脊髓内NMDA受体NR2B在胍丁胺拮抗吗啡耐受中的作用

目的:探讨脊髓N-甲基-D-天门冬氨酸(N-methyl-D-aspartate,NMDA)受体NR2B亚单位在胍丁胺抗吗啡耐受中的作用.方法:给大鼠皮下注射吗啡(10 mg/kg,Bid)建立慢性吗啡耐受大鼠模型.应用热水甩尾法测定甩尾潜伏期观察吗啡的镇痛效果.应用免疫印迹法(Western blot)检测脊髓NR2B蛋白表达.结果:皮下注射吗啡的第9 d,大鼠对吗啡镇痛已产生明显的耐受.此时,吗啡耐受大鼠脊髓NMDA受体NR2B蛋白表达显著增多.胍丁胺(10 mg/kg)不仅拮抗吗啡耐受,而且明显地抑制脊髓NR2B蛋白表达上调.结论:抑制慢性吗啡注射引起脊髓NMDA受体NR2B亚单位增多可能是胍丁胺抗吗啡耐受的作用机制之一.     

脊髓NMDAR1受体在吗啡耐受过程中的变化

目的　研究脊髓NMDA受体在吗啡耐受过程中的变化 ,旨在探讨NMDA受体在吗啡耐受机制中的作用 ,为进一步阐明吗啡耐受的受体机制提供实验材料。方法　建立慢性吗啡耐受大鼠模型 ,用MK 80 1进行干预 ,用免疫组织化学方法测定脊髓后角NMDA受体在吗啡耐受过程中的变化 ,MK 80 1抗吗啡耐受过程中是否对NMDA受体数量有影响。结果　吗啡耐受形成过程中NMDA受体数量增加 ;MK 80 1与吗啡合用有抗吗啡耐受作用 ,MK 80 1可以阻断吗啡耐受过程中NMDA受体数量的增加。结论　吗啡耐受的机制可能涉及NMDA受体的上调 ,MK 80 1可能通过抑制NMDA受体上调而具有部分抗吗啡耐受作用。     

脊髓NMDAR1受体在吗啡耐受过程中的变化

目的研究脊髓NMDA受体在吗啡耐受过程中的变化,旨在探讨NMDA受体在吗啡耐受机制中的作用,为进一步阐明吗啡耐受的受体机制提供实验材料.方法建立慢性吗啡耐受大鼠模型,用MK-801进行干预,用免疫组织化学方法测定脊髓后角NMDA受体在吗啡耐受过程中的变化,MK-801抗吗啡耐受过程中是否对NMDA受体数量有影响.结果吗啡耐受形成过程中NMDA受体数量增加;MK-801与吗啡合用有抗吗啡耐受作用,MK-801可以阻断吗啡耐受过程中NMDA受体数量的增加.结论吗啡耐受的机制可能涉及NMDA受体的上调,MK-801可能通过抑制NMDA受体上调而具有部分抗吗啡耐受作用.     

Akt通路及细胞凋亡在瘦素介导的大鼠慢性吗啡镇痛耐受中的作用

目的:探讨Akt(又称蛋白激酶B)及活化的caspase-3在瘦素介导的大鼠慢性吗啡镇痛耐受中的作用。方法:在SD大鼠建立慢性吗啡镇痛耐受模型;采用Western blotting法测定脊髓Akt和cleaved caspase-3的水平;免疫组织化学染色法检测脊髓磷酸化Akt(p-Akt)及cleaved caspase-3阳性细胞;免疫双染检测p-Akt及cleaved caspase-3阳性细胞的定位。结果:鞘内慢性注射吗啡(15μg)7 d可明显上调大鼠脊髓p-Akt及cleaved caspase-3的蛋白水平;在注射吗啡前30 min,鞘内注射瘦素拮抗剂(3μg)7 d能显著地抑制慢性吗啡处理对p-Akt和cleaved caspase-3的上调作用;p-Akt只定位在脊髓神经元,而cleaved caspase-3仅定位在星形胶质细胞;瘦素拮抗剂、Akt抑制剂及caspase-3抑制剂均能抑制慢性吗啡镇痛耐受。结论:脊髓Akt通路及活化的caspase-3参与瘦素介导的大鼠慢性吗啡镇痛耐受。     

