胆碱能神经元在恐惧条件化中调控前额叶皮层神经元活性与集群同步化机制的研究

Fear emotionally elicits defensive behavioral responses that have evolved to enable the animals to avoid or reduce harm and thus ensure its survival. Fear behavior is known to depend on the interaction between the medial prefrontal cortex (mPFC) and the basolateral amygdala (BLA) neuronal circuits. Cholinergic signaling has long been implicated in attending and remembering emotionally potent experiences. Basal forebrain (BF) is best known brain areas for acetylcholine containing neurons that provide most of the cholinergic innervation of the neocortex. The degeneration of the cholinergic neurons in BF is correlated with Alzheimer’s disease and forms of dementia and is associated with normal cognitive aging. BF cholinergic neurons encode a precisely timed signal and modulate the neocortex signals and thereby could support learning and plasticity as a reinforcement signal. Also cholinergic modulate of BLA circuits in the inscription and retention of fear memories. but the precise role of ACh signaling in neocortex especially in mPFC circuits in fear processing and behavior has remained elusive. We combined with in vivo behaving optogenetics and multi-channel electrophysiological techniques, selective specific regulation of BF cholinergic neuron activity in BF or in mPFC of the terminals of the neurons, while using electrophysiological techniques to record mPFC neurons activities and field potential changes in fear condition. After that, analysis and compare the dynamic changes and information coding of the mPFC neuronal microcircuits correlate to fear condition during the local modulation of terminals of the cholinergic neurons and the entire circuit modulation of the BF cholinergic neurons. Looking for revealing the dynamical neuronal mechanisms of BF cholinergic system regulate the fear learning & memory in the mPFC neuronal circuits.

恐惧是动物体为了减少伤害和保证存活而对外界刺激产生防御性行为的一种生死攸关的情绪反应。而前额叶皮层（mPFC）-腹外侧杏仁核（BLA）环路是调控恐惧条件化的主要神经环路。乙酰胆碱是调控行为的基本神经递质之一, 皮层胆碱投射主要来源于基底前脑(BF)胆碱能神经元，其丢失被认为与认知障碍有关。调控BF胆碱能神经元不仅可调节皮层的突触可塑性来调控学习， 而且可直接调控BLA神经环路突触可塑性控制恐惧学习。但BF胆碱能的皮层投射调控恐惧行为及其神经环路机制仍不明晰。本研究结合在体光遗传学技术与多道电生理技术,清醒活体状态光遗传调控BF胆碱能胞体或者mPFC投射末梢来控制恐惧行为变化，同时记录mPFC神经元活性变化以及场电位，对比分析mPFC的神经微环路神经元在BF胆碱能局部或整体光刺激下调控恐惧行为中的动态变化及集群信息编码。期待阐明胆碱系统对mPFC恐惧神经微环路的动态调控编码机制。

中枢的乙酰胆碱是重要的兴奋性神经递质，对于维持正常的觉醒、认知、注意以及学习与记忆等十分重要。胆碱能神经元主要位于PPT/LDT和基底前脑（BF），而皮层的乙酰胆碱主要来源是BF的胆碱能神经元。BF的胆碱能神经元分布比较广泛，散布于从喙侧到尾侧的整个BF区域，其向皮层、皮层下、脑干各区域都具有广泛的投射，进而参与睡眠、学习与记忆等多种功能。研究发现BF的胆碱能神经元轴突纤维广泛分布在内侧前额叶皮质（medial prefrontal cortex, mPFC）。mPFC属于新皮质的一部分，涉及规划复杂的认知行为、人格表达、决策和调节社会行为等。因此了解胆碱能神经元对于皮层神经元对精细调控机制尤其时对于前额叶皮层的神经元的精细调控机制对于理解多种高级认知行为如恐惧学习等具有重要的意义。本研究首先用逆向示踪剂（Fluoro-Glod）在CHAT-Chr2-EYFP转基因小鼠的前额叶皮层部位标记发现前额叶皮层的胆碱能投射主要来自于基底前脑的SI与HDB两个亚区，而两个亚区中只有HDB的胆碱能神经元对恐惧记忆的获取有关。我们的研究进一步发现胆碱能神经元可以特异性调控前额叶皮层的神经元活动，以及皮层的神经环路震荡特性。胆碱能神经元的输入强度与皮层特定神经元的响应有关，胆碱输入强时可以激活锥体神经元与中间神经元，但是胆碱输入较弱时的中间神经元的激活也较弱，但是锥体神经元的兴奋不变。而且中间神经元的兴奋是受到30-80Hz的Gamma频带的能量门控，只有当30-80Hz的频带能量高时，中间神经元才能够被胆碱能神经元激活。光遗传学激活SI的胆碱能神经元降低小鼠对异氟醚麻醉的敏感性，延长小鼠发生意识消失的时间，同时促进异氟醚麻醉后苏醒。基底前脑的胆碱能神经元可调控前额叶皮层的神经元，包括中间神经元和锥体神经元。基底前脑的胆碱能神经元能够引起前额叶皮层局部场电位的活跃脑电尤其是（30-150Hz）频段的增加。本研究对于胆碱皮层激活的基本机制研究，揭示了皮层胆碱调控的信息编码机制以及在特定行为如恐惧行为、麻醉行为中的特定编码机制，为相关疾病的诊治提供了新的参考机制。