β内酰胺类药物对吗啡耐受的影响

新近发现阿片类药物的长期应用必然导致胶质细胞的激活，而伴随激活所释放的细胞因子能放大神经元对谷氨酸盐的反应，继而造成阿片类耐受及戒断性痛敏的发生。2005年NATURE的一篇章证明，某些β-内酰胺抗生素（头孢曲松），能抑制谷氨酸引起的兴奋性传递，推迟ALS的发生和发展，提高存活率。也有学研究发现，在吗啡依赖的动物模型中，脊髓及部分脑区谷氨酸转运体GLT-1的表达下凋。提示，吗啡慢性处理可能抑制GLT-1的蛋白合成。而β-内酰胺如是谷氨酸转运体的激动剂，促进谷氨酸的清除，将为预防吗啡耐受及缓解神经源性痛的新药开发提供了一条新的思路。目的：考察β内酰胺类药物对吗啡耐受模型的影响。方法：用小鼠热板法和大鼠热辐射甩尾法测痛，实验分组（n=6）分别为盐水对照组、吗啡对照组、吗啡＋药物不同剂量组，皮下给药，每天三次，比较给药前后动物痛阈的变化。     

GLT-1激动剂头孢曲松钠对慢性神经病理性痛的影响

目的：探讨头孢曲松钠（Ceftriaxone,Cef）对慢性神经病理性痛过敏及GLT-1表达的影响。方法雄性SD大鼠90只,随机分为Sham组、CCI 14 d组、Cef预防组、 Cef治疗组,后2组设腹腔注射NS组为对照,在不同时间点测定热缩足反射潜伏期;另设CCI 1 d、4 d、7 d组。应用免疫组化观察不同时间点脊髓后角GLT-1表达的变化。结果CCI诱导大鼠产生了热痛敏,腹腔注射NS对CCI诱导的热痛敏无影响。 Cef预防组大鼠CCI侧后肢热缩足反射潜伏期于CCI后第5天、第7天明显延长（ P ＜0°．05）;Cef 治疗组大鼠CCI侧后肢热缩足反射潜伏期在术后第11天、第14天明显延长（ P ＜0．05）。免疫组化检测发现,Cef预防组和Cef治疗组分别抑制和逆转了GLT-1在CCI后期表达的降低。结论 Cef可通过上调GLT-1的表达对慢性神经病理性痛起到预防和治疗作用。     

头孢曲松钠对大鼠局灶性脑缺血的神经保护作用及其机制

目的：探讨头孢曲松钠对局灶性脑缺血大鼠的神经保护作用及其机制。方法：将Sprague-Dawley（SD）大鼠随机分为头孢曲松钠预处理组、单纯缺血组和假手术组。头孢曲松钠预处理组于术前7 d腹腔注射头孢曲松钠200 mg?kg-1?d-1,然后制备大鼠局灶性脑缺血模型,缺血后3,6,12,24和48 h进行神经行为学评分,应用免疫组化法测定大鼠海马胶质细胞性谷氨酸转运体（glutamate transporter-1,GLT-1）水平。结果：局灶性脑缺血3 h后,脑组织GLT-1蛋白水平显著降低（P<0.01）,并且随着缺血时间的延长,GLT-1蛋白水平呈下降趋势,脑缺血后48 h降至最低（P<0.01）。与单纯缺血组比较,头孢曲松钠预处理组大鼠的神经行为学评分均显著降低（P<0.05）,海马GLT-1蛋白的表达显著增加（P<0.01）。结论：头孢曲松钠对局灶性脑缺血大鼠具有神经保护作用,其机制可能与增加GLT-1的表达、降低谷氨酸的兴奋性毒性作用有关。     

