Synaptic mechanims underlying reward seeking and comupulsive drug use

奖励寻求和强迫性药物使用的突触机制

• 批准号: 8559269
• 负责人: Veronica A Alvarez
• 金额: $ 96.09万
• 依托单位: NATIONAL INSTITUTE ON ALCOHOL ABUSE AND ALCOHOLISM
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8559269
• 关键词: AMPA Receptors; Acute; Addictive Behavior; Address; Affect; Agonist; Agreement; Alcohol consumption; Alcohols; Amphetamines; Animals; Area; Bathing; Behavior; Behavioral; Biochemistry; Blood; Brain; Brain region; Cells; Chemosensitization; Chronic; Circadian Rhythms; Cocaine; Cocaine Users; Consumption; Corpus striatum structure; DRD2 gene; Data; Dependence; Depressed mood; Development; Disease; Dissection; Dopamine D2 Receptor; Drug usage; Electric Stimulation; Electrophysiology (science); Ethanol; Globus Pallidus; Glutamates; Hour; Individual; Inhibitory Concentration 50; Intake; Interneurons; Intoxication; Investigation; Laboratories; Laser Scanning Microscopy; Lasers; Length; Mediating; Mental Depression; Midbrain structure; Modeling; Morphology; Motivation; Mouse Strains; Mus; N-Methylaspartate; Neurobiology; Neurons; Nucleus Accumbens; Obsessive compulsive behavior; Output; Pathway interactions; Patients; Pattern; Persons; Pharmaceutical Preparations; Photons; Physiologic pulse; Play; Predisposition; Prefrontal Cortex; Preparation; Property; Psychiatry; Recruitment Activity; Research; Resolution; Rewards; Role; Scanning; Self Administration; Self-control as a personality trait; Signal Transduction; Speed; Structure; Sucrose; Sulpiride; Synapses; Techniques; Testing; Therapeutic Uses; Time; Vertebral column; Wild Type Mouse; addiction; carbon fiber; cholinergic; cocaine exposure; cocaine use; density; dopaminergic neuron; drinking; drinking behavior; drug of abuse; extracellular; fighting; gamma-Aminobutyric Acid; motor impairment; mouse model; novel; postsynaptic; preference; presynaptic; research study; response; success; tool; transmission process

Project 1: Synaptic potentiation in D2 receptor expressing neurons in the accumbens confers protection against the development of compulsive cocaine use. (Bock, Shin et al.; under revision) The hypothesis behind this study is that the vulnerability to develop compulsive cocaine use arises in part from inherent differences across animals in the ability to recruit the D2-MSNs and engage the indirect accumbal-tegmental pathway. Evidence from previous studies suggests that activation of D2 receptors is involved in the locomotor response to cocaine and conditioned place preference (Durieux et al., 2009; Ferguson et al., 2011). However, it is still unclear what the role of D2-MSNs is with regard to voluntary cocaine self-administration and the development of compulsive cocaine use. Experiments also test the hypothesis that inhibition of D2-MSNs impairs self-control over cocaine intake and renders individuals more susceptible to the rewarding effects of the drug. The results showed that potentiation of excitatory inputs onto D2-MSNs occurs only in mice that can exert self-control over cocaine intake, and suggest that the potentiation might confer protection. Furthermore, the experiments suggested that inhibition of D2-MSN output renders mice vulnerable to the expression of compulsive behaviors by enhancing the motivation to obtain cocaine, without affecting drug use when it is readily available. These data are in agreement with previous studies showing that reinstatement of cocaine seeking is associated with reduced extracellular GABA in the ventral pallidum (Tang et al., 2005). In conclusion, this study establishes synaptic potentiation in D2-MSN inputs as a critical mechanism for controlling the expression of compulsive behaviors towards cocaine. We propose that this cell-specific synaptic potentiation facilitates the recruitment of indirect pathway neurons and protects against the development addictive behaviors. This study also showed that manipulations of D2-MSN activity, even when introduced after several weeks of drug taking, can successfully alter the motivation to obtain cocaine. The use of therapeutic brain stimulation to silence ventral pallidum neurons or to selectively activate D2-MSNs could enhance self-control in patients fighting dependence on drugs of abuse. Project 2: Acute cocaine effects on glutamatergic and dopaminergic transmission in the nucleus accumbens (Adrover, Shin and Alvarez, in preparation) Glutamatergic inputs to the NAc that originate in the VTA have been recently demonstrated and recent studies suggest that glutamatergic transmission from VTA DA neurons plays an important role in the rewarding properties of cocaine and amphetamine (Birgner et al., 2010; Kozorovitskiy et al., 2012), as well as enhanced sucrose and cocaine self-administration (Alsio et al., 2011). However, the properties of these synapses are poorly understood and the effect of cocaine unknown. In