Magnesium ions and opioid agonists in vincristine-induced neuropathy

Neuropathic pain is difficult to treat. Classic analgesics (i.e., opioid receptor agonists) usually possess low activity. Therefore other agents such as antidepressants, anticonvulsants, and corticosteroids are used. It is commonly known that NMDA antagonists increase analgesic activity of opioids. Unfortunately, clinical use of NMDA antagonists is limited because of the relatively frequent occurrence of adverse effects e.g., memory impairment, psychomimetic effects, ataxia and motor in-coordination. Magnesium ions (Mg²⁺) are NMDA receptor blockers in physiological conditions. Therefore, in this study the effect of opioid receptor agonists and the influence of Mg²⁺ on the action of opioid agonists in vincristine-induced hyperalgesia were examined. Opioid agonists such as morphine (5 mg/kg, ip), and fentanyl (0.0625 mg/kg, ip), as well as the partial agonist buprenorphine (0.075 mg/kg, ip) administered alone on 5 consecutives days did not modify the hyperalgesia in vincristine rats. In contrast, pretreatment with a low dose of magnesium sulfate (30 mg/kg, ip) resulted in a progressive increase of the analgesic action of all three investigated opioids. After discontinuation of drug administration, the effect persisted for several days.     

Effect of mexiletine on vincristine-induced painful neuropathy in mice

In the present study, we examined the effect of mexiletine on vincristine-induced thermal hyperalgesia in mice. Mice were intraperitoneally treated with vincristine at a dose of 0.05 mg/kg one day after the measurement of the pre-drug latency in the tail-flick test, and then treated with a dose of 0.125 mg/kg twice a week for 6 weeks. In vincristine-treated mice, a significant decrease in tail-flick latency developed at 6 weeks after treatment. Pretreatment with mexiletine, at doses of 3, 10 and 30 mg/kg, i.p., dose-dependently increased the tail-flick latency in vincristine-treated mice. A significant reduction of the tail-flick latency was observed when the tail-flick latency was examined 60 min after i.t. administration of NG-nitro-L-arginine methyl ester (L-NAME, 30 nmol), a nitric oxide synthase (NOS) inhibitor, in naive mice. This L-NAME-induced thermal hyperalgesia was dose-dependently attenuated by pretreatment with mexiletine (10 and 30 mg/kg, i.p.), 10 min before the injection of L-NAME. The duration of nociceptive behavioral response induced by fenvalerate, at a dose of 0.1 microg, i.t., was significantly increased by pretreatment with L-NAME (30 nmol, i.t.). Intrathecal pretreatment with L-arginine (300 pmol) significantly reversed the L-NAME-induced enhancement of fenvalerate-induced nociceptive responses. The present study demonstrates that systemic mexiletine can effectively attenuate vincristine-induced thermal hyperalgesia. Furthermore, these results suggest that blockade of nitric oxide-induced enhancement of nociceptive transmission, in which tetrodotoxin-resistant sodium channels play an important role, may participate in the antinociceptive effect of mexiletine on vincristine-induced thermal hyperalgesia.     

Systematic evaluation of the nefopam–paracetamol combination in rodent models of antinociception

1. The aim of the present study was to explore the concept of multimodal anaesthesia using a combination of two non‐opioid analgesics, namely nefopam, a centrally acting non‐opioid that inhibits monoamine reuptake, and paracetamol, an inhibitor of central cyclo‐oxygenases. The antinociceptive characteristics of the combination were evaluated using four different animal models of pain. 2. In the mouse writhing test, antinociceptive properties were observed with ED₅₀ values of 1.5 ± 0.2 and 120.9 ± 14.8 mg/kg for nefopam and paracetamol, respectively. In the mouse formalin test, both compounds significantly inhibited the licking time of the injected hind paw, with ED₅₀ values in the early phase of 4.5 ± 1.1 and 330.7 ± 80.3 mg/kg for nefopam and paracetamol, respectively, compared with 4.3 ± 0.2 and 206.1 ± 45.1 mg/kg for nefopam and paracetamol, respectively, in the inflammatory phase. Isobolographic analysis revealed that this drug combination was synergistic in the writhing test and additive in the formalin test. 3. In a rat incision model of postoperative thermal hyperalgesia, coadministration of nefopam at a non‐analgesic dose (3 mg/kg) with paracetamol at a low analgesic dose (300 mg/kg) showed the appearance of a strong antihyperalgesic effect, maintained for at least 3 h. In rat carrageenan‐induced tactile allodynia, the combination of low analgesic doses of nefopam (10 or 30 mg/kg) with a non‐analgesic dose of paracetamol (30 mg/kg), significantly blocked allodynia with a longer duration of efficacy. 4. In conclusion, coadministration of nefopam with paracetamol is worthy of clinical evaluation.     

