环氧酶2介导鞘内注射血小板活化因子诱发的触觉痛敏和热痛敏

目的：研究环氧酶（COX）及前列腺素（PGs）在鞘内注射血小板活化因子（PAF）诱导大鼠痛敏机制中的作用。方法：鞘内置管的雄性SD大鼠60只,随机分为脊液组（注射人工脑脊液）,PAF组（鞘内注射PAF）,盐水组（注射盐水）,SC-560组（注射PAF及SC-560）,NS-398组（注射PAF及NS-398）,吲哚美辛组（注射PAF及吲哚美辛）各10只。各组注射前及鞘内给药后均检测大鼠机械缩爪阈值和热缩爪潜伏期,每15min测1次,5h后RT-PCR和放射免疫分析检测腰段脊髓COX-1,COX-2及COX-3的表达和PGE2的含量。结果：鞘内注射PAF后的PAF组迅速诱发大鼠触觉痛敏和热痛敏,并诱导脊髓COX-2表达增强和PGE2含量升高;与PAF组比较,NS-398组和吲哚美辛组能明显抑制PAF诱发的痛敏和脊髓PGE2含量升高。结论：鞘内注射PAF可诱发大鼠触觉异常痛敏和热痛敏;脊髓COX-2的激活和表达增强以及PGE2的产生可能参与其机制。     

外周N-甲基-D-天门冬氨酸受体在福尔马林外周注射引起长时程痛敏中的作用

目的 观察外周N-甲基-D-天门冬氨酸(NMDA)受体对福尔马林外周注射所致长时程痛敏的作用.方法 雄性SD大鼠脚掌注射福尔马林,之前注射或不注射MK-801.免疫组化方法检测脊髓背角小胶质细胞OX-42表达,测定热辐射痛行为.结果 注射MK-801侧脊髓背角Ⅰ、Ⅱ层小胶质细胞OX-42阳性表达水平较对侧(仅注入福尔马林侧)明显降低.单独注入福尔马林后第3天发生热痛敏,第7天达高峰,第10天仍未完全恢复至正常值;外周应用MK-801后,热痛敏反射潜伏期延长.结论 NM-DA受体参与长时程痛敏的产生和维持.     

代谢性谷氨酸受体亚型5对骨癌痛小鼠痛行为及脊髓水平炎症反应的影响

目的:探讨鞘内注射mGluR5拮抗剂MTEP对骨癌痛小鼠热痛觉过敏及脊髓水平IL-1β、IL-6、TNF-α表达的影响。方法:C3H/HeNCrlVr雄性小鼠60只,随机分为:①MTEP+Tumor组:癌痛组从第14 d开始鞘内注射MTEP150nmol,qd,共7次;②生理盐水+Tumor组:以等体积的生理盐水代替MTEP;③MTEP+Sham组:用等剂量MTEP给予假手术组;④生理盐水+Sham组:用等体积的生理盐水给予假手术组;⑤正常组:正常饲养21d。应用热辐射刺激仪测定缩足潜伏期(PWL)。应用Real-time PCR技术检测mRNA表达。结果:各组小鼠术前基础PWL差异无统计学意义(P>0.05)。术后14 d,与正常组相比,骨癌痛组PWL明显降低(P<0.05),假手术组PWL差异无统计学意义(P>0.05)。术后21 d,和正常组相比,MTEP+Sham组、生理盐水+Sham组PWL和脊髓IL-1β、IL-6、TNF-α表达差异均无统计学意义(P>0.05);生理盐水+Tumor组PWL(6.18±1.29)s明显低于正常组(15.91±1.65)s(P<0.05),脊髓IL-1β、IL-6、TNF-α表达则高于正常组;MTEP+Tumor组(9.39±1.94)s PWL高于生理盐水+Tumor组,脊髓IL-1β、IL-6、TNF-α表达则低于生理盐水+Tumor组(P<0.05)。结论:鞘内注射mGluR5拮抗剂抑制脊髓水平表达释放炎症因子IL-1β、IL-6和TNF-α可能是其抗癌痛作用机制之一。     

