联合运动学习的神经调节机制——海马－前额叶投射通路的作用研究

Little is known about how hippocampus－prefrontal cortex circuitry is involved in the regulation of associative motor learning. Using mice eyeblink conditioning (EBC) as animal model and applying approaches of optogenetics and calcium imaging, etc., this project is designed to explore the regulation role of hippocampus-prefrontal cortex circuitry and the related circuit mechanism on associative motor learning. The investigation included: during the processes of establishment and expression of trace EBC, inhibit the exciting neurons in the hippocampal CA1 subregions selectively, instantly and synchronously. The influence of inhibition on behaviour establishment and expression will be analyzed. The regulation pathway is designed to be confirmed by observing the interfering effect through instantaneous intervention on activities of axons projecting from the hippocampus onto various subregions of mPFC. The effect of mPFC on hippocampal regulation of associative motor learning is designed to be observed by measuring the interfering effect through instantaneous intervention with optogenetics on activities of axons projecting from mPFC onto hippocampus. We also plan to investigate in subcellular level the functions and characteristics of single synapses formed by projections from hippocampus to different subtypes of inhibitory neurons in the target zone of prefrontal cortex in mice. This work will be of significance in understanding both the brain mechanisms of specific behaviour and the pathophysiology of motor regulation dysfunctions and motor disorders, as well as treatment exploring of these dysfunctions.

海马－前额叶回路是否以及如何参与联合运动学习的调节目前知之甚少。本项目计划以小鼠条件化瞬目行为（eyeblink conditioning, EBC）为模型，依托光遗传学技术、钙成像技术等，探讨海马－前额叶回路对联合运动学习的调节作用及其回路机制。内容包括：在建立和表达EBC的过程中，同步对海马CA1区兴奋性神经元的活动实施选择性瞬时抑制，分析其对行为建立和表达的影响；通过对海马投射到mPFC不同亚区的轴突末稍的瞬时干预，确认有关调节通路；通过光遗传学技术抑制mPFC 到海马的投射，分析mPFC对海马调节运动学习作用的影响；通过可视化脑片膜片钳技术，在亚细胞水平研究海马－前额叶皮层投射与靶区内不同亚型抑制性神经元所形成的单突触投射的功能特点。该工作不仅有助于理解特定行为的脑机制，对于理解和认识运动调节和运动障碍性疾病的病理生理机制也具有重要意义。

联合运动学习是个体通过联合学习而获得的条件化运动行为，对于个体生存进化具有重要意义，但目前对其调节机制特别是海马调节机制知之甚少。本项目以条件化瞬目行为（eyeblink conditioning, EBC）为模型，依托光遗传学、化学遗传学、行为药理学等技术，探讨海马及相关回路对联合运动学习的调节作用。通过对于EBC行为的建立和主动的细胞选择性干预，我们得出的初步结论：海马神经元活动对于联合运动学习具有调节作用，该调节效应是通过海马—mPFC投射通路实现的；非选择性NMDA（N-methyl-D-aspartic acid）受体拮抗剂苯己环哌啶（PCP）腹腔注射可建立Hip－mPFC 的功能障碍模型，在这种模型中，EBC联合运动学习受到明显影响，而通过光遗传学抑制方法进行细胞特异性地恢复药物所造成的海马活动变化后，可以缓解延迟型EBC联合学习功能障碍；直接以光遗传学技术刺激小脑中脚的苔藓纤维作为条件刺激的结果表明，小脑有能力独立支持简单的延迟型EBC（dEBC）和短痕迹间期（350毫秒以内）的痕迹型EBC（tEBC），但不能支持痕迹间期超过500毫秒的tEBC。这些结果对我们深入理解联合运动学习的机制具有重要意义。