[Show abstract][Hide abstract] ABSTRACT: The pathophysiology of chronic inflammatory pain remains poorly understood. In this context, we developed an experimental model in which successive daily injection of prostaglandin E2 (PGE2) for 14 days into rat hind paws produces a persistent state of hypernociception (i.e. decrease in mechanical nociceptive threshold). This state persists for more than 30 days after discontinuing PGE2 injection. In the present study, we investigated the participation of nuclear factor kappa B (NF-κB), in the maintenance of this process. Mechanical hypernociception was evaluated using the electronic von Frey test. Activation of NF-κB signaling was measured through the determination of NF-κB p65 subunit translocation to the nucleus of dorsal root ganglion neurons (DRG) by immunofluorescence and western blotting. Herein, we detected an increase in NF-κB p65 subunit translocation to the nucleus of DRG neurons along with persistent inflammatory hypernociception compared with controls. Intrathecal treatment with either dexamethasone or PDTC (NF-κB activation inhibitor) after ending of the induction phase of the persistent inflammatory hypernociception, curtailed the hypernociception period as well as reducing NF-κB p65 subunit translocation. Treatment with antisense oligonucleotides against the NF-κB p65 subunit for 5 consecutive days also reduced persistent inflammatory hypernociception. Inhibition of PKA and PKCε reduced persistent inflammatory hypernociception, which was associated with inhibition of NF-κB p65 subunit translocation. Together these results suggest that peripheral activation of NF-κB by PKA and PKC in primary sensory neurons plays an important role in maintaining persistent inflammatory pain.
[Show abstract][Hide abstract] ABSTRACT: The present study evaluated the role of N-methyl-D-aspartate receptors (NMDARs) expressed in the dorsal root ganglia (DRG) in the inflammatory sensitization of peripheral nociceptor terminals to mechanical stimulation. Injection of NMDA into the fifth lumbar (L5)-DRG induced hyperalgesia in the rat hind paw with a profile similar to that of intraplantar injection of prostaglandin E2 (PGE2), which was significantly attenuated by injection of the NMDAR antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP-5) in the L5-DRG. Moreover, blockade of DRG AMPA receptors by the antagonist 6,7-dinitroquinoxaline-2,3-dione
had no effect in the PGE2-induced hyperalgesia in thepaw, showing specific involvement of NMDARs in this modulatory effect and suggesting that activation of NMDAR in the DRG plays an important role in the peripheral inflammatory hyperalgesia. In following experimentswe observed attenuation of PGE2-induced hyperalgesia in the paw by the knockdown of NMDAR subunits NR1, NR2B, NR2D, and NR3A with antisense-oligodeoxynucleotide treatment in the DRG. Also, in vitro experiments showed that the NMDA induced sensitization of cultured DRG neurons depends on satellite cell activation and on those same NMDAR subunits, suggesting their importance for the PGE2-induced hyperalgesia. In addition, fluorescent calcium imaging experiments in cultures of DRG cells showed induction of calcium transients by glutamate or NMDA only in satellite cells, but not in neurons. Together, the present results suggest that the mechanical inflammatory nociceptor sensitization is dependent on glutamate release at the DRG and subsequent NMDAR activation in satellite glial cells, supporting the idea that the peripheral hyperalgesia is an event modulated by a glutamatergic system in the DRG.
Full-text · Article · Dec 2014 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The activation of the satellite glial cells (SGCs) surrounding the dorsal root ganglion (DRG) neurons appears to play a role in pathological pain. We tested the hypothesis that fractalkine, which is constitutively expressed by primary nociceptive neurons, is the link between peripheral inflammation and the activation of SGCs and is thus responsible for the genesis of the inflammatory pain. The injection of carrageenin into the rat hind paw induced a decrease in the mechanical nociceptive threshold (hypernociception), which was associated with an increase in mRNA and GFAP protein expression in the DRG. Both events were inhibited by anti-fractalkine antibody administered directly into the DRG (L5) [intraganglionar (i.gl.)]. The administration of fractalkine into the DRG (L5) produced mechanical hypernociception in a dose-, time-, and CX3C receptor-1 (CX3CR1)-dependent manner. Fractalkine's hypernociceptive effect appears to be indirect, as it was reduced by local treatment with anti-TNF-α antibody, IL-1-receptor antagonist, or indomethacin. Accordingly, the in vitro incubation of isolated and cultured SGC with fractalkine induced the production/release of TNF-α, IL-1β, and prostaglandin E2. Finally, treatment with i.gl. fluorocitrate blocked fractalkine (i.gl.)- and carrageenin (paw)-induced hypernociception. Overall, these results suggest that, during peripheral inflammation, fractalkine is released in the DRG and contributes to the genesis of inflammatory hypernociception. Fractalkine's effect appears to be dependent on the activation of the SGCs, leading to the production of TNFα, IL-1β, and prostanoids, which are likely responsible for the maintenance of inflammatory pain. Thus, these results indicate that the inhibition of fractalkine/CX3CR1 signaling in SGCs may serve as a target to control inflammatory pain.