P2X7受体在神经病理性疼痛和吗啡耐受中的作用研究进展

嘌呤能离子通道型受体7(P2X7R)属于嘌呤能受体家族中的一员,广泛分布于中枢神经系统与外周神经系统。大量研究数据表明P2X7R在神经病理性痛和吗啡耐受中起到重要作用,以P2X7R为靶点治疗神经病理性疼痛和吗啡耐受在近些年受到广泛关注。本文综述了P2X7R在神经病理性疼痛和吗啡耐受中的作用。     

内吗啡肽-1对成年大鼠脊髓胶状质内突触传递的抑制作用强于内吗啡肽-2

本实验采用全细胞电压钳记录方法,研究了内吗啡肽1(EM1)和内吗啡肽2(EM2)对脊髓背角胶状质神经元突触传递的抑制性作用。EM1(1μmol/L)和EM2(1μmol/L)都能够显著抑制微小兴奋性突触后电流(mEPSCs)和微小抑制性突触后电流(mIPSCs)的频率而不改变其幅值。这种抑制作用能被μ受体选择性拮抗剂βfunaltrexamine(βFNA,10μmol/L)阻断。值得注意的是,EM1对mEPSCs和mIPSCs的频率的抑制作用强于EM2。上述结果提示在脊髓胶状质,内吗啡肽通过激活突触前膜上的μ受体,抑制兴奋性和抑制性的突触传递;与EM2相比,EM1可能是脊髓水平的更强效的内源性镇痛剂。     

芍药苷激活2型大麻素受体保护脑缺血再灌注大鼠海马神经元

目的探究芍药苷通过激活2型大麻素受体(CBR2)对脑缺血再灌注大鼠神经的保护作用。方法 144只雄性SD大鼠随机分为假手术组、模型组、溶媒组、10mg/kg芍药苷组、40mg/kg芍药苷组、CBR2选择性拮抗剂3mg/kg AM630组、40mg/kg芍药苷联合3mg/kg AM630组、CBR2选择性激动剂3mg/kg HU308处理组。线栓法制作大鼠局灶性脑缺血/再灌注模型。观察芍药苷对神经功能缺损评分、梗塞体积、脑水肿的影响;采用HE染色观察脑组织病理形态学改变;采用免疫组织化学染色法观察芍药苷对海马区环氧合酶2(COX-2)和caspase-3表达的影响。结果芍药苷能显著改善脑缺血大鼠神经功能评分,降低梗塞体积及缺血侧脑含水量,减轻脑组织病变,抑制海马区caspase-3和COX-2的表达;但预先注射AM630可显著拮抗芍药苷的脑神经保护作用。结论 CBR2可能参与芍药苷对脑缺血再灌注大鼠海马神经元的保护作用。     

大麻素CB_1受体活化对神经病理性疼痛大鼠脊髓背角嘌呤能P2X_2受体表达的抑制作用

目的:观察脊髓背角大麻素CB_1受体(CB_1R)在坐骨神经缩窄性损伤(CCI)所致的神经病理性疼痛中的作用及其对嘌呤能P2X_2受体表达的调节。方法:7~8周龄SD大鼠分为4组:(1)sham组;(2)CCI组;(3)CP55940+CCI组;(4)AM251+CP55940+CCI组。分别于CCI术前1 d,术后1、3、5、7、10、14 d测定热缩足反射潜伏期(TWL);免疫印迹技术检测各组大鼠损伤侧L_4~L_6段脊髓背角P2X_2受体表达。结果:CCI术后大鼠出现热痛敏,TWL明显缩短;鞘内给予非选择性大麻素受体激动剂CP55940可明显延长CCI大鼠TWL(P0.05);预先鞘内注射CB_1R拮抗剂AM251(0.05 mg/kg)可显著降低CP55940的镇痛效果(P0.05)。免疫印迹实验结果显示:CCI大鼠脊髓背角P2X_2受体在术后7、14 d表达明显增加(P0.05);鞘内给予CP55940可显著降低P2X_2受体表达(P0.05),而预先给予AM251可降低CP55940抑制P2X_2受体表达的效应(P0.05)。结论:脊髓背角CB_1受体激活对CCI所致的神经病理性疼痛具有良好的镇痛作用,其镇痛效应可能与抑制CCI大鼠嘌呤能P2X_2受体表达有关。     

