利用嗜神经病毒研究初级视觉皮层至丘脑环路的精细结构

Vision is an important way for animals to perceive the outside world. Vision and vision-evoked behaviors rely on the elegantly organized visual circuits. Resolving the fine structure of visual circuits is pivotal to elucidate visual function. The afferent visual circuits from retina to primary visual cortex are relatively well-studied. However, the fine map of neural circuits from primary visual cortex (V1) to other brain regions especially the thalamus remains elusive, restraining the functional study of the circuits. In this project, based on our expertise in circuit tracing by neurotropic virus, we will carry out the following studies: (1) constructing trans-monosynaptic circuit tracing toolkit with multi-color rabies virus to resolve the fine map of mice neural circuit from V1 to thalamus (including the location and sorting of V1 neurons targeting to different thalamic nuclei, the location and characteristics of their upstream neurons, and the fine structure of multi-targeting neurons from V1 to thalamus) with the help of fluorescence microscopy and fluorescence Micro-Optical Sectioning Tomography (fMOST) imaging; (2) analyzing the structural alteration of V1 to thalamus circuit under monocular deprivation, and detecting changes of functional output from V1 to thalamus through optogenetic manipulation and in vivo fiber photometry. Our study will help to resolve coding and integration of visual information, and provide new clues to study on the function and plasticity of visual circuits.

视觉是动物感知外部世界的重要途径。视觉及其引发的行为依赖于精密构筑的视觉环路。解析视觉环路的精细结构是阐明视觉功能的关键。目前，从视网膜到初级视觉皮层（V1）的传入环路研究得较为清楚。但是从V1到其他脑区特别是丘脑的传出环路的精细结构仍知之甚少，制约了对该环路功能的研究。本项目将基于我们在利用嗜神经病毒示踪神经环路的优势，开展以下研究：（1）构建跨单级突触的多色荧光狂犬病毒示踪工具包，并结合荧光显微成像、荧光显微光学切片断层成像（fMOST），解析小鼠V1至丘脑环路的精细结构（包括靶向丘脑不同核团的V1神经元的定位与分群、上级神经元的分布与定性、靶向丘脑的V1 “多靶神经元”的精细投射）；（2）分析单眼视觉剥夺下V1至丘脑环路的结构变化，并通过光遗传和在体光纤记录手段检测单眼视觉剥夺下该环路输出功能的改变。本项目将有助于解析视觉信息的编码与整合，为视觉环路的功能与可塑性研究提供新线索。

该项目成功构建了跨单级突触的多色荧光狂犬病毒示踪工具包（rRV-∆G-tagBFP、rRV-∆G-eGFP、rRV-∆G-DsRed、AAV-G），利用病毒示踪、fMOST成像、活体双光子钙成像、光遗传和光纤记录等手段，解析了小鼠V1至丘脑环路的精细结构包括靶向丘脑不同核团的V1神经元的定位特点、上级神经元的分布、靶向丘脑的V1“多靶神经元”精细投射和单眼视觉剥夺后的环路变化，发现：靶向丘脑不同核团的V1神经元的分布有差异；V1皮层存在靶向丘脑多个核团的“多靶神经元”；V1-dLGN、V1-LP、V1-LD环路的上游神经元分布既有相同的脑区，也有特有的脑区；不同V1-丘脑投射神经元亚群的神经元树突钙波的幅度和频率不同；不同逆行示踪病毒在标记V1-丘脑投射神经元上存在差异；单眼视觉剥夺下V1至丘脑的投射和突触连接减少，V1-丘脑的兴奋性输入减少。本研究将为视觉功能研究提供一定的环路基础，有助于解析视觉信息在皮层与丘脑间的传递与整合，也将有助于补充人们对视觉环路可塑性的认识，促进对弱视疾病发病机理的理解。目前，该项目的研究结果已经被整理，分别发表在Neuroscience Bulletin（IF=4.3）和Molecular Neurodegeneration（IF=9.59）杂志上，另有一篇文章在Brain Structure & Function杂志二审修改中。