this study, optogenic tools are used to selectively activate terminals from VTA DA neurons into the NAc and investigate the acute effect of cocaine on DA and glutamatergic transmission. ChR2 activation in the NAc shell region was achieved by a brief laser pulse and triggered DA transients that were recorded with a carbon fiber using fast scanning cyclic voltammetry (FSCV). DA transients evoked by ChR2 activation also had similar properties to those evoked by electrical stimulation. This same ChR2 activation evoked glutamatergic excitatory postsynaptic currents (EPSCs) in MSNs of the shell that were abolished by TTX but were insensitive to D1R and D2R antagonists. The average amplitude of the AMPA receptor-mediated EPSC was 101 9 pA and the average AMPA/NMDA ratio was 1.5 0.2. Bath-application of cocaine (10 M) prolonged the DA transients and increasing the decay time constant by a factor of 10 (3.5 0.6 s). The area of the DA transient was increased 2.5 times and the peak was transiently enhanced. In contrast, cocaine inhibited AMPA-R mediated EPSCamplitude by half. A similar pattern of depression was observed in the NMDA-R mediated EPSCs.The D2R antagonist sulpiride reversed the inhibition of both AMPA-R and NMDA-R mediated EPSCs when applied after cocaine. These data indicated that D2R activation is required for cocaine-induced inhibition of EPSCs and indeed, a D2-like agonist inhibited the DA transients and also glutamatergic EPSCs in a concentration dependent manner and with a similar IC50, indicating that VTA terminals that release glutamate also express presynaptic D2Rs. D2R are expressed by indirect pathway MSNs, cholinergic interneurons and also on presynaptic DA terminals where they inhibit DA release. Mice lacking D2R only in DA neurons were also tested. Cocaine increased DA transients by 50% and had no effect on AMPA-R EPSCs in these mice. Furthermore, the DA transient response to cocaine was similar to those of wild-type mice when cocaine was added in the presence of sulpiride. These results indicate that acute cocaine, in addition to causing larger DA transients, acts on presynaptic D2R to inhibit DA and glutamate release from VTA terminals. Furthermore, these results suggest that cocaine, acting via these mechanisms, has opposite effects on DA and glutamatergic transmission from midbrain DA neurons, enhancing the first and depressing the latter. Project 3: Dissection of the drinking behavior and analysis of spine morphology in a mouse model of binge-like ethanol drinking (Wilcox et al., under review) Research into the neurobiology of heavy and binge-like ethanol drinking has been limited by the low-levels of voluntary ethanol consumption shown by most mouse strains (Crabbe et al., 2011). Recently, a model of intermittent access to ethanol has been shown to elicit binge-like drinking and pharmacologically relevant blood ethanol concentrations (BECs) in mice (Rhodes et al., 2005). Termed Drinking in the Dark, this model takes advantage of the circadian patterns of mice to achieve reliably high levels of consumption in a two hour drinking session. C57BL/6J mice reach BECs higher than 80 mg/dl, and show signs of intoxication such as motor impairment (Rhodes et al., 2007). DID is a robust paradigm that has been successfully used to investigate neuronal circuits and signals that modulate binge-like ethanol consumption (Sprow, 2012). Despite the success of this intermittent access model, the mechanisms underlying the acquisition of voluntary ethanol drinking are not completely understood. In this study, we established DID in our laboratory and showed that it produces reliable escalation of voluntary ethanol intake and blood ethanol concentration. We characterized the drinking pattern of mice with intermittent access to ethanol using lickometers to record each bout with high temporal resolution over many weeks of voluntary ethanol consumption, and analyzed the synaptic morphology of striatal neurons 2 days and 30 days after the last ethanol binge. The results represent a novel and important contribution to the alcohol field because they identify the bottle exchange, an integral part of DID, as a likely mechanism by which intermittent access facilitates the acquisition of voluntary ethanol drinking behavior by inducing mice to drink at a higher rate. Over time, mice change their ethanol drinking pattern and increase the speed of drinking at the beginning of each DID session. Faster ethanol drinking is associated with higher BEC, and an enhanced preference for ethanol was observed after 6 weeks of treatment. Interestingly, no changes were detected in either striatal or accumbal spine density, and a shortening of spine length was seen only transiently, suggesting that these behavioral changes occur independent of long-term changes in synaptic morphology in brain regions involved in the reward pathway.

