孤啡肽在痛和痛觉调制方面的研究进展

孤啡肽是新近发现的一种结构与功能均与已知阿片肽有所不同的全新的神经肽,有关其在痛和痛觉调制方面的研究是当前神经科学研究的一个热点。本文对孤啡肽在脊髓上（脑）区的抗阿片作用,在脊髓的抗伤害或痛觉过敏作用,以及在吗啡和电针耐受形成方面的作用等研究现状作一综述,以期对孤啡肽的进一步深入研究起到促进作用。     

综述与专论：运动诱发的镇痛效应：脊髓、皮层下和皮层机制

在健康受试者或部分慢性疼痛人群中，一定强度和时长的运动锻炼或针对性的运动疗法，已被广泛验证可以有效提高疼痛阈值并改善疼痛症状。上述运动诱发的镇痛效应（exercise induced hypoalgesia,EIH）被认为与痛觉内源性调控系统在神经系统不同水平上的调控作用紧密联系；合适类型的运动刺激可以在脊髓水平诱发镇痛效应，亦可激活脊髓以上高位中枢神经系统的痛觉内源性调控系统，进而对脊髓水平的伤害性反应进行调控。病理性痛状态下，EIH的产生与运动皮层的激活水平以及痛觉下行抑制作用均有关。研究脊髓、皮层下和皮层水平EIH效应的确切机制，将为非药物运动手段预防疼痛慢性化提供帮助。     

腹外侧眶皮层在痛觉调制和针刺镇痛中的作用

腹外侧眶皮层 (ventrolateral orbital cortex, VLO) 是眶皮层的主要成分,它与导水管周围灰质(PAG)、丘脑和其它皮层之间有广泛的纤维联系.VLO不仅是一个痛觉感受中枢,而且也是一个痛觉调制中枢,通过激活PAG脑干下行抑制系统在脊髓和三叉水平抑制伤害性信息的输入.研究还证实,阿片、 5-HT和GABA等神经递质及其受体参与VLO的抗伤害效应.此外,VLO在针刺镇痛中也发挥重要作用.本文就腹外侧眶皮层在痛觉调制和针刺镇痛中的作用进行综述.     

大鼠侧脑室及鞘内注射孤啡肽对痛反应及电针镇痛的影响

孤啡肽（ＯＦＱ）是最近发现的一种１７肽,为阿片受体家族中一个新成员－“孤儿受体”的内源性配基。ＯＦＱ在痛觉调制中的作用与内阿片肽明显不同。本实验在大鼠电刺激甩尾测痛模型上,观察了侧脑室（ＩＣＶ）及鞘内注射（ＩＴ）ＯＦＱ对伤害性电刺激引起的痛反应及电针镇痛的影响。结果发现,大量ＩＣＶ及ＩＴ０．１μｇ（０．０５５ｎｍｏｌ）ＯＦＱ对痛觉反应无影响,而１．０μｇ（０．５５ｎｍｏｌ）的ＯＦＱ可明显降低痛阈;     

孤啡肽——新发现的内阿片肽及其受体

孤啡肽是最近发现的一个１７肽,其结构与已知的内阿片肽,尤其是强啡肽Ａ类似;但具有明显不同的药理学特性;与经典的阿片受体结合能力很弱,而与阿片受体家族中的一个新成员－－“孤儿受体”结合能力很强,因而认为是该受体的天然配基,孤啡肽脑室注射可使小鼠痛觉过敏,运动减少。孤啡肽受体是阿片受体家族中的新成员,属于Ｇ蛋白偶联受体,与经典的阿片受体配基亲和力均很弱,该受体激活后介导对腺苷酸环化酶活力的抑制。     

促肾上腺皮质激素的中枢抗阿片镇痛效应及其作用机制分析

本研究采用多种方法在行为学、细胞受体、受体后第二信使以及脑内Ｆｏｓ蛋白的诱导表达等多个水平,对ＡＣＴＨ的中枢抗阿片镇痛效应、作用机制以及作用部位进行了深入的观察。结果表明,ＡＣＴＨ在脊髓水平可以对抗阿片μ和δ受体介导的镇痛,不对抗Ｋ受体所介导的镇痛。进一步研究表明,ＡＣＴＨ的这一效应可能不是直接发生在阿片受体上的对抗,而是在受体的ｃＡＭＰ和Ｃａ＾２＋信使通路上与阿片相互作用发生在阿片受体上的对抗,     

