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，对中间神经元的成熟知之甚少，尽管它们对神经回路的形成、功能和功能障碍很重要。我们专注于脊髓运动回路的开发。新生儿表现出不成熟的脊髓运动回路，表现为反射异常，进行有效姿势调整的能力有限，激动剂和拮抗剂的共同收缩高于正常。对于负责正常运动活动成熟的脊髓神经元间回路是如何发育的知之甚少。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环境的影响，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代转基因小鼠表达这些人群的谱系标记的表征，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”胚胎interneuron。我们的长期目标是了解突触输入是如何在多样性的脊髓中间神经元上进行差异选择和成熟的。我们建议调查的出现成人突触组织的中间神经元来自V1组的胚胎中间神经元。使用转基因小鼠表达lacZ或GAP 43-EGFP的索马或轴突的V1-衍生的中间神经元，我们将能够遵循他们的位置，结构和发展从出生到成年。我们的初步数据表明，V1衍生的中间神经元产生了几个脊髓末级抑制性中间神经元，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，这种独特的突触组织是稳定和成熟的出生后，因此V1-interneurons多样化成几个成年亚型。我们提出了以下具体目标：1）识别成人V1-衍生神经元的特征，2）研究每个突触输入到V1-神经元亚群的正常发育，从而产生Renshaw细胞和lalNs，3）研究这些输入的超微结构和分子成熟，以及4）测试肌肉传入中枢分支在不同神经元间表型的特化中的影响。

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 importance for neural circuit formation, function and dysfunction. Our focus in on the development of spinal cord motor circuits. Newborns display immature spinal motor circuits manifest in abnormal reflexes, limited capacity to make effective postural adjustments and higher than normal co-contraction of agonists and antagonists. Little is known about how the spinal interneuronal circuits responsible for the maturation of normal locomotor activity develop. Adult interneurons are characterized by specific synaptic inputs and outputs and a major unresolved question is the interrelationship between genetic factors and environmental influences 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 generation 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" embryonic interneurons. Our long-term objective is to understand how synaptic inputs are differentially selected and mature on the large diversity of spinal interneurons. We propose to investigate the emergence of adult synaptic organization on interneurons derived from the V1 group of embryonic interneurons. Using transgenic mice that express either lacZ or GAP43-EGFP in the soma or axons of V1- derived interneurons we will be able to follow their location, structure and development from birth to adulthood. Our preliminary data suggests that V1-derived interneurons give rise to several spinal cord last-order inhibitory interneurons, 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 organization is stabilized and matured postnatally and as a consequence V1- interneurons diversify into several adult subtypes. We propose the following specific aims 1) identify the characteristics of adult V1-derived neurons, 2) study the normal development of each synaptic input onto V1-neuron subgroups giving rise to Renshaw cells and lalNs, 3) study the ultrastructural and molecular maturation of these inputs, and 4) test the influence of muscle afferent central arborizations in the specification of different interneuronal phenotypes.