香叶醇对神经痛模型大鼠的镇痛作用及机制研究

目的研究香叶醇对神经病理性疼痛的镇痛效用,并初步研究其发挥效用的可能机制。方法制作大鼠保留性神经痛(spared nerve injury,SNI)模型,在行为学水平检测给药前后大鼠机械痛阈的变化;体外急性分离SNI模型大鼠背根神经节细胞(dorsal root ganglion,DRG),膜片钳检测Na通道的活性变化;体外采用膜片钳技术分别检测稳定转染h Nav1.7通道和TRPA1通道的HEK293细胞,记录给药前后通道的活性变化。结果香叶醇能够快速发挥对SNI模型大鼠机械痛敏的镇痛效应,对急性分离的SNI模型大鼠DRG细胞Na通道表现明显抑制作用,对HEK293细胞株表达的h Nav1.7通道表现明显抑制作用,对HEK293细胞株表达的h TRPA1通道无抑制作用,高浓度下表现促进AITC激活h TRPA1通道作用。结论香叶醇可能通过抑制DRG细胞的Nav1.7通道起到对SNI大鼠机械痛敏的镇痛作用。     

预先给予酪氨酸激酶抑制剂IPTRK3对神经源性疼痛的影响

目的探讨预先给予酪氨酸激酶(tyrosine kinase,Tr-kA)抑制剂IPTRK3对神经源性疼痛的抑制作用及其可能作用机制。方法建立小鼠坐骨神经部分结扎(partial sciaticnerve ligation,PSNL)模型,术前10 min单次腹腔给予IPTRK3 10 mg·kg-1,测定给药前后不同时间点小鼠的热痛觉过敏阈值(paw withdrawal latency,PWL)和机械痛觉过敏阈值(paw withdrawal threshold,PWT),免疫印迹法测量左侧L4-5背根神经节瞬时感受器电位香草酸受体1(transient re-ceptor potential vanilloid 1,TRPV1)的表达情况,免疫组织化学染色法测定Fos蛋白在L4-5脊髓背角的表达变化。结果与假手术(sham)组相比,PSNL组小鼠出现明显热、机械痛觉过敏(P<0.05),背根节TRPV1蛋白表达及脊髓背角Fos蛋白阳性神经元数目明显增多(P<0.05)。与PSNL组相比,预先给予IPTRK3 10 mg·kg-1明显减轻小鼠热痛觉过敏,背根神经节TRPV1蛋白表达水平及脊髓背角Fos蛋白阳性神经元数目明显降低(P<0.05),但仍明显高于sham组(P<0.05)。结论预先给予IPTRK3可以明显减轻神经源性疼痛症状,抑制背根神经节TRPV1及脊髓背角Fos蛋白的表达可能部分参与其早期迅速减轻伤害性刺激信息传递。     

酸敏感离子通道3在关节炎疼痛中的作用

疼痛相关的酸敏感离子通道3（Acid-sensingion channels 3,ASIC3）主要分布在周围神经系统,是对pH值改变最敏感的酸受体。最近,越来越多的研究证实,在脊髓背根神经节（DRG）丰富表达的ASIC3,与痛觉及伤害性感受密切相关,在慢性炎性疼痛的病理过程中发挥重要的作用。研究表明在炎性痛模型中可以上调脊髓背角ASIC3在转录和蛋白水平的表达;阻断或敲除ASIC3基因（ASIC3-/-）能明显抑制炎症性关节痛。上述各点提示,在生理或病理情况下,脊髓背角ASIC3对脊髓水平的感觉信息传递特别是痛觉的传导可能发挥着重要作用,这可能是关节炎疼痛的治疗靶点。本文将ASIC3的生物学特征以及它在关节炎疼痛和治疗中的作用作一综述。     