Full-text · Article · Jun 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: It is well established that dorsal root ganglion (DRG) cells synthesize prostaglandin. However, the role that prostaglandin plays in the inflammatory hyperalgesia of peripheral tissue has not been established. Recently, we have successfully established a technique to inject drugs (3 μL) directly into the L5-DRG of rats, allowing in vivo identification of the role that DRG cell-derived COX-1 and COX-2 play in the development of inflammatory hyperalgesia of peripheral tissue. IL-1β (0.5 pg) or carrageenan (100 ng) was administered in the L5-peripheral field of rat hindpaw and mechanical hyperalgesia was evaluated after 3 h. Administration of a nonselective COX inhibitor (indomethacin), selective COX-1 (valeryl salicylate), or selective COX-2 (SC-236) inhibitors into the L5-DRG prevented the hyperalgesia induced by IL-1β. Similarly, oligodeoxynucleotide-antisense against COX-1 or COX-2, but not oligodeoxynucleotide-mismatch, decreased their respective expressions in the L5-DRG and prevented the hyperalgesia induced by IL-1β in the hindpaw. Immunofluorescence analysis demonstrated that the amount of COX-1 and COX-2, constitutively expressed in TRPV-1(+) cells of the DRG, significantly increased after carrageenan or IL-1β administration. In addition, indomethacin administered into the L5-DRG prevented the increase of PKCε expression in DRG membrane cells induced by carrageenan. Finally, the administration of EP1/EP2 (7.5 ng) or EP4 (10 µg) receptor antagonists into L5-DRG prevented the hyperalgesia induced by IL-1β in the hindpaw. In conclusion, the results of this study suggest that the inflammatory hyperalgesia in peripheral tissue depends on activation of COX-1 and COX-2 in C-fibers, which contribute to the induction and maintenance of sensitization of primary sensory neurons.
Full-text · Article · Feb 2013 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: In addition to their central effects, opioids cause peripheral analgesia. There is evidence showing that peripheral activation of kappa opioid receptors (KORs) inhibits inflammatory pain. Moreover, peripheral μ-opioid receptor (MOR) activation are able to direct block PGE(2)-induced ongoing hyperalgesia However, this effect was not tested for KOR selective activation. In the present study, the effect of the peripheral activation of KORs on PGE(2)-induced ongoing hyperalgesia was investigated. The mechanisms involved were also evaluated.
Local (paw) administration of U50488 (a selective KOR agonist) directly blocked, PGE(2)-induced mechanical hyperalgesia in both rats and mice. This effect was reversed by treating animals with L-NMMA or N-propyl-L-arginine (a selective inhibitor of neuronal nitric oxide synthase, nNOS), suggesting involvement of the nNOS/NO pathway. U50488 peripheral effect was also dependent on stimulation of PI3Kγ/AKT because inhibitors of these kinases also reduced peripheral antinociception induced by U50488. Furthermore, U50488 lost its peripheral analgesic effect in PI3Kγ null mice. Observations made in vivo were confirmed after incubation of dorsal root ganglion cultured neurons with U50488 produced an increase in the activation of AKT as evaluated by western blot analyses of its phosphorylated form. Finally, immunofluorescence of DRG neurons revealed that KOR-expressing neurons also express PI3Kγ (≅ 43%).
The present study indicates that activation of peripheral KORs directly blocks inflammatory hyperalgesia through stimulation of the nNOS/NO signaling pathway which is probably stimulated by PI3Kγ/AKT signaling. This study extends a previously study of our group suggesting that PI3Kγ/AKT/nNOS/NO is an important analgesic pathway in primary nociceptive neurons.
