RESUMO
Glial activation plays a pivotal role in morphine tolerance. This study investigated effects of Mas-related gene (Mrg) C receptor on morphine-induced activation of microglia and astrocytes in the spinal cord and its underlying mechanisms. Intrathecal administration of morphine (20 µg, daily) for 6 days induced a great decline in morphine antinociception and increased expression of glial fibrillary acidic protein and OX-42 in the spinal dorsal horn. These changes were greatly attenuated by the intermittent coinjection of bovine adrenal medulla 8-22 (BAM8-22, 1 nmol), a specific agonist of MrgC receptor. These modulatory effects were accompanied by the reduction of P2X4 and interleukin-1ß expressions in the spinal dorsal horn. Chronic morphine increased the expression of fractalkine in medium- and small-sized neurons of dorsal root ganglia (DRG). Treatment with BAM8-22 inhibited these changes as well as an increase in Toll-like receptor 4 (TLR4) protein in DRG. Chronic treatment of DRG explant cultures with morphine (3.3 µM, 5 days) increased the levels of fractalkine mRNA. Application of BAM8-22 (10 nM) for 60 minutes completely blocked the increase of fractalkine mRNA induced by morphine. Our findings indicate that the inhibition of morphine tolerance by MrgC receptor was associated with the modulation of astrocytes and microglia in the spinal dorsal horn and fractalkine and TLR4 expressions in DRG. As MrgC receptor is exclusively located in DRG, intermittent combination of MrgC receptor agonist could be a promising adjunct with limited side effects for chronic use of opiates.
Assuntos
Analgésicos Opioides/administração & dosagem , Gânglios Espinais/metabolismo , Morfina/administração & dosagem , Neuroglia/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Animais , Bovinos , Gânglios Espinais/efeitos dos fármacos , Injeções Espinhais , Masculino , Neuroglia/efeitos dos fármacos , Técnicas de Cultura de Órgãos , Fragmentos de Peptídeos/administração & dosagem , Células do Corno Posterior/efeitos dos fármacos , Células do Corno Posterior/metabolismo , Ratos , Ratos Sprague-Dawley , Receptores Acoplados a Proteínas G/agonistasRESUMO
The pain peptide adrenomedullin (AM) plays a pivotal role in pathological pain. The present study was designed to investigate the effect of blockade of AM receptor on bone cancer pain (BCP) and its mechanism. BCP was developed by inoculation of Walker 256 mammary gland carcinoma cells in the tibia medullary cavity of Sprague Dawley rats. The selective AM receptor antagonist AM22-52 was administered intrathecally on 15 d after the inoculation. Quantitative real-time PCR was used to detect mRNA level of CC chemokine ligand 2 (CCL2) in dorsal root ganglion (DRG). Double immunofluorescence staining was used to analyze the localizations of CCL2 and AM in DRG of normal rats. The results showed that, from 6 to15 d after the inoculation, the animals showed significant reduction in the mechanical pain threshold in the ipsilateral hindpaw, companied by the decline in bone density of tibia bone. The expression of CCL2 mRNA in DRG of BCP rats was increased by 3 folds (P < 0.001 vs saline group). Intrathecal administration of AM22-52 abolished bone cancer-induced mechanical allodynia and increase of CCL2 mRNA level (P < 0.001). In normal rats, CCL2 was co-localized with AM in DRG neurons. These results suggest that AM may play a role in the pathogenesis of BCP. The increased AM bioactivity up-regulates CCL2 expression in DRG, which may contribute to the induction of pain hypersensitivity in bone cancer.