前炎性细胞因子白细胞介素1β和肿瘤坏死因子在保留神经损伤所致机械性痛敏发生中的不同作用

背景：脊髓胶质细胞的激活参与了保留神经损伤(spared nerve injury.SNI)诱致的机械性痛敏的发生。脊髓胶质细胞激活释放的前炎性细胞因子在这个过程中是否扮演了重要的角色。目的：探讨了白细胞介素1(interleukin-1，IL-1)和肿瘤坏死因子(tumor necrosis factor，TNF)在SNI诱致的机械性痛敏中的不同作用。设计：随机对照试验。地点和对象：解放军第四军医大学实验动物中心提供的40只健康成年雄性Sprague-Dawlev大鼠.干预：实验分两组：实验组：鞘内分别给予白细胞介素-1受体拮抗剂(interleukin-1 receptor antagonist，IL-1ra)．肿瘤坏死因子抗血清(tumor necrosis factor anti-serum，anti-TNF)和同时给予IL-1ra和anti-TNF。对照组：鞘内给予相应的溶媒。术前和术后分别检测大鼠后爪机械性刺激阈值。主要观察指标：大鼠检测机械性刺激缩足阈值。结果：①鞘内给予IL-1ra可以对大鼠单侧后爪内侧和外侧在术后1周内产生一个明显的对机械性痛敏的抑制，而anti-TNF没有这样的作用，②同时鞘内给予IL-1ra和anti-TNF可以产生更加明显的机械性痛敏抑制，抑制作用可以长达术后6周。结论：脊髓胶质细胞激活释放的前炎性细胞因子IL-1和TNF在SNI诱致的机械性痛敏中扮演了重要的角色。IL-1和TNF在SNI诱致的机械性痛敏中的作用不同。     

鞘内注射银杏内酯B对神经病理痛大鼠痛阈及脊髓c-fos表达的影响

目的:观察鞘内注射银杏内酯B(BN52021)对SNI神经病理痛大鼠痛阈及脊髓c-fos表达的影响,探讨脊髓血小板活化因子及其受体参与痛觉信号调节的可能机制.方法:鞘内置管后的SD大鼠24只随机等分为4组:假手术组(sham组),SNI组,SNI+DMSO对照组和SNI+BN52021组,建立SNI疼痛模型,手术后1,3,5,7,10和14d鞘内给药并测痛阈,第14d取大鼠腰段脊髓,冰冻切片,免疫组织化学染色检测Fos免疫阳性细胞.结果:SNI神经损伤大鼠机械缩爪阈明显降低(P<0.05),同侧脊髓背角浅层内Fos阳性神经元明显增多(P<0.05);鞘内应用银杏内酯B明显减少脊髓背角神经元c-fos的表达,同时伴有大鼠机械异常痛敏的减轻,各组大鼠辐射热缩爪潜伏期无明显差异.结论:鞘内注射银杏内酯B可减轻SNI大鼠机械异常痛敏,抑制神经损伤后脊髓背角c-fos的表达.     

前炎性细胞因子白细胞介素1β和肿瘤坏死因子在保留神经损伤所致机械性痛敏发生中的不同作用

背景脊髓胶质细胞的激活参与了保留神经损伤(spared nerve injury,SNI)诱致的机械性痛敏的发生.脊髓胶质细胞激活释放的前炎性细胞因子在这个过程中是否扮演了重要的角色.目的探讨了白细胞介素1(interleukin-1,IL-1)和肿瘤坏死因子(tumor necrosis factor,TNF)在SNI诱致的机械性痛敏中的不同作用.设计随机对照试验.地点和对象解放军第四军医大学实验动物中心提供的40只健康成年雄性Sprague-Dawley大鼠.干预实验分两组实验组鞘内分别给予白细胞介素-1受体拮抗剂(interleukin-1 receptor antagonist,IL-1ra),肿瘤坏死因子抗血清(tumornecrosisfactor anti-serum,anti-TNF)和同时给予IL-1ra和anti-TNF.对照组鞘内给予相应的溶媒.术前和术后分别检测大鼠后爪机械性刺激阈值.主要观察指标大鼠检测机械性刺激缩足阈值.结果①鞘内给予IL-1ra可以对大鼠单侧后爪内侧和外侧在术后1周内产生一个明显的对机械性痛敏的抑制,而anti-TNF没有这样的作用.②同时鞘内给予IL-1ra和anti-TNF可以产生更加明显的机械性痛敏抑制,抑制作用可以长达术后6周.结论脊髓胶质细胞激活释放的前炎性细胞因子IL-1和TNF在SNI诱致的机械性痛敏中扮演了重要的角色.IL-1和TNF在SNI诱致的机械性痛敏中的作用不同.     