ZD7288抑制急性内脏痛大鼠痛觉敏化

观察超极化激活环核苷酸门控阳离子通道（HCN通道）的特异性阻断剂ZD7288对急性内脏痛大鼠痛觉敏化的影响。方法：选用成年雄性SD大鼠,通过结肠内注射1％醋酸1mL,建立急性内脏痛模型;免疫组织化学法检测HCN2在模型大鼠腰骶段背根神经节及胸腰段与腰骶段脊髓背角的表达;通过腹壁撤退反射评分和腹外斜肌放电测量,观察模型大鼠鞘内分别给予50与100nmol／LZD7288后内脏痛觉敏化是否发生改变。结果：HCN2在模型大鼠腰骶段背根神经节及胸腰段与腰骶段脊髓背角的表达均较对照大鼠增强（P〈0．05）。鞘内注射50～100nmol／LZD7288可以剂量依赖性降低急性内脏痛模型大鼠的腹壁撤退反射评分和腹外斜肌放电幅值（P〈0．05）。结论：ZD7288可抑制急性内脏痛大鼠的痛觉敏化,而背根神经节和脊髓的HCN2通道可能在其发病中起作用。     

瞬时受体电位香草酸亚型1（TRPV1）与N-甲基-D-天冬氨酸（NMDA）受体相互作用的研究进展

辣椒素是从辣椒中提取的天然产品,可以激活瞬时受体电位香草酸亚型1(TRPV1)受体,它们的分子作用模式涉及重要的生理过程,这些过程是疼痛和内源性调节机制的基础。TRPV1和N-甲基-D-天冬氨酸(NMDA)受体均广泛分布和表达于多种组织器官中,均具有较为复杂的生物学功能,这也预示着它们之间关系的探索,将为更多实验研究提供理论基础,并对新型药物的研发及临床应用有着深远意义。总结了TRPV1与背根神经节NMDA受体之间相互作用与瑞芬太尼痛觉过敏的关系、与神经毒性和神经保护间的关系以及与抗焦虑样效应间的关系的研究进展。     

脊髓背角神经元上调Nav1.8通道参与缺血再灌注损伤后痛觉过敏的机制

目的观察鞘内注射钠通道抑制剂619C89对脊髓缺血再灌注损伤引起的痛觉过敏大鼠的痛阈、脊髓背角神经元中Nav1.8通道表达的影响。方法 SD大鼠随机分为3组:假手术组(S组)、痛觉过敏组(H组,缺血再灌注前3 d鞘内注射30μL生理盐水)、钠通道抑制剂组(I组,缺血再灌注前3 d鞘内注射619C895μg/30μL)。S组仅暴露主动脉弓而不结扎,其他各组开胸后无创动脉夹夹闭主动脉弓14 min后再开放,建立SCIRI引起的痛觉过敏模型。各组手术前均于L_(5-6)鞘内置管并连续注射3 d。术后1、3、5、7、14 d分别测定各组大鼠的热痛阈及机械性痛阈;取第4~6节腰段脊髓,采用免疫双荧光法观察背角神经元状态及其Nav1.8的表达,Real time-PCR法检测各组大鼠脊髓组织Nav1.8表达。结果与S组相比,术后各观察点(尤以第7天为著)H组大鼠热痛阈和机械性痛阈降低,损伤后7 d脊髓组织中Nav1.8 mRNA的表达增加(P<0.05);I组大鼠热痛阈和机械性痛阈值明显提高(P<0.05),脊髓组织中Nav1.8 mRNA的表达降低(P<0.05)。免疫双荧光染色显示,损伤后7 d,H组大鼠脊髓背角Nav1.8的荧光强度明显增加,且主要表达在NeuN表达阳性的神经元的胞浆中;且与S组相比,H组中NeuN/Nav1.8双阳性的细胞数量明显增多,而I组双阳性的细胞数量减少(P<0.05)。结论脊髓背角神经元通过上调Nav1.8通道参与缺血再灌注损伤后痛觉过敏的形成。     