Assuntos
Adrenomedulina/farmacologia , Neoplasias Ósseas/tratamento farmacológico , Quimiocina CCL2/metabolismo , Hiperalgesia/tratamento farmacológico , Dor/tratamento farmacológico , Fragmentos de Peptídeos/farmacologia , Adrenomedulina/administração & dosagem , Animais , Gânglios Espinais/fisiopatologia , Limiar da Dor , Fragmentos de Peptídeos/administração & dosagem , Ratos , Ratos Sprague-Dawley , Reação em Cadeia da Polimerase em Tempo Real , Receptores de Adrenomedulina/antagonistas & inibidoresRESUMO
The rodent Mas-related gene (Mrg) receptor subtype C has been demonstrated to inhibit pathological pain. This study investigated the mechanisms underlying the reversal of pain hypersensitivity by the selective MrgC receptor agonist bovine adrenal medulla 8-22 (BAM8-22) in a rat model of L5 spinal nerve ligation (SNL). Intrathecal (i.t.) administration of BAM8-22 (0.1-10nmol) attenuated mechanical allodynia in a dose-dependent manner on day 10 after SNL. The antiallodynia effect of BAM8-22 was abolished by MrgC receptor antibody, but not by naloxone. I.t. BAM8-22 (10nmol) inhibited SNL-induced upregulation of neuronal nitric oxide synthesis (nNOS) and phosphorylation of cyclic AMP response element-binding protein (p-CREB) in the spinal dorsal horn. The BAM8-22 treatment reversed the SNL-induced astrocyte activation, increase of interleukin-1ß (IL-1ß) expression and phosphorylation of extracellular signal-regulated kinase (p-ERK) in the spinal cord. BAM8-22 also reversed the upregulation of fractalkine and IL-1ß in small- and medium-sized dorsal root ganglion (DRG) neurons. Furthermore, the BAM8-22 exposure suppressed the lipopolysaccharide (LPS)-induced increase of nNOS and IL-1ß in the DRG explant cultures and the BAM8-22-induced suppression disappeared in the presence of MrgC receptor antibody. The present study provides evidence that activation of MrgC receptors inhibits nerve injury-induced increase of pronociceptive molecules in DRG neurons, suppressing astrocyte activation, the upregulation of excitatory mediators and phosphorylation of transcription factors in the spinal dorsal horn. As MrgC receptors are unequally expressed in the dorsal root and trigeminal ganglia, this study suggests that targeting MrgC receptors could be a new therapy for neuropathic pain with limited unwanted effects.
Assuntos
Gânglios Espinais/metabolismo , Hiperalgesia/metabolismo , Neuralgia/fisiopatologia , Receptores Acoplados a Proteínas G/metabolismo , Nervos Espinhais/lesões , Animais , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Modelos Animais de Doenças , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Masculino , Neuralgia/metabolismo , Neurônios/metabolismo , Ratos Sprague-DawleyRESUMO
This study was designed to investigate the contribution of prostaglandins to the maintenance of inflammatory pain. Inflammation was induced by intraplantar (i.pl.) injection of carrageenan in right hindpaw in rats. Indomethacin (non-selective COX inhibitor) was administered i.pl. 1 h after the carrageenan injection, and paw withdrawal latency (PWL) responding to noxious heat was measured. ß-endorphin (ß-END) and µ-opioid receptor (MOR) expressed in the inflamed site were examined by using immunocytochemistry, ELISA and RT-PCR techniques. The results showed that indomethacin dose-dependently increased PWL to the levels that were above the baseline on the day 2 and 3, referred to as hypoalgesia. The hypoalgesia was abolished by a local injection of the non-selective opioid receptor inhibitor naloxone methiodide. The number of ß-END-positive cells, the content of ß-END and the expression of MOR mRNA in the inflammatory site of inflammation model rats were all significantly increased by indomethacin. These results reveal a novel mechanism of prostaglandins for the inhibition of inflammation-induced endogenous opioid activity. This study provides further evidence that inhibition of prostaglandins in inflamed site could be a promising therapy for inflammatory pain.
Assuntos
Inflamação , Analgésicos Opioides , Animais , Carragenina , Indometacina , Naloxona , Dor , Prostaglandinas , Ratos , Receptores Opioides , beta-EndorfinaRESUMO
Mas oncogene-related G protein-coupled receptor C (MrgC) is unequally expressed in sensory ganglia and has been shown to modulate pathologic pain. This study investigated the mechanism underlying the effect of MrgC receptors on inflammatory pain. Intrathecal administration of the selective MrgC receptor agonist bovine adrenal medulla 8-22 (BAM8-22) (30 nmol) inhibited complete Freund's adjuvant-evoked hyperalgesia. This was associated with the inhibition of protein kinase C-γ and phosphorylated extracellular signal-regulated protein kinase in the spinal cord and/or dorsal root ganglia (DRG). The complete Freund's adjuvant injection in the hindpaw induced an increase in Gq, but not Gi and Gs, protein in the spinal dorsal horn. This increase was inhibited by the intrathecal administration of BAM8-22. The exposure of DRG cultures to bradykinin (10 µM) and prostaglandin E2 (1 µM) increased the expression of calcitonin gene-related peptide (CGRP) and neuronal nitric oxide synthase in small- and medium-sized neurons as well as the levels of CGRP, aspartate, and glutamate in the cultured medium. The bradykinin/prostaglandin E2-induced alterations were absent in the presence of BAM8-22 (10 nM). These results suggest that the activation of MrgC receptors can modulate the increase in the expression of CGRP and neuronal nitric oxide synthase as well as the release of CGRP and excitatory amino acids in DRG associated with inflammatory pain. This modulation results in the inhibition of pain hypersensitivity by suppressing the expression of Gq protein and protein kinase C-γ and extracellular signal-regulated protein kinase signaling pathways in the spinal cord and/or DRG. The present study suggests that MrgC receptors may be a novel target for relieving inflammatory pain.
