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Potent opioid-based therapies are often unsuccessful in promoting satisfactory analgesia in neuropathic pain. Moreover, the side-effects associated with opioid therapy are still manifested in neuropathy-like diseases, including tolerance, abuse, addiction and hyperalgesia, although the mechanisms underlying these effects remain unclear. Studies in the spinal cord and periphery indicate that neuropathy alters the expression of mu-[MOR], delta-[DOR] or kappa-[KOR] opioid receptors, interfering with their activity. However, there is no consensus as to the supraspinal opioidergic modulation provoked by neuropathy, the structures where the sensory and affective-related pain components are processed. In this study we explored the effect of chronic constriction of the sciatic nerve over 7 and 30 days (CCI-7d and CCI-30d, respectively) on MOR, DOR and KOR mRNAs expression, using in situ hybridization, and the efficacy of G-protein stimulation by DAMGO, DPDPE and U-69593 (MOR, DOR and KOR specific agonists, respectively), using [35S]GTPγS binding, within opioid-sensitive brain structures. After CCI-7d, CCI-30d or both, opioid receptor mRNAs expression was altered throughout the brain: MOR – in the paracentral/centrolateral thalamic nuclei, ventral posteromedial thalamic nuclei, superior olivary complex, parabrachial nucleus and posterodorsal tegmental nucleus; DOR – in the somatosensory cortex [SSC], ventral tegmental area, caudate putamen [CPu], nucleus accumbens [NAcc], raphe magnus [RMg] and PB; and KOR – in the locus coeruleus. Agonist-stimulated [35S]GTPγS binding was altered following CCI: MOR – CPu and RMg; DOR – prefrontal cortex [PFC], SSC, RMg and NAcc; and KOR -PFC and SSC. Thus, this study shows that several opioidergic circuits in the brain are recruited and modified following neuropathy.
Learn More >Non-steroidal anti-inflammatory drugs (NSAIDs), commonly known as COX-1/COX-2 inhibitors, can be effective in treating mild to moderate migraine headache. However, the mechanism by which these drugs act in migraine is not known, nor is the specific contribution of COX-1 versus COX-2 known. We sought to investigate these unknowns using celecoxib, which selectively inhibits the enzymatic activity of COX-2, by determining its effects on several migraine-associated vascular and inflammatory events. Using in vivo two-photon microscopy, we determined intraperitoneal celecoxib effects on CSD-induced blood vessel responses, plasma protein extravasation, and immune cell activation in the dura and pia of mice and rats. Compared to vehicle (control group), celecoxib reduced significantly CSD-induced dilatation of dural arteries and activation of dural and pial macrophages but not dilatation or constriction of pial arteries and veins, or the occurrence of plasma protein extravasation. Collectively, these findings suggest that a mechanism by which celecoxib-mediated COX-2 inhibition might ease the intensity of migraine headache and potentially terminate an attack is by attenuating dural macrophages activation and arterial dilatation outside the blood brain barrier (BBB), and pial macrophages activation inside the BBB.
Learn More >Low back pain is a chronic, highly prevalent, and hard-to-treat condition in the elderly. Clinical studies indicate that AXL, which belongs to the tyrosine kinase receptor subfamily, mediates pathological pain. However, it is not clear exactly how AXL regulates pain behaviors. In the present study, we used a model of chronic compression of dorsal root ganglion (CCD)-induced neuropathic pain to recreate clinical intervertebral foramen stenosis and related lumbocrural pain to explore whether AXL in primary sensory neurons contributes to this neuropathic pain in rats. Using double-labeling immunofluorescence, we observed that both phosphorylated AXL (p-AXL) and AXL were localized primarily on isolectin B4 (IB4)-positive and calcitonin gene-related peptide (CGRP)-positive neurons, while AXL was also localized in neurofilament-200 (NF200)-positive neurons. CCD-induced pain was associated with the upregulation of AXL mRNA and protein in injured DRGs. Repeated intrathecal administration of the AXL inhibitor, TP0903, or the AXL small interfering RNA (AXL siRNA), effectively alleviated CCD-induced pain hypersensitivities. Moreover, repeated intrathecal administration of either TP0903, or AXL siRNA, reduced the expression of mTOR in injured DRGs, suggesting that mTOR may mediate AXL's actions. These results indicate that the upregulation of DRG AXL may be part of a peripheral mechanism of neuropathic pain via an intracellular mTOR-signaling pathway. Thus, while AXL inhibitors have so far primarily shown clinical efficacy in tumor treatment, AXL intervention could also serve as a potential target for the treatment of neuropathic pain.
Learn More >We pursued the hypothesis that complex regional pain syndrome (CRPS) signs observed by neurologic examination display a structure allowing for alignment of patients to particular phenotype clusters.
Learn More >Women remain underrepresented on faculties of medicine and the life sciences more broadly. Whether gender differences in self presentation of clinical research exist and may contribute to this gender gap has been challenging to explore empirically. The objective of this study was to analyze whether men and women differ in how positively they frame their research findings and to analyze whether the positive framing of research is associated with higher downstream citations.