项目 1：伏隔核中表达 D2 受体的神经元的突触增强可防止形成强迫性可卡因使用。 （Bock、Shin 等人；正在修订中） 这项研究背后的假设是，产生强迫性可卡因使用的脆弱性部分源于动物在募集 D2-MSN 和参与间接伏盖-被盖通路的能力方面的固有差异。先前研究的证据表明，D2 受体的激活涉及对可卡因的运动反应和条件性位置偏好（Durieux 等，2009；Ferguson 等，2011）。然而，目前尚不清楚 D2-MSN 对于自愿可卡因自我给药和强迫性可卡因使用的发展有何作用。实验还验证了这样的假设：抑制 D2-MSN 会损害对可卡因摄入的自我控制，并使个体更容易受到药物的奖励作用的影响。 结果表明，D2-MSN 上的兴奋性输入增强仅发生在能够对可卡因摄入进行自我控制的小鼠中，并表明这种增强可能会带来保护作用。此外，实验表明，抑制 D2-MSN 输出会增强小鼠获取可卡因的动机，从而使小鼠容易表现出强迫行为，而不会影响容易获得的药物使用。这些数据与之前的研究一致，表明恢复可卡因寻求与腹侧苍白球细胞外 GABA 减少有关（Tang 等，2005）。 总之，本研究将 D2-MSN 输入中的突触增强作为控制可卡因强迫行为表达的关键机制。 我们认为这种细胞特异性突触增强促进了间接通路神经元的募集并防止发育成瘾行为。这项研究还表明，即使在吸毒几周后进行 D2-MSN 活性的操纵，也可以成功改变获取可卡因的动机。使用治疗性脑刺激来沉默腹侧苍白球神经元或选择性激活 D2-MSN 可以增强患者的自我控制能力，以对抗滥用药物的依赖。 项目 2：可卡因对伏隔核谷氨酸能和多巴胺能传递的急性影响（Adrover、Shin 和 Alvarez，准备中） 起源于 VTA 的 NAc 的谷氨酸输入最近已得到证实，最近的研究表明，来自 VTA DA 神经元的谷氨酸传输在可卡因和安非他明的奖励特性中发挥着重要作用（Birgner 等人，2010；Kozorovitskiy 等人， 2012），以及增强蔗糖和可卡因的自我给药（Alsio 等人， 2011）。然而，人们对这些突触的特性知之甚少，可卡因的作用也未知。 在本研究中，使用光原性工具选择性激活 VTA DA 神经元至 NAc 的末端，并研究可卡因对 DA 和谷氨酸能传递的急性影响。 NAc 壳区域中的 ChR2 激活是通过短暂的激光脉冲和触发的 DA 瞬态来实现的，并使用快速扫描循环伏安法 (FSCV) 用碳纤维记录该瞬态。 ChR2 激活引起的 DA 瞬变也与电刺激引起的具有相似的特性。同样的 ChR2 激活在壳的 MSN 中诱发谷氨酸能兴奋性突触后电流 (EPSC)，这种电流被 TTX 消除，但对 D1R 和 D2R 拮抗剂不敏感。 AMPA受体介导的EPSC的平均振幅为101±9pA，平均AMPA/NMDA比率为1.5±0.2。 可卡因 (10 M) 的浴应用延长了 DA 瞬态，并将衰减时间常数增加了 10 倍（3.5 ± 0.6 s）。 DA瞬态面积增加2.5倍，峰瞬态增强。