DEVELOPMENTAL REGULATION OF NEURON NUMBER

成年神经元群体的大小是如何被调节的还不清楚。 尽管该信息与解释差异和/或 神经元种群大小的相似性是通过发育来影响的。 一种可能性是神经元群体与它们的 突触后靶点通过竞争连接，而神经元 细胞死亡消除了那些不成功的神经元。对于无尾两栖动物 尤其是两栖动物，尚不清楚神经元是否也是如此 自肢体大小起支配肢体的种群和运动神经元种群 在以下情况下，大小(即神经元数量)的相关性似乎很差 手术改变了正常的发育。拟议的研究将审查 大鼠腰椎外侧运动神经元数量的调节 非洲爪哇无尾两栖动物的三个类群：正常发育， 丙基硫氧嘧啶处理和三倍体。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 将测量运动神经元的数量(细胞数量和平均细胞大小) 来自六个发育阶段的个体。它们之间的相互关系 运动神经元的数量和肢体的这两个方面从来没有 以及细胞大小和细胞数量的变化 显然发生在这三种类型之间的X.laevis可以用来检测 大小匹配的想法解释了运动神经元数量的调节。这些 实验避免了与手术相关的特殊问题。如果这些 后肢的各个部位确实调节神经元的数量，然后是神经元 异常大小的种群很容易与发育事件有关 从而改变了四肢的这些特征。如果后肢大小的这些方面是 不调节运动神经元的数量，那么后肢的其他方面需要 将被识别并测试其角色，或其他神经元数量模式 需要对监管进行调查。确定任何发展中的 神经元数量的调节将使我们能够更好地理解 细胞死亡在产生适当大小的神经元中的意义 整个神经系统的种群。

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.