头孢曲松钠对大鼠局灶性脑缺血的神经保护作用及其机制

目的：探讨头孢曲松钠对局灶性脑缺血大鼠的神经保护作用及其机制。方法：将Sprague-Dawley（SD）大鼠随机分为头孢曲松钠预处理组、单纯缺血组和假手术组。头孢曲松钠预处理组于术前7 d腹腔注射头孢曲松钠200 mg?kg-1?d-1,然后制备大鼠局灶性脑缺血模型,缺血后3,6,12,24和48 h进行神经行为学评分,应用免疫组化法测定大鼠海马胶质细胞性谷氨酸转运体（glutamate transporter-1,GLT-1）水平。结果：局灶性脑缺血3 h后,脑组织GLT-1蛋白水平显著降低（P<0.01）,并且随着缺血时间的延长,GLT-1蛋白水平呈下降趋势,脑缺血后48 h降至最低（P<0.01）。与单纯缺血组比较,头孢曲松钠预处理组大鼠的神经行为学评分均显著降低（P<0.05）,海马GLT-1蛋白的表达显著增加（P<0.01）。结论：头孢曲松钠对局灶性脑缺血大鼠具有神经保护作用,其机制可能与增加GLT-1的表达、降低谷氨酸的兴奋性毒性作用有关。     

头孢曲松钠对大鼠局灶性脑缺血的神经保护作用及其机制

目的：探讨头孢曲松钠对局灶性脑缺血大鼠的神经保护作用及其机制。方法：将Sprague-Dawley（SD）大鼠随机分为头孢曲松钠预处理组、单纯缺血组和假手术组。头孢曲松钠预处理组于术前7 d腹腔注射头孢曲松钠200 mg?kg-1?d-1，然后制备大鼠局灶性脑缺血模型，缺血后3,6,12,24和48 h进行神经行为学评分，应用免疫组化法测定大鼠海马胶质细胞性谷氨酸转运体（glutamate transporter-1，GLT-1）水平。结果：局灶性脑缺血3 h后，脑组织GLT-1蛋白水平显著降低（P<0.01），并且随着缺血时间的延长，GLT-1蛋白水平呈下降趋势，脑缺血后48 h降至最低（P<0.01）。与单纯缺血组比较，头孢曲松钠预处理组大鼠的神经行为学评分均显著降低（P<0.05），海马GLT-1蛋白的表达显著增加（P<0.01）。结论：头孢曲松钠对局灶性脑缺血大鼠具有神经保护作用，其机制可能与增加GLT-1的表达、降低谷氨酸的兴奋性毒性作用有关。     

头孢曲松钠对大鼠局灶性脑缺血的神经保护作用及其机制

目的：探讨头孢曲松钠对局灶性脑缺血大鼠的神经保护作用及其机制。方法：将Sprague-Dawley（SD）大鼠随机分为头孢曲松钠预处理组、单纯缺血组和假手术组。头孢曲松钠预处理组于术前7 d腹腔注射头孢曲松钠200 mg?kg-1?d-1，然后制备大鼠局灶性脑缺血模型，缺血后3,6,12,24和48 h进行神经行为学评分，应用免疫组化法测定大鼠海马胶质细胞性谷氨酸转运体（glutamate transporter-1，GLT-1）水平。结果：局灶性脑缺血3 h后，脑组织GLT-1蛋白水平显著降低（P<0.01），并且随着缺血时间的延长，GLT-1蛋白水平呈下降趋势，脑缺血后48 h降至最低（P<0.01）。与单纯缺血组比较，头孢曲松钠预处理组大鼠的神经行为学评分均显著降低（P<0.05），海马GLT-1蛋白的表达显著增加（P<0.01）。结论：头孢曲松钠对局灶性脑缺血大鼠具有神经保护作用，其机制可能与增加GLT-1的表达、降低谷氨酸的兴奋性毒性作用有关。     

头孢曲松钠对大鼠局灶性脑缺血的神经保护作用及其机制

目的：探讨头孢曲松钠对局灶性脑缺血大鼠的神经保护作用及其机制。方法：将Sprague-Dawley（SD）大鼠随机分为头孢曲松钠预处理组、单纯缺血组和假手术组。头孢曲松钠预处理组于术前7 d腹腔注射头孢曲松钠200 mg?kg-1?d-1，然后制备大鼠局灶性脑缺血模型，缺血后3,6,12,24和48 h进行神经行为学评分，应用免疫组化法测定大鼠海马胶质细胞性谷氨酸转运体（glutamate transporter-1，GLT-1）水平。结果：局灶性脑缺血3 h后，脑组织GLT-1蛋白水平显著降低（P<0.01），并且随着缺血时间的延长，GLT-1蛋白水平呈下降趋势，脑缺血后48 h降至最低（P<0.01）。与单纯缺血组比较，头孢曲松钠预处理组大鼠的神经行为学评分均显著降低（P<0.05），海马GLT-1蛋白的表达显著增加（P<0.01）。结论：头孢曲松钠对局灶性脑缺血大鼠具有神经保护作用，其机制可能与增加GLT-1的表达、降低谷氨酸的兴奋性毒性作用有关。     

