中脑边缘奖赏系统参与阿片类药物成瘾的环路机制

阿片类药物成瘾发生率高,对个人和社会危害极大。中脑边缘奖赏系统在阿片类药物成瘾中发挥着重要作用,以往研究多集中于中脑边缘奖赏系统中特定脑区的功能变化,而对脑区之间神经元的相互作用研究较少。该文对近年来中脑边缘奖赏系统参与阿片类药物成瘾的环路机制进行综述,以期从更广阔的视野了解阿片类药物成瘾机制。     

M受体的研究进展

M受体是机体中最重要的受体之一，根据药理学分类可分为M1，M2，M3和M4 4种药理学亚,发子克隆技术可将其分为m1,m2,m3,m4和m5，其中M1，M2和M3分别对应于m1,m2和m3。各种亚型基本结构相似，主要差别在于胞浆内3环（i3环）的不同，这决定了它们功能的不同。m1，m3和m5结构功能相似，可激活PI系统和cAMP，m2和m4则可抑制腺苷酸环化酶系统。不同部位各种亚型的分布和功能也有所不同。M受体亚型的分布和功能及其活性药物对临床具有重要意义。     

胆碱能M受体调控细胞周期蛋白依赖性激酶5及其在敌敌畏诱导SH-SY5Y细胞毒性损伤中的作用

目的研究胆碱能M受体(主要为M1受体)参与SH-SY5Y细胞周期依赖性蛋白激酶5(Cdk5)调控及其在敌敌畏(DDVP)诱导SH-SY5Y细胞毒性损伤中的作用。方法①应用免疫荧光结合共聚焦显微镜检测胆碱能M1受体及Cdk5在SH-SY5Y细胞中的分布和表达。②细胞对照组、氧化震颤素(Oxo-M)组(1×10^-4mol·L^-1作用48 h)、罗考唯亭(Rosc)组(培养结束前1 h加入Rosc 1×10^-4mol·L^-1)、Rosc+Oxo-M组(Rosc 1×10^-4mol·L^-1预处理1 h后,再加入Oxo-M 1×10^-4mol·L^-1作用至48 h),应用MTT比色法检测细胞存活率,Western印迹法检测Cdk5表达。③细胞对照组、DDVP组(1×10^-5mol·L^-1作用48 h)、Rosc组(培养结束前1 h加入1×10^-4mol·L<...     

病理性赌博与中脑边缘奖赏系统的活性下降有关

病理性赌博(pathological gambling)的许多特点与药物成瘾相似,比如两者都能获得高度欣快感,并产生渴求和耐受.中脑边缘奖赏系统在药物成瘾的形成和维持过程中起着重要的作用.已有研究表明成瘾药物的长期作用能使中脑奖赏系统的敏感性下降.吸毒者的摄药行为在很大程度上可以理解为以外源性的药物来弥补中脑边缘奖赏系统活性的下降.于是人们推测,中脑边缘多巴胺系统也可能参与了病理性赌博的形成和维持过程.最近Renter等人发表在2005年<自然·神经科学>上的研究论文证实了上述的推测.     

毒蕈碱型M5受体亚型及生物学特性

M5是最后一个被克隆出的乙酰胆碱毒蕈碱型受体亚型,具有G蛋白偶联受体家族的基本结构特征, 其信号转导方式既可以与G蛋白偶联,激活多种效应酶 (腺苷酸环化酶、磷脂酶C、磷脂酶A2 )产生相应的生物学效应,又可作用于离子通道来调节细胞间的信号传递。M5生理作用主要与调节中枢NO的生成和DA的释放有关,可能为药物滥用成瘾、DA系统功能障碍性疾病、阿尔采末病、脑缺血等的药物治疗提供一个新靶标。     

M1受体激动剂介导的神经保护作用机制

阿尔茨海默病(AD)是老年期常见的一类慢性、进行性神经细胞退行性病变。应用毒蕈碱M1受体激动剂是治疗AD的策略之一。M1受体激动剂可通过对抗淀粉样β蛋白产生的神经毒性,减少tau蛋白的过度磷酸化,产生神经生长因子样作用,以及缩短后超极化时程等机制而产生神经保护作用。     