孤啡肽（Orphanin－FQ）─—新发现的内阿片肽及其受体

孤啡肽（Ｏｒｐｈａｎｉｎ－ＦＱ）是最近发现的一个１７肽,其结构与已知的内阿片肽,尤其是强啡肽Ａ类似;但具有明显不同的药理学特性：与经典的阿片受体（μ、δ和）结合能力很弱,而与阿片受体家族中的一个新成员——“孤儿受体”（ｏｒｐｈａｎｒｅｃｅｐｔｏｒ）结合能力很强,因而认为是该受体的天然配基．孤啡肽脑室注射可使小鼠痛觉过敏,运动减少．孤啡肽受体是阿片受体家族中的新成员,属于Ｇ蛋白偶联受体,与经典的阿片受体配基亲和力均很弱．该受体激活后介导对腺苷酸环化酶活力的抑制．     

孤啡肽在大鼠脑内对抗吗啡镇痛

脑内全新的阿片受体样受体（１９９４）及其内源性配体孤啡肽（１９９５）的发现形成了中枢神经系统阿片／抗阿片相互关系的研究领域中一个新的推动力。基于它们与阿片家族的高同源性及在脑内痛觉整合相关区域的丰富表达,本实验观察了ＯＦＱ在大鼠脑内对吗啡镇痛作用的影响。结果表明：（１）ＯＦＱ可以对抗脑室注射生理盐水引起的镇痛,后者可能是一种由内源性阿片系统介导的应激镇痛。（２）脑室注射ＯＦＱ在很大的剂量范围（４０     

鞘内注射孤啡肽对大鼠足底注入蜜蜂毒诱致长时程自发痛、痛敏和炎症的不同效果

为进一步了解孤啡肽在脊髓水平是否具有抗伤害及抗炎作用,本实验在具有多种痛行为表现的蜜蜂毒模型上观察了鞘内注射孤啡肽对大鼠一侧后足底注入蜜蜂毒所诱致的同侧自发缩足反射、原发热和机械性痛敏以及注射部位炎症反应的影响,同时观察了新的高选择性孤啡肽受体拮抗剂CompB的作用.结果表明与生理盐水对照组比较,鞘内注射孤啡肽(3、10、30 nmol/10μl)对蜜蜂毒诱发的自发缩足反射次数的抑制作用随剂量提高而增大,抑制率分别为37±7,43±6and57±11%(三个剂量vs对照,P＜0.05);而对蜜蜂毒诱发的注射部位炎症反应(爪体积、爪背腹厚度和蛋白渗出的增加)无显著影响.CompB(30 nmo1)可完全翻转10 nmol孤啡肽对自发缩足反射的抑制作用.鞘内单次或重复注射孤啡肽(10 nmol/10μl)对蜜蜂毒诱致的原发性热和机械性痛敏的发生和维持均无作用.本实验结果提示,外源性孤啡肽在脊髓通过孤啡肽受体的介导产生一定的镇痛作用,但是它可能仅对持续性自发痛有抑制作用,而对热和机械性痛敏及炎症反应均无影响.     

孤啡肽受体的配体研究进展

孤啡肽(nociceptin或orphanin FQ)发现于1995年底, 它是阿片受体样受体(ORL1或LC 132) 的内源性配体,在痛觉调节、心血管系统、离子通道、依赖和耐受、学习和记忆等方面具有广泛的生物学活性. 最近几年, 对孤啡肽受体与相关配体构效关系的研究成为一个新的热点.对在研究构效关系过程中所发现的孤啡肽受体相关配体（片段、拮抗剂、激动剂、部分激动剂和阻断剂）的研究情况进行了介绍.     