Assuntos
Gânglios Espinais/metabolismo , Inflamação/metabolismo , Dor/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Corno Dorsal da Medula Espinal/metabolismo , Animais , Bradicinina/farmacologia , Dinoprostona/farmacologia , Adjuvante de Freund/farmacologia , Gânglios Espinais/efeitos dos fármacos , Hiperalgesia/tratamento farmacológico , Hiperalgesia/metabolismo , Inflamação/tratamento farmacológico , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Masculino , Dor/tratamento farmacológico , Fragmentos de Peptídeos/farmacologia , Proteína Quinase C/metabolismo , Ratos , Ratos Sprague-Dawley , Corno Dorsal da Medula Espinal/efeitos dos fármacosRESUMO
The increase of pronociceptive mediators in the dorsal root ganglia (DRG) and spinal dorsal horn is an important mechanism in the pathogenesis of inflammatory pain and opioid tolerance. Adrenomedullin (AM) belongs to calcitonin gene-related peptide (CGRP) family and has been recently demonstrated to be a pain-related peptide. It has also been shown that the expression and release of AM are increased in the DRG and spinal dorsal horn during inflammation and repeated use of morphine. Intrathecal administration of the selective AM receptor antagonist AM22-52 abolishes inflammatory pain and morphine tolerance, suggesting that enhanced AM receptor signaling in the DRG and spinal dorsal horn contributes to the induction of inflammatory pain and morphine tolerance. The present review highlights the recent developments regarding the involvement of AM in these two disorders. The neurological mechanisms of AM's actions are also discussed.
Assuntos
Adrenomedulina/farmacologia , Tolerância a Medicamentos , Inflamação/tratamento farmacológico , Morfina/farmacologia , Dor/tratamento farmacológico , Fragmentos de Peptídeos/farmacologia , Animais , Peptídeo Relacionado com Gene de Calcitonina , Gânglios Espinais/efeitos dos fármacos , Inflamação/metabolismo , Dor/metabolismo , Ratos , Ratos Sprague-Dawley , Receptores de Adrenomedulina/metabolismoRESUMO
5-hydroxytryptamine (5-HT) released in inflammatory tissues plays a pivotal role in pain hypersensitivity. However, it is not clear whether 5-HT2A receptors in the inflamed tissues mediate this effect. The present study investigated the contribution of 5-HT2A receptors in the periphery to chronic inflammatory pain. Complete Freund's adjuvant (CFA) was injected subcutaneously in the hindpaw of rats. The selective 5-HT2A receptor antagonist ketanserin was given in the inflamed site. Paw withdrawal latency responding to heat or mechanical stimuli was measured. Expression of neuropeptide Y (NPY) in the spinal dorsal horn and dorsal root ganglia (DRG) was assayed using immunohistochemistry technique. The results showed that ketanserin administered in the inflamed site inhibited thermal hyperalgesia in a dose-dependent manner (20, 40 and 80 µg) induced by the intraplantar injection of CFA. Ketanserin given once per day at a dose of 80 µg abolished heat hyperalgesia and also attenuated mechanical allodynia on the third day. CFA injection increased the expression of NPY in superficial laminae of the spinal cord, but not in the DRG. The local treatment of ketanserin completely inhibited CFA-induced increase in NPY expression in superficial laminae of the spinal cord. These results indicated that activation of 5-HT2A receptors in the inflamed tissues was involved in the pathogenesis of inflammatory pain and the blockade of 5-HT2A receptors in the periphery could relieve pain hypersensitivity and normalize the cellular disorder in the spinal dorsal horn associated with pathological pain. The present study suggests that the peripheral 5-HT2A receptors can be a promising target for pharmaceutical therapy to treat chronic inflammatory pain without central nervous system side effects.
