突触前代谢型谷氨酸受体调节神经递质的释放

谷氨酸通过激活离子型受体（iGluR)介导快速兴奋性突触传递,参与脑内几乎所有生理过程。谷氨酸过量释放可导致与脑缺血,缺氧及变性疾病有关的兴奋毒作用,最终引起神经元的死亡。代谢型谷氨酸受体（mGluRs)是一个与G－蛋白偶联的受体家族,分三型共八个亚型。其中Ⅱ和Ⅲ型mGluRs主要位于突触前,发挥对谷氨酸释放的负反馈调节。Ⅲ型mGluRs中的mGluR7位于谷氨酸能末梢突触前膜的活性区,发挥自身受体的作用,对正常情况下突触传递过程的谷氨酸释放进行负反馈调节;而属于Ⅱ型的mGluR2及属于Ⅲ型的mGluR4和mGluR8,则位于远离突有膜活性区的外突触区,因而正常突触传递过程中释放的谷氨酸量不能激活它们。只有在突触传递增强的情况下才被激活,抑制递质的释放。国外,mGluRs还分布在GABA能纤维末梢,通过突触前机制抑制GABA的释放。对突触前膜受体尤其是位于外突触区的mGluRs受体的研究,将有可能开发出理想的工具药,从而预防和阻止谷氨酸过量释放引起的神经毒及神经元的死亡。     

谷氨酸性突触在痛觉和记忆中的突触和分子机制

谷氨酸是哺乳动物脑中的兴奋性递质。中枢神经系统的谷氨酸性突触广泛参与痛觉传递,突触可塑性和递质的调节。谷氨酸的NMDA受体参与前脑相关的学习及功能。在这篇综述中,我们提出前脑的NMDA受体通过增强谷氨酸性突触传递导致长期性的炎痛。具有增强NMDA受体功能的小鼠会产生更多的慢性痛。NMDA NR2B受体抑制剂在未来可能被用来控制人类的慢性痛。     

瞬时受体电位香草酸亚型1(TRPV1)与炎性痛

瞬时受体电位香草酸亚型1(transient receptor potential vanilloid 1,TRPV1)是TRP超家族的成员之一,是一种非选择性的阳离子通道。TRPV1广泛分布于伤害性感受器上,并且在伤害性感受器中起重要作用。TRPV1能够感受伤害性刺激,将之转化为动作电位,传至中枢形成痛觉。炎症时释放的许多炎症介质都能够与TRPV1发生相互作用,产生疼痛或痛觉过敏,并且通过各种不同的信号通路来调制TRPV1的活性。深入研究TRPV1的作用机制,有助于理解痛觉生理和开发新型镇痛药物。     

NMDA受体参与小鼠的前额扣带回的神经突触传递

谷氨酸性突触是哺乳动物神经系统的主要兴奋性突触。在正常条件下,大多数的突触反应是由谷氨酸的AMPA受体传递的。NMDA受体在静息电位下为镁离子抑制。在被激活时,NMDA受体主要参与突触的可塑性变化。但是,许多NMDA受体拮抗剂在全身或局部注射时能产生行为效应,提示NMDA受体可能参与静息状态的生理功能。此文中,我们在离体的前额扣带回脑片上进行电生理记录,发现NMDA受体参与前额扣带回的突触传递。在重复刺激或近于生理性温度时,NMDA受体传递的反应更为明显。本文直接显示了NMDA受体参与前额扣带回的突触传递,并提示NMDA受体在前额扣带回中起着调节神经元兴奋的重要作用。     

孕酮与疼痛调节

孕酮(progesterone,PROG)不仅存在于生殖系统,而且在神经系统也有合成.孕酮受体在中枢和外周神经系统中均有分布,参与神经系统的各项功能,其中包括对疼痛的调节.孕酮及其代谢产物对生理性痛和炎性痛均有抑制效应,孕酮对雌激素介导的外周痛觉增敏也有抑制效应.另一方面,孕酮增强神经病理性痛的痛觉异常和痛觉过敏.孕酮可以通过调节某些痛觉相关的神经递质受体的表达和功能以及影响疼痛下行抑制通路,从而完成对痛觉调节.     

