DEVELOPMENT OF SPECIFIC NEURONAL CONNECTIONS

解剖学实验被建议用来研究发育过程， 有助于建立，完善和稳定的初始神经支配模式， 小鸡翅膀 这些实验的结果将提供额外的 关于参与建立的细胞机制的基本信息 并维持神经元和它们的目标之间的连接。 这 信息对于理解开发过程 可能因疾病、损伤或遗传缺陷而受到干扰。 提出了三组实验。 第一，主要强调 将在肌神经形成和孵化后之间的时期 消除多神经元的神经支配。 总的目标是 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，包括一些具有两个突起的侧枝 不同的神经 实验来确定什么样的神经元类型形成两个- 神经侧支，其随后的损失的机制提出。 在其他实验中，个体的前末端分支模式 还将表征运动轴突以确定运动轴突的空间范围。 单纤维的预测，并确定何时前终端分支 模式变得固定。 这些方法包括标记特定的神经元 不同染料的群体和重建投影模式 使用光学显微镜。 这些实验应该提供关于 初始投影模式的细化，以及 参与建立精细地形投影 运动神经元到肌肉上。 另一组被提议的实验是研究一个人的能力。 神经营养因子预防具有运动神经元的鸡胚运动神经元死亡 没有肌肉的翅膀 拯救目标剥夺所需的治疗方案 将确定运动神经元。 一项相关研究将确定 细胞死亡被因子给药永久阻断，或者细胞 死亡被推迟了。 轴突分支和 神经元存活将通过表征前终末 无肌和因子治疗的无肌肢体的分支模式。 第三组实验将探索许旺细胞在肢体运动中的作用。 神经支配 鸡/鹌鹑嵌合体将用于特异性标记 沿着外周神经通路的神经嵴来源的雪旺细胞。 雪旺细胞沿着周围神经的分布，将是 在不同的发育阶段进行研究，试图证实我们的 先前的发现表明雪旺细胞聚集在肌肉神经分支处， 点在周围神经形成的早期。 实验以确定 周围神经的形成是否被延迟或阻止 许旺氏细胞也被提出。

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.