Debski E A, Cline H T, Constantine-Paton M
Department of Biology, Yale University, New Haven, Connecticut 06511.
J Neurobiol. 1990 Jan;21(1):18-32. doi: 10.1002/neu.480210103.
The refinement of the topographic map of visual space within the optic tectum of the frog is activity-dependent. The use of the three-eyed frog preparation to assay the operation of this fine-tuning mechanism indicates that this process is mediated by the NMDA receptor: Chronic in vivo treatment with APV, an NMDA antagonist, disrupts the segregation of retinal afferents into eye-specific zones while NMDA treatment sharpens this pattern. This latter effect is accompanied by a decreased sensitivity of the system to applied NMDA. Activation of the NMDA receptor may mediate the fine-tuning mechanism by initiating the stabilization of appropriate synapses. The requirements for NMDA receptor activation necessitate the convergence of terminals carrying correlated activity patterns. Such patterns of activity are provided by ganglion cells whose cell bodies lie near one another in the retina, and who should therefore, in an accurate visual map, terminate near one another in the tectum. Synapses from ganglion cells who do not neighbor one another in the retina have uncorrelated firing patterns and therefore do not activate the NMDA receptor. These synapses then would not be stabilized relative to one another. In addition to organizing the retinal projection, NMDA receptor activation may also modulate retinal ganglion cell arbor morphology, since chronic in vivo APV or NMDA treatments decrease arbor density. These results are discussed in terms of the effect of NMDA receptor activation on branch initiation and the rate of branch retraction.
青蛙视顶盖内视觉空间地形图的细化取决于活动。利用三眼青蛙制备物来分析这种微调机制的运作表明，这一过程由NMDA受体介导：用NMDA拮抗剂APV进行慢性体内治疗会破坏视网膜传入纤维向眼特异性区域的分离，而NMDA治疗则会使这种模式更加清晰。后一种效应伴随着系统对所施加NMDA的敏感性降低。NMDA受体的激活可能通过启动适当突触的稳定来介导微调机制。NMDA受体激活的要求需要携带相关活动模式的终末的汇聚。这种活动模式由视网膜中细胞体彼此相邻的神经节细胞提供，因此，在精确的视觉图谱中，它们在视顶盖中应该彼此相邻终止。来自视网膜中彼此不相邻的神经节细胞的突触具有不相关的放电模式，因此不会激活NMDA受体。这些突触相对于彼此不会稳定。除了组织视网膜投射外，NMDA受体激活还可能调节视网膜神经节细胞树突形态，因为慢性体内APV或NMDA治疗会降低树突密度。根据NMDA受体激活对分支起始和分支回缩速率的影响对这些结果进行了讨论。