孕酮与疼痛调节

孕酮（progesterone,PROG）不仅存在于生殖系统,而且在神经系统也有合成。孕酮受体在中枢和外周神经系统中均有分布,参与神经系统的各项功能,其中包括对疼痛的调节。孕酮及其代谢产物对生理性痛和炎性痛均有抑制效应,孕酮对雌激素介导的外周痛觉增敏也有抑制效应。另一方面,孕酮增强神经病理性痛的痛觉异常和痛觉过敏。孕酮可以通过调节某些痛觉相关的神经递质受体的表达和功能以及影响疼痛下行抑制通路,从而完成对痛觉调节。     

代谢型谷氨酸受体

代谢型谷氨酸受体（ｍＧｌｕＲｓ）的发现是中枢兴奋性突触性研究中的一些重要进展,ｍＧｌｕＲｓ激活后通过不同的胞内信号转导系统（如ＰＩ水解,ｃＡＭＰ水平变化等）产生生理效应,目前已有八种ｍＧｌｕＲｓ亚基被克隆并成功表达,由于缺少选择性工具药,对其药理学特性及生理功能尚了解甚少,现有证据表明ｍＧｌｕＲｓ在中枢神经系统的活动中起重要作用,包括调制离子通道活动神经元兴奋性和神经递质释放,参与突触传递和突触可     

锌离子对配体门控型离子通道的调节作用

在中枢神经系统(central nervous system,CNS)中,锌离子对配体门控型离子通道具有重要的调节作用。锌离子随着神经元的活动从突触前膜的囊泡中释放到突触间隙,对突触内受体进行调控。锌离子抑制N-甲基-D-天冬氨酸(N-methyl-D-aspartate,NMDA)型谷氨酸受体的活性,而对非NMDA型谷氨酸受体的调控具有多样性。由γ氨基丁酸(γ-aminobutyric acid,GABA)受体所介导的抑制性突触传递活动也受到锌离子的抑制;而锌离子对glycine受体则呈现出浓度依赖的双向调节效应。病理条件下,锌离子参与了兴奋性细胞毒作用所触发的神经元凋亡过程。本文主要阐述了在CNS中,锌离子对配体门控型离子通道所介导的突触传递活动的调控作用,以及这些调控作用的生理功能和病理意义。     

腹外侧眶皮层在痛觉调制和针刺镇痛中的作用

腹外侧眶皮层 (ventrolateral orbital cortex, VLO) 是眶皮层的主要成分,它与导水管周围灰质(PAG)、丘脑和其它皮层之间有广泛的纤维联系.VLO不仅是一个痛觉感受中枢,而且也是一个痛觉调制中枢,通过激活PAG脑干下行抑制系统在脊髓和三叉水平抑制伤害性信息的输入.研究还证实,阿片、 5-HT和GABA等神经递质及其受体参与VLO的抗伤害效应.此外,VLO在针刺镇痛中也发挥重要作用.本文就腹外侧眶皮层在痛觉调制和针刺镇痛中的作用进行综述.     

神经营养因子对神经肌肉接头传递的调制作用

运动单位由运动神经元及其支配的肌纤维组成。神经肌肉接头(neuromuscular junction,NMJ)传递受到严密的调节,因而能和运动单位的活动协调一致。在NMJ,神经调制物质的释放与运动单位的活动有关,并能决定突触传递的效能。脑源性神经营养因子(brain—derived neurotrophic factor,BDNF)和神经营养因子4(neurotrophin-4,NT-4)由运动神经末梢和肌纤维产生。肌肉释放营养因子受肌肉活动调节。在NMJ,BDNF和NT-4通过激活酪氨酸激酶B受体(tyrosine kinase receptor B,TrkB),能加强自发性和诱导性的突触活动。突触前Ca^2 量的迅速增加或突触胞吐过程的易化,都能增加突触囊泡的释放,从而改善NMJ的突触传递。事实上,BDNF能促进突触前细胞内Ca^2 的释放,TrkB的激活也能通过有丝分裂活化蛋白激酶,引起突触素I(synapsinI)的磷酸化,进而增加可释放的突触囊泡的数量。在NMJ,神经营养因子还能通过影响神经调节素(neuregulin)或其他神经源性调制物质的局部释放,对接头传递进行调节。本文对近年来在NMJ突触传递的调节,运动单位的NMJ特性以及神经营养因子对突触传递效能的影响等方面的研究进展做一综述。     

The George B. Koelle symposium on the cholinergic synapse.

