathway in the development of inflammatory and neuropathic pain. The present study used interleukin (IL)-1ß-induced pronociception as an inflammatory pain model. Subcutaneous injection of IL-1ß produced significant mechanical allodynia and thermal hyperalgesia. Subcutaneous injection of a Piezo2 inhibitor significantly blocked mechanical allodynia and thermal hyperalgesia induced by subcutaneously injected IL-1ß. Furthermore, the present study also used a neuropathic pain model caused by the misplacement of a dental implant, leading to notable mechanical allodynia as a consequence of inferior alveolar nerve injury. Western blot analysis revealed increased levels of Piezo2 in the trigeminal ganglion and the trigeminal subnucleus caudalis after inferior alveolar nerve injury. Furthermore, subcutaneous and intracisternal injections of a Piezo2 inhibitor blocked neuropathic mechanical allodynia. These results suggest that the Piezo2 pathway plays a critical role in the development of inflammatory and neuropathic pain in the orofacial area. Therefore, blocking the Piezo2 pathway could be the foundation for developing new therapeutic strategies to treat orofacial pain conditions.

IL-33/ST2 induces macrophage-dependent ROS production and TRPA1 activation that mediate pain-like responses by skin incision in mice.

Background: Insufficiently managed incisional (INC) pain severely affects patients' life quality and rehabilitation after a major operation. However, mechanisms underlying INC pain still remain poorly understood. Methods: A mouse model of INC pain was established by skin plus deep muscle incision. Biochemistry assay, in vivo reactive oxygen species (ROS) imaging, Ca2+ imaging combined with retrograde labelling, neuron tracing and nocifensive behavior test, etc. were utilized for mechanism investigation. Results: We found pro-nociceptive cytokine interleukin -33 (IL-33) ranked among top up-regulated cytokines in incised tissues of INC pain model mice. IL-33 was predominantly expressed in keratinocytes around the incisional area. Neutralization of IL-33 or its receptor suppression of tumorigenicity 2 protein (ST2) or genetic deletion of St2 gene (St2 -/-) remarkably ameliorated mechanical allodynia and improved gait impairments of model mice. IL-33 contributes to INC pain by recruiting macrophages, which subsequently release ROS in incised tissues via ST2-dependent mechanism. Transfer of excessive macrophages enhanced oxidative injury and reproduced mechanical allodynia in St2 -/- mice upon tissue incision. Overproduced ROS subsequently activated functionally up-regulated transient receptor potential ankyrin subtype-1 (TRPA1) channel innervating the incisional site to produce mechanical allodynia. Neither deleting St2 nor attenuating ROS affected wound healing of model mice. Conclusions: Our work uncovered a previously unrecognized contribution of IL-33/ST2 signaling in mediating mechanical allodynia and gait impairment of a mouse model of INC pain. Targeting IL-33/ST2 signaling could be a novel therapeutic approach for INC pain management.

Oxa-Iboga alkaloids lack cardiac risk and disrupt opioid use in animal models.

Ibogaine and its main metabolite noribogaine provide important molecular prototypes for markedly different treatment of substance use disorders and co-morbid mental health illnesses. However, these compounds present a cardiac safety risk and a highly complex molecular mechanism. We introduce a class of iboga alkaloids - termed oxa-iboga - defined as benzofuran-containing iboga analogs and created via structural editing of the iboga skeleton. The oxa-iboga compounds lack the proarrhythmic adverse effects of ibogaine and noribogaine in primary human cardiomyocytes and show superior efficacy in animal models of opioid use disorder in male rats. They act as potent kappa opioid receptor agonists in vitro and in vivo, but exhibit atypical behavioral features compared to standard kappa opioid agonists. Oxa-noribogaine induces long-lasting suppression of morphine, heroin, and fentanyl intake after a single dose or a short treatment regimen, reversal of persistent opioid-induced hyperalgesia, and suppression of opioid drug seeking in rodent relapse models. As such, oxa-iboga compounds represent mechanistically distinct iboga analogs with therapeutic potential.

Mast cell extracellular trap formation underlies vascular and neural injury and hyperalgesia in sickle cell disease.