鞘内注射氯胺酮对镜像痛大鼠热痛敏的影响及可能机制

目的：探讨氯胺酮鞘内注射对镜像痛大鼠热痛敏的影响及可能机制.方法：30只雄性SD大鼠建立大鼠坐骨神经镜像痛模型,随机分为3组（n=10）：Ⅰ组鞘内注射生理盐水,Ⅱ组鞘内注射氯胺酮25 μg,Ⅲ组鞘内注射氯胺酮50 μg,分别测定鞘内给药前（T1）、给药后2 h（T2）、4 h（T3）、6 h（T4）的大鼠热缩足反射潜伏期（TWL）、运动功能.每组大鼠在给药6h后处死,取出腰段脊髓背角,石蜡切片,采用免疫组化检测单核细胞趋化蛋白-1（MCP-1）的表达.结果：鞘内给药后,Ⅱ组、Ⅲ组在各时间点与Ⅰ组及给药前相比,两侧TWL明显延长,比较有显著差异（P＜0.01）.Ⅰ组MCP-1平均积分光密度值（IOD）表达明显高于Ⅱ组和Ⅲ组（P＜0.01）,鞘内注射氯胺酮后大鼠运动功能不受明显影响.结论：鞘内注射氯胺酮可抑制镜像痛大鼠的热痛觉过敏,该作用可能与抑制脊髓背角的MCP-1表达有关.     

鞘内注射氟柠檬酸对福尔马林致痛大鼠脊髓c-Fos和GFAP、OX42表达变化的影响

目的:通过鞘内注射氟柠檬酸(fluorocitrate,FCA)抑制脊髓胶质细胞功能后,对比观察足底注射福尔马林(formalin)模型大鼠热痛敏行为及脊髓后角c-Fos和胶质纤维酸性蛋白(glial fibrillaryacidic protein,GFAP)、OX42表达的变化,以探讨脊髓胶质细胞在痛觉过敏中的作用。方法:雄性SD大鼠40只,随机分为空白对照组(Blank组)、足底皮下注射生理盐水组(NS组)、足底皮下注射formalin组(F组)、鞘内注射生理盐水后皮下注射formalin组(NS+F组)、鞘内注射FCA后皮下注射formalin组(FCA+F组),每组8只。采用向大鼠右侧后肢足底皮下注射2.5%formalin(120μl)造成动物的伤害性刺激模型。造模后先测量记录各组大鼠的热刺激潜伏期(pawwithdrawalthermal latency,PWTL),然后灌注取脊髓组织切片进行抗c-Fos、抗GFAP和抗OX42标记的免疫组织化学染色。结果:足底注射formalin后,大鼠PWTL明显缩短,自发缩足反射次数明显增加,且在脊髓后角浅层有大量c-Fos、GFAP和OX42免疫产物表达;与blank照组和NS组比较,差异有统计学意义。而预先鞘内注射FCA再注射formalin后,大鼠PWTL明显延长,自发缩足反射次数明显减少(P<0.01),同时c-Fos、GFAP和OX42免疫产物表达亦明显降低(P<0.01),与F组和NS+F组比较差异有统计学意义。结论:抑制脊髓胶质细胞功能可明显减轻大鼠足底皮下注射formalin的痛觉过敏作用,脊髓胶质细胞主动参与了疼痛信息的调节作用。     

抑制脊髓内NF-κB/p65对骨性关节炎后期产生的痛觉过敏的影响

目的:研究核转录因子kappa B/p65(nuclear factor-kappa B/p65,NF-κB/p65)在骨性关节炎(osteoarthritis,OA)导致的痛觉敏感中的作用。方法:6~8周SD雌性大鼠,体重250~300 g,随机分为生理盐水对照组、骨性关节炎模型组和鞘内给予NF-κB阻滞剂吡咯烷二硫代氨基甲酸酯(pyrrolidine dithiocarbamate,PDTC)模型组(n=30),并于造模前1天和造模后7、14、21、28天测定大鼠的机械痛阈,测定完成后处死大鼠,采用Western blotting的方法检测NF-κB/p65在各组大鼠脊髓内的表达情况。结果:模型组大鼠脊髓内NF-κB/p65的表达量较对照组明显增加,大鼠机械痛阈的变化趋势与其相一致;与模型组相比,在大鼠骨性关节炎后期鞘内注射PDTC能够明显改善机械痛敏。结论:NF-κB/p65在骨性关节炎大鼠脊髓内表达量显著增加,抑制脊髓内NF-κB/p65的表达能明显改善骨性关节炎大鼠的机械痛敏。     

