Continuous naloxone administration via osmotic minipump decreases autotomy but has no effect on nociceptive threshold in the rat

Rats with unilaterally sectioned sciatic nerves were continuously administered naloxone HCl (80 or 800 micrograms/h) or equivalent volumes of saline (1 or 10 microliters/h) subcutaneously via osmotic minipumps over a 2 or 5 week period. Rats receiving 80 micrograms/h naloxone for 5 weeks exhibited significantly less self-mutilation (autotomy) of the denervated foot than saline controls or rats receiving 80 micrograms/h naloxone for 2 weeks. The nociceptive threshold of intact rats infused with the same dose of naloxone was tested on a hot plate. In these animals there was no influence on the nociceptive threshold during naloxone administration for 1 week. Autotomy was also reduced in rats infused with 800 micrograms/h naloxone. The nociceptive threshold of intact rats infused with this dose of naloxone or an equivalent volume of saline (10 microliters/h) was increased, suggesting that the presence of the larger osmotic pump caused analgesia.     

IL-6 has no acute effect on the regulation of urea synthesis in vivo in rats

Abstract

Background. Clinical or experimentally induced, active inflammation up-regulates the in vivo capacity of urea synthesis (CUNS), which promotes nitrogen removal from the body and metabolic catabolism. We have shown that tumor necrosis factor α (TNF-α) up-regulates CUNS and increases interleukin 6 expression (IL-6) within hours of administration. The described effect of TNF-α on nitrogen homeostasis may, therefore, depend on IL-6. Methods. Three hours after the i.v. injection of 125 μg.kg^?1 of IL-6 or placebo, we evaluated the CUNS, hepatocyte urea cycle enzyme protein levels and the mRNA levels of the urea cycle enzyme genes in rats. The prevailing rat serum acute phase proteins and their liver mRNA levels were also measured. Results. IL-6 did not change CUNS or hepatocyte urea cycle enzyme protein levels, whereas urea cycle enzyme mRNA levels, except for ornithine transcarbamylase (OTC), decreased by approximately 20%. The liver mRNA levels of α2MG, haptoglobin and α1AGP all increased by 1.5- to 2-fold (p < 0.001). In serum, only the α2MG concentration slightly increased (p < 0.001), whereas the levels of the other circulating acute phase proteins remained unchanged. Conclusion. IL-6 is not the mediator of the in vivo CUNS up-regulation observed 3 h after TNF-α administration, but it may be involved in the down-regulation of urea cycle genes. IL-6 may also mediate TNF-α effects on acute phase protein gene expression. Thus, IL-6 did not contribute to the in vivo hepatic component of inflammation-associated catabolism.     

Effect of ursolic acid in attenuating chronic constriction injury‐induced neuropathic pain in rats

Ursolic acid (UA; 3b‐hydroxy‐12‐urs‐12‐en‐28‐oic acid), a natural pentacyclic triterpenoid carboxylic acid, has been known to possess potent anti‐inflammatory, antioxidant, and antinociceptive effects in various animal models. Therefore, this study was designed to investigate the antihyperalgesic, anti‐inflammatory, and antioxidant effects of UA at 5, 10, and 20 mg/kg of doses via per os (p.o.) route for 14 days in chronic constriction injury (CCI)‐induced neuropathic pain in rats. Pain behavior in rats was evaluated before and after UA administration via mechanical and heat hyperalgesia. CCI caused significant increase in levels of pro‐inflammatory cytokines and oxido‐nitrosative stress. In addition, significant increase in myeloperoxidase, malondialdehyde, protein carbonyl, nitric oxide (NO), and total oxidant status (TOS) levels in sciatic nerve and spinal cord concomitant with mechanical and heat hyperalgesia is also noted for CCI‐induced neuropathic pain. Administration of UA significantly reduced the increased levels of pro‐inflammatory cytokines and TOS. Further, reduced glutathione is also restored by UA. UA also showed in vitro NO and superoxide radical scavenging activity. UA has a potential in attenuating neuropathic pain behavior in CCI model which may possibly be attributed to its anti‐inflammatory and antioxidant properties.     