NMDA受体NR2B亚单位在慢性内脏痛觉敏化中的作用

目的探讨外周与脊髓NMDA受体NR2B亚单位在慢性内脏痛觉敏化中的作用。方法模型组大鼠出生后d8～15,每天接受一次伤害性结直肠扩张刺激,8wk龄后用腹壁撤退反射(AWR)评估大鼠肠道敏感性。对腰骶背根神经节及胸腰与腰骶脊髓背角神经元进行免疫组织化学染色,比较对照与模型大鼠NR2B的表达。并比较对照与模型两组大鼠腹腔注射AP-7(NMDA受体拮抗剂)前后原发传入神经对结直肠扩张刺激的反应。结果①模型组大鼠AWR评分显著增高。②模型大鼠脊髓背根神经节NR2B亚单位表达增强。③模型大鼠脊髓内脏相关神经元NR2B亚单位表达增强。④AP-7显著抑制模型大鼠腰骶传入神经纤维对结直肠刺激的反应。结论NMDA受体NR2B亚单位可能参与慢性内脏痛外周与脊髓痛觉敏化的过程。     

川芎嗪对糖尿病神经组织并发症保护作用及机制的研究进展

川芎嗪(TMP)对以糖尿病为代表的代谢性疾病并发中枢神经系统、周围神经系统和眼底视神经病变均具有一定保护作用,TMP对中枢神经细胞保护机制为:对神经细胞和血管内皮细胞起到抗凋亡作用,抑制神经细胞炎症反应,抗氧化作用,钙离子通道阻滞作用,促进中枢神经营养因子表达,保护中枢神经细胞尼氏体以及促进中枢血管内皮生长等。TMP对糖尿病周围神经系统并发症的保护作用机制主要倾向研究与疼痛传导有关的背根神经节嘌呤能P2受体-离子通道型受体3受体相关作用。TMP对视网膜变性的保护作用机制为:减轻氧化应激损伤,干扰神经血管内皮细胞增殖,抗光感细胞凋亡。本文综述了TMP对糖尿病中枢神经系统和周围神经系统并发症的保护作用及其机制。     

丹参注射液对背根神经节细胞超极化激活电流通道的影响

目的观察丹参对背根神经节细胞超极化激活通道电流的影响，探讨丹参缓解疼痛和阻滞钙内流，以及减轻钙超载的作用机制。方法应用全细胞膜片钳技术，观察了丹参注射液对大鼠背根神经节细胞超极化激活电流(I_h)通道的影响。结果10%，25%和50%的丹参注射液对大鼠背根神经节细胞I_h通道的电流幅值、激活时间常数和翻转电位均没有影响，但可使I_h通道电流的半激活电压向超极化方向偏移。结论丹参特异性地使I_h通道电流的半激活电压向超极化方向偏移所产生的对外周痛敏的对抗作用，可能也是其缓解疼痛的作用机制之一。     

化疗引起的神经痛治疗靶点温度选择性TRP通道的研究进展

作为钙离子渗透性的瞬时受体电位(TRP),5种通道(TRPV1~4和TRPM2)被不同的高温激活,两种通道(TRPV1和TRPV8)被低温激活。越来越多的证据表明,TRPA1和TRPM8拮抗剂可预防顺铂、奥沙利铂和紫杉醇诱导的线粒体氧化应激、炎症、冷痛和痛觉过敏。TRPV1在顺铂引起的感觉神经元热痛觉和机械异常中有应答。TRPA1、TRPM8和TRPV2蛋白表达水平主要通过这些治疗方法在背根(DRG)和三叉神经节中增加。主要总结了5种温度调节TRP通道(TRPA1、TRPM8、TRPV1、TRPV2和TRPV4)。     

Discovery and biological evaluation of 5-aryl-2-furfuramides, potent and selective blockers of the Nav1.8 sodium channel with efficacy in models of neuropathic and inflammatory pain

Nav1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons and has been implicated in the pathophysiology of inflammatory and neuropathic pain. Recent studies using an Nav1.8 antisense oligonucleotide in an animal model of chronic pain indicated that selective blockade of Nav1.8 was analgesic and could provide effective analgesia with a reduction in the adverse events associated with nonselective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 5-substituted 2-furfuramides, which are potent, voltage-dependent blockers (IC50 < 10 nM) of the human Nav1.8 channel. Selected derivatives, such as 7 and 27, also blocked TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons with comparable potency and displayed >100-fold selectivity versus human sodium (Nav1.2, Nav1.5, Nav1.7) and human ether-a-go-go (hERG) channels. Following systemic administration, compounds 7 and 27 dose-dependently reduced neuropathic and inflammatory pain in experimental rodent models.     

