Udin S B, Fawcett J W
Department of Physiology, State University of New York, Buffalo 14214.
Annu Rev Neurosci. 1988;11:289-327. doi: 10.1146/annurev.ne.11.030188.001445.
The catalogue of data presented here form many systems demonstrates that multiple mechanisms are involved in the formation of topographic maps. We are not yet in a position to explain why a particular mechanism appears to dominate in some situations and not in others. Certain generalizations can be made, however. First, at least some form of chemospecificity can be invoked to help explain connectivity in all of the experiments we have cited. Often, the differential identities of a population of neurons can be reflected in an orderly pattern of axon outgrowth and in the actively maintained preservation of neighbor relations as the axons grow toward their targets; such orderly arrangements are not obligatory, but, where present, they facilitate the speedy establishment of orderly maps when the axons reach their target nuclei. Within a terminal zone, chemospecific cues may dominate and constrain a given axon to terminate in a specific location, but axon-axon interactions commonly supercede chemospecific matching. At least two forms of axon-axon interaction occur, one based on some sort of biochemical properties related to the axon's embryological identity and another based on the axons' electrical activity. Tasks for the future are to identify the cellular bases of each of these mechanisms and to understand the situations in which each is manifested.
此处呈现的来自多个系统的数据目录表明，地形图的形成涉及多种机制。我们尚无法解释为何特定机制在某些情况下似乎占主导地位，而在其他情况下则不然。然而，可以进行一些概括。首先，至少可以援引某种形式的化学特异性来帮助解释我们所引用的所有实验中的连接性。通常，一群神经元的不同特性可以反映在轴突生长的有序模式以及轴突向其靶标生长时对相邻关系的积极维持中；这种有序排列并非必然，但一旦存在，当轴突到达其靶核时，它们有助于快速建立有序的图谱。在一个终末区内，化学特异性线索可能占主导并限制给定轴突在特定位置终止，但轴突 - 轴突相互作用通常会取代化学特异性匹配。至少发生两种形式的轴突 - 轴突相互作用，一种基于与轴突胚胎学特性相关的某种生化特性，另一种基于轴突的电活动。未来的任务是确定每种机制的细胞基础，并了解每种机制表现出来的情况。