BoNT-A对慢性坐骨神经结扎大鼠疼痛行为学及脊髓中Fos蛋白的影响

目的 探讨肉毒毒素A(BoNT-A)对神经病理性疼痛大鼠疼痛行为学及脊髓背角Fos蛋白表达的影响.方法 建立雄性SD大鼠慢性坐骨神经结扎(CCI)疼痛模型,CCI术后第3天开始,同侧肢体足底皮下注射BoNT-A 30 U/kg和等容积生理盐水,给药前、给药后1、3、5、7、14 d,采用von-Frey纤维细丝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(MWT)和热刺激缩足反射潜伏期(TWL),观察大鼠疼痛行为学变化,根据变化结果,给药后第5天取相应脊髓节段标本,运用免疫组织化学法观察脊髓背角Fos蛋白表达.结果 CCI神经病理性疼痛模型大鼠建立后,CCI组同侧MWT和TWL均明显降低,且脊髓水平Fos蛋白表达明显增多;同侧足底注射BoNT-A 30 U/kg后,其MWT和TWL,均显著增加,脊髓水平Fos蛋白表达明显减少.结论 足底注射BoNT-A抑制脊髓水平Fos蛋白的表达,能减轻神经病理性疼痛模型大鼠的机械性触诱发痛和热痛觉过敏.     

高压氧对神经病理性痛大鼠疼痛行为学及脊髓背角NOS 表达的影响

目的：观察高压氧对神经病理性痛大鼠疼痛行为学及脊髓背角 NOS 表达的影响。方法成年雄性 SD大鼠32只,随机分成4组,每组8只,包括：假手术组（S 组）、坐骨神经结扎组（CCI 组）、HBO 预处理组（pre－HBO 组）和 HBO 后处理组（post－HBO 组）。所有大鼠 CCI 术前1 d 测量机械痛阈值基线（MWT）。 CCI 术后第1、2、3、7、14、21和第28天观察疼痛反应行为,测量 MWT。 CCI 术后第28天,对脊髓背角中 nNOS、 eNOS 及 iNOS 阳性神经元进行计数。结果CCI 术前4组 MWT 值无明显差异（ P ＞0．05）。每个时间点,与 S 组比较,pre－HBO、post－HBO 和 CCI 组MWT 值明显降低（ P ＜0．05）,且 CCI 组下降幅度最大。每个时间点,与 CCI 组比较,pre－HBO 组和 post－HBO 组 MWT值明显高于 CCI 组（ P ＜0．05）。与 S 组比较,CCI 后第28天 CCI 组、pre－HBO 组和 post－HBO 组大鼠脊髓 nNOS 和iNOS 阳性神经元数量明显增多（ P ＜0．05）。 CCI 组大鼠脊髓 nNOS 和 iNOS 阳性神经元数量明显高于 pre－HBO 组和post－HBO 组（ P ＜0．05）。4组大鼠脊髓 eNOS 阳性神经元数量未见明显差异（ P ＞0．05）。结论高压氧对神经痛的发生有预防和治疗作用,可能通过降低 NOS 的表达缓解疼痛。     