Sickle cell disease (SCD) is the most common inherited monogenetic disorder. Chronic and acute pain are hallmark features of SCD involving neural and vascular injury and inflammation. Mast cells reside in the vicinity of nerve fibers and vasculature, but how they influence these structures remains unknown. We therefore examined the mechanism of mast cell activation in a sickle microenvironment replete with cell-free heme and inflammation. Mast cells exposed to this environment showed an explosion of nuclear contents with the release of citrullinated histones, suggestive of mast cell extracellular trap (MCET) release. MCETs interacted directly with the vasculature and nerve fibers, a cause of vascular and neural injury in sickle cell mice. MCET formation was dependent upon peptidylarginine deiminase 4 (PAD4). Inhibition of PAD4 ameliorated vasoocclusion, chronic and acute hyperalgesia, and inflammation in sickle mice. PAD4 activation may also underlie neutrophil trap formation in SCD, thus providing a novel target to treat the sequelae of vascular and neural injury in SCD.

Altered Sensory Processing in People Attending Specialist Orthopaedic Consultation for Management of Persistent Shoulder Pain: An Observational Cross-Sectional Study.

OBJECTIVES: The primary objective was to compare sensory processing measures in people attending specialist orthopaedic consultation for management of persistent shoulder pain with control participants. The secondary objective was to compare the groups' sociodemographic, clinical, general health and lifestyle, and psychological characteristics. DESIGN: Observational cross-sectional. METHODS: Participants with shoulder pain for ≥3 months, who attended a public hospital orthopaedic department (n = 119), and community participants without shoulder pain (n = 44) underwent a standardized quantitative sensory testing protocol, measuring pressure pain threshold, temporal summation, and conditioned pain modulation. Sociodemographic, clinical, general health and lifestyle, and psychological characteristics were also collected. RESULTS: Participants with shoulder pain had significantly lower pressure pain thresholds at all sites (ie, local and widespread mechanical hyperalgesia) and significantly decreased conditioned pain modulation effect (ie, descending inhibition of nociception) than control participants. There was no significant difference between groups for temporal summation. Participants with shoulder pain had decreased general health and function, less healthy lifestyles, and poorer psychological health compared with controls. CONCLUSION: People referred to specialist orthopaedic care for management of persistent shoulder pain had clinical signs of altered sensory processing and poor health outcomes. J Orthop Sports Phys Ther 2024;54(10):1-10. Epub 25 July 2024. doi:10.2519/jospt.2024.12512.

A neural circuit for alcohol withdrawal-induced hyperalgesia in a nondependent state.

Alcohol use disorder is highly prevalent worldwide, with characteristically severe pain sensitivity during withdrawal. Here, we established a mouse model of hyperalgesia during ethanol withdrawal (EW) before addiction to investigate the window for onset and underlying mechanisms. Viral tracing with in vivo microendoscopic and two-photon calcium imaging identified a circuit pathway from dorsal hippocampal CA1 glutamatergic neurons (dCA1Glu) to anterior cingulate cortex glutamatergic neurons (ACCGlu) activated in EW mice with hyperalgesia. Chemogenetic inhibition of this pathway can alleviate hyperalgesia in EW mice, whereas artificial activation recapitulates EW-induced hyperalgesia in naïve mice. These findings demonstrate that the dCA1Glu → ACCGlu neuronal pathway participates in driving EW-induced hyperalgesia before ethanol dependence in mice.

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

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

Involvement of basolateral amygdala-rostral anterior cingulate cortex in mechanical allodynia and anxiety-like behaviors and potential mechanisms of electroacupuncture.

AIMS: Chronic pain is highly associated with anxiety. Electroacupuncture (EA) is effective in relieving pain and anxiety. Currently, little is known about the neural mechanisms underlying the comorbidity of chronic pain and anxiety and the EA mechanism. This study investigated a potential neural circuit underlying the comorbid and EA mechanisms. METHODS: Spared nerve injury (SNI) surgery established the chronic neuropathic pain mouse model. The neural circuit was activated or inhibited using the chemogenetic method to explore the relationship between the neural circuit and mechanical allodynia and anxiety-like behaviors. EA combined with the chemogenetic method was used to explore whether the effects of EA were related to this neural circuit. RESULTS: EA attenuated mechanical allodynia and anxiety-like behaviors in SNI mice, which may be associated with the activity of CaMKII neurons in the basolateral amygdala (BLA). Inhibition of BLACaMKII-rACC induced mechanical allodynia and anxiety-like behaviors in sham mice. Activation of the BLACaMKII-rACC alleviated neuropathic pain and anxiety-like behaviors in SNI mice. The analgesic and anxiolytic effects of 2 Hz EA were antagonized by the inhibition of the BLACaMKII-rACC. CONCLUSION: BLACaMKII-rACC mediates mechanical allodynia and anxiety-like behaviors. The analgesic and anxiolytic effects of 2 Hz EA may be associated with the BLACaMKII-rACC.

