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Fatty acid amide hydrolase inhibition may be used to control bladder function and pain by modulating endocannabinoid levels in cystitis. We studied the effect of the peripherally restricted fatty acid amide hydrolase inhibitor URB937 in bladder reflex activity and bladder pain using the lipopolysaccharide model of cystitis. We also correlated the URB937's effects with tissue levels of the endocannabinoids anandamide and palmitoylethanolamine. URB937 did not change the reflex activity of normal bladders. In inflamed bladders, URB937 had a U-shaped dose-response curve; following an initial cannabinoid receptor type 1-mediated reduction in pain responses and normalisation of bladder reflex activity, URB937 gradually increased both pain responses and bladder reflex activity through the transient receptor potential ion channel subfamily V member 1. Chronic cystitis increased the tissue levels of anandamide and decreased those of palmitoylethanolamine. At the dose that normalised bladder reflex activity and decreased pain responses, URB937 normalised the levels of anandamide and palmitoylethanolamine in the bladder. At high doses that induced excitatory effects, URB937 apparently did not change anandamide and palmitoylethanolamine levels, which therefore were in the range of the inflamed bladder. Fatty acid amide hydrolase inhibition results in complex changes in bladder endocannabinoid levels. The therapeutic effect of fatty acid amide hydrolase inhibitors is not related to increase in anandamide levels but rather a normalisation of the anandamide and palmitoylethanolamine level ratio.
Learn More >Tissue injury produces a delicate balance between latent pain sensitization (LS) and compensatory endogenous opioid receptor analgesia that continues for months, even after re-establishment of normal pain thresholds. To evaluate the contribution of mu (MOR), delta (DOR), and/or kappa (KOR) opioid receptors to the silencing of chronic postoperative pain, we performed plantar incision at the hindpaw, waited 21 days for the resolution of hyperalgesia, and then intrathecally injected subtype-selective ligands. We found that the MOR-selective inhibitor CTOP (1-1000 ng) dose-dependently reinstated mechanical hyperalgesia. Two DOR-selective inhibitors naltrindole (1-10 μg) and TIPP[Ψ] (1-20 μg) reinstated mechanical hyperalgesia, but only at the highest dose that also produced itching, licking, and tail biting. Both the prototypical KOR-selective inhibitors nor-BNI (0.1-10 μg) and the newer KOR inhibitor with more canonical pharmocodynamic effects, LY2456302 (0.1-10 μg), reinstated mechanical hyperalgesia. Furthermore, LY2456302 (10 μg) increased the expression of phosphorylated signal-regulated kinase (pERK), a marker of central sensitization, in dorsal horn neurons but not glia. Sex studies revealed that LY2456302 (0.3 μg) reinstated hyperalgesia and pERK expression to a greater degree in female as compared to male mice. Our results suggest that spinal MOR and KOR, but not DOR, maintain LS within a state of remission to reduce the intensity and duration of postoperative pain, and that endogenous KOR but not MOR analgesia is greater in female mice.
Learn More >Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) is a common chronic pelvic disorder with sensory symptoms of urinary urgency, frequency, and pain, indicating a key role for hypersensitivity of bladder-innervating sensory neurons. The inflammatory mast cell mediator histamine has long been implicated in IC/BPS, yet the direct interactions between histamine and bladder afferents remain unclear. Here we show, using a mouse bladder afferent preparation, that intravesical histamine enhanced the mechanosensitivity of sub-populations of afferents to bladder distension. Histamine also recruited 'silent afferents', which were previously unresponsive to bladder distension. Furthermore, intravesical histamine enhanced activation of dorsal horn neurons within the lumbosacral spinal cord, indicating increased afferent signaling into the central nervous system. qRT-PCR revealed significant expression of histamine receptor subtypes () in mouse lumbosacral dorsal root ganglia (DRG), bladder detrusor smooth muscle, mucosa, and isolated urothelial cells. In DRG, was the most abundantly expressed. Acute histamine exposure evoked calcium influx in select populations of DRG neurons but did not elicit calcium transients in isolated primary urothelial cells. Histamine-induced mechanical hypersensitivity was abolished in the presence of the histamine H receptor (HR) antagonist pyrilamine and was not present in preparations from mice lacking the TRPV1 receptor. Together, these results indicate that histamine enhances the sensitivity of bladder afferents to distension via interactions with HR and TRPV1. This hypersensitivity translates to increased sensory input and activation in the spinal cord, which may underlie the symptoms of bladder hypersensitivity and pain experienced in IC/BPS.
