Dissecting Mechanisms of GABAB-GIRK Plasticity with Psychostimulants

描述(由申请人提供)：成瘾药物篡夺大脑的内在奖励机制，导致强迫和破坏性行为。虽然在了解成瘾的神经化学和生理变化方面取得了重大进展，但临床上有效的治疗方法一直没有得到研究人员的支持。值得注意的是，目前还没有FDA批准的治疗精神刺激剂滥用的药物。在大脑奖赏中心腹侧被盖区(VTA)，GABA能抑制控制神经元的兴奋性。GABA能抑制途径的一个主要组成部分是由GABAβ受体与G蛋白门控钾(GIRK)通道偶联形成的。研究表明，小鼠急性注射精神刺激剂可强烈抑制VTA-GABA神经元的GABAβ受体GIRK抑制通路，但不能抑制DA神经元的GIRK抑制通路。这种药物引起的对GABA神经元GABAbetaR信号的抑制消除了对GABA神经元放电的内在抑制，这将导致GABA介导的对DA神经元的抑制增强，并潜在地减少奖赏感觉。精神刺激剂的这种急性效应提供了一个独特的机会，学习如何通过改变VTA GABA神经元内源性表达的GABAbeta-GIRK蛋白水平来控制VTA的输出。然而，需要详细的临床前研究来更好地了解VTA GABA神经元中GABAbetaR-GIRK信号的适应如何影响VTA的输出和动机行为。这个项目的主要目的是确定受体的磷酸化在GABAbeta-GIRK信号变化中的作用，并评估GABAbeta受体的下调是否改变了精神刺激剂的成瘾特性。具体地说，我们将(I)检验该受体的去磷酸化是精神刺激剂下调VTA GABA神经元中GABAβ受体活性的基础的假设，(Ii)阐明控制蛋白磷酸酶2A(PP2A)与GABAβ受体相关的结构和分子相互作用，以及(Iii)确定GABA神经元中的GABAβ-GIRK信号对VTA功能和动机行为的影响。研究小组将使用一种综合的方法，结合分子遗传学、结构生物学、生物化学、生理学和行为学。心理刺激剂通过调节GABAβ受体磷酸化来调节突触抑制的假说，这一过程依赖于与受体直接相关的一部分PP2A，这是一个创新且未经检验的模型。GABAbeta受体的C末端结构域是协调受体功能调节蛋白的中心，这一概念可以为理解大脑中其他GPCRs的分子调控提供框架。巴氯芬(利福沙尔)是一种GABAβ受体激动剂，目前正在被评估用于治疗酒精中毒、成瘾和自闭症。如本文所述，选择性地靶向GABA能抑制系统可能会改善巴氯芬的临床使用，并可能开发出治疗成瘾和其他神经疾病的新药。

DESCRIPTION (provided by applicant): Addictive drugs usurp the brain's intrinsic mechanism for reward, leading to compulsive and destructive behaviors. While there have been significant advances in understanding the neurochemical and physiological changes in addiction, clinically effective treatments have eluded researchers. Remarkably, there are no FDA approved drugs for treating psychostimulant abuse. In the ventral tegmental area (VTA), the center of the brain's reward center, GABAergic inhibition controls the excitability of neurons. A primary component of the GABAergic inhibitory pathway is formed by GABAbeta receptors that couple to G protein-gated potassium (GIRK) channels. Studies show that an acute injection of psychostimulant in mice produces a robust depression of the GABAbeta receptor GIRK inhibitory pathway in VTA GABA neurons but not in DA neurons. This drug-evoked depression of GABAbetaR signaling in GABA neurons removes an intrinsic brake on GABA neuron firing that would result in enhanced GABA-mediated inhibition of DA neurons and potentially reducing reward perception. This acute effect of psychostimulants provides a unique opportunity learn how to control the VTA output through alterations in the levels of endogenously expressed GABAbeta-GIRK proteins in VTA GABA neurons. However, detailed pre-clinical studies are needed to better understand how adaptations in GABAbetaR-GIRK signaling in VTA GABA neurons affect the output of the VTA and motivated behavior. The main objectives of this project are to determine the role of phosphorylation of the receptor in this change of GABAbeta-GIRK signaling and assess whether down-regulation of GABAbeta receptor alters the addictive properties of psychostimulants. Specifically, we will (i) test the hypothesis that dephosphorylation of the receptor underlies the ability of psychostimulants to down regulate GABAbeta receptor activity in VTA GABA neurons, (ii) elucidate the structural and molecular interactions governing protein phosphatase 2A (PP2A) association with the GABAbeta receptor, and (iii) determine impact of GABAbeta-GIRK signaling in GABA neurons on VTA function and motivated behavior. The research team will use a comprehensive approach that combines molecular genetics, structural biology, biochemistry, physiology and behavior. The hypothesis that psychostimulants regulate synaptic inhibition by modulating GABAbeta receptor phosphorylation, a process that is dependent upon a fraction of PP2A directly associating with the receptor, is an innovative and untested model. The concept that the C terminal domain of the GABAbeta receptor serves as the epicenter for coordinating regulatory proteins for receptor function could provide the framework for understanding the molecular regulation of other GPCRs in the brain. Baclofen (Lioresal) is an agonist of the GABAbeta receptor and is being evaluated for treating alcoholism, addiction and autism. Selectively targeting the GABAergic inhibitory system as described here could lead to improved clinical use of baclofen and perhaps to new drugs for treating addiction and other neurological disorders.