谷氨酸转运体亚型谷氨酸转运体1与其调控药物的研究进展

胞外谷氨酸浓度的动态平衡是由谷氨酸转运体精确调控的,谷氨酸转运体功能或表达失调时导致胞外谷氨酸水平异常,引起一系列神经系统疾病。其中谷氨酸转运体1(GLT-1)起着"谷氨酸泵"作用,近年来还发现了仅在肽链C末端发生改变的GLT-1剪切变异体;其中GLT-1a、GLT-1b和GLT-1v发现与某些疾病具有相关性。药物调控谷氨酸转运体的表达或功能,维持胞外谷氨酸正常浓度,能有效改善病理状况。目前已有多种药物被报道对谷氨酸转运体具有激动或抑制作用,如能够上调GLT-1活性的药物有头孢曲松、苯环己哌啶、胞二磷胆碱、利鲁唑、凝血酶、蛋白激酶B等;下调GLT-1活性的药物有依托咪酯、氯氮平、天冬酰胺类衍生物、内皮素等。该文将调控谷氨酸转运体的药物做一总结,为药物开发和临床治疗提供新的思路。     

虎杖提取物对神经病理性疼痛模型大鼠的镇痛作用研究

目的：研究虎杖提取物对神经病理性疼痛模型大鼠的镇痛作用,并探讨其作用机制。方法雄性SD大鼠,随机分为对照组和坐骨神经缩狭模型（chronic construction injury, CCI）组。CCI术后14 d,应用Von Frey法测定机械刺激缩足反射阈值（mechanical withdrawal threshold, MWT）,观察口服不同剂量的虎杖提取物对CCI大鼠机械性痛觉超敏的影响。并考察不同剂量虎杖提取物对CCI大鼠脊髓p-ERK、p-P38水平及小胶质细胞活化的影响。结果虎杖提取物可明显升高CCI大鼠术侧的MWT值（P〈0.05）,而对正常大鼠的MWT值没有显著影响（P〉0.05）。同时虎杖提取物可显著抑制CCI模型大鼠脊髓ERK和p38的磷酸化,并显著抑制IBA-1表达增加。结论虎杖提取物对CCI诱导的机械性痛觉超敏具有显著性的抑制作用,且镇痛作用维持时间长于吗啡,其机制可能是通过抑制脊髓水平ERK和p38的磷酸化,及通过抑制小胶质细胞活化而实现。     

鞘内注射米诺四环素对慢性坐骨神经结扎大鼠机械痛敏和热痛敏的影响

目的观察鞘内注射小胶质细胞抑制剂米诺四环素对慢性坐骨神经结扎大鼠机械痛敏和热痛敏的影响。方法所有大鼠术前8d鞘内置管,用机械缩足反射阈值和热缩足潜伏期来分别评价大鼠机械痛敏和热痛敏。前给药组:生理盐水10μl或米诺四环素50μg,于坐骨神经结扎前1d开始持续到术后1d(每天2次)鞘内注射,机械缩足反射阈值和热缩足潜伏期分别于术前2d,术后1,3,5,7,14d测定;后给药组:坐骨神经结扎后7d,鞘内注射1次生理盐水10μl或米诺四环素50μg,其对机械缩足反射阈值和热缩足潜伏期的影响分别于给药后0.5、1、2、4、8h测定。结果CCI大鼠从术后1d形成稳定的热痛敏和机械痛敏,前鞘内注射米诺四环素明显增加CCI大鼠MWT和TWL(P<0.05,P<0.01),相反,后鞘内注射米诺四环素对CCI大鼠MWT和TWL无明显影响。结论前鞘内注射米诺四环素明显抑制CCI大鼠机械痛敏和热痛敏,提示小胶质细胞的活化参与慢性坐骨神经结扎引发神经病理痛的形成。     

肉毒毒素A对慢性坐骨神经结扎大鼠机械痛敏和热痛敏的影响

目的探讨肉毒毒素A(botulinum toxin type A,BoNT-A)后处理对神经病理性疼痛大鼠疼痛行为学的影响。方法建立SD大鼠右侧慢性坐骨神经结扎模型(chronic con-striction injury of sciatic nerve,CCI)。CCI术后d3始,CCI同侧肢体足底注射BoNT-A7.5、15、30U·kg-1或等容积生理盐水,或对侧肢体足底注射BoNT-A15或30U·kg-1。分别于术前、术后1、3、5、7、14d,测定大鼠的机械缩足反射阈值(MWT)和热缩足潜伏期(TWL)。结果CCI手术同侧足底皮下注射BoNT-A可以增加大鼠的MWT和TWL,对侧应用BoNT-A对MWT和TWL无影响。结论BoNT-A可以通过局部作用减轻CCI手术同侧肢体的机械痛敏和热痛敏。     

