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The Journal of Neuroscience : the... Aug 2023Aberrant activation of presynaptic NMDARs in the spinal dorsal horn is integral to opioid-induced hyperalgesia and analgesic tolerance. However, the signaling mechanisms...
Aberrant activation of presynaptic NMDARs in the spinal dorsal horn is integral to opioid-induced hyperalgesia and analgesic tolerance. However, the signaling mechanisms responsible for opioid-induced NMDAR hyperactivity remain poorly identified. Here, we show that repeated treatment with morphine or fentanyl reduced monomeric mGluR5 protein levels in the dorsal root ganglion (DRG) but increased levels of mGluR5 monomers and homodimers in the spinal cord in mice and rats of both sexes. Coimmunoprecipitation analysis revealed that monomeric and dimeric mGluR5 in the spinal cord, but not monomeric mGluR5 in the DRG, directly interacted with GluN1. By contrast, mGluR5 did not interact with μ-opioid receptors in the DRG or spinal cord. Repeated morphine treatment markedly increased the mGluR5-GluN1 interaction and protein levels of mGluR5 and GluN1 in spinal synaptosomes. The mGluR5 antagonist MPEP reversed morphine treatment-augmented mGluR5-GluN1 interactions, GluN1 synaptic expression, and dorsal root-evoked monosynaptic EPSCs of dorsal horn neurons. Furthermore, CRISPR-Cas9-induced conditional mGluR5 knockdown in DRG neurons normalized mGluR5 levels in spinal synaptosomes and NMDAR-mediated EPSCs of dorsal horn neurons increased by morphine treatment. Correspondingly, intrathecal injection of MPEP or conditional mGluR5 knockdown in DRG neurons not only potentiated the acute analgesic effect of morphine but also attenuated morphine treatment-induced hyperalgesia and tolerance. Together, our findings suggest that opioid treatment promotes mGluR5 trafficking from primary sensory neurons to the spinal dorsal horn. Through dimerization and direct interaction with NMDARs, presynaptic mGluR5 potentiates and/or stabilizes NMDAR synaptic expression and activity at primary afferent central terminals, thereby maintaining opioid-induced hyperalgesia and tolerance. Opioids are essential analgesics for managing severe pain caused by cancer, surgery, and tissue injury. However, these drugs paradoxically induce pain hypersensitivity and tolerance, which can cause rapid dose escalation and even overdose mortality. This study demonstrates, for the first time, that opioids promote trafficking of mGluR5, a G protein-coupled glutamate receptor, from peripheral sensory neurons to the spinal cord; there, mGluR5 proteins dimerize and physically interact with NMDARs to augment their synaptic expression and activity. Through dynamic interactions, the two distinct glutamate receptors mutually amplify and sustain nociceptive input from peripheral sensory neurons to the spinal cord. Thus, inhibiting mGluR5 activity or disrupting mGluR5-NMDAR interactions could reduce opioid-induced hyperalgesia and tolerance and potentiate opioid analgesic efficacy.
Topics: Male; Female; Rats; Mice; Animals; Receptors, N-Methyl-D-Aspartate; Analgesics, Opioid; Hyperalgesia; Receptor, Metabotropic Glutamate 5; Rats, Sprague-Dawley; Morphine; Spinal Cord Dorsal Horn; Spinal Cord; Neuralgia; Sensory Receptor Cells
PubMed: 37451981
DOI: 10.1523/JNEUROSCI.0601-23.2023 -
The Journal of Pain Jan 2024Most reports agree that aging negatively impacts pain processing and that the prevalence of chronic pain increases significantly with age. To improve current therapies,...
Most reports agree that aging negatively impacts pain processing and that the prevalence of chronic pain increases significantly with age. To improve current therapies, it is critical that aged animals be included in preclinical studies. Here we compared sensitivities to pain and itch-provoking stimuli in naïve and injured young and aged mice. Surprisingly, we found that in the absence of injury, aged male and female mice are significantly less responsive to mechanical stimuli and, in females, also to noxious thermal (heat) stimuli. In both older male and female mice, compared to younger (6-month-old mice), we also recorded reduced pruritogen-evoked scratching. On the other hand, after nerve injury, aged mice nevertheless developed significant mechanical hypersensitivity. Interestingly, however, and in contrast to young mice, aged mice developed both ipsilateral and contralateral postinjury mechanical allodynia. In a parallel immunohistochemical analysis of microglial and astrocyte markers, we found that the ipsilateral to the contralateral ratio of nerve injury-induced expression decreased with age. That observation is consistent with our finding of contralateral hypersensitivity after nerve injury in the aged but not the young mice. We conclude that aging has opposite effects on baseline versus postinjury pain and itch processing. PERSPECTIVE: Aged male and female mice (22-24 months) are less sensitive to mechanical, thermal (heat), and itch-provoking stimuli than are younger mice (6 months).
