ORGANIZED GROWTH OF THALAMOCORTICAL AXONS FROM THE DEEP TIER OF TERMINATIONS INTO LAYER-IV OF DEVELOPING MOUSE BARREL CORTEX
ORGANIZED GROWTH OF THALAMOCORTICAL AXONS FROM THE DEEP TIER OF TERMINATIONS INTO LAYER-IV OF DEVELOPING MOUSE BARREL CORTEX
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DOI：
10.1523/jneurosci.13-12-05365.1993
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发表时间：
1993-12-01
影响因子：
5.3
通讯作者：
JONES, EG
中科院分区：
文献类型：
--
作者：
AGMON, A;YANG, LT;JONES, EG
丘脑皮质投射到啮齿动物躯体感觉（“桶”）皮质是高度有序的径向和切线维度。在出生后发育的短暂时期内，丘脑皮质轴突建立两层终端，在深层和第四层，并在第四层内形成胡须特定的集群;然而，很少有人知道的线索，引导他们到适当的径向和切向位置。为了深入了解这一过程的潜在机制，我们研究了高空间分辨率下小鼠桶状皮质中丘脑皮质终止模式的发展。用亲脂性碳菁染料Dil在固定切片中标记发育中的丘脑皮质轴突，并用激光扫描共聚焦显微镜成像。在出生当天（出生后第0天，PO）轴突通过层VI和V，很少或没有分支。到P2时，在第VI层和第V层的边界处的较低层的终端可以清楚地识别。在这一层之下，轴突斜向或切向延伸，形成一个密集的交叉纤维网，但没有明显的分支。到P4时，在第IV层中的上层终端可以清楚地识别，并且由周期性的、密集的终端分支簇组成。与VI层和下层V中轴突遵循的倾斜且明显无序的路线形成鲜明对比，上层V中朝向上层的轴突组织成放射状排列的松散束，这表明注定终止于特定IV层的轴突桶已经到达了下层内适当的切向坐标。因此，在第四层的丘脑皮质终端的模式似乎是从深层的终端，并没有发展从一个最初丰富的树枝化模式，通过修剪不适当的分支。
The thalamocortical projection to rodent somatosensory (''barrel'') cortex is highly ordered in both the radial and the tangential dimensions. During a brief period of postnatal development, thalamocortical axons establish two tiers of terminations, in the deep layers and in layer IV, and form whisker-specific clusters within layer IV; however, little is known about the cues that guide them to their appropriate radial and tangential positions. To gain insight into potential mechanisms underlying this process, we studied the development of thalamocortical termination patterns in mouse barrel cortex at high spatial resolution. Developing thalamocortical axons were labeled in fixed slices with the lipophilic carbocyanine dye Dil and imaged with a laser scanning confocal microscope. On the day of birth (postnatal day 0, PO) axons coursed through layers VI and V, with little or no branching. By P2 the lower tier of terminations, at the border of layers VI and V, was clearly identifiable. Below this tier axons coursed obliquely or tangentially, forming a dense meshwork of intersecting fibers, but with no apparent branching. By P4 the upper tier of terminations, in layer IV, was clearly recognizable, and consisted of periodic, dense clusters of terminal arborizations. In marked contrast to the oblique and apparently disorderly course followed by axons in layer VI and lower layer V, axons in upper layer V heading toward the upper tier were organized in loose bundles running radially, suggesting that axons destined to terminate in a particular layer IV barrel had already reached their appropriate tangential coordinates within the lower tier. Thus, the pattern of thalamocortical terminations in layer IV seems to be projected from the deep tier of terminations, and does not develop from an initially profuse arborization pattern through pruning of inappropriate branches.