Myocardial ischaemic preconditioning in the pig has no effect on the ventricular fibrillation and defibrillation thresholds

INTRODUCTION: The effects of myocardial ischaemia preconditioning in pigs on the vulnerability to ventricular fibrillation during subsequent ischaemic events are controversial. This study examined the time course of changes in ventricular fibrillation (VFT) and defibrillation (DFT) thresholds during transient myocardial ischaemia after a 45 min preconditioning period. METHODS AND RESULTS: In five open-chest pigs, VFT was measured after 3 min of regional myocardial ischaemia, at time 0, 2, 15, 30, 60 and 90 min (Control group). In seven other pigs (Test group), VFT was measured before (time 0) and 2, 15, 30, 60 and 90 min after ischaemic preconditioning by three consecutive 5 min periods of regional coronary occlusion, followed by 10 min of reperfusion. DFT was measured by increasing the stored energy systematically until successful defibrillation. Ischaemic preconditioning caused no significant change in the effective refractory period (ERP), VFT or DFT over the 90 min of the experiments. In the Control group, ERP remained stable for 30 min, though was significantly lower at 90 min (178 +/- 28 ms) than at baseline (204 +/- 32 ms, P = 0.007). VFT and DFT remained unchanged throughout the experiments, and no difference was observed in ERP, VFT and DFT between the two groups at any time during the experiment. CONCLUSION: No changes were observed in the refractory duration, ventricular vulnerability or defibrillation energy requirements up to 90 min after ventricular ischaemic preconditioning in the pig.     

Aspirin prevents stroke but not MI in women; vitamin E has no effect on CV disease or cancer

Low-dose aspirin taken every other day helps prevent stroke in women aged 45 years and older, but does not prevent a first myocardial infarction (MI) or cardiovascular death among healthy women. Women receive no benefit from alternate-day vitamin E in the primary prevention of cardiovascular disease or cancer. These were the findings of the Women's Health Study, in which investigators followed 39,876 female health professionals over 10 years. The women were randomized to receive either 100 mg of aspirin or a placebo tablet every other day; they were also randomized to take 600 IU of vitamin E or a placebo capsule on the intervening days. No statistically significant differences were seen between the aspirin and placebo groups in the primary cardiovascular end point, which was the combined number of nonfatal MIs, nonfatal strokes, and cardiovascular deaths. Analysis of secondary cardiovascular end points revealed that aspirin use was associated with no significant effect on the number of total MIs, fatal MIs, and nonfatal MIs, and a nonsignificant decrease in cardiovascular mortality. However, aspirin users did experience significantly fewer strokes, in particular ischemic strokes. Vitamin E had very little impact on the primary prevention of both cardiovascular events and cancer.     

Fast non-genomic effects of progesterone-derived neurosteroids on nociceptive thresholds and pain symptoms

Fast Inhibitory controls mediated by glycine (GlyRs) and GABAA receptors (GABAARs) play an important role to prevent the apparition of pathological pain symptoms of allodynia and hyperalgesia. The use of positive allosteric modulators of these receptors, specifically expressed in the spinal cord, may represent an interesting strategy to limit or block pain expression. In this study, we have used stereoisomers of progesterone metabolites, acting only via non-genomic effects, in order to evaluate the contribution of GlyRs and GABAARs for the reduction of mechanical and thermal heat hypernociception. We show that 3alpha neurosteroids were particularly efficient to elevate nociceptive thresholds in naive animal. It also reduced mechanical allodynia and thermal heat hyperalgesia in the carrageenan model of inflammatory pain. This effect is likely to be mediated by GABAA receptors since 3beta isomer was inefficient. More interestingly, 3alpha5beta neurosteroid was only efficient on mechanical allodynia while having no effect on thermal heat hyperalgesia. We characterized these paradoxical effects of 3alpha5beta neurosteroid using the strychnine and bicuculline models of allodynia. We clearly show that 3alpha5beta neurosteroid exerts an antinociceptive effect via a positive allosteric modulation of GABAARs but, at the same time, is pronociceptive by reducing GlyR function. This illustrates the importance of the inhibitory amino acid receptor channels and their allosteric modulators in spinal pain processing. Moreover, our results indicate that neurosteroids, which are synthesized in the dorsal horn of the spinal cord and have limited side effects, may be of significant interest in order to treat pathological pain symptoms.     