[Show abstract][Hide abstract] ABSTRACT: Morphine is one of the most prescribed and effective drugs used for the treatment of acute and chronic pain conditions. In addition to its central effects, morphine can also produce peripheral analgesia. However, the mechanisms underlying this peripheral action of morphine have not yet been fully elucidated. Here, we show that the peripheral antinociceptive effect of morphine is lost in neuronal nitric-oxide synthase null mice and that morphine induces the production of nitric oxide in primary nociceptive neurons. The activation of the nitric-oxide pathway by morphine was dependent on an initial stimulation of PI3Kgamma/AKT protein kinase B (AKT) and culminated in increased activation of K(ATP) channels. In the latter, this intracellular signaling pathway might cause a hyperpolarization of nociceptive neurons, and it is fundamental for the direct blockade of inflammatory pain by morphine. This understanding offers new targets for analgesic drug development.
Full-text · Article · Feb 2010 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Hydrogen sulfide (H(2)S) is an endogenous gas involved in several biological functions, including modulation of nociception. However, the mechanisms involved in such modulation are not fully elucidated. The present study demonstrated that the pretreatment of mice with PAG, a H(2)S synthesis inhibitor, reduced LPS-induced mechanical paw hypernociception. This inhibition of hypernociception was associated with the prevention of neutrophil recruitment to the plantar tissue. Conversely, PAG had no effect on LPS-induced production of the hypernociceptive cytokines, TNF-alpha, IL-1beta and CXCL1/KC and on hypernociception induced by PGE(2), a directly acting hypernociceptive mediator. In contrast with the pro-nociceptive role of endogenous H(2)S, systemic administration of NaHS, a H(2)S donor, reduced LPS-induced mechanical hypernociception in mice. Moreover, this treatment inhibited mechanical hypernociception induced by PGE(2), suggesting a direct effect of H(2)S on nociceptive neurons. The antinociceptive mechanism of exogenous H(2)S depends on K((ATP))(+) channels since the inhibition of PGE(2) hypernociception by NaHS was prevented by glibenclamide (K((ATP))(+) channel blocker). Finally, NaHS did not alter the thermal nociceptive threshold in the hot-plate test, confirming that its effect is mainly peripheral. Taken together, these results suggest that H(2)S has a dual role in inflammatory hypernociception: 1. an endogenous pro-nociceptive effect due to up-regulation of neutrophil migration, and 2. an antinociceptive effect by direct blockade of nociceptor sensitization modulating K((ATP))(+) channels.
Full-text · Article · Jul 2008 · European Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: We have shown that endogenous glucocorticoids control neutrophil mobilization in the absence of inflammation. In this study the role of the glucocorticoid receptor (GR) in the physiological control of neutrophil mobilization was investigated, focusing on the specific mechanisms for mature neutrophils in bone marrow, circulating neutrophils and endothelial cells.
Male Wistar rats were treated with RU 38486 or adrenalectomized. Cell numbers in bone marrow and circulation were morphologically quantified and expressions of L-selectin determined by flow cytometry. Expressions of P-selectin, E-selectin, PECAM-1, VCAM-1 and ICAM-1 were measured by immunohistochemistry on vessels of cremaster muscle and their mRNA levels quantified in primary cultured endothelial cells. NF-kappaB activity in neutrophils and endothelium was quantified by EMSA.
RU 38486 treatment altered the maturation phases of neutrophilic lineage and reduced expression of L-selectin in mature neutrophils from bone marrow; increased the number of neutrophils in the circulation and elevated the expression of L-selectin in these cells. P-selectin and E-selectin expression in endothelial cells was unchanged by adrenalectomy or RU 38486 treatment. Membrane expressions, mRNA levels of ICAM-1, VCAM-1 and PECAM-1 and NF-kappaB translocation into the nucleus were higher in the endothelium of adrenalectomized and RU 38486 treated rats.
Endogenous glucocorticoids, through activation of GR on neutrophils, physiologically control the rolling behaviour of these cells and, by modulating endothelial functions, affect their adhesiveness. The molecular mechanism induced by activated GR is different in each cell, as NF-kappaB translocation was only altered in endothelial cells.
