Contributions of Glial Glutamate Transport and Transmission to Drug Abuse

描述（由申请人提供）：成瘾的最阴险的临床特征之一是在长期戒断后容易复发。现有证据表明，伏隔核内谷氨酸稳态的破坏是这种慢性复发脆弱性的促进机制。谷氨酸内稳态是指突触外和突触内神经元谷氨酸浓度的平衡，调节突触的可塑性。在长期暴露于可卡因后发生的长期神经适应中，胱氨酸-谷氨酸交换器（xCT）的催化亚基和高亲和力胶质谷氨酸转运体GLT-1的功能和蛋白质表达下降，这是两种非突触细胞外谷氨酸的完整调节因子。因此，细胞外谷氨酸浓度下降后测量可卡因自行给药伏隔核。用n -乙酰半胱氨酸（NAC）或头孢曲松进行全身治疗会损害对可卡因的恢复，并增加GLT-1和xCT的表达。[为了更全面地了解谷氨酸体内平衡持续中断的适应机制及其对成瘾的贡献，我采用了反义敲低策略来确定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治疗效果的关键中介。因此，本研究的目的是验证可卡因暴露后神经胶质细胞的适应性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性的假设。这将在授奖的指导阶段完成，使用(i)体内微透析来测量GLT-1基因操作后的谷氨酸浓度，以及（ii）膜片钳电生理学来比较相同条件下中等脊髓神经元（mEPSCs， AMPA:NMDA比率，[胶质细胞衍生的缓慢内向电流]）的生理特性。该奖项独立阶段提出的实验将继续这些研究，并调查（iii）代谢性谷氨酸受体在这些过程中的作用。

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.