脊髓损伤后炎症性细胞因子表达的变化及甲基强的松龙的影响

目的 观察大鼠脊髓损伤(SCI)后,甲基强的松龙(MP)对炎症性细胞因子白细胞介素-1β(IL-1β)、白细胞介素-6(IL-6)和肿瘤坏死因子-α(TNF-α) mRNA表达及运动功能恢复的影响。方法 采用改良 Allen氏法建立大鼠脊髓(T9、T10)中度损伤模型,56只SD大鼠随机分为假手术组(n=4)、SCI组(n=24)、生理盐水组(n=14)和 MP组(n=14),分别于损伤后 1 h、4 h、12 h、24 h、72 h和7 d取材,利用半定量RT PCR方法观察损伤段脊髓组织中上述 3 种细胞因子 mRNA表达的变化规律;于 SCI后30 min经尾静脉给予MP(30 mg/kg),利用半定量RT-PCR方法检测 SCI后 4 h时 MP对各炎症性细胞因子 mRNA表达的影响;利用BBB评分检测MP对大鼠SCI后运动功能恢复的影响。结果 假手术组动物脊髓组织中炎症性细胞因子mRNA仅有微弱表达。SCI后1h,各炎症性细胞因子mRNA表达明显升高,其中 IL-1β,IL-6表达于损伤后 12 h达峰值,TNF-α于损伤后 4 h达峰值,至损伤后72 h仍高于假手术组( P <0.05)。SCI后4 h时,MP组大鼠 IL-1β和TNF-αmRNA的表达明显受到抑制,但MP并未对运动功能的恢复产生有益的影响。结论 MP可明显抑制SCI后的炎症反应。     

Systemic adenosine infusion reduces the area of tactile allodynia in neuropathic pain following peripheral nerve injury: a multi-centre, placebo-controlled study.

Systemic adenosine has been shown in earlier case reports and a small placebo-controlled study to reduce pathological sensory dysfunction such as tactile allodynia in neuropathic pain. To evaluate this further, the effects of systemic adenosine infusion (50 microg/kg/min for 60 min) on tactile sensory dysfunction and pain was evaluated in 26 patients suffering peripheral neuropathic pain characterized by dynamic tactile allodynia. A randomized, cross-over, double-blind, placebo-controlled technique was used in this multi-centre study.Psychophysical methods were used to evaluate sensory dysfunction and spontaneous pain. The area of dynamic tactile allodynia was significantly reduced by adenosine compared with placebo (p=0.043), but spontaneous pain and tactile pain threshold were not significantly improved compared with the effects of placebo treatment. As a secondary outcome, a higher incidence of positive subjective effects on the clinical pain condition, in a few cases with long duration (several months), following adenosine treatment was found when the global effect of respective treatment was assessed (p=0.028). The results demonstrate involvement of adenosine receptor-sensitive pain mechanisms in some aspects of the sensory dysfunction often found in neuropathic pain.     

The Effect of Preoperative Intra-Articular Methylprednisolone on Pain After TKA: A Randomized Double-Blinded Placebo Controlled Trial in Patients With High-Pain Knee Osteoarthritis and Sensitization

