情绪记忆的海马突触可塑性机制研究

	情绪记忆的海马突触可塑性机制研究
	段婷婷
学位类型	博士
导师	徐林研究员
	2013-05
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	神经生物学
关键词	海马突触可塑性学习记忆情绪
摘要	海马是参与记忆和情绪信息处理的关键脑区，但其细胞分子机理至今并不完全清楚。自Tim Bliss 等发现海马长时程增强（long-term potentiation, LTP）现象以来，人们对突触可塑性的机制在学习记忆过程中的作用进行了深入研究。LTP诱导过程中，突触前谷氨酸释放增加，激活突触后NMDA 受体，导致钙离子内流，触发系列细胞内信号通路，最终引起AMPA 受体磷酸化和上膜，从而表达LTP。长时程抑制（long-term depression，LTD）是另一种形式的突触可塑性，最早也在海马中发现。LTD 有NMDA 受体依赖和非依赖的两类形式，但最终机制都是激活细胞内信号通路，引起AMPA 受体的内吞下膜，从而降低突触传递效能。目前海马LTP 和LTD 都被认为是学习记忆的细胞分子机制。但突触可塑性是否是海马处理情绪的细胞分子机制目前仍不清楚。抑郁症是以情绪障碍和负性记忆增强等为主要特征的常见精神疾病，已有的研究显示海马在抑郁的发病和治疗过程中起重要作用，但海马突触可塑性如何参与抑郁症发病过程并不清楚。一些精神活性物质，如氯胺酮，大麻等由于在低剂量时具有抗抑郁症和镇痛等很好的疗效，在临床上被广泛使用。但高剂量时可以导致精神错乱，记忆损伤等负性作用。目前这些精神活性物质损伤记忆的细胞分子机制仍然不清楚。由于海马同时负责了情绪和记忆信息的加工处理，海马突触可塑性很可能是它们的共同机理。清醒自由移动动物电生理记录技术具有可以在动物清醒自由移动状态下长时间观察突触可塑性的改变，神经环路完整且没有麻醉剂干扰等优势。在本研究中，我们利用清醒自由移动动物电生理记录技术，结合大鼠习得性绝望（强迫游泳）抑郁症模型以及记忆损伤模型，进行了两方面研究：（1）利用清醒自由移动动物电生理技术，研究了大鼠强迫游泳对海马CA1 突触传递在电生理和分子水平的影响，以及干扰海马CA1 突触可塑性对抑郁样行为的影响；利用清醒自由移动动物电生理技术，我们研究了亚麻醉剂量氯胺酮以及人工合成大麻素HU210 对海马CA1 突触传递和记忆的损伤效应及其机制。（2）利用清醒自由移动动物电生理技术，研究了抗抑郁症天然小分子CXZ-123 对清醒自由移动大鼠海马CA1 突触传递的影响。我们发现：大鼠习得性绝望抑郁症模型-强迫游泳训练可以在清醒自由移动大鼠上诱导内源性的长时程增强，这种增强可以维持至少一个小时。这种内源性的长时程增强是依赖于海马NMDA 受体，注入NMDA 受体的拮抗剂（AP-5）可以阻断内源性长时程增强。而其它可以阻断长时程增强维持的手段，如BDNF 受体Trk 受体拮抗剂和蛋白质合成抑制剂都可以阻断习得性绝望。而我们在海马脑区给予深部脑刺激，抑制了内源性的长时程增强且阻断了习得性绝望的形成。同时发现天然小分子化合物CXZ-123 在清醒自由移动大鼠上诱导了长时程抑制且可以阻断习得性绝望。通过这些研究我们首次证实了，海马突触的长时程增强参与了抑郁样行为的形成，表明海马内源性长时程增强对习得性绝望的形成是必需的。另一部分的实验研究了精神分裂症的大鼠模型中记忆损伤的细胞分子机制。我们建立亚麻醉剂量氯胺酮致精神分裂症的大鼠模型。与以前的报道一致，我们发现氯胺酮诱导了一系列拟精神分裂症的症状。除此之外，我们发现氯胺酮导致大鼠的空间记忆受损，而同样剂量的氯胺酮在清醒自由移动大鼠海马脑区 Schaeffer collateral-CA1 通路上可以诱导至少维持四个小时的突触抑制。氯胺酮诱导的突触抑制不依赖于NMDA 受体的激活而是依赖于D1/D5 受体调节的，AMPA 受体的内吞。因为D1/D5 受体的选择性拮抗剂SCH23390 和AMPA 受体内吞的干扰肽Tat-GluR23Y 都可以阻断氯胺酮诱导的突触抑制。而SCH23390 和干扰肽Tat-GluR23Y 在阻断突触抑制的同时也可以阻断氯胺酮对空间记忆的损伤。因此，我们的结果表明受D1/D5 受体调节的，依赖于AMPA 受体内吞的海马突触抑制在氯胺酮诱导的记忆损伤中发挥了关键作用。我们研究了人工合成大麻素HU210 诱发空间工作记忆损伤的细胞分子机制。合作者实验室发现急性给予大麻素可以损伤空间工作记忆且在海马CA3-CA1 通路上诱导出长时程抑制。而CB1 受体的拮抗剂可以阻断HU210 诱发的空间工作记忆损伤和长时程抑制。条件性敲除星形胶质细胞上CB1 受体，而不是谷氨酸能和GABA 能神经元上的CB1 受体敲除可以阻断大麻素诱导的长时程抑制和空间工作记忆损伤。而阻断NMDA 受体的活动和AMPA 受体的下膜可以阻断大麻素诱导的空间工作记忆损伤和长时程抑制的诱导与表达。我们的实验发现腹腔注射HU210 可以在清醒自由移动的大鼠海马脑区诱导出长达两天的LTD。这些研究表明大麻素通过激活星形胶质细胞上的CB1 受体，导致谷氨酸大量释放，激活突触外含NR2B 的NMDA 受体引起突触后膜上AMPA 受体的内吞。这些事件最终诱导了CB1 受体依赖的LTD，改变了海马环路的功能，从而导致海马不能正确的处理空间工作记忆的信息。综合以上的结果，我们发现情绪问题和记忆问题均涉及海马突触可塑性，因此有两个可能推测：1、情绪影响行为表现的机理也是属于记忆，因为行为改变的根本基础就是记忆。2、情绪和记忆仅共享突触可塑性机理，可能还有一些下游机理的不同。习得性绝望模型诱发的LTP 可能通过增强与抑郁相关的记忆而最终导致抑郁症的产生。因此介导突触传递增强的分子信号可能提供了一个新颖且有效的治疗靶点，可以逆转抑郁症的某些症状。而大麻素和氯胺酮可以通过损伤与抑郁相关的记忆达到抗抑郁的疗效。
其他摘要	The hippocampus is the critical brain region involved in memory and emotion process, but the cellular and molecular mechanisms remain elusive. Since Tim Bliss found hippocampal long-term potentiation (LTP), the mechanism and function of synaptic plasticity in learning and memory have been intensively investigated. During LTP induction, increased glutamate release from presynaptic terminals activates postsynaptic NMDA receptors, which lead to calcium concentration increase. Calcium triggers the activation of signaling cascades, leading to LTP expression through AMPAR phosphorylation and insertion into postsynaptic membrane. Long-term depression (LTD) is another form of hippocampal synaptic