cAMP-PKA信号通路介导大鼠骨癌痛的产生和维持

目的:探讨c AMP-PKA信号通路在大鼠骨癌痛发生发展中的作用。方法:雌性SD大鼠52只,随机分为5组:正常组(n=8),假手术组(n=8),骨癌痛组(n=12),骨癌痛+生理盐水组(n=8)和骨癌痛+PKA抑制剂组(n=16)。各组于造模前3天、1天以及造模后1、3、5、7、10、14天分别测定热缩足阈值和机械缩足阈值。PKA抑制剂Rp-c AMPS(1 mmol/20μl)分别于造模后早期(3、4、5天)和造模后后期(7、8、9天)经鞘内注射(每天1次)。采用酶联免疫吸附法(ELISA)检测大鼠背根神经节(DRG)和脊髓中c AMP的浓度和PKA的活性。结果:造模后,大鼠DRG和脊髓中c AMP的浓度显著增高,PKA的活性明显增强,与假手术组相比,差异有统计学意义(P<0.01)。早期和后期给予PKA抑制剂Rp-c AMPS治疗,均能显著延迟或抑制骨癌诱发的热痛敏和机械痛敏(P<0.01)。结论:骨癌显著增强DRG和脊髓中c AMP-PKA信号通路的活性,该信号通路的异常活动在骨癌痛的产生和维持中起着重要作用,抑制该信号通路的激活能有效减轻骨癌痛。     

Development of tactile allodynia and thermal hyperalgesia by intrathecally administered platelet-activating factor in mice

Platelet-activating factor (PAF) is a potent inflammatory lipid mediator in peripheral tissues. However, its role in mediation of nociception in central nervous system is unknown. In the present study, whether PAF plays some role in pain transduction in the spinal cord was studied in mice. Intrathecal injection of PAF induced tactile pain, tactile allodynia at as low as 10 fg to 1 pg with a peak response at 100 fg, while lyso-PAF was without effect in the range of doses. Tactile allodynia induced by PAF was blocked by a PAF receptor antagonists, TCV-309, WEB 2086 and BN 50739. The expression of PAF receptor mRNA by RT-PCR was observed in DRG and spinal cord in mice. ATP P2X receptor antagonists, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid and 2',3'-O-(2,4,6-trinitrophenyl)adenosine 5-triphosphate, NMDA receptor antagonist, MK 801 and nitric oxide synthetase inhibitor, 7-nitroindazole blocked the PAF-induced tactile allodynia. PAF-induced tactile allodynia and thermal hyperalgesia disappeared in neonatally capsaicin-treated adult mice, while tactile allodynia but not thermal hyperalgesia induced by intrathecally injected alpha,beta-methylene ATP, a P2X receptor agonist, was capsaicin-insensitive. The present study demonstrated that PAF is a potent inducer of tactile allodynia and thermal hyperalgesia at the level of the spinal cord. PAF-evoked tactile allodynia is suggested to be mediated by ATP and the following NMDA and NO cascade through capsaicin-sensitive fiber, different from exogenously injected alpha,beta-methylene ATP which is insensitive to capsaicin treatment.     

Glycinergic mediation of tactile allodynia induced by platelet-activating factor (PAF) through glutamate-NO-cyclic GMP signalling in spinal cord in mice

Our previous study showed that intrathecal (i.t.) injection of platelet-activating factor (PAF) induced tactile allodynia, suggesting that spinal PAF is a mediator of neuropathic pain. The present study further examined the spinal molecules participating in PAF-induced tactile allodynia in mice. I.t. injection of L-arginine, NO donor (5-amino-3-morpholinyl-1,2,3-oxadiazolium (SIN-1) or 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (NOC-18)) or cGMP analog (8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate; pCPT-cGMP) induced tactile allodynia. PAF- and glutamate- but not SIN-1- or pCPT-cGMP-induced tactile allodynia was blocked by an NO synthase inhibitor. NO scavengers and guanylate cyclase inhibitors protected mice against the induction of allodynia by PAF, glutamate and SIN-1, but not by pCPT-cGMP. cGMP-dependent protein kinase (PKG) inhibitors blocked the allodynia induced by PAF, glutamate, SIN-1 and pCPT-cGMP. To identify signalling molecules through which PKG induces allodynia, glycine receptor alpha3 (GlyR alpha3) was knocked down by spinal transfection of siRNA for GlyR alpha3. A significant reduction of GlyR alpha3 expression in the spinal superficial layers of mice treated with GlyR alpha3 siRNA was confirmed by immunohistochemical and Western blotting analyses. Functional targeting of GlyR alpha3 was suggested by the loss of PGE(2)-induced thermal hyperalgesia and the enhancement of allodynia induced by bicuculline, a GABA(A) receptor antagonist in mice after GlyR alpha3 siRNA treatment. pCPT-cGMP, PAF, glutamate and SIN-1 all failed to induce allodynia after the knockdown of GlyR alpha3. These results suggest that the glutamate-NO-cGMP-PKG pathway in the spinal cord may be involved in the mechanism of PAF-induced tactile allodynia, and GlyR alpha3 could be a target molecule through which PKG induces allodynia.     