Distinct effect of intracerebroventricular and intrathecal injections of nociceptin/orphanin FQ in the rat formalin test

Nociceptin/orphanin FQ (nociceptin/OFQ), a newly discovered heptadecapeptide has been regarded as an endogenous ligand for orphan opioid receptor. The present study was designed to investigate the effect of nociceptin/OFQ on pain response and opioid analgesia in the rat formalin test. The results showed that intracerebroventricular injection of 1 microg nociceptin/OFQ enhanced the pain response, and 0.1 or 0.5 microg nociceptin/OFQ had no effect on formalin-induced pain. When 0.1 or 1 microg nociceptin/OFQ were used together with mu-, delta-, or kappa-opioid receptor agonists, endomorphin-1, DSLET or U50488H, respectively, it attenuated mu- and kappa- but not delta-receptor mediated analgesia. On the other hand, intrathecal injection of nociceptin/OFQ (0.1, 1 and 5 microg) reduced the pain response in the formalin test. In conclusion, nociceptin/OFQ potentiated formalin-induced pain response and antagonized opioid analgesia in the rat brain but inhibited pain response in the spinal cord.     

Nociceptin/orphanin FQ in spinal nociceptive mechanisms under normal and pathological conditions

Nociceptin and its receptor are present in dorsal spinal cord, indicating a possible role for this peptide in pain transmission. The majority of functional studies using behavioral and electrophysiological studies have shown that nociceptin applied at spinal level produces antinociception through pre- and post-synaptic mechanisms. The spinal inhibitory effect of nociceptin is not sensitive to antagonists of opioid receptors such as naloxone. Thus, nociceptin-induced antinociception is mediated by a novel mechanism independent of activation of classic opioid receptors. This has raised the possibility that agonists of the nociceptin receptor may represent a novel class of analgesics. Supporting this hypothesis, several groups have shown that intrathecal nociceptin alleviated hyperalgesic and allodynic responses in rats after inflammation or partial peripheral nerve injury. Electrophysiological studies have also indicated that the antinociceptive potency of spinal nociceptin is maintained or enhanced after nerve injury. It is concluded that the predominant action of nociceptin in the spinal cord appears to be inhibitory. The physiological role of nociceptin in spinal nociceptive mechanisms remains to be defined. Moreover, further evaluation of nociceptin as a new analgesic calls the development of non-peptide brain penetrating agents.     

Unrestrained nociceptive response and disregulation of hearing ability in mice lacking the nociceptin/orphaninFQ receptor.

In the G-protein-coupled receptor superfamily, the opioid receptor subfamily is constituted of the three distinct opioid receptors (namely delta-, mu- and kappa-subtypes) and the receptor for nociceptin (also designated orphaninFQ). The members of the opioid receptor subfamily were known to mediate a variety of cellular inhibitory effects. The three opioid receptors are known to play central roles in mediating analgesia and many other physiological activities; however, the nociceptin receptor was identified recently and less is known about its physiological roles. Here we report the generation and characterization of mice lacking the nociceptin receptor. The knockout mice showed no significant differences in nociceptive threshold and locomotor activity compared with control mice, but they lost nociceptin-induced behavioral responses. These results indicate that the nociceptin system is not essential for regulation of nociception or locomotor activity. On the other hand, we found insufficient recovery of hearing ability from the adaptation to sound exposure in the mutant mice. Thus, the nociceptin system appears to participate in the regulation of the auditory system.     

Functional studies using antibodies against orphanin FQ/nociceptin

Orphanin FQ/nociceptin (OFQ) is a recently discovered endogenous ligand for the novel opioid receptor-like receptor (ORL-1). There are numerous reports in the literature demonstrating paradoxical effects of exogenous OFQ on pain modulation. For example, OFQ produces a pronociceptive effect in the brain and an analgesic effect in the spinal cord. In order to better understand the physiological actions of OFQ, the present study focused on the pain-modulatory effect of endogenously released OFQ measured using antibody microinjection techniques. We found that electroacupuncture analgesia (EA) was increased by intracerebroventricular (i.c.v.) injection of an OFQ-antibody and decreased following intrathecal injection. Furthermore, i.c.v. OFQ-antibody partially reversed tolerance to both chronic morphine and chronic EA. These data suggest that endogenously released OFQ plays an important role in pain modulation, where pain sensitivity in the brain and spinal cord is increased and decreased, respectively.     

