DEVELOPMENTAL REGULATION OF NEURON NUMBER

成年神经元群体的大小是如何调节的尚不清楚 尽管该信息与解释差异和/或 神经元数量大小的相似性是通过发育来实现的。 一种可能性是神经元群体与它们的神经元群体相匹配 通过竞争连接来实现突触后目标，并且神经元 细胞死亡消除了那些不成功的神经元。 对于蜮 特别是两栖动物，尚不清楚神经元是否如此 由于肢体大小和运动神经元群体而支配四肢的群体 大小（即神经元数量）在以下情况下似乎相关性很差： 手术改变了正常发育。 拟议的研究将检验 腰椎侧向运动柱运动神经元数量的调节 三类无尾两栖动物，非洲爪蟾：正常发育， 丙基硫氧嘧啶处理的和三倍体。 两个可能的运动神经元数 调节器（肌纤维数量和后肢肌肉体积）和大小 将测量运动神经元群体（细胞数量和平均细胞大小） 在六个发展阶段的个体中。 之间的相关性 运动神经元数量和肢体的这两个方面从未 已确定，并且细胞大小和细胞数量的变化 显然发生在这三种类型的 X. laevis 之间，可用于测试 大小匹配解释了运动神经元数量调节的想法。 这些 实验避免了与手术相关的特殊问题。 如果这些 后肢的各个方面确实调节神经元数量的大小，然后神经元 异常大小的种群很容易与发育事件相关 改变四肢的这些特征。 如果后肢尺寸的这些方面是 不调节运动神经元数量，那么后肢的其他方面需要 待识别并测试其作用，或神经元数量的其他模式 监管需要进行调查。 识别任何发育 神经元数量的调节器将有助于更好地理解 细胞死亡对于产生适当大小的神经元具有重要意义 整个神经系统的人群。

How the size of adult neuron populations is regulated is not understood although the information is relevant to explaining how differences and/or similarities in neuron population sizes are effected through development. One possibility is that neuron populations are matched to their postsynaptic targets through competition for connections, and that neuronal cell death eliminates those neurons that are unsuccessful. For anuran amphibians in particular, it is unclear that this is true for the neuron populations innervating the limbs since limb size and motoneuron population size (i.e., neuron number) appear to be poorly correlated in cases where surgery altered normal development. The proposed research will examine the regulation of motoneuron numbers in the lumbar lateral motor column in three groups of the anuran amphibian, Xenopus laevis: normally-developing, propylthiouracil-treated and triploids. Two likely motoneuron number regulators (muscle fiber number and hindlimb muscle volume) and the size of the motoneuron population (cell number and mean cell size) will be measured in individuals from six developmental stages. The correlations between motoneuron population size and these two aspects of the limb have never been determined, and the variations in cell size and cell number that apparently occur between these three types of X. laevis can be used to test the idea that a size match explains motoneuron number regulation. These experiments avoid particular problems associated with surgery. If these aspects of the hindlimb do regulate neuron population size, then neuron populations of abnormal size can readily be related to developmental events that change these features of limbs. If these aspects of hindlimb size are not regulating motoneuron numbers, then other aspects of the hindlimb need to be identified and their roles tested, or other modes of neuron number regulation need to be investigated. Identifying any developmental regulators of neuron numbers will allow a better understanding of the significance that cell death has in producing appropriately size neuron populations throughout the nervous system.