Extraterritorial neuropathic pain correlates with multisegmental elevation of spinal dynorphin in nerve-injured rats

Neuropathic pain is often associated with the appearance of pain in regions not related to the injured nerve. One mechanism that may underlie neuropathic pain is abnormal, spontaneous afferent drive which may contribute to NMDA-mediated central sensitization by the actions of glutamate and by the non-opioid actions of spinal dynorphin. In the present study, injuries to lumbar or sacral spinal nerves elicited elevation in spinal dynorphin content which correlated temporally and spatially with signs of neuropathic pain. The increase in spinal dynorphin content was coincident with the onset of tactile allodynia and thermal hyperalgesia. Injury to the lumbar (L(5)/L(6)) spinal nerves produced elevated spinal dynorphin content in the ipsilateral dorsal spinal quadrant at the L(5) and L(6) spinal segments and in the segments immediately adjacent. Lumbar nerve injury elicited ipsilateral tactile allodynia and thermal hyperalgesia of the hindpaw. In contrast, S(2) spinal nerve ligation elicited elevated dynorphin content in sacral spinal segments and bilaterally in the caudal lumbar spinal cord. The behavioral consequences of S(2) spinal nerve ligation were also bilateral, with tactile allodynia and thermal hyperalgesia seen in both hindpaws. Application of lidocaine to the site of S(2) ligation blocked thermal hyperalgesia and tactile allodynia of the hindpaws suggesting that afferent drive was critical to maintenance of the pain state. Spinal injection of antiserum to dynorphin A((1-17)) and of MK-801 both blocked thermal hyperalgesia, but not tactile allodynia, of the hindpaw after S(2) ligation. These data suggest that the elevated spinal dynorphin content consequent to peripheral nerve injury may drive sensitization of the spinal cord, in part through dynorphin acting directly or indirectly on the NMDA receptor complex. Furthermore, extrasegmental increases in spinal dynorphin content may partly underlie the development of extraterritorial neuropathic pain.     

TRAF6 upregulation in spinal astrocytes maintains neuropathic pain by integrating TNF-α and IL-1β signaling

The proinflammatory cytokines tumor necrosis factor (TNF) α and interleukin (IL) 1β have been strongly implicated in the pathogenesis of neuropathic pain, but the intracellular signaling of these cytokines in glial cells is not fully understood. TNF receptor-associated factor 6 (TRAF6) plays a key role in signal transduction in the TNF receptor superfamily and the IL-1 receptor superfamily. In this study, we investigated the role of TRAF6 in neuropathic pain in mice after spinal nerve ligation (SNL). SNL induced persistent TRAF6 upregulation in the spinal cord. Interestingly, TRAF6 was mainly colocalized with the astrocytic marker glial fibrillary acidic protein on SNL day 10 and partially expressed in microglia on SNL day 3. In cultured astrocytes, TRAF6 was upregulated after exposure to TNF-α or IL-1β. TNF-α or IL-1β also increased CCL2 expression, which was suppressed by both siRNA and shRNA targeting TRAF6. TRAF6 siRNA treatment also inhibited the phosphorylation of c-Jun N-terminal kinase (JNK) in astrocytes induced by TNF-α or IL-1β. JNK inhibitor D-NKI-1 dose-dependently decreased IL-1β–induced CCL2 expression. Moreover, spinal injection of TRAF6 siRNA decreased intrathecal TNF-α– or IL-1β–induced allodynia and hyperalgesia. Spinal TRAF6 inhibition via TRAF6 siRNA, shRNA lentivirus, or antisense oligodeoxynucleotides partially reversed SNL-induced neuropathic pain and spinal CCL2 expression. Finally, intrathecal injection of TNF-α–activated astrocytes induced mechanical allodynia, which was attenuated by pretreatment of astrocytes with TRAF6 siRNA. Taken together, the results suggest that TRAF6, upregulated in spinal cord astrocytes in the late phase after nerve injury, maintains neuropathic pain by integrating TNF-α and IL-1β signaling and activating the JNK/CCL2 pathway in astrocytes.     

