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Chronic low back pain is a common condition, with high societal costs and often ineffectual treatments. Communication between macrophages/monocytes (MØ) and sensory neurons has been implicated in various preclinical pain models. However, few studies have examined specific MØ subsets, although distinct subtypes may play opposing roles. This study used a model of low back pain/radiculopathy involving direct local inflammation of the dorsal root ganglia (DRG). Reporter mice were employed that had distinct fluorescent labels for two key MØ subsets: CCR2-expressing (infiltrating pro-inflammatory) MØ, and CX3CR1-expressing (resident) macrophages. We observed that local DRG inflammation induced pain behaviors in mice, including guarding behavior and mechanical hypersensitivity, similar to the previously described rat model. The increase in MØ in the inflamed DRG was dominated by increases in CCR2 MØ, which persisted for at least 14 days. The primary endogenous ligand for CCR2, CCL2, was upregulated in inflamed DRG. Three different experimental manipulations that reduced the CCR2 MØ influx also reduced pain behaviors: global CCR2 knockout; systemic injection of INCB3344 (specific CCR2 blocker); and intravenous injection of liposomal clodronate. The latter two treatments when applied around the time of DRG inflammation reduced CCR2 but not CX3CR1 MØ in the DRG. Together these experiments suggest a key role for the CCR2/CCL2 system in establishing the pain state in this model of inflammatory low back pain and radiculopathy. Intravenous clodronate given after pain was established had the opposite effect on pain behaviors, suggesting the role of macrophages or their susceptibility to clodronate may change with time.
Learn More >Endometriosis is an estrogen-dependent gynecological disease, with an associated chronic inflammatory component, characterized by the presence of endometrial tissue outside the uterine cavity. Its predominant symptom is pain, a condition notably altering the quality of life of women with the disease. This review is intended to exhaustively gather current knowledge on purinergic signaling in endometriosis-associated pain. Altered extracellular ATP hydrolysis, due to changes in ectonucleotidase activity, has been reported in endometriosis; the resulting accumulation of ATP in the endometriotic microenvironment points to sustained activation of nucleotide receptors (P2 receptors) capable of generating a persistent pain message. P2X3 receptor, expressed in sensory neurons, mediates nociceptive, neuropathic, and inflammatory pain, and is enrolled in endometriosis-related pain. Pharmacological inhibition of P2X3 receptor is under evaluation as a pain relief treatment for women with endometriosis. The role of other ATP receptors is also discussed here, e.g., P2X4 and P2X7 receptors, which are involved in inflammatory cell-nerve and microglia-nerve crosstalk, and therefore in inflammatory and neuropathic pain. Adenosine receptors (P1 receptors), by contrast, mainly play antinociceptive and anti-inflammatory roles. Purinome-targeted drugs, including nucleotide receptors and metabolizing enzymes, are potential non-hormonal therapeutic tools for the pharmacological management of endometriosis-related pain.
Learn More >Peripheral denervation and pain are hallmarks of small fiber neuropathy (SFN). We investigated the contribution of skin cells on nociceptor degeneration and sensitization. We recruited 56 patients with SFN and 31 healthy controls, and collected skin punch biopsies for immunohistochemical and immunocytochemical analysis of netrin-1 (NTN1) and pro- and anti-inflammatory cytokine expression patterns. We further applied co-culture systems with murine dorsal root ganglion (DRG) neurons for skin cell-nerve interaction studies and patch-clamp analysis. Human keratinocytes attract murine DRG neuron neurites and the gene expression of the axon guidance cue NTN1 is higher in keratinocytes of SFN patients than in controls. NTN1 slows and reduces murine sensory neurite outgrowth in vitro, but does not alter keratinocyte cytokine expression. In the naïve state, keratinocytes of SFN patients show a higher expression of transforming growth factor-β1 (p<0.05), while fibroblasts display higher expression of the algesic cytokines interleukin (IL)-6 (p<0.01) and IL-8 (p<0.05). IL-6 incubation of murine DRG neurons leads to an increase in action potential firing rates compared to baseline (p<0.01). Our data provide evidence for a differential effect of keratinocytes and fibroblasts on nociceptor degeneration and sensitization in SFN compared to healthy controls and further supports the concept of cutaneous nociception.
