DEVELOPMENT OF SYNAPTIC INPUTS ON SPINAL INTERNEURONS

描述（申请人提供）：神经生物学中的一个基本问题是成熟的突触回路如何在出生后从未分化的突触和胚胎神经元的复杂阵列中出现。特别是，很少有人知道中间神经元的成熟，尽管他们的神经回路的形成，功能和功能障碍的重要性。成人interneurons的特点是特定的突触输入和输出和一个主要的未解决的问题是遗传因素和活动依赖的机制，在这些不同的突触结构的发展之间的相互关系。最近的几个主要的胚胎interneuron亚型在脊髓中，定义不同的遗传背景和发展的转基因小鼠表达这些人群的谱系标志物的表征，打开了研究成人型interneuron和他们的突触输入的发展的可能性，从几组遗传确定的“前身”interneuron在胚胎中产生。我们的长期目标是了解突触输入是如何在形成脊髓运动突触回路的大量多样性的脊髓中间神经元上进行差异选择和成熟的。这种突触网络的功能障碍，包括其发育的错误，导致成年人和新生儿的运动异常。许多这些综合征的病因目前尚不清楚。我们建议调查成人突触组织的出现，来自胚胎中间神经元的一个亚类，V1组的中间神经元。使用在VI衍生的中间神经元的索马或轴突中表达lacZ或GAP 43-EGFP的转基因小鼠，我们将能够从出生到成年跟踪它们的位置、结构和发育。我们的初步数据表明，VI衍生的中间神经元产生几个成年脊髓lastorder抑制性中间神经元，其中包括Renshaw细胞和la抑制性中间神经元（laIN）。有趣的是，每种细胞类型的特征在于不同的兴奋性突触输入：胆碱能/肌肉传入优先靶向lalN，而胆碱能/运动轴突在Renshaw细胞上突触。我们假设，这种独特的突触结构是稳定和成熟的出生后超过V1的遗传背景，通过活动依赖性机制，因此V1- interneurons多样化成几个成年亚型。为了检验该假设，我们提出1）鉴定成人V1-衍生神经元的特征，2）研究每个突触输入到V1-神经元亚群上的正常发育，产生Renshaw细胞和IaLN，3）研究两种输入的超微结构和分子成熟，和4）测试在出生后发育期间实验性地偏置神经元能传递或胆碱能运动轴突活性对V1的影响。神经元间突触组织我们还将研究可能有助于这些过程的V1- interneurons的神经营养因子和trk受体的表达的时间模式。

DESCRIPTION (provided by applicant): A fundamental problem in neurobiology is how mature synaptic circuits emerge postnatally from a complex array of undifferentiated synapses and embryonic neurons. In particular, little is known about the maturation of interneurons, despite their great importance for neural circuit formation, function and dysfunction. Adult interneurons are characterized by specific synaptic inputs and outputs and a major unresolved question is the interrelationship between genetic factors and activity dependent mechanisms in the development of these different synaptic architectures. The recent characterization of a few cardinal embryonic interneuron subtypes in the spinal cord, defined by different genetic backgrounds and the development of transgenic mice expressing lineage markers for these populations, opens the possibility of investigating the development of adult-type interneurons and their synaptic inputs, from a few groups of genetically determined "predecessor" interneurons generated in embryo. Our long-term objective is to understand how synaptic inputs are differentially selected and mature on the large diversity of spinal interneurons that form the spinal cord motor synaptic circuits. Dysfunction of this synaptic network, including errors in its development, leads to motor abnormalities in adults and newborns. The etiologies of many of these syndromes are currently unknown. We propose to investigate the emergence of adult synaptic organization on interneurons derived from one subclass of embryonic interneurons, the V1 group. Using transgenic mice that express either lacZ or GAP43-EGFP in the soma or axons of Vl-derived interneurons we will be able to follow their location, structure and development from birth to adulthood. Our preliminary data suggests that Vl-derived interneurons give rise to several adult spinal cord lastorder inhibitory interneurons and, among others, Renshaw cells and la Inhibitory Interneurons (laIN). Interestingly each cell type is characterized by different excitatory synaptic inputs: glutamatergic/muscle afferents preferentially target lalNs while cholinergic/motor axons synapse on Renshaw cells. We hypothesize that this distinctive synaptic structure is stabilized and matured postnatally over the V1 genetic background through activity-dependent mechanisms, and as a consequence V1- interneurons diversify into several adult subtypes. To test the hypothesis we propose to 1) identify the characteristics of adult Vl-derived neurons, 2) study the normal development of each synaptic input onto Vl-neuron subgroups giving rise to Renshaw cells and lalNs, 3) study the ultrastructural and molecular maturation of both inputs, and 4) test the effect of experimentally biasing either glutamatergic transmission or cholinergic motor axon activity during postnatal development on Vl-interneuron synaptic organization. We will also examine temporal patterns of expression of neurotrophins and trk receptors in V1- interneurons that could contribute to these processes.