Growth of Thalamic Afferents into Mouse Barrel Cortex
Growth of Thalamic Afferents into Mouse Barrel Cortex
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DOI：
10.1093/cercor/1.4.308
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发表时间：
1991-07-01
期刊：
影响因子：
3.7
通讯作者：
Woolsey, Thomas A.
中科院分区：
文献类型：
--
作者：
Senft, Stephen L.;Woolsey, Thomas A.
我们研究了出生后小鼠胡须桶出现时丘脑皮质传入 (TCA) 向体感皮层的生长。通过两种方法选择性标记腹基底（VB）丘脑的向内生长纤维。在直视下，在含有丘脑源核及其皮质靶标的脑片中，在体外用 HRP 标记单个轴突和轴突群，或者在固定组织中用 Dil（1,1'-双十八烷基-3,3,3',3'-四甲基吲哚羰花青高氯酸盐）标记。许多简单的丘脑皮质传入神经在出生时就已经位于上皮质板内[出生后第一天（PND1）]。最初，丘脑中每个点的 TCA 以二维“高斯”分布在皮层中，横向重叠以构成均匀的投影模式。该投影是地形投影，因为 VB 内的相邻焦点注射标记了相邻的皮质位点。随后桶状体（胡须的丘脑表示）的发展将 TCA 投影划分为一组与胡须相关的高斯，以皮质目标为中心，其集体地形反映了源模式的地形。在大约PND3上形成桶状体之后，但在大约PND5上的细胞结构中出现桶状体之前，重叠的TCA在第四层中分离成密集的末端簇，随后桶状体围绕该簇成熟。用透明相机追踪的单纤维时间序列解释了这种在人群水平上如此明显的转变。早在 PND1 时，各个 TCA 就在其水平方向上发出多个上升的络脉，穿过白质并倾斜上升到上皮层。随后，通过 PND4，并且至少继续通过 PND7，加速选定适当侧枝的末端分枝，并修剪其他不适当的侧枝。选择机制似乎是由组内强化事件产生的，对于每个与晶须相关的高斯分布的中心的分支来说，组内强化事件更强。
We studied thalamocortical afferent (TCA) growth into somatosensory cortex as the whisker barrels emerge in postnatal mice. Ingrowing fibers from the ventrobasal (VB) thalamus were selectively labeled by two means. Under direct vision, individual axons and populations of axons were labeled in vitro with HRP, or in fixed tissue with Dil (1,1'-dioctodecyl-3,3,3',3'- tetramethylindocarbocyanine perchlorate), in pieces of brain containing both the source nucleus in the thalamus and its cortical target. Many simple thalamocortical afferents are already within the upper cortical plate at birth [postnatal day one (PND1)]. Initially, TCAs from each point in the thalamus distribute in the cortex as two-dimensional "Gaussians," which overlap laterally to constitute a uniform projection pattern. The projection is topographic, because adjacent focal injections within VB label adjacent cortical loci. Subsequent development of barreloids (thalamic representations of the whiskers) partitions the TCA projection into a set of whisker-related Gaussians, centered on cortical targets whose collective topography reflects that of the source pattern. After barreloids form on about PND3, but before barrels appear in cytoarchitecture on about PND5, the overlapping TCAs segregate into dense terminal clusters in layer IV, around which barrels later mature. Time series of single fibers traced with camera lucida explain this transformation that is so noticeable at the population level. As early as PND1, individual TCAs emit multiple ascending collaterals on their horizontal run through white matter and oblique ascent into upper cortex. Subsequently, by PND4, and proceeding at least through PND7, there is accelerated terminal arborization of selected appropriate collateral branches and pruning back of other inappropriate ones. The selection mechanism appears to result from within-group reinforcement events that are stronger for branches toward the center of each whisker-related Gaussian distribution.