In a randomized, double-blind, placebo controlled trial, we investigated the postoperative analgesic effect of a single intra-articular injection of 40?mg methylprednisolone acetate (MP) administered 1 week before total knee arthroplasty (TKA). Forty-eight patients with high pain osteoarthritis (≥5 on a numeric rating scale during walk) and sensitization (pressure pain threshold?<250?kPa), aged 50 to 80 years and scheduled for primary unilateral TKA under spinal anaesthesia were included. The primary outcome was the proportion of patients with moderate/severe pain during a 5-m walk test 24 hours postoperatively. Secondary outcomes included pain at 48 hours, during the first 14 days, sensitization (quantitative sensory testing with pressure pain threshold and wind-up from temporal summation), and inflammatory changes (systemic C-reactive protein, intra-articular interleukin [IL]-6). No difference in the proportion of patients with moderate/severe pain was found between MP/placebo groups at 24 hours (67% and 74%, χ²?=?.2, P?=?.63, odds ratio = .7, 95% confidence interval = .2–2.8) or at 48 hours (57% and 68%, χ²?=?.5, P?=?.46, odds ratio = .6, 95% confidence interval = .2–2.3), and no difference between groups in postoperative sensitization was found (P?>?.4) despite reduced preoperative intra-articular inflammation (IL-6) in the MP group versus placebo (median change in IL-6 = ?70?pg/mL, interquartile range = ?466 to 0 vs. 32?pg/mL, interquartile range = ?26 to 75, P = .029). Alternative central or peripheral analgesic interventions in this high-risk group are required.

甲基强地松龙对颅脑损伤后脑水肿及脂质过氧化反应的影响

目的观察甲基强的松龙对大鼠颅脑损伤后脑水肿及脂质过氧化反应的影响,并探讨其作用机制。方法将75只SD大鼠随机分为3组:治疗组(35只)、对照组(35只)、正常组(5只),均采用骨窗形成后硬膜外打击法造成鼠脑挫裂伤。正常组麻醉后,只行开颅手术,不作头颅打击,治疗组大鼠致伤后即刻腹腔内注射50 mg/kg甲基强的松龙,对照组则注射50 mg/kg生理盐水。对照组和治疗组大鼠分别在伤后6、12、24、48、72、96、120 h断头取脑,观察各组各时点血肿周围脑组织超氧化物歧化酶(SOD)活力和丙二醛(MDA)含量。结果对照组各时点SOD活性明显低于正常组,而MDA含量明显高于正常组,对照组各时间点含水量与SOD活力呈明显负相关,与MDA含量呈明显正相关。实验组SOD活力显著高于对照组,12~96 h时间点MDA明显低于对照组,实验组含水量与SOD活力呈显著负相关,与MDA呈显著正相关。结论甲基强的松龙使脑出血氧化损害明显减轻,激素可能是治疗脑出血后脑水肿的一个重要途径。     

Tetrodotoxin inhibits the development and expression of neuropathic pain induced by paclitaxel in mice

We evaluated the effect of low doses of systemically administered tetrodotoxin (TTX) on the development and expression of neuropathic pain induced by paclitaxel in mice. Treatment with paclitaxel (2 mg/kg, i.p., once daily during 5 days) produced long-lasting (2–4 weeks) heat hyperalgesia (plantar test), mechanical allodynia (electronic Von Frey test) and cold allodynia (acetone drop method), with maximum effects observed on days 7, 10 and 10–14, respectively. Acute subcutaneous treatment with 1 or 3 μg/kg of TTX reduced the expression of mechanical allodynia, whereas higher doses (3 or 6 μg/kg) were required to reduce the expression of cold allodynia and heat hyperalgesia. In contrast, TTX (3 or 6 μg/kg, s.c.) did not affect the response to the same thermal and mechanical stimuli in control animals, which indicates that the antihyperalgesic and antiallodynic effects of TTX were not due to unspecific inhibition of the perception of these stimuli. Administration of TTX (6 μg/kg, s.c.) 30 min before each of the 5 doses of paclitaxel did not modify the development of heat hyperalgesia produced by the antineoplastic, but abolished the development of mechanical and cold allodynia. Coadministration of a lower dose of TTX (3 μg/kg) also prevented the development of mechanical allodynia. No signs of TTX-induced toxicity or motor incoordination were observed. These data suggest that low doses of TTX can be useful to prevent and treat paclitaxel-induced neuropathic pain, and that TTX-sensitive subtypes of sodium channels play a role in the pathogenesis of chemotherapy-induced neuropathic pain.     