Minocycline can delay the development of morphine tolerance,but cannot reverse existing tolerance in the maintenance period of neuropathic pain in rats

Neuropathic pain is a challenge for physicians and basic science researchers, because it often does not respond to routine treatment. The administration of morphine has been considered one of the effective recommended treatments, but its wide application is limited because of the development of antinociceptive tolerance. In general, basic science studies focus on neuropathic pain and morphine tolerance separately. However, we tried to investigate the effect of microglial activation on morphine tolerance in spinal nerve ligation (SNL) rats during the maintenance period of neuropathic pain. This study produced the following results. The morphine tolerance model in neuropathic pain was established by repeated administration of morphine twice daily (10 mg/kg s.c) in the maintenance period of SNL rats. Minocycline, the microglial activation inhibitor, was given once daily (30 mg/kg, i.p.) at different time‐points. The CD11b protein level was measured by western blot to monitor microglial activation. Rats’ mechanical allodynia was assessed using the 50% paw withdrawal threshold, and the tail antinociception was determined using the percentage of the maximal possible antinociceptive effect. First, the repeated administration of morphine induced the development of antinociceptive tolerance during the maintenance period of neuropathic pain. Second, during the development of morphine tolerance, microglial activation, which is related to the analgesic effect of morphine, decreased in the first few days, but this pattern was reversed in the following days with the development of morphine tolerance. Third, the repeated administration of minocycline, a microglial activation inhibitor, did not influence the antinociceptive effect of a single dose of morphine. Fourth, the pre‐administration of minocycline can delay the development of morphine tolerance, but repeated minocycline administration cannot reverse existing morphine tolerance. We concluded that microglial activation contributes to the morphine tolerance of SNL rats in the maintenance period of neuropathic pain, and that minocycline delays the development of morphine tolerance, but does not reverse existing morphine tolerance during the maintenance period of neuropathic pain in rats. These findings might be useful for clinical pain management.     

Post-injury repeated administrations of minocycline improve the antinociceptive effect of morphine in chronic constriction injury model of neuropathic pain in rat

It is confirmed that pharmacological attenuation of glial cells can alleviate neuropathic pain by lowering proinflammatory cytokine expression. The present study tries to confirm that post-injury administration of glia inhibitor, minocycline, can attenuate the neuropathic pain symptoms and improves the efficacy of morphine anti-nociception in chronic constriction injury (CCI). Male Wistar rats (230-270 g) underwent surgery for induction CCI model of neuropathy. For assessment of the thermal hyperalgesia and mechanical allodynia after CCI induction, morphine (2.5, 5, 7.5, 10 and 15 mg/kg; s.c.) and saline were administered on post-operative days (PODs) 0, 6 and 14. Hargreaves and Von-Frey tests were performed before and 30 min after morphine administration, respectively. The results showed significant decrease in antinociceptive effect of morphine on POD 6 compared to POD 0 only at the dose of 5 mg/kg. On the other hand, on POD 14 the antinociceptive effect of morphine (5, 7.5, 10 and 15 mg/kg) significantly decreased in comparison with POD 0. In another set of experiments, animals received minocycline (10, 20 and 40 mg/kg; i.p.) for eight days from POD 6 to 13 and then the antinociceptive effect of single dose of morphine 5 mg/kg was tested on POD 14. Behavioral tests showed that minocycline (40 mg/kg) could effectively attenuate the thermal hyperalgesia and mechanical allodynia on POD 13. Moreover, minocycline (40, 20 mg/kg) improved the anti-hyperalgesic, and minocycline (40 mg/kg) improved the anti-allodynic effects of morphine 5 mg/kg on POD 14. It seems that the reduction of antinociceptive effect of morphine after CCI may be mediated through glia activation. Modulation of glial activity by minocycline can attenuate CCI-induced neuropathic pain. It is also shown that repeated post-injury administration of minocycline improves the antinociceptive effect of morphine in neuropathic pain.     

