Superior colliculus (SC) is a midbrain structure that integrates sensory inputs and generates motor commands to initiate innate motor behaviors. Its retinorecipient superficial layers (sSC) receive dense cholinergic projections from the parabigeminal nucleus (PBN). Our previous in vitro study revealed that acetylcholine induces fast inward current followed by prominent GABAergic inhibition within the sSC circuits (Endo et al. 2005). Acetylcholine-mediated facilitation of GABAergic inhibition may play an important role in visual signal processing in the sSC; however, both the anatomical and physiological properties of cholinergic inputs from PBN have not been studied in detail in vivo. In this study, we specifically visualized and optogenetically manipulated the cholinergic neurons in the PBN following focal injections of Cre-dependent viral vectors in mice that express Cre in cholinergic neurons. We revealed that the cholinergic projections terminated densely in the medial part of the mouse sSC. This suggests that the cholinergic inputs mediate visual processing in the upper visual field, which would be critical for predator detection. We further analyzed the physiological roles of the cholinergic inputs by recording looming-evoked visual responses from sSC neurons during optogenetic activation or inactivation of PBN cholinergic neurons in anesthetized mice. We found that optogenetic manipulations in either direction induced response suppression in most neurons, whereas response facilitation was observed in a few neurons following the optogenetic activation. These results support a circuit model which suggests that the PBN cholinergic inputs enhance functions of the sSC in detecting the visual targets by facilitating the center excitation-surround inhibition.

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从副二叉神经核到浅上丘的胆碱能输入的解剖学和电生理学分析

上丘 (SC) 是一种中脑结构，可整合感觉输入并生成运动命令以启动先天运动行为。其视网膜受体表层 (sSC) 接收来自副二叉神经核 (PBN) 的密集胆碱能投射。我们之前的体外研究表明，乙酰胆碱诱导快速内向电流，然后在 sSC 回路中产生显着的 GABA 能抑制（Endo 等人，2005 年）。乙酰胆碱介导的 GABA 能抑制促进作用可能在 sSC 的视觉信号处理中发挥重要作用；然而，尚未在体内详细研究来自 PBN 的胆碱能输入的解剖学和生理学特性。在这项研究中，在胆碱能神经元中表达 Cre 的小鼠体内局部注射 Cre 依赖性病毒载体后，我们专门对 PBN 中的胆碱能神经元进行了可视化和光遗传学操作。我们发现胆碱能投射在小鼠 sSC 的内侧部分密集终止。这表明胆碱能输入介导上视野中的视觉处理，这对于捕食者检测至关重要。我们通过记录麻醉小鼠中 PBN 胆碱能神经元的光遗传学激活或失活期间 sSC 神经元的隐约诱发的视觉反应，进一步分析了胆碱能输入的生理作用。我们发现任一方向的光遗传学操作都会在大多数神经元中诱导反应抑制，而在光遗传学激活后的一些神经元中观察到反应促进。这些结果支持一个电​​路模型，该模型表明 PBN 胆碱能输入通过促进中心激发周围抑制来增强 sSC 在检测视觉目标方面的功能。