Dissecting Mechanisms of GABAB-GIRK Plasticity with Psychostimulants

描述（由申请人提供）：成瘾性药物篡夺了大脑内在的奖励机制，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，但临床有效的治疗方法却一直困扰着研究人员。值得注意的是，FDA还没有批准治疗精神兴奋剂滥用的药物。在腹侧被盖区（VTA），大脑奖励中心的中心，gaba能抑制控制神经元的兴奋性。GABAbeta受体与G蛋白门控钾（GIRK）通道偶联形成GABAbeta能抑制途径的主要成分。研究表明，急性注射精神兴奋剂对小鼠VTA GABA神经元的GABAbeta受体GIRK抑制通路产生强烈的抑制作用，但对DA神经元没有抑制作用。这种药物引起的GABA神经元中GABAbetaR信号的抑制消除了GABA神经元放电的内在制动，这将导致GABA介导的DA神经元抑制增强，并可能降低奖励感知。这种精神兴奋剂的急性效应提供了一个独特的机会来学习如何通过改变内源性表达GABAbeta-GIRK蛋白在VTA GABA神经元中的水平来控制VTA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。该项目的主要目的是确定受体磷酸化在GABAbeta- girk信号变化中的作用，并评估GABAbeta受体的下调是否会改变精神兴奋剂的成瘾特性。具体来说，我们将(i)验证受体去磷酸化是精神兴奋剂下调VTA GABA神经元中GABAbeta受体活性的基础这一假设，（ii）阐明控制蛋白磷酸酶2A （PP2A）与GABAbeta受体关联的结构和分子相互作用，以及（iii）确定GABA神经元中GABAbeta- girk信号对VTA功能和动机行为的影响。研究小组将采用综合的方法，结合分子遗传学、结构生物学、生物化学、生理学和行为学。精神兴奋剂通过调节GABAbeta受体磷酸化来调节突触抑制，这一过程依赖于与受体直接相关的PP2A的一小部分，这是一个创新的未经检验的模型。GABAbeta受体的C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gpcr的分子调控提供框架。巴氯芬（lioreal）是GABAbeta受体的激动剂，目前正在评估治疗酒精中毒、成瘾和自闭症的效果。如本文所述，选择性地靶向GABAergic抑制系统可能会改善巴氯芬的临床应用，并可能开发出治疗成瘾和其他神经系统疾病的新药。

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.