Rapid cleavage of IL-1ß in DRG neurons produces tissue injury-induced pain hypersensitivity.

Background: IL-1ß plays a critical role in the pathophysiology of neuroinflammation. The presence of cleaved IL-1ß (cIL-1ß) in the neurons of the dorsal root ganglion (DRG) implicates its function in biological signaling arising from the sensory neuron. This study was conducted to analyze the role of IL-1ß in nociceptive transduction after tissue injury. Methods: A plantar incision was made in C57BL/6 mice, following which immunohistochemistry and RNA scope in situ hybridization were performed at various time points to analyze cIL-1ß, caspase-1, and IL-1 receptor 1 (IL-1R1) expression in the DRG. The effect of intrathecal administration of a caspase-1 inhibitor or regional anesthesia using local anesthetics on cIL-1ß expression and pain hypersensitivity was analyzed by immunohistochemistry and behavioral analysis. ERK phosphorylation was also analyzed to investigate the effect of IL-1ß on the activity of spinal dorsal horn neurons. Results: cIL-1ß expression was significantly increased in caspase-1-positive DRG neurons 5 min after the plantar incision. Intrathecal caspase-1 inhibitor treatment inhibited IL-1ß cleavage and pain hypersensitivity after the plantar incision. IL-1R1 was also detected in the DRG neurons, although the majority of IL-1R1-expressing neurons lacked cIL-1ß expression. Regional anesthesia using local anesthetics prevented cIL-1ß processing. Plantar incision-induced phosphorylation of ERK was inhibited by the caspase-1 inhibitor. Conclusion: IL-1ß in the DRG neuron undergoes rapid cleavage in response to tissue injury in an activity-dependent manner. Cleaved IL-1ß causes injury-induced functional activation of sensory neurons and pain hypersensitivity. IL-1ß in the primary afferent neurons is involved in physiological nociceptive signal transduction.

Agomelatine-loaded nanostructured lipid carriers alleviate neuropathic pain in rats by Nrf2/HO-1 signalling pathway.

Neuropathic pain arises from impairments or malfunctions within the nervous system, resulting in atypical transmission and interpretation of pain signals. In the present study, we examined the neuroprotective effects of agomelatine (AGM) and agomelatine-loaded nanostructured lipid carriers (AGM-NLCs) in neuropathic animal models induced by chronic constriction injury (CCI) of the sciatic nerve. Male Sprague Dawley rats were divided into seven experimental groups to compare the effects of AGM and AGM-NLCs, which were administered at 20 mg/kg for 14 consecutive days after CCI. Our finding demonstrated that CCI triggered the onset of analgesia in these animals, corroborated by mechanical allodynia and thermal hyperalgesia. Furthermore, CCI induced an elevation in inflammatory mediators such as interleukin (IL)-1ß and inducible nitric oxide synthase (iNOS), and downregulated heme oxygenase-1 (HO-1) and nuclear factor E2-related factor (Nrf2). Treatment with AGM and AGM-NLCs reversed inflammatory cascades and elevated antioxidant enzyme levels, leading to a reduction in paw withdrawal latency and threshold in rats. To further investigate the effect of AGM and AGM-NLCs, all-trans retinoic acid (ATRA) was administered, which antagonizes Nrf2. ATRA substantially downregulated Nrf2 expression and exacerbated thermal hyperalgesia, whereas Nrf2 and HO-1 expressions were significantly upregulated after AGM-NLCs administration. Overall, the results demonstrated that AGM-NLCs offer promising antinociceptive and anti-inflammatory properties in alleviating neuropathic pain symptoms, which can be attributed to improved drug delivery and therapeutic outcomes compared with AGM alone.

Amitriptyline nanoparticle repositioning prolongs the anti-allodynic effect of enhanced microglia targeting.

