CENTRIFUGAL FIBRES TO RETINA IN MONKEY AND CAT
CENTRIFUGAL FIBRES TO RETINA IN MONKEY AND CAT
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DOI：
10.1038/2071365a0
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发表时间：
1965-01-01
期刊：
影响因子：
64.8
通讯作者：
POWELL, TPS
中科院分区：
文献类型：
--
作者：
BROOKE, RNL;DOWNER, JDC;POWELL, TPS
在用高尔基法染色的正常物质中，离心纤维在鸟类和哺乳动物的视网膜中被描述过。最近，实验神经组织学证据已经提供了鸽子这种纤维的起源，路线和终止，以及传入连接的组织细节和它们的起源核的投射。从电生理实验中有很好的证据表明哺乳动物中存在这种纤维；但到目前为止，还不可能用轴突变性方法明确地证明它们。现在我们知道，中枢神经系统某些部分的正常和退化的神经末梢不能用银染色法染色，但可以用电子显微镜识别它们。”由于这些原因，人们认为在电子显微镜下可以在哺乳动物视网膜的超薄切片上看到退化的离心纤维。在初步实验中，用电子显微镜检查了鸽子的视网膜，其中离心纤维的起源核已被破坏。在鸽子身上进行的这些实验表明，电子显微镜技术可以用来证明视网膜中退化的离心纤维，之后在两种哺乳动物身上进行了类似的研究。鸽子的中脑有很大的损伤，猴子的视神经束被分开，猫的视神经与视交叉的连接处被切断。在6 - 14天的生存期后，动物被麻醉，眼睛被移除，前半部分和玻璃体被移除，然后用维罗那缓冲的锇酸固定视网膜；猴子和猫的视网膜在靠近视盘的地方被垂直切割成“鼻”和“颞”两半，而这两半又依次垂直分为“内”和“外”两半。然后将这四个部分切成大约1毫米的小块。经脱水、磷钨酸染色后包埋于“Araldite”中。所有动物的大脑都用福尔马林固定，切片并用Nauta法染色，以确定病变的部位和程度。在鸽子中，纤维和终末变性的证据仅在脑干病变部位对面的眼睛视网膜中发现。在视神经纤维层中，偶有纤维或由两到三个相邻纤维组成的一组在外观上明显异常。这些改变的纤维比正常的视神经纤维更大，含有电子密集的“膜”，并有许多萎缩的、不透明的线粒体（图1）。类似的退化纤维在神经节细胞的细胞体之间和内丛状层的所有层之间，甚至在双极细胞层的内部也可见。在无毛细胞的细胞体上发现退化的纤维和非常致密的突触前末梢，通常是由<s:1>勒细胞的薄过程介入的。退化的纤维或终末直接贴在无毛细胞的膜上；但是，由于缺乏局部膜增厚，不可能确定退化的突触前末端与无突细胞直接形成轴体细胞突触。在某些情况下，退化的突触前末端在两者之间的连接处的对面
N normal material stained by the Golgi method, centrifugal fibres have been described in the retinae of birds and mammals". Recently, experimental neurohistological evidence has been provided for the origin, course and termination of such fibres in the pigeon together with the details of the organization of the afferent connexions and projection of their nucleus of originº. There is good evidence from electrophysiological experiments for the presence of such fibres in mammalsº; but so far it has not been possible to demonstrate them unequivocally with axonal degeneration methods. It is now known that both normal and degenerating nerve endings in certain parts of the central nervous system cannot be stained by silver methods, but that it is possible to recognize them with the electron microscope". For these reasons it was thought that degenerating centrifugal fibres might be seen in ultra-thin sections of the retinae of mammals with the electron microscope. In preliminary experiments the retinae of pigeons, in which the nucleus of origin of the centrifugal fibres had been destroyed, were examined with the electron microscope. After these experiments on the pigeon had shown that electron microscopical techniques can be used to demonstrate degenerating centrifugal fibres in the retina, similar investigations were made in two mammals.In the pigeons large lesions were placed in the midbrain, in monkeys the optic tract was divided, and in cats the optic nerve was cut at its junction with the optic chiasma. After survival periods varying from six to fourteen days the animals were anaesthetized, the eyes removed and their anterior halves and vitreous removed before fixation of the retinae with veronal-buffered osmic acid; the retinae of the monkeys and cats were cut vertically close to the optic disk into “nasal” and “temporal'halves, and each of these halves was in turn divided vertically into “inner” and “outer” halves. All four parts were then cut into small blocks approximately 1 mm? in size, and after dehydration and staining with phospho-tungstic acid were embedded in “Araldite'". The brains of all the animals were fixed in formalin, and sections were cut and stained with the method of Nauta" in order to determine the site and extent of the lesion. In the pigeon, evidence of degeneration of fibres and terminals is found only in the retina of the eye on the side opposite to that of the lesion in the brain stemº. In the optic nerve fibre layer an occasional fibre, or group of two or three adjoining fibres, are distinctly abnormal in appearance. These altered fibres are larger than the normal optic nerve fibres, contain whorls of electron-dense “membranes” and have numerous shrunken, opaque mitochondria (Fig. 1). Similar degenerating fibres are seen between the cell bodies of the ganglion cells and at all lovels of the inner plexiform layer as far out as the inner aspect of the bipolar cell layer. Degenerating fibres and very dense presynaptic endings are found in relation to the cell bodies of the amacrine cells, a thin process of a Müller cell usually intervening. A degenerating fibre or terminal has been seen directly apposed to the membrane of an amacrine cell; but, because of the absence of localized membrane thickening, it has not been possible to identify with certainty a degenerating presynaptic ending making a direct axo-somatic synapse with an amacrine cell. In some instances, where a degenerating presynaptic ending is opposite the junction between two