The George B. Koelle Symposium on the Cholinergic Synapse described the early development of the importance of ACh as a transmitter at both cholinergic synapses of the CNS, ganglion and neuromuscular junction. While a great deal is known about the function of cholinergic transmission at the neuromuscular junction, the integrated role of cholinergic, nicotinic and muscarinic receptors in the overall process of CNS functions, i.e., behavior, motor control, abstract thinking, memory and speech remains as a challenge for future investigation. The architecture of the cholinergic synapse appears to be a dynamic process involving ARIA, Agrin and the various forms of ACh esterase. The regulation of gene expression and site directed localization of postsynaptic cholinergic receptor proteins during the life cycle involves the dynamic interactions of these agents with the postsynaptic membrane and postsynaptic gene express. The last two papers at the symposium dealt with the chemistry of the nicotinic receptor regulated channel involved in ACh binding and the consequent cationic channel conductional changes.     

The mechanism of μ-opioid receptor (MOR)-TRPV1 crosstalk in TRPV1 activation involves morphine anti-nociception,tolerance and dependence

Initiated by the activation of various nociceptors, pain is a reaction to specific stimulus modalities. The μ-opioid receptor (MOR) agonists, including morphine, remain the most potent analgesics to treat patients with moderate to severe pain. However, the utility of MOR agonists is limited by the adverse effects associated with the use of these drugs, including analgesic tolerance and physical dependence. A strong connection has been suggested between the expression of the transient receptor potential vanilloid type 1 (TRPV1) ion channel and the development of inflammatory hyperalgesia. TRPV1 is important for thermal nociception induction, and is mainly expressed on sensory neurons. Recent reports suggest that opioid or TRPV1 receptor agonist exposure has contrasting consequences for anti-nociception, tolerance and dependence. Chronic morphine exposure modulates TRPV1 activation and induces the anti-nociception effects of morphine. The regulation of many downstream targets of TRPV1 plays a critical role in this process, including calcitonin gene-related peptide (CGRP) and substance P (SP). Additional factors also include capsaicin treatment blocking the anti-nociception effects of morphine in rats, as well as opioid modulation of TRPV1 responses through the cAMP-dependent PKA pathway and MAPK signaling pathways. Here, we review new insights concerning the mechanism underlying MOR-TRPV1 crosstalk and signaling pathways and discuss the potential mechanisms of morphine-induced anti-nociception, tolerance and dependence associated with the TRPV1 signaling pathway and highlight how understanding these mechanisms might help find therapeutic targets for the treatment of morphine induced antinociception, tolerance and dependence.     

The mechanism of μ-opioid receptor (MOR)-TRPV1 crosstalk in TRPV1 activation involves morphine anti-nociception,tolerance and dependence

Initiated by the activation of various nociceptors, pain is a reaction to specific stimulus modalities. The μ-opioid receptor (MOR) agonists, including morphine, remain the most potent analgesics to treat patients with moderate to severe pain. However, the utility of MOR agonists is limited by the adverse effects associated with the use of these drugs, including analgesic tolerance and physical dependence. A strong connection has been suggested between the expression of the transient receptor potential vanilloid type 1 (TRPV1) ion channel and the development of inflammatory hyperalgesia. TRPV1 is important for thermal nociception induction, and is mainly expressed on sensory neurons. Recent reports suggest that opioid or TRPV1 receptor agonist exposure has contrasting consequences for anti-nociception, tolerance and dependence. Chronic morphine exposure modulates TRPV1 activation and induces the anti-nociception effects of morphine. The regulation of many downstream targets of TRPV1 plays a critical role in this process, including calcitonin gene-related peptide (CGRP) and substance P (SP). Additional factors also include capsaicin treatment blocking the anti-nociception effects of morphine in rats, as well as opioid modulation of TRPV1 responses through the cAMP-dependent PKA pathway and MAPK signaling pathways. Here, we review new insights concerning the mechanism underlying MOR-TRPV1 crosstalk and signaling pathways and discuss the potential mechanisms of morphine-induced anti-nociception, tolerance and dependence associated with the TRPV1 signaling pathway and highlight how understanding these mechanisms might help find therapeutic targets for the treatment of morphine induced antinociception, tolerance and dependence.     

