Stop and Branch Behaviors of Geniculocortical Axons: A Time-Lapse Study in Organotypic Cocultures
Stop and Branch Behaviors of Geniculocortical Axons: A Time-Lapse Study in Organotypic Cocultures
复制标题
生殖皮质轴突的停止和分支行为：器官共培养的延时研究
作者：
N. Yamamoto;S. Higashi;K. Toyama
在外侧膝状核（LGN）与视觉皮层（VC）的器官型共培养中研究了丘脑轴突生长的行为，以揭示形成椎板特异性丘脑皮质连接的细胞相互作用。将 LGN 外植体放置在 VC 外植体的腹侧、软脑膜表面或侧边缘，并通过共聚焦显微镜在固定组织和活体组织中观察荧光染料标记的 LGN 轴突。体外固定共培养物 1 周后的轴突投影模式表明，在所有三种配置中，LGN 轴突主要在第 4 层形成原始分支。延时研究进一步检查了活皮质外植体中的轴突生长和分支形成。无论轴突进入的方向如何，大多数分支出现在轴突尖端后面的第 4 层内。此外，大多数从 VC 腹侧或软脑膜侧进入的轴突在第 4 层及其周围表现出轴突生长的短暂或持续停止，而从 VC 侧边缘进入的轴突则沿着第 4 层行进，但没有表现出停止行为。轴突停止常常伴随生长锥塌陷和轻微回缩。这些结果表明，皮层第 4 层中存在可被 LGN 轴突识别的分支和停止线索。
The behavior of growing thalamic axons was studied in an organotypic coculture of the lateral geniculate nucleus (LGN) with the visual cortex (VC) to reveal cellular interactions that underlie the formation of lamina-specific thalamocortical connections. The LGN explant was placed at the ventral side, pial surface, or lateral edge of the VC explant, and fluorescent dye-labeled LGN axons were observed by confocal microscopy in fixed and living tissue. The axonal projection pattern in fixed cocultures after 1 week in vitro demonstrated that, in all three configurations, LGN axons formed primitive branches mainly in layer 4. A time-lapse study further examined axonal growth and branch formation in the living cortical explant. The majority of branches emerged within layer 4 behind the axonal tip, regardless of the direction of axonal entry. In addition, most axons entering from the ventral or pial side of the VC exhibited a transient or persistent stop of axonal growth in and around layer 4, whereas those entering from the lateral edge of the VC traveled along layer 4 without exhibiting stop behavior. The axonal stop often was accompanied by growth cone collapse and a slight retraction. These results suggest the existence of branch and stop cues in layer 4 of the cortex that are recognized by LGN axons.