plasticity, which has two distinct forms, i.e. NMDA receptor-dependent and independent. Both LTD trigger the intracelluar signaling cascades, commonly leading to AMPAR endocytosis and expression of LTD. Hippocampal LTP and LTD are believed to be the cellular and molecular mechanism that underlies the hippocampus-dependent learning and memory. However, it is not known whether synaptic plasticity is implicated in hippocampus-dependent emotion processing. Major depression is a common mental illness characterized by mood dysfunction and enhanced negative emotional memory. Previous evidence shows that the hippocampus is involved in pathogenesis of depression and in response to antidepressive treatment, but the underlying mechanisms are essentially unknown. Some psychoactive substances, such as ketamine and cannabinoids, have been popularly used for antidepression and analgesia at low doses. However, at high doses they can induce side effects, such as psychosis and memory impairment. The underlying mechanisms of memory impairment induced by ketamine and cannabinoids remain elusive. As the hippocampus is critical for emotion and memory, hippocampal synaptic plasticity may be their common mechanism. Electrophysiological recording technique in freely moving rats has many advantages, such as it is allowed long lasting observation, even for months in conscious and anaesthetic-free rats, and the neural circuitry is intact, etc. In our studies, in the first part, combining freely moving rat recording and learned despair model of depression (forced swimming test, FST), we investigated the effects of FST on hippocampal CA1 synaptic transmission at the cellular and molecular levels, and the effects of interfering hippocampal synaptic plasticity on despair-like behaviors. Combining morris water maze, we studied the mechanisms of subanesthetic ketamine or cannabinoid-induced hippocampal CA1 synaptic depression and memory impairment. In the second part, we also investigated the effects of CXZ-123 a natural product that can rapidly exert antidepressive effect, on hippocampal synaptic transmission in freely moving rats. We found that forced swimming test, one of the most commonly used models to evaluate the antidepressant effects, induced endogenous LTP that lasted more than one hour. Pretreatment with NMDA receptor antagonist （AP-5） blocked the endogenous LTP, indicating that this endogenous LTP is NMDA receptor-dependent. The BDNF Trk receptor antagonist K252a and protein synthesis inhibitor anisomycin, which are known to impair LTP maintenance, also blocked the endogenous LTP and the learned despair behavior. Then, by applying deep brain stimulation in the hippocampus immediately after training produced the same effect. In freely moving rats, a small natural product CXZ-123 induced long-term depression and blocked learned despair behavior. Thus, our data suggest that hippocampal LTP is implicated in the formation of learned despair behavior, a mechanism suggesting the development of depression. Next, we investigated the cellular and molecular mechanisms underlying memory impairment in schizophrenia-like animal model. We used subanesthetic