Aim: Amitriptyline (AMI) has been used to treat neuropathic pain. However, the clinical outcomes remain unsatisfactory, presumably due to a limited understanding of the underlying molecular mechanisms. Here, we investigated a drug repositioning strategy using a low-dose of AMI encapsulated in poly (D, L lactic-co-glycolic acid) (PLGA) nanoparticles (AMI NPs) for neuropathic pain, since PLGA nanoparticles are known to enhance delivery to microglia.Methods: We evaluated the anti-allodynic effects of AMI and AMI NPs on neuropathic pain by assessing behaviors and inflammatory responses in a rat model of spinal nerve ligation (SNL). While the anti-allodynic effect of AMI (30 µg) drug injection on SNL-induced neuropathic pain persisted for 12 h, AMI NPs significantly alleviated mechanical allodynia for 3 days.Results: Histological and cytokine analyses showed AMI NPs facilitated the reduction of microglial activation and pro-inflammatory mediators in the spinal dorsal horn. This study suggests that AMI NPs can provide a sustained anti-allodynic effect by enhancing the targeting of microglia and regulating the release of pro-inflammatory cytokines from activated microglia.Conclusion: Our findings suggest that the use of microglial-targeted NPs continuously releasing AMI (2 µg) as a drug repositioning strategy offers long-term anti-allodynic effects.

[Box: see text].

Efficacy of galcanezumab in migraine central sensitizatio.

Galcanezumab, a monoclonal antibody targeting the calcitonin gene-related peptide pathway (CGRP mAb), acts peripherally due to its large size. However, recent studies have suggested that CGRP mAbs may also have a central mode of action. This study aimed to evaluate the central effects of galcanezumab on migraine central sensitization.This prospective real-world study was conducted at three headache centers in Japan between May 2021 and May 2022. Patients treated with galcanezumab for migraines were included in the study. The primary outcome was the change in the validated Central Sensitization Inventory (CSI) score from baseline to six months of treatment. We also assessed changes in the Allodynia Symptom Checklist (ASC-12) score. Eighty-six patients with migraine (73 female and 13 male) were analyzed. At 6 months, CSI and ASC-12 scores were significantly reduced compared to baseline (CSI: 36.0 vs. 29.3, p < 0.001; and ASC-12: 5.55 vs. 4.26, p < 0.01). Furthermore, these effects were observed as early as three months of treatment. In this study, we demonstrated the real-world efficacy of galcanezumab in improving central sensitization in migraine, with significant effects seen in the early phase of treatment. Trial registration: This study was registered with UMIN-CTR on May 2, 2021 (UMIN000044096).

Vitamin D3 Attenuates Neuropathic Pain via Suppression of Mitochondria-Associated Ferroptosis by Inhibiting PKCα/NOX4 Signaling Pathway.

AIMS: Neuropathic pain remains a significant unmet medical challenge due to its elusive mechanisms. Recent clinical observations suggest that vitamin D (VitD) holds promise in pain relief, yet its precise mechanism of action is still unclear. This study explores the therapeutical role and potential mechanism of VitD3 in spared nerve injury (SNI)-induced neuropathic pain rat model. METHODS: The analgesic effects and underlying mechanisms of VitD3 were evaluated in SNI and naïve rat models. Mechanical allodynia was assessed using the Von Frey test. Western blotting, immunofluorescence, biochemical assay, and transmission electron microscope (TEM) were employed to investigate the molecular and cellular effects of VitD3. RESULTS: Ferroptosis was observed in the spinal cord following SNI. Intrathecal administration of VitD3, the active form of VitD, activated the vitamin D receptor (VDR), suppressed ferroptosis, and alleviated mechanical nociceptive behaviors. VitD3 treatment preserved spinal GABAergic interneurons, and its neuroprotective effects were eliminated by the ferroptosis inducer RSL3. Additionally, VitD3 mitigated aberrant mitochondrial morphology and oxidative metabolism in the spinal cord. Mechanistically, VitD3 inhibited SNI-induced activation of spinal PKCα/NOX4 signaling. Inhibition of PKCα/NOX4 signaling alleviated mechanical pain hypersensitivity, accompanied by reduced ferroptosis and mitochondrial dysfunction in SNI rats. Conversely, activation of PKCα/NOX4 signaling in naïve rats induced hyperalgesia, ferroptosis, loss of GABAergic interneurons, and mitochondrial dysfunction in the spinal cord, all of which were reversed by VitD3 treatment. CONCLUSIONS: Our findings provide evidence that VitD3 attenuates neuropathic pain by preserving spinal GABAergic interneurons through the suppression of mitochondria-associated ferroptosis mediated by PKCα/NOX4 signaling, probably via VDR activation. VitD, alone or in combination with existing analgesics, presents an innovative therapeutic avenue for neuropathic pain.