胍丁胺对吗啡镇痛耐受大鼠脊髓和海马锌含量变化的影响

目的观察胍丁胺对吗啡耐受大鼠脊髓和海马组织中锌(Zn2+)含量变化的影响。方法采用SD成年雄性大鼠,建立慢性吗啡耐受大鼠模型,用热水甩尾法测定甩尾潜伏期观察痛反应的变化。动物随机分为4组:生理盐水(NS-NS)组、吗啡(NS-Mor)组、胍丁胺(Ag-NS)组、胍丁胺-吗啡(Ag-Mor)组。用原子吸收光谱法测定各组大鼠的脊髓和海马Zn2+含量。结果胍丁胺(10mg/kg)与吗啡合用具有显著的抗吗啡耐受作用,并阻断慢性吗啡耐受引起的脊髓和海马Zn2+含量的降低(P<0.001)。结论逆转吗啡耐受时脊髓和海马组织中Zn2+含量的减少,可能是胍丁胺抗吗啡耐受的机制之一。     

mu-Opioid receptor internalization-dependent and -independent mechanisms of the development of tolerance to mu-opioid receptor agonists: Comparison between etorphine and morphine

A growing body of evidences suggests that receptor desensitization is implicated in the development of tolerance to opioids, which is generally regulated by protein kinases and receptor trafficking proteins. In the present study, we demonstrated that repeated s.c. treatment with etorphine, but not morphine, produced a significant increase in protein levels of G protein-coupled receptor kinase 2, dynamin II, beta-arrestin 2 and phosphorylated-conventional protein kinase C in membranes of the mouse spinal cord, suggesting that the etorphine-induced mu-opioid receptor desensitization may result from G protein-coupled receptor kinase 2/dynaminII/beta-arrestin2-dependent phosphorylation of mu-opioid receptors. Unlike etorphine, morphine failed to change the levels of these trafficking proteins. Furthermore, we found that the level of glial fibrillary acidic protein in the mouse spinal cord was clearly increased by chronic in vivo and in vitro treatment with morphine, whereas no such effect was noted by etorphine. In the behavioral study, intraperitoneal pretreatment with the glial-modulating agent propentofylline suppressed the development of tolerance to morphine-induced antinociception. In addition, intrathecal injection of astrocytes and astrocyte-conditioned medium mixture, which were obtained from cultured astrocytes of the newborn mouse spinal cord, aggravated the development of tolerance to morphine. In contrast, these agents failed to affect the development of tolerance induced by etorphine. These findings provide direct evidence for the distinct mechanisms between etorphine and morphine on the development of tolerance to spinal antinociception. These findings raise the possibility that the increased astroglia response produced by chronic morphine could be associated with the lack of mu-opioid receptor internalization.     

A light and electron microscopic study of the CB1 cannabinoid receptor in the primate spinal cord

The distribution of cannabinoid receptors was studied in the monkey spinal cord by immunocytochemistry and electron microscopy, using an antibody to the CB1 brain cannabinoid receptor. Large numbers of labelled neurons were observed in all portions of the grey matter of the spinal cord. These included small diameter 9–16µm neurons in the dorsal horn, larger (40–60µm) neurons in the intermediate grey, and very large (60–100µm), motor neurons in the ventral horn. Reaction product was observed in dendrites postsynaptic to unlabelled axon terminals. Since cannabinoid receptor activation decreases neuronal excitability by several mechanisms, including inhibition of voltage dependent calcium channels, the dense staining of CB1 in dorsal horn neurons suggests that CB1 could reduce calcium influx through such channels in these neurons. This, in turn, could decrease calcium-dependent changes in synaptic transmission and decrease sensitisation to nociceptive stimuli in these neurons. Similarly, the dense staining of CB1 in ventral horn cells suggests that cannabinoid receptors could limit calcium influx through voltage dependent calcium channels in these neurons, and could be significant in terms of neuroprotection to these neurons.     