Molecular diversity of structure and function of the voltage-gated Na+ channels

A variety of different isoforms of voltage-sensitive Na+ channels have now been identified. The recent three-dimensional analysis of Na+ channels has unveiled a unique and unexpected structure of the Na+ channel protein. Na+ channels can be classified into two categories on the basis of their amino acid sequence, Nav1 isoforms currently comprising nine highly homologous clones and Nax that possesses structure diverging from Nav1, especially in several critical functional motifs. Although the functional role of Nav1 isoforms is primarily to form an action potential upstroke in excitable cells, recent biophysical studies indicate that some of the Nav1 isoforms can also influence subthreshold electrical activity through persistent or resurgent Na+ currents. Nav1.8 and Nav1.9 contain an amino acid sequence common to tetrodotoxin resistant Na+ channels and are localized in peripheral nociceptors. Recent patch-clamp experiments on dorsal root ganglion neurons from Nav1.8-knock-out mice unveiled an additional tetrodotoxin-resistant Na+ current. The demonstration of its dependence on Nav1.9 provides evidence for a specialized role of Nav1.9, together with Nav1.8, in pain sensation. Although Nax has not been successfully expressed in an exogenous system, recent investigations using relevant native tissues combined with gene-targeting have disclosed their unique "concentration"-sensitive but not voltage-sensitive roles. In this context, these emerging views of novel functions mediated by different types of Na+ channels are reviewed, to give a perspective for future research on the expanding family of Na+ channel clones.     

Analysis of human Nav1.8 expressed in SH-SY5Y neuroblastoma cells

The tetrodotoxin-resistant voltage-gated sodium channel alpha-subunit Nav1.8 is expressed in nociceptors and has been implicated in chronic pain. Difficulties of heterologous expression have so far precluded analysis of the pharmacological properties of human Nav1.8. To address this we have introduced human Nav1.8 in neuroblastoma SH-SY5Y cells. Voltage-clamp analysis showed that human Nav1.8 generated an inward tetrodotoxin-resistant sodium current with an activating threshold around -50 mV, half maximal activation at -11+/-3 mV and a reversal potential of 67+/-4 mV. These properties closely match those of the endogenous rat tetrodotoxin-resistant sodium current in dorsal root ganglia suggesting that the expressed human channel is in a near physiological conformation. Human Nav1.8 was resistant to tetrodotoxin and activated by the pyrethroid toxin deltamethrin. Both voltage-activated and deltamethrin-activated human Nav1.8 were inhibited by the sodium channel blockers BIII 890 CL, NW-1029, and mexiletine. Inhibition of Nav1.8 by these compounds may underlie their known analgesic effects in animal models.     

Involvement of cyclooxygenase-2 and EP3 prostaglandin receptor in acute herpetic but not postherpetic pain in mice

The precise mechanisms of zoster-associated pain and postherpetic neuralgia remain unknown. Inoculation of mice with herpes simplex virus type-1 elicits acute herpetic pain- and delayed postherpetic pain-related responses. We investigated the role of prostaglandins (PGs) and their synthases in both types of pain. Deficiency in EP3 but not EP1, IP or TP prostanoid receptor markedly diminished the acute herpetic pain and resulted in the decrease of the incidence of the delayed postherpetic pain. Preventive but not therapeutic administration of the EP3 antagonist ONO-AE3-240 inhibited the acute herpetic pain. The non-selective cyclooxygenase (COX) inhibitor diclofenac and the selective COX-2 inhibitors NS-398 and JTE-522 dose dependently reduced the acute herpetic pain, and NS-398 was without effect on delayed postherpetic pain. COX-2 was induced and PGE2 content was increased in the affected dorsal root ganglia at the stage of acute herpetic pain. COX-2-like immunoreactivities were found around the nuclear membrane of many dorsal root ganglion neurons that were negative for herpesvirus antigen. COX-2 mRNA expression and PGE2 content in the affected dorsal root ganglia at the stage of delayed postherpetic pain were similar to those of naive mice. The propagation of herpes virus in dorsal root ganglion may induce COX-2 and produce PGE2 in uninfected neurons. The results suggest the important roles of COX-2 induction and the PGE2-EP3 receptor system in the dorsal root ganglia in the development but not maintenance of acute herpetic pain. It was further confirmed that the PG systems do not play a key role in delayed postherpetic pain.     