Topics: Male; Female; Mice; Animals; Pain; Pruritus; Hyperalgesia
PubMed: 37482234
DOI: 10.1016/j.jpain.2023.07.018 -
IScience Nov 2023In neuropathic pain, recent evidence has highlighted a sex-dependent role of the P2X4 receptor in spinal microglia in the development of tactile allodynia following...
In neuropathic pain, recent evidence has highlighted a sex-dependent role of the P2X4 receptor in spinal microglia in the development of tactile allodynia following nerve injury. Here, using internalization-defective P2X4mCherryIN knockin mice (P2X4KI), we demonstrate that increased cell surface expression of P2X4 induces hypersensitivity to mechanical stimulations and hyperexcitability in spinal cord neurons of both male and female naive mice. During neuropathy, both wild-type (WT) and P2X4KI mice of both sexes develop tactile allodynia accompanied by spinal neuron hyperexcitability. These responses are selectively associated with P2X4, as they are absent in global P2X4KO or myeloid-specific P2X4KO mice. We show that P2X4 is expressed in reactive microglia in neuropathic WT and P2X4KI mice of both sexes and that tactile allodynia is relieved by pharmacological blockade of P2X4 or TrkB. These results show that the upregulation of P2X4 in microglia is crucial for neuropathic pain, regardless of sex.
PubMed: 37860691
DOI: 10.1016/j.isci.2023.108110 -
Brain, Behavior, and Immunity Mar 2024Microglia, resident immune cells in the central nervous system, play a role in neuroinflammation and the development of neuropathic pain. We found that the stimulator of...
Microglia, resident immune cells in the central nervous system, play a role in neuroinflammation and the development of neuropathic pain. We found that the stimulator of interferon genes (STING) is predominantly expressed in spinal microglia and upregulated after peripheral nerve injury. However, mechanical allodynia, as a marker of neuropathic pain following peripheral nerve injury, did not require microglial STING expression. In contrast, STING activation by specific agonists (ADU-S100, 35 nmol) significantly alleviated neuropathic pain in male mice, but not female mice. STING activation in female mice leads to increase in proinflammatory cytokines that may counteract the analgesic effect of ADU-S100. Microglial STING expression and type I interferon-ß (IFN-ß) signaling were required for the analgesic effects of STING agonists in male mice. Mechanistically, downstream activation of TANK-binding kinase 1 (TBK1) and the production of IFN-ß, may partly account for the analgesic effect observed. These findings suggest that STING activation in spinal microglia could be a potential therapeutic intervention for neuropathic pain, particularly in males.
Topics: Animals; Female; Male; Mice; Analgesics; Antibodies; Microglia; Neuralgia; Peripheral Nerve Injuries
PubMed: 38190983
DOI: 10.1016/j.bbi.2024.01.003 -
Neurology(R) Neuroimmunology &... Nov 2023Neuropathic pain is common and distressing. Improved mechanistic understanding and pharmacotherapies are urgently needed. Molecularly specific pain syndromes may provide...
OBJECTIVES
Neuropathic pain is common and distressing. Improved mechanistic understanding and pharmacotherapies are urgently needed. Molecularly specific pain syndromes may provide insights with translational relevance. Glycine receptors are known to play a key role in inhibitory neurotransmission in the spinal dorsal horn and have therefore been considered as targets for analgesic development. While autoantibodies directed against glycine receptors may rarely arise spontaneously in humans, a detailed phenotype of neuropathic pain and allodynia in association with these autoantibodies has not been described.
METHODS
We describe the case of a previously well adult presenting with severe neuropathic pain and allodynia as part of an autoimmune brainstem and spinal syndrome with glycine receptor autoantibodies.
RESULTS
Our patient experienced a severe illness, including marked neuropathic pain and allodynia, hypoventilation, tetraparesis, and ophthalmoplegia. A diagnosis of progressive encephalomyelitis with rigidity and myoclonus was made. Neuropathic pain was characterized with validated instruments and responded promptly to cause-directed immunotherapy.
DISCUSSION
A detailed longitudinal phenotyping, using validated pain measurement instruments, of severe neuropathic pain and allodynia associated with likely pathogenic glycine receptor autoantibodies is reported. This case may have relevance for translational development of analgesics targeting glycinergic neurotransmission.
Topics: Adult; Humans; Receptors, Glycine; Hyperalgesia; Neuralgia; Autoantibodies; Immunotherapy
PubMed: 37640544
DOI: 10.1212/NXI.0000000000200160 -
IScience Oct 2023Thousand and one amino acid kinase 2 (TAOK2) is a member of the mammalian sterile 20 kinase family and is implicated in neurodevelopmental disorders; however, its role...