Effects of intrathecal epigallocatechin gallate, an inhibitor of Toll-like receptor 4, on chronic neuropathic pain in rats

Numerous studies revealed that spinal inflammation and immune response play an important role in neuropathic pain. In this study, we investigated the effects of intrathecal injection of a Toll-like receptor (TLR4) inhibitor epigallocatechin gallate (EGCG) on neuropathic pain induced by chronic constriction injury of the sciatic nerve (CCI). A total of 120 rats were randomly assigned into 4 groups: sham-operated group, CCI group, CCI plus normal saline group and CCI plus EGCG group. CCI and sham surgeries were performed and both thermal hyperalgesia and mechanical allodynia were tested. Lumbar spinal cord was sampled and the mRNA and protein expressions of TLR4 and High Mobility Group 1 protein (HMGB1) were detected, the contents of tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β) and interleukin-10 (IL-10) were measured by ELISA, and immunohistochemistry for nuclear factor kappa B (NF-κB) was also carried out. When compared with the sham group, both mechanical and heat pain thresholds were significantly decreased, and the mRNA and protein expressions of TLR4 and HMGB1, the contents of TNF-α, IL-1β and IL-10 in the spinal cords and NF-κB expression in the spinal dorsal horn were markedly increased in CCI rats (P<0.05). After intrathecal injection of EGCG (1mg/kg) once daily from 1day before to 3days after CCI surgery, the expressions of TLR4, NF-κB, HMGB1, TNF-α and IL-1β were markedly decreased while the content of IL-10 in the spinal cord increased significantly accompanied by dramatical improvement of pain behaviors in CCI rats (P<0.05). These results show that the TLR4 signaling pathway plays an important role in the occurrence and development of neuropathic pain, and the therapy targeting TLR4 might be a novel strategy in the treatment of neuropathic pain.     

Involvement of an increased spinal TRPV1 sensitization through its up-regulation in mechanical allodynia of CCI rats

Vanilloid receptor 1 (TRPV1) antagonists are known to attenuate the neuropathic pain symptoms in peripheral nerve injury models, but the mechanism(s) of their effect remains unclear. At the same time, the role of spinal TRPV1 in pain transduction system has not been fully understood. In this study, the role of spinal TRPV1 in mechanical allodynia in rat chronic constriction injury (CCI) model was investigated. Intrathecal administration of a selective TRPV1 antagonist, N-(4-tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl)tetrahydropryazine-1(2H)-carbox-amide (BCTC) significantly attenuated mechanical allodynia in CCI rats at 100 and 300 nmol. In vitro, BCTC inhibited capsaicin (300 nM)-induced releases of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) and substance P-like immunoreactivity (SP-LI) from the rat spinal cord slice preparations with IC(50)s of 37.0 and 36.0 nM, respectively, confirming that BCTC potently inhibits TRPV1 function in the rat spinal cord. TRPV1 expression levels in the spinal cord following CCI were quantified in by Western blot analysis. TRPV1 protein levels were significantly increased in the ipsilateral side of the lumbar spinal cord at 7 and 14 days following CCI surgery, but not in the contralateral side. Furthermore, capsaicin (300 nM)-evoked release of CGRP-LI was significantly higher in the ipsilateral spinal cord of CCI rats (14 days after surgery) than that of sham-operated rats. These findings suggest that an increased sensitization of the spinal TRPV1 through its up-regulation is involved in the development and/or maintenance of mechanical allodynia in rat CCI model.     

Tramadol has a better potency ratio relative to morphine in neuropathic than in nociceptive pain models

