Influence of ethanol and morphine on pain perception evoked by deep tissue injury

O objetivo deste estudo foi avaliar o efeito do etanol e da morfina sobre as respostas comportamentais nociceptivas provocadas pelo teste da formalina na ATM de ratos (Teste da formalina na ATM). No experimento 1, os animais receberam uma solução de etanol 6,5 % ou água comum para beber durante 4 e 10 dias, antes da realização do teste da formalina na ATM. No grupo tratado por 4 dias, observou-se analgesia significativa ao teste da formalina, enquanto que no grupo tratado por 10 dias esse efeito não ocorreu, demonstrando o desenvolvimento de tolerância aos efeitos antinociceptivos do etanol. No experimento 2, os animais foram submetidos ao regime crônico de etanol (6,5% por 10 dias) e o grupo controle recebeu água comum para beber. Após esse período, foi administrado morfina (10 mg/kg i.p.) 30 minutos antes da realização do teste da formalina na ATM. A morfina teve o mesmo efeito analgésico nos 2 grupos, demonstrando que o tratamento com etanol não foi capaz de alterar a potência analgésica da morfina. Os resultados mostraram que o etanol é capaz de alterar as respostas nociceptivas relacionadas à dor proveniente de tecidos profundos, como a ATM, e a ausência de interação entre o etanol e a morfina indica que a analgesia induzida pelo etanol é mediada por mecanismos não-opióides.The aim of this study was to evaluate the effect of ethanol and morphine on nociceptive behavioral responses evoked by the injection of formalin into the temporomandibular joint region of rats (the TMJ formalin test). In experiment 1, animals were given an ethanol solution (6.5%) or tap water to drink for 4 and 10 days, before the procedure for TMJ pain. In the group treated for 4 days, significant analgesia was observed in the TMJ formalin test, whereas the group treated for 10 days did not show this effect, revealing the development of tolerance to ethanol antinociceptive effects. In experiment 2, animals were submitted to chronic regimen of ethanol (6.5% for 10 days) and the control group was given tap water to drink. After this period, morphine (10 mg/kg i.p.) was administrated 30 minutes before the TMJ formalin test. Morphine had the same analgesic effect in both groups, showing that the treatment with ethanol was not able to alter the analgesic potency of morphine. The results showed that ethanol can affect nociceptive behavioral responses related to pain from deep tissues, like the TMJ, and the absence of interaction between ethanol and morphine suggest that ethanol-induced analgesia was mediated by nonopiate mechanisms

Peripheral Mechanisms Underlying The Essential Role Of P2x7 Receptors In The Development Of Inflammatory Hyperalgesia.

Activation of P2X7 receptors by endogenous ATP contributes to the development of inflammatory hyperalgesia. Given the clinical importance of mechanical hyperalgesia in inflammatory states, we hypothesized that the activation of the P2X7 receptor by endogenous ATP contributes to carrageenan-induced mechanical hyperalgesia, and that this contribution is mediated by an indirect sensitization of the primary afferent nociceptors. Co-administration of the selective P2X7 receptor antagonist, A-438079, or the P2X7 receptor antagonist, oATP, with carrageenan blocked the mechanical hyperalgesia induced by carrageenan and significantly reduced the increased concentration of TNF-alpha, IL-6 and CINC-1, but not of IL-1beta induced by carrageenan in the subcutaneous tissue of the rat's hind paw. We concluded that the activation of P2X7 receptors by endogenous ATP is essential to the development of the mechanical hyperalgesia induced by carrageenan in the subcutaneous tissue. It is suggested that this essential role of P2X7 receptors in the development of carrageenan-induced mechanical hyperalgesia is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of TNF-alpha, IL-6 and CINC-1, but not of IL-1beta.64455-6

P2x3 And P2x2/3 Receptors Mediate Mechanical Hyperalgesia Induced By Bradykinin, But Not By Pro-inflammatory Cytokines, Pge₂ Or Dopamine.