Thousand and one amino acid kinase 2 (TAOK2) is a member of the mammalian sterile 20 kinase family and is implicated in neurodevelopmental disorders; however, its role in neuropathic pain remains unknown. Here, we found that TAOK2 was enriched and activated after chronic constriction injury (CCI) in the rat spinal dorsal horn. Meanwhile, cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling was also activated with hyperalgesia. Silencing TAOK2 reversed hyperalgesia and suppressed the activation of cGAS-STING signaling induced by CCI, while pharmacological activation of TAOK2 induced pain hypersensitivity and upregulation of cGAS-STING signaling in naive rats. Furthermore, pharmacological inhibition or gene silencing of cGAS-STING signaling attenuated CCI-induced hyperalgesia. Taken together, these data demonstrate that the activation of spinal TAOK2 contributes to CCI-induced hyperalgesia via cGAS-STING signaling activation, providing new molecular targets for the treatment of neuropathic pain.
PubMed: 37720090
DOI: 10.1016/j.isci.2023.107792 -
BioRxiv : the Preprint Server For... Dec 2023G protein coupled receptor 37-like 1 (GPR37L1) is an orphan GPCR and its function remains largely unknown. Here we report that GPR37L1 transcript is highly expressed...
G protein coupled receptor 37-like 1 (GPR37L1) is an orphan GPCR and its function remains largely unknown. Here we report that GPR37L1 transcript is highly expressed compared to all known GPCRs in mouse and human dorsal root ganglia (DRGs) and selectively expressed in satellite glial cells (SGCs). Peripheral neuropathy following diabetes and chemotherapy by streptozotocin and paclitaxel resulted in downregulations of surface GPR37L1 in mouse and human DRGs. Transgenic mice with deficiency exhibited impaired resolution of neuropathic pain symptom (mechanical allodynia), whereas overexpression of in mouse DRGs can reverse neuropathic pain. Notably, GPR37L1 is co-expressed and coupled with potassium channels in SGCs. We found striking species differences in potassium channel expression in SGCs, with predominant expression of KCNJ10 and KCNJ3 in mouse and human SGCs, respectively. GPR37L1 regulates the surface expression and function of KCNJ10 and KCNJ3. We identified the pro-resolving lipid mediator maresin 1 (MaR1) as a GPR37L1 ligand. MaR1 increases KCNJ10/KCNJ3-mediated potassium influx in SGCs via GPR37L1. MaR1 protected chemotherapy-induced suppression of KCNJ13/KCNJ10 expression and function in SGCs. Finally, genetic analysis revealed that the variant is associated with increased chronic pain risk by destabilizing the protein. Thus, GPR37L1 in SGCs offers a new target for neuropathy protection and pain control.
PubMed: 38106084
DOI: 10.1101/2023.12.03.569787 -
Animals : An Open Access Journal From... Mar 2024Traumatic nerve injuries are common lesions that affect several hundred thousand humans, as well as dogs and cats. The assessment of nerve regeneration through animal... (Review)
Review
Traumatic nerve injuries are common lesions that affect several hundred thousand humans, as well as dogs and cats. The assessment of nerve regeneration through animal models may provide information for translational research and future therapeutic options that can be applied mutually in veterinary and human medicine, from a One Health perspective. This review offers a hands-on vision of the non-invasive and conservative approaches to peripheral nerve injury, focusing on the role of neurorehabilitation in nerve repair and regeneration. The peripheral nerve injury may lead to hypersensitivity, allodynia and hyperalgesia, with the possibility of joint contractures, decreasing functionality and impairing the quality of life. The question remains regarding how to improve nerve repair with surgical possibilities, but also considering electrical stimulation modalities by modulating sensory feedback, upregulation of BDNF, GFNF, TrKB and adenosine monophosphate, maintaining muscle mass and modulating fatigue. This could be improved by the positive synergetic effect of exercises and physical activity with locomotor training, and other physical modalities (low-level laser therapy, ultrasounds, pulsed electromagnetic fields, electroacupuncture and others). In addition, the use of cell-based therapies is an innovative treatment tool in this field. These strategies may help avoid situations of permanent monoplegic limbs that could lead to amputation.
PubMed: 38539981
DOI: 10.3390/ani14060884 -
The Journal of Headache and Pain Jul 2023Migraine is more prevalent in females, raising the possibility that sex and gonadal hormones modulate migraine. We recently demonstrated that minimally invasive...
BACKGROUND
Migraine is more prevalent in females, raising the possibility that sex and gonadal hormones modulate migraine. We recently demonstrated that minimally invasive optogenetic spreading depolarization (opto-SD) elicits robust periorbital allodynia. The objective of this study was to test the hypothesis that opto-SD induced migraine-like pain behavior is worse in females and varies during the estrus cycle.