吗啡对糖尿病神经病理痛大鼠机械及冷刺激痛敏症状的影响

目的探讨吗啡对糖尿病神经病理痛大鼠机械及冷刺激痛敏症状的影响。方法35只SD雄性大鼠(180～220 g)腹腔注射链脲佐菌素(STZ)制备成糖尿病神经病理痛模型,出现痛敏症状后,随机分为5组,采用von Frey测试针和冷板(5度)法,测量鞘内给予吗啡后不同时间机械缩腿阈值和冷刺激后的抬足次数(次/5min)变化。结果吗啡以剂量依赖方式提高糖尿病神经痛大鼠机械缩腿阈值、降低冷刺激后的抬足次数,给予吗啡后30 min,0.5、1.0、5.0μg剂量吗啡组的机械缩腿阈值明显增高,而冷刺激抬足次数分别为显著下降,分别与用药前和对照组相比,差异有统计学意义(P<0.05)。结论吗啡能显著提高糖尿病神经痛大鼠的机械缩腿阈值,有效减少冷刺激的抬足次数,对神经源性痛具有明显的镇痛作用。     

Antiallodynic and Antihyperalgesic Activities of Fentanyl-Loaded Dermal Clay Dressings in Rat Model of Second-Degree Burn Injury

Second-degree burn injury is the most common type of burn injury, which usually takes 2-3 weeks for complete healing. However, such patients suffer with intense pain associated with development of hyperalgesia and allodynia. Here, we prepare a silver clay patch using montmorillonite clay, betaine, and silver nitrate. Later, the silver clay patches were loaded with fentanyl. Furthermore, the patches were fabricated into burn wound dressings. The dressings were first subjected to ex vivo skin penetration studies and were later evaluated for thermal hyperalgesia and mechanical allodynia using second-degree burn injury rodent model. Our results show that application of fentanyl-loaded dermal clay (FLDC) dressings for 3 h showed significant increase of paw withdrawal latency (p <0.001) against hyperalgesia starting from 30 min after removal of patch to up to 6 h. Similarly, the FLDC dressings also potentiated the paw withdrawal threshold for up to 4 h after application (p <0.001). From these studies, we can conclude that FLDC dressings are ideal topical formulations for better management of pain in second-degree burns.     

Role of peripheral and spinal 5-HT(3) receptors in development and maintenance of formalin-induced long-term secondary allodynia and hyperalgesia

The role of peripheral and spinal 5-HT₃ receptors in formalin-induced secondary allodynia and hyperalgesia in rats was assessed. Formalin produced acute nociceptive behaviors (flinching and licking/lifting) followed by long-term secondary mechanical allodynia and hyperalgesia in both paws. In experiments where the test drug was anticipated to augment or antagonize the response, 0.5 or 1% formalin, respectively, was used for injection. Peripheral ipsilateral, but not contralateral, pre-treatment (− 10 min) with serotonin (5-HT, 10-100 nmol/paw) and the selective 5-HT₃ receptor agonist 1-(m-chlorophenyl)-biguanide (m-CPBG, 10-300 nmol/paw) increased 0.5% formalin-induced secondary allodynia and hyperalgesia in both paws. Moreover, spinal pre-treatment with m-CPBG (10-300 nmol/rat) increased 0.5% formalin-induced secondary hyperalgesia but not allodynia in both paws. Accordingly, peripheral ipsilateral (30-300 nmol/paw), but not contralateral (300 nmol/paw), and spinal (10-100 nmol) pre-treatment with the selective 5-HT₃ receptor antagonist ondansetron prevented 1% formalin-induced secondary mechanical allodynia and hyperalgesia in both paws. The peripheral pronociceptive effects of 5-HT (100 nmol/paw) and m-CPBG (300 nmol/paw) as well as the spinal effect of m-CPBG (300 nmol/rat) were completely prevented by the peripheral (10 nmol/paw) and spinal (1 nmol/rat) injection, respectively, of ondansetron. At these doses, ondansetron did not modify per se formalin-induced nociceptive behaviors. Spinal (30-300 nmol/rat), but not peripheral (300 nmol/paw), post-treatment (on day 6) with ondansetron reversed established formalin-induced secondary mechanical allodynia and hyperalgesia in both paws. Results suggest that a barrage of afferent input induced by 5-HT at peripheral 5-HT₃ receptors participates in the development of formalin-induced long-term secondary allodynia and hyperalgesia in the rat. In addition, our data suggest that spinal 5-HT₃ receptors play an important role during development and maintenance of these evoked long-term behaviors.     

