Regulation of Cocaine Reward and Reinforcement by MeCP2

描述(由申请人提供)：慢性可卡因滥用是由于持续的可卡因诱导的中脑边缘皮质奖赏回路内神经元功能的适应。对可卡因改变这些神经回路功能的分子机制的了解可能会导致开发治疗可卡因成瘾的新疗法。这一提议的总体假设是，可卡因通过诱导伏核(NAC)新基因产物的转录而对行为产生长期影响，从而改变NAC神经元的兴奋性和/或突触连接。我们已经证明，在成年纹状体的特定区域通过基因操作甲基DNA结合蛋白MeCP2的表达，可以调节可卡因和相关的精神刺激剂苯丙胺在啮齿类动物中诱导成瘾行为的能力。此外，我们还发现可卡因选择性地诱导NAc内小白蛋白(PV)阳性的快速尖峰GABA能中间神经元(FSIS)Ser421位MeCP2(PMeCP2)的磷酸化。这项提议的目的是检验这一新的假设，即FSIS中MeCP2的磷酸化提供了一种机制，将可卡因暴露与纹状体回路功能的转录依赖性变化联系起来，这些变化限制了可卡因的奖励特性。为了解决这一假设，在目标1中，我们将通过评估携带MeCP2基因突变的小鼠的可卡因自我给药(SA)来测试MeCP2磷酸化对可卡因奖励和增强特性的影响，MeCP2基因突变将Ser421改变为Ala，使MeCP2在该位置不可磷酸化。在目标2中，我们将检验这一假设，即MeCP2在NAC的FSIS中作用于限制可卡因SA。我们将通过立体定向地将loxP条件病毒从在PV阳性神经元中表达Cre重组酶的转基因品系注射到成年小鼠的NAC中来实现这一目标。我们将使用这些病毒来操纵MeCP2在这些细胞中的表达和磷酸化，作为改变FSI功能的一种手段，我们将确定这些操纵对可卡因SA的影响。最后，在目标3中，我们将测试这一假设，即pMeCP2通过调节NAC FSIS中即刻早期基因的诱导能力来调节纹状体的可塑性，从而限制可卡因SA。我们研究的结果将是一种特定的基于电路的机制的实验演示，通过该机制，染色质调节蛋白MeCP2限制可卡因奖励。这些研究有望对影响可卡因成瘾敏感性的神经生物学机制产生重要的新见解。

DESCRIPTION (provided by applicant): Chronic cocaine abuse arises as a result of persistent cocaine-induced adaptations in the function of neurons within mesolimbocortical brain reward circuits. An understanding of the molecular mechanisms by which cocaine alters the function of these neural circuits may lead to development of novel therapies for the treatment of cocaine addiction. The overall hypothesis of this proposal is that cocaine exerts long-lasting effects on behavior by inducing the transcription of new gene products in the nucleus accumbens (NAc) that change the excitability and/or synaptic connectivity of NAc neurons. We have shown that genetically manipulating the expression of the methyl-DNA binding protein MeCP2 in specific regions of the adult striatum modulates the ability of cocaine and the related psychostimulant amphetamine to induce addictive-like behaviors in rodents. Furthermore, we find that cocaine induces phosphorylation of MeCP2 at Ser421 (pMeCP2) selectively in parvalbumin (Pv)-positive fast-spiking GABAergic interneurons (FSIs) in the NAc. The objective of this proposal is to test the novel hypothesis that phosphorylation of MeCP2 in FSIs provides a mechanism to link cocaine exposure with transcription-dependent changes in striatal circuit function that limit the rewarding properties of cocaine. To address this hypothesis, in Aim 1 we will test the consequences of MeCP2 phosphorylation on the rewarding and reinforcing properties of cocaine by assessing cocaine self-administration (SA) in mice bearing a mutation knocked into the Mecp2 gene that changes Ser421 to Ala, rendering MeCP2 non-phosphorylatable at this site. In Aim 2 we will test the hypothesis that MeCP2 acts in FSIs in the NAc to limit cocaine SA. We will achieve this goal by stereotaxically injecting LoxP-conditional viruses into the NAc of adult mice from a transgenic strain that expresses the Cre recombinase in Pv-positive neurons. We will use these viruses to manipulate MeCP2 expression and phosphorylation in these cells as a means to alter FSI function and we will determine the effects of these manipulations on cocaine SA. Finally in Aim 3 we will test the hypothesis that pMeCP2 regulates a striatal plasticity that limits cocaine SA by modulating the inducibility of immediate-early genes in FSIs of the NAc. The outcome of our study will be the experimental demonstration of a specific circuit-based mechanism by which the chromatin regulatory protein MeCP2 limits cocaine reward. These studies promise to yield significant new insights into the neurobiological mechanisms that impact susceptibility to cocaine addiction.