Assuntos
Hiperalgesia/tratamento farmacológico , Ketanserina/farmacologia , Neuropeptídeo Y/metabolismo , Receptor 5-HT2A de Serotonina/metabolismo , Antagonistas do Receptor 5-HT2 de Serotonina/farmacologia , Corno Dorsal da Medula Espinal/metabolismo , Animais , Adjuvante de Freund/efeitos adversos , Gânglios Espinais/metabolismo , Temperatura Alta , Hiperalgesia/induzido quimicamente , Inflamação/tratamento farmacológico , Dor/tratamento farmacológico , Medição da Dor , Ratos , SerotoninaRESUMO
This study was aimed to investigate the mechanisms of the modulation effect of activation of spinal Mas-related gene C (MrgC) receptors on hyperalgesia induced by intraplantar (i.pl.) injection of (Tyr6)-γ2-MSH-6-12 (MSH) or complete Freund's adjuvant (CFA). Paw withdrawal latency test and immunohistochemistry were used to observe the effect of intrathecal (i.t.) administration of MSH or BAM8-22, two selective agonists of MrgC receptor, in hyperalgesia in rats. The results showed that i.t. administration of MSH inhibited acute hyperalgesic response induced by i.pl. application of MSH, while did not change thermal nociceptive threshold in naïve rats. The i.t. administration of MSH also attenuated CFA-induced inflammatory hyperalgesia. However, i.t. administration of the µ-opioid receptor (MOR) antagonist CTAP blocked the induction of delayed anti-hyperalgesia by MSH. The i.t. injection of BAM8-22 at a dose of 30 nmol evidently reduced the number of CFA-evoked nitric oxide synthase (NOS)-positive neurons and the expression of calcitonin gene-related peptide (CGRP)-immunoreactivity positive nerve fibers at L3-L5 segments of the spinal cord. These results suggest that the activation of MrgC receptor in CFA-induced inflammation reduces inflammatory hyperalgesia through inactivation of NOS neurons and down-regulation of CGRP expressions, and generates delayed but long-lasting anti-nociception through the endogenous activation of MOR via indirect mechanisms. Agonists for MrgC receptors may, therefore, represent a new class of antihyperalgesics for treating inflammatory pain because of the highly specific expression of their targets.
Assuntos
Hiperalgesia/tratamento farmacológico , Receptores Acoplados a Proteínas G/metabolismo , Medula Espinal/metabolismo , Animais , Regulação para Baixo , Adjuvante de Freund/farmacologia , Inflamação/metabolismo , Injeções Espinhais , Medição da Dor , Fragmentos de Peptídeos/farmacologia , Ratos , gama-MSH/farmacologiaRESUMO
This study was aimed to investigate the mechanisms underlying the modulation effect of Mas-related gene (Mrg) C receptors (MrgC) on morphine tolerance. Saline, morphine (20 µg), morphine plus bovine adrenal medulla 8-22 (BAM8-22, 1 nmol) or (Tyr(6))-2-MSH-6-12 (MSH, 5 nmol) were administered intrathecally in rats for 6 days. Pain-related molecules in the spinal cord and dorsal root ganglion (DRG) were examined using Western blot, immunocytochemistry and RT-PCR techniques. The results showed that intrathecal administration of the selective MrgC receptor agonists (BAM8-22 or MSH) remarkably attenuated or abolished chronic morphine-evoked reduction in glutamate transporters (GLAST, GLT-1 and EAAC1) in the spinal cord and increase in neuronal nitric oxide synthase (nNOS) in the spinal cord as well as DRG. In addition, MrgC receptor-like immunoreactivity (IR) was detected in superficial laminae of the spinal cord. Chronic morphine induced significant increases in MrgC receptor-IR in the spinal cord and MrgC receptor mRNA levels in DRG. These results suggest that the modulation of pro-nociceptive mediators in the spinal cord and DRG underlies the inhibition of morphine tolerance by MrgC receptor activation.
Assuntos
Sistema X-AG de Transporte de Aminoácidos/metabolismo , Morfina/farmacologia , Óxido Nítrico Sintase Tipo I/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Medula Espinal/metabolismo , Animais , Tolerância a Medicamentos , Gânglios Espinais/metabolismo , Glutamatos , Dor , Medição da Dor , Fragmentos de Peptídeos/farmacologia , Ratos , Ratos Sprague-DawleyRESUMO
The calcitonin gene-related peptide (CGRP) family mainly includes CGRPα, CGRPß, adrenomedullin, calcitonin and amylin. The members of CGRP family and their receptors are widely distributed in the central and peripheral nervous systems. Studies show that members of CGRP family such as CGRP and adrenomedullin play important roles in the transmission of nociceptive information. At spinal level, CGRP promotes the transmission of nociceptive information, spinal morphine tolerance, migraine, inflammatory pain and neuropathic pain. At superspinal level, CGRP suppresses the transmission of nociceptive information. Adrenomedullin is a pain-related neuropeptide which has recently been demonstrated. It facilitates the transmission of nociceptive information and is involved in the development and maintenance of opioid tolerance. The involvement of amylin and calcitonin in pain is not clear yet.