Comparative analgesic efficacy of pregabalin administered according to either a prevention protocol or an intervention protocol in rats with cisplatin‐induced peripheral neuropathy

Chemotherapy‐induced peripheral neuropathy (CIPN) is a type of peripheral neuropathic pain that may be dose‐limiting in patients administered potentially curative cancer chemotherapy dosing regimens. In cancer survivors, persistent CIPN adversely affects patient quality of life and so adjuvant drugs (anticonvulsants eg pregabalin or antidepressants eg amitriptyline) are recommended for the relief of CIPN. However, most studies in rodent models of CIPN involve administration of single bolus doses of adjuvant drugs to assess pain‐relieving efficacy. Hence this study was designed to assess the efficacy of pregabalin administered to CIPN‐rats according to either a prevention or an intervention protocol. Groups of male Sprague‐Dawley rats received four single intraperitoneal bolus doses of cisplatin at 3 mg/kg at once‐weekly intervals to induce CIPN. For the prevention protocol, oral pregabalin (or vehicle) was administered to CIPN‐rats once‐daily for 21 consecutive days from day 0 to day 20 inclusive. For the intervention protocol, oral pregabalin was administered once‐daily for 21 consecutive days from day 28 to day 48, inclusive. Mechanical allodynia and mechanical hyperalgesia in the bilateral hindpaws were assessed just prior to each dose of cisplatin and at least once weekly until study completion (day 27, prevention protocol; or day 48, intervention protocol). Mechanical allodynia and mechanical hyperalgesia were also determined at the time of peak effect at about 2 hours post pregabalin/vehicle administration, once weekly until study completion. For the prevention protocol in CIPN‐rats, pregabalin alleviated mechanical hyperalgesia but not mechanical allodynia. For the intervention protocol, pregabalin alleviated both mechanical allodynia and mechanical hyperalgesia in the hindpaws.     

Transient allodynia pain models in mice for early assessment of analgesic activity

BACKGROUND AND PURPOSE: The most common preclinical models of neuropathic pain involve surgical ligation of sensory nerves, which is especially difficult in mice. Transient models of chemically sensitized allodynia are potentially useful for rapidly characterizing the analgesic profile of compounds and conducting mechanistic studies.EXPERIMENTAL APPROACH: Increasing doses of NMDA, sulprostone (an EP1/EP3 prostaglandin receptor agonist) or phenylephrine (an alpha (1) adrenoceptor agonist) were injected intrathecally (i.t.) or i.p., and animals were subsequently assessed for allodynia. The effects of receptor antagonists and analgesic compounds on allodynia were also assessed.KEY RESULTS: A comparison of total body doses that cause allodynia following spinal or systemic administration indicated that NMDA induces allodynia in the spinal cord while sulprostone and phenylephrine act through a peripheral mechanism. Inhibition of the allodynia with receptor antagonists indicated that each agent induces allodynia by a distinct mechanism. The three models were benchmarked using compounds known to be active in neuropathic pain patients and nerve injury animal models, including gabapentin, amitriptyline and clonidine.CONCLUSIONS AND IMPLICATIONS: These transient allodynia models are a useful addition to the toolbox of preclinical pain models. They are simple, rapid and reproducible, and will be especially useful for characterizing the pain phenotype of knockout mice.     