5-HT6受体及其拮抗剂研究进展

5-羟色胺能神经系统与认知功能和摄食行为密切相关。目前研究人员正在对多种化合物进行生物评价,以确定其是否具有5-HT6受体拮抗作用。临床前研究结果表明,部分化合物对大鼠和人5-HT6受体具有较强的选择性拮抗作用,并能增强大鼠的认知功能,包括记忆保存与巩固,以及空间学习能力。因此,5-HT6受体拮抗剂在治疗神经精神疾病相关的认知损伤方面(如阿尔茨海默病、精神分裂症)较有前景。另外,这些化合物还有助于减少遗传型和饮食型肥胖者的食物摄入、脂肪吸收和体重增加。本文介绍了5-HT6受体拮抗剂用于治疗阿尔茨海默病和精神分裂症相关的认知功能障碍,以及肥胖症的研究进展。     

5—HT3受体拮抗剂的发展与临床比较

有效地控制癌症患者因放、化疗引起的恶心呕吐，近年来一类新的高效低毒的抗呕吐药物5－HT3受体桔抗剂发展迅速。本文就其发展及国内外临床常用的品种进行综述和比较。1．5－HT3受体措抗剂的发展：1948年从血液中分离得到血清素，不久确定了其化学结构为5一羟色胺（5－HT），它广泛存在于动植物界并对生理功能起重要地调节作用。近Ic年来，5－HT受体的类型及其选择性激动剂和桔抗剂逐渐被认识并引起重视。由于现代放射配位体技术和自显影技术的研究进展，发现5－HT受体有岑个亚型，即为：5－HTI、5－HT、5－HT3和5－HT4。其中5－HT…     

M_5受体参与激活吗啡奖赏大鼠腹侧背盖区nNOS表达

目的　研究不同毒蕈碱受体亚型 (M4,M5)对吗啡诱发大鼠奖赏效应的影响 ,同时观察腹侧背盖区 (ventraltegmentalarea ,VTA)神经型一氧化氮合酶 (nNOS)表达的变化。方法　实验通过侧脑室置管给药 ,采用反义寡核苷酸技术 ,免疫组织化学技术和条件位置偏爱 (conditionedplacepreference,CPP)程序 ,研究M4,M5反义寡脱氧核苷酸干预下吗啡的奖赏行为 ,以及VTA内nNOS表达情况。结果　吗啡 (5mg·kg-1)皮下注射 ,可以建立起稳定的大鼠对伴吗啡环境的位置偏爱 ,同时VTA内nNOS阳性神经元表达也显著增加。而M5反义寡脱氧核苷酸 (M5 AS) (2nmol)侧脑室预注射则可阻断吗啡诱发CPP的形成 ,同时也显著减少VTA内nNOS表达。在吗啡诱发的CPP形成后 ,侧脑室单次注射M5 AS(2nmol)也可以逆转大鼠对伴吗啡环境的位置偏爱 ,同时也明显减少VTA内nNOS表达。相比之下 ,M4反义寡脱氧核苷酸 (M4 AS)对吗啡诱发的CPP形成以及VTA内nNOS表达的影响均不明显。实验前后所有大鼠的运动活性并未发生显著改变 ,可排除运动活性对实验的影响。结论　M5毒蕈碱受体在大鼠吗啡诱发的条件位置偏爱形成过程中起重要作用 ;M5毒蕈碱受体可能是通过激活大鼠VTA内nNOS的表达 ,参与调控吗啡奖赏效应的。     

Muscarinic Receptors Modulate the Intrinsic Excitability of Infralimbic Neurons and Consolidation of Fear Extinction

There is considerable interest in identifying pharmacological compounds that could be used to facilitate fear extinction. Recently, we showed that the modulation of M-type K⁺ channels regulates the intrinsic excitability of infralimbic (IL) neurons and fear expression. As muscarinic acetylcholine receptors inhibit M-type K⁺ channels, cholinergic inputs to IL may have an important role in controlling IL excitability and, thereby, fear expression and extinction. To test this model, we combined whole-cell patch-clamp electrophysiology and auditory fear conditioning. In prefrontal brain slices, muscarine enhanced the intrinsic excitability of IL neurons by reducing the M-current and the slow afterhyperpolarization, resulting in an increased number of spikes with shorter inter-spike intervals. Next, we examined the role of endogenous activation of muscarinic receptors in fear extinction. Systemic injected scopolamine (Scop) (muscarinic receptor antagonist) before or immediately after extinction training impaired recall of extinction 24-h later, suggesting that muscarinic receptors are critically involved in consolidation of extinction memory. Similarly, infusion of Scop into IL before extinction training also impaired recall of extinction 24-h later. Finally, we demonstrated that systemic injections of the muscarinic agonist, cevimeline (Cev), given before or immediately after extinction training facilitated recall of extinction the following day. Taken together, these findings suggest that cholinergic inputs to IL have a critical role in modulating consolidation of fear extinction and that muscarinic agonists such as Cev might be useful for facilitating extinction memory in patients suffering from anxiety disorders.     

