Role of FMRP in Cocaine-Dependent Behavioral Plasticity

描述（由申请人提供）：确定介导大脑奖励可塑性的关键分子仍然是当前药物滥用研究的重要目标。我们最近发现了脆性X智力迟钝蛋白（FMRP）的关键作用，这是一种RNA结合蛋白，参与调节树突中的蛋白质合成，是mef2依赖性突触消除的重要下游组分。此外，我们在fmrp缺陷小鼠中观察到可卡因诱导的行为可塑性显著缺陷。结合最近记录的MEF2在重复可卡因诱导的结构和功能可塑性中的作用，我们在Fmr1 KO小鼠中的研究结果表明，突触消除在促进与慢性可卡因使用相关的持久行为可塑性的过程中发挥了重要作用。在这项提议中，我们将验证FMRP介导NAc中突触消除/重构的急性过程的假设，这是与重复可卡因暴露相关的行为可塑性所必需的。具体目的1：我们的初步研究结果表明，Fmr1-/-小鼠显着降低了可卡因致敏性和对可卡因的位置偏好。由于这些是发育性基因敲除小鼠，FMRP对可卡因诱导行为发挥作用的确切细胞群尚不清楚。为此，我们将采取双管管下的方法：1)在Fmr1 KO小鼠中，通过病毒介导的基因传递在伏隔核（NAc）中表达WT FMRP，并测试可卡因行为的功能拯救；2)在成年条件Fmr1敲除小鼠中，通过病毒介导的Cre重组酶基因传递，选择性敲除NAc中的Fmr1基因，并测试成年NAc在可卡因诱导的行为可塑性过程中对FMRP的需求。具体目的2：我们最近的研究结果表明，FMRP对海马锥体神经元中MEF2依赖的突触数量的调节是严格必需的，活性MEF2的NAc表达增强了对可卡因的致敏运动和位置偏好。因此，我们将验证FMRP在NAc中介导mef2诱导的可卡因致敏行为反应的假设。为此，我们将使用已建立的病毒介导的基因传递来确定mef2调节的可卡因行为反应是否需要FMRP在体内的功能，使用Fmr1-/-小鼠和已建立的行为分析。特异性目的3：我们之前证明，MEF2活性的抑制是必要的，足以调节慢性可卡因诱导的NAc MSN脊柱密度的增加。由于我们发现FMRP是mef2调节的海马神经元兴奋性突触密度所必需的，我们将在体内验证可卡因引起的NAc脊柱密度增加需要FMRP的假设。使用已建立的脊柱成像方法，我们将评估Fmr1 KO小鼠的基础和慢性可卡因调节的NAc脊柱密度。

DESCRIPTION (provided by applicant): Identifying key molecules that mediate brain reward plasticity remains an important goal of current drug abuse research. We recently identified a key role for the Fragile X Mental Retardation Protein (FMRP), a RNA binding protein involved in regulating protein synthesis in dendrites, as an essential downstream component of MEF2-dependent synapse elimination. Moreover, we observed significant deficits in cocaine-induced behavioral plasticity in FMRP-deficient mice. Taken together with the recently documented role for MEF2 in repeated cocaine-induced structural and functional plasticity, our findings in the Fmr1 KO mice suggest an important role for synapse elimination as a process that promotes long-lasting behavioral plasticity associated with chronic cocaine use. In this proposal, we will test the hypothesis that FMRP mediates an acute process of synapse elimination/remodeling in the NAc that is required for behavioral plasticity associated with repeated cocaine exposure. To this end, we propose the following: Specific Aim 1: Our preliminary findings indicate that Fmr1-/- mice have significantly reduced cocaine sensitization and place preference to cocaine. As these are developmental knockout mice, the precise populations of cells where FMRP exerts its function on cocaine-induced behaviors is not clear. To this end, we will take a two-pronged approach: 1) we will express WT FMRP in the nucleus accumbens (NAc) using viral- mediated gene delivery in the Fmr1 KO mice and test for functional rescue of cocaine behaviors, and 2) we will selectively knockout the Fmr1 gene in the NAc using viral-mediated gene delivery of Cre recombinase in adult conditional Fmr1 knockout mice and test the requirement for FMRP in the adult NAc during cocaine-induced behavioral plasticity. Specific Aim 2: Our recent findings revealed that FMRP is strictly required for MEF2-dependent regulation of synapse number in hippocampal pyramidal neurons, and NAc expression of active MEF2 enhances both sensitized locomotion and place preference to cocaine. Therefore, we will test the hypothesis that FMRP functions in the NAc to mediate MEF2-induced sensitized behavioral responses to cocaine. To this end, we will use established viral-mediated gene delivery to determine whether MEF2-modulated behavioral responses to cocaine require FMRP function in vivo using Fmr1-/- mice and established behavioral assays. Specific Aim 3: We previously demonstrated that inhibition of MEF2 activity is necessary and sufficient to regulate the chronic cocaine-induced increase in NAc MSN spine density. Since we found that FMRP is required for MEF2-regulated excitatory synapse density in hippocampal neurons, we will test the hypothesis that the cocaine-induced increase in NAc spine density requires FMRP in vivo. Using established spine imaging methods, we will assess the basal and chronic cocaine-regulated NAc spine density in Fmr1 KO mice. PUBLIC HEALTH RELEVANCE: Drug addiction is a chronic human disease characterized by uncontrolled drug use despite severe adverse consequences to the addict. The results of the proposed studies would provide valuable new insights into molecular and neural circuit mechanisms that contribute to long-lasting behavioral responses to chronic drug use, and could generate new therapeutic targets for the treatment of drug addiction for which there are currently very limited treatment options.