Nrf2/ARE信号通路激活对偏头痛大鼠神经源性炎症的影响

目的 探讨核因子E2相关因子2/抗反应元件(Nrf2/ARE)通路激活对硝酸甘油(NTG)诱导的偏头痛模型大鼠神经源性炎症的影响.方法 将大鼠随机分为NS组、莱菔硫烷(SFN)+NS组、NTG组、H2O+NTG组及SFN+NTG组,6只/组.拍摄大鼠挠头视频,应用ELISA检测颈静脉血CGRP浓度,应用Western ...     

The threshold for the depressive effect of intrathecal morphine on the spinal nociceptive flexor reflex is increased during autotomy after sciatic nerve section in rats.

The effect of intrathecal (i.t.) morphine on the spinal nociceptive flexor reflex in doses ranging between 10 ng and 10 micrograms was studied in decerebrate, spinalized, unanesthetized rats with intact sciatic nerves or in rats in which the sciatic nerve had been unilaterally sectioned. In rats with intact nerves the initial effect of i.t. morphine on the flexor reflex was a brief facilitation followed by depression. The threshold dose of morphine for reflex depression was 100 ng. In animals which did not develop autotomy after nerve section or in which autotomy had ceased for several days prior to the acute experiments, i.t. morphine had a similar depressive effect on the flexor reflex as in animals with intact nerves. However, in rats which were autotomizing at the time of the acute experiment, the threshold dose of the depressive effect of morphine was increased 3-5 fold. With higher doses of morphine (1-3 micrograms), similar depression of the reflex was found in all groups. The present results revealed a decreased sensitivity of spinal reflex mechanisms to low, but not high, doses of morphine after sciatic nerve section accompanied by autotomy. Nerve section per se did not alter opioid sensitivity. Thus, decreased effectiveness of morphine in this model for neuropathic pain may be partially due to a desensitization to the analgesic action of opioids in the spinal cord. Since after sciatic nerve section there is a differential sensitivity to the antinociceptive effect of i.t. morphine between autotomizing and non-autotomizing rats, it is further suggested that autotomy after peripheral nerve section in rats is a useful model for the study of neuropathic pain.     

褪黑素对大鼠急性脊髓损伤的保护作用

目的：探讨褪黑素对大鼠急性脊髓损伤的作用。方法：将72只Wistar成熟健康大鼠随机分为褪黑素组、甲泼尼龙琥珀酸钠组、生理盐水组、无水乙醇组，采用改良Allen’s技术（5g×10cm）以1、9为中心制作急性脊髓损伤模型：损伤后10min分别予以褪黑素（100mg／kg）、甲泼尼龙琥珀酸钠（30mg／kg）、生理盐水及5％无水乙醇腹腔内注射，伤后2h、24h、72h分别观察各组BBB评分变化，取T8、T9、T10 3个脊髓节段，应用免疫组化对脊髓组织及P53阳性细胞进行标记，探讨褪黑素对急性脊髓损伤有无保护作用。结果：在急性脊髓损伤后，各观测时间点褪黑素组与甲泼尼龙琥珀酸钠组BBB评分均较生理盐水组及无水乙醇组明显升高（P〈0．01），褪黑素组与甲泼尼龙琥珀酸钠组之间差异无显著性（P〉0.05）；P53阳性细胞的表达在脊髓损伤后各组均呈逐渐增高趋势，但褪黑素组与甲泼尼龙琥珀酸钠组较生理盐水组及无水乙醇组P53阳性细胞表达降低（P〈0．01），褪黑素组与甲泼尼龙琥珀酸钠组之间P53阳性细胞表达差异无显著性（P〉0．05），无水乙醇组与生理盐水组差异无显著性（P〉0．05）。结论：褪黑素对大鼠急性脊髓损伤具有保护性治疗作用，其作用效果与甲泼尼龙琥珀酸钠相似。     