Rapid disassembly of dynamic microtubules upon activation of the capsaicin receptor TRPV1

The transmission of pain signalling involves the cytoskeleton, but mechanistically this is poorly understood. We recently demonstrated that the capsaicin receptor TRPV1, a non-selective cation channel expressed by nociceptors that is capable of detecting multiple pain-producing stimuli, directly interacts with the tubulin cytoskeleton. We hypothesized that the tubulin cytoskeleton is a downstream effector of TRPV1 activation. Here we show that activation of TRPV1 results in the rapid disassembly of microtubules, but not of the actin or neurofilament cytoskeletons. TRPV1 activation mainly affects dynamic microtubules that contain tyrosinated tubulins, whereas stable microtubules are apparently unaffected. The C-terminal fragment of TRPV1 exerts a stabilizing effect on microtubules when over-expressed in F11 cells. These findings suggest that TRPV1 activation may contribute to cytoskeleton remodelling and so influence nociception.     

Intragastric administration of allyl isothiocyanate increases carbohydrate oxidation via TRPV1 but not TRPA1 in mice

The transient receptor potential (TRP) channel family is composed of a wide variety of cation-permeable channels activated polymodally by various stimuli and is implicated in a variety of cellular functions. Recent investigations have revealed that activation of TRP channels is involved not only in nociception and thermosensation but also in thermoregulation and energy metabolism. We investigated the effect of intragastric administration of TRP channel agonists on changes in energy substrate utilization of mice. Intragastric administration of allyl isothiocyanate (AITC; a typical TRPA1 agonist) markedly increased carbohydrate oxidation but did not affect oxygen consumption. To examine whether TRP channels mediate this increase in carbohydrate oxidation, we used TRPA1 and TRPV1 knockout (KO) mice. Intragastric administration of AITC increased carbohydrate oxidation in TRPA1 KO mice but not in TRPV1 KO mice. Furthermore, AITC dose-dependently increased intracellular calcium ion concentration in cells expressing TRPV1. These findings suggest that AITC might activate TRPV1 and that AITC increased carbohydrate oxidation via TRPV1.     

TRP channel structural biology: new roles for an old fold

The capsaicin receptor, TRPV1, contributes to thermal and chemical sensitivity of primary afferent neurons of the pain pathway, but many aspects of its regulation remain elusive. In this issue of Neuron, Lishko et al. describe a high-resolution structure of a TRPV1 domain, providing insight into the molecular basis of channel modulation while revealing new functions for a widely expressed protein interaction fold.     

Coexpression and activation of TRPV1 suppress the activity of the KCNQ2/3 channel

Transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated nonselective cation channel expressed predominantly in peripheral nociceptors. By detecting and integrating diverse noxious thermal and chemical stimuli, and as a result of its sensitization by inflammatory mediators, the TRPV1 receptor plays a key role in inflammation-induced pain. Activation of TRPV1 leads to a cascade of pro-nociceptive mechanisms, many of which still remain to be identified. Here, we report a novel effect of TRPV1 on the activity of the potassium channel KCNQ2/3, a negative regulator of neuronal excitability. Using ion influx assays, we revealed that TRPV1 activation can abolish KCNQ2/3 activity, but not vice versa, in human embryonic kidney (HEK)293 cells. Electrophysiological studies showed that coexpression of TRPV1 caused a 7.5-mV depolarizing shift in the voltage dependence of KCNQ2/3 activation compared with control expressing KCNQ2/3 alone. Furthermore, activation of TRPV1 by capsaicin led to a 54% reduction of KCNQ2/3-mediated current amplitude and attenuation of KCNQ2/3 activation. The inhibitory effect of TRPV1 appears to depend on Ca(2+) influx through the activated channel followed by Ca(2+)-sensitive depletion of phosphatidylinositol 4,5-bisphosphate and activation of protein phosphatase calcineurin. We also identified physical interactions between TRPV1 and KCNQ2/3 coexpressed in HEK293 cells and in rat dorsal root ganglia neurons. Mutation studies established that this interaction is mediated predominantly by the membrane-spanning regions of the respective proteins and correlates with the shift of KCNQ2/3 activation. Collectively, these data reveal that TRPV1 activation may deprive neurons from inhibitory control mediated by KCNQ2/3. Such neurons may thus have a lower threshold for activation, which may indirectly facilitate TRPV1 in integrating multiple noxious signals and/or in the establishment or maintenance of chronic pain.     

