Kuramoto Eriko, Iwai Haruki, Yamanaka Atsushi, Ohno Sachi, Seki Haruka, Tanaka Yasuhiro R, Furuta Takahiro, Hioki Hiroyuki, Goto Tetsuya
Department of Oral Anatomy and Cell Biology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
Department of Dental Anesthesiology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
J Comp Neurol. 2017 Dec 15;525(18):3821-3839. doi: 10.1002/cne.24306. Epub 2017 Sep 12.
The rodent orbitofrontal cortex is involved in a variety of cognitive and behavioral functions that require thalamic input to be successfully expressed. Although the thalamic nucleus submedius (Sm) is a major source of afferents to the orbitofrontal cortex, thalamocortical projection from the Sm has not been fully elucidated. In the present study, we first divided the rat Sm into dorsal and ventral parts according to the distribution of vesicular glutamate transporter 2-immunoreactive varicosities, which were somatosensory afferents from the brain stem. Subsequently we investigated dendritic and axonal arborizations of individual dorsal and ventral Sm neurons by visualizing the processes with Sindbis virus vectors expressing membrane-targeted fluorescent proteins. The number of dendritic processes of ventral Sm neurons was greater than that of dorsal Sm neurons. In the cerebral cortex, all the reconstructed Sm neurons sent axons primarily to layers 2-5. Interestingly, dorsal Sm neurons formed a single axon arbor exclusively within the ventrolateral orbital area, whereas ventral Sm neurons made two axon arbors in the lateral orbital and ventral orbital areas simultaneously. The spread of each axon arbor was 500-1000 µm in diameter in the direction tangential to the cortical surface. These results indicate that the dorsal and ventral Sm comprise two distinct thalamocortical pathways. The dorsal Sm pathway relay somatosensory information to the ventrolateral orbital area and may be involved in emotional and aversive aspects of nociceptive information processing, whereas the ventral Sm pathway seems to co-activate distant orbitofrontal cortical areas, and may link their functions under certain circumstances.
啮齿动物的眶额皮质参与多种认知和行为功能，这些功能需要丘脑输入才能成功表达。虽然丘脑中介核（Sm）是眶额皮质传入纤维的主要来源，但来自Sm的丘脑皮质投射尚未完全阐明。在本研究中，我们首先根据囊泡谷氨酸转运体2免疫反应性曲张体的分布，将大鼠的Sm分为背侧和腹侧部分，这些曲张体是来自脑干的躯体感觉传入纤维。随后，我们通过用表达膜靶向荧光蛋白的辛德毕斯病毒载体可视化神经元的突起，研究了背侧和腹侧Sm单个神经元的树突和轴突分支。腹侧Sm神经元的树突分支数量多于背侧Sm神经元。在大脑皮质中，所有重建的Sm神经元主要将轴突发送到第2-5层。有趣的是，背侧Sm神经元仅在腹外侧眶区形成单个轴突分支，而腹侧Sm神经元同时在外侧眶区和腹侧眶区形成两个轴突分支。每个轴突分支在与皮质表面相切的方向上的直径为500-1000μm。这些结果表明，背侧和腹侧Sm构成两条不同的丘脑皮质通路。背侧Sm通路将躯体感觉信息传递到腹外侧眶区，可能参与伤害性信息处理的情绪和厌恶方面，而腹侧Sm通路似乎共同激活远处的眶额皮质区域，并可能在某些情况下连接它们的功能。