病理性疼痛的分子机制

持续性或慢性疼痛是很多患者的主要描述症状。然而,现在的治疗手段还不能充分解决某些疼痛或会引起不能忍受的副作用。近来疼痛生物学者阐明了大量的参与疼痛发生和维持的细胞和分子活动。如何更好的理解这些分子活动的机制将有助于发展高效的,特异性的治疗手段。背根神经节中小细胞神经元向脊髓传递温觉和伤害性信息的感觉传递。这些神经元的外周突感受生理性和化学性刺激后,可以在脊髓背角的中枢突通过突触囊泡和大致密性囊泡释放兴奋性的神经递质和神经肽。这种兴奋性突触传递可以被一些抑制因子调控如脊髓中间神经元和下行系统中分泌的阿片肽、GABA、甘氨酸、5-羟色胺。本文将回顾脊髓抑制性系统所取得的一些研究进展,将重点介绍在阿片受体转运,阿片镇痛以及吗啡耐晋研究中的进展,这些发现可能的治疗前景也会一并讨论。     

Melatonin: A hormone that modulates pain

AimsMelatonin is a hormone synthesized principally in the pineal gland that has been classically associated with endocrine actions. However, several lines of evidence suggest that melatonin plays a role in pain modulation. This paper reviews the available evidence on melatonin's analgesic effects in animals and human beings.Main methodsA medline search was performed using the terms “melatonin”, “inflammatory pain”, “neuropathic pain”, “functional pain”, “rats”, “mice”, “human”, “receptors”, “opioid” and “free radicals” in combinations.Key findingsThe antinociceptive effect of melatonin has been evaluated in diverse pain models, and several findings show that melatonin receptors modulate pain mechanisms as activation induces an antinociceptive effect at spinal and supraspinal levels under conditions of acute and inflammatory pain. More recently, melatonin induced-antinociception has been extended to neuropathic pain states. This effect agrees with the localization of melatonin receptors in thalamus, hypothalamus, dorsal horn of the spinal cord, spinal trigeminal tract, and trigeminal nucleus. The effects of melatonin result from activation of MT₁ and MT₂ melatonin receptors, which leads to reduced cyclic AMP formation and reduced nociception. In addition, melatonin is able to activate opioid receptors indirectly, to open several K⁺ channels and to inhibit expression of 5-lipoxygenase and cyclooxygenase 2. This hormone also inhibits the production of pro-inflammatory cytokines, modulates GABA_A receptor function and acts as a free radical scavenger.SignificanceMelatonin receptors constitute attractive targets for developing analgesic drugs, and their activation may prove to be a useful strategy to generate analgesics with a novel mechanism of action.     

Opioid and nociceptin receptors regulate cytokine and cytokine receptor expression

Opioids were originally discovered because of their ability to induce analgesia, but further investigation has shown that the opioids regulate the function of cells involved in the immune response. We suggest that the regulation of cytokine, chemokine, and cytokine receptor expression is a critical component of the immunomodulatory activity of the opioids. In this paper we review the literature dealing with the regulation of cytokine and cytokine receptor expression by agonists for the three major opioid receptor types (mu, kappa, and delta), and nociceptin, the natural agonist for the orphanin FQ/nociceptin receptor. Although the opioid receptors share a high degree of sequence homology, opposing roles between the kappa opioid receptor (KOR) and the mu opioid receptor (MOR) have become apparent. We suggest that activation of the KOR induces an anti-inflammatory response through the down-regulation of cytokine, chemokine and chemokine receptor expression, while activation of the MOR favors a pro-inflammatory response. Investigation into the opioid receptor-like (ORL1)/nociceptin system also suggests a role for this receptor as a down-regulator of immune function. These effects suggest a broad role for opioids in the modulation of the function of the immune system, and suggest possible targets for the development of new therapeutics for inflammatory and infectious diseases.     

