Matthews M A
Exp Brain Res. 1985;58(3):473-89. doi: 10.1007/BF00235864.
The developing lateral geniculate complex was excised from fetal albino rats at 18 days of gestation and implanted into the occipital cortex of host animals at 5 days of postnatal age. Groups of host animals were sacrificed at 10, 20 and 30 days following this procedure. The transplant tissue of selected animals was stereotaxically lesioned 2 days prior to scheduled sacrifice and their brains subjected to either Fink-Heimer or electron microscopic analysis of the distribution and density of degenerating efferents from the transplant. The remaining animals were analysed by means of Bodian, Golgi-Cox or electron microscopic techniques. Transplanted neurons displayed typical dendritic branching patterns of geniculate relay neurons by 20 days following implantation. Intrinsic neurons, characterized by a small ovoid soma and two main stem dendrites, only became evident in transplant tissue by 30 days and were much reduced in number. Synapses developed by 10 days and rapidly increased in number by 20 and 30 days. Most complexes were simple axo-dendritic, asymmetric junctions. Multiple serial and reciprocal complexes, as well as the characteristic glomerular complex, failed to appear. Analysis of Bodian stained material revealed a dense network of fibers coursing about the transplant. Distinct bundles of these fibers were observed extending from the medial edge of the transplant into area 17 by 20 days following implantation. A Fink-Heimer analysis of animals whose transplants were stereotaxically lesioned revealed degeneration in Layers II-VI of the primary visual cortex but the majority of these fibers terminated within the lateral two-thirds of Layer IV. Few degenerated fibers could be found in the underlying white matter indicating that efferents from the transplant found their way to their "correct" target zone by growing through a complex neuropil which provided minimal physical substrates to guide such growth. Most of the contacts formed by these fibers were simple junctions along the shafts of dendrites with a wide range in diameter. It is concluded that the nearby host visual neurons, which are the correct target cells for the afferents arising in the transplant, induced a directed growth of these fibers.
在妊娠18天时从胎龄白化大鼠中切除发育中的外侧膝状体复合体，并在出生后5天将其植入宿主动物的枕叶皮质。在此操作后的10、20和30天处死宿主动物组。在预定处死前2天，对选定动物的移植组织进行立体定向损伤，并对其大脑进行Fink-Heimer分析或对来自移植体的变性传出纤维的分布和密度进行电子显微镜分析。其余动物通过Bodian、Golgi-Cox或电子显微镜技术进行分析。移植的神经元在植入后20天显示出典型的膝状体中继神经元树突分支模式。以小卵形胞体和两个主要主干树突为特征的固有神经元，直到30天才在移植组织中明显可见，且数量大大减少。突触在10天时形成，并在20天和3０天时数量迅速增加。大多数复合体是简单的轴突-树突不对称连接。多重串联和交互复合体以及特征性的小球复合体均未出现。对Bodian染色材料的分析显示，移植体周围有密集的纤维网络。在植入后20天时，观察到这些纤维的明显束从移植体的内侧边缘延伸到17区。对移植体进行立体定向损伤的动物的Fink-Heimer分析显示，初级视皮质的II-VI层有变性，但这些纤维大多数终止于IV层外侧三分之二范围内。在下方的白质中几乎找不到变性纤维，这表明来自移植体的传出纤维通过生长穿过一个复杂的神经毡到达其“正确”的靶区，而该神经毡提供的引导这种生长的物理基质极少。这些纤维形成的大多数接触是沿着直径范围很宽的树突轴的简单连接。得出的结论是，附近的宿主视觉神经元是移植体中传入纤维的正确靶细胞，诱导了这些纤维的定向生长。
