越鞠甘麦大枣汤增强突触可塑性产生抗抑郁样作用＊

目的 研究越鞠甘麦大枣汤的抗抑郁样作用并分析其对小鼠海马突触可塑性的影响。方法 昆明小鼠随机分为对照组和越鞠甘麦大枣汤组，给药24 h和7 天后进行悬尾测试（Tail suspension test，TST）和强迫游泳测试（Forced swimming test，FST）。运用电生理（electrophysiological experiment）技术检测小鼠海马区Schaffe侧枝-CA1的长时程增强（long term potentiation，LTP），利用western blot方法分析海马脑区α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid receptor，AMPAR）和N-甲基-d-天冬氨酸受体（N-methyl-D-aspartate receptor， NMDAR）相关突触蛋白的表达水平。结果 给药24 h和7天后，与对照组小鼠相比，越鞠甘麦大枣汤给药组小鼠在TST（P <0.001）和FST（P <0.01）中的不动时间均明显降低，氯胺酮在给药24 h后显示出抗抑郁作用，但到第7天不能降低小鼠不动时间，越鞠甘麦大枣汤显示出更持久的抗抑郁样作用。电生理实验中，越鞠甘麦大枣汤可增强小鼠海马区的LTP（P < 0.001）。Western blot结果显示，GluR1、NR2B以及NR1的表达水平在给药后均明显增加（P < 0.05）。结论 越鞠甘麦大枣汤可能通过增强昆明小鼠海马脑区LTP，以及增加AMPA和NMDA受体相关突触蛋白的表达水平以提高突触传递效能，从而产生抗抑郁样作用。     

Pain after Discontinuation of Morphine Treatment Is Associated with Synaptic Increase of GluA4-Containing AMPAR in the Dorsal Horn of the Spinal Cord

Withdrawal from prescribed opioids results in increased pain sensitivity, which prolongs the treatment. This pain sensitivity is attributed to neuroplastic changes that converge at the spinal cord dorsal horn. We have recently reported that repeated morphine administration triggers an insertion of GluA2-lacking (Ca²⁺-permeable) α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPAR) in the hippocampus. This finding together with the reported involvement of AMPAR in the mechanisms underlying inflammatory pain led us to hypothesize a role for spinal AMPAR in opioid-induced pain behavior. Mice treated with escalating doses of morphine showed hypersensitivity to mechanical stimulation. Intrathecal administration of a Ca²⁺-permeable AMPAR selective blocker disrupted morphine-induced mechanical sensitivity. Analysis of the expression and phosphorylation levels of AMPAR subunits (GluA1/2/3/4) in homogenates and in postsynaptic density fractions from spinal cord dorsal horns showed an increase in GluA4 expression and phosphorylation in the postsynaptic density after morphine. Co-immunoprecipitation analyses suggested an increase in GluA4 homomers (Ca²⁺-permeable AMPAR) and immunohistochemical staining localized the increase in GluA4 levels in laminae III–V. The excitatory postsynaptic currents (EPSCs) recorded in laminae III–V showed enhanced sensitivity to Ca²⁺-permeable AMPAR blockers in morphine-treated mice. Furthermore, current–voltage relationships of AMPAR-mediated EPSCs showed that rectification index (an indicator of Ca²⁺-permeable AMPAR contribution) is increased in morphine-treated but not in saline-treated mice. These effects could be reversed by infusion of GluA4 antibody through patch pipette. This is the first direct evidence for a role of GluA4-containing AMPAR in morphine-induced pain and highlights spinal GluA4-containing AMPAR as targets to prevent the morphine-induced pain sensitivity.     

Neurologic Autoimmunity in the Era of Checkpoint Inhibitor Cancer Immunotherapy

Neurologic autoimmune disorders in the context of systemic cancer reflect antitumor immune responses against onconeural proteins that are autoantigens in the nervous system. These responses observe basic principles of cancer immunity and are highly pertinent to oncological practice since the introduction of immune checkpoint inhibitor cancer therapy. The patient’s autoantibody profile is consistent with the antigenic composition of the underlying malignancy. A major determinant of the pathogenic outcome is the anatomic and subcellular location of the autoantigen. IgGs targeting plasma membrane proteins (eg, muscle acetylcholine receptor -IgG in patients with paraneoplastic myasthenia gravis) have pathogenic potential. However, IgGs specific for intracellular antigens (eg, antineuronal nuclear antibody 1 [anti-Hu] associated with sensory neuronopathy and small cell lung cancer) are surrogate markers for CD8⁺ T lymphocytes targeting peptides derived from nuclear or cytoplasmic proteins. In an inflammatory milieu, those peptides translocate to neural plasma membranes as major histocompatibility complex class I protein complexes. Paraneoplastic neurologic autoimmunity can affect any level of the neuraxis and may be mistaken for cancer progression. Importantly, these disorders generally respond favorably to early-initiated immunotherapy and cancer treatment. Small cell lung cancer and thymoma are commonly associated with neurologic autoimmunity, but in the context of checkpoint inhibitor therapy, other malignancy associations are increasingly recognized.     

