Rossi F, Borsello T
Department of Human Anatomy and Physiology, University of Turin, Italy.
J Comp Neurol. 1993 Nov 1;337(1):70-82. doi: 10.1002/cne.903370105.
The abnormal location of large numbers of neurones is characteristic of genetic mutations which impair the migratory processes of developing nerve cells. Nevertheless, the presence of small amounts of ectopic neurones is a fairly common finding even in normal adult animals. The first aim of this study was to investigate a series of features of ectopic Purkinje cells in normal adult rats and particularly to assess whether these cells are still capable of interacting with their normal afferents. Several displaced Purkinje cells, identified by anti-D28k calbindin immunolabelling as well as by typical morphological features, were present in the brainstem and cerebellum of all the examined animals. Two distinct morphological types of such cells could be recognized: 1) noncortical Purkinje cells, located in several areas of the dorsal brainstem and cerebellum, characterised by poorly developed and randomly oriented dendrites; and 2) cortical Purkinje cells, exclusively located in the dorsal cochlear nucleus, characterised by large dendritic trees oriented along parasagittal planes. Tracing experiments, in which Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into the inferior olive, revealed that several ectopic Purkinje cells, belonging to both types, were contacted by the terminal arbours of olivary axons, structurally similar to cerebellar climbing fibres. On the basis of the observation that ectopic Purkinje cells were more frequent in the dorsal cochlear nucleus than in any other of the examined regions, we tested the hypothesis that this nucleus might represent a particularly favourable environment for the survival and development of Purkinje cells. By grafting embryonic cerebellar tissue in the fourth ventricle, only minimal migration of Purkinje cells into the recipient parenchyma was observed when the transplant was placed on the brainstem surface caudal to the cochlear nucleus. By contrast, when the graft was apposed to the latter nucleus, large numbers of Purkinje cells migrated and developed in its superficial layers. These Purkinje cells passed through all the different phases which characterise the normal ontogenesis of this neuronal population and finally developed mature structural features similar to those displayed by cortical ectopic Purkinje cells. This study demonstrates that at least some of the ectopic Purkinje cells receive their physiological olivary input. This fact indicates that Purkinje cells are able to attract olivary axons and establish specific connections, even if they are displaced in an abnormal environment. In addition, we show that the dorsal cochlear nucleus represents a particularly favourable environment for the survival and the development of Purkinje cells.
大量神经元的异常定位是基因突变的特征，这些基因突变会损害发育中神经细胞的迁移过程。然而，即使在正常成年动物中，少量异位神经元的存在也是相当常见的发现。本研究的首要目的是调查正常成年大鼠中异位浦肯野细胞的一系列特征，特别是评估这些细胞是否仍能与它们的正常传入神经相互作用。通过抗D28k钙结合蛋白免疫标记以及典型的形态学特征鉴定出的几个移位的浦肯野细胞，存在于所有被检查动物的脑干和小脑中。可以识别出两种不同形态类型的此类细胞：1）非皮质浦肯野细胞，位于背侧脑干和小脑的几个区域，其特征是树突发育不良且方向随机；2）皮质浦肯野细胞，仅位于背侧耳蜗核，其特征是沿矢状旁平面排列的大的树突树。在将菜豆白细胞凝集素（PHA-L）注入下橄榄核的追踪实验中，发现两种类型的几个异位浦肯野细胞都与橄榄轴突的终末分支接触，其结构类似于小脑攀缘纤维。基于异位浦肯野细胞在背侧耳蜗核中比在任何其他被检查区域中更常见的观察结果，我们测试了这样一个假设，即该核可能代表浦肯野细胞存活和发育的特别有利环境。通过将胚胎小脑组织移植到第四脑室，当移植置于耳蜗核尾侧的脑干表面时，仅观察到少量浦肯野细胞迁移到受体实质中。相比之下，当移植物与后者的核相邻时，大量浦肯野细胞在其表层迁移并发育。这些浦肯野细胞经历了表征该神经元群体正常个体发育的所有不同阶段，最终发育出与皮质异位浦肯野细胞所显示的成熟结构特征相似的特征。这项研究表明，至少一些异位浦肯野细胞接受其生理性橄榄体输入。这一事实表明，浦肯野细胞能够吸引橄榄轴突并建立特定连接，即使它们在异常环境中移位。此外，我们表明背侧耳蜗核代表浦肯野细胞存活和发育的特别有利环境。