Learn More >Over the past three decades, there has been a significant growth in the use of natural products, with approximately 80% of individuals using them for some aspect of primary healthcare. Our laboratories have identified and studied natural compounds with analgesic effects from dry land plants or their associated fungus during the past ten years. Here, we isolated and characterized thirteen betulin analogs and fifteen betulinic acid analogs for their capacity to prevent calcium influx brought on by depolarization in sensory neurons. The in vitro inhibition of voltage-gated calcium channels by the top drugs was then assessed using whole cell patch clamp electrophysiology. In vivo experiments, conducted at two sites, evaluated the best compound in acute and tonic, neuropathic, inflammatory, post-operative and visceral models of pain. We found that the betulinic acid analog inhibited calcium influx in rat dorsal root ganglion neurons by inhibiting N- (CaV2.2) and T- (CaV3) type voltage-gated calcium channels. Moreover, intrathecal delivery of analog had analgesic activity in both spared nerve injury model of neuropathic pain and acute and tonic pain induced by formalin. The results presented herein highlight the potential antinociceptive properties of betulinic acid analog and set the stage for the development of novel non-opioid pain therapeutics based on the triterpenoid scaffold of betulinic acid.
Learn More >Our study aimed to identify differentially methylated regions (i.e., genomic region where multiple adjacent CpG sites show differential methylation) and their enriched genomic pathways associated with knee osteoarthritis pain (KOA). We recruited cognitively healthy middle to older aged (age 45-85) adults with (n = 182) and without (n = 31) self-reported KOA pain. We also extracted DNA from peripheral blood that was analyzed using MethylationEPIC arrays. The R package (Aryee et al., 2014) was used to perform methylation data preprocessing and quality control. To investigate biological pathways impacted by differential methylation, we performed pathway enrichment analysis using Ingenuity Pathway Analysis (IPA) to identify canonical pathways and upstream regulators. Annotated genes within ± 5 kb of the putative differentially methylated regions (DMRs, p < 0.05) were subjected to the IPA analysis. There was no significant difference in age, sex, study site between no pain and pain group (p > 0.05). Non-Hispanic black individuals were overrepresented in the pain group (p = 0.003). At raw p < 0.05 cutoff, we identified a total of 19,710 CpG probes, including 13,951 hypermethylated CpG probes, for which DNA methylation level was higher in the groups with highest pain grades. We also identified 5,759 hypomethylated CpG probes for which DNA methylation level was lower in the pain groups with higher pain grades. IPA revealed that pain-related DMRs were enriched across multiple pathways and upstream regulators. The top 10 canonical pathways were linked to cellular signaling processes related to immune responses (i.e., antigen presentation, PD-1, PD-L1 cancer immunotherapy, B cell development, IL-4 signaling, Th1 and Th2 activation pathway, and phagosome maturation). Moreover, in terms of upstream regulators, NDUFAF3 was the most significant (p = 8.6E-04) upstream regulator. Our findings support previous preliminary work suggesting the importance of epigenetic regulation of the immune system in knee pain and the need for future work to understand the epigenetic contributions to chronic pain.
Learn More >The opioid epidemic is one of the biggest public health crises of our time, and overprescribing of opioids after surgery has the potential to lead to long-term use. The purpose of this review was to identify and summarize the available evidence on interventions aimed at reducing opioid use after orthopedic surgery.
Learn More >Amitriptyline is a major tricyclic antidepressant that is also used to relieve chronic orofacial pain. Recently, alterations in gut flora due to various antidepressants have been demonstrated. However, it remains unknown how antidepressants affect the oral environment, including microbiota and innate immunity. The aim of this study was to investigate the effects of amitriptyline on oral microflora and antimicrobial peptides.
Learn More >Serine racemase (SR) catalyzes L-serine racemization to activate the N-methyl-D-aspartate receptor (NMDAR). NMDAR activation is associated with the progression of acute-to-chronic neuropathic pain. This study aimed to investigate NMDAR antagonist interactions with SR to obtain potential chronic pain target therapy. Several NMDAR antagonist drugs were obtained from the drug bank, and malonate was used as a control inhibitor. Ligands were prepared using the open babel feature on PyRx. The SR structure was obtained from Protein data bank (PDB) (3l6B) and then docked with ligands using the AutoDock Vina. Haloperidol had a lower binding affinity than malonate and other ligands. Ethanol had the highest binding affinity than other drugs but could bind to the Adenosine triphosphate (ATP)-binding domain. Haloperidol is bound to reface that function for reprotonation in racemization reaction to produce D-serine. Halothane bond with Arg135 residues aligned negatively charged substrates to be reprotonated properly by reface. Tramadol is bound to amino acid residues in the triple serine loop, which determines the direction of the SR reaction. Several NMDAR antagonists such as haloperidol, halothane, ethanol, and tramadol bind to SR in the specific binding site. It reveals that SR potentially becomes an alternative target for chronic pain treatment.
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