DEVELOPMENT OF SPECIFIC NEURONAL CONNECTIONS

动物肢体的正常功能依赖于高度有序的 脊髓运动神经元与脊髓背角运动神经元的联系模式 四肢的各种肌肉。这一模式是在 通过特定的轴突生长发育。运动神经元轴突通常会使 从脊髓到靶点的一系列路径选择 肌肉。这些选择需要轴突识别并做出适当的反应 到与其精确位置和细胞相关的多个生长线索 在任何脊椎动物中，身份目前都是未知的。各种不同元素的组合 外科手术和几种解剖技术将被用来 本地化并识别提供 引导生长中的运动轴突至其目标肌肉的环境线索。 所有的实验都将在鸡胚或鹌鹑胚胎上进行。第一 问题是肢体的两个轴的线索是否分开 位于神经通路上。其他实验将确定 运动神经元的靶标--肌肉细胞的存在是 准确的寻路，或者结缔组织细胞是否足够。 最后一系列实验将探索假设鞘的作用 细胞，或雪旺细胞，以确保四肢肌肉的正常神经支配。 对制导的位置和蜂窝身份的了解增加 在正常发育过程中生长的轴突使用的线索应该有助于努力 了解神经肌肉疾病并促进特定的再生 指因疾病或受伤而受损的成人神经组织。

The normal functioning of an animal's limb depends on a highly ordered pattern of connections between motoneurons in the spinal cord and the various muscles of the limb. This pattern is established during development by specific axonal growth. Motoneuron axons normally make a series of pathway choices as they grow from the spinal cord to their target muscle. These choices require axons to recognize and respond appropriately to multiple growth cues associated with cells whose precise location and identity are presently unknown in any vertebrate. A combination of various surgical manipulations and several anatomical techniques will be used to localize and to identify the cell populations which provide the environmental cues to guide growing motor axons to their target muscles. All of the experiments will be done on chick or quail embryos. The first question is whether the cues for the two axes of the limb are separately located along the nerve pathways. Other experiments will determine whether the presence of muscle cells, the targets of motoneurons, are required for accurate pathfinding, or whether connective tissue cells are sufficient. The final series of experiments will explore the role of presumptive sheath cells, or Schwann cells, in assuring normal innervation of limb muscles. An increased knowledge of the location and cellular identity of guidance cues used by growing axons during normal development should aid efforts to understand neuromuscular disorders as well as to promote specific regrowth of adult nervous tissue following damage due either to disease or injury.