鞘内注射醋酸泼尼松龙对背根节压迫大鼠的镇痛作用及其机制的探讨

目的：研究鞘内注射醋酸泼尼松龙（PA）对背根节慢性压迫（CCD）大鼠痛阈和脊髓背角nNOS表达的影响及其镇痛机制.方法：鞘内置管手术成功雄性SD大鼠100只,随机分为7天组和15天组两组,每组再随机分为假手术（Sham）组,人工脑脊液（ACSF）组,鞘内注射PA 0.5、1.0、2.0mg/kg组（n=10）.分别于CCD术前（0）及术后1,3,5,7,9,11,13,15天采用von Frey纤毛机械刺激法和热辐射刺激法评定大鼠机械刺激缩足反射阈值（PWMT）和热刺激缩足反射潜伏期（PWTL）;术后第7天和第15天运用免疫组织化学法和Western blot法观察脊髓背角nNOS表达的变化.结果：与术前基础阈值相比,除假手术组外,CCD术后各组的PWMT和PWTL均出现明显地下降（P＜0.01）,各组间无明显差异（P＞0.05）.术后第5天开始,PA 2.0 mg/kg组与ACSF组相比,PWMT和PWTL显著升高（P＜0.05）.免疫组织化学方面,背根节压迫后第7和第15天,ACSF组与PA 0.5、1.0 mg/kg组脊髓背角阳性神经元数量明显增多,三组之间比较无显著差异（P＞0.05）.PA 2.0 mg/kg组和ACSF相比,第7天和第15天均显著降低（P＜0.01）.脊髓背角Westernblot检测与免疫组织化学的结果基本一致.结论：鞘内注射PA有镇痛作用,其作用机制可能与抑制脊髓背角nNOS的表达有关.     

Calcium channel alpha-2-delta-1 protein upregulation in dorsal spinal cord mediates spinal cord injury-induced neuropathic pain states

Spinal cord injury (SCI) commonly results in the development of neuropathic pain, which can dramatically impair the quality of life for SCI patients. SCI-induced neuropathic pain can be manifested as both tactile allodynia (a painful sensation to a non-noxious stimulus) and hyperalgesia (an enhanced sensation to a painful stimulus). The mechanisms underlying these pain states are poorly understood. Clinical studies have shown that gabapentin, a drug that binds to the voltage-gated calcium channel alpha-2-delta-1 subunit (Ca_vα2δ-1) proteins is effective in the management of SCI-induced neuropathic pain. Accordingly, we hypothesized that tactile allodynia post SCI is mediated by an upregulation of Ca_vα2δ-1 in dorsal spinal cord. To test this hypothesis, we examined whether SCI-induced dysregulation of spinal Ca_vα2δ-1 plays a contributory role in below-level allodynia development in a rat spinal T9 contusion injury model. We found that Ca_vα2δ-1 expression levels were significantly increased in L4-6 dorsal, but not ventral, spinal cord of SCI rats that correlated with tactile allodynia development in the hind paw plantar surface. Furthermore, both intrathecal gabapentin treatment and blocking SCI-induced Ca_vα2δ-1 protein upregulation by intrathecal Ca_vα2δ-1 antisense oligodeoxynucleotides could reverse tactile allodynia in SCI rats. These findings support that SCI-induced Ca_vα2δ-1 upregulation in spinal dorsal horn is a key component in mediating below-level neuropathic pain states, and selectively targeting this pathway may provide effective pain relief for SCI patients.     

Spinal gap junctions: potential involvement in pain facilitation.