Animal Toxins Can Alter the Function of Nav1.8 and Nav1.9

Human voltage-activated sodium (Nav) channels are adept at rapidly transmitting electrical signals across long distances in various excitable tissues. As such, they are amongst the most widely targeted ion channels by drugs and animal toxins. Of the nine isoforms, Nav1.8 and Nav1.9 are preferentially expressed in DRG neurons where they are thought to play an important role in pain signaling. Although the functional properties of Nav1.8 have been relatively well characterized, difficulties with expressing Nav1.9 in established heterologous systems limit our understanding of the gating properties and toxin pharmacology of this particular isoform. This review summarizes our current knowledge of the role of Nav1.8 and Nav1.9 in pain perception and elaborates on the approaches used to identify molecules capable of influencing their function.     

Block of voltage-gated potassium channels by Pacific ciguatoxin-1 contributes to increased neuronal excitability in rat sensory neurons

The present study investigated the actions of the polyether marine toxin Pacific ciguatoxin-1 (P-CTX-1) on neuronal excitability in rat dorsal root ganglion (DRG) neurons using patch-clamp recording techniques. Under current-clamp conditions, bath application of 2-20 nM P-CTX-1 caused a rapid, concentration-dependent depolarization of the resting membrane potential in neurons expressing tetrodotoxin (TTX)-sensitive voltage-gated sodium (Nav) channels. This action was completely suppressed by the addition of 200 nM TTX to the external solution, indicating that this effect was mediated through TTX-sensitive Nav channels. In addition, P-CTX-1 also prolonged action potential and afterhyperpolarization (AHP) duration. In a subpopulation of neurons, P-CTX-1 also produced tonic action potential firing, an effect that was not accompanied by significant oscillation of the resting membrane potential. Conversely, in neurons expressing TTX-resistant Nav currents, P-CTX-1 failed to alter any parameter of neuronal excitability examined in this study. Under voltage-clamp conditions in rat DRG neurons, P-CTX-1 inhibited both delayed-rectifier and 'A-type' potassium currents in a dose-dependent manner, actions that occurred in the absence of alterations to the voltage dependence of activation. These actions appear to underlie the prolongation of the action potential and AHP, and contribute to repetitive firing. These data indicate that a block of potassium channels contributes to the increase in neuronal excitability, associated with a modulation of Nav channel gating, observed clinically in response to ciguatera poisoning.     

N58A Exerts Analgesic Effect on Trigeminal Neuralgia by Regulating the MAPK Pathway and Tetrodotoxin-Resistant Sodium Channel

The primary studies have shown that scorpion analgesic peptide N58A has a significant effect on voltage-gated sodium channels (VGSCs) and plays an important role in neuropathic pain. The purpose of this study was to investigate the analgesic effect of N58A on trigeminal neuralgia (TN) and its possible mechanism. The results showed that N58A could significantly increase the threshold of mechanical pain and thermal pain and inhibit the spontaneous asymmetric scratching behavior of rats. Western blotting results showed that N58A could significantly reduce the protein phosphorylation level of ERK1/2, P38, JNK, and ERK5/CREB pathways and the expression of Nav1.8 and Nav1.9 proteins in a dose-dependent manner. The changes in current and kinetic characteristics of Nav1.8 and Nav1.9 channels in TG neurons were detected by the whole-cell patch clamp technique. The results showed that N58A significantly decreased the current density of Nav1.8 and Nav1.9 in model rats, and shifted the activation curve to hyperpolarization and the inactivation curve to depolarization. In conclusion, the analgesic effect of N58A on the chronic constriction injury of the infraorbital (IoN-CCI) model rats may be closely related to the regulation of the MAPK pathway and Nav1.8 and Nav1.9 sodium channels.     

