Mechanisms of Synaptic Depression: Focus on Rap Signaling Pathways

长时程突触抑制（LTD）和去电位，这两种形式的持续性突触 在一段重复的突触活动之后的抑制，是脊椎动物突触的广泛研究的例子。 可塑性。LTD和去电位的细胞和分子机制可能 阐明神经发育、适应、学习和 记忆 现在有令人信服的证据表明，重复的突触活动导致NMDA的激活- 敏感性谷氨酸受体（NMDA-Rs）和突触后AMPA敏感性谷氨酸受体的去除 （AMPA-Rs）的兴奋性突触在LTD和去电位。然而，生物化学途径 将NMDA-R活性与AMPA-R贩运联系起来的证据在很大程度上是未知的。我们此前曾报道， 小的GT3 Rapl通过激活p38 MAPK控制LTD。在初步研究中，我们观察到， 小GTdR Rap 2通过激活JNK控制去增强作用。基于这些发现，我提出了一个新的 模型表明Rap 1和Rap 2通过两条独立的信号传导途径传递突触抑制信号。我们将测试 该模型有三个假设，分别采用器官型培养海马脑片， 准备.这种准备使我们能够操纵突触活动和信号分子的活动 使用生理学、药理学和重组蛋白递送方法。我们将分析 这些操作通过检查电生理标记的重组AMPA-R介导的电流， 测量GluRl和GluR 2敲除小鼠中的突触反应，以及定量磷酸化或 活性内源性信号分子和谷氨酸受体。结合这些方法，我们将 确定是否：（Aim 1）Rap 1-p38 MAPK信号LTD，而Rap 2-JNK信号去增强;（Aim 2)不同的下游信号传导分子中继Rapl-p38 MAPK和Rap 2-JNK途径;以及（目的3） 不同的上游信号分子控制Rap 1-p38 MAPK和Rap 2-JNK途径。 因为控制Rap信号通路的信号分子或酶的遗传缺陷导致 严重精神发育迟滞，这项研究的结果也应该提出其他的分子靶点， 新的遗传和药理学策略，可能有效地治疗这些潜伏的精神疾病。

Long-term synaptic depression (LTD) and depotentiation, the two forms of sustained synaptic depression after periods of repetitive synaptic activity, are extensively studied examples of vertebrate synaptic plasticity. The cellular and molecular mechanisms responsible for LTD and depotentiation will likely elucidate physiological and pathological phenomena of neural development, adaptation, learning and memory. There is now compelling evidence that repetitive synaptic activity leads to activation of NMDA- sensitive glutamate receptors (NMDA-Rs) and removal of postsynaptic AMPA-sensitive glutamate receptors (AMPA-Rs) from excitatory synapses during LTD and depotentiation. However, the biochemical pathways that link NMDA-R activity to AMPA-R trafficking are largely unknown. We have previously reported that small GTPase Rapl controls LTD via activation of p38MAPK. In a preliminary study, we observed that small GTPase Rap2 controls depotentiation via activation of JNK. Based on these findings, I proposed a new model that Rapl and Rap2 signal synaptic depression via two independent signaling pathways. We will test three hypotheses in this model with three aims, respectively, using an organotypic culture hippocampal slice preparation. This preparation allows us to manipulate synaptic activity and signaling molecules' activity using physiology, pharmacology and recombinant protein delivery methods. We will assay the effects of these manipulations by examining electrophysiologically tagged recombinant AMPA-R-mediated currents, measuring synaptic responses in GluRl and GluR2 knockout mice, as well as quantifying phosphorylated or active endogenous signaling molecules and glutamate receptors. Combining these approaches, we will determine whether: (Aim 1) Rapl-p38MAPK signals LTD whereas Rap2-JNK signals depotentiation; (Aim 2) different downstream signaling molecules relay Rapl-p38MAPK and Rap2-JNK pathways; and (Aim 3) different upstream signaling molecules control Rapl-p38MAPK and Rap2-JNK pathways. Because genetic defects in signaling molecules or enzymes controlling Rap signaling pathways lead to severe mental retardation, the findings from this study should also suggest additional molecular targets for novel genetic and pharmacological strategies that may efficaciously treat these insidious mental diseases.