DEVELOPMENT OF SPECIFIC NEURONAL CONNECTIONS

解剖学实验被建议用来研究 用来建立、提炼和稳定最初的神经支配模式 小鸡的翅膀。这些实验的结果将提供额外的 有关细胞机制的基本信息 以及维持神经元和它们的目标之间的联系。这 信息可能对于理解开发过程 可能会因疾病、伤害或遗传缺陷而受到干扰。 提出了三套实验方案。第一，主要强调 将处于肌肉神经形成和孵化后之间的时期 消除多神经元神经支配。总体目标是 确定单个神经元的投射模式最初是如何形成的 并随后进行修改。初步实验表明， 轴突分支，包括一些侧支投射到两个 不同的神经。确定哪种神经元类型形成两种类型的实验- 提出了神经侧支及其随后丢失的机制。 在其他实验中，个体的末端前分支模式 运动轴突也将被特征化，以确定 单纤维投射，并确定前端分叉的时间 图案就会变得固定。这些方法包括标记特定的神经元。 不同染料的种群及其重构投影模式 使用光学显微镜。这些实验应该提供关于 初始投影模式的精化，以及关于过程的 参与建立细粒度地形投影 运动神经元连接到肌肉上。 另一组拟议的实验是研究一种 神经营养因子预防雏鸡胚胎运动神经元死亡 没有肌肉的翅膀。抢救被剥夺的目标所需的治疗方案 运动神经元将被确定。一项相关研究将确定 细胞死亡被因子给药永久阻止，或者细胞 死亡被推迟了。轴突分支和轴突分支之间的可能关系 神经元存活将通过表征前终末来研究。 无肌肉和因子治疗的无肌肉肢体的分支模式。 第三组实验将探索雪旺细胞在肢体中的作用 神经支配。鸡/鹌鹑嵌合体将被用于特定的盟友标签 沿周围神经通路的神经脊来源的雪旺细胞。 雪旺细胞沿周围神经的分布将是 在不同的发展阶段进行了研究，试图证实我们的 先前发现雪旺细胞聚集在肌神经分支 在周围神经形成的早期阶段。实验以确定 在缺乏的情况下，周围神经的形成是否被延迟或阻止 本文还提出了雪旺细胞的分类。

Anatomical experiments are proposed to study developmental processes which serve to establish, refine and stabilize the initial innervation pattern of the chick wing. The results of these experiments will provide additional basic information about the cellular mechanisms involved in establishing and maintaining connections between neurons and their targets. This information may be important for understanding how development processes may be disturbed as a result of disease, injury or genetic defects. Three sets of experiments are proposed. In the first, the major emphasis will be on the period between muscle nerve formation and the post-hatching elimination of polyneuronal innervation. The general objective is to determine how projection patterns of single neurons are initially formed and subsequently modified. Preliminary experiments have shown extensive axonal branching, including some collateral having projections to two different nerves. Experiments to determine what neuron types form two- nerve collaterals, and the mechanism of their subsequent loss are proposed. In other experiments, the pre-terminal branching patterns of individual motor axons will also be characterized to determine the spatial extent of single fiber projections, and to determine when the preterminal branching pattern becomes fixed. The methods involve labeling specific neuronal populations with different dyes and the reconstructing projection patterns using light microscopy. These experiments should provide information about the refinement of initial projection patterns, and about the processes involved in the establishment of the fine-grained topographic projections of motoneurons onto muscles. Another set of proposed experiments is to study the ability of a neurotrophic factor to prevent motoneuron death in chick embryos having one muscleless wing. The treatment regimens needed to rescue target deprived motoneurons will be determined. A related study will determine whether cell death is permanently blocked by factor administration, or whether cell death is delayed. A possible relationship between axon branching and neuron survival will be studied by characterizing the pre-terminal branching patterns in muscleless and factor-treated muscleless limbs. The third set of experiments will explore the role of Schwann cells in limb innervation. Chick/quail chimeras will be used to specific ally label neural crest-derived Schwann cells along the peripheral nerve pathways. The distribution of Schwann cells along the peripheral nerves, will be studied at different developmental stages in an attempt to confirm our previous finding that Schwann cells cluster at muscle nerve branching points early during peripheral nerve formation. Experiments to determine whether peripheral nerve formation is delayed or prevented in the absence of Schwann cells are also proposed.