BACKGROUND AND OBJECTIVE: Treatment of neuropathic pain remains a challenge and the role of various analgesics in this setting is still debated. The effects of tramadol, an atypically acting analgesic with a combined opioid and monoaminergic mechanism of action, and morphine, a prototypical opioid, were tested in rat models of neuropathic and nociceptive pain. METHODS: Cold allodynia and mechanical hypersensitivity, symptoms of neuropathic pain, were studied in rat models of mononeuropathic pain. Cold allodynia was analyzed in the chronic constriction injury (CCI) model and mechanical hypersensitivity was analyzed in the spinal nerve ligation (SNL) model. Heat-induced rat tail-flick latencies were determined as measure for nociceptive pain. RESULTS: Cold allodynia and mechanical hypersensitivity were strongly attenuated with similar absolute potency after intravenous administration of tramadol and morphine. The doses of drug that were calculated to result in 50% pain inhibition (ED(50)) for tramadol and morphine were 2.1 and 0.9 mg/kg, respectively, in CCI rats and 4.3 and 3.7 mg/kg, respectively, in SNL rats. In the tail-flick assay of acute nociception, the potency of the two drugs differed markedly, as seen by ED(50) values of 5.5 and 0.7 mg/kg intravenously for tramadol and morphine, respectively. Accordingly, the analgesic potency ratio (ED(50) tramadol/ED(50) morphine) of both compounds differed in neuropathic (potency ratio 2.3 in CCI and 1.2 in SNL) and nociceptive pain models (potency ratio 7.8), suggesting a relative increase in potency of tramadol in neuropathic pain compared with nociceptive pain. CONCLUSION: The results of this study are consistent with clinical data supporting the efficacy of opioids in neuropathic pain conditions, and furthermore suggest an additional contribution of the monoaminergic mechanism of tramadol in the treatment of neuropathic pain states.     

Role of reactive oxygen species and spinal cord apoptotic genes in the development of neuropathic pain.

A mouse model of neuropathic pain consisting of chronic constriction injury (CCI) of the sciatic nerve was used to examine the involvement of reactive oxygen species (ROS) in early spinal cord pro-apoptotic gene over-expression during the development of neuropathic pain. RT-PCR analysis showed increased expression of bax, apoptotic protease-activating factor-1 (apaf-1), and caspase-9 in the dorsal horn spinal cord 3 days after chronic constriction injury of sciatic nerve. Consistent with biomolecular data, a marked increase in TUNEL-positive and caspase-3 active form was observed by 3 days CCI. Administration of phenyl-N-tert-butylnitrone (PBN), a potent ROS scavenger, reduced the development of thermal hyperalgesia and mechanical allodynia at 1 and 3 days post-CCI, and decreased the mRNA levels of bax, apaf-1, and caspase-9. PBN also reduced apoptotic and active Caspase-3 positive profiles in the superficial laminae (I-III) of the spinal cord. This study provides evidence that PBN inhibits over-expression of pro-apoptotic genes and neural apoptosis in the spinal cord dorsal horn induced by early-CCI of the sciatic nerve. These findings suggest that ROS regulate expression of some apoptotic genes which might play a role in the onset of neuropathic pain.     

Pentoxifylline decreases allodynia and hyperalgesia in a rat model of neuropathic pain

BACKGROUND AND THE PURPOSE OF THE STUDY: Pentoxifylline (PTX) is a non-specific cytokite pain in several animal models and humans. However, long-term therapeutic effects of PTX on neuropathic pain in a rat model of chronic constriction injury (CCI) are not completely clear. This study was conducted to examine the effect of long-term administration of PTX on neuropathic pain in rats. METHODS : Neuropathic pain was induced by sciatic nerve ligation using of CCI model in rats. Rats were randomly assigned into sham, CCI-saline treated, and CCI-PTX treated (30 or 60 mg/kg ip) groups. PTX or saline administered at 30 min before CCI and daily for 14 days post-CCI. At the days of 3, 7, 11 and 14 following CCI, by using standard methods effects of thermal hyperalgesia, thermal and mechanical allodynia in all groups were examined using the standard methods. RESULTS : The CCI-saline treated group showed a significant increase in mechanical and thermal allodynia, and thermal hyperalgesia as compared with the sham group in the tested days. Administration of the higher dose of PTX (60 mg/kg/day), but not the lower dose (30 mg/kg/day) significantly reduced mechanical and thermal allodynia, as compared with the CCI-saline treated group on days of 3, 7, 11 and 14 (all P values<0.001). Also, both doses of PTX significantly reduced thermal hyperalgesia as compared with the CCI-saline treated group on these days (all P values<0.001). CONCLUSION : Results of this study show that chronic administration of PTX reduces the neuropathic pain in a rat model of CCI. Thus, this drug may have a therapeutic application in the treatment and management of neuropathic pain in humans.