Alvarado-Mallart R M, Sotelo C
J Comp Neurol. 1982 Dec 10;212(3):247-67. doi: 10.1002/cne.902120304.
Pieces of cerebellar primordia from (days 14 or 15 of gestation) E14 or E15 rat embryos were dissected out and transplanted into a cavity of the occipital cortex and underlying hippocampus, over the superior colliculus of 2-month-old rats. The host animals were allowed to survive for 2 to 3 months. The cytoarchitectonic and the synaptic organizations were analyzed in 16 of such transplants. Only 4 of the implants established connections with the host brain through several thin peduncles composed of myelinated fibers. The remaining 12 implants survived in an extraparenchymal situation. Independently of its partial linking to the host brain, the graft grew and developed a cerebellar structure composed of nuclear and cortical regions. The latter exhibited normal lamination and foliation, and contained the five categories of neurons which characterize normal cerebellar cortex. Electron microscopic examination disclosed that the synaptic connections normally present in the cerebellar cortex were also formed in the implants with the exception of climbing fibers, which were absent. The cerebellar interneurons kept their normal topographic distribution and gave origin to numerous synapses which maintained their own specificity. Some mossy fibers were present in the granule cell layer at the center of typical glomeruli. However, abnormal synaptic arrangements were also observed within the neuropil of this granule cell layer. They consisted of pseudoglomerular formations composed of clusters of tightly packed small axon terminals covered by granule cell dendrites. The origin of these boutons was not established. Since they did not correspond to the classes of presynaptic elements normally synapsing on these dendrites, they constitute a new example of cerebellar heterologous synapses. Their presence could be related to changes in the cellular environment due to the rarity of mossy afferents. HRP tracing experiments, carried out in extraparenchymal transplants, have allowed us to determine that the corticonucleocortical loop of normal cerebellum is also developed in the implants. Nuclear neurons are at the origin of the mossy fibers involved in glomerular formations, whereas Purkinje cells project to the nuclear region. The establishment of these reciprocal connections could determine the functional stabilization of both kinds of cerebellar neurons and thus the long survival of extraparenchymal grafts. These results allow the conclusion that the presence of extracerebellar afferents is not necessary for the organotypic and synaptotypic differentiation of cerebellar anlage.
从妊娠第14天或15天（E14或E15）的大鼠胚胎中取出小脑原基碎片，移植到2月龄大鼠上丘上方枕叶皮质和海马体下方的腔中。让宿主动物存活2至3个月。对16个这样的移植体进行了细胞构筑和突触组织分析。只有4个植入物通过由有髓纤维组成的几条细蒂与宿主脑建立了连接。其余12个植入物在脑实质外的情况下存活。不管其与宿主脑的部分连接情况如何，移植体生长并发育出由核区和皮质区组成的小脑结构。后者表现出正常的分层和叶状结构，并包含正常小脑皮质特有的五类神经元。电子显微镜检查显示，除了不存在的攀缘纤维外，小脑皮质中正常存在的突触连接在植入物中也形成了。小脑中间神经元保持其正常的拓扑分布，并产生许多保持自身特异性的突触。在典型小球中心的颗粒细胞层中存在一些苔藓纤维。然而，在该颗粒细胞层的神经毡内也观察到异常的突触排列。它们由假小球结构组成，这些结构由紧密堆积的小轴突终末簇组成，被颗粒细胞树突覆盖。这些终扣的起源尚未确定。由于它们与通常与这些树突形成突触的突触前元件类别不对应，它们构成了小脑异源突触的一个新例子。它们的存在可能与苔藓传入纤维稀少导致的细胞环境变化有关。在脑实质外移植体中进行的HRP追踪实验使我们能够确定，正常小脑的皮质-核-皮质环路在植入物中也得到了发育。核神经元是参与小球形成的苔藓纤维的起源，而浦肯野细胞投射到核区。这些相互连接的建立可能决定了两种小脑神经元的功能稳定，从而决定了脑实质外移植体的长期存活。这些结果可以得出结论，小脑外传入纤维的存在对于小脑原基的器官型和突触型分化不是必需的。
