Davydova T V, Goncharova N V, Boyko V P
J Hirnforsch. 1976;17(5):463-88.
The optic nerve and mesencephalic optic centre (tectum opticum, TO) of the tortoise, Testudo horsfieldi, Gray, in the norm and after the enucleation have been studies using Golgi's method, electron microscopy and the electrophysiological technique. The optic nerve comprises about 400,000 fibres represented by two classes of axons: myelinated (10%) and unmyelinated (90%). The diameters of the former vary within 0.3-3 mum, of the latter within 0.3-1.1 mum. The neurogramms of the optic nerve contain two components corresponding to the two rates of conduction through different groups of fibres (1.3 musec and 0.5 musec). The stratified synaptic organization of the TO has been investigated. The optic terminals are shown to join in complex synaptic formations at certain levels of the upper layers of the TO (Strata I, II and III). The process of degeneration in the optic system of Testudo is drastically stretched in time. It was demonstrated by the electrophysiological control that the TO potentials induced in response to the nerve stimulation were not registered any longer only 6-6.5 months after the enucleation. Certain groups of retinal fibres of the optic nerve and their terminals in the TO are shown to degenerate differently and asynchronously. Earlier unknown types of destructive changes of the terminals (vesicular, neurofilamentous, glycogen and others) are described. It is suggested that the different types of degeneration of the optic fibres and their terminals are the result of possible biochemical heterogeneity of the retinal ganglious cells. The comparison of the terms and types of degeneration of different groups of nervous fibres in the optic nerve and their terminals in the TO has revealed some correlations suggesting that the myelinated optic fibres produce nervous terminals degenerating by the "dark" type, whereas the unmyelinated optic axons may be subdivided into several groups, each producing nervous terminals subjected to a definite type of destruction ("clear", "vesicular", "neurofilamentous" etc.). The localization of certain groups of therminals at certain levels of the cortical plate of the TO confirms the electrophysiological data on the stratified organization of the retino-tectal projections in the TO of lower vertebrates. It has been shown by the comparison of the results obtained with those reported for Emys orbicularis, L. that the two species have marked differences in the morpho-functional characteristics of the retino-tectal system, neuronic composition of the TO, the character of destructive changes of the terminals after the enucleation and the component composition of polysynaptic complexes and glomerules. Probably these differences may come from the peculiarities of the perception and transformation of visual information in the species.
采用高尔基染色法、电子显微镜技术和电生理技术，对正常状态及摘除眼球后的印度星龟（Testudo horsfieldi，Gray）的视神经和中脑视中枢（视顶盖，TO）进行了研究。视神经约由400,000根纤维组成，这些纤维可分为两类轴突：有髓鞘的（10%）和无髓鞘的（90%）。前者直径在0.3 - 3μm之间，后者直径在0.3 - 1.1μm之间。视神经的神经电图包含两个成分，分别对应不同纤维组的两种传导速度（1.3μsec和0.5μsec）。对TO的分层突触组织进行了研究。结果显示，视终端在TO上层的特定层面（第I、II和III层）形成复杂的突触结构。印度星龟视觉系统的退化过程在时间上被极大地延长。电生理监测表明，摘除眼球后仅6 - 6.5个月，对神经刺激产生的TO电位就不再被记录到。视神经的某些视网膜纤维组及其在TO中的终端显示出不同程度和不同时间的退化。描述了此前未知的终端破坏类型（泡状、神经丝状、糖原等）。研究表明，视神经纤维及其终端的不同退化类型可能是视网膜神经节细胞生化异质性的结果。对视神经中不同神经纤维组及其在TO中的终端的退化术语和类型进行比较，揭示了一些相关性，表明有髓鞘的视神经纤维产生“暗”型退化的神经终端，而无髓鞘的视神经轴突可分为几组，每组产生经历特定破坏类型（“清亮”型、“泡状”型、“神经丝状”型等）的神经终端。某些终端组在TO皮质板特定层面的定位证实了关于低等脊椎动物TO中视网膜 - 顶盖投射分层组织的电生理数据。通过将所得结果与关于欧洲泽龟（Emys orbicularis，L.）报道的结果进行比较表明，这两个物种在视网膜 - 顶盖系统的形态功能特征、TO的神经元组成、摘除眼球后终端的破坏特征以及多突触复合体和小球的成分组成方面存在显著差异。这些差异可能源于物种在视觉信息感知和转换方面的特性。