Role of TRPV1 and ASIC3 in formalin-induced secondary allodynia and hyperalgesia

BackgroundIn the present study we determined the role of transient receptor potential V1 channel (TRPV1) and acid-sensing ion channel 3 (ASIC3) in chronic nociception.Methods1% formalin was used to produce long-lasting secondary allodynia and hyperalgesia in rats. Western blot was used to determine TRPV1 and ASIC3 expression in dorsal root ganglia.ResultsPeripheral ipsilateral, but not contralateral, pre-treatment (−10 min) with the TRPV1 receptor antagonists capsazepine (0.03–0.3 μM/paw) and A-784168 (0.01–1 μM/paw) prevented 1% formalin-induced secondary mechanical allodynia and hyperalgesia in the ipsilateral and contralateral paws. Likewise, peripheral ipsilateral, but not contralateral, pre-treatment with the non-selective and selective ASIC3 blocker benzamil (0.1–10 μM/paw) and APETx2 (0.02–2 μM/paw), respectively, prevented 1% formalin-induced secondary mechanical allodynia and hyperalgesia in both paws. Peripheral ipsilateral post-treatment (day 6 after formalin injection) with capsazepine (0.03–0.3 μM/paw) and A-784168 (0.01–1 μM/paw) reversed 1% formalin-induced secondary mechanical allodynia and hyperalgesia in both paws. In addition, peripheral ipsilateral post-treatment with benzamil (0.1–10 μM/paw) and APETx2 (0.02–2 μM/paw), respectively, reversed 1% formalin-induced secondary mechanical allodynia and hyperalgesia in both paws. TRPV1 and ASIC3 proteins were expressed in dorsal root ganglion in normal conditions, and 1% formalin injection increased expression of both proteins in this location at 1 and 6 days compared to naive rats.ConclusionsData suggest that TRPV1 and ASIC3 participate in the development and maintenance of long-lasting secondary allodynia and hyperalgesia induced by formalin in rats. The use of TRPV1 and ASIC3 antagonists by peripheral administration could prove useful to treat chronic pain.     

AM404, an anandamide transport inhibitor, reduces plasma extravasation in a model of neuropathic pain in rat: role for cannabinoid receptors

Neuropathic pain consequent to peripheral nerve injury has been associated with local inflammation. Following noxious stimulation afferent fibres release substance P (SP) and calcitonin-gene related peptide (CGRP), which are closely related to oedema formation and plasma leakage. The effect of the anandamide transport blocker AM404 has been studied on plasma extravasation after chronic constriction injury (CCI) which consists in a unilateral loose ligation of the rat sciatic nerve (Bennett and Xie, 1988). AM404 (1-3-10 mg kg(-1)) reduced plasma extravasation in the legated paw, measured as mug of Evans Blue per gram of fresh tissue. A strong effect on vascular permeability was also produced by the synthetic cannabinoid agonist WIN 55,212-2 (0.1-0.3-1 mg kg(-1)). Using specific antagonists or enzyme inhibitors, we demonstrate that cannabinoids act at several levels: data on the 3rd day suggest a strong involvement of substance P (SP) and calcitonin gene-related peptide (CGRP) in the control of vascular tone, whereas at the 7th and 14th days the major role seems to be played by prostaglandins (PGs) and nitric oxide (NO). Capsaicin injection in ligated paws of AM404- or WIN 55,212-2-treated rats resulted in an increase of Evans Blue extravasation, suggesting the involvement of the cannabinergic system in the protective effect of C fibres of ligated paws. Taken together, these data demonstrate the efficacy of cannabinoids in controlling pain behaviour through the modulation of several pain mediators and markers of vascular reactivity, such as SP, CGRP, PGs and NO.     

γ-氨基丁酸转运体抑制剂NO-711术前鞘内注射对坐骨神经慢性挤压伤大鼠神经病理性痛觉过敏的影响

γ-氨基丁酸是哺乳动物中枢神经系统主要的抑制性神经递质。近年来的研究发现GABA递质受体系统在伤害性信息传递和调节方面起着重要的作用。定位在突触前膜和神经胶质细胞的转运体GAT1是最重要的神经递质转运体之一，能快速摄取GABA从而终止其抑制作用。GABA转运体抑制剂已经被广泛用于癫痫研究，但是这种药是否对疼痛动物或人有镇痛作用仍然不是十分清楚。本实验目的是在大鼠神经病理痛模型建立前鞘内给予NO-711，观察其对大鼠热痛敏和触诱发痛的影响。     

人组织激肽释放酶对周围神经系统损伤后的修复效应

目的:评价人组织激肽释放酶(HTK)促进周围神经系统损伤后的修复作用.方法:取30只体重180～200 g的雄性SD大鼠,随机分成3组:假手术组、HTK组(17.5×10~(-3) PNAU/kg)、对照组,每组各10只.术前第0天和术后第1、第3、第5、第7、第9、第11、第13天测定坐骨神经功能指数(SFI)以及静止坐骨神经指数(SSI),术后第14天测定坐骨神经干动作电位传导速度(NCV).结果:SFI、SSI值在假手术组手术前后未见明显改变.HTK组和对照组中,术后第1天SFI、SSI均为-100左右.以后发现HTK组的SFI、SSI恢复的情况要优于对照组,从第5天开始两组SFI、SSI值有统计学差异(P<0.05).术后第14天HTK组的NCV值要高于对照组,两组间有统计学差异(P<0.05).结论:HTK具有促进周围神经系统损伤后的修复作用.     