Full-text · Article · Jan 2008 · British Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: A considerable amount of evidence suggests that temporomandibular joint (TMJ) pain associated with temporomandibular disorder results, at least in part, from an inflammatory episode. Although histamine can cause pain, it is not clear whether this mediator induces nociception in the TMJ. In this study, we investigated the contribution of endogenous histamine to formalin-induced nociception in the TMJ of rats. We also investigated whether the administration of histamine induces nociception in the TMJ and, if so, whether this effect is mediated by an indirect action on primary afferent nociceptors. Local administration of the H1-receptor antagonist pyrilamine prevented formalin-induced nociception in the TMJ in a dose-dependent manner. Local administration of histamine (250 microg) in the TMJ induced nociceptive behavior that was inhibited by co-administration of the lidocaine N-ethyl bromide quaternary salt QX-314 (2%) or the selective H1-receptor antagonist pyrilamine (400 microg). Nociception induced by histamine was also inhibited by pre-treatment with sodium cromoglycate (800 microg) and by co-administration of the 5-HT(3) receptor antagonist tropisetron (400 mug), while pyrilamine (400 mug) did not inhibit nociception induced by 5-hydroxytryptamine (5-HT, 250 microg) in the TMJ. Furthermore, histamine, in a dose that did not induce nociception by itself, strongly enhanced 5-HT-induced nociception. Finally, the administration of a sub-threshold dose of 5-HT (100 microg), but not of histamine (100 microg), elicited nociception in the TMJ previously challenged with the inflammatory agent carrageenan (100 microg). In conclusion, these data suggest that histamine induces TMJ nociception by an indirect mechanism involving endogenous release of 5-HT and activation of 5-HT(3) receptors on sensory afferents. It is proposed that histamine activates the H1 receptor to induce the release of 5-HT which depolarizes the nociceptor by activating 5-HT(3) receptor.
[Show abstract][Hide abstract] ABSTRACT: The failure of neutrophils to migrate to an infection focus during severe sepsis is an important determinant of the inability of a host to deal with an infectious insult. Our laboratory has shown that inducible nitric oxide synthase (iNOS) induction and NO production contribute to the failure of neutrophils to migrate in the context of sepsis. Objectives and
We investigated whether CXCR2 expression contributed to the failure of neutrophils to migrate during severe sepsis and the role of NO in modulating CXCR2 expression on neutrophils in mice subjected to nonsevere (NS) or severe (S) cecal ligation and puncture (CLP).
Neutrophil migration to the infection focus was deficient in S-CLP mice, a phenomenon prevented by pharmacologic (aminoguanidine, l-canavanine) or genetic (iNOS gene deletion) inhibition of iNOS. The expression of CXCR2 on neutrophils from S-CLP mice was significantly reduced when compared with neutrophils from NS-CLP or sham-operated mice. CXCR2 expression was reestablished by pharmacologic and genetic inhibition of iNOS. Immunofluorescence and confocal analysis revealed that iNOS blockade reduced neutrophil CXCR2 internalization. Adhesion and emigration of neutrophils in macrophage inflammatory protein-2-stimulated mesentery microcirculation were reduced in S-CLP mice, compared with NS-CLP mice, and reestablished by pretreatment with aminoguanidine or l-canavanine. The NO donor S-nitroso-N-acetyl-d,l-penicillamine inhibited CXCL8-induced human neutrophil chemotaxis and CXCR2 expression on human and murine neutrophils.
These results highlight evidences that the failure of neutrophils to migrate to an infection focus during severe sepsis is associated with excessive NO production and NO-dependent regulation of the expression of CXCR2 on the neutrophil surface.