Activity-dependent synaptic GRIP1 accumulation drives synaptic scaling up in response to action potential blockade

Synaptic scaling is a form of homeostatic plasticity that stabilizes neuronal firing in response to changes in synapse number and strength. Scaling up in response to action-potential blockade is accomplished through increased synaptic accumulation of GluA2-containing AMPA receptors (AMPAR), but the receptor trafficking steps that drive this process remain largely obscure. Here, we show that the AMPAR-binding protein glutamate receptor-interacting protein-1 (GRIP1) is essential for regulated synaptic AMPAR accumulation during scaling up. Synaptic abundance of GRIP1 was enhanced by activity deprivation, directly increasing synaptic GRIP1 abundance through overexpression increased the amplitude of AMPA miniature excitatory postsynaptic currents (mEPSCs), and shRNA-mediated GRIP1 knockdown prevented scaling up of AMPA mEPSCs. Furthermore, knockdown and replace experiments targeting either GRIP1 or GluA2 revealed that scaling up requires the interaction between GRIP1 and GluA2. Finally, GRIP1 synaptic accumulation during scaling up did not require GluA2 binding. Taken together, our data support a model in which activity-dependent trafficking of GRIP1 to synaptic sites drives the forward trafficking and enhanced synaptic accumulation of GluA2-containing AMPAR during synaptic scaling up.Proper development of neuronal circuits, as well as efficient information storage during learning and memory, are thought to depend upon the presence of homeostatic mechanisms that stabilize neuronal excitability (1–3). One such mechanism is synaptic scaling, which compensates for perturbations in average firing by scaling up or down the postsynaptic strength of all of a neuron’s excitatory synapses (4). Synaptic scaling is a cell-autonomous process in which neurons detect changes in their own firing through a set of calcium-dependent sensors that then regulate receptor trafficking to increase or decrease the accumulation of AMPA receptors (AMPAR) at synaptic sites and thus increase or decrease synaptic strength (4–6). Despite great recent interest, the AMPA receptor-trafficking events that underlie synaptic scaling remain largely obscure. Defects in synaptic scaling have been postulated to contribute to disorders as diverse as Alzheimer’s disease (7) and epilepsy (8), so illuminating the underlying AMPAR trafficking steps could shed light into the genesis of a wide range of neurological disorders.Most neocortical AMPAR are heteromeric receptors composed of both GluA1 and GluA2 subunits, which have unique phosphorylation sites and interact with distinct trafficking proteins (9). During synaptic scaling up in response to action potential blockade, synaptic strength is increased through enhanced synaptic accumulation of GluA1 and GluA2-containing AMPAR (5, 10–13) and requires the C-terminal domain of the GluA2 subunit (12), but which subunit-specific interactions underlie synaptic scaling remain controversial (12, 14). Several trafficking proteins are known to interact with the GluA2, but not the GluA1, C-tail, including glutamate receptor interacting protein-1 (GRIP1) (15) and protein interacting with C-kinase-1 (PICK1) (16). Many studies have examined the role of GRIP1 and PICK1 in AMPAR trafficking and surface accumulation (15, 17–22), but little is known about their potential roles in regulating AMPAR synaptic accumulation during synaptic scaling. It was recently shown that deletion of PICK1, which competes with GRIP1/2 for binding to GluA2, enhances AMPAR accumulation and occludes synaptic scaling up (23), suggesting GRIP/PICK1-GluA2 interactions as possible critical players in synaptic scaling.GRIP1 was one of the first AMPAR-binding proteins identified (15), and yet its exact function in synaptic transmission and plasticity remains controversial. GRIP1 is an abundant multi-PDZ domain-containing protein that interacts with GluA2 through its fourth and fifth PDZ domains (15) and has known interactions with several other signaling and trafficking proteins, including itself (24), ABP (25), EphB receptors (26); the rasGEF GRASP-1 (27), the scaffold protein liprin-α (28), and the microtubule motor protein KIF5, or kinesin 1 (29). The role of GRIP1 in AMPAR trafficking is complicated and may involve AMPAR trafficking to and stabilization at synapses (17), as well as microtubule-based transport into dendrites (29) and the regulation of AMPAR movement between intracellular recycling compartments and the cell surface (22, 30). How GRIP1 influences basal AMPAR trafficking is not entirely clear. Overexpression of GRIP1 or gain-of-function GRIP1 mutants have been consistently observed to enhance surface AMPAR levels (21, 31), but knockout or dominant-negative GRIP1 constructs have had inconsistent effects, with slower synaptic AMPAR accumulation observed in one study (17) but no effects on basal AMPAR recycling and transmission in others (22, 32). Interestingly, GRIP1 and -2 are critical for the expression of cerebellar long-term depression (LTD), where they play redundant roles in regulated AMPAR endocytosis (33, 34). Currently no direct role for GRIP1 in activity-dependent synaptic strengthening or homeostatic plasticity has been established.Here, we show that the GRIP1–GluA2 interaction plays an essential role in the activity-dependent synaptic AMPAR accumulation and enhanced excitatory synaptic strength that underlies synaptic scaling up. Activity blockade with TTX increased the accumulation of GRIP1 at synaptic sites, whereas directly enhancing synaptic GRIP1 accumulation through overexpression (OE) was sufficient to mimic synaptic scaling. GRIP1 was necessary for synaptic scaling, because scaling up was prevented by shRNA-mediated knock down (KD) of endogenous GRIP1 and rescued by replacement with an RNAi-insensitive (RNAiI) GRIP1 but not a GRIP1 mutant that lacks the GluA2 interaction domain. We showed previously that GluA2 KD blocks synaptic scaling (12). Here, we show that synaptic scaling after GluA2 KD can be rescued by wild-type (RNAiI) GluA2 or point mutants that do not interfere with GRIP1 binding but not by GluA2 point mutants (Y876E and S880E) that reduce GluA2- GRIP1 binding, strongly suggesting that GRIP1 mediates synaptic scaling through interactions with GluA2. Finally, TTX still induced GRIP1 synaptic accumulation even when AMPAR accumulation was prevented by expression of GluA2 Y876E; thus, during synaptic scaling GluA2 synaptic accumulation depends on GRIP1 binding, but GRIP1 translocation and synaptic accumulation occur independently of GluA2 binding. Together our data show that activity-dependent regulation of synaptic GRIP1 abundance is critical for the forward trafficking and accumulation of AMPA receptors at synapses during synaptic scaling.     