Assuntos
Analgésicos Opioides/farmacologia , Peptídeo Relacionado com Gene de Calcitonina/fisiologia , Tolerância a Medicamentos , Nociceptividade , Dor/fisiopatologia , Adrenomedulina/fisiologia , Animais , Humanos , Polipeptídeo Amiloide das Ilhotas Pancreáticas/fisiologiaRESUMO
Adrenomedullin (AM) belongs to calcitonin gene-related peptide (CGRP) family and is a pronociceptive mediator. This study investigated whether AM plays a role in the development of tolerance to morphine-induced analgesia. Repetitive intrathecal injection of morphine increased the expression of AM-like immunoreactivity (AM-IR) in the spinal dorsal horn and dorsal root ganglion (DRG) neurons. Ganglion explant culture study showed that this upregulation of AM-IR was µ-opioid receptor dependent through the use of another agonist, fentanyl, and a selective antagonist, CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)). The coadministration of the selective AM receptor antagonist AM(22-52) markedly attenuated the development of morphine tolerance, associated thermal hyperalgesia, and increase in AM-IR. A likely autocrine mechanism is supported by the finding that AM-IR is colocalized with AM receptor components in DRG neurons. Furthermore, opiate-induced increase in AM content was blocked by protein kinase C (PKC) inhibitors, whereas a PKC activator increased AM synthesis and release. A treatment with AM(22-52) also inhibited increases in the expression of CGRP-IR in the spinal cord and DRGs as well as in culture ganglion explants, whereas exposure to CGRP failed to alter AM content. Together, these results reveal that a sustained opiate treatment induces an upregulation of AM through the activation of µ-opioid receptors and the PKC signaling pathway. This phenomenon contributes to the development of tolerance to the antinociceptive effects of opiates at least partially via the upregulation of CGRP. Targeting AM and its receptors should be considered as a novel approach to preserve the analgesic potency of opiates during their chronic use.
Assuntos
Adrenomedulina/biossíntese , Analgésicos Opioides/administração & dosagem , Tolerância a Medicamentos/fisiologia , Morfina/administração & dosagem , Proteína Quinase C/fisiologia , Regulação para Cima/fisiologia , Adrenomedulina/metabolismo , Adrenomedulina/fisiologia , Animais , Proteína Semelhante a Receptor de Calcitonina , Células Cultivadas , Modelos Animais de Doenças , Ativação Enzimática/fisiologia , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/metabolismo , Injeções Espinhais , Masculino , Entorpecentes/administração & dosagem , Técnicas de Cultura de Órgãos , Ratos , Ratos Sprague-Dawley , Receptores de Adrenomedulina , Receptores da Calcitonina/metabolismo , Receptores de Peptídeos/antagonistas & inibidores , Receptores de Peptídeos/metabolismo , Regulação para Cima/efeitos dos fármacosRESUMO
The present study investigated the effects of intrathecal (i.t.) application of bovine adrenal medulla 22 (BAM22), an endogenous opioid peptide potently activating opioid receptors and sensory neuron-specific receptor (SNSR), on a model of complete Freund's adjuvant (CFA)-induced inï¬ammatory pain. Unilateral, but not bilateral, inï¬ammatory pain was induced by intraplantar (i.pl.) injection of CFA in one side, as indicated by the shortened paw withdrawal latency and the increased edema of paw. Paw withdrawal latency test, paw edema determination and immunohistochemistry were used in CFA-induced inï¬ammatory pain model after i.t. administration of BAM22 or saline. It was found that administration of BAM22 dose-dependently attenuated CFA-induced hyperalgesia and edema, and resumed antinociceptive effects against thermal stimulation in behavioral test. In 10 nmol BAM22 group, paw withdrawal latency was resumed to 83.2% of normal, and edema increased only by 60% of normal at 48 h. The potency of BAM22 was 33.5% of maximal possible effect (MPE) at 24 h, and the antinociception persisted for at least 1 h. Furthermore, i.t. treatment of 10 nmol BAM22 evidently decreased the expressions of CFA-evoked neuronal nitric oxide synthase (nNOS)-positive cells and calcitonin gene-related peptide (CGRP)-immunoreactivity positive nerve fibers by 25.6% (P<0.01) and 25.2% (P<0.001) compared with saline group, respectively, at L3-L5 segments of the spinal cord. Small and medium CGRP-positive cells were 57.4% and 35.2% in dorsal root ganglion (DRG) in 10 nmol BAM22 group, respectively, which were remarkably lower than those in saline group (P<0.001). The present study suggests that BAM22 relieves CFA-induced thermal hyperalgesia in the early phase and resumes antinociceptive effects through down-regulation of nNOS and CGRP expressions in DRG and spinal cord, which is possibly mediated via SNSR.
Assuntos
Encefalina Metionina/análogos & derivados , Hiperalgesia/fisiopatologia , Inflamação/induzido quimicamente , Medição da Dor/efeitos dos fármacos , Precursores de Proteínas/farmacologia , Receptores Acoplados a Proteínas G/fisiologia , Animais , Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Encefalina Metionina/farmacologia , Adjuvante de Freund , Hiperalgesia/etiologia , Inflamação/complicações , Masculino , Óxido Nítrico Sintase Tipo I/metabolismo , Dor/etiologia , Dor/fisiopatologia , Ratos , Ratos Sprague-DawleyRESUMO
Protein kinase C (PKC) belongs to the AGC (cAMP-dependent protein kinase/PKG/PKC) protein kinase family which plays an important role in the morphine-induced desensitization of R-opioid receptors. This cellular process is believed to contribute to the development and maintenance of morphine tolerance. Therefore, the study of PKC signaling transduction on morphine tolerance has an important clinical significance. The present review summarizes the possible involvement of PKC in opioid tolerance.
