Browse by Audience
The mechanisms underlying type-2 diabetic neuropathic pain (DNP) are unclear. This study investigates the coupling of postsynaptic density-95 (PSD-95) to N-methyl-D-aspartate receptor subunit 2B (GluN2B), and the subsequent phosphorylation of GluN2B (Tyr1472-GluN2B) in the spinal cord in a rat model of type-2 DNP. Expression levels of PSD-95, Tyr1472-GluN2B, Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its phosphorylated counterpart (Thr286-CaMKII), and α-amino-3-hydroxy-5-methyl-4-soxazole propionic acid receptor subtype 1 (GluR1) and its phosphorylated counterpart (Ser831-GluR1) were significantly increased versus controls in the spinal cord of type-2 DNP rats whereas the expression of total spinal GluN2B did not change. The intrathecal injection of Ro25-6981 (a specific antagonist of GluN2B) or Tat-NR2B9c (a mimetic peptide disrupting the interaction between PSD-95 and GluN2B) induced an antihyperalgesic effect and blocked the increased expression of Tyr1472-GluN2B, CaMKII, GluR1, Thr286-CaMKII, and Ser831-GluR1 in the spinal cords; the increase in spinal cord PSD-95 was not affected. These findings indicate that the PSD-95-GluN2B interaction may increase phosphorylation of GluN2B, and subsequently induce the expression of phosphorylation of CaMKII and GluR1 in the spinal cord of type-2 DNP rats. Targeting the interaction of PSD-95 with GluN2B may provide a new therapeutic strategy for type-2 DNP.
Learn More >HDAC6 is a class IIB histone deacetylase expressed at many levels of the nociceptive pathway. This study tested the ability of novel and selective HDAC6 inhibitors to alleviate sensory hypersensitivity behaviors in mouse models of peripheral nerve injury and peripheral inflammation.
Learn More >The sodium channels Na1.7, Na1.8 and Na1.9 are critical for pain perception in peripheral nociceptors. Loss of function of Na1.7 leads to congenital insensitivity to pain in humans. Here we show that the spider peptide toxin called HpTx1, first identified as an inhibitor of K4.2, restores nociception in Na1.7 knockout (Na1.7-KO) mice by enhancing the excitability of dorsal root ganglion neurons. HpTx1 inhibits Na1.7 and activates Na1.9 but does not affect Na1.8. This toxin produces pain in wild-type (WT) and Na1.7-KO mice, and attenuates nociception in Na1.9-KO mice, but has no effect in Na1.8-KO mice. These data indicate that HpTx1-induced hypersensitivity is mediated by Na1.9 activation and offers pharmacological insight into the relationship of the three Na channels in pain signalling.
Learn More >Psychological stress is a trigger for the development of irritable bowel syndrome (IBS) and associated symptoms including abdominal pain. Although IBS patients exhibit increased activation in the limbic brain, including the amygdala, the underlying molecular and cellular mechanisms regulating visceral nociception in the central nervous system (CNS) are incompletely understood. In a rodent model of chronic stress, we explored the role of microglia in the central nucleus of amygdala (CeA) in controlling visceral sensitivity. Microglia are activated by environmental challenges such as stress, and are able to modify neuronal activity via synaptic remodeling and inflammatory cytokine release. Inflammatory gene expression and microglial activity are negatively regulated by nuclear glucocorticoid receptors (GR), which are suppressed by the stress-activated pain mediator P38 MAPK.
Learn More >Synaptic neurotransmission with dopamine (DA), norepinephrine (NE), and serotonin (5-HT) is terminated primarily by reuptake into presynaptic terminals via the DA, NE, and 5-HT transporters (DAT/NET/SERT, respectively). Monoamine transporter inhibitors constitute one class of drugs used to treat both depression and pain, and therapeutic effects by these compounds often require repeated treatment for days or weeks.
Learn More >Chronic pain is associated with persistent structural and functional changes throughout the neuroaxis, including in the prefrontal cortex (PFC). The PFC is important in the integration of sensory, cognitive and emotional information and in conditioned pain modulation. We previously reported wide-spread epigenetic reprogramming in the PFC many months following nerve injury in rodents. Epigenetic modifications, including DNA methylation, can drive changes in gene expression without modifying DNA sequences. To date, little is known about epigenetic dysregulation at the onset of acute pain or how it progresses as pain transitions from acute to chronic. We hypothesize that acute pain following injury results in rapid and persistent epigenetic remodelling in the PFC that evolves as pain becomes chronic. We further propose that understanding epigenetic remodelling will provide insights into the mechanisms driving pain-related changes in the brain. Epigenome-wide analysis was performed in the mouse PFC 1 day, 2 weeks, 6 months, and 1 year following peripheral injury using the spared nerve injury (SNI) in mice. SNI resulted in rapid and persistent changes in DNA methylation, with robust differential methylation observed between SNI and sham-operated control mice at all time points. Hundreds of differentially methylated genes were identified, including many with known function in pain. Pathway analysis revealed enrichment in genes related to stimulus response at early time points, immune function at later time points and actin and cytoskeletal regulation throughout the time course. These results emphasize the importance of considering pain chronicity in both pain research and in treatment optimization.
