DEVELOPMENT OF SYNAPTIC INPUTS ON SPINAL INTERNEURONS

描述(申请人提供)：神经生物学的一个基本问题是，成熟的突触回路是如何在出生后从复杂的未分化突触和胚胎神经元阵列中出现的。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。我们的重点是脊髓运动回路的发展。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，以及激动剂和拮抗剂的共同收缩高于正常水平。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展的，我们知之甚少。成体中间神经元以特定的突触输入和输出为特征，在这些不同突触结构的发育过程中，遗传因素和环境影响之间的相互关系是一个尚未解决的主要问题。最近对脊髓中几种主要的胚胎中间神经元亚型的鉴定，由不同的遗传背景和表达这些群体谱系标记的转基因小鼠的产生，为研究成人型中间神经元及其突触输入的发育提供了可能性，这些中间神经元是由几组基因决定的“前身”胚胎中间神经元组成的。我们的长期目标是了解突触输入是如何在大量多样性的脊髓中间神经元上差异地选择和成熟的。我们建议研究来自胚胎中间神经元V1组的中间神经元上的成体突触组织的出现。使用在V1来源的中间神经元的胞体或轴突中表达LacZ或GAP43-EGFP的转基因小鼠，我们将能够跟踪它们从出生到成年的位置、结构和发育。我们的初步数据表明，V1来源的中间神经元产生了多个脊髓末级抑制中间神经元，其中包括Renshaw细胞和LA抑制中间神经元(LAIN)。有趣的是，每种细胞类型都有不同的兴奋性突触输入：谷氨酸/肌肉传入优先靶向LALN，而胆碱能/运动轴突触位于Renshaw细胞。我们假设这种独特的突触组织在出生后是稳定和成熟的，结果是V1中间神经元多样化成几个成体亚型。我们提出的具体目标如下：1)鉴定成年V1来源神经元的特征；2)研究每个突触输入到V1神经元亚群的正常发育，产生Renshaw细胞和LALN；3)研究这些输入的超微结构和分子成熟；4)测试肌肉传入中枢分支对不同神经元间表型规范的影响。

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.