METHODS
Single or repeated opto-SDs were induced in male and female adult Thy1-ChR2-YFP transgenic mice. Von Frey monofilaments were used to test periorbital mechanical allodynia. Mouse grimace was also examined under increasing light intensity to quantify spontaneous discomfort and light-aversive behavior. Vaginal smears were obtained for estrus cycle staging at the end of behavioral testing.
RESULTS
A multi-variable regression analysis was performed using a male and female cohort to test the effect of independent variables on periorbital allodynia. Opto-SD predicted lower periorbital thresholds as compared with sham stimulation (p < 0.0001). Additionally, female sex predicted lower periorbital thresholds compared with males (p = 0.011). There were significant interactions between opto-SD and time (interaction p = 0.030) as animals tended to recover from opto-SD allodynia over time, and between sex and time (p = 0.020) as females tended to take longer to recover. Proestrus, estrus (PE) and metestrus, diestrus (MD) stages were combined to represent high versus low circulating estradiol relative to progesterone, respectively. Multi-variable regression revealed an effect of estrus cycle (p = 0.015) on periorbital thresholds. In the sham group, PE had lower thresholds than MD. However, there was no interaction between opto-SD and the estrus cycle (p = 0.364). Grimace scores were also examined at incremental light intensities. There was an effect of opto-SD (p < 0.0001), light intensity (p = 0.001) and estrus cycle (p = 0.024) on grimace without interaction among them (three-way ANOVA).
CONCLUSIONS
Female sex and estrus stages with high circulating estradiol relative to progesterone lower trigeminal pain thresholds and augment photosensitivity. In females, opto-SD increased pain behavior and photosensitivity irrespective of the estrus stage.
Topics: Rats; Male; Mice; Female; Animals; Hyperalgesia; Rats, Sprague-Dawley; Progesterone; Depression; Optogenetics; Estrus; Migraine Disorders; Pain Threshold; Phenotype; Estradiol
PubMed: 37464297
DOI: 10.1186/s10194-023-01621-1 -
Anesthesiology Mar 2024Endoplasmic reticulum stress plays a crucial role in the pathogenesis of neuroinflammation and chronic pain. This study hypothesized that PRKR-like endoplasmic reticulum...
BACKGROUND
Endoplasmic reticulum stress plays a crucial role in the pathogenesis of neuroinflammation and chronic pain. This study hypothesized that PRKR-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme type 1 (IRE1) regulate lipocalin-2 (LCN2) and Nod-like receptor family pyrin domain containing 3 (NLRP3) expression in astrocytes, thereby contributing to morphine tolerance and hyperalgesia.
METHODS
The study was performed in Sprague-Dawley rats and C57/Bl6 mice of both sexes. The expression of LCN2 and NLRP3 was assessed by Western blotting. The tail-flick, von Frey, and Hargreaves tests were used to evaluate nociceptive behaviors. Chromatin immunoprecipitation was conducted to analyze the binding of activating transcription factor 4 (ATF4) to the promoters of LCN2 and TXNIP. Whole-cell patch-clamp recordings were used to evaluate neuronal excitability.
RESULTS
Pharmacologic inhibition of PERK and IRE1 attenuated the development of morphine tolerance and hyperalgesia in male (tail latency on day 7, 8.0 ± 1.13 s in the morphine + GSK2656157 [10 μg] group vs. 5.8 ± 0.65 s in the morphine group; P = 0.04; n = 6 rats/group) and female (tail latency on day 7, 6.0 ± 0.84 s in the morphine + GSK2656157 [10 μg] group vs. 3.1 ± 1.09 s in the morphine group; P = 0.0005; n = 6 rats/group) rats. Activation of PERK and IRE1 upregulated expression of LCN2 and NLRP3 in vivo and in vitro. Chromatin immunoprecipitation analysis showed that ATF4 directly bound to the promoters of the LCN2 and TXNIP. Lipocalin-2 induced neuronal hyperexcitability in the spinal cord and dorsal root ganglia via melanocortin-4 receptor.
CONCLUSIONS
Astrocyte endoplasmic reticulum stress sensors PERK and IRE1 facilitated morphine tolerance and hyperalgesia through upregulation of LCN2 and NLRP3 in the spinal cord.
Topics: Rats; Mice; Male; Female; Animals; Morphine; Inflammasomes; NLR Family, Pyrin Domain-Containing 3 Protein; Astrocytes; Hyperalgesia; Rodentia; Up-Regulation; Lipocalin-2; Rats, Sprague-Dawley; Protein Serine-Threonine Kinases; Spinal Cord; Cell Cycle Proteins
PubMed: 38079113
DOI: 10.1097/ALN.0000000000004858