DEVELOPMENT OF SPECIFIC NEURONAL CONNECTIONS

动物肢体的正常功能依赖于高度有序的 脊髓运动神经元和脊髓前角运动神经元之间的连接模式 四肢的各种肌肉。 这种模式是在 通过特殊的轴突生长发育。 运动神经元轴突通常会产生 当它们从脊髓生长到它们的目标时， 肌肉. 这些选择需要轴突识别并做出适当的反应 与细胞相关的多种生长线索， 身份在任何脊椎动物中是未知。 各种组合 手术操作和几种解剖技术将用于 定位并鉴定提供细胞的细胞群， 环境线索来引导运动轴突生长到目标肌肉。 所有的实验都将在鸡或鹌鹑胚胎上进行。 第一 问题是肢体的两个轴的线索是否分别 位于沿着神经通路。 其他实验将确定 肌肉细胞的存在，运动神经元的目标，是必需的， 准确的寻路，或者结缔组织细胞是否足够。 最后一系列的实验将探讨假定鞘的作用 细胞或雪旺氏细胞，以确保肢体肌肉的正常神经支配。 增加了对导航位置和蜂窝身份的了解 在正常发育过程中，轴突生长所使用的线索应该有助于 了解神经肌肉疾病以及促进特定的再生 成年人的神经组织由于疾病或受伤而受到损伤。

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.