Learn More >To determine whether transgenic mouse models of migraine exhibit upper gastrointestinal dysmotility comparable to those observed in migraine patients.
Learn More >We investigated the efficacy of duloxetine on hyperalgesia, histopathological and radiographic findings, pain-related sensory innervation of dorsal-root ganglia (DRG), and spinal changes in a rat model of induced hip osteoarthritis (OA). The right hip joints of male Sprague-Dawley rats (n = 6 rats/group) in the Sham group were injected with 25 μL of sterile saline and 25 μL of sterile saline with 2 mg of monosodium iodoacetate (MIA) were injected to the MIA + Vehicle and MIA + Duloxetine groups. We injected duloxetine 20 mg/kg intraperitoneally in the MIA + Duloxetine group 28 days after injection, whereas rats in the MIA + Vehicle group were injected with 0.5 mL of 20% dimethyl sulfoxide. We assessed hyperalgesia, histopathological changes, immunoreactive (-ir) neurons for calcitonin gene-related peptide and activating transcription factor 3 in DRG, and immunoreactive neurons for ionized-calcium-binding adaptor molecule 1 (Iba1) in the dorsal horn of the spinal cord. MIA administration into the hip joint let to mechanical hyperalgesia of the ipsilateral hind paw (p < 0.05). A single injection of duloxetine significantly attenuated it in induced hip OA (p < 0.05) and suppressed the number of Iba1-ir microglia of the ipsilateral dorsal horn (p < 0.05). These results suggest that a single injection of duloxetine suppressed mechanical hyperalgesia and may influence the expression of Iba1 in the microglia of the ipsilateral dorsal horn in the MIA-induced hip OA. This finding implies the inhibitory effects of duloxetine against neuropathic pain, which may lead to a change of microglial activities. This article is protected by copyright. All rights reserved.
Learn More >This study aimed to disclose differentially expressed genes (DEGs) in dorsal root ganglia (DRGs) of neuropathic pain (NP) from spared nerve injury (SNI) model, thereby identifying specific and meaningful genetic targets for the diagnosis and treatment of NP. The GSE89224 was downloaded from the GEO database. DEGs were screened using the GEO2R online tool. Functional enrichment analysis of DEGs was then performed using the DAVID and constructed using the R ggplot2 package. Protein-protein interaction (PPI) network was constructed from the STRING database and visualized in Cytoscape software. MicroRNA targeting these DEGs was obtained from the TarBase and miRTarBase database, while transcription factor (TF)-targeting DEGs were predicted from the ENCODE database, both of which utilized the visual analytics platform NetworkAnayst. Finally, a merged microRNA-TF network was constructed based on the above two networks and was then analyzed with Cytoscape. Eighty DEGs were screened, only Vstm2b and Htr3a were downregulated and 78 genes were upregulated. The real-time polymerase chain reaction was applied to validate the gene expression of the top five DEGs (Npy, Atf3, Gpr151, Sprr1a, and Cckbr) in the DRG tissue 5 days after SNI surgery. It was found that Npy, Atf3, and Sprr1a have a significant increase after SNI stimulation, while Gpr151 and Cckbr showed a slight upward trend. Functional analysis was performed on all DEGs, of which 58 biological processes were enriched by gene ontology analysis, and 11 signaling pathways were enriched by KEGG analysis. In the PPI network, Atf3, Jun, Timp, and Npy had a higher degree. Thus, combined with various bioinformatic analyses, Npy and Atf3 may serve as the prognostic and therapeutic targets of NP. Key microRNA (mmu-mir-16-5p) and TF (MEF2A) were predicted to be associated with the pathogenetic process of NP with microRNA-TF regulatory network analysis, which were also identified as key regulators in the progression of NP.