Involvement of cannabinoid (CB1)-receptors in the development and maintenance of opioid tolerance

Sustained exposure to opioid agonists such as morphine increases levels of calcitonin gene-related peptide (CGRP) in the spinal dorsal horn, a response implicated in the development of opioid tolerance and physical dependence. Recent evidence suggests that both the opioid-induced increase in CGRP and the development of opioid physical dependence are suppressed by blockade of spinal cannabinoid (CB1)-receptors. The present study examined whether CB1-receptor activity also has a role in the development of opioid tolerance. In rats implanted with spinal catheters, repeated acute injections of morphine (15 microg) delivered over 4 h resulted in a rapid decline of thermal and mechanical antinociception and a significant loss of analgesic potency, reflecting development of acute opioid tolerance. In another set of experiments, chronic administration of spinal morphine (15 microg) once daily for 5 days produced a similar loss of analgesic effect and a marked increase in CGRP-immunoreactivity in the superficial laminae of the dorsal horn. Consistent with the in vivo findings, primary cultures of adult dorsal root ganglion (DRG) neurons exposed to morphine for 5 days showed a significant increase in the number of CGRP-immunoreactive neurons. Co-administration of acute or chronic morphine with a CB1-receptor antagonist/inverse agonist, 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM-251), inhibited the development of both acute and chronic analgesic tolerance. In animals already exhibiting tolerance to morphine, intervention with AM-251 restored morphine analgesic potency. Co-administration with AM-251 attenuated the morphine-induced increase in CGRP-immunoreactivity in the spinal cord and in DRG cultured neurons. Collectively, the results of this study suggest that activity of endocannabinoids, mediated via CB1-receptors, contributes to both the development and maintenance of opioid tolerance by influencing the opioid-induced increase in spinal CGRP.     

Melanocortin 4 receptor antagonists attenuates morphine antinociceptive tolerance,astroglial activation and cytokines expression in the spinal cord of rat

Chronic use of morphine is accompanied by the development of morphine tolerance, which is one of the major problems associated with opiate treatment. Experimental evidence indicates that melanocortin 4 receptor (MC4R) is involved in development of morphine tolerance. Therefore, we investigated the influence of repeated intrathecal injection of a MC4R antagonist (HS014) on the development of morphine tolerance as measured by hot-plate test. It was also examined whether a single i.t. HS014 administration could counteract the loss of analgesic potency of morphine in morphine tolerant rats. We examined also the influence of i.t. HS014 administration on astrocytes activation and cytokines expression in the spinal cord of rat during morphine tolerance. Morphine treatment (10 mg/kg, i.p. twice daily) over 5 days induced tolerance as reflected by a significant reduction of withdrawal latency from 29.67 ± 1.81 s to 8.67 ± 1.70 s in the hot-plate test. Repeated coadministration of HS014 and morphine, significantly prevented the development of morphine tolerance. A single administration of an MC4R antagonist restored morphine analgesic potency in morphine tolerant rats. Using immunohistochemical staining, we demonstrated the administration of MC4R during the induction of morphine tolerance inhibited the activation of astrocytes; reduced the expression of proinflammatory cytokines interleukin-1β, IL-6, and tumor necrosis factor-α; upregulated the expression of anti-inflammatory cytokines IL-10 at the L5 lumbar spinal cord. These results suggest that MC4R may be involved in the mechanisms of morphine tolerance and antagonists of this receptor may be a possible new target in the search for strategies preventing the development of morphine tolerance.     

NMDA receptors are involved in upstream of the spinal JNK activation in morphine antinociceptive tolerance

