Spontaneous firing and evoked responses of spinal nociceptive neurons are attenuated by blockade of P2X3 and P2X2/3 receptors in inflamed rats

P2X3 and P2X2/3 receptors are selectively expressed on primary afferent nociceptors and have been implicated in modulating nociception in different models of pathological pain, including inflammatory pain. In an effort to delineate further the role of P2X3 receptors (homomeric and heteromeric) in the modulation of nociceptive transmission after a chronic inflammation injury, A-317491, a potent and selective P2X3-P2X2/3 antagonist, was administered to CFA-inflamed rats in order to examine its effects on responses of spinal dorsal horn neurons to mechanical and thermal stimulation. Systemic injection of A-317491 (30 μmol/kg, i.v.) reduced the responses of wide-dynamic-range (WDR) and nociceptive specific (NS) neurons to both high-intensity mechanical (pinch) and heat (49°C) stimulation. A-317491 also decreased low-intensity (10 g von Frey hair) mechanically evoked activity of WDR neurons but did not alter WDR neuronal responses to cold stimulation (5°C). Spontaneous firing of WDR neurons in CFA-inflamed rats was also significantly attenuated by A-317491 injection. By using immunohistochemistry, P2X3 receptors were demonstrated to be enhanced in lamina II of the spinal dorsal horn after inflammation. In summary, blockade of P2X3 and P2X2/3 receptors dampens mechanical- and heat-related signaling, as well as nonevoked activity of key classes of spinal nociceptive neurons in inflamed animals. These data suggest that P2X3 and/or P2X2/3 receptors have a broad contribution to somatosensory/nociceptive transmission in rats with a chronic inflammatory injury and are consistent with previous behavioral data demonstrating antiallodynic and antihyperalgesic effects of receptor antagonists.     

The p75 receptor is associated with inflammatory thermal hypersensitivity

Inflammatory pain, characterized by a decrease in the nociceptive threshold, arises through the actions of inflammatory mediators, and one of the key molecules is nerve growth factor (NGF). Here we report that the administration of neutralizing antibody to the neurotrophin receptor p75 (p75(NTR)) blocks hyperalgesia, which develops with complete Freund's adjuvant (CFA)-induced inflammation or with an intraplantar injection of NGF. Although CFA injection results in the up-regulation of calcitonin gene-related peptide (CGRP) levels in the primary sensory neurons, blocking p75(NTR) abolishes this effect. We further demonstrate that pro-NGF is the predominant ligand of p75(NTR) in vivo. Plasmin treatment, which is intended to decompose pro-NGF, ameliorates CFA-induced hyperalgesia. In addition, an intraplantar injection of pro-NGF induces hyperalgesia. These data together suggest that pro-NGF, as well as mature NGF, binding to p75(NTR) plays an important role in inflammation-induced hyperalgesia. Interference in the binding may provide a therapeutic approach for the treatment of inflammatory pain.     

Low-dose morphine induces hyperalgesia through activation of G alphas, protein kinase C, and L-type Ca 2+ channels in rats

Opioids can induce analgesia and also hyperalgesia in humans and in animals. It has been shown that systemic administration of morphine induced a hyperalgesic response at an extremely low dose. However, the exact mechanism(s) underlying opioid-induced hyperalgesia has not yet been clarified. Here, we have investigated cellular events involved in low-dose morphine hyperalgesia in male Wistar rats. The data showed that morphine (0.01 microg i.t.) could elicit hyperalgesia as assessed by the tail-flick test. G(alphas) mRNA and protein levels increased significantly following exposure to the hyperalgesic dose of morphine. Furthermore, morphine at an analgesic dose (20 microg i.t.) significantly decreased cAMP levels in the dorsal half of the lumbar spinal cord, whereas the tissue cAMP levels were not affected by morphine treatment at a hyperalgesic dose. Intrathecal administration of nifedipine, an L-type calcium channel blocker, antagonized the hyperalgesia induced by the low-dose of morphine. Furthermore, pretreatment with the selective protein kinase C (PKC) inhibitor chelerytrine resulted in prevention of the morphine-induced hyperalgesia. KT 5720, a specific inhibitor of protein kinase A (PKA), did not show any effect on low-dose morphine-induced hyperalgesia. These results indicate a role for G(alphas), the PLC-PKC pathway, and L-type calcium channels in intrathecal morphine-induced hyperalgesia in rats. Activation of ordinary G(alphas) signaling through cAMP levels did not appear to play a major role in the induction of hyperalgesia by low-dose of morphine.     

