Role of AMPA receptors in the nucleus accumbens shell in morphine depedence

描述(申请人提供)：本R03提案的目的是研究伏隔核(NASH)中AMPA谷氨酸受体(NASH)的突触可塑性如何调节吗啡依赖。长期服用吗啡等鸦片类药物会导致依赖，其特征是身体(短期)和情感(长期)戒断症状。与戒毒相关的这些厌恶状态的缓解被认为是吸毒复发的主要动机(Koob和Le Moal，1997)。AMPA谷氨酸受体负责大脑中大部分快速兴奋性突触传递。它们是由GluR1-4亚基组成的异构体四聚体，赋予受体不同的生理和功能特性(Palmer等，2005年)。先前的工作已经证明，NASH中升高的GluR1水平减少，而GluR2增加，这是可卡因和外侧下丘脑刺激的奖赏效应(Kelz等人，1999；Todtenkopf等人，提交)，表明AMPA受体亚单位可以影响动机状态。在吗啡依赖大鼠中，阿片拮抗剂纳洛酮引起戒断症状(Schulteis等人，1994；Chartoff等人，2006)，并增加伏隔核细胞外谷氨酸水平(Sepulveda等人，1998)，这表明AMPA传递增强可能有助于戒断症状。与此一致，全身应用AMPA受体拮抗剂可减轻躯体戒断症状(Rasmussen等人，1996)。此外，我们还发现纳洛酮增加了吗啡依赖大鼠GluR1的磷酸化。GluR1的磷酸化可以增加AMPA电流并促进受体亚单位的突触插入(Malinow和Malenka，2002)。基于这些观察结果，我们假设AMPAR的激活和GluR亚单位功能的调节与吗啡戒断症状有关。我们将使用两种独立(但互补)的方法来检验我们的假设。首先，我们将AMPA或AMPA受体拮抗剂NBQX微量注入NASH，并检测其对纳洛酮诱导的吗啡依赖大鼠条件性位置厌恶和躯体戒断体征的影响。其次，我们将使用蛋白质交联法来确定吗啡依赖和戒断如何调节细胞表面和细胞内GluR1和GluR2 AMPAR亚单位的运输。这些研究的数据将指导未来的拨款申请，在这些申请中，我们将建议使用病毒介导的基因转移来确定操纵NASH中GluR1或GluR2亚单位水平对吗啡依赖的影响，以及确定吗啡诱导突触可塑性的分子和细胞机制。拟议的研究将有助于我们理解与慢性吗啡戒断相关的厌恶状态背后的神经生物学机制，这一点很重要，因为缓解戒断症状的愿望是复发的一个主要因素。我们的目标是确定伏隔核壳中AMPA谷氨酸受体功能的突触可塑性是否有助于吗啡依赖，从而导致吗啡戒断的厌恶迹象。伏隔核壳是调节动机状态的关键脑区。这些研究的结果可能会确定AMPA受体的大脑区域特定功能，这些功能可以作为未来成瘾治疗的靶点。

DESCRIPTION (provided by applicant): The purpose of this R03 proposal is to investigate how synaptic plasticity of AMPA glutamate receptors in the nucleus accumbens shell (NASh) mediates morphine dependence. Chronic administration of opiates such as morphine can lead to dependence, characterized by physical (short-lasting) and affective (long-lasting) withdrawal signs. Alleviation of these aversive states associated with drug withdrawal is considered a major motivation for relapse to drug taking (Koob and Le Moal, 1997). AMPA glutamate receptors are responsible for the majority of fast excitatory synaptic transmission in the brain. They are heteromeric tetramers composed of GluR1-4 subunits that confer distinct physiological and functional properties to the receptor (Palmer et al., 2005). Prior work has demonstrated that elevating GluR1 levels in the NASh decreases, and GluR2 increases, the rewarding effects of cocaine and lateral hypothalamic brain stimulation (Kelz et al., 1999; Todtenkopf et al., submitted), suggesting that AMPA receptor subunits can impact motivational state. In morphine-dependent rats, the opiate antagonist naloxone elicits withdrawal signs (Schulteis et al., 1994; Chartoff et al., 2006) and increases extracellular glutamate levels in the nucleus accumbens (Sepulveda et al., 1998), suggesting that enhanced AMPA transmission might contribute to withdrawal signs. Consistent with this, systemic administration of an AMPA receptor antagonist attenuates somatic withdrawal signs (Rasmussen et al., 1996). Furthermore, we found that naloxone increases the phosphorylation of GluR1 in morphine-dependent rats. GluR1 phosphorylation can increase AMPA currents and facilitate synaptic insertion of receptor subunits (Malinow and Malenka, 2002). Based on these observations, we hypothesize that activation of AMPARs and modulation of GluR subunit function contribute to morphine withdrawal signs. We will test our hypothesis using two independent (but complementary) approaches. First we will microinject AMPA or the AMPA receptor antagonist NBQX into the NASh and measure the effects on naloxone-induced conditioned place aversions and somatic withdrawal signs in morphine-dependent rats. Second, we will use a protein cross-linking assay to determine how morphine dependence and withdrawal regulate the cell surface versus intracellular trafficking of GluR1 and GluR2 AMPAR subunits. Data from these studies will guide the formulation of future grant applications in which we will propose to use viral mediated gene transfer to determine the effects of manipulating either GluR1 or GluR2 subunit levels in the NASh on morphine dependence as well as determine molecular and cellular mechanisms underlying morphine-induced synaptic plasticity. The proposed studies will contribute to our understanding of the neurobiological mechanisms underlying aversive states associated with withdrawal from chronic morphine, which is important because the desire to alleviate withdrawal symptoms is a major factor in relapse to drug taking. Our goal is to determine whether synaptic plasticity of AMPA glutamate receptor function in the nucleus accumbens shell-a brain region critical for regulating motivational states-contributes to morphine dependence and hence aversive signs of morphine withdrawal. Results from these studies might identify brain region-specific functions of AMPA receptors that can be targeted in future treatments for addiction.