Assuntos
Tolerância a Medicamentos , Morfina/farmacologia , Proteína Quinase C/fisiologia , Receptores Opioides mu/metabolismo , Analgésicos Opioides/farmacologia , Animais , HumanosRESUMO
Prevention of opiate tolerance is a critical issue in pain management. The present study was designed to characterize the pharmacological properties of sensory neuron-specific receptors (SNSR; also known as Mas-related gene receptors, or Mrg) for their modulation in the development of morphine tolerance and to investigate the underlying mechanism(s). Daily coadministration of the SNSR agonist BAM8-22 at a dose of 0.01 or 0.001, but not 1.0, nmol with morphine (intrathecally, or i.t., 20 microg/day) for 6 days significantly decreased the development of morphine tolerance. Coadministration of BAM8-22 (i.t., 1.0 nmol) on days 1, 3, and 5 completely blocked tolerance to morphine-induced analgesia. Intermittent coadministration of the structurally dissimilar SNSR agonist (Tyr(6))-2-MSH-6-12 (MSH; 5 nmol) also produced similar modulation. Chronic administration of morphine (20 microg, i.t.) increased expression of neuronal nitric oxide synthase (nNOS) and calcitonin gene-related peptide (CGRP) in superficial layers of the spinal cord and dorsal root ganglia. All these increases were abolished when BAM8-22 or MSH was intermittently coadministered. Furthermore, intermittent administration of BAM8-22 inhibited morphine-induced increase in protein kinase C gamma (PKC gamma) in both membrane and cytosol of spinal dorsal horn neurons. These results suggest that moderate activation of SNSR modulated morphine tolerance by inhibition of the PKC signaling pathway, leading to abolishment of enhancement of nNOS and CGRP. As SNSR are uniquely located ina subset of small-sized neurons in dorsal root and trigeminal ganglia, intermittent combination of SNSR agonist could be a promising adjunct for sustained use of opiates without central nervous system side effects.
Assuntos
Tolerância a Medicamentos/fisiologia , Morfina/efeitos adversos , Limiar da Dor/fisiologia , Precursores de Proteínas/metabolismo , Células Receptoras Sensoriais/metabolismo , Análise de Variância , Animais , Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Interações Medicamentosas , Gânglios Espinais/citologia , Regulação da Expressão Gênica/efeitos dos fármacos , Masculino , Hormônios Estimuladores de Melanócitos/farmacologia , Óxido Nítrico Sintase Tipo I/metabolismo , Medição da Dor/métodos , Limiar da Dor/efeitos dos fármacos , Peptídeos/farmacologia , Proteína Quinase C/metabolismo , Precursores de Proteínas/administração & dosagem , Ratos , Ratos Sprague-Dawley , Células Receptoras Sensoriais/efeitos dos fármacos , Medula Espinal/efeitos dos fármacos , Medula Espinal/metabolismoRESUMO
This study investigated the effect of adrenomedullin (AM) on mechanical pain sensitivity and its possible mechanisms. Intrathecal injection of AM receptor agonist AM1-50 (20⯵g) once per day briefly reduced mechanical pain threshold on days 1 and 2 but induced prolonged mechanical allodynia on day 3. However, AM1-50 did not change mechanical pain sensation when the AM receptor antagonist AM22-52 (20⯵g) was intrathecally co-administered. Daily administration of AM1-50 (20⯵g) for 3â¯days increased expression of phosphorylated extracellular signal-regulated protein kinase (pERK) and neuronal nitric oxide synthase (nNOS) in the spinal dorsal horn. The AM-induced increase in pERK and nNOS was inhibited by the co-administration of AM22-52. The chronic administration of AM1-50 also increased expression of microglial maker Iba1 and astrocytic marker GFAP (glial fibrillary acidic protein) in the spinal dorsal horn in an AM22-52-sensitive manner. Furthermore, the application of AM1-50 (10â¯nM, 3â¯h) to dorsal root ganglion (DRG) explant cultures induced an increase in the expression of transient receptor potential vanilloid 1 (TRPV1). The treatment with AM1-50 did not change TRPV1 expression in DRG in the presence of AM22-52 (2⯵M). These results suggest that the increased AM bioactivity induced mechanical allodynia and may contribute to the mechanical pain hypersensitivity under pathological conditions. The mechanisms may involve the activation of ERK signaling pathway and spinal glia as well as the recruitment of nNOS and TRPV1 in the spinal dorsal horn or DRG. The present study indicates that inhibition of the activation AM receptor might provide a fruitful strategy to relieving chronic pain.