Learn More >The present study was designed to investigate whether the antinociceptive effect of bone marrow-derived mesenchymal stem/stromal cells (MSC) during oxaliplatin (OXL)-induced sensory neuropathy is related to antioxidant properties.
Learn More >Interstitial cystitis/bladder pain syndrome (IC/BPS) is a type of chronic bladder inflammation characterized by increased voiding frequency, urgency and pelvic pain. The sensitization of bladder afferents is widely regarded as one of the pathophysiological changes in the development of IC/BPS. There is evidence that adenosine A receptors are involved in regulating the sensitization of sensory afferents. However, the effect of adenosine A receptors on cystitis remains unknown. In the present study, a rat model of chronic cystitis was established by intraperitoneal injection with cyclophosphamide (CYP). Cystometry and behavioral tests were performed to investigate bladder micturition function and nociceptive pain. The rats with chronic cystitis showed symptoms of bladder overactivity, characterized by an increase in bladder voiding frequency and voiding pressure. CYP treatment significantly increased the expression of the A receptor in bladder afferent fibers and dorsal root ganglion (DRG) neurons. The A receptor antagonist ZM241385 prevented bladder overactivity and hyperalgesia elicited by CYP-induced cystitis. In addition, the A receptor and TRPV1 were coexpressed on DRG neurons. The TRPV1 antagonist capsazepine blocked bladder overactivity induced by the A receptor agonist CGS21680. In contrast, ZM241385 significantly inhibited the capsaicin-induced increase in intracellular calcium concentration in DRG neurons. These results suggest that suppression of adenosine A receptors in bladder afferents alleviates bladder overactivity and hyperalgesia elicited by CYP-induced cystitis in rats by inhibiting TRPV1, indicating that the adenosine A receptor in bladder afferents is a potential therapeutic target for the treatment of IC/BPS.
Learn More >While the prognosis of patients with Ewing sarcoma (EwS) is improving, little is known about the frequency of pain and its risk factors in survivors of EwS. This study aims to analyse the prevalence and risk factors of pain and its predictive value for recurrence.
Learn More >Partner's responses to pain behaviours play a pivotal role in the patient's adjustment. This study aims to further our knowledge regarding patients' and partners' interpretation of partners' responses to pain behaviours, and the possible discrepancies between patients' and partners' perceptions. Further, this study examines patients' preferred responses to pain behaviours and possible discrepancies between received and preferred responses to pain behaviours.
Learn More >Migraine preventive medications are used to reduce headache frequency, severity, and duration. In patients with chronic migraine (CM), reversion to episodic migraine (EM) is an important treatment goal.
Learn More >Cluster headache (CH) is a highly disabling primary headache disorder. To date, characterization of outcomes in the preventive treatment of episodic CH, including precise definitions of clinically meaningful attack frequency reduction and impact on acute treatment management, is lacking.
Learn More >The Sigma-1 receptor (σ1R) has emerged as an interesting pharmacological target because it inhibits analgesia mediated by mu-opioid receptors (MOR), and also facilitates the development of neuropathic pain. Based on these findings, the recent cloning of the Sigma-2 receptor (σ2R) led us to investigate its potential role as a regulator of opioid analgesia and of pain hypersensitivity in σ2R knockout mice. In contrast to σ1R deficient mice, σ2R knockout mice developed mechanical allodynia following establishment of chronic constriction injury-induced neuropathic pain, which was alleviated by the σ1R antagonist S1RA. The analgesic effects of morphine, [D-Ala, N-MePhe, Gly-ol]-encephalin (DAMGO) and β-endorphin increased in σ1R mice and diminished in σ2R mice. The analgesic effect of morphine was increased in σ2R mice by treatment with S1RA. However, σ2R mice and wild-type mice exhibited comparable antinociceptive responses to the delta receptor agonist [D-Pen2,5]-encephalin (DPDPE), the cannabinoid type 1 receptor agonist WIN55,212-2 and the α2-adrenergic receptor agonist clonidine. Therefore, while σR1 inhibits and σ2R facilitates MOR-mediated analgesia these receptors exchange their roles when regulating neuropathic pain perception. Our study may help identify new pharmacological targets for diminishing pain perception and improving opioid detoxification therapies.
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