New trends in the development of AMPA receptor antagonists

The interest in AMPA glutamate receptors has grown enormously in recent years, due to their crucial role in physiological and pathological processes. This led to the development of AMPA ligands as research tools and potential therapeutic agents. In particular, extensive work was addressed towards the development of selective antagonists, which proved to be particularly useful in the prevention and treatment of a variety of neurological and non-neurological diseases. This review focuses on the primary and patent literature from 2000 onwards.     

逍遥散调节肝郁脾虚大鼠中枢AMPA受体及相关蛋白的机制研究

目的:观察逍遥散和6-氰基-7-硝喹啉-2,3-双酮(CNQX)对慢性束缚应激所致肝郁脾虚证大鼠中枢AMPA受体及其相关蛋白表达的影响,探讨逍遥散的作用机制。方法:将100只雄性SD大鼠随机分为正常组(A组)、假手术组(B组)、模型组(C组)、逍遥散组(D组)、CNQX组(E组)和逍遥散+CNQX组(F组)。C、D、E、F组大鼠通过连续21d慢性束缚应激建立肝郁脾虚证候模型,D、F组大鼠每天束缚前灌服逍遥散5.32g/kg,E、F组大鼠隔天右侧杏仁核区微量注射α-氨基羟甲基恶唑丙酸(AMPA)受体拮抗剂CNQX 0.5μL。各组动物第22d处死,免疫组化方法检测海马CA1区、CA3区、基底外侧杏仁核(BLA)谷氨酸受体2/3(GluR2/3)、N-乙基顺丁烯二酰亚胺敏感性的融合蛋白(NSF)、PKC作用蛋白1(PICK1)水平。结果:模型大鼠GluR2/3在海马CA1、CA3区明显减少,BLA区明显增加;NSF在海马CA1、CA3区有减少趋势;PICK1在海马CA3区明显增加。CNQX和逍遥散对模型大鼠GluR2/3 PICK1在海马的变化均有调节作用。逍遥散联合CNQX作用于慢性束缚应激大鼠与单独使用逍遥散或CNQX后呈现一致性。结论:调节AMPA受体及其相关蛋白在海马各区和杏仁核的兴奋性至少是逍遥散调节突触可塑性、进一步治疗应激和抑郁的作用途径之一。     

Early-life epileptiform discharges exert both rapid and long-lasting effects on AMPAR subunit composition and distribution in developing neurons