Learn More >Chemotherapeutic agents can cause peripheral neuropathy, a deleterious side effect of cancer treatment. Hyperbaric oxygen (HBO2) treatment has shown great potential for decreasing pain in numerous clinical pain conditions and in preclinical studies. This study was designed to test whether HBO2 might also be useful for treating chemotherapy-induced peripheral neuropathy. Male and female Sprague-Dawley rats were injected with 1 mg/kg paclitaxel or vehicle every other day for 7 days to induce allodynia, followed by either one single, or four daily 60-min exposures to HBO2 or room air. Mechanical and cold allodynia as well as locomotor behavior and body weight were assessed intermittently for several weeks. Estrous cycling was also tracked in female rats. Paclitaxel caused pronounced mechanical allodynia in both sexes that was completely reversed by either one or four treatments of HBO2. Females in all treatment groups showed greater cold acetone scores than males, and acetone scores were not reliably reduced by HBO2 treatment. Neither paclitaxel nor HBO2 treatment altered locomotor behavior or estrous cycling. We conclude that HBO2 treatment was highly effective at reducing mechanical allodynia in paclitaxel-treated rats without affecting weight gain, locomotion, or estrous cycling, suggesting that HBO2 may be effective for treating chemotherapy-induced neuropathic pain without producing significant side effects.
Learn More >The aminosteroid U73122 is frequently used as a phospholipase C (PLC) inhibitor and as such was used to investigate PLC-dependent activation and modulation of the transient receptor potential ankyrin type 1 (TRPA1) receptor channel. However, U73122 was recently shown to activate recombinant TRPA1 directly, albeit this interaction was not further explored. Our aim was to perform a detailed characterization of this agonistic action of U73122 on TRPA1. We used Fura-2 calcium microfluorimetry and the patch clamp technique to investigate the effect of U73122 on human and mouse wild type and mutant (C621S/C641S/C665S) TRPA1 expressed in HEK293t cells, as well as native TRPA1 in primary afferent neurons from wild type and TRPV1 and TRPA1 null mutant mice. In addition, we measured calcitonin gene-related peptide (CGRP) release from skin isolated from wild-type and TRPA1 null mutant mice. Human and mouse TRPA1 channels were activated by U73122 in the low nanomolar range. This activation was only partially dependent upon modification of the N-terminal cysteines 621, 641, and 665. U73122 also activated a subpopulation of neurons from wild-type and TRPV1 null mutant mice, but this effect was absent in mice deficient of TRPA1. In addition, U73122 evoked marked calcitonin gene-related peptide (CGRP) release from skin preparations of wild type but not TRPA1 null mutant mice. Our results indicate that U73122 is a potent and selective TRPA1 agonist. This effect should be taken into account when U73122 is used to inhibit PLC in TRPA1-expressing cells, such as primary nociceptors. In addition, U73122 may present a novel lead compound for the development of TRPA1-targeting drugs.
Learn More >With the shifting role of placebos, there is a need to develop animal models of placebo analgesia and elucidate the mechanisms underlying the effect. In the present study, male Sprague-Dawley rats with chronic inflammatory pain caused by complete Freund's adjuvant (CFA) underwent a series of conditioning procedures, in which morphine was associated with different cues, but they failed to induce placebo analgesia. Then, conditioning with the conditioned place preference apparatus successfully induced analgesic expectancy and placebo analgesia in naïve rats but only induced analgesic expectancy and no analgesic effect in CFA rats. Subsequently, we found enhanced c-fos expression in the nucleus accumbens and reduced expression in the anterior cingulate cortex in naïve rats while c-fos expression in the anterior cingulate cortex in CFA rats was not altered. In summary, the behavioral conditioning model demonstrated the difficulty of establishing a placebo analgesia model in rats with a pathological condition.
Learn More >Despite the large comorbidity between PTSD and opioid use disorders, as well as the common treatment of physical injuries resulting from trauma with opioids, the ability of opioid treatments to subsequently modify PTSD-related behavior has not been well studied. Using the stress-enhanced fear learning (SEFL) model for PTSD, we characterized the impact of chronic opioid regimens on the sensitization of fear learning seen following traumatic stress in mice. We demonstrate for the first time that chronic opioid pretreatment is able to robustly augment associative fear learning. Highlighting aversive learning as the cognitive process mediating this behavioral outcome, these changes were observed after a considerable period of drug cessation, generalized to learning about multiple aversive stimuli, were not due to changes in stimulus sensitivity or basal anxiety, and correlated with a marker of synaptic plasticity within the basolateral amygdala. Additionally, these changes were not observed when opioids were given after the traumatic event. Moreover, we found that neither reducing the frequency of opioid administration nor bidirectional manipulation of acute withdrawal impacted the subsequent enhancement in fear learning seen. Given the fundamental role of associative fear learning in the generation and progression of PTSD, these findings are of direct translational relevance to the comorbidity between opioid dependence and PTSD, and they are also pertinent to the use of opioids for treating pain resulting from traumas involving physical injuries.
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