Activation of peripheral P2X3 and P2X2/3 receptors by endogenous ATP is essential to the development of inflammatory hyperalgesia. We have previously demonstrated that this essential role of P2X3 and P2X2/3 receptors in the development of mechanical hyperalgesia induced by the inflammatory agent carrageenan is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of tumor necrosis factor alpha (TNF-α) and by a direct sensitization of the primary afferent nociceptors. Therefore, in this study we asked whether activation of P2X3 and P2X2/3 receptors contribute to the mechanical hyperalgesia induced by the inflammatory mediators involved in carrageenan-induced mechanical hyperalgesia, such as bradykinin, tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), chemokine-induced chemoattractant-1 (CINC-1), prostaglandin E₂ (PGE₂) and dopamine. Co-administration of the non-selective P2X3 receptor antagonist TNP-ATP or the selective P2X3 and P2X2/3 receptor antagonist A-317491 with bradykinin, but not with TNF-α, IL-1β, IL-6, CINC-1, PGE₂ or dopamine, prevented in a dose-dependent manner the mechanical hyperalgesia. We also verified whether the activation of P2X3 and P2X2/3 receptors by endogenous ATP contributes to bradykinin-induced mechanical hyperalgesia via neutrophil migration and/or cytokine release. Co-administration of TNP-ATP or A-317491 did not affect either neutrophil migration or the increased concentration of TNF-α, IL-1β, IL-6 and CINC-1 induced by bradykinin. These findings demonstrate that the activation of P2X3 and P2X2/3 receptors by endogenous ATP mediates bradykinin-induced mechanical hyperalgesia by a mechanism that does not depend on neutrophil migration or cytokines release.649177-8

Influence of ethanol and morphine on pain perception evoked by deep tissue injury A influência do etanol e da morfina sobre a percepção dolorosa provocada por injúria tecidual profunda

The aim of this study was to evaluate the effect of ethanol and morphine on nociceptive behavioral responses evoked by the injection of formalin into the temporomandibular joint region of rats (the TMJ formalin test). In experiment 1, animals were given an ethanol solution (6.5%) or tap water to drink for 4 and 10 days, before the procedure for TMJ pain. In the group treated for 4 days, significant analgesia was observed in the TMJ formalin test, whereas the group treated for 10 days did not show this effect, revealing the development of tolerance to ethanol antinociceptive effects. In experiment 2, animals were submitted to chronic regimen of ethanol (6.5% for 10 days) and the control group was given tap water to drink. After this period, morphine (10 mg/kg i.p.) was administrated 30 minutes before the TMJ formalin test. Morphine had the same analgesic effect in both groups, showing that the treatment with ethanol was not able to alter the analgesic potency of morphine. The results showed that ethanol can affect nociceptive behavioral responses related to pain from deep tissues, like the TMJ, and the absence of interaction between ethanol and morphine suggest that ethanol-induced analgesia was mediated by nonopiate mechanisms.<br>O objetivo deste estudo foi avaliar o efeito do etanol e da morfina sobre as respostas comportamentais nociceptivas provocadas pelo teste da formalina na ATM de ratos (Teste da formalina na ATM). No experimento 1, os animais receberam uma solução de etanol 6,5 % ou água comum para beber durante 4 e 10 dias, antes da realização do teste da formalina na ATM. No grupo tratado por 4 dias, observou-se analgesia significativa ao teste da formalina, enquanto que no grupo tratado por 10 dias esse efeito não ocorreu, demonstrando o desenvolvimento de tolerância aos efeitos antinociceptivos do etanol. No experimento 2, os animais foram submetidos ao regime crônico de etanol (6,5% por 10 dias) e o grupo controle recebeu água comum para beber. Após esse período, foi administrado morfina (10 mg/kg i.p.) 30 minutos antes da realização do teste da formalina na ATM. A morfina teve o mesmo efeito analgésico nos 2 grupos, demonstrando que o tratamento com etanol não foi capaz de alterar a potência analgésica da morfina. Os resultados mostraram que o etanol é capaz de alterar as respostas nociceptivas relacionadas à dor proveniente de tecidos profundos, como a ATM, e a ausência de interação entre o etanol e a morfina indica que a analgesia induzida pelo etanol é mediada por mecanismos não-opióides

