COMPETITIVE INTERACTIONS BETWEEN RETINAL GANGLION-CELLS DURING PRENATAL DEVELOPMENT
COMPETITIVE INTERACTIONS BETWEEN RETINAL GANGLION-CELLS DURING PRENATAL DEVELOPMENT
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DOI：
10.1002/neu.480210113
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发表时间：
1990-01-01
期刊：
影响因子：
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通讯作者：
SHATZ, CJ
中科院分区：
文献类型：
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作者：
SHATZ, CJ
在哺乳动物视觉系统中，视网膜神经节细胞轴突终止于LGN内的一系列交替的眼特异性层中。这些层在开发过程中最初不存在。在猫身上，它们是在出生前的一段时期之后出现的，在这段时期里，最初来自两只眼睛的混合输入逐渐彼此分离，从而产生了出生时特有的一组层次。许多证据表明，来自双眼的神经节细胞轴突之间对LGN神经元的活性依赖性竞争相互作用在视网膜膝状体连接的最终模式中起着重要作用。对单个神经节细胞轴突分支模式的研究表明，在来自两只眼睛的输入混合的时期，来自一只眼睛的轴突将侧分支发送到后来被来自另一只眼睛的轴突完全占据的区域。超微结构研究表明，这些分支实际上是突触接触的部位，后来随着轴突在适当的区域形成成熟的终末分支，这些分支消失了。LGN神经元的体外微电极记录表明，它们可以在眼特异性层形成之前（而不是之后）接受来自视神经电刺激的会聚性突触兴奋，这表明至少在超微结构水平上看到的一些突触接触是功能性的。最后，在眼特异性层正常形成的两周时间内颅内输注河豚毒素的实验表明，可以防止或至少延迟层的形成。因此，单个轴突不能发展其受限的末端乔木分支模式，而是在整个LGN中广泛地分支。这些结果表明，突触功能和竞争所需的所有机制都存在于胎儿期。此外，很可能需要神经元活动来形成眼睛特异性层。如果是这样的话，那么活动必须以自发产生的动作电位的形式存在，因为在这些早期年龄段，视力是不可能的。因此，视网膜膝状体系统在最终被设计使用之前的许多周的功能可能有助于成人中存在的连接的最终模式。
In the mammalian visual system, retinal ganglion cell axons terminate within the LGN in a series of alternating eye‐specific layers. These layers are not present initially during development. In the cat they emerge secondarily following a prenatal period in which originally intermixed inputs from the two eyes gradually segregate from each other to give rise to the characteristic set of layers by birth. Many lines of evidence suggest that activity‐dependent competitive interactions between ganglion cell axons from the two eyes for LGN neurons play an important role in the final patterning of retinogeniculate connections. Studies of the branching patterns of individual ganglion cell axons suggest that during the period when inputs from the two eyes are intermixed, axons from one eye send side branches into territory later occupied exclusively by axons from the other eye. Ultrastructural studies indicate that these branches in fact are sites of synaptic contacts, which are later eliminated since the side branches disappear as axons form their mature terminal arbors in appropriate territory.In vitromicroelectrode recordings from LGN neurons indicate that they can receive convergent synaptic excitation from electrical stimulation of the optic nerves before but not after the eye‐specific layers form, suggesting that at least some of the synaptic contacts seen at the ultrastructural level are functonal. Finally, experiments in which tetrodotoxin was infused intracranially during the two week period during which the eye‐specific layers normally form demonstrate that it is possible to prevent, or at least delay, the formation of the layers. Accordingly, individual axons fail to develop their restricted terminal arbor branching pattern and instead branch widely throughout the LGN. These results indicate that all of the machinery necessary for synaptic function and competition is present during fetal life. Moreover, it is highly likely that neuronal activity is required for the formation of the eye‐specific layers. If so, then activity would have to be present in the form of spontaneously generated action potentials, since vision is not possible at these early ages. Thus, the functioning of the retinogeniculate system many weeks before it is put to the use for which it is ultimately designed may contribute to the final patterning of connections present in the adult.