Potentiation of Imipramine-Induced Anti-hyperalgesic and Anti-Nociceptive Effects by Citicoline in the Sciatic Nerve Ligated Mice.

BACKGROUND: Peripheral neuropathic pain is a result of damage/illness of the peripheral nerves. The mechanisms caused by its pathophysiology are not completely understood. METHODS: Imipramine is a tricyclic antidepressant that is sometimes used to treat neuropathic pain. Moreover, citicoline is considered a novel adjuvant for painful disorders such as neuropathic pain. So, a possible interaction between imipramine and citicoline on pain behavior was examined in nerve-ligated mice using tail-flick and hot plate tests. RESULTS: The results indicated that induction of neuropathic pain by sciatic nerve ligation caused hyperalgesia in nerve-ligated mice. On the other hand, intraperitoneal (i.p.) administration of citicoline (50, 75, and 100 mg/kg), and imipramine (2.5 and 5 mg/kg) induced anti-hyperalgesic and anti-nociceptive effects in nerve-ligated mice. Furthermore, citicoline potentiated the anti-hyperalgesic and anti-nociceptive effects of imipramine when they were co-administrated in nerve-ligated mice. Interestingly, there was an additive effect between imipramine and citicoline upon induction of anti-hyperalgesic and anti-nociceptive effects in nerve-ligated mice. CONCLUSION: Therefore, it can be concluded that citicoline (as an adjuvant substance) enhanced the efficacy of imipramine for the modulation of pain behavior in nerve-ligated mice.

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

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

The link between cutaneous allodynia and pain/sensitivity in teeth and gums during migraine episodes.

BACKGROUND: Migraine is one of the most common primary headaches worldwide, while toothache is the most common pain in the orofacial region. The association of migraine pain, and oral pain is unknown. This study aims to investigate the association between migraine and dental and gingival pain with the presence of allodynia. METHODS: A questionnaire comprising demographic data with the ID-Migraine (IDM) tool, an Allodynia Symptom Checklist (ASC), and inquiries about pain and sensitivity in the teeth and gums during migraine attacks was administered to the participants and 762 responded the survey. The study classified participants based on the ASC, and the relationship between allodynia and pain/sensitivity in the teeth and/or gums during migraine attacks was analyzed. The statistical analyses utilized Chi-square tests and the Fisher-Exact test. RESULTS: Among 762 migraine patients, 430 (56.44%) were classified as allodynia (+), while 332 (43.56%) were classified as allodynia (-) (p < 0.001). Additionally, 285 participants (37.5%) reported experiencing pain and sensitivity in the teeth and gums during migraine attacks, with a significant relationship observed between allodynia and pain/sensitivity in the teeth and/or gums during migraine attacks (p < 0.001). CONCLUSION: The findings of this study have important clinical implications. For migraine patients who are non-allodynic, the presence of pain and sensitivity in their teeth and gums during migraine attacks may indicate underlying dental diseases or the need for dental treatment especially root canal treatment. However, for allodynic patients, such symptoms may not necessarily indicate the presence of dental diseases or the need for dental treatment especially root canal treatment. These results underscore the significance of considering the presence of allodynia in the assessment and management of oral symptoms during migraine attacks.

Combined use of CLP290 and bumetanide alleviates neuropathic pain and its mechanism after spinal cord injury in rats.

