源于内嗅皮层的胆囊收缩素在皮层长时程增强中的功能及在学习记忆中的作用

We found recently that the medial temporal lobe is critical for encoding and retrieval of visuoauditory associative memory. Its entorhinal cortex switches neural plasticity in the neocortex through their neocortical projection cholecystokinin (CCK) neurons. On the other hand, we understand that long-term potentiation (LTP) is the foundation for learning and memory. In the present study we hypothesize that entorhinal CCK is the switch for LTP in the neocortex. We would like to examine the hypothesis and relationship between the CCK and LTP through the following specific experiments. 1) We will examine whether the CCKB antagonist blocks the neocortical LTP, and whether CCKB agonist can induce LTP without high frequency stimulation; 2) We will examine whether neocortical LTP can be induced with high-frequency stimulation on the CCK knockout mouse, and the difference of learning and memory of the CCK knockout mouse and their wide-type counterpart; 3) We will examine whether high-frequency stimulation of the auditory cortex can induce LTP to the natural sound stimulus; 4) We will examine whether high-frequency stimulation of the entorhinal cortex of the ChR2 transgenic mouse can induce LTP in the auditory cortex to the natural sound stimulus; and 5) We will examine whether LTP can be induced the natural sound stimulus or the cortical electrical stimulation in the auditory cortex, after we pair them with the optogenic activation of the entorhinal CCK fibers in the auditory cortex of the CCK-CRE mouse. 6）We will further examine whether the association with the optogenetic method can be reflected in a behavioral experiment.The proposed study will unveil the mechanism of how CCK induce cortical LTP and its role in learning and memory.

我们之前的研究发现内侧颞叶在视听联合记忆的编码和提取过程中有重要作用。其内嗅皮层（Ent）通过表达胆囊收缩素（CCK）神经元调控皮层可塑性。长时程增强（LTP）是学习记忆的基础。我们将通过以下实验探索Ent来源的CCK在皮层LTP中起到的功能及在学习记忆中作用。1）观察CCKB受体拮抗剂能否阻断皮层LTP，激动剂能否在没有高频刺激时诱发LTP；2）观察CCK敲除小鼠的皮层能否用高频电刺激诱发LTP，其学习记忆能力是否受到损害；3）观察高频电刺激能否诱发听皮层对声音刺激的LTP；4）在ChR2转基因小鼠上观察在Ent的高频激光刺激能否诱发听皮层对声音刺激的LTP；5）在CCK-CRE转基因小鼠特异激活来自Ent的表达CCK神经元的投射，观察其能否诱发听皮层对声音刺激和电刺激的LTP，6）并在行为学上观察其表现。本研究将揭示Ent释放到皮层的CCK与皮层LTP之间的关系及其在学习记忆中的作用。

记忆通过突触连接强度的改变存储在神经网络中，而长时程增强（long-term potentiation, LTP）被认为是形成记忆痕迹的基础。内嗅皮层通过在皮层释放胆囊收缩素（cholecystokinin, CCK）促使新皮层神经可塑性的形成。在本项目中，我们显示CCK B型受体拮抗剂可以阻断高频电刺激在皮层诱发的LTP的形成，而局部施加CCK可以诱发LTP。CCK基因敲除小鼠不能在新皮层形成LTP，且在学习和记忆任务中表现出缺陷。在高频刺激内嗅皮层CCK神经元到听皮层的投射的条件下，声音刺激和皮层电刺激的配对可以诱导对声音刺激反应的LTP。并且在皮层电刺激和足刺激配对形成对电刺激的条件恐惧后，小鼠同样会对经过配对的声音刺激表现出恐惧反应，证明动物形成了声音和电刺激的联合记忆。这些发现证明了内嗅皮层来源的CCK促使新皮层形成LTP，并对记忆的形成有重要贡献。