N-methyl-d-aspartate (NMDA) receptors and c-Jun N-terminal kinase (JNK) have been shown to be involved in morphine antinociceptive tolerance. However, whether chronic morphine-induced activation of the spinal JNK is NMDA receptor-dependent is unknown. The present study investigated the link between the spinal NMDA receptor NR2B subunit and the JNK activation during morphine antinociceptive tolerance in rats. Our results showed that chronic morphine treatment induced upregulation of the NR2B expression and activation of JNK in the spinal cord. Moreover, the increased NR2B-immunoreactivity (IR) and phosphorylated JNK-IR were observed mainly at the superficial dorsal horn laminae of the spinal cord; the spinal p-JNK was mainly expressed in astrocytes and NR2B in neurons. SP600125, a selective inhibitor of JNK, significantly attenuated morphine tolerance. MK-801, a noncompetitive NMDA receptor antagonist, not only suppressed morphine antinociceptive tolerance and the increase in NR2B, but also reduced the spinal JNK activation induced by chronic morphine treatment. These findings demonstrated for the first time that NMDA receptor-dependent activation of the spinal JNK contributes to morphine antinociceptive tolerance and that MK-801 attenuates morphine tolerance partly due to its inhibition on the spinal JNK activation.     

大鼠中缝背核参与NO介导的脊髓对吗啡依赖和戒断的调节

目的:探索大鼠脑干内神经核团中缝背核(dorsal raphe nucleus,DRN)在吗啡依赖和戒断形成过程中的作用及其机制。方法:雄性成年SD大鼠、(260±20)g,随机分为戒断组,依赖组,生理盐水组,纳洛酮组和抑制剂组。建立吗啡依赖与戒断并进行行为学观测评分后取材相关部位,连续冠状冰冻切片,神经元型一氧化氮合酶(neuron nitric oxide synthase,nNOS)免疫组织化学标记。计数各组动物相同层面脑片和脊髓背角nNOS标记细胞的表达情况。结果:戒断组大鼠,戒断症状及总评分较对照组和依赖组大鼠差异显著(P<0.01);给NOS抑制剂组戒断症状评分较戒断组明显降低(P<0.05)。生理盐水组和纳洛酮组于中缝背核相应区域计数到部分nNOS标记神经元,但两但间无显著性差异(P<0.05);依赖组与戒断组大鼠nNOS标记神经元计数明显增加(P<0.05);而NOS抑制剂组大鼠nNOS标记神经元数量较戒断组明显减少(P<0.05)。脊髓背角切片显示,依赖组与戒断组大鼠nNOS标记神经元计数均较各对照组明显增加(P<0.05);而NOS抑制剂组大鼠nNOS标记神经元数量较戒断组减少显著(P<0.05),其变化与中缝背核结果一致。结论:脑内中缝背核可能参与通过一氧化氮(nitric oxide,NO)信号通路介导的脊髓对吗啡依赖和戒断形成的调节。     

Spinal mediators that may contribute selectively to antinociceptive tolerance but not other effects of morphine as revealed by deletion of GluR5

Several groups maintain that morphine tolerance and dependence correlate with increased activity of protein kinases ERK1/2 and P38 MAPK and PKC as well as elevated levels of the neuropeptides dynorphin (DYN), substance P (sP), and calcitonin gene-related peptide (CGRP) in spinal cord dorsal horn (SCDH). They demonstrate that tolerance and dependence can be prevented, and sometimes reversed, by constitutive genetic deletion or pharmacological inhibition of these factors. Recently, we showed that mice with a constitutive deletion of the GluR5 subunit of kainate receptors (GluR5 KO) are not different from wild type (WT) littermates with respect to baseline nociceptive thresholds as well as acute morphine antinociception, morphine physical dependence and conditioned place preference. However, unlike WT, GluR5 KO mice do not develop antinociceptive tolerance following systemic morphine administration. In this report, we examined levels of these mediators in SCDH of WT and GluR5 KO mice following subcutaneous implantation of placebo or morphine pellets. Surprisingly, spinal DYN and CGRP, along with phosphorylated ERK2 (pERK2), P38 (pP38) and PKCgamma (pPKCγ) are elevated by deletion of GluR5. Additionally, chronic systemic morphine administration increased spinal pERK2, pP38 and pPKCγ levels in both tolerant WT and non-tolerant GluR5 KO mice. In contrast, while morphine increased spinal DYN and CGRP in WT mice, DYN remained unchanged and CGRP was reduced in GluR5 KO mice. These observations suggest that spinal ERK2, P38 and PKCγ are likely involved in multiple adaptive responses following systemic morphine administration, whereas DYN and CGRP may contribute selectively to the development of antinociceptive tolerance.