相比之下，可卡因将 AMPA-R 介导的 EPSCamplitude 抑制一半。在 NMDA-R 介导的 EPSC 中观察到类似的抑郁模式。在可卡因后施用 D2R 拮抗剂舒必利，可逆转 AMPA-R 和 NMDA-R 介导的 EPSC 的抑制。这些数据表明 D2R 激活是可卡因诱导的 EPSC 抑制所必需的，实际上，D2 样激动剂以浓度依赖性方式抑制 DA 瞬变以及谷氨酸能 EPSC，并具有相似的 IC50，表明释放谷氨酸的 VTA 末端也表达突触前 D2R。 D2R 由间接途径 MSN、胆碱能中间神经元以及突触前 DA 末端表达，在突触前 DA 末端抑制 DA 释放。还测试了仅 DA 神经元缺乏 D2R 的小鼠。可卡因使 DA 瞬变增加 50%，但对这些小鼠的 AMPA-R EPSC 没有影响。此外，当在舒必利存在的情况下添加可卡因时，DA 对可卡因的瞬时反应与野生型小鼠相似。这些结果表明，急性可卡因除了引起更大的 DA 瞬变之外，还作用于突触前 D2R，抑制 VTA 末端释放 DA 和谷氨酸。此外，这些结果表明，可卡因通过这些机制起作用，对中脑 DA 神经元的 DA 和谷氨酸能传递具有相反的作用，增强前者并抑制后者。 项目 3：暴饮乙醇小鼠模型的饮酒行为剖析和脊柱形态分析（Wilcox 等人，正在审查中） 对大量和狂饮乙醇的神经生物学研究受到大多数小鼠品系显示的低水平自愿乙醇消耗的限制（Crabbe 等，2011）。最近，间歇性摄入乙醇的模型已被证明会引起小鼠的暴饮暴食和药理学相关的血液乙醇浓度（BEC）（Rhodes 等，2005）。该模型被称为“黑暗中饮酒”，利用小鼠的昼夜节律模式在两小时的饮酒过程中实现可靠的高水平消耗。 C57BL/6J 小鼠的 BEC 达到高于 80 mg/dl，并显示出中毒迹象，例如运动障碍（Rhodes 等，2007）。 DID 是一种强大的范例，已成功用于研究调节暴饮暴食型乙醇消耗的神经元回路和信号（Sprow，2012）。尽管这种间歇性获取模式取得了成功，但自愿饮用乙醇的机制尚不完全清楚。在这项研究中，我们在实验室建立了 DID，并表明它可以可靠地提高自愿乙醇摄入量和血液乙醇浓度。我们使用舔度计对间歇性摄入乙醇的小鼠的饮酒模式进行了表征，以高时间分辨率记录自愿乙​​醇消耗数周内的每次发作，并分析了最后一次乙醇暴饮后 2 天和 30 天纹状体神经元的突触形态。这些结果对酒精领域做出了新颖且重要的贡献，因为他们发现瓶子交换是 DID 的一个组成部分，它是一种可能的机制，通过该机制间歇性获取通过诱导小鼠以更高的速率饮酒来促进自愿乙醇饮酒行为的获得。 随着时间的推移，小鼠会改变其乙醇饮用模式，并在每次 DID 开始时加快饮用速度。 更快地饮用乙醇与更高的 BEC 相关，并且在治疗 6 周后观察到对乙醇的偏好增强。有趣的是，纹状体或伏棘密度没有检测到变化，并且棘长度的缩短只是短暂的，这表明这些行为变化的发生独立于参与奖励途径的大脑区域突触形态的长期变化。