Studies on the antinociception effect of melatonin and its mechanism in the rat

The antinociception effect of melatonin（Mel） and its mechanisms were studied on the trauma- pain model in the rat. A trauma - pain model was established in Wistar rats by combining right - hind limb amputation with 50℃ tail - flick test. The effects of Mel on central sensitization were studied through measuring the changes of the expression of c - fos （ an indicator of nociceptive transmission at the spinal level ） , subtance P（SP） and brain - derived neurotrophic factor （BDNF） in the spinal cord using immunohistochemistry. In addition, the contents of nitric oxide （NO） in brain and spinal tissues were also observed. The results showed that the immunoreactivity of BDNF and c - fos in spinal dorsal horn in injuried rats began to increase at the first day,     

Aquaporin 4 deficiency attenuates neurophathic pain through its suppressing the activation of astrocytes

OBJECTIVE Accumulating evidence reveals that spinal glias,including astrocytes and microglias,play an important role in the processing of chronic pain,especially neuropathic pain.Aquaporin 4(AQP4),the predominant water channel existing in astrocytes,has been proved to modulate astrocytic functions,as well as neuronal functions via the interaction between astrocytes and neurons.In the present study,we investigated the role of AQP4 in acute and chronic pain and the possible mechanism.METHODS We first studied the effect of acetazolamide,a non-selective AQP4 inhibitor,on pain.Then we investigated the role of AQP4 deficiency in acute pain and chronic pain including neuropathic pain and inflammatory pain.In the SNI model,the AQP4 expression,the GFAP and CR3 expressions,markers of astrocytes activation and microglia activation,were analyzed by Western blot and the proinflammatory cytokines(IL-1β,IL-6 and TNF-α) contents in spinal cord were detected by ELISA.RESULTS Acetazolamide,non-selective AQP4 inhibitor,produced dose-dependent analgesia in the rat sciatic nerve chronic constriction injury(CCI) model(P<0.01),a model of neuropathic pain,but not in the mouse tail-flick and hot-plate tests,two models of thermal-stimulated acute pain,suggesting AQP4 might participate in chronic pain,rather than acute pain.Then we used wild-type(WT) and AQP4 knockout(KO) mice to study the role of AQP4 in acute pain and chronic pain.We found that AQP4 deficiency failed to affect the responses of mice to the acute pain induced by thermal(tail-flick and hot-plate tests),chemical(formalin and capsaicin tests) and mechanical(von Frey hair test) stimuli.However,AQP4 deficiency attenuated the mechanical allodynia in the models of spared nerve injury(SNI)-induced neuropathic pain and complete Freund′s adjuvant(CFA)-induced inflammatory pain.Furthermore,the possible mechanism was investigated.In the SNI model,A*QP4 expression was significantly increased in WT-SNI group(P<0.001) compared with WT-sham group,14 d after injury.Meanwhile,GFAP expression in the spinal cord was also significantly increased in WT-SNI group(P<0.001) compared with WT-sham group,whereas no changes of the GFAP expression were detected in KO-Sham group and KO-SNI group.However,no changes of the CR3 expression were detected in all the groups.In addition,the IL-1β,IL-6 and TNF-α contents were elevated in the spinal cord of WT-SNI group compared with WT-sham group(P<0.05),whereas no changes of the proinflammatory cytokines contents were detected in KO-sham group and KO-SNI group.CONCLUSION Taken together,our findings demonstrated that AQP4 appears to contribute to chronic pain,especially neuropathic pain,but not acute pain.The suppression of astrocytes activation and proinflammatory cytokines release might mediate the attenuation of AQP4 deficiency to the neuropathic pain.     

鞘内注射大麻酚类抑制大鼠脊髓内有毒刺激引起的Fos蛋白样免疫反应及其与吗啡的比较(英文)

AIM: To determine whether cannabinoids suppressnoxious stimulu-evoked Fos protein-like immunoreac-tivity (FLI) through direct actions at the spinal level.METHODS: Rats were implanted with intrathecal(ith) catheters at least one week prior to evaluation inthe formalin test. Effects of the cannabinoid agonist,CP55,940 (80 μg ith) on formalin pain and FLI in ratspinal cord were compared with that of the prototypicnarcotic analgesic, morphine (20 μg ith). CP55, 940suppressed pain behavior and FLI induced by intra-plantar formalin. The cannabinoid suppressed Fos inthe neck region of the dorsal horn and in the ventralhorn,but not in the nucleus proprius. The efficacy ofthe cannabinoid in suppressing FLI in these laminae and     

Widespread enhancement of pain sensitivity in MRL/MpJ mice following infraorbital nerve transection

OBJECTIVE Neuropathic pain in humans may spread to regions beyond the area innervated by the injured nerve.This study aims to verify the appearance of wide-spread neuropathic pain following infraorbital nerve transection and investigate the mechanisms underlying wide-spread pain.METHODS The infraorbital nerve of male MRL/MPJ mice was transected(ION-T) to induce trigeminal neuralgia under isoflurane anesthesia.The sensitivities to tactile and heat stimuli of different body parts including the vibrissal pads,hindpaws,and tail were tested after surgery.Activation of microglia in the dorsal horn at levels of medulla(MDH) and L4/L5(SDH) were measured by immunohistochemistry.RESULTS Compared to sham-operated mice,injured mice showed significantly mechanical allodynia,heat allodynia and hyperalgesia in the ipsilateral vibrissal pad,and extraterritorially in the contralateral vibrissal pad,bilateral hindpaws and tail.There was a negative correlation between the evoked pain in denervated area and extraterritorial areas.Microglia in the MDH of injured mice were significantly activated 3 d postoperatively.However,the activation of microglia in L4/L5 SDH occurred until 7 d postoperatively.Moreover,intraperitoneal injection of minocycline inhibited the wide-spread pain abnormalities in the vibrissal pads,hindpaws,and tail.CONCLUSION These results indicate the appearance of wide-spread neuropathic pain following infraorbital nerve transection.Microglia activation may be involved in the mechanisms of this phenomenon.     

大麻酚类受体-1在脊髓、背角、背根神经节和周围神经的分布(英文)

AIM: The localization of CB1 receptors in the spinalcord, spinal roots, dorsal root ganglion (DRG), andperipheral nerve of the rat was determined.METHODS: We studied the distribution of CB1cannabinoid receptors by immunohistochemistry usingan antibody raised against the N-termina1 of thereceptor. RESULTS: The spinal cord showednumerous transverse fibers labelled for CB1 receptorsthroughout and concentrated in the dorsal horn.Lightly-stained cells were observed throughout thespinal cord gray matter. The DRG also showed cellsand fibers labelled for CB1 receptors. Labelled fiberswere observed in both dorsal and ventral roots as well as     

Role of the NR2B-containing NMDA receptor-ERK pathway in nucleus accumbens shell in morphine-associated contextual memory

Learned associations between the rewarding effect of addictive drugs and drug-paired contexts resist extinction and contribute to the high rate of relapse observed in drug addicts.Although it has been shown that extracellular signal-regulated kinase 1/2(ERK1/2) activity in the nucleus accumbens(NAc) is modulated by the primary rewarding effect of opiates,little is known as to its role in the morphine-associated contextual memory.In the present study,we investigated the ERK1/2 activity indicated by phosphorylated ERK1/2(pERK1/2) levels in rats using a morphine-induced conditioned place preference(CPP) procedure.Our results showed that,in rats that had undergone morphine conditioning,after testing(expression phase) pERK1/2 in the NAc shell but not the NAc core or the adjacent caudate putamen was specifically increased.pERK1/2 levels in several other parts of the brain involved in drug-seeking,such as the medial prefrontal cortex,dorsal hippocampus,and basolateral amygdala,showed no significant changes.A significant positive correlation was observed between the elevated pERK1/2 level in the NAc shell and the degree of conditioned preference for morphine-associated contexts.Bilateral injection of an inhibitor of ERK activation into the NAc shell attenuated ERK1/2 phosphorylation and the expression of morphine CPP,but injections into the core did not.Selective inhibition of NR2B-containing NMDA receptor in the NAc shell by ifenprodil prevented CPP expression and down-regulated local ERK1/2 phosphorylation.These findings collectively suggest that recall of morphine-associated contextual memory depends specifically upon ERK1/2 activation in the NAc shell and that ERK1/2 phosphorylation is regulated by the upstream NR2B-containing NMDA receptor.     

Gonadectomy affects brain derived neurotrophic factor in rats after chronic constriction nerve injury

INTRODUCTION The development of animal models of neuropathicpainhas beenof value in characterizingthe neuralmecha-nisms involved in neuropathic pain syndromes and as-sociated processes following peripheral nerve injury.The chronic constriction injury (CCI) model[1], producedby loose ligation of the sciatic nerve with four chromicgut sutures, has been known as one of the most reliablemodels of neuropathic pain. With CCI of the rat sciaticnerve, animals show symptoms similar to the clinic…     

D2 receptor activation relieves pain hypersensitivity by inhibiting superficial dorsal horn neurons in parkinsonian mice

Chronic pain is a common and undertreated nonmotor symptom in Parkinson’s disease(PD).Although chronic pain is improved by L-dopa in some PD patients,the underlying mechanisms remain unclear.In this study,we established PD mice by unilateral microinjection of 6-OHDA in the medial forebrain bundle to investigate the contribution of spinal cord dopamine receptors to parkinsonian pain hypersensitivity.The von Frey filament tests and thermal pain tests revealed that these PD mice displayed decreased nociceptive thresholds in both hindpaws;intrathecal injection of L-dopa or apomorphine significantly increased the mechanical and thermal nociceptive thresholds,and the analgesic effect was mimicked by ropinirole(a D2 receptor agonist),but not SKF38393(a D1/D5 receptor agonist),and blocked by sulpiride(a D2 receptor antagonist),but not SKF83566(a D1/D5 receptor antagonist).Whole-cell recordings in lumber spinal cord slices showed that superficial dorsal horn(SDH)neurons in PD mice exhibited hyperexcitability,including more depolarized resting membrane potentials and more action potentials evoked by depolarizing current steps,which were mitigated by ropinirole.Furthermore,ropinirole inhibited the frequency of spontaneous excitatory postsynaptic currents(sEPSCs)in SDH neurons more strongly in PD mice than in control mice.However,sulpiride caused less disinhibition of sEPSCs in PD mice than in control mice.Taken together,our data reveal that pain hypersensitivity in PD mice is associated with hyperexcitability of SDH neurons,and both events are reversed by activation of spinal D2 receptors.Therefore,spinal D2 receptors can be promising therapeutic targets for the treatment of PD pain.     

Molecular mechanisms of ZD1839 （Iressa）-induced apoptosis in human leukemic U937 cells

Aim： To investigate the molecular mechanisms of ZD 1839-induced apoptosis in human leukemic U937 cells. Methods： The inhibition of human leukemic U937 cell growth was assessed by 3-（4,5-dimethyl-2-thiazolyl）-2,5-diphnyl-2H-tetrazolim bromide （MTT） assays, lactate dehydrogenase （LDH） release, and cell cycle distribution. The expression of anti- and pro-apoptotic proteins was detected by Western blot analysis. Results： This study demonstrated that ZD1839 induced apoptosis in leukemic U937 cells by the downregulation of Bcl-2, caspase activation and subsequent apoptotic features. Cotreatment with ZD 1839 and the caspase- 3 inhibitor z-DEVD-fmk blocked apoptosis, indicating that caspase-3 activation is at least partially responsible for ZD 1839-induced apoptosis. The ectopic expression of Bcl-2 attenuated caspase-3 activation, PARP cleavage, and subsequent indicators of apoptosis, including sub-G1 DNA content and LDH release. These results indicate that the downregulation of Bcl-2 plays a major role in the initiation of ZD1839-induced apoptosis, and that the activation of a caspase cascade is involved in the execution of apoptosis. Furthermore, ZD1839 treatment triggered the activation of p38 mitogen-activated protein kinase （MAPK） and the downregulation of c-Jun-N-terminal kinase （JNK）, extracellular signal-regulated kinase （ERK） and phosphatidyl inositol 3-kinase （PI3K）/Akt. The inhibition of the ERK and PI3K/Akt pathways also significantly increased cellular death. Conclusion： ZD 1839 activated caspase-3 and the inhibited Bcl-2 in human leukemic U937 cells through the downregulation of the ERK and PI3K/Akt pathways.     

外周疼痛模型大鼠脊髓背角环氧化酶表达时程的研究

Objective To compare the expression of two cyclooxygenase (COX) isoforms (COX-1 and COX-2) in the spinal cord of rats with inflammatory pain following peripheral formalin injection. Methods Experiments were performed on adult male Sprague-Dawley rats. 100μl of 5% formalin were injected subcutaneously into plantar hind paw of 30 rats to induce pain. The changes of COX-1 and COX-2 expression were evaluated by western blot in 30 rats, respectively at 2 hours, 6 hours, 1 day, 3 days, 7 days and 14 days after injection. The control group rats were injected with 100 μl of 0.9% saline instead of formalin in 20 rats. Results The expression of COX-1 significantly increased at 1day, 3 days, 7 days and 14 days, but the expression of COX-2 only transiently increased at 2 hours. Conclusions COX-1 and COX-2 are increasingly expressed in the spinal cord, furthermore,spinal COX-2 expression is induced early and transiently increased. COX-1 is up-regulated later and remains elevated for long time, which may explain the long-term hyperalgesia evoked by formalin injection.     

骨癌痛大鼠鞘内注射U0126的抗痛觉过敏作用

目的研究鞘内注射(it)U0126对骨癌痛大鼠机械痛敏的影响和对脊髓背角磷酸化cAMP反应元件结合蛋白(pCREB)表达的影响,探讨ERK-CREB信号转导通路在骨癌痛中的作用。方法①40只成年♀SD大鼠分为5组,假模型组Ⅰ和骨癌痛模型组Ⅱ、Ⅲ、Ⅳ、Ⅴ。建模后d 10每只大鼠分别it 10μg U0126、5%二甲亚砜10μl和U0126 0.1、1、10μg(U0126溶于10μl 5%二甲亚砜中),测机械性缩爪阈值(MWT)和双下肢负重差(WBD);②25只成年♀SD大鼠分为5组,T1、T2和T3组在制作骨癌痛模型后d 10,itU0126 10μg后1、6、24 h处死大鼠,M组为模型对照组,it5%二甲亚砜10μl后6 h处死大鼠,S组为空白对照组。免疫组化方法测定L4-6术侧脊髓背角pCREB免疫反应阳性神经元数量。结果鞘内注射U0126 1μg和10μg明显逆转了骨癌痛引起的机械痛敏;鞘内注射10μg U0126明显减少脊髓背角pCREB表达,且效果至少可持续6 h。结论 ERK-CREB通路可能参与骨癌痛。     

Down-regulation of GFRalpha-1 expression by antisense oligodeoxynucleotide aggravates thermal hyperalgesia in a rat model of neuropathic pain

Glial cell line-derived neurotrophic factor (GDNF) has been hypothesized to play an important role in the modulation of nociceptive signals especially during neuropathic pain. The present study examined the expression of GDNF and GFRalpha-1 (the high-affinity receptor of GDNF) in dorsal root ganglions (DRG) in a rat model of neuropathic pain induced by chronic constriction injury (CCI) to the sciatic nerve. In order to address the role of GDNF and GFRalpha-1 in neuropathic pain, antisense oligodeoxynucleotide (ODN) specifically against GFRalpha-1 was intrathecally administered to result in down-regulation of GFRalpha-1 expression. The results showed that both the protein and mRNA levels of GDNF and GFRalpha-1 were significantly increased after CCI, while the thermal hyperalgesia of neuropathic pain rats could be significantly aggravated by antisense ODN treatment, but not by normal saline (NS) or mismatch ODN treatment. The present study demonstrated that endogenous GDNF and GFRalpha-1 might play an anti-hyperalgesic role in neuropathic pain of rats. In addition, we found a down-regulation of somatostatin (SOM) in DRG and spinal dorsal horn after expression of GFRalpha-1 was knocked down, which suggested the possible relationship between the anti-hyperalgesic effect of GDNF and GFRalpha-1 on neuropathic pain and endogenous SOM.     

Knock down of the alpha 5 nicotinic acetylcholine receptor in spinal nerve-ligated rats alleviates mechanical allodynia

Nicotinic acetylcholine receptor (nAChR) agonists are known to alleviate neuropathic and inflammatory pain via activation of a heterogeneous population of receptors. However, the function of nAChRs in the maintenance of neuropathic pain is not known. Spinal nerve ligation (SNL) increases the spinal expression of the alpha5 nAChR subunit ipsilateral to injury. The alpha5 subunit is unique because it modifies numerous characteristics of existing functional nAChRs, but it does not form functional nAChRs when expressed alone or with beta nicotinic subunits. Because there are no alpha5 subunit selective ligands, we used antisense oligonucleotides (ODNs) to assess the contribution of the alpha5 subunit to the maintenance of mechanical allodynia following SNL. Intrathecal antisense oligonucleotides were administered to SNL rats after the development of mechanical allodynia (10-12 days post-SNL). I.t. antisense specifically reduced alpha5 immunoreactivity (alpha5-IR) by 50-70% in the outer laminae of the dorsal horn and moderately alleviated mechanical allodynia. Furthermore, using the phosphorylation of cAMP response element-binding protein (pCREB) as a general marker of neuronal activation, a significant increase in pCREB immunoreactivity was observed in SNL rats. Treatment of SNL rats with alpha5-antisense significantly reduced pCREB immunoreactivity. These results suggest that the increased expression of the alpha5 nAChR subunit following SNL contributes to spinal CREB phosphorylation and the maintenance of mechanical allodynia.     

Activation of spinal ERK signaling pathway contributes to pain-related responses induced by scorpion Buthus martensi Karch venom

It has been demonstrated that spontaneous nociceptive behaviors, cutaneous hyperalgesia and paw edema can be induced by intraplantar injection of scorpion Buthus martensi Karch (BmK) venom in rats. In the present study, activation of spinal extracellular signal-regulated kinase (ERK) signaling pathway and its contribution to pain-related responses induced by scorpion BmK venom were investigated. It was found that ERK was activated not only in the superficial layers but also in deep layers of L4–L5 spinal cord dorsal horn, which started at 2 min, peaked at 30–60 min and almost disappeared at 4 h following intraplantar injection of BmK venom. Intrathecal injection of U0126 (0.1, 1.0 and 10 μg), a widely used specific MAP kinase kinase (MEK) inhibitor, suppressed spontaneous nociceptive responses and reduced primary heat hyperalgesia and bilateral mechanical hyperalgesia induced by BmK venom. In addition, BmK venom-induced spinal c-Fos expression could be inhibited by U0126 dose-dependently. Intrathecal delivery of NMDA receptor antagonist (5R, 10S)-(+)-5-methyl-10, 11-dihydro-5H-dibenzo [a,d]-cyclohepten-5-10-imine hydrogen maleate (MK-801) and the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) could partially inhibit activation of spinal ERK induced by BmK venom at 30 min. Thus, activation of ERK in spinal cord dorsal horn, partially mediated by NMDA and non-NMDA receptor, potentially contributes to BmK venom-induced pain-related behaviors.     

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.     

Intrathecal lemnalol, a natural marine compound obtained from Formosan soft coral, attenuates nociceptive responses and the activity of spinal glial cells in neuropathic rats

The investigators previously found that the administration of lemnalol, a natural marine compound isolated from the Formosan soft coral Lemnalia cervicorni, produced anti-inflammatory and analgesic effects in carrageenan-injected rats. Recently, several studies have demonstrated that the development and maintenance of neuropathic pain are accompanied by releasing of proinflammatory mediators from activated glial cells in the spinal cord. In this study, we investigated the antinociceptive properties of lemnalol, a potential anti-inflammatory compound, on chronic constriction injury (CCI) in a well-established rat model of neuropathic pain. Our results demonstrated that a single intrathecal administration of lemnalol (0.05-10 μg) significantly attenuated CCI-induced thermal hyperalgesia and mechanical allodynia, 14 days postsurgery. Furthermore, immunohistofluorescence analyses showed that lemnalol (10 μg) also significantly inhibits CCI-induced upregulation of microglial and astrocytic immunohistochemical activation markers in the dorsal horn of the lumbar spinal cord. Double immunofluorescent staining demonstrated that intrathecal injection of lemnalol (10 μg) markedly inhibited spinal proinflammatory mediator tumor necrosis factor-α expression in microglial cells and astrocytes in neuropathic rats. Collectively, our results indicate that lemnalol is a potential therapeutic agent for neuropathic pain, and that further exploration of the effects of lemnalol on glial proinflammatory responses is warranted.     

Cross talk between nitric oxide and ERK1/2 signaling pathway in the spinal cord mediates naloxone-precipitated withdrawal in morphine-dependent rats

Our recent study has shown activation of spinal extracellular signal-regulated kinase-1 and -2 (ERK1/2), a member of the mitogen-activated protein kinase (MAPK) family, contributes to naloxone-precipitated withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats. However, the mechanism and significance of the spinal ERK1/2 activation during morphine dependence and withdrawal remain unknown. In this study, we reported that intrathecal (i.t.) pretreatment with either the non-selective nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), neuronal NOS (nNOS) inhibitor 7-nitro indazole (7-NI), or the inducible NOS (iNOS) inhibitor aminoguanidine (AG), could reduce morphine withdrawal-induced increase of phospho-ERK1/2 (pERK1/2) expression in the rat spinal cord. On the other hand, attenuation of the spinal ERK phosphorylation by the MAPK kinase (MEK) inhibitor U0126 also could inhibit the increase of nNOS and iNOS expression in the spinal cord of morphine withdrawal rats. Inhibitory expression of pERK1/2 by i.t. NOS inhibitor L-NAME, 7-NI or AG and of nNOS and iNOS by i.t. U0126 in the spinal cord were accompanied by decreased scores of morphine withdrawal and the inhibited spinal Fos protein (a maker for neuronal excitation or activation) expression induced by morphine withdrawal. These findings suggest cross talk between nitric oxide (NO) and the ERK1/2 signaling pathway mediates morphine withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats.     

坐骨神经慢性压迫损伤性疼痛与脊髓背角P物质关系研究

目的观察大鼠坐骨神经慢性压迫性损伤（CCI）后脊髓背角P物质表达的变化,探讨P物质在疼痛发生机制中的作用。方法SD雄性大鼠60只,随机分为：A组：CCI组（30只）;B组：对照组（30只）。术前及术后3、7、14、28 d分别测定大鼠热痛阈值、机械痛阈值和行为学评分。术后3、7、14、28d每组取4只,麻醉后用4%多聚甲醛灌注固定,取L4-6段脊髓,以备免疫组化,测定SP的变化。结果所有CCI动物从术后第3天起,出现明显的疼痛行为学改变和热痛阈值、机械痛阈值的降低,与对照组比较差异有统计学意义（P〈0.05或P〈0.01）。免疫组织化学结果表明,A组术后术侧明显高于B组（P〈0.05或P〈0.01）;A组术侧明显高于健侧（P〈0.05或P〈0.01）;而B组仅在第4天术侧高于健侧（P〈0.05）。结论慢性坐骨神经损伤后,脊髓背角SP的表达增加,而且表达增加与CCI大鼠的痛觉过敏、行为变化在时相上基本一致,说明CCI大鼠痛觉过敏与脊髓背角SP的表达增加有关。     

Identification of MEK1 as a novel target for the treatment of neuropathic pain

(1) In the present study we have attempted to identify changes in gene expression which are associated with neuropathic pain using subtractive suppression hybridization analysis of the lumbar spinal cord of animals suffering streptozocin induced diabetic neuropathy. (2) Using this approach, we found a significant up-regulation of several key components of the extracellular signal-regulated kinase (ERK) cascade. These findings were confirmed by Western blot analysis, which demonstrated that the levels of active ERK1 and 2 correlated with the onset of streptozocin-induced hyperalgesia. (3) Intrathecal administration of the selective MAPK/ERK-kinase (MEK) inhibitor PD 198306 dose-dependently (1-30 micro g) blocked static allodynia in both the streptozocin and the chronic constriction injury (CCI) models of neuropathic pain. (4) The antihyperalgesic effects of PD 198306, in both the streptozocin and CCI models of neuropathic pain, correlated with a reduction in the elevated levels of active ERK1 and 2 in lumbar spinal cord. (5) Intraplantar administration of PD 198306 had no effect in either model of hyperalgesia, indicating that changes in the activation of ERKs and the effect of MEK inhibition are localized to the central nervous system. (6) In summary, we have demonstrated for the first time that the development of neuropathic pain is associated with an increase in the activity of the MAPK/ERK-kinase cascade within the spinal cord and that enzymes in this pathway represent potential targets for the treatment of this condition.     

The ERK/MAPK pathway,as a target for the treatment of neuropathic pain

Peripheral nerve injury produces neuropathic pain as well as phosphorylation of mitogen activated protein kinase (MAPK) family in dorsal root ganglia (DRG) and dorsal horn. Following nerve injury, phosphorylation of extracellular signal-regulated protein kinase (ERK), an important member of this family, is sequentially increased in neurons, microglia and astrocytes of the dorsal horn and gracile nucleus, and in injured large DRG neurons. Nerve injury-induced phosphorylation of ERK occurs early and is long-lasting. In several animal models of neuropathic pain, MEK inhibitors, known to suppress the synthesis of ERK, have proven effective to alleviate pain at various time points. Thus, the regulation of ERK/MAPK can be considered as a promising therapeutic target for the treatment of neuropathic pain.