Ethanol and Plasticity of Tripartite Synapses

星形胶质细胞（星形胶质细胞）在控制神经元的兴奋性方面起着重要作用，并参与与学习和新记忆形成相关的细胞机制，这一点已经得到了广泛的认识。学习和记忆形成的可塑性涉及神经元谷氨酸能突触树突棘的变化，星形胶质细胞在大多数成熟的棘上形成三方突触结构。星形胶质细胞调节细胞外谷氨酸水平，分泌影响三方突触结构功能和结构的胶质递质、神经营养因子和蛋白酶。正是星形胶质细胞与谷氨酸能突触的这种紧密的物理定位，使星形胶质过程处于控制神经元兴奋性和突触可塑性的位置。此外，谷氨酸能突触星形胶质细胞的存在调节了脊柱的结构，并控制了海马CA1锥体神经元的NMDA受体依赖性元可塑性。众所周知，长期暴露于酒精的海马神经元会增加谷氨酸能突触中NMDA受体的数量，也有研究表明，这种增加可能会促进脊柱大小的肌动蛋白依赖性增加。这些变化被认为有助于酒精依赖和耐受性。然而，目前尚不清楚星形胶质细胞在调节与慢性酒精暴露和戒断相关的谷氨酸能突触的结构和功能可塑性方面起什么作用。在这个探索性的R21应用中，我们将研究慢性酒精诱导的三边突触的结构重塑。最重要的假设是，酒精暴露诱导神经元和星形胶质细胞释放某些蛋白酶，这些蛋白酶控制着脊柱-星形胶质细胞的结构和功能可塑性。我们提出了三个具体目标来测试我们提出的酒精诱导的三方突触结构可塑性模型：目标1将测试急性和慢性体外酒精暴露改变活细胞制备中三方突触结构动力学的假设；目的2将检验慢性体内乙醇暴露改变三边突触形态和密度的假设；目的3将验证乙醇诱导的三方突触的结构可塑性与作用于突触细胞外基质的蛋白酶的释放有关的假设。这些研究将利用新的二合一染料加载程序和荧光蛋白的慢病毒感染来可视化三方突触结构，并结合共聚焦成像和复杂的3d图像分析酒精诱导的脊柱星形胶质细胞结构的改变。本研究的长远目标是确定星形胶质细胞是否参与酒精诱导的谷氨酸突触可塑性，以及星形胶质细胞是否可以被确定为治疗酒精滥用和依赖的新靶点。

DESCRIPTION (provided by applicant): It is now widely recognized that astrocytes (astroglia) play a central role in controlling excitability of neurons and contribute to the cellular mechanisms associated with learning and the formation of new memories. The plasticity of learning and memory formation involve changes in dendritic spines at glutamatergic synapses on neurons, and astrocytes form tripartite synaptic structures at a majority of mature spines. Astrocytes regulate extracellular glutamate levels and secrete gliotransmitters, neurotrophic factors, and proteases that affect the function and structure of the tripartite synaptic structure. It is this close physical localization of astroglia with glutamatergic synapses that places the astroglial process in a position to control neuronal excitability and synaptic plasticity. Moreover, the presence of astrocytes at glutamatergic synapses modulated the structure of the spine and controls NMDA receptor-dependent metaplasticity of hippocampal CA1 pyramidal neurons. It is well- established that chronic exposure of alcohol to hippocampal neurons increases the number of NMDA receptors at glutamatergic synapses, and it has also been suggested that this increase may promote actin-dependent increases in the size of the spine. These changes are suggested to contribute to alcohol dependence and tolerance. However, it is unknown what role astrocytes play in regulating the structural and functional plasticity of glutamatergic synapses associated with chronic alcohol exposure and withdrawal. In this exploratory R21 application, we will examine chronic alcohol-induced structural remodeling of the tripartite synapse. The over-arching hypothesis is that alcohol exposure induces the release of certain proteases from both neurons and astroglia that control spine-astroglial structural and functional plasticity. Three specific aims are proposed that will test our proposed model of alcohol- induced plasticity of tripartite synaptic structure: Aim 1 will test the hypothesis that acute and chronic in-vitro alcohol exposure alters the structural dynamics of the tripartite synapse in a live-cell preparation; Aim 2 will test the hypothesis that chronic in-vivo ethanol exposure alters the morphology and density of tripartite synapses; and Aim 3 will test the hypothesis that ethanol-induced structural plasticity of the tripartite synapse is associated with the release of proteases that act upon the synaptic extracellular matrix. These studies will utilize novel diolistic dye loading procedures and lentiviral infection of fluorescent proteins to visualize tripartite synaptic structures coupled with confocal imaging and sophisticated 3D-image analysis of alcohol-induced alterations in spine-astrocyte structures. The broad, long term objectives of this proposal are to determine if astrocytes contribute to alcohol-induced plasticity of glutamatergic synapses and whether astrocytes can be identified as a novel therapeutic target for the treatment of alcohol abuse and dependence. PUBLIC HEALTH RELEVANCE: Alcoholism is characterized by craving for alcohol and compulsive alcohol-seeking behavior. Thus, determining the processes by which alcohol exposure leads to aberrant and inappropriate synaptic connections of the brain may lead to novel approaches to effective treatments of alcoholism and alcohol related disorders.