Effects of ethanol on deep pain evoked by formalin injected in TMJ of rat

It has been reported that ethanol can alter nociceptive sensitivity from superficial tissues, such as skin and subcutaneous region. However, the influence of ethanol on deep pain conditions is not understood. The aim of this study was to demonstrate the acute, chronic and ethanol withdrawal effects on nociceptive behavioral responses induced by the injection of formalin into the temporomandibular joint (TMJ) region of rats. In experiment 1, rats were injected with ethanol (2,5 g/Kg, i.p.) or an equal volume of saline 15 min before the administration of formalin (1.5%) into the TMJ. Rats pretreated with ethanol showed a decrease in nociceptive behavioral responses. In experiment 2, rats were given an ethanol solution (6.5%) or tap water to drink for 4 and 10 days. On day 4, the animals (ethanol group) showed amounts of analgesia when submitted to the TMJ formalin test. Tolerance to the antinociceptive effects was observed on day 10. Behavioral hyperalgesia was verified 12 hr after withdrawal in another group that drank ethanol for 10 days. These results show that ethanol can affect the nociceptive responses related to deep pain evoked by the TMJ formalin test.It has been reported that ethanol can alter nociceptive sensitivity from superficial tissues, such as skin and subcutaneous region. However, the influence of ethanol on deep pain conditions is not understood. The aim of this study was to demonstrate the acute, chronic and ethanol withdrawal effects on nociceptive behavioral responses induced by the injection of formalin into the temporomandibular joint (TMJ) region of rats. In experiment 1, rats were injected with ethanol (2,5 g/Kg, IP) or an equal volume of saline 15 min before the administration of formalin (1,5%) into the TMJ. Rats pretreated with ethanol showed a decrease in nociceptive behavioral responses. In experiment 2, rats were given an ethanol solution (6,5%) or tap water to drink for 4 and 10 days. On day 4, the animals (ethanol group) showed amounts of analgesia when submitted to the TMJ formalin test. Tolerance to the antinociceptive effects was observed on day 10. Behavioral hyperalgesia was verified 12 hr after withdrawal in another group that drank ethanol for 10 days. These results show that ethanol can affect the nociceptive responses related to deep pain evoked by the TMJ formalin test73263351336

Evidence for the involvement of endogenous ATP and P2x receptors in TMJ pain

Evidence is accumulating which supports a role for ATP in the initiation of pain by acting on P2X receptors expressed on nociceptive afferent nerve terminals. To investigate whether these receptors play a role in temporomandibular (TMJ) pain, we studied the presence of functional P2X receptors in rat TMJ by examining the nociceptive behavioral response to the application of the selective P2X receptor agonist alpha,beta-methylene ATP (alpha,beta-meATP) into the TMJ region of rat. The involvement of endogenous ATP in the development of TMJ inflammatory hyperalgesia was also determined by evaluating the effect of the general P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on carrageenan-induced TMJ inflammatory hyperalgesia. Application of alpha,beta-meATP into the TMJ region of rats produced significant nociceptive responses that were significantly reduced by the co-application of lidocaine N-ethyl bromide quaternary salt, QX-314, (2%) or of the P2 receptor antagonist PPADS. Co-application of PPADS with carrageenan into the TMJ significantly reduced inflammatory hyperalgesia. The results indicate that functional P2X receptors are present in the TMJ and suggest that endogenous ATP may play a role in TMJ inflammatory pain mechanisms possibly by acting primarily in these receptors.Evidence is accumulating which supports a role for ATP in the initiation of pain by acting on P2X receptors expressed on nociceptive afferent nerve terminals. To investigate whether these receptors play a role in temporomandibular (TMJ) pain, we studied the presence of functional P2X receptors in rat TMJ by examining the nociceptive behavioral response to the application of the selective P2X receptor agonist α,β‐methylene ATP (α,β‐meATP) into the TMJ region of rat. The involvement of endogenous ATP in the development of TMJ inflammatory hyperalgesia was also determined by evaluating the effect of the general P2 receptor antagonist pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS) on carrageenan‐induced TMJ inflammatory hyperalgesia. Application of α,β‐meATP into the TMJ region of rats produced significant nociceptive responses that were significantly reduced by the co‐application of lidocaine N‐ethyl bromide quaternary salt, QX‐314, (2%) or of the P2 receptor antagonist PPADS. Co‐application of PPADS with carrageenan into the TMJ significantly reduced inflammatory hyperalgesia. The results indicate that functional P2X receptors are present in the TMJ and suggest that endogenous ATP may play a role in TMJ inflammatory pain mechanisms possibly by acting primarily in these receptors91879

