Role of FMRP in Cocaine-Dependent Behavioral Plasticity

描述(由申请人提供)：确定调节大脑奖赏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智力低下蛋白(FMRP)的一个关键作用，它是一种参与调节树突蛋白质合成的RNA结合蛋白，是MEF2依赖的突触消除的关键下游成分。此外，我们观察到FMRP缺陷小鼠在可卡因诱导的行为可塑性方面存在显著缺陷。结合最近报道的MEF2在反复可卡因诱导的结构和功能可塑性中的作用，我们在Fmr1 KO小鼠中的发现表明，突触消除作为一个过程，促进了与长期使用可卡因相关的长期行为可塑性，具有重要作用。在这项提议中，我们将测试FMRP介导NAC中突触消除/重塑的急性过程的假设，这是与重复暴露可卡因相关的行为可塑性所必需的。为此，我们提出如下建议：具体目标1：我们的初步发现表明，Fmr1-/-小鼠显著降低了可卡因的敏感度和对可卡因的偏爱。由于这些是发育中的基因敲除小鼠，FMRP在可卡因诱导行为中发挥作用的确切细胞群尚不清楚。为此，我们将采取双管齐下的方法：1)我们将在Fmr1 KO小鼠的伏隔核(NAC)中通过病毒介导的基因传递表达WT FMRP并测试可卡因行为的功能挽救；2)我们将在成年条件Fmr1基因敲除小鼠中使用病毒介导的Cre重组酶基因选择性敲除NAC中的Fmr1基因，并测试在可卡因诱导的行为可塑性过程中成年NAC对FMRP的需求。具体目的2：我们最近的发现表明，FMRP是依赖MEF2的海马锥体神经元突触数量调节所严格需要的，而激活的MEF2的NAC表达增强了对可卡因的敏化运动和位置偏好。因此，我们将检验FMRP在NAC中起作用的假设，以介导MEF2诱导的可卡因敏化行为反应。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体内FMRP功能，并使用Fmr1-/-小鼠和已建立的行为测试。具体目标3：我们先前证明，抑制MEF2活性对于调节慢性可卡因诱导的NAC MSN脊柱密度增加是必要的，也是充分的。由于我们发现MEF2调节的海马神经元兴奋性突触密度需要FMRP，因此我们将在体内验证可卡因诱导的NAC脊椎密度增加需要FMRP的假设。使用已建立的脊柱成像方法，我们将评估Fmr1KO小鼠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.