So K F, Campbell G, Lieberman A R
Department of Anatomy, University of Hong Kong.
J Exp Biol. 1990 Oct;153:85-104. doi: 10.1242/jeb.153.1.85.
This review is concerned with the development of the mammalian retinogeniculate projection from the perspective of our studies on the hamster and to a lesser extent on the cat. In these, and other mammalian species, axons from the two eyes initially spread throughout the dorsal lateral geniculate nucleus (dLGN) and thus completely overlap. Later they segregate, the axons from each eye coming to occupy discrete, non-overlapping territories within the dLGN. The process of segregation to establish the adult pattern coincides with the death of retinal ganglion cells projecting to inappropriate areas of the dLGN and with the loss, by degeneration or retraction, of the axons and/or axonal branches initially located within inappropriate territory of the dLGN. These events occur in the early postnatal period in hamsters, before the eyes have opened, and in cats and monkeys they occur entirely during embryonic life: thus, they do not depend on the onset of normal visual function. If one eye is removed before segregation has begun, the terminal fields of the crossed and uncrossed axons from the remaining eye do not segregate, suggesting that segregation in normal development may depend on some form of interaction between retinal ganglion cells from the two eyes. Attractive and/or repulsive influences exerted by the dLGN on retinogeniculate axons may also be involved in the formation of eye-specific territories. Experimental ultrastructural studies in hamster and cat show that the overlap phase is associated with the formation, by inappropriately located axons, of transient synapses similar to those made by retinogeniculate axons in appropriate parts of the dLGN. In the cat, the transient synapses are made by the axon trunk and by side branches of retinogeniculate axons with terminal arbors in appropriate parts of the nucleus; the transient synapses disappear as the side branches are shed or retracted during the segregation period. Because of good evidence that electrical activity of the retinogeniculate axons may be involved in binocular segregation of inputs, we suggest that the formation and elimination of transient synapses play a significant role in the development of the orderly retinogeniculate projections.
本综述从我们对仓鼠以及在较小程度上对猫的研究角度，探讨哺乳动物视网膜膝状体投射的发育过程。在这些以及其他哺乳动物物种中，来自双眼的轴突最初遍布背外侧膝状体核（dLGN），因此完全重叠。随后它们分离，来自每只眼睛的轴突开始占据dLGN内离散的、不重叠的区域。建立成年模式的分离过程与投射到dLGN不适当区域的视网膜神经节细胞的死亡以及最初位于dLGN不适当区域的轴突和/或轴突分支通过退化或回缩而丧失同时发生。这些事件在仓鼠出生后的早期发生，即在眼睛睁开之前，而在猫和猴子中，它们完全在胚胎期发生：因此，它们不依赖于正常视觉功能的开始。如果在分离开始前摘除一只眼睛，来自另一只眼睛的交叉和未交叉轴突的终末场不会分离，这表明正常发育中的分离可能依赖于来自双眼的视网膜神经节细胞之间某种形式的相互作用。dLGN对视网膜膝状体轴突施加的吸引和/或排斥影响也可能参与眼特异性区域的形成。对仓鼠和猫的实验性超微结构研究表明，重叠阶段与由位置不当的轴突形成类似于视网膜膝状体轴突在dLGN适当部位形成的瞬态突触有关。在猫中，瞬态突触由轴突主干以及视网膜膝状体轴突的侧支与核内适当部位的终末分支形成；随着侧支在分离期脱落或回缩，瞬态突触消失。由于有充分证据表明视网膜膝状体轴突的电活动可能参与输入的双眼分离，我们认为瞬态突触的形成和消除在有序的视网膜膝状体投射的发育中起重要作用。