Assuntos
Adrenomedulina/fisiologia , Gânglios Espinais/metabolismo , Hiperalgesia/fisiopatologia , Medula Espinal/metabolismo , Adrenomedulina/administração & dosagem , Adrenomedulina/agonistas , Adrenomedulina/antagonistas & inibidores , Adrenomedulina/farmacologia , Animais , Proteínas de Ligação ao Cálcio/biossíntese , Células Cultivadas , Interações Medicamentosas , MAP Quinases Reguladas por Sinal Extracelular/biossíntese , Proteína Glial Fibrilar Ácida/biossíntese , Hiperalgesia/metabolismo , Injeções Espinhais , Masculino , Proteínas dos Microfilamentos/biossíntese , Óxido Nítrico Sintase Tipo I/biossíntese , Medição da Dor/efeitos dos fármacos , Fragmentos de Peptídeos/administração & dosagem , Fragmentos de Peptídeos/farmacologia , Fosforilação/efeitos dos fármacos , Ratos , Corno Dorsal da Medula Espinal/metabolismo , Canais de Cátion TRPV/biossínteseRESUMO
The sensory neuron-specific receptor (SNSR) is exclusively distributed in dorsal root ganglion (DRG) cells. We have demonstrated that intrathecal (i.t.) administration of SNSR agonists inhibits formalin-evoked responses and the development of morphine tolerance [Chen, T., Cai, Q., Hong, Y., 2006. Intrathecal sensory neuron-specific receptor agonists bovine adrenal medulla 8-22 and (tyr(6))-gamma2-msh-6-12 inhibit formalin-evoked nociception and neuronal fos-like immunoreactivity in the spinal cord of the rat. Neuroscience 141, 965-975]. The present study was undertaken to examine the possible impact of the activation of SNSR on NMDA receptors. I.t. administration of NMDA (6.8 nmol) induced nociceptive behaviors, including scratching, biting and lifting, followed by thermal hypoalgesia and hyperalgesia. These responses were associated with the expression of Fos-like immunoreactivity (FLI) throughout the spinal dorsal horn with highest effect seen in laminae I-II. I.t. NMDA also induced an increase in nitric oxide synthase (NOS) activity in superficial layers of the dorsal horn, but not around the central canal, as revealed by NADPH diaphorase histochemistry. Pretreatment with the SNSR agonist bovine adrenal medulla 8-22 (3, 10 and 30 nmol) dose-dependently diminished NMDA-evoked nocifensive behaviors and hyperalgesia. This agonist also reduced NMDA-evoked expression of FLI and NADPH reactivity in the spinal dorsal horn. Taken together, these data suggest that the activation of SNSR induces spinal analgesia by suppressing NMDA receptor-mediated activation of spinal dorsal horn neurons and an increase in NOS activity.
Assuntos
Limiar da Dor/efeitos dos fármacos , Dor/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Células Receptoras Sensoriais/química , Animais , Comportamento Animal/efeitos dos fármacos , Relação Dose-Resposta a Droga , Vias de Administração de Medicamentos , Interações Medicamentosas , Agonistas de Aminoácidos Excitatórios/efeitos adversos , Formaldeído , Regulação da Expressão Gênica/efeitos dos fármacos , Masculino , N-Metilaspartato/efeitos adversos , NADP/metabolismo , Dor/induzido quimicamente , Medição da Dor/métodos , Ratos , Ratos Sprague-Dawley , Tempo de Reação/efeitos dos fármacos , Receptores Citoplasmáticos e Nucleares/metabolismo , Células Receptoras Sensoriais/fisiologiaRESUMO
The aim of the present study was to investigate the effects of chronic administration of morphine on the expression of an endogenous opioid peptide in the spinal dorsal horn. Bovine adrenal medulla 22-like immunoreactivity (BAM22-IR) was found in the superficial layers of the spinal cord. Intrathecal (i.t.) administration of morphine (20 microg) for 6 days, but not 2 days, significantly reduced the expression of BAM22-IR whereas i.t. administration of saline for 2 and 6 days did not alter the expression of BAM22-IR. The present study suggests that reduction of BAM22-IR in the spinal cord is involved in the development of morphine tolerance.
