Molecular mechanisms of memrory retrieval

描述（由申请人提供）：本提案的目标是更好地理解陈述性/情景性记忆检索发生的分子机制。该建议侧重于在记忆检索过程中，去甲肾上腺素（NE）和1-肾上腺素能信号在海马体中发挥的时间限制作用。第一个目标是确定海马细胞的信号传导是如何促进记忆恢复的。情境恐惧依赖于NE和¿1信号，将用于评估海马体依赖性记忆。不依赖于NE或¿1信号的提示（音调）恐惧将被用来测试操作是否会影响性能或记忆。小鼠立即早期基因诱导的成像将被用作暴露于显著和中性环境后神经元活动的标记物，小鼠中的信号将被药理学和遗传学操纵，以便在全身范围内仅在海马背区或海马的特定子区被阻断或激活。因为¿1信号激活cAMP /蛋白激酶A通路，第二个目标将确定该通路是否需要记忆恢复。在对照小鼠海马背侧输注阻断该通路的药物，在缺乏信号传导的突变小鼠中输注刺激该通路的药物。NE与细胞外信号调节激酶和磷脂酰肌醇3-激酶的激活之间的关系也将被确定，这也是检索所需的。此外，海马体中1信号最突出的生理效应之一是减少介导放电调节的慢后超极化（sAHP）。第三个目的是确定通过电压依赖性钙通道的钙内流是否会影响恢复，以及sAHP的药物阻断是否会挽救缺乏1信号的突变小鼠的恢复。这一目标还将确定在恐惧条件反射而非假条件反射后，在小鼠的大脑切片中是否可以观察到sAHP的短暂减少，如果是，这种减少是否取决于信号传导。最后，我们将在第四个目标中测试一个关键假设，该假设解释了为什么某些而不是所有的记忆提取都需要NE。相关性：肾上腺素能信号的功能障碍可能导致抑郁症和创伤后应激障碍的症状，包括前者记忆检索困难和后者创伤记忆的不必要的侵入性检索。这项建议的结果也可能与使用阻断受体的药物治疗心力衰竭、高血压和表现焦虑时可能出现的潜在认知副作用有关。最后，研究结果也应该与理解老年人神经元钙++稳态失调如何导致记忆缺陷有关。

DESCRIPTION (provided by applicant): The goal of this proposal is to better understand the molecular mechanisms by which the retrieval of declarative/episodic memory occurs. The proposal focuses on the time-limited role that norepinephrine (NE) and ¿1-adrenergic signaling play in the hippocampus during memory retrieval. The first aim will determine in which hippocampal cell(s) ¿1 signaling acts to promote memory retrieval. Contextual fear, which depends to NE and ¿1 signaling, will be used to assess hippocampus-dependent memory. Cued (tone) fear, which does not depend on NE or ¿1 signaling, will be used to test whether manipulations affect performance or memory. Imaging of immediate-early gene induction in mice will be employed as a marker of neuronal activity following exposure to salient and neutral contexts, ¿1 signaling in the mice will be manipulated pharmacologically and genetically so that it is blocked or activated either, systemically, only in the dorsal hippocampus, or in specific subfields of the hippocampus. Because ¿1 signaling activates the cAMP / protein kinase A pathway, the second aim will determine whether this pathway is required for memory retrieval. Dorsal hippocampal infusions of agents that block this pathway will be performed in control mice, and infusions of agents that stimulate this pathway will be performed in mutant mice that lack ¿1 signaling. The relationship between NE and activation of extracellular signal-regulated kinase and phosphatidylinositol 3- kinase, which are also required for retrieval, will be determined. Further, one of the most prominent physiological effects of ¿1 signaling in the hippocampus is reduction of the slow afterhyperpolarization (sAHP) that mediates accommodation of firing. The third aim will determine whether calcium influx through voltage-dependent calcium channels influences retrieval, and whether pharmacologic block of the sAHP rescues retrieval in mutant mice lacking ¿1 signaling. This aim will also determine whether there is a transient reduction in the sAHP that can be observed in brain slices of mice after fear conditioning but not pseudoconditioning and, if so, whether the reduction depends on ¿1 signaling. Finally, a key hypothesis explaining why NE is required for some but not all memory retrieval will be tested in the fourth aim. Relevance: Dysfunction of adrenergic signaling may contribute to symptoms of depression and post- traumatic stress disorder that include difficulties with memory retrieval in the former and unwanted, intrusive retrieval of traumatic memories in the latter. Results from this proposal may also be relevant to potential cognitive side effects that might arise when treating heart failure, hypertension and performance anxiety with drugs that block ¿ receptors. Finally, results should also be relevant to understanding how dysregulation of neuronal Ca++ homeostasis in the elderly may lead to memory deficits.