甲基强的松龙对大鼠肠缺血再灌注损伤的保护作用

目的研究甲基强的松龙对大鼠小肠缺血再灌注肠黏膜损伤的保护作用,为扩展其临床新用途提供实验依据。方法通过建立大鼠小肠缺血再灌注模型,检测缺血再灌注1 h后血清和小肠组织的超氧化物歧化酶(SOD)和丙二醛(MDA)的含量,并观察小肠黏膜病理变化。结果小肠缺血再灌注后,血清及小肠组织中反映氧化损伤程度的MDA明显升高,抗氧化酶SOD则明显减少,小肠黏膜损伤,应用甲基强的松龙后能显著改善上述改变。结论甲基强的松龙对肠缺血再灌注引起的肠黏膜损伤具有明显保护作用。     

Contribution of peripheral endothelin ETA and ETB receptors in neuropathic pain induced by spinal nerve ligation in rats

Endothelins (ETs) contribute to the sensory changes seen in animals models of inflammatory, cancer and diabetic neuropathic pain, but little is known about their nociceptive role following peripheral nerve injury. The current study evaluated mechanisms by which ETs can drive changes in nociceptive responses to thermal stimulation of the hind paw of rats induced by unilateral lumbar L5/L6 spinal nerve ligation (SNL) injury. SNL sensitizes rats to acetone-evoked cooling of and radiant heat application (Hargreaves test) to the ipsilateral hind paw (throughout 3–40 and 9–40 days after surgery, respectively). At 12 days after SNL, intraplantar (i.pl.) injection of endothelin-1 (ET-1, 10 pmol) induces greater overt nociception that was reduced only by treatment with the selective ET_A peptidic antagonist (BQ-123, 10 nmol, i.pl), but unchanged by the selective ET_B peptidic antagonist (BQ-788). Cold allodynia evoked by cooling the ipsilateral hind paw with acetone was reduced by i.pl. injection of both antagonists BQ-123 or BQ-788 (3 or 10 nmol). In contrast, heat hyperalgesia evaluated by Hargreaves method was reduced only by BQ-123. SNL enhanced the [Ca⁺²]_i increases induced by ET-1 (100 nM) in neurons from L5/L6 (injured) and L4 (intact) cultured dorsal root ganglion, but did not change the responses of non-neuronal cells. Furthermore, Western blot analysis revealed that SNL increased ET_A and ET_B receptor protein expression in spinal nerves. Thus, SNL induces marked hind paw hypersensitivity to thermal stimulation in part via up-regulation of peripheral sensory nerve pronociceptive ET_A and ET_B receptor-operated mechanisms.     

TRPV1 is important for mechanical and heat sensitivity in uninjured animals and development of heat hypersensitivity after muscle inflammation

Inflammatory thermal hyperalgesia is principally mediated through transient receptor potential vanilloid 1 (TRPV1) channels, as demonstrated by prior studies using models of cutaneous inflammation. Muscle pain is significantly different from cutaneous pain, and the involvement of TRPV1 in hyperalgesia induced by muscle inflammation is unknown. We tested whether TRPV1 contributes to the development of mechanical and heat hypersensitivity of the paw in TRPV1(-/-) mice after muscle inflammation. Because TRPV1(-/-) mice lack TRPV1 at the site of inflammation (muscle) and at the testing site (paw), we do not know whether TRPV1 is important as a mediator of nociceptor sensitization in the muscle or as a heat sensor in the paw. Using recombinant herpesviruses, we reexpressed TRPV1 in TRPV1(-/-) mice in primary afferents innervating skin, muscle, or both to determine which sites were important for the behavioral deficits. Responses to repeated application of noxious mechanical stimuli to the hind paw were enhanced in TRPV1(-/-) mice; this was restored by reexpression of TRPV1 into skin. Withdrawal latencies to noxious heat were increased in TRPV1(-/-) mice; normal latencies were restored by reexpression of TRPV1 in both skin and muscle. Heat hypersensitivity induced by muscle inflammation did not develop in TRPV1(-/-) mice; mechanical hypersensitivity was similar between TRPV1(-/-) and TRPV1(+/+) mice. Heat hypersensitivity induced by muscle inflammation was restored by reexpression of TRPV1 into both muscle and skin of TRPV1(-/-) mice. These results suggest that TRPV1 serves as both a mediator of nociceptor sensitization at the site of inflammation and as a heat sensor at the paw.