Hazama M, Kimura A, Donishi T, Sakoda T, Tamai Y
Department of Physiology, Wakayama Medical University, Wakayama Kimiidera 811-1, 641-0012, Japan.
Neuroscience. 2004;124(3):655-67. doi: 10.1016/j.neuroscience.2003.12.027.
Corticothalamic projections from cortical auditory field to the medial geniculate body (MG) in the rat were systematically examined by making small injections of biocytin in cortical area Te1. All injections, confined to 400 microm in diameter, resulted in two projections terminating in the ventral (MGV) and dorsal divisions (MGD) of the MG. The projections to the MGV were evidently topographic. The rostral and caudal portions of area Te1 projected to the ventromedial and dorsolateral parts of the MGV, respectively, forming narrow bands of terminal axons that extended in the mediolateral direction in the coronal plane of the MGV. The minimum dorsoventral width of the bands ranged approximately from 100 to 300 microm. Besides, the more rostral portion of area Te1 tended to project to the more rostral side of the MGV. The projections to the MGD consistently arborized in its ventral margin made up of the deep dorsal nucleus of the MGD. A similar weak topography along the rostrocaudal direction was observed in the projections to the MGD. Large terminals were occasionally found in the MGD after the injections involving cortical layer V. The distribution of large terminals also appeared topographic along with small terminals that were the major component of labeling. Collaterals of labeled axons produced slabs of terminal field in the thalamic reticular nucleus, which also exhibited a weak topography of distribution. These results provide insights into the structural basis of corticofugal modulations related to the tonotopic organizations in the cortex and MG.
通过在大鼠听觉皮层区域Te1微量注射生物胞素，系统研究了从皮层听觉区到内侧膝状体（MG）的皮质丘脑投射。所有注射范围限制在直径400微米，结果显示有两个投射终止于MG的腹侧部（MGV）和背侧部（MGD）。投射到MGV的明显具有拓扑结构。Te1区域的吻侧和尾侧部分分别投射到MGV的腹内侧和背外侧部分，形成在MGV冠状平面内沿内外侧方向延伸的狭窄终末轴突带。这些带的最小背腹宽度约为100至300微米。此外，Te1区域更吻侧的部分倾向于投射到MGV更吻侧的一侧。投射到MGD的在由MGD深背核组成的腹侧边缘持续分支。在投射到MGD的过程中也观察到沿吻尾方向有类似的弱拓扑结构。在涉及皮层V层的注射后，偶尔在MGD中发现大型终末。大型终末的分布与作为标记主要成分的小型终末一起也呈现出拓扑结构。标记轴突的侧支在丘脑网状核中产生终末场板层，其分布也呈现出弱拓扑结构。这些结果为与皮层和MG中的音调组织相关的皮质离心调制的结构基础提供了见解。