The role of spinal cord vanilloid (TRPV1) receptors in pain modulation

Transient receptor potential vanilloid 1 (TRPV1) receptor is a nonselective cation channel activated by capsaicin, a pungent substance from chili peppers. It is considered to act as an integrator of various physical and chemical nociceptive stimuli, as it can be gated by noxious heat (>43 oC), low pH (protons) and also by recently described endogenous lipids. The structure and function of TRPV1 receptors was vigorously studied, especially since its cloning in 1997. However, most of the research was pointed towards the role of TRPV1 receptors in the peripheral tissues. Mounting evidence now suggests that TRPV1 receptors on the central branches of dorsal root ganglion neurons in the spinal cord may play an important role in modulation of pain and nociceptive transmission. The aim of this short review was to summarize the knowledge about TRPV1 receptors in the spinal cord dorsal horn, preferentially from morphological and electrophysiological studies on spinal cord slices and from in vivo experiments.     

Anatomical localization of protease-activated receptor-1 and protease-mediated neuroglial crosstalk on peri-synaptic astrocytic endfeet

We studied the localization, activation and function of protease-activated receptor 1 (PAR-1) at the CNS synapse utilizing rat brain synaptosomes and slices. Confocal immunofluoresence and transmission electron microscopy in brain slices with pre-embedding diaminobenzidine (DAB) immunostaining found PAR-1 predominantly localized to the peri-synaptic astrocytic endfeet. Structural confocal immunofluorescence microscopy studies of isolated synaptosomes revealed spherical structures stained with anti-PAR-1 antibody which co-stained mainly for glial-filament acidic protein compared with the neuronal markers synaptophysin and PSD-95. Immunoblot studies of synaptosomes demonstrated an appropriate major band corresponding to PAR-1 and activation of the receptor by a specific agonist peptide (SFLLRN) significantly modulated phosphorylated extracellular signal-regulated kinase. A significant membrane potential depolarization was produced by thrombin (1 U/mL) and the PAR-1 agonist (100 μM) and depolarization by high K(+) elevated extracellular thrombin-like activity in the synaptosomes preparation. The results indicate PAR-1 localized to the peri-synaptic astrocytic endfeet is most likely activated by synaptic proteases and induces cellular signaling and modulation of synaptic electrophysiology. A protease mediated neuron-glia pathway may be important in both physiological and pathological regulation of the synapse.     

Effect of cholesterol depletion on the pore dilation of TRPV1

The TRPV1 ion channel is expressed in nociceptors, where pharmacological modulation of its function may offer a means of alleviating pain and neurogenic inflammation processes in the human body. The aim of this study was to investigate the effects of cholesterol depletion of the cell on ion-permeability of the TRPV1 ion channel. The ion-permeability properties of TRPV1 were assessed using whole-cell patch-clamp and YO-PRO uptake rate studies on a Chinese hamster ovary (CHO) cell line expressing this ion channel. Prolonged capsaicin-induced activation of TRPV1 with N-methyl-D-glucamine (NMDG) as the sole extracellular cation, generated a biphasic current which included an initial outward current followed by an inward current. Similarly, prolonged proton-activation (pH 5.5) of TRPV1 under hypocalcemic conditions also generated a biphasic current including a fast initial current peak followed by a larger second one. Patch-clamp recordings of reversal potentials of TRPV1 revealed an increase of the ion-permeability for NMDG during prolonged activation of this ion channel under hypocalcemic conditions. Our findings show that cholesterol depletion inhibited both the second current, and the increase in ion-permeability of the TRPV1 channel, resulting from sustained agonist-activation with capsaicin and protons (pH 5.5). These results were confirmed with YO-PRO uptake rate studies using laser scanning confocal microscopy, where cholesterol depletion was found to decrease TRPV1 mediated uptake rates of YO-PRO. Hence, these results propose a novel mechanism by which cellular cholesterol depletion modulates the function of TRPV1, which may constitute a novel approach for treatment of neurogenic pain.