Peripheral sympathetic component of the temporomandibular joint inflammatory pain in rats

The aim of this study was to further validate our carrageenan-induced temporomandibular joint (TMJ) inflammatory hyperalgesia model in rats by showing that administration of indomethacin before the initiation of inflammation would diminish the TMJ hyperalgesia. Using this model, we investigated whether norepinephrine and local beta-adrenoceptors contribute to the development of inflammatory TMJ hyperalgesia. Carrageenan-induced TMJ hyperalgesia was assessed by measuring the behavioral nociceptive responses, such as rubbing the orofacial region and flinching the head, induced by the injection of a low dose of 5-hydroxytryptamine into the TMJ sensitized 1 h before by a TMJ injection of carrageenan. Blockade of prostaglandin synthesis by indomethacin prior to initiation of inflammation by carrageenan significantly attenuated the TMJ hyperalgesia. The guanethidine depletion of norepinephrine or the blockade of beta(2)but not the blockade of the beta(1)-adrenoceptor by the selective adrenoceptor antagonists ICI 118.55 and atenolol, respectively, significantly reduced carrageenan-induced TMJ hyperalgesia. In the present study, we further validated our carrageenan-induced TMJ hyperalgesia model to study the mechanisms involved in inflammatory TMJ hyperalgesia and to test the analgesic effect of different types of peripheral analgesics. We also demonstrated that norepinephrine released at the site of injury contributes to the development of the inflammatory TMJ hyperalgesia by the activation of beta(2)-adrenoceptors. The findings that local sympathomimetic amines contribute to the inflammatory TMJ hyperalgesia by activating beta(2)-adrenoceptors may be relevant to clinical TMJ inflammatory pain states less sensitive to nonsteroidal anti-inflammatory drugs.The aim of this study was to further validate our carrageenan-induced temporomandibular joint (TMJ) inflammatory hyperalgesia model in rats by showing that administration of indomethacin before the initiation of inflammation would diminish the TMJ hyperalgesia. Using this model, we investigated whether norepinephrine and local β-adrenoceptorscontribute to the development of inflammatory TMJ hyperalgesia. Carrageenan-induced TMJ hyperalgesia was assessed by measuring the behavioral nociceptive responses, such as rubbing the orofacial region and flinching the head, induced by the injection of a low dose of 5-hydroxytryptamine into the TMJ sensitized 1 h before by a TMJ injection of carrageenan. Blockade of prostaglandin synthesis by indomethacin prior to initiation of inflammation by carrageenan significantly attenuated the TMJ hyperalgesia. The guanethidine depletion of norepinephrine or the blockade of β2but not the blockade of the β1-adrenoceptor by the selective adrenoceptor antagonists ICI 118.55 and atenolol, respectively, significantly reduced carrageenan-induced TMJ hyperalgesia. In the present study, we further validated our carrageenan-induced TMJ hyperalgesia model to study the mechanisms involved in inflammatory TMJ hyperalgesia and to test the analgesic effect of different types of peripheral analgesics. We also demonstrated that norepinephrine released at the site of injury contributes to the development of the inflammatory TMJ hyperalgesia by the activation of β2-adrenoceptors71292993