Allosteric Modulation of Muscarinic Acetylcholine Receptors

Muscarinic acetylcholine receptors (mAChRs) are prototypical Family A G protein coupled-receptors. The five mAChR subtypes are widespread throughout the periphery and the central nervous system and, accordingly, are widely involved in a variety of both physiological and pathophysiological processes. There currently remains an unmet need for better therapeutic agents that can selectively target a given mAChR subtype to the relative exclusion of others. The main reason for the lack of such selective mAChR ligands is the high sequence homology within the acetylcholine-binding site (orthosteric site) across all mAChRs. However, the mAChRs possess at least one, and likely two, extracellular allosteric binding sites that can recognize small molecule allosteric modulators to regulate the binding and function of orthosteric ligands. Extensive studies of prototypical mAChR modulators, such as gallamine and alcuronium, have provided strong pharmacological evidence, and associated structure-activity relationships (SAR), for a “common” allosteric site on all five mAChRs. These studies are also supported by mutagenesis experiments implicating the second extracellular loop and the interface between the third extracellular loop and the top of transmembrane domain 7 as contributing to the common allosteric site. Other studies are also delineating the pharmacology of a second allosteric site, recognized by compounds such as staurosporine. In addition, allosteric agonists, such as McN-A-343, AC-42 and N-desmethylclozapine, have also been identified. Current challenges to the field include the ability to effectively detect and validate allosteric mechanisms, and to quantify allosteric effects on binding affinity and signaling efficacy to inform allosteric modulator SAR.     

M3-Type Muscarinic Receptors Predominantly Mediate Neurogenic Quick Contraction of Bovine Ciliary Muscle

• 1.The present experiments were designed to investigate which subtypes of muscarinic receptors are involved in the neurogenic quick contraction of bovine ciliary muscle in connection to quick eye focal accommodation.
• 2.Transmural electrical stimulation (TES) produced a transient contraction, which was abolished in the presence of 3×10⁻⁷ M tetrodotoxin and 10⁻⁶ M atropine, but greatly augmented by 3×10⁻⁷ M physostigmine.
• 3.The exogenously applied acetylcholine (ACh: 10⁻⁹ to 3×10⁻⁶ M) produced a concentration-dependent contraction, which was competitively antagonized by 10⁻⁶ M atropine and augmented by 3×10⁻⁷ M physostigmine, but unaffected by 3×10⁻⁷ M tetrodotoxin.
• 4.The magnitude and time to peak of the maximal contraction produced by TES were significantly greater (1267.5±86.0 mg, P<0.005) and shorter (9.0±0.2 sec, P<0.005) than corresponding values (97.0±9.9 mg and 20.3±2.1 sec, respectively) of the phasic contraction caused by exogenously applied 10⁻⁵ M ACh, at which concentration the agonist caused the maximal contraction. The velocity (140.6±7.8 mg/sec) of the transient contraction caused by TES was approximately 28-fold greater than that of the phasic contraction caused by ACh (5.1±0.9 mg/sec).
• 5.The contractions produced by TES were greatly attenuated by 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) as an M₃ antagonist and slightly by pirenzepine as an M₁ antagonist (20.2±7.9% inhibition at the highest concentration), but not by methoctramine (MET) as an M₂ antagonist. The IC₅₀ value (−log M) for 4-DAMP was determined to be 7.17±0.14.
• 6.Scatchard plot analysis of [³H]-quinuclidinylbenzilate (QNB) binding revealed that the binding sites constituted a single population with a K_d of 31.2±0.8 pM and a B_max of 895.5±93.2 fmol/mg protein. The activity in inhibiting [³H]-QNB binding was most potent with 4-DAMP (-log K_i=7.98±0.02), but less potent with pirenzepine (−log K_i=6.43±0.04) and MET (−log K_i=7.32±0.16). 4-DAMP was approximately 35- and 5-fold more potent than pirenzepine and MET in terms of −log K_i values, respectively, suggesting the predominant localization of M₃ receptor subtypes in the bovine ciliary muscle membrane.
• 7.These results suggest that TES produces a neurogenic quick contraction of the bovine ciliary muscle, which would be mediated mainly by ACh released from the intramural nerve terminals and subsequent excitation of M₃ receptor subtypes localized on the ciliary muscle cells, and that neurogenic quick contraction of the ciliary muscle is possibly involved in part in eye focal accommodation.