电针对慢性内脏痛敏大鼠延髓头端腹内侧核NMDA-R1受体表达的影响

目的在电针（EA）缓解肠易激综合征（IBS）模型大鼠慢性内脏痛敏基础上,观察电针处理对IBS模型大鼠延髓头端腹内侧核（RVM）N-甲基-D-门冬氨酸1型（NMDA-R1）受体表达的影响。方法将新生9 d SD幼鼠分为两组,第一组通过结直肠机械扩张刺激制作IBS慢性内脏痛敏模型,持续两星期;另一组仅轻柔肛周皮肤作为对照。饲养至6～8星期后,分别观察两组大鼠由结直肠扩张（CRD）诱发的腹部撤回反射（AWR）评分和痛阈压力值（PTP）变化。继而随机将IBS模型大鼠分为模型组（M）、模型加电针组（EA）和模型加假电针组（SEA）。模型组不做任何治疗,电针组穴位取双侧＂足三里＂和＂上巨虚＂,连续隔日治疗4次,假电针不通电,余与电针组同。治疗结束后,取材并用免疫组化方法观察各组大鼠RVM中NMDA-R1受体表达变化。结果成年IBS大鼠AWR评分明显升高（P〈0.01）,PTP值明显降低（P〈0.01）;电针可以明显降低AWR评分（P〈0.05）,并使PTP值明显升高（P〈0.01）;假电针则没有此作用。IBS大鼠RVM中NMDA-R1受体阳性神经元数目和积分光密度明显高于正常对照大鼠（P〈0.05）;而电针可使其表达明显降低（P〈0.05）;假电针则没有这样的作用。结论电针对IBS大鼠的慢性内脏痛敏具有良好的治疗作用,其作用机制可能通过调节脑内RVM中NMDA-R1受体表达来发挥的。     

瘀血痹片通过抑制外周炎症缓解慢性炎性痛小鼠痛觉过敏及足肿胀

目的:观察瘀血痹片对慢性炎性痛小鼠痛觉过敏及足肿胀的影响,并探索初步作用机制.方法:使用完全弗氏佐剂(CFA)左侧足底注射建立小鼠慢性炎性痛模型,并分为模型组、阳性药布洛芬组(91 mg·kg-1)和瘀血痹片低、中、高剂量组(55,110,220 mg· kg-1),同时以假手术组作对照.造模后每日剂量等分为早晚2次灌...     

GABA_A受体部分介导丙泊酚在中脑导水管周围灰质腹外侧区的致痛觉过敏作用

目的观察丙泊酚在vlPAG对大鼠伤害性感受的影响及GABAA受体在其中可能的作用。方法Sprague-Daw ley(SD)♀大鼠随机分组,丙泊酚(Propofol,Pro)和荷包牡丹碱(B icucu lline,B ic)采用中脑导水管周围灰质腹外侧区(ven-trolateral portion of the PAG,vlPAG)注射。行为学实验采用热板法和福尔马林实验,分别以舔后爪潜伏时间(Hot-p latelatency,HPL)和疼痛(累计)评分为指标。免疫组化方法观察丙泊酚在vlPAG对福尔马林单侧足底皮下注射诱发的脊髓背角Fos蛋白表达的影响。结果行为学部分:两种疼痛模型中丙泊酚(10 g.L-1)vlPAG注射引起痛敏(P<0.01)。热板法实验中,丙泊酚vlPAG微量注射的痛敏作用可被相同部位预先注射25 mg.L-1B ic在10和20 m in时间点分别拮抗70%和71%(均P<0.01),在30和40 m in完全拮抗。在福尔马林实验中,丙泊酚vlPAG微量注射使福尔马林疼痛评分增加,此作用可被B ic(25 mg.L-1)在60 m in拮抗57%(P<0.05)。免疫组化部分中,丙泊酚vlPAG微量注射使福尔马林引起的脊髓背角各层FLI阳性细胞数明显增多(P<0.01),B ic vlPAG微量注射(25 mg.L-1)可部分拮抗丙泊酚vlPAG微量注射的作用(P<0.01)。结论在大鼠vlPAG微量注射丙泊酚能产生痛敏作用;GABAA受体部分介导了丙泊酚的以上作用。