Gauvain Gregory, Murphy Gabe J
Howard Hughes Medical Institute/Janelia Research Campus, Ashburn, Virginia 20147.
Howard Hughes Medical Institute/Janelia Research Campus, Ashburn, Virginia 20147
J Neurosci. 2015 Apr 22;35(16):6575-83. doi: 10.1523/JNEUROSCI.4298-14.2015.
The brain receives information about the direction of object motion from several types of retinal ganglion cells (RGCs). On-Off direction-selective (DS) RGCs respond preferentially to stimuli moving quickly in one of four directions and provide a significant (but difficult to quantify) fraction of RGC input to the SC. On DS RGCs, in comparison, respond preferentially to stimuli moving slowly in one of three directions and are thought to only target retinorecipient nuclei comprising the accessory optic system, e.g., the medial terminal nucleus (MTN). To determine the fraction of SC-projecting RGCs that exhibit direction selectivity, and the specificity with which On-Off and On DS RGCs target retinorecipient areas, we performed optical and electrophysiological recordings from RGCs retrogradely labeled from the mouse SC and MTN. We found, surprisingly, that both On-Off and On DS RGCs innervate the SC; collectively they constitute nearly 40% of SC-projecting RGCs. In comparison, only On DS RGCs project to the MTN. Subsequent experiments revealed that individual On DS RGCs innervate either the SC or MTN and exhibit robust projection-specific differences in somatodendritic morphology, cellular excitability, and light-evoked activity; several projection-specific differences in the output of On DS RGCs correspond closely to differences in excitatory synaptic input the cells receive. Our results reveal a robust projection of On DS RGCs to the SC, projection-specific differences in the response properties of On DS RGCs, and biophysical and synaptic mechanisms that underlie these functional differences.
大脑从几种类型的视网膜神经节细胞（RGCs）接收有关物体运动方向的信息。开-关方向选择性（DS）RGCs优先对在四个方向之一中快速移动的刺激作出反应，并向视皮层提供相当一部分（但难以量化）的RGC输入。相比之下，开DS RGCs优先对在三个方向之一中缓慢移动的刺激作出反应，并且被认为仅靶向构成辅助视系统的视网膜接受核，例如内侧终核（MTN）。为了确定表现出方向选择性的投射到视皮层的RGCs的比例，以及开-关和开DS RGCs靶向视网膜接受区域的特异性，我们对从小鼠视皮层和MTN逆行标记的RGCs进行了光学和电生理记录。令人惊讶的是，我们发现开-关和开DS RGCs都支配视皮层；它们共同构成了投射到视皮层的RGCs的近40%。相比之下，只有开DS RGCs投射到MTN。随后的实验表明，单个开DS RGCs要么支配视皮层要么支配MTN，并且在树突状形态、细胞兴奋性和光诱发活动方面表现出强大的投射特异性差异；开DS RGCs输出中的几个投射特异性差异与这些细胞接受的兴奋性突触输入的差异密切对应。我们的结果揭示了开DS RGCs向视皮层的强大投射、开DS RGCs反应特性中的投射特异性差异，以及这些功能差异背后的生物物理和突触机制。