AIM: We aimed to explore whether the combination of CLP290 and bumetanide maximally improves neuropathic pain following spinal cord injury (SCI) and its possible molecular mechanism. METHODS: Rats were randomly divided into five groups: Sham, SCI + vehicle, SCI + CLP290, SCI + bumetanide, and SCI + combination (CLP290 + bumetanide). Drug administration commenced on the 7th day post-injury (7 dpi) and continued for 14 days. All rats underwent behavioral assessments for 56 days to comprehensively evaluate the effects of interventions on mechanical pain, thermal pain, cold pain, motor function, and other relevant parameters. Electrophysiological assessments, immunoblotting, and immunofluorescence detection were performed at different timepoints post-injury, with a specific focus on the expression and changes of KCC2 and NKCC1 proteins in the lumbar enlargement of the spinal cord. RESULTS: CLP290 and bumetanide alleviated SCI-associated hypersensitivity and locomotor function, with the combination providing enhanced recovery. The combined treatment group exhibited the most significant improvement in restoring Rate-Dependent Depression (RDD) levels. In the combined treatment group and the two individual drug administration groups, the upregulation of potassium chloride cotransporter 2 (K+-Cl-cotransporter 2, KCC2) expression and downregulation of sodium potassium chloride cotransporter 1 (Na+-K+-Cl-cotransporter 1, NKCC1) expression in the lumbar enlargement area resulted in a significant increase in the KCC2/NKCC1 ratio compared to the SCI + vehicle group, with the most pronounced improvement seen in the combined treatment group. Compared to the SCI + vehicle group, the SCI + bumetanide group showed no significant paw withdrawal thermal latency (PWTL) improvement at 21 and 35 dpi, but a notable enhancement at 56 dpi. In contrast, the SCI + CLP290 group significantly improved PWTL at 21 days, with non-significant changes at 35 and 56 days. At 21 dpi, KCC2 expression was marginally higher in monotherapy groups versus SCI + vehicle, but not significantly. At 56 dpi, only the SCI + bumetanide group showed a significant difference in KCC2 expression compared to the control group. CONCLUSION: Combined application of CLP290 and bumetanide effectively increases the ratio of KCC2/NKCC1, restores RDD levels, enhances GABAA receptor-mediated inhibitory function in the spinal cord, and relieves neuropathic pain in SCI; Bumetanide significantly improves neuropathic pain in the long term, whereas CLP290 demonstrates a notable short-term effect.

Oxytocin shortens spreading depolarization-induced periorbital allodynia.

BACKGROUND: Migraine is among the most prevalent and burdensome neurological disorders in the United States based on disability-adjusted life years. Cortical spreading depolarization (SD) is the most likely electrophysiological cause of migraine aura and may be linked to trigeminal nociception. We previously demonstrated, using a minimally invasive optogenetic approach of SD induction (opto-SD), that opto-SD triggers acute periorbital mechanical allodynia that is reversed by 5HT1B/1D receptor agonists, supporting SD-induced activation of migraine-relevant trigeminal pain pathways in mice. Recent data highlight hypothalamic neural circuits in migraine, and SD may activate hypothalamic neurons. Furthermore, neuroanatomical, electrophysiological, and behavioral data suggest a homeostatic analgesic function of hypothalamic neuropeptide hormone, oxytocin. We, therefore, examined the role of hypothalamic paraventricular nucleus (PVN) and oxytocinergic (OXT) signaling in opto-SD-induced trigeminal pain behavior. METHODS: We induced a single opto-SD in adult male and female Thy1-ChR2-YFP transgenic mice and quantified fos immunolabeling in the PVN and supraoptic nucleus (SON) compared with sham controls. Oxytocin expression was also measured in fos-positive neurons in the PVN. Periorbital mechanical allodynia was tested after treatment with selective OXT receptor antagonist L-368,899 (5 to 25 mg/kg i.p.) or vehicle at 1, 2, and 4 h after opto-SD or sham stimulation using von Frey monofilaments. RESULTS: Opto-SD significantly increased the number of fos immunoreactive cells in the PVN and SON as compared to sham stimulation (p < 0.001, p = 0.018, respectively). A subpopulation of fos-positive neurons also stained positive for oxytocin. Opto-SD evoked periorbital mechanical allodynia 1 h after SD (p = 0.001 vs. sham), which recovered quickly within 2 h (p = 0.638). OXT receptor antagonist L-368,899 dose-dependently prolonged SD-induced periorbital allodynia (p < 0.001). L-368,899 did not affect mechanical thresholds in the absence of opto-SD. CONCLUSIONS: These data support an SD-induced activation of PVN neurons and a role for endogenous OXT in alleviating acute SD-induced trigeminal allodynia by shortening its duration.