Contributions of Glial Glutamate Transport and Transmission to Drug Abuse

描述（由申请人提供）：成瘾最隐蔽的临床特征之一是在长期戒断后容易复发。现有的证据表明，谷氨酸内稳态的破坏核内丘脑是这种慢性复发的脆弱性的一个贡献机制。谷氨酸稳态是指调节突触可塑性的突触外和突触神经元谷氨酸浓度之间的平衡。在长期暴露于可卡因后发生的持久的神经适应中，胱氨酸-谷氨酸交换器（xCT）和高亲和力胶质细胞谷氨酸转运体GLT-1的催化亚基的功能和蛋白表达降低，这两个非突触细胞外谷氨酸的整合调节剂。因此，降低的细胞外谷氨酸浓度测量可卡因自我管理后，在脑桥核。用N-乙酰半胱氨酸（NAC）或头孢曲松全身治疗损害可卡因的恢复并增加GLT-1和xCT两者的表达。[As为了更全面地理解负责谷氨酸稳态持久破坏的变应性机制及其对成瘾的贡献，我采用了反义敲除策略来确定GLT-1和xCT在大鼠成瘾恢复模型中的相对贡献。初步数据表明，胶质细胞GLT-1的表达，而不是xCT，是NAC治疗效果的关键介质。因此，本提案的目标是检验以下假设：可卡因暴露后神经胶质中的适应影响谷氨酸的释放和摄取，进而影响谷氨酸的稳态平衡以及可卡因诱导的细胞和突触神经适应。这将在该奖项的指导阶段使用（i）体内微透析来测量GLT-1遗传操作后的谷氨酸浓度，以及（ii）膜片钳电生理学来比较在这些相同条件下中等多刺神经元（mEPSC，AMPA：NMDA比率，[神经胶质源性慢内向电流]）的生理特性。该奖项的独立阶段提出的实验将继续继续这些研究和调查（iii）在这些过程中的代谢型谷氨酸受体的参与。 公共卫生相关性：由于高复吸率是丧失健康和生活质量的主要原因，因此必须确定候选治疗机制。负责破坏谷氨酸稳态的神经胶质机制的调查将阐明谷氨酸水平的严格控制的平衡的失调如何有助于与成瘾相关的突触和行为病理学，并代表了治疗干预的直接途径。

DESCRIPTION (provided by applicant): One of the most insidious clinical features of addiction is the vulnerability to relapse following extended abstinence. Existing evidence suggests that a disruption in glutamate homeostasis within the nucleus accumbens is a contributing mechanism to this chronic relapse vulnerability. Glutamate homeostasis refers to the balance between extrasynaptic and synaptic neuronal glutamate concentrations that regulate synaptic plasticity. Among the long-lasting neuroadaptations which occur following chronic exposure to cocaine are decreased function and protein expression of the catalytic subunit of the cystine-glutamate exchanger (xCT) and high affinity glial glutamate transporter GLT-1, two integral regulators of nonsynaptic extracellular glutamate. Accordingly, decreased extracellular glutamate concentrations are measured following cocaine self-administration in the nucleus accumbens. Systemic treatment with either N-acetylcysteine (NAC) or ceftriaxone impairs reinstatement to cocaine and increases expression of both GLT-1 and xCT. [As a means of understanding more fully the allostatic mechanisms responsible for enduring disruptions of glutamate homeostasis and their contribution to addiction, I have employed an antisense knockdown strategy to determine the relative contributions of GLT-1 and xCT in a rat reinstatement model of addiction. Preliminary data indicate that expression of glial GLT-1, but not xCT, is the critical mediator of the therapeutic effect of NAC. Thus, a goal of this proposal i to test the hypothesis that adaptations in glia following cocaine exposure influence the release and uptake of glutamate, in turn affecting the homeostatic balance of glutamate and the cellular and synaptic neuroadaptations induced by cocaine.] This will be accomplished during the mentored phase of the award using (i) in vivo microdialysis to measure glutamate concentrations following genetic manipulation of GLT-1, and (ii) patch clamp electrophysiology to compare physiological properties of medium spiny neurons (mEPSCs, AMPA:NMDA ratios, [glial-derived slow inward currents]) under these same conditions. Experiments proposed for the independent phase of the award will go on to continue these studies and investigate (iii) the engagement of metabotropic glutamate receptors in these processes. PUBLIC HEALTH RELEVANCE: Because high rates of drug relapse represent a major cause of lost health and quality of life, identification of candidate therapeutic mechanisms is imperative. Investigation of glial mechanisms responsible for disruptions in glutamate homeostasis will elucidate how deregulation of the tightly controlled balance of glutamate levels contributes to synaptic and behavioral pathologies associated with addiction, and represents a direct avenue for therapeutic intervention.