     

吗啡依赖与毒蕈碱型乙酰胆碱受体的适应

毒蕈碱型乙酰胆碱(muscarinic acetylcholine)能神经在阿片依赖中的作用可以追溯到30年代,当时认为吗啡可以抑制迷走神经.到60年代认为吗啡镇痛耐受与毒蕈碱乙酰胆碱能神经的慢性适应有关;70年代有作者认为吗啡戒断时毒蕈碱能神经兴奋[1].本文系统地介绍M受体介导吗啡镇痛耐受、吗啡戒断反应和吗啡精神依赖的作用机制.     

Molecular Characteristics of Mammalian Dopamine Receptors

Abstract: Abstract: Dopamine receptors belong to a large super-gene family of receptors which are linked to their signal transduction pathways through heterotrimeric G proteins. A variety of signalling events are known to be regulated by dopamine receptors including adenylate cyclase and phospholipase activities and various ion channels. Prior to the advent of molecular cloning technology, dopamine receptors were believed to belong to two subtypes, D₁ and D₂. This distinction was based on both pharmacological and functional criteria. We now know that at least five different dopamine receptors exist although they can still be described as to belonging within “D₁” and “D₂” subfamilies. The D₁ subfamily consists of two receptors—the D₁ and D₅, whereas the D₂, D₃ and D₄ receptors comprise the D₂ subfamily. The cloning and molecular characteristics of these five receptors are described in this review.     

Cocaine Decreases Metabotropic Glutamate Receptor mGluR1 Currents in Dopamine Neurons by Activating mGluR5

Midbrain dopamine neurons are important mediators of reward and movement and are sensitive to cocaine-induced plasticity. After even a single injection of cocaine, there is an increase in AMPA-dependent synaptic transmission. The present study examines cocaine-induced plasticity of mGluR-dependent currents in dopamine neurons in the substantia nigra. Activation of mGluR1 and mGluR5 resulted in a mixture of inward and outward currents mediated by a nonselective cation conductance and a calcium-activated potassium conductance (SK), respectively. A single injection of cocaine decreased the current activated by mGluR1 in dopamine neurons, and it had no effect on the size of the mGluR5-mediated current. When the injection of cocaine was preceded by treatment of the animals with a blocker of mGluR5 receptors (MPEP), cocaine no longer decreased the mGluR1 current. Thus, the activation of mGluR5 was required for the cocaine-mediated suppression of mGluR1-mediated currents in dopamine neurons. The results support the hypothesis that mGluR5 coordinates a reduction in mGluR1 functional activity after cocaine treatment.     

Role of Dopamine D2 Receptors in Human Reinforcement Learning

Influential neurocomputational models emphasize dopamine (DA) as an electrophysiological and neurochemical correlate of reinforcement learning. However, evidence of a specific causal role of DA receptors in learning has been less forthcoming, especially in humans. Here we combine, in a between-subjects design, administration of a high dose of the selective DA D2/3-receptor antagonist sulpiride with genetic analysis of the DA D2 receptor in a behavioral study of reinforcement learning in a sample of 78 healthy male volunteers. In contrast to predictions of prevailing models emphasizing DA''s pivotal role in learning via prediction errors, we found that sulpiride did not disrupt learning, but rather induced profound impairments in choice performance. The disruption was selective for stimuli indicating reward, whereas loss avoidance performance was unaffected. Effects were driven by volunteers with higher serum levels of the drug, and in those with genetically determined lower density of striatal DA D2 receptors. This is the clearest demonstration to date for a causal modulatory role of the DA D2 receptor in choice performance that might be distinct from learning. Our findings challenge current reward prediction error models of reinforcement learning, and suggest that classical animal models emphasizing a role of postsynaptic DA D2 receptors in motivational aspects of reinforcement learning may apply to humans as well.