Involvement of peripheral TRPV1 in TMJ hyperalgesia induced by ethanol withdrawal

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEthanol withdrawal increases nociception after the injection of formalin into the rat's temporomandibular joint (TMJ). Little is known about the neurological basis for hyperalgesia induced by ethanol withdrawal, but it has been reported that ethanol can potentiate the response of transient receptor potential vanilloid receptor-1 (TRPV1) in superficial tissues. The present study was designed to test the hypothesis that peripheral TRPV1 could be involved on nociceptive behavioral responses induced by the injection of formalin into the TMJ region of rats exposed to chronic ethanol administration and ethanol withdrawal. Behavioral hyperalgesia was verified 12 h after ethanol withdrawal in rats that drank an ethanol solution (6.5%) for 10 days. In another group submitted to the same ethanol regimen, the selective vanilloid receptor antagonist capsazepine (300, 600 or 1200 microg/25 microl) or an equal volume of vehicle were injected into the TMJ regions 30 min before the TMJ formalin test. The local injections of capsazepine reduced the increased nociceptive responses induced by ethanol withdrawal. The effect of capsazepine on rats that did not drink ethanol was not significant. These results indicate that the peripheral TRPV1 can contribute to the hyperalgesia induced by ethanol withdrawal on deep pain conditions.Ethanol withdrawal increases nociception after the injection of formalin into the rat's temporomandibular joint (TMJ). Little is known about the neurological basis for hyperalgesia induced by ethanol withdrawal, but it has been reported that ethanol can potentiate the response of transient receptor potential vanilloid receptor-1 (TRPV1) in superficial tissues. The present study was designed to test the hypothesis that peripheral TRPV1 could be involved on nociceptive behavioral responses induced by the injection of formalin into the TMJ region of rats exposed to chronic ethanol administration and ethanol withdrawal. Behavioral hyperalgesia was verified 12 h after ethanol withdrawal in rats that drank an ethanol solution (6.5%) for 10 days. In another group submitted to the same ethanol regimen, the selective vanilloid receptor antagonist capsazepine (300, 600 or 1200 μg/25 μl) or an equal volume of vehicle were injected into the TMJ regions 30 min before the TMJ formalin test. The local injections of capsazepine reduced the increased nociceptive responses induced by ethanol withdrawal. The effect of capsazepine on rats that did not drink ethanol was not significant. These results indicate that the peripheral TRPV1 can contribute to the hyperalgesia induced by ethanol withdrawal on deep pain conditions8123-2416221626CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOsem informaçã

Involvement of temporomandibular joint P2x3 and P2x2/3 receptors in carrageenan-induced inflammatory hyperalgesia in rats