Assuntos
Analgésicos Opioides/administração & dosagem , Tolerância a Medicamentos , Encefalina Metionina/análogos & derivados , Morfina/administração & dosagem , Precursores de Proteínas/metabolismo , Medula Espinal/efeitos dos fármacos , Animais , Bovinos , Encefalina Metionina/metabolismo , Imuno-Histoquímica , Injeções Espinhais , Masculino , Células do Corno Posterior/efeitos dos fármacos , Células do Corno Posterior/metabolismo , Ratos , Ratos Sprague-Dawley , Medula Espinal/metabolismo , Fatores de TempoRESUMO
We observed that intrathecal (i.t.) bovine adrenal medulla 22, an endogenous opioid peptide, partially reverses morphine tolerance. However, its mechanism remains unclear. The present study determined the effects of BAM8-22, a derivative of BAM22 and selective sensory neuron-specific receptor (SNSR) agonist, on the development and maintenance of tolerance to spinal morphine. Intrathecal administration of BAM8-22 at various doses (0.1, 1 and 10nmol) did not alter withdraw latencies assessed in both paw withdraw and tail flick tests. Co-administration of BAM8-22 (0.1nmol) every other day, but not daily, with morphine remarkably attenuated the development of morphine tolerance. Pretreatment and co-treatment with BAM8-22 (0.1nmol) significantly reversed established morphine tolerance. Furthermore, intermittent administration of BAM8-22 with morphine consistently resumed morphine-induced antinociception. However, i.t. BAM8-22 did not alter morphine-induced hyperalgesia. These results suggested that SNSR may be able to modulate the sensitivity of opioid receptor serving as a most probable underlying mechanism for the effects of BAM8-22 on morphine tolerance. This study also demonstrated that intermittent combination of SNSR agonist BAM8-22 with morphine might be better regimen for long-term use of opioids to treat chronic pain.
Assuntos
Tolerância a Medicamentos/fisiologia , Encefalina Metionina/análogos & derivados , Morfina/farmacologia , Neurônios Aferentes/metabolismo , Limiar da Dor/fisiologia , Precursores de Proteínas/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Analgésicos/farmacologia , Animais , Relação Dose-Resposta a Droga , Encefalina Metionina/administração & dosagem , Encefalina Metionina/metabolismo , Injeções Espinhais , Masculino , Limiar da Dor/efeitos dos fármacos , Fragmentos de Peptídeos , Precursores de Proteínas/administração & dosagem , Ratos , Receptores Acoplados a Proteínas G/agonistasRESUMO
Opiate tolerance is a critical issue in pain management. Previous studies show that activation of Mas-related gene (Mrg) C receptor can modulate the development of morphine tolerance. This study was designed to investigate the underlying mechanism(s). Intrathecal (i.t.) administration of morphine (20µg) increased the expression of interleukin-1ß (IL-1ß) and matrix metalloproteinase-9 (MMP-9) in small- and medium-sized neurons in dorsal root ganglia (DRG). Co-administration of bovine adrenal medulla 8-22 (BAM8-22), a selective MrgC receptor agonist, via i.t. route inhibited the increase of IL-1ß and MMP-9 in the DRG. Exposure of DRG cultures to morphine (3.3µM) for 3 or 5 days, but not for 1 day, induced an increase in MMP-9 mRNA expression. The treatment with BAM8-22 (10nM) for 20, 40 or 60min abolished chronic (5 days) morphine-induced increase of MMP-9 mRNA in the cultured DRG. The treatment with BAM8-22 for 1h inhibited chronic morphine-induced increase of MMP-9 and IL-1ß mRNA in DRG but these effects were abolished by MrgC receptor antibody. The treatment with BAM8-22 for 24 and 72h respectively inhibited and enhanced morphine-induced expression of MMP-9 and IL-1ß mRNA in the cultured DRG. The BAM8-22-induced inhibition and enhancement were abolished by MrgC receptor antibody. The results suggest that the inhibition of IL-1ß and MMP-9 expressions in DRG underlain the modulation of morphine tolerance by the acute activation of MrgC receptors. The chronic activation of MrgC receptors can facilitate morphine-induced increase of MMP-9 and IL-1ß expressions in DRG.
Assuntos
Tolerância a Medicamentos , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/metabolismo , Interleucina-1beta/metabolismo , Metaloproteinase 9 da Matriz/metabolismo , Morfina/farmacologia , Receptores Acoplados a Proteínas G/metabolismo , Analgésicos/farmacologia , Animais , Regulação Enzimológica da Expressão Gênica/efeitos dos fármacos , Interleucina-1beta/genética , Masculino , Metaloproteinase 9 da Matriz/genética , Fragmentos de Peptídeos/farmacologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-DawleyRESUMO
Acute intrathecal (i.t.) bovine adrenal medulla 22 (BAM22, 10 nmol), an endogenous opioid peptide, induced equipotent thermal antinociception in naïve and morphine-tolerant rats while chronic BAM22 resulted in hyperalgesia and decrease in the effectiveness of antinociception. In rats made tolerant to morphine, prior administration of BAM22 (10 nmol, i.t.) significantly resumed antinociceptive response of morphine. The present study demonstrated that BAM22 was able to modulate maintenance of morphine tolerance.