Nociceptin, OP4 receptor ligand in different models of experimental epilepsy

The anticonvulsive activity of nociceptin, endogenous OP4 receptors agonist was investigated in pentylenetetrazole (PTZ), N-methyl D-aspartic acid (NMDA), bicucculine (BCC) and electrically evoked seizure models of experimental epilepsy. Nociceptin, at the dose of 10 nmol, suppressed the clonic seizures induced by PTZ, NMDA and BCC. [Phe1(psi)(CH2-NH)Gly2]nociceptin-(1-13)-NH2 which has been proposed to be selective antagonist OP4 receptors, did not prevent the action of nociceptin. The effect of [Phe1(psi)(CH2-NH)Gly2]nociceptin-(1-13)-NH2 on seizures induced by PTZ, NMDA and BCC was very similar to that of nociceptin. These data support the hypothesis that it possesses agonistic properties. Naloxone did not reverse the anticonvulsive action of nociceptin as well as [Phe1(psi)(CH2-NH)Gly2]nociceptin-(1-13)-NH2 which excludes the participation of opioid receptor in this action. On the other hand in the electroconvulsive model of generalized seizures, nociceptin as well as [Phe1(psi)(CH2-NH)Gly2]nociceptin-(1-13)-NH2 influenced neither the electroconvulsive threshold nor the maximal electroshock test. The data suggest that nociceptin and [Phe1(psi)(CH2-NH)Gly2]nociceptin-(1-13)-NH2 can exert anticonvulsive action. These properties depend on OP4 but not opioid receptors activation.     

Central administration of oxytocin reduces hyperalgesia in mice: Implication for cannabinoid and opioid systems

The neuropeptide oxytocin (OXT) contributes to the regulation of diverse cognitive and physiological functions including nociception. Indeed, OXT has been reported to be analgesic when administered directly into the brain, the spinal cord, or systemically. Although many authors have reported the analgesic effects of OXT, its mechanism has not been well elucidated. Recently, it has been also hypothesize that OXT, increasing intracellular concentration of calcium, could regulate the production of mediators, like endocannabinoids (eCB). It has been well documented that eCB are able to suppress pain pathways. The present study investigates the effect of OXT in paw carrageenan-induced pain. Intracerebroventricular (icv) administration of OXT, but neither intraperitoneal nor intraplantar route, induces an antihyperalgesic effect increasing paw withdrawal latency to mechanical or thermal stimuli. Our results clearly demonstrate that 3 and 6 h following carrageenan challenge, central administration of OXT (30 ng/mouse) shows a significant antihyperalgesic activity. Moreover, for the first time, we demonstrate that CB1 receptor plays a key role in the antihyperalgesic effect of OXT. In fact our results show CB1 antagonist, but not the specific CB2 antagonist reduce OXT-induced antihyperalgesic effect. In addition, our data show that central OXT administration is able to reduce carrageenan-induced hyperalgesia but does not modify carrageenan-induced paw edema. Finally, using opioid antagonists we confirm an important role of opioid receptors. In conclusion, our experiments suggest that central administration of OXT reduces hyperalgesia induced by intraplantar injection of carrageenan, and this effect may work via cannabinoid and opioid systems.     

Changes in expression of nociceptin/orphanin FQ and its receptor in spinal dorsal horn during electroacupuncture treatment for peripheral inflammatory pain in rats

The neuropeptide nociceptin/orphanin FQ (N/OFQ), the endogenous agonist of the N/OFQ peptide receptor (NOP receptor), has been demonstrated to be involved in many physiological and pathological functions including pain modulation. It was reported that electroacupuncture (EA) had a potent analgesic effect on inflammatory pain by activating various endogenous transmitters such as the opioid peptides. In the present study, we investigated the effect of EA on peripheral inflammatory pain and the expression of N/OFQ and the NOP receptor in the spinal dorsal horn of rats, using a behavioral test, RT-PCR, immunohistochemistry and Western blot analysis techniques. The results showed: (1) EA had an accumulative analgesic effect on chronic inflammatory pain; (2) in the superficial layers of the spinal dorsal horn, the level of mRNA of the precursor protein for N/OFQ (preproN/OFQ, ppN/OFQ) was increased and the N/OFQ immunoreactivity was decreased after peripheral inflammation, and could be significantly increased by EA treatment; (3) both mRNA and protein levels of the NOP receptor in the spinal dorsal horn were significantly increased after chronic inflammatory pain and could be further enhanced by EA treatment. The present data demonstrated that EA could activate the endogenous N/OFQ-NOP receptor system, and this might underlie the effectiveness of EA in the treatment of inflammatory pain.