Glia are now recognized as important contributors in pathological pain creation and maintenance. Spinal cord glia exhibit extensive gap junctional connectivity, raising the possibility that glia are involved in the contralateral spread of excitation resulting in mirror image pain. In the present experiments, the gap junction decoupler carbenoxolone was administered intrathecally after induction of neuropathic pain in response to sciatic nerve inflammation (sciatic inflammatory neuropathy) or partial nerve injury (chronic constriction injury). In both neuropathic pain models, a low dose of carbenoxolone reversed mirror image mechanical allodynia, while leaving ipsilateral mechanical allodynia unaffected. Ipsilateral thermal hyperalgesia was briefly attenuated. Critically, blockade of mechanical allodynia and thermal hyperalgesia was not observed in response to intrathecal glycyrrhizic acid, a compound similar to carbenoxolone in all respects but it does not decouple gap junctions. Thus, blockade of mechanical allodynia and thermal hyperalgesia by carbenoxolone does appear to reflect an effect on gap junctions. Examination of carbenoxolone's effects on intrathecal human immunodeficiency virus type 1 gp120 showed that blockade of pain facilitation might result, at least in part, via suppression of interleukin-1 and, in turn, interleukin-6. These data provide the first suggestion that spread of excitation via gap junctions might contribute importantly to inflammatory and traumatic neuropathic pain. PERSPECTIVE: The current studies provide evidence for involvement of gap junctions in spinal cord pain facilitation. Intrathecal carbenoxolone, a gap junction decoupler, reversed neuropathy-induced mirror image pain and intrathecal gp120-induced allodynia. In addition, it decreased gp120-induced proinflammatory cytokines. This suggests gap junction activation might lead to proinflammatory cytokine release by distantly activated glia.     

Relative potency of epidural to intrathecal clonidine differs between acute thermal pain and capsaicin-induced allodynia

Clonidine is approved in the US for epidural administration in the treatment of intractable neuropathic cancer pain, but is also administered intrathecally for this indication and both epidurally and intrathecally in the treatment of acute, postoperative pain. The purpose of the current study was to estimate the relative potency of clonidine by epidural and intrathecal routes in the treatment of capsaicin-induced hyperalgesia and allodynia as a model of central hypersensitivity and of noxious heat as a model of acute pain. Twenty-four healthy volunteers were randomized to receive either intrathecal clonidine (75, 150, or 300 micrograms) or epidural clonidine (150, 300, or 600 micrograms) and rated pain from a Peltier-controlled thermode at a lumbar, thoracic, and cervical dermatomal site before and after drug administration. In addition, they rated pain from intradermal capsaicin injections at a lumbar dermatome before and 60 min after clonidine injection and described areas of hyperalgesia and allodynia to mechanical stimuli. Clonidine's effect differed with route of administration and modality of sensory testing. For acute thermal pain, intrathecal clonidine produced a dose-dependent analgesia with a lumbar>thoracic>cervical gradient, whereas only one dose of epidural clonidine reduced thermal pain and this was at the thoracic testing site. In contrast, the potency of clonidine to reduce capsaicin-induced allodynia was similar between the two routes of injection, and for hyperalgesia, clonidine was only slightly more potent after intrathecal than epidural injection. These data support clinical studies from non-comparative trials and suggest there is a >6-fold potency ratio of intrathecal:epidural administration of clonidine for acute pain, but a <2-fold potency ratio for these routes for mechanical hypersensitivity.     

LipoxinA4 induced antinociception and decreased expression of NF-κB and pro-inflammatory cytokines after chronic dorsal root ganglia compression in rats

Inflammatory and immune responses following nerve injury have been shown to play an important role in neuropathic pain. Lipoxins are endogenous lipoxygenase-derived eicosanoids performing protective roles in a range of pathophysiologic processes. Here, we examined the effects of intrathecal lipoxinA4 (LXA4) on NF-κB activation and pro-inflammatory cytokine (TNF-α, IL-1β and IL-6) expression in dorsal root ganglia (DRG) following chronic compression of DRG (CCD), a model of neuropathic pain. Daily intrathecal injection of vehicle or LXA4 (10 ng or 100 ng) was performed for three successive days post-CCD. CCD induced both mechanical allodynia and thermal hyperalgesia, and increased the expression of TNF-α, IL-1β, IL-6 and NF-κB. Intrathecal injection of LXA4 prevented the development of neuropathic pain and inhibited NF-κB activation and pro-inflammatory cytokine upregulation in a dose-dependent manner. In this study, we have shown the strong protective effect of intrathecal LXA4 on the development of nociceptive behaviors induced by CCD and that these effects might be associated with its anti-inflammatory and pro-resolution properties.