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.     

青藤碱对SSNI模型大鼠镇痛效应及脑内兴奋性氨基酸递质的影响

目的观察青藤碱对部分坐骨神经损伤(SSNI)模型大鼠疼痛敏感行为及纹状体细胞外液兴奋性氨基酸-谷氨酸(Glu)的影响。方法 SD大鼠,随机分为假手术组和SSNI手术组,后者再分为模型组、加巴喷丁组(100 mg.kg-1)、青藤碱低剂量组(20 mg.kg-1)和青藤碱高剂量组(40 mg.kg-1)。采用机械痛敏和冷痛敏测试,评价大鼠的疼痛行为,以最大镇痛效应百分比(%MPE)反映药效。纹状体微透析采样,高效液相-荧光方法检测其细胞外液Glu浓度。结果 SSNI模型大鼠的机械、冷刺激痛感行为明显改变,脑内Glu水平明显升高。%MPE效应-时间曲线在120min内青藤碱高剂量组最高(达81.28%),加巴喷丁组第2(达50.56%),青藤碱低剂量组第3(达7.22%)。与模型组纹状体细胞外液Glu水平相比,加巴喷丁组有3个时间点、青藤碱低剂量组有4个时间点、青藤碱高剂量组有5个时间点明显降低(P<0.05或P<0.01)。结论青藤碱减轻SSNI模型大鼠疼痛敏感行为,其镇痛效应可能与抑制纹状体细胞外液Glu水平有关。     

Macrophage depletion delays progression of neuropathic pain in diabetic animals

Despite the fact that it is a frequent diabetic complication, the mechanisms underlying the manifestation of diabetic neuropathic pain remain poorly understood. In this study, we hypothesized that the depletion of peripheral macrophages with liposome-encapsulated clodronate (LEC) can prevent, at least delay, the progression of diabetes-induced neuropathic pain. Therefore, the aim of this study was to evaluate the effects of macrophage depletion on mechanical allodynia and thermal hyperalgesia in the streptozotocin (STZ)-induced rat model of diabetic neuropathy. LEC was intravenously administrated to rats three times with 5-day intervals. A single intravenous injection of STZ caused an increase in the average blood glucose levels and a decrease in body weight. Although LEC treatment did not affect the body weight gain, the blood glucose level was lower and serum insulin level higher in LEC-treated diabetic rats than in that of diabetic rats. In addition, LEC treatment alleviated the excessive damage in beta cells in diabetic rats. Diabetic animals displayed marked mechanical allodynia and thermal hyperalgesia. While the treatment of diabetic rats with LEC did not significantly change the thermal withdrawal latency, diabetes-induced decrease in mechanical paw withdrawal threshold was significantly corrected by the LEC treatment. The results of this study show that thermal hyperalgesia and mechanical allodynia induced by diabetes may be associated with alterations in blood glucose level. Depletion of macrophages with LEC in diabetic rats may reduce mechanical allodynia without affecting thermal hyperalgesia. Taken together, these results suggested that depletion of macrophages in diabetes may partially postpone the development of diabetic neuropathic pain.     

Antinociceptive and pronociceptive effect of levetiracetam in tonic pain model

Background

Levetiracetam (LEV) is a novel anticonvulsant with proven antinociceptive properties. However, the antinociceptive and pronociceptive effect of this drug has not yet been fully elucidated in a tonic pain model.

骨癌痛小鼠CT影像学及痛行为学特征

目的 观察骨癌痛小鼠CT影像学及痛行为学的改变.方法 将2×105个NCTC2472小鼠纤维肉瘤细胞注射到C3H/HeJ小鼠右侧股骨远端骨髓腔内制作骨癌痛动物模型.分别于注射前、注射后3、5、7、14、21、28d观察小鼠自发性疼痛反应,通过行走评分评价行走诱发患肢痛,热辐射刺激法测量热缩腿反射潜伏期.CT检查观察股骨破坏情况.取股骨行组织切片,HE染色光镜下观察肿瘤组织和骨结构破坏情况.结果 模型组小鼠在注射肿瘤细胞后第14天出现自发性疼痛、热痛敏现象和行走诱发患肢痛,一直持续至28d.CT检查显示有明显的骨破坏,出现病理性骨折.组织学研究显示骨髓腔内肿瘤生长,向外侵蚀破坏骨皮质.结论 从疼痛行为学、CT检查以及组织学等多方面的研究表明,小鼠注射纤维肉瘤细胞后可表现出癌痛的特点.