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

描述(申请人提供)：临床治疗可卡因成瘾的一个主要挑战是戒毒者在再次暴露于以前与可卡因有关的环境线索时复发的倾向。在急性停药阶段之后，这种复发的脆弱性可能会增加。同样，在戒断的头几个月里，线索诱导的大鼠寻求可卡因的行为会加剧或“孵化”。这是由伏隔核(NAC)中缺乏GluA2的、可渗透钙(CP)的AMPAR增加所介导的。CP-AMPAR在药物幼稚大鼠的NAc中只占AMPAR的一个非常小的百分比，但随着线索诱导寻找的孵化而在这个区域积累。这些CP-AMPAR比其他AMPAR表现出更高的电导，因此可能使NAC神经元对药物相关的提示更敏感；事实上，阻断CP-AMPAR可以阻止孵化寻找的表达。因此，识别可卡因戒断后导致CP-AMPAR升高的机制可能有助于确定治疗线索诱导的渴求和复发的潜在治疗靶点。在其他脑区，I组代谢性谷氨酸受体(MGluR)的激活导致突触后CP-AMPAR的选择性内化。虽然I组mGluRs似乎不会在NAC内化AMPAR，但这只在药物初治的啮齿动物的NAC中进行了评估，那里的CP-AMPAR水平非常低。重要的是，几项研究报告说，在戒断反复接触可卡因的过程中，NAC中I组mGluR水平降低。我的中心假设是，I组mGluR的激活选择性地内化NAC中的CP-AMPAR，并且由于NAC中I组mGluR水平的下降，CP-AMPAR在长期戒断可卡因自我给药期间积累。我还假设，NAC中I组mGluR的激活将通过选择性地内化CP-AMPAR在这些可卡因经历的大鼠中阻止孵化线索诱导的寻找的表达。目的1利用培养的表达CP-AMPAR的NAC神经元，验证I组mGluR激活导致CP-AMPAR选择性内化的工作假说。免疫细胞化学实验将确定急性和长期激活或抑制I组mGluR是否会改变CP-AMPAR的表面表达。目的2验证工作假说，即在长时间戒断长时间戒断可卡因的过程中，NAC中I组mGluRs的水平降低，并且NAC I组mGluRs在体内的药理激活减少了线索诱导的可卡因寻求。大鼠将自行给予可卡因或生理盐水(对照组)，生化研究将确定I组mGluR表面、突触或突触外水平是否降低。行为学研究将确定急性NAC内注射I组mGluR激动剂是否减少孵化线索诱导的可卡因寻找并内化CP-AMPAR。在这些研究进行期间，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来发展所需的非板凳技能，以实现我成为学术环境中的首席研究员的目标。 公共卫生相关性：这项建议使用大鼠成瘾模型来研究导致线索诱导的可卡因渴望加剧的细胞机制，可卡因渴望是可卡因戒断后复发的常见触发因素。我们的结果可能确定一个分子靶点(I组代谢性谷氨酸受体)，用于开发药物以减少线索诱导的可卡因成瘾者的渴求。

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.