Learn More >The opioid epidemic has plagued the United States with high levels of abuse and poor quality of life for chronic pain patients requiring continuous use of opioids. New drug discovery efforts have been implemented to mitigate this epidemic, however, new medications are still limited by low efficacy and/or high side effect and abuse potential. Intermittent fasting (IF) has recently been shown to improve a variety of pathological states, including stroke and neuroinflammation. Numerous animal and human studies have shown the benefits of IF in these disease states, but not in pain and opioid treatment. We thus subjected male and female CD-1 mice to 18-hour fasting intervals followed by 6-hour feed periods with standard chow for 1 week. Mice which underwent this diet displayed an enhanced anti-nociceptive response to morphine both in efficacy and duration using thermal tail flick and post-operative paw incision pain models. While showing enhanced anti-nociception, IF mice also demonstrated no morphine reward and reduced tolerance and constipation. Seeking a mechanism for these improvements, we found that the mu opioid receptor (MOR) showed enhanced efficacy and reduced tolerance in the spinal cord and periaqueductal grey (PAG) respectively from IF mice using a S-GTPγS coupling assay. These improvements in receptor function were not due to changes in MOR protein expression. These data suggest that a daily IF diet may improve the therapeutic index of acute and chronic opioid therapies for pain patients in the clinic, providing a novel tool to improve patient therapy and reduce potential abuse.
Learn More >The mu opioid receptor (MOR) modulates nociceptive pathways, reward processing, and mediates the strong analgesic and addictive properties of both medicinal as well as abused opioid drugs. MOR function has been extensively studied, and tools to manipulate or visualize the receptor protein are available. However, circuit mechanisms underlying MOR-mediated effects are less known, because genetic access to MOR-expressing neurons is lacking. Here we report the generation of a knock-in -Cre mouse line, which allows targeting and manipulating MOR opioid-responsive neurons. A cDNA encoding a T2A cleavable peptide and Cre-recombinase fused to enhanced green fluorescent protein (eGFP/Cre) was inserted downstream of the gene sequence. The resulting Cre line shows intact gene transcription. MOR and eGFP/Cre proteins are co-expressed in the same neurons, and localized in cytoplasmic and nuclear compartments, respectively. MOR signaling is unaltered, demonstrated by maintained DAMGO-induced G protein activation, MOR function is preserved as indicated by normal morphine-induced analgesia, hyperlocomotion and sensitization. The Cre-recombinase efficiently drives expression of Cre-dependent reporter genes, shown by local-virally-mediated expression in the medial habenula and brain wide fluorescence upon breeding with tdTomato reporter mice, the later showing a distribution patterns typical of MOR expression. Finally, we demonstrate that optogenetic activation of MOR neurons in the ventral tegmental area of -Cre mice evokes strong avoidance behavior, as anticipated from the literature. The -Cre line is therefore an excellent tool for both mapping and functional studies of MOR-positive neurons, and will be of broad interest for opioid, pain and addiction research. Here we develop an innovative tool to characterize circuit mechanisms underlying opioid actions, which may help the research communities to improve the knowledge on circuitry adaptation and response to opioid. The tool is particularly relevant in the context of the current opioid crisis. Medicinal and abused opioids act primarily on Mu Opioid Receptor (MOR) and we developed here a Cre mouse line to specifically target and manipulate MOR-expressing neurons. This resource is with huge potential for mapping, molecular characterization and functional studies of opioid-responsive neurons.
Learn More >We previously reported that interleukin (IL)-6 in the red nucleus (RN) is involved in the maintenance of neuropathic pain induced by spared nerve injury (SNI), and exerts a facilitatory effect via Janus-activated kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) and extracellular signal-regulated kinase (ERK) signal transduction pathways. The present study aimed at investigating the roles of tumor necrosis factor-α (TNF-α) and IL-1β in RN IL-6-mediated maintenance of neuropathic pain and related signal transduction pathways. Being similar to the elevation of RN IL-6 three weeks after SNI, increased protein levels of both TNF-α and IL-1β were also observed in the contralateral RN three weeks after the nerve injury. The upregulations of TNF-α and IL-1β were closely correlative with IL-6 and suppressed by intrarubral injection of a neutralizing antibody against IL-6. Administration of either the JAK2 antagonist AG490 or the ERK antagonist PD98059 to the RN of rats with SNI remarkably increased the paw withdrawal threshold (PWT) and inhibited the up-regulations of local TNF-α and IL-1β. Further experiments indicated that intrarubral injection of exogenous IL-6 in naive rats apparently lowered the PWT of the contralateral hindpaw and boosted the local expressions of TNF-α and IL-1β. Pretreatment with AG490 could block IL-6-induced tactile hypersensitivity and suppress the up-regulations of both TNF-α and IL-1β. However, injection of PD98059 in advance only inhibited the upregulation of IL-1β, but not TNF-α. These findings indicate that RN IL-6 mediates the maintenance of neuropathic pain by inducing the productions of TNF-α and IL-1β. IL-6 induces the expression of TNF-α through the JAK2/STAT3 pathway, and the production of IL-1β through the JAK2/STAT3 and ERK pathways.
Learn More >Nerve-binding fluorophores with near-infrared (NIR; 650 to 900 nm) emission could reduce iatrogenic nerve injury rates by providing surgeons precise, real-time visualization of the peripheral nervous system. Unfortunately, current systemically administered nerve contrast agents predominantly emit at visible wavelengths and show nonspecific uptake in surrounding tissues such as adipose, muscle, and facia, thus limiting detection to surgically exposed surface-level nerves. Here, a focused NIR fluorophore library was synthesized and screened through multi-tiered optical and pharmacological assays to identify nerve-binding fluorophore candidates for clinical translation. NIR nerve probes enabled micrometer-scale nerve visualization at the greatest reported tissue depths (~2 to 3 mm), a feat unachievable with previous visibly emissive contrast agents. Laparoscopic fluorescent surgical navigation delineated deep lumbar and iliac nerves in swine, most of which were invisible in conventional white-light endoscopy. Critically, NIR oxazines generated contrast against all key surgical tissue classes (muscle, adipose, vasculature, and fascia) with nerve signal-to-background ratios ranging from ~2 (2- to 3-mm depth) to 25 (exposed nerve). Clinical translation of NIR nerve-specific agents will substantially reduce comorbidities associated with surgical nerve damage.
Learn More >