Molecular genetic dissection of the development and function of spinal somatosensory circuitry

了解功能是如何从发育中的神经网络中产生的，对于揭示成熟的大脑功能至关重要。为了解决这个问题，有必要在定义的功能网络中访问单个神经元群体的突触发育。体感系统和其中的神经元回路是研究回路形成和功能的一个很好的模型系统，它介导疼痛、瘙痒、温度、触觉和肢体/身体的相对位置的感觉。虽然在发育过程中很难解析，但相对而言，从物理上接近脊髓是比较容易的，而且目前有强大的遗传工具可以识别和操纵成熟神经系统中涉及的神经元。体感觉系统的中心是位于脊髓背角的感觉神经元，它们通过背根神经节（DRG）接收来自外周的信息，并将其传递给大脑。这些背侧中间神经元（dINs）亚群的许多早期特性，包括转录谱和迁移路线，已经被描绘出来。然而，脊髓感觉神经元如何整合到功能电路中，以及在成熟阶段，哪些亚群服务于每种体感觉功能，仍然知之甚少。造成这种情况的一个主要原因是，允许识别单个亚群的遗传标记在早期发育期间是短暂表达的，不能依赖于随着回路成熟而选择性识别组成神经元。该项目旨在开发一种方法，暂时扩展对特定dINs种群dI1的遗传访问，并允许使用最先进的跨突触病毒示踪剂，基因表达和活性修饰剂，识别和操纵从DRG到大脑的dI1特定电路。可视化dI1细胞与DRG神经元的特定功能类别之间的突触连接，识别这些神经元的中心靶点和轴突路线，并最终操纵它们的活动，将为脊髓体感回路的功能组织提供新的见解。此外，这项工作将实质性地为我们的疾病、神经性疼痛和脊髓损伤的治疗方法提供信息。

Understanding how function emerges from developing neuronal networks is critical for unraveling mature brain function. To address this question, it is essential to access the synaptic development of individual neuronal populations within defined functional networks. An excellent model system for studying circuit formation and function is the somatosensory system and the neuronal circuits within, which mediate the sensation of pain, itch, temperature, touch and relative limb/body position. The spinal cord is relatively easy to access physically and powerful genetic tools are available today to identify and manipulate involved neurons in the mature nervous system, although challenging to parse during development. Central to the somatosensory system are sensory neurons in the dorsal horn of the spinal cord that receive information from the periphery, via the dorsal root ganglia (DRG), and relay it to the brain. Many early properties of defined subpopulations of these dorsal interneurons (dINs), including transcriptional profiles and migratory routes, have been delineated. However, how spinal sensory neurons integrate into functional circuits and which subsets serve each somatosensory function in mature stages remain poorly understood. A major reason for this is that genetic markers permitting the identification of individual subpopulations are transiently expressed during early development and cannot be relied on for selective identification of component neurons as the circuitry matures. This project aims to develop methods that extend, temporally, genetic access to one specific population of dINs, the dI1s, and permit identification and manipulation of dI1 specific circuits from DRG to brain, using state of the art trans-synaptic viral tracers, gene expression and activity modifiers. Visualizing the synaptic connections between dI1 cells and specific functional classes of DRG neurons, identifying central targets and the axonal routes of these neurons, and eventually manipulating their activities, will provide novel insights into the functional organization of somatosensory circuits in the spinal cord.Moreover, this work will substantially inform our approaches to treatment in disease, neuropathic pain, and following spinal cord injury.