The perinatal period of brain is characterized by dynamic changes in structure and high propensity for epilepsy. Animal models have shown that alterations of AMPA receptor (AMPAR) assembly or function may be related to seizure-induced cell damage, long-lasting impairments in brain development and seizure threshold. However, effects of earlier epileptiform discharges on AMPAR composition and sub-cellular distribution remain understudied. In this study, we analyzed age-dependent variation of relative GluR1 and GluR2 protein levels in primary cultured rat cortical neurons at 7 DIV, 12 DIV, 17 DIV and 21 DIV. By inducing a single event of epileptiform activity at 6 DIV, we tested the effects of early-life seizure-like insults on AMPAR subunit distribution. We found a significant increase in synaptosomal membrane GluR1 expression in magnesium-free (MGF) medium-treated neurons at each time point detected (p < 0.05), while GluR2 expression increased at 7 DIV, and declined at 17 DIV and 21 DIV respectively (p < 0.05). That is, a trend of high GluR1 with much lower GluR2 expression on the surface membrane of epileptiform discharges experienced neurons over time in culture was presented. These findings in an in vitro model of early-life seizure may inform rodent models of epilepsy, as well as the cellular mechanism involved in epilepsy-associated brain dysfunction.     

电针对VD大鼠海马神经细胞PKC mRNA、mGluRs和AMPAR表达的影响

目的 观察电针对血管性痴呆(VD)大鼠海马神经细胞PKC mRNA、mGluRs、AMPAR表达的影响,探讨电针的治疗作用机制.方法 将SD大鼠随机分为假手术组、模型组和电针组,每组10只.模型组和电针组采用重复脑缺血再灌注方法建立VD大鼠模型.将电针组大鼠放入大鼠固定器中,暴露大鼠头部和背部,将电针浅刺入大鼠“百会”、“大椎”穴,每天电针1次,留针20 min,连续治疗10 d.3组大鼠均于造模10d后采用逆转录聚合酶链式反应(RT-PCR)检测海马神经细胞PKC mRNA,免疫组织化学染色技术观察脑组织海马神经细胞mGluRs、AMPAR染色结果.结果 模型组海马PKC mRNA表达较假手术组降低,而与模型组比较,电针组海马PKC mRNA表达显著增加,差异有统计学意义(P＜0.05).海马mGluRs免疫阳性细胞积分光密度在假手术组、模型组和电针组分别为(58.6±3.6)、(36.3±2.5)和(51.5±4.8),与假手术组比较,模型组海马mGluRs免疫阳性细胞积分光密度显著降低,差异有统计学意义(P＜0.01);而与模型组比较,电针组海马mGluRs免疫阳性细胞积分光密度显著增加,差异有统计学意义(P＜0.05);海马AMPAR免疫阳性细胞积分光密度在假手术组、模型组和电针组分别为(66.5±2.8)、(40.1±5.1)和(58.3±4.6),与假手术组比较,模型组海马AMPAR免疫阳性细胞积分光密度显著降低,差异有统计学意义(P＜0.01),而与模型组比较,电针组海马AMPAR免疫阳性细胞积分光密度显著增加,差异有统计学意义(P＜0.05).结论 电针可增加VD大鼠海马PKC mRNA、mGluRs和AMPAR表达.电针大鼠“百会”、“大椎”穴改善大鼠学习记忆能力的机制可能与提高海马mGluRs、AMPAR和PKC mRNA表达有关.     

Distinct cellular mediators drive the Janus faces of toll-like receptor 4 regulation of network excitability which impacts working memory performance after brain injury

The mechanisms by which the neurophysiological and inflammatory responses to brain injury contribute to memory impairments are not fully understood. Recently, we reported that the innate immune receptor, toll-like receptor 4 (TLR4) enhances AMPA receptor (AMPAR) currents and excitability in the dentate gyrus after fluid percussion brain injury (FPI) while limiting excitability in controls. Here, we examine the cellular mediators underlying TLR4 regulation of dentate excitability and its impact on memory performance. In ex vivo slices, astrocytic and microglial metabolic inhibitors selectively abolished TLR4 antagonist modulation of excitability in controls, but not in rats after FPI, demonstrating that glial signaling contributes to TLR4 regulation of excitability in controls. In glia-depleted neuronal cultures from naïve mice, TLR4 ligands bidirectionally modulated AMPAR charge transfer consistent with neuronal TLR4 regulation of excitability, as observed after brain injury. In vivo TLR4 antagonism reduced early post-injury increases in mediators of MyD88-dependent and independent TLR4 signaling without altering expression in controls. Blocking TNFα, a downstream effector of TLR4, mimicked effects of TLR4 antagonist and occluded TLR4 agonist modulation of excitability in slices from both control and FPI rats. Functionally, transiently blocking TLR4 in vivo improved impairments in working memory observed one week and one month after FPI, while the same treatment impaired memory function in uninjured controls. Together these data identify that distinct cellular signaling mechanisms converge on TNFα to mediate TLR4 modulation of network excitability in the uninjured and injured brain and demonstrate a role for TLR4 in regulation of working memory function.