Full-text · Article · Apr 2007 · American Journal of Respiratory and Critical Care Medicine
[Show abstract][Hide abstract] ABSTRACT: The aim of the present study was to determine the effect of pertussis toxin (PTX) on inflammatory hypernociception measured by the rat paw pressure test and to elucidate the mechanism involved in this effect. In this test, prostaglandin E(2) (PGE(2)) administered subcutaneously induces hypernociception via a mechanism associated with neuronal cAMP increase. Local intraplantar pre-treatment (30 min before), and post-treatment (5 min after) with PTX (600 ng/paw1, in 100 microL) reduced hypernociception induced by prostaglandin E(2) (100 ng/paw, in 100 microL, intraplantar). Furthermore, local intraplantar pre-treatment (30 min before) with PTX (600 ng/paw, in 100 microL) reduced hypernociception induced by DbcAMP, a stable analogue of cAMP (100 microg/paw, in 100 microL, intraplantar), which indicates that PTX may have an effect other than just G(i)/G(0) inhibition. PTX-induced analgesia was blocked by selective inhibitors of nitric oxide synthase (L-NMMA), guanylyl cyclase (ODQ), protein kinase G (KT5823) and ATP-sensitive K(+) channel (Kir6) blockers (glybenclamide and tolbutamide). In addition, PTX was shown to induce nitric oxide (NO) production in cultured neurons of the dorsal root ganglia. In conclusion, this study shows a peripheral antinociceptive effect of pertussis toxin, resulting from the activation of the arginine/NO/cGMP/PKG/ATP-sensitive K(+) channel pathway.
No preview · Article · Sep 2006 · European Journal of Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Deficiency of adrenal hormones promotes exacerbated neutrophil influx into inflammatory sites. We investigated the effect of adrenal deficiency on neutrophil mobilization comparing adrenalectomized (ADX) male Wistar rats to sham-operated (SO) or non-manipulated (N) animals, as controls. Seven days after surgeries, the number of neutrophils in peripheral blood was increased in ADX rats, by accelerating neutrophil maturation steps in the bone marrow. The investigation of adhesive properties on neutrophil membranes indicated reduced and increased expressions of L-selectin on cells present in the bone marrow and circulating blood, respectively. Similar levels of L-selectin mRNA in both cells from ADX or non-manipulated rats suggest that these effects do not depend on gene expression. Even though no differences in the expression of beta(2) integrin by neutrophils were detected, modulation on subsequent PMN activation may occur by adrenal hormones, since circulating neutrophils from ADX exhibit lower in vitro adherence to the endothelium. We conclude that adrenal hormones control the adhesive interactions of neutrophils with the bone marrow microenvironment and with the vascular endothelium chiefly by modulation of L-selectin on PMN membrane in a mechanism independent of L-selectin gene expression.
No preview · Article · May 2006 · Molecular and Cellular Endocrinology
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to investigate the effect of melatonin on the inflammatory increase in vascular permeability. Vascular permeability was stimulated by a nonspecific pro-inflammatory agent (carrageenan), by drugs that disrupt endothelial cells junction (histamine, serotonin or bradykinin) or drugs that promote neutrophil recruitment (leukotriene B4 or N-formyl-methionyl-leucyl-phenylalanine fMLP). Vascular permeability was measured by Evan's blue dye extravasation after simultaneous injection of melatonin and the pro-inflammatory drugs in rat dorsal skin. Melatonin only reduced the increase in vascular permeability induced by leukotriene B4, which activates both neutrophil and endothelial cells. The neutrophil expression of CD18 induced by leukotriene B4 or fMLP was not changed by melatonin. On the other hand, melatonin inhibited the leukotriene B4-induced endothelial cells hyperadhesiveness. Our findings suggest that vascular permeability reduction induced by local melatonin injection is mediated by a reduction of endothelial cells ability to interact with neutrophils.
No preview · Article · Apr 2006 · European Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: The hormone melatonin produced by the pineal gland during the daily dark phase regulates a variety of biological processes in mammals. The aim of this study was to determine the effect of melatonin and its precursor N-acetylserotonin on the microcirculation during acute inflammation. Arteriolar diameter, blood flow rate, leukocyte rolling and adhesion were measured in the rat microcirculation in situ by intravital microscopy. Melatonin alone or together with noradrenaline did not affect the arteriolar diameter or blood flow rate. Melatonin inhibited both leukocyte rolling and leukotriene B(4) induced adhesion while its precursor N-acetylserotonin inhibits only leukocyte adhesion. The rank order of potency of agonists and antagonist receptor selective ligands suggested that the activation of MT(2) and MT(3) melatonin binding sites receptors modulate leukocyte rolling and adhesion, respectively. The effect of melatonin and N-acetylserotonin herein described were observed with concentrations in the range of the nocturnal surge, providing the first evidence for a possible physiological role of these hormones in acute inflammation.
Full-text · Article · Dec 2001 · European Journal of Pharmacology