Differential modulation of Nav1.7 and Nav1.8 peripheral nerve sodium channels by the local anesthetic lidocaine

1 Voltage-gated Na+ channels are transmembrane proteins that are essential for the propagation of action potentials in excitable cells. Nav1.7 and Nav1.8 dorsal root ganglion Na+ channels exhibit different kinetics and sensitivities to tetrodotoxin (TTX). We investigated the properties of both channels in the presence of lidocaine, a local anesthetic (LA) and class I anti-arrhythmic drug. 2 Nav1.7 and Nav1.8 Na+ channels were coexpressed with the beta1-subunit in Xenopus oocytes. Na+ currents were recorded using the two-microelectrode voltage-clamp technique. 3 Dose-response curves for both channels had different EC50 (dose producing 50% maximum current inhibition) (450 microm for Nav1.7 and 104 microm for Nav1.8). Lidocaine enhanced current decrease in a frequency-dependent manner. Steady-state inactivation of both channels was also affected by lidocaine, Nav1.7 being the most sensitive. Only the steady-state activation of Nav1.8 was affected while the entry of both channels into slow inactivation was affected by lidocaine, Nav1.8 being affected to a larger degree. 4 Although the channels share homology at DIV S6, the LA binding site, they differ in their sensitivity to lidocaine. Recent studies suggest that other residues on DI and DII known to influence lidocaine binding may explain the differences in affinities between Nav1.7 and Nav1.8 Na+ channels. 5 Understanding the properties of these channels and their pharmacology is of critical importance to developing drugs and finding effective therapies to treat chronic pain.     

Inhibition of Nav1.7 channel by a novel blocker QLS-81 for alleviation of neuropathic pain

Voltage-gated sodium channel Nav1.7 robustly expressed in peripheral nociceptive neurons has been considered as a therapeutic target for chronic pain, but there is no selective Nav1.7 inhibitor available for therapy of chronic pain. Ralfinamide has shown anti-nociceptive activity in animal models of inflammatory and neuropathic pain and is currently under phase III clinical trial for neuropathic pain. Based on ralfinamide, a novel small molecule (S)-2-((3-(4-((2-fluorobenzyl) oxy) phenyl) propyl) amino) propanamide (QLS-81) was synthesized. Here, we report the electrophysiological and pharmacodynamic characterization of QLS-81 as a Nav1.7 channel inhibitor with promising anti-nociceptive activity. In whole-cell recordings of HEK293 cells stably expressing Nav1.7, QLS-81 (IC₅₀ at 3.5 ± 1.5 μM) was ten-fold more potent than its parent compound ralfinamide (37.1 ± 2.9 μM) in inhibiting Nav1.7 current. QLS-81 inhibition on Nav1.7 current was use-dependent. Application of QLS-81 (10 μM) caused a hyperpolarizing shift of the fast and slow inactivation of Nav1.7 channel about 7.9 mV and 26.6 mV, respectively, and also slowed down the channel fast and slow inactivation recovery. In dissociated mouse DRG neurons, QLS-81 (10 μM) inhibited native Nav current and suppressed depolarizing current pulse-elicited neuronal firing. Administration of QLS-81 (2, 5, 10 mg· kg⁻¹· d⁻¹, i.p.) in mice for 10 days dose-dependently alleviated spinal nerve injury-induced neuropathic pain and formalin-induced inflammatory pain. In addition, QLS-81 (10 μM) did not significantly affect ECG in guinea pig heart ex vivo; and administration of QLS-81 (10, 20 mg/kg, i.p.) in mice had no significant effect on spontaneous locomotor activity. Taken together, our results demonstrate that QLS-81, as a novel Nav1.7 inhibitor, is efficacious on chronic pain in mice, and it may hold developmental potential for pain therapy.