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。我们最近确定了脆性X智力迟钝蛋白（FMRP）的关键作用，这是一种参与调节树突蛋白质合成的RNA结合蛋白，是MEF2依赖性突触消除的重要下游成分。此外，我们观察到可卡因诱导的FMRP缺陷小鼠的行为可塑性的显着缺陷。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小鼠中的发现表明突触消除作为促进与慢性可卡因使用相关的持久行为可塑性的过程具有重要作用。在这个建议中，我们将测试的假设，FMRP介导的急性过程中的突触消除/重塑的NAC所需的行为可塑性与可卡因反复暴露。为此，我们提出以下建议：具体目标1：我们的初步研究结果表明，Fmr1-/-小鼠显着降低可卡因的敏感性和位置偏好可卡因。由于这些是发育敲除小鼠，FMRP对可卡因诱导行为发挥作用的精确细胞群尚不清楚。为此，我们将双管齐下：1）我们将在Fmr1 KO小鼠中使用病毒介导的基因递送在延髓核（NAc）中表达WT FMRP，并测试可卡因行为的功能性拯救，和2）我们将使用病毒选择性地敲除NAc中的Fmr1基因，在成年条件性Fmr1敲除小鼠中介导Cre重组酶的基因递送，并测试可卡因诱导的行为可塑性期间成年NAc中对FMRP的需求。 具体目标二：我们最近的研究结果表明，FMRP是严格需要的MEF2依赖性调节突触数量在海马锥体神经元，和NAc表达的活性MEF2增强敏化运动和位置偏好可卡因。因此，我们将测试的假设，FMRP功能在NAc介导MEF2诱导的可卡因致敏行为反应。为此，我们将使用已建立的病毒介导的基因传递，以确定是否MEF2调制的可卡因的行为反应需要FMRP功能在体内使用Fmr1-/-小鼠和已建立的行为测定。 具体目标3：我们以前证明，抑制MEF2活性是必要的，足以调节慢性可卡因诱导的NAc MSN棘密度增加。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，我们将测试可卡因诱导的NAc棘密度增加需要体内FMRP的假设。使用已建立的脊柱成像方法，我们将评估基础和慢性可卡因调节的Fmr1基因敲除小鼠的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.