ketamine-induced animal model of schizophrenia. Consistent with previous reports, we found that subanesthetic ketamine induced a series of schizophrenia-like symptoms. Ketamine induced long-term spatial memory impairment as assessed in the Morris water maze. The same dose of ketamine also produced synaptic depression lasting at least 4 hr at hippocampal Schaeffer collateral-CA1 synapses in freely moving rats. The synaptic depression induced by ketamine is unlikely to depend on NMDA receptors but may depend on dopamine D1/D5 receptors and AMPA receptors endocytosis. Pretreatment with the D1/D5 receptors antagonist SCH23390 or the AMPA receptors endocytosis interfering peptide Tat-GluR23Y blocked synaptic depression and spatial memory impairment induced by ketamine. Thus, our data indicate that dopamine D1/D5 receptors may modulate AMPA receptors endocytosis, which plays a critical role in memory impairment induced by ketamine. We investigated the cellular and molecular mechanisms underlying exogenous cannabinoid-induced spatial working memory impairment. We found that acute exposure of exogenous cannabinoids induced the impairment of spatial working memory and in vivo long-term depression of synaptic strength at hippocampal CA3-CA1 synapses. CB1 receptor antagonist blocked memory impairment and synaptic depression induced by exogenous cannabinoid. Memory impairment and synaptic depression was also fully abolished in conditional mutant mice lacking type-1 cannabinoid receptors (CB1R) in brain astroglial cells but is conserved in mice lacking CB1R in glutamatergic or GABAergic neurons. The blockade of either neuronal glutamate NMDA receptors or synaptic trafficking of glutamate AMPAR also abolished cannabinoid effects on spatial working memory and LTD induction and expression. Thus, the data indicate that cannabinoid exposure in vivo activates astroglial CB1 receptor to increase ambient glutamate, which in turn activates NR2B-containing NMDAR to trigger AMPA receptor internalization at CA3-CA1 synapses. These events ultimately induce CB1R-LTD at these synapses, altering the function of hippocampal circuits that likely become unable to process spatial working memory. Altogether, we found that both emotion and memory are implicated in hippocampal synaptic plasticity. Therefore, we speculate that: 1. The process of emotion impacting on behavior just share that of memory, because the fundamental basis of behavioral alteration is memory. 2. Emotion and memory only share the common mechanism of synaptic plasticity. Learned despair-induced LTP leads to major depression via enhancement of depression related memory. Future studies aimed at determining the changes in molecular signaling that underlies the synaptic potentiation may lead to novel and effective treatments able to reverse some forms of depressive disorders. Therefore, ketamine and cannabinoid lead to antidepressant treatment possibly through impairing depression related memory.
语种	中文
文献类型	学位论文
条目标识符	http://ir.kiz.ac.cn/handle/152453/7565
专题	科研部门_学习记忆的分子神经机制（徐林）
推荐引用方式 GB/T 7714	段婷婷. 情绪记忆的海马突触可塑性机制研究[D]. 北京. 中国科学院研究生院,2013.

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