海人藻酸受体在岛叶皮层突触前长时程增强和恐惧记忆中的作用

Kainate receptors are one kind of very important ionic glutamate receptors in the central nervous system. It plays an important role in synaptic transmission and synaptic plasticity. Synaptic plasticity is the main mechanism of fear memory in neuron circuit. The roles of KARs mediated long term potentiation in fear memory are still unclear. Our data showed that LTP was induced in pyramidal neurons in the insular cortex by the training protocol (2Hz for 2min holding membrane at -70mV). Bath application of NMDA inhibitor and calcium-chelating agents in patch pipette have no effect on this kind of LTP, but selective GluK1 inhibitor can significantly block the LTP. This LTP increased after contextual fear conditioning. It implicated that this kind of LTP is likely to be caused by a large increase of neurotransmitter release through the activation of presynaptic KARs GluK1 receptor, or “Pre-LTP” and plays an important role in fear conditioning. Therefore, we hypothesize that KARs mediated Pre-LTP in insular cortex maybe participates in the process of fear memory. In this study, we will investigate the mechanism of KARs mediated Pre-LTP and the possibility of KARs as drug targets for diseases associated with fear memory. To the end, this study will shed light on the ways and theory basis for fear memory mechanisms and potential drug targets.

海人藻酸受体（KARs）是中枢神经系统中一类十分重要的离子型谷氨酸受体，在突触传递和可塑性中发挥重要调节作用。突触可塑性与恐惧记忆密切相关。而KARs介导突触可塑性在恐惧记忆中的作用尚未明确。我们发现将岛叶皮层椎体神经元钳制在-70mV，给予低频双脉冲刺激能够诱导出LTP。该LTP不被NMDA受体拮抗剂和电极內液中钙离子螯合剂阻断，而能被KARs的GluK1受体拮抗剂所阻断，且在环境条件恐惧后显著增强。提示我们该类型LTP很可能是由于突触前膜GluK1受体激活，引起递质释放增加，产生的突触前长时程增强，即“Pre-LTP”，介导条件恐惧形成过程。因此，本项目首次提出岛叶皮层KARs介导Pre-LTP很可能参与恐惧记忆发生过程，拟探讨KARs介导Pre-LTP的分子机制和作为治疗恐惧记忆相关精神疾病药物靶点的可行性。课题结果将为深入研究突触可塑性与恐惧记忆的关系和发掘药物作用新靶点提供依据。

焦虑症是世界范围内严重的社会问题。大量神经影像学研究发现，高度紧张的个体，岛叶皮层的活跃度升高和功能联结的改变可能是导致负性情感状态的主要原因。然而，具体的突触可塑性机制还有待研究。为了评估恐惧或焦虑模型小鼠岛叶皮层神经元的电生理特性，我们分别利用不同的刺激方式诱导产生突触前和突触后的长时程增强。结果发现，条件恐惧后岛叶皮层同时存在有突触前和突触后的长时程增强。而突触前的长时程增强主要由突触前膜上的海人藻酸受体的Gluk1亚型介导产生，给予Gluk1抑制剂可以明显抑制动物恐惧样行为。为了排除足底电击对可塑性变化的影响，我们采用一种单纯的情感刺激模型，即升高平台实验，结果发现该模型刺激不能引起突触后的长时程增强，而只能引起突触前Gluk1介导的长时程增强现象，给予Gluk1抑制剂同样可以增加小鼠对开放臂的探索时间。因此我们推测岛叶皮层突触前递质释放增加可能是引起动物焦虑状态升高的可能机制。以往研究都认为杏仁核是“恐惧中心”，然而临床资料显示，杏仁核损毁病人虽然没有了恐惧样身体反应，但依然可以产生恐惧情绪。这说明杏仁核对于恐惧引起逃避反应的调控至关重要，但对于恐惧情感的产生可能需要别的脑区参与。岛叶皮层作为内感受处理中心，在意识情感产生过程中发挥重要作用，但可能作用机制并不清楚。本研究发现突触前可塑性在恐惧记忆调节中的新机制，为恐惧记忆相关精神疾病的药物研发提供新思路和新策略。