Cocaine-induced AMPAR plasticity: modulation by metabotropic glutamate receptors?

描述（由申请人提供）：可卡因成瘾临床治疗的一个主要挑战是戒断使用者在重新暴露于先前与可卡因相关的环境线索后复发的倾向。在急性药物戒断阶段之后，这种复发的脆弱性可能会增加。同样，大鼠在戒断的头几个月，线索诱导的可卡因寻找会加剧或“潜伏”。这是通过增加GluA 2-缺乏，Ca 2+渗透（CP）-AMPAR在脑桥核（NAc）介导的。CP-AMPAR在未用药大鼠NAc中占AMPAR的很小比例，但在该区域积累，与线索诱导的寻找的孵育有关。这些CP-AMPAR表现出比其他AMPAR更高的电导，因此可能使NAc神经元对药物相关的线索更敏感;事实上，阻断CP-AMPAR可以阻止孵化寻求的表达。因此，确定可卡因戒断后导致CP-AMPAR升高的机制可能有助于确定治疗线索诱导的渴望和复发的潜在治疗靶点。在其他脑区，I组代谢型谷氨酸受体（mGluR）激活导致突触后CP-AMPAR的选择性内化。虽然I组mGluRs似乎不内化NAc中的AMPAR，但这仅在未用药啮齿动物的NAc中进行了评估，其中CP-AMPAR水平非常低。重要的是，几项研究报告了在从重复可卡因暴露中戒断期间NAc中I组mGluR水平降低。我的中心假设是I组mGluR活化选择性地内化NAc中的CP-AMPAR，并且由于NAc中I组mGluR水平的降低，CP-AMPAR在可卡因自我给药的长期戒断期间积累。我还假设，I组mGluR的激活NAC将防止表达的孵化线索诱导寻求选择性内化CP-AMPAR在这些可卡因经验丰富的大鼠。目的1将使用表达CP-AMPAR的培养的NAc神经元来测试工作假设，即I组mGluR激活导致CP-AMPAR的选择性内化。免疫细胞化学实验将确定CP-AMPAR的表面表达是否被急性和长期组I mGluR激活或抑制改变。目的2将检验以下工作假设：在从长期使用可卡因自我给药中长时间戒断期间，NAc中I组mGluR的水平降低，并且体内NAc I组mGluR的药理学活化减少线索诱导的可卡因寻找。大鼠将自我施用可卡因或盐水（对照），并且生物化学研究将确定“孵育”大鼠的NAc中I组mGluR表面、突触或突触外水平是否降低。行为研究将确定急性NAc内注射I组mGluR激动剂是否减少孵育的线索诱导的可卡因寻求并内化CP-AMPAR。在这些研究进行的同时，我将参加一个培训计划，该计划采用课程作业，个人指导和协作互动，以发展实现我成为学术环境中首席研究员的目标所需的非板凳技能。 公共卫生相关性：这项提议使用成瘾大鼠模型来研究导致线索诱导的可卡因渴望加剧的细胞机制，这是可卡因戒断后复发的常见触发因素。我们的研究结果可能会确定一个分子靶点（第一组代谢型谷氨酸受体），用于开发药物，以减少戒断可卡因成瘾者的线索诱导的渴望。

DESCRIPTION (provided by applicant): A major challenge for the clinical treatment of cocaine addiction is the propensity for abstinent users to relapse upon re-exposure to environmental cues previously associated with cocaine. This vulnerability to relapse may increase after the acute drug withdrawal stage. Similarly, cue-induced cocaine seeking in rats intensifies or "incubates" during the first months of withdrawal. This is mediated by an increase in GluA2-lacking, Ca2+ permeable (CP)-AMPARs in the nucleus accumbens (NAc). CP-AMPARs represent a very small percentage of the AMPARs in the NAc of drug-naive rats but accumulate in this region in association with the incubation of cue-induced seeking. These CP-AMPARs exhibit higher conductance than other AMPARs and are therefore likely to make NAc neurons more responsive to drug-related cues; in fact, blocking CP-AMPARs prevents the expression of incubated seeking. Thus, identifying the mechanism that leads to elevation of CP-AMPARs after cocaine withdrawal may help identify potential therapeutic targets for the treatment of cue-induced craving and relapse. In other brain regions, group I metabotropic glutamate receptor (mGluR) activation leads to the selective internalization of postsynaptic CP-AMPARs. While group I mGluRs do not seem to internalize AMPARs in the NAc, this has only been assessed in the NAc of drug-naive rodents, where CP-AMPAR levels are very low. Importantly, several studies report decreased group I mGluR levels in the NAc during withdrawal from repeated cocaine exposure. My central hypothesis is that group I mGluR activation selectively internalizes CP-AMPARs in the NAc and that CP-AMPARs accumulate during prolonged withdrawal from cocaine self- administration due to a decrease in group I mGluR levels in the NAc. I also hypothesize that group I mGluR activation in the NAc will prevent the expression of incubated cue-induced seeking by selectively internalizing CP-AMPARs in these cocaine-experienced rats. Aim 1 will use cultured NAc neurons, which express CP- AMPARs, to test the working hypothesis that group I mGluR activation leads to the selective internalization of CP-AMPARs. Immunocytochemical experiments will determine if surface expression of CP-AMPARs is altered by acute and long-term group I mGluR activation or inhibition. Aim 2 will test the working hypothesis that levels of group I mGluRs in the NAc decrease during prolonged withdrawal from extended access cocaine self- administration, and that pharmacological activation of NAc group I mGluRs in vivo reduces cue-induced cocaine seeking. Rats will self-administer cocaine or saline (controls) and biochemical studies will determine if group I mGluR surface, synaptic or extrasynaptic levels decrease in the NAc of "incubated" rats. Behavioral studies will determine if acute intra-NAc injection of a group I mGluR agonist reduces incubated cue-induced cocaine seeking and internalizes CP-AMPARs. While these studies are underway, I will participate in a Training Plan that employs coursework, individual mentoring, and collaborative interactions to develop the non- bench skills needed to reach my goal of becoming a principal investigator in an academic setting. PUBLIC HEALTH RELEVANCE: This proposal uses a rat model of addiction to study the cellular mechanisms that lead to intensification of cue- induced cocaine craving, a common trigger for relapse, after cocaine withdrawal. Our results may identify a molecular target (group I metabotropic glutamate receptors) for the development of medications to reduce cue- induced craving in abstinent cocaine addicts.