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOThe aim of this study was to investigate the role of P2X3, P2X2/3 and P2X7 receptors in the development of TMJ hyperalgesia induced by carrageenan. We also investigated the expression of mRNA of P2X7 receptors in the trigeminal ganglia and the existence of functional P2X7 receptors in the rat's TMJ. The P2X1, P2X3 and P2X2/3 receptor antagonist TNP-ATP, but not the selective P2X7 receptor antagonist A-438079, significantly reduced carrageenan-induced TMJ inflammatory hyperalgesia. The qPCR assay showed that mRNA of P2X7 receptors are expressed in the trigeminal ganglia but this expression is not increased by the inflammation induced by carrageenan in the TMJ region. The P2X7 receptor agonist BzATP induced TMJ inflammatory hyperalgesia that was significantly reduced by pretreatment with dexamethasone. These results indicate that P2X3 and P2X2/3 but not P2X7 receptors are involved in carrageenan-induced TMJ inflammatory hyperalgesia. However, functional P2X7 receptors are expressed in the TMJ region. The activation of these receptors by BzATP sensitizes the primary afferent nociceptors in the TMJ through the previous release of inflammatory mediators. The findings of this study point out P2X3 and P2X2/3 receptors, but not P2X7 receptors, as potential targets for the development of new analgesic drugs to control TMJ inflammatory pain.The aim of this study was to investigate the role of P2X3, P2X2/3 and P2X7 receptors in the development of TMJ hyperalgesia induced by carrageenan. We also investigated the expression of mRNA of P2X7 receptors in the trigeminal ganglia and the existence of functional P2X7 receptors in the rat's TMJ. The P2X1, P2X3 and P2X2/3 receptor antagonistTNP-ATP, but not the selective P2X7 receptor antagonist A-438079, significantly reduced carrageenan-induced TMJ inflammatory hyperalgesia. The qPCR assay showed that mRNA of P2X7 receptors are expressed in the trigeminal ganglia but this expression is not increased by the inflammation induced by carrageenan in the TMJ region. The P2X7 receptor agonist BzATP induced TMJ inflammatory hyperalgesia that was significantly reduced by pretreatment with dexamethasone. These results indicate that P2X3 and P2X2/3 but not P2X7 receptors are involved in carrageenan-induced TMJ inflammatory hyperalgesia. However, functional P2X7 receptors are expressed in the TMJ region. The activation of these receptors by BzATP sensitizes the primary afferent nociceptors in the TMJ through the previous release of inflammatory mediators. The findings of this study point out P2X3 and P2X2/3 receptors, but not P2X7 receptors, as potential targets for the development of new analgesic drugs to control TMJ inflammatory pain6451-37985FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçã

The effects of restraint stress on nociceptive responses induced by formalin injected in rat's TMJ

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOIt has been reported that stress can alter nociception from superficial tissues, such as skin and subcutaneous region. However, the influence of stress on an experimental deep nociception model is not understood. In this study, the temporomandibular joint (TMJ) formalin test was used to evaluate the effects of acute and chronic restraint stress on nociceptive responses in rats. Animals were initially submitted to one session of acute restraint stress (1 h) or exposed to chronic stress (40 days-1 h/day). Then, animals were killed immediately to collect blood for hormonal determinations by radioimmunoassay, or submitted to the TMJ formalin test to evaluate nociception. Rats submitted to acute restraint presented a performance similar to unstressed controls in the TMJ formalin test, whereas chronically stressed rats showed an increase in nociceptive responses. After 40 days of restraint, morphine was injected i.p. (1, 5 mg/kg or saline). The stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. These findings suggest that repeated stress can produce hyperalgesia, which is, at least in part, due to alterations in the activity of opioid systems. This model may help elucidate the underlying neural mechanisms that mediate the effects of repeated stress on orofacial pain.It has been reported that stress can alter nociception from superficial tissues, such as skin and subcutaneous region. However, the influence of stress on an experimental deep nociception model is not understood. In this study, the temporomandibular joint (TMJ) formalin test was used to evaluate the effects of acute and chronic restraint stress on nociceptive responses in rats. Animals were initially submitted to one session of acute restraint stress (1 h) or exposed to chronic stress (40 days—1 h/day). Then, animals were killed immediately to collect blood for hormonal determinations by radioimmunoassay, or submitted to the TMJ formalin test to evaluate nociception. Rats submitted to acute restraint presented a performance similar to unstressed controls in the TMJ formalin test, whereas chronically stressed rats showed an increase in nociceptive responses. After 40 days of restraint, morphine was injected i.p. (1, 5 mg/kg or saline). The stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. These findings suggest that repeated stress can produce hyperalgesia, which is, at least in part, due to alterations in the activity of opioid systems. This model may help elucidate the underlying neural mechanisms that mediate the effects of repeated stress on orofacial pain822338344CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAUL