Antihyperalgesic and antiallodynic effect of sirolimus in neuropathic pain and the role of cytokines in this effect

Recent studies have revealed that T lymphocytes play a role in neuropathic pain following nerve injury in rats through releasing several cytokines. Sirolimus is an immunosuppressive antibiotic inhibiting T cell activation. This study aimed to determine the effect of sirolimus on hyperalgesia and allodynia and on serum and spinal cord TNF-α, IL-1β and IL-6 levels in rat neuropathic pain. Neuropathic pain was induced by loose ligation of the sciatic nerve and evaluated by tests measuring the mechanical hyperalgesia and allodynia. Sirolimus (0.75 and 1.5 mg/kg) was administered intraperitoneally once every 3 days for 2 weeks (7 doses totally). This dosing regimen revealed acceptable blood concentrations in neuropathic rats. Chronic constriction injury of the sciatic nerve resulted in hyperalgesia and allodynia. Serum levels of cytokines remained unchanged in neuropathic rats. However, TNF-α, but not IL-1β or IL-6, protein level was increased in the spinal cord tissue as evaluated by Western blotting analysis. Treatment with sirolimus resulted in antihyperalgesic and antiallodynic effects and prevented the increased spinal cord TNF-α level. It seems that sirolimus could be a promising immunosuppressive agent in the treatment of neuropathic pain.     

氯胺酮鞘内给药对神经病理性痛大鼠脊髓背角小胶质细胞活化、TNF-α和IL-1β产生的影响

目的:探究鞘内注射氯胺酮(ketamine,KTM)对坐骨神经结扎(CCI)神经病理性疼痛大鼠模型行为、脊髓背角肿瘤坏死因子-α(TNF-α)和白介素1β(IL-1β)以及小胶质细胞标记蛋白OX42表达的影响。方法:(1)建立CCI模型大鼠,鞘内注射KTM或MI(米诺四环素)进行干预,测定大鼠机械缩足阈值(MWT)和热缩足潜伏期(TWL)。(2)运用ELISA法检测TNF-α和IL-1β表达水平。(3)使用Western Blot法检测OX42的表达情况。结果:(1)KTM组和MI组大鼠MWT和TWL值较CCI组显著升高;KTM组大鼠MWT和TWL值高于CCI组(P0.05)。(2)KTM组和MI组TNF-α和IL-1β表达水平低于CCI组(P0.05);其中KTM组TNF-α和IL-1β表达水平显著高于MI组(P0.05)。(3)KTM组和MI组OX42表达水平显著低于CCI组;KTM组OX42表达水平高于MI组(P0.05)。结论:鞘内KTM可以抑制脊髓背角小胶质细胞激活,减少TNF-α和IL-1β表达,显著改善坐骨神经结扎引起的神经病理性疼痛。     

Antihyperalgesic and Anti-inflammatory Effects of Atorvastatin in Chronic Constriction Injury-Induced Neuropathic Pain in Rats

Atorvastatin is a 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitor used in treatment of hypercholesterolemia and prevention of coronary heart disease. The aim of this study is to investigate the antihyperalgesic and anti-inflammatory effects of atorvastatin (3, 10, and 30 mg/kg by oral gavages for 14 days) in chronic constriction injury (CCI) model of neuropathic pain in rats. CCI caused significant increase in tumor necrosis factor-α, interleukin 1 beta, prostaglandin E2, along with matrix metalloproteases (MMP-2) and nerve growth factor (NGF) levels in sciatic nerve and spinal cord concomitant with mechanical and thermal hyperalgesia, which were significantly reduced by oral administration of atorvastatin for 14 days as compared to CCI rats. Our study demonstrated that atorvastatin attenuates neuropathic pain through inhibition of cytokines, MMP-2, and NGF in sciatic nerve and spinal cord suggesting that atorvastatin could be an additional therapeutic strategy in management of neuropathic pain.     

医用臭氧通过下调神经病理性痛大鼠核因子κB/核因子κB抑制蛋白α/核因子κB抑制蛋白激酶β的表达发挥镇痛效应

目的观察医用臭氧(OZ)对坐骨神经慢性缩窄性损伤(CCI)致神经病理性痛大鼠的镇痛作用及对核因子κB(NF-κB)、核因子κB抑制蛋白α(IκBα)及核因子κB抑制蛋白激酶β(IKKβ)表达水平的影响。方法采用CCI法复制大鼠神经病理性痛动物模型,同时给予不同剂量(0.8、0.4、0.2ml)的OZ予以干预,用Von Frey纤维丝机械刺激触痛仪及冷板测痛仪测定不同剂量OZ对CCI大鼠的机械缩足反射阈值与冷缩足反射阈值的影响;用RT-PCR法和Western blotting法检测不同剂量OZ对CCI大鼠脊髓组织NF-κB p65、IκBα及IKKβmRNA和蛋白表达水平的影响。结果与CCI神经病理性痛模型组比较,OZ 0.8、0.4ml剂量升高CCI大鼠机械缩足反射阈值,降低冷缩足反射阈值(P0.05,P0.01);OZ 0.8、0.4ml剂量可下调CCI大鼠脊髓组织NF-κB p65、IκBα及IKKβmRNA和蛋白表达水平(P0.05,P0.01)。结论 OZ对CCI致神经病理性痛大鼠有镇痛作用,其机制可能与下调NF-κB p65、IκBα及IKKβ的表达有关。     

Transient early expression of TNF-alpha in sciatic nerve and dorsal root ganglia in a mouse model of painful peripheral neuropathy

The proinflammatory cytokine tumor necrosis factor-alpha (TNF) is an important mediator in neuropathic pain. We investigated the temporal pattern of TNF mRNA expression in the sciatic nerve, in dorsal root ganglia (DRG) and spinal cord in the mouse chronic constriction injury model of neuropathy with quantitative real-time polymerase chain reaction. Neuropathic pain-like behaviour was monitored by evaluating thermal hyperalgesia and mechanical allodynia. Pain-related behaviour and TNF expression were evaluated 6 h, 1, 3, 7 and 14 days after injury. Naive animals and sham-operated mice were used as controls. We found an early upregulation of sciatic nerve TNF mRNA levels in chronic constriction injury (CCI) and sham-operated animals 6 h after surgery: 1 day later TNF overexpression was present in CCI mice only and disappeared 3 days after injury. The mRNA cytokine levels were elevated in DRG 1 and 3 days after surgery in CCI animals only, while the cytokine was not modulated in the spinal cord. A significant hyperalgesia was present in CCI and sham-operated mice at 6 h and 1 day, while at later time point only CCI mice presented lower thresholds. Mechanical allodynia was already present only in CCI animals 6 h from surgery and remained constant up to the 14 th day. The results indicate that a transient early TNF upregulation takes place in peripheral nervous system after CCI that can activate a cascade of proinflammatory/pronociceptive mediators.     

Intrathecal siRNA against Toll-like receptor 4 reduces nociception in a rat model of neuropathic pain

Background: Neuropathic pain is characterized by hyperalgesia, allodynia and spontaneous pain. It often occurs as a result of injury to peripheral nerves, dorsal root ganglions (DRG), spinal cord, or brain. Recent studies have suggested that Toll-like receptor 4 (TLR4) might play a role in neuropathic pain. Methodology/Principal Findings: In this study, we investigated the role of TLR4 in a rat chronic constriction injury (CCI) model and explored the feasibility of treating neuropathic pain by inhibiting TLR4. Our results demonstrated that intrathecal siRNA-mediated suppression of TLR4 attenuated CCI-induced mechanical allodynia and thermal hyperalgesia through inhibiting the activation of NF-κB p65 and production of proinflammatory cytokines (e.g., TNF-α and IL-1β). Conclusions/Significance: These findings suggest that suppression of TLR4 mediated by intrathecally administered siRNA may be a new strategy for the treatment of neuropathic pain.     

Oxytocin ameliorates bone cancer pain by suppressing toll-like receptor 4 and proinflammatory cytokines in rat spinal cord

Abstract

Bone cancer pain is considered to be mechanistically unique compared with inflammatory or neuropathic pain states. Toll-like receptor 4 (TLR4) is a transmembrane receptor protein which has been reported to be involved in neuropathic pain. However, the role of TLR4 in bone cancer pain is still unclear. Therefore, the aim of this study is to investigate the hypothesis that oxytocin may ameliorate bone cancer pain by suppressing TLR4 in spinal cord. Behavioral analysis and molecular biological experiments were carried out. Our data demonstrated that intrathecally delivery of oxytocin significantly ameliorated the mechanical allodynia and thermal hyperalgesia in bone cancer pain rats. Moreover, oxytocin suppressed the up-regulation of TLR4 and proinflammatory cytokines TNFα and IL-1β in spinal cord of bone cancer pain rats. Therefore, we concluded that intrathecal administration of oxytocin relieves bone cancer pain by suppressing the up-regulation of TLR4, TNFα and IL-1β in spinal cord. Oxytocin possesses analgesic efficacy against bone cancer pain and deserves further to confirm its effectiveness in clinically relevant of cancer pain.     

Early cytokine gene expression in mouse CNS after peripheral nerve lesion

The generation and maintenance of pain after peripheral nerve injury are thought to be influenced by cytokine signaling. Chronic constriction injury (CCI) to mouse sciatic nerve leads to an early local upregulation of pro-inflammatory cytokines already 1 h after the lesion. The early regulation of cytokines in pain related CNS areas is largely unknown. We investigated cytokine regulation in the lumbar spinal cord, hypothalamus, thalamus, hippocampus, and frontal cortex in C57Bl/6J mice after lesioning the right sciatic nerve by CCI. The gene expression of tumor necrosis factor-alpha (TNF), interleukin (IL)-1beta, IL-4, and IL-10 was analyzed by quantitative real-time-PCR from 1 to 12 h after surgery or until values were back to baseline. CCI led to an early downregulation of TNF and IL-1beta mRNA in distinct brain areas and in the lumbar spinal cord with a maximum decrease within the first 6h after CCI. The reduction of TNF mRNA was inhibited by the NMDA receptor antagonist (+)-MK-801, while the calpain inhibitor MDL-28170 had no effect. Our results suggest an early cytokine regulation in the CNS after peripheral nerve lesion, which is opposite in direction to that in the periphery and which is partly mediated by the NMDA receptor system.     

神经源性痛大鼠模型腰髓后角A_β纤维生芽的变化(英文)

已有研究表明 ,外周神经损伤后 Aβ神经元的初级传入末梢在脊髓的病理性生芽与损伤后痛觉超敏的形成有关。为了证实外周神经损伤后形成的这种生芽是否具有可逆性 ,本研究以大鼠坐骨神经压迫造成神经源性痛模型 ,采用跨神经节的霍乱毒素 B亚单位结合辣根过氧化物酶 ( CB-HRP)作为示踪剂 ,四甲基联苯胺 ( TMB)反应呈色追踪 Aβ初级传入末梢。结果证实 :对坐骨神经的压迫也能够导致痛觉过敏和 Aβ纤维末梢生芽侵入脊髓后角 层 ,并且这种生芽不伴随对神经压迫的解除而逆转。中枢神经系统的这种结构重组及其不可逆性可能是神经源性痛的产生和维持的重要原因     

T lymphocytes play a role in neuropathic pain following peripheral nerve injury in rats

A catastrophic consequence of peripheral nerve injury is the development of abnormal, chronic neuropathic pain. The inflammatory response at the injury site is believed to contribute to the generation and maintenance of such persistent pain. However, the physiological significance and potential contribution of T cells to neuropathic pain remains unclear. Here we show that T cells infiltrate injured sciatic nerves following chronic constriction injury (CCI), but not uninjured nerves. Congenitally athymic nude rats, which lack mature T cells, developed a significantly reduced mechanical allodynia and thermal hyperalgesia following CCI, compared with their heterozygous littermates. To understand further the role played by different T-cell subsets, we generated polarized populations of type 1 and type 2 T cells, with different cytokine secretion profiles, from spleens of sciatic nerve-injured heterozygous rats. Passive transfer of type 1 T cells, which produce proinflammatory cytokines, into nude rats enhanced the recipients' pain hypersensitivity to a level similar to that of heterozygous donor rats. In contrast, passive transfer of polarized type 2 T cells, which produce anti-inflammatory cytokines, into heterozygous rats modestly though significantly attenuated their pain hypersensitivity. Thus, injection of type 1 and type 2 T-cell subsets produces opposing effects on neuropathic pain. These findings suggest the modulation of the T-cell immune response as a potential target for the treatment of neuropathic pain.     

MiR-139-3p通过靶向下调TRPV1缓解大鼠神经病理性疼痛

目的:研究miR-139-3p在大鼠神经病理性疼痛发生发展中的作用及其作用机制。方法:将大鼠随机分为假手术组(sham)、坐骨神经慢性压迫损伤模型组(chronic constriction injury group,CCI)、2 mg/kg miR-139-3p模拟物(mimic)鞘内注射组、4 mg/kg miR-139-3p mimic鞘内注射组。术后的第14 d,Real-time PCR法检测大鼠背根神经节(DRG)中miR-139-3p及TRPV1的表达。于注射前及注射后的第1、3、7、14 d,利用von Frey检测大鼠机械性痛阈及热辐射法检测大鼠热痛阈值。Western Blot法检测DRG中TRPV1的表达;ELISA法检测脊髓L4-L5组织中TNF-α及IL-1β的含量;双荧光素酶报告基因法检测miR-139-3p与TRPV1的靶向关系。结果:(1)与sham组相比较,miR-139-3p在CCI大鼠DRG中的表达显著下降,而TRPV1的表达显著上升(P0.05)。(2)与sham组相比较,CCI组中大鼠机械刺激缩足反射阈值及热刺激缩足反射潜伏期显著下降(P0.05);而与CCI组相比较,鞘内注射miR-139-3p mimic可显著促进大鼠机械刺激缩足反射阈值及热刺激缩足反射潜伏期的上升,抑制TRPV1的表达(P0.05)。(3)与sham组相比较,CCI组大鼠TNF-α及IL-1β含量显著上升(P0.05);而与CCI组相比较,鞘内注射miR-139-3p mimic可显著抑制TNF-α及IL-1β的产生(P0.05)。(4)miR-139-3p mimic转染可显著降低荧光素酶报告基因的荧光强度。结论:miR-139-3p通过靶向下调TRPV1的表达缓解大鼠神经病理性疼痛。     

p38MAPK抑制剂对神经病理性疼痛大鼠脊髓TNF-α合成的影响

 摘要：目的：通过建立坐骨神经慢性压迫损伤模型,研究p38丝裂原激活蛋白激酶（p38MAPK,p38）与TNF-α在神经病理性疼痛发生与发展中的相互作用。方法：SD大鼠分5组：1）空白对照组,2）假手术组,3）CCI手术未治疗组,4）CCI手术生理盐水治疗组,5）CCI手术SB203580（p38抑制剂）治疗组。上述治疗组中,生理盐水或SB203580分别于术前1天、术后第1天,和术后第7天鞘内注射。各组大鼠分别于术后3、7、14天测定机械痛阈。采用Western blot和免疫组化方法测定脊髓中TNF-α含量及p38活化水平。结果：与假手术组相比,CCI手术后3、7、14天磷酸化p38（p-p38）水平明显增加（p<0.05）。外周神经损伤后引起机械性触诱发痛,并且使脊髓中TNF-α浓度增加（p<0.05）。预先或术后立即给予SB203580抑制p38活化可以减少脊髓TNF-α合成,从而有效缓解病理性疼痛(p<0.05)。结论：外周神经损伤后,作为信号转导通路之一的p38可能通过促进脊髓TNF-α合成,引发神经病理性疼痛。     

Neuropathic pain in aged rats: behavioral responses and astrocytic activation

We used the Bennett and Xie (1988) model of chronic neuropathic pain to study the effect of age on thermal and tactile sensitivity and on astrocytic activation in the dorsal horn of the spinal cord after nerve injury. Fischer 344 FBNF1 hybrid rats in three age groups, 4-6, 14-16, and 24-26 months, were studied. Rats were either unligated (day 0, control) or the left sciatic nerve was loosely ligated to cause a chronic constriction injury (CCI). CCI causes a neuropathic pain condition characterized by tactile allodynia and thermal hyperalgesia. Rats were behaviorally assessed for tactile and thermal sensitivity of their ligated and unligated hind paws up to 35 days postligation. Rats were sacrificed before or at various days postligation, and activated astrocytes were identified at the L4-L5 levels of their spinal cords by use of an antibody to glial fibrillary acid protein (GFAP). The number of GFAP-ir astrocytes in the dorsal horn of the spinal cord in the control, uninjured condition decreased with age (P < or = 0.001) but increased after CCI in all three age groups. After CCI, astrocytic activation in the cord was less robust in aged rats than in younger ones (P < or = 0.01). Not all the CCI rats displayed hyperalgesia to touch and to heat. Rats with an increased sensitivity to heat had increased levels of GFAP-ir in their cords; however, rats with decreased thermal sensitivity also displayed increased GFAP-ir. Thus the presence of activated astrocytes was not correlated with a single behavioral manifestation of neuropathic pain.     

CC-chemokine MIP-1α in the spinal cord contributes to nerve injury-induced neuropathic pain

We investigated the involvement of spinal macrophage inflammatory protein-1α (MIP-1α), an inflammatory chemokine, in partial sciatic nerve ligation (PSL)-induced neuropathic pain in mice. PSL increased MIP-1α mRNA levels as well as levels of the MIP-1α receptor, CCR1, but not CCR5 in the spinal dorsal horn. PSL-induced tactile allodynia and thermal hyperalgesia were prevented by intrathecal (i.t.) injection of a neutralizing antibody of MIP-1α (2 ng). Recombinant MIP-1α (10 pmol, i.t.) elicited long-lasting tactile allodynia and thermal hyperalgesia in naïve mice. These results suggest that peripheral nerve injury elicits the up-regulation of spinal MIP-1α and CCR1 to participate in neuropathic pain.     

Intrathecally administered Sema3A protein attenuates neuropathic pain behavior in rats with chronic constriction injury of the sciatic nerve

Semaphorins, one of the repulsive axonal guidance factors during development, are produced under pathological conditions in adult animals. In the neuropathic pain state associated with peripheral nerve injury, synaptic reorganization occurs in spinal cord dorsal horn. In the present study, we investigated the roles of intrathecal administration of Sema3A, a secreted semaphorin, in the spinal cord of chronic constriction injury (CCI) model rat. Neuropilin 1 (NPR1) and Plexin A (PlexA), co-receptors of Sema3A, were expressed in the dorsal horn of na?ve rats. NPR1, and not PlexA, protein expression increased in the dorsal spinal cord of CCI rats. Recombinant Sema3A protein attenuated mechanical allodynia and heat hyperalgesia in CCI rats, whereas heat-inactivated Sema3A had no effect. Immunohistochemistry revealed that Sema3A partially restored the decrease of isolectin B4-positive unmyelinated nerve terminals in lamina II of the ipsilateral dorsal horn of CCI rats. Contrary to our expectations, Sema3A did not change the distribution of myelinated fibers in lamina II at 7 days after CCI. Those results suggested that the suppressive role for Sema3A in the development of neuropathic pain associated with peripheral nerve injury in adult rats, which seemed to be independent from prevention of the myelinated fiber sprouting into lamina II.     

Alteration in sensitivity of ionotropic glutamate receptors and tachykinin receptors in spinal cord contribute to development and maintenance of nerve injury-evoked neuropathic pain

Allodynia or hyperalgesia induced by peripheral nerve injury may be involved in changes in the sensitivity of neurotransmitters at the spinal cord level. In order to clarify the functional role of neurotransmitters in peripheral nerve injury, we used rats with nerve injury induced by chronic constriction of the sciatic nerve (CCI rat model) and estimated the effects of the intrathecal injection of drugs known to affect glutamate and tachykinin receptors. In sham-operated rats, the NMDA receptor agonist NMDA and AMPA-kinate receptor agonist RS-(5)-bromowillardin reduced withdrawal latency. The non-competitive NMDA receptor antagonist MK-801, competitive NMDA receptor antagonist AP-5 and AMPA-kinate receptor antagonist NBQX increased withdrawal latency. Substance P (SP) increased the withdrawal latency but only transitorily. The NK1 receptor antagonist RP67580 increased withdrawal latency, but the NK2 receptor antagonist SR48968 did not show an effect. In CCI rats, RS-(5)-bromowillardin reduced withdrawal latency, but NMDA did not show an effect. NBQX increased withdrawal latency, while MK-801 and AP-5 showed little or no effect. SP reduced withdrawal latency, and both RP67580 and SR48968 increased it. These results indicate that the alteration in sensitivity of ionotropic glutamate receptors and tachykinin receptors in the spinal cord contribute to development and maintenance of nerve injury-evoked neuropathic pain.     

Effects of peripheral nerve injury on alpha-2A and alpha-2C adrenergic receptor immunoreactivity in the rat spinal cord.

Neuropathic pain resulting from peripheral nerve injury can often be relieved by administration of alpha-adrenergic receptor antagonists. Tonic activation of alpha-adrenergic receptors may therefore facilitate the hyperalgesia and allodynia associated with neuropathic pain. It is currently unclear whether alpha2A- or alpha2c-adrenergic receptor subtypes are involved in the pro-nociceptive actions of alpha-adrenergic receptors under neuropathic conditions. We therefore investigated the effects of peripheral nerve injury on the expression of these subtypes in rat spinal cord using immunohistochemical techniques. In addition, neuropeptide Y immunoreactivity was examined as an internal control because it has previously been shown to be up-regulated following nerve injury. We observed a decrease in alpha2A-adrenergic receptor immunoreactivity in the spinal cord ipsilateral to three models of neuropathic pain: complete sciatic nerve transection, chronic constriction injury of the sciatic nerve and L5/L6 spinal nerve ligation. The extent of this down-regulation was significantly correlated with the magnitude of injury-induced changes in mechanical sensitivity. In contrast, alpha2c-adrenergic receptor immunoreactivity was only increased in the spinal nerve ligation model; these increases did not correlate with changes in mechanical sensitivity. Neuropeptide Y immunoreactivity was up-regulated in all models examined. Increased expression of neuropeptide Y correlated with changes in mechanical sensitivity. The decrease in alpha2A-adrenergic receptor immunoreactivity and the lack of consistent changes in alpha2C-adrenergic receptor immunoreactivity suggest that neither of these receptor subtypes is likely to be responsible for the abnormal adrenergic sensitivity observed following nerve injury. On the contrary, the decrease in alpha2A-adrenergic receptor immunoreactivity following nerve injury may result in an attenuation of the influence of descending inhibitory noradrenergic input into the spinal cord resulting in increased excitatory transmitter release following peripheral stimuli.     

Interleukin-17 levels in rat models of nerve damage and neuropathic pain

In the present study, we assessed IL-17 levels at 3 and 8 days following various forms of injuries to the sciatic nerve and related the cytokine levels to the pain behaviors associated with the injuries. The four experimental models employed were chronic constriction injury (CCI), partial sciatic ligation (PSL), complete sciatic transection (CST) and perineural inflammation (Neuritis). Behavior withdrawal thresholds for mechanical stimulus and withdrawal latency for thermal stimulation were used to measure mechanical allodynia and thermal hyperalgesia. IL-17 levels of the affected, contralateral and naïve rats’ sciatic nerve were assessed employing enzyme-linked immunosorbent assay (ELISA). Rats exposed to CCI and Neuritis displayed significant mechanical allodynia and thermal hyperalgesia 3, 5 and 8 days following the procedure, rats exposed to PSL displayed significant mechanical allodynia 5 and 8 days following the procedure and rats exposed to CST developed significant hypoesthesia. Three days following the procedure, IL-17 levels increased significantly compared to naïve rats only in the PSL model. Eight days following the procedure, IL-17 levels in nerves exposed to CCI, CST, PSL and Neuritis were significantly elevated compare to intact nerve levels. It is likely that IL-17 has a limited role in the acute phase of nerve injury and the associated acute pain, but may have a role in later phases of the processes of the development of neuropathic pain.     

慢性压迫性神经损伤大鼠中透明质酸合成变化及其在神经源性疼痛中的作用

慢性神经源性疼痛由于其发病机制尚不完全明确,目前还没有十分有效的治疗手段;神经损伤后炎症反应和免疫调节机制在疼痛的发生中发挥着重要作用,透明质酸(HA)近来被认为是炎症和免疫调节中一个重要的调节分子。为了进一步研究HA是否参与到神经损伤后的病理过程中,我们检测了慢性压迫性神经损伤(CC I)大鼠损伤神经的HA含量。结果显示:与正常神经比较,HA的含量在损伤后7 d明显增加,HA合成酶(HAS)的表达也明显上调。4-甲基伞形酮(4-MU)是HAS的一种抑制剂,我们通过给予4-MU抑制HA的合成,研究HA在慢性神经源性疼痛中的作用,发现给药组CC I大鼠损伤足对热痛刺激的敏感性低于未给药组,同时IL-1β的表达量低于未给药组。以上结果提示HA可能通过对炎症因子的调控参与到损伤后的疼痛机制中,这一结果将有助于慢性神经源性疼痛的治疗。     

Involvement of substance P and calcitonin gene-related peptide in development and maintenance of neuropathic pain from spinal nerve injury model of rat

Recently, it has been suggested that uninjured primary sensory neurons contribute to neuropathic pain induced by peripheral nerve injury. However, there is lack of evidences of roles of normal pain transmitting substances such as substance P and calcitonin gene-related peptide (CGRP) in neuropathic pain. Whether substance P and CGRP have a role in spinal nerve-injured neuropathic pain model was tested. Male rats were subjected to L5 and L6 spinal nerve transection (SNT), and mechanical hyperalgesia was evaluated by measuring paw withdrawal threshold (PWT). SNT induced a persistent PWT decrease, a sign of neuropathic pain. Lidocaine was soaked on spinal nerves or intrathecally injected 10 min before SNT to block neuronal discharges caused by the injury, and L703,606 (NK1 receptor antagonist) and CGRP8-37 (CGRP receptor antagonist) were intrathecally injected into the rats to block actions of substance P and CGRP released from central nerve terminals in the spinal cord by injury discharges. The treatments with lidocaine, L703,606 and CGRP8-37 delayed the onset of neuropathic pain by 1-4 days, compared with the saline-treated rats. After neuropathic pain was established, intrathecal injections of L703,606 and CGRP8-37 significantly mitigated mechanical hyperalgesia for 20 min. These results suggest that substance P and CGRP are involved in the development and maintenance of neuropathic pain and that these peptides from the central terminals of intact sensory neurons contribute to the maintenance of peripheral nerve injury-induced neuropathic pain.