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

了解发育中的神经元网络是如何产生功能的，对于解开成熟的大脑功能至关重要。为了解决这个问题，必须了解特定功能网络中单个神经元群体的突触发育情况。一个很好的研究回路形成和功能的模型系统是躯体感觉系统和其中的神经元回路，它们调节疼痛、瘙痒、温度、触摸和相对肢体/身体位置的感觉。脊髓在物理上相对容易接近，目前已有强大的基因工具可用于识别和操纵成熟神经系统中涉及的神经元，尽管在发育过程中解析具有挑战性。躯体感觉系统的中心是脊髓背角的感觉神经元，它们通过背根神经节(DRG)接收来自外围的信息，并将信息传递给大脑。这些背侧中间神经元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回路中，以及在成熟阶段哪些亚群服务于每一种体感功能仍然知之甚少。这其中的一个主要原因是，允许识别单个亚群的遗传标记在早期发育期间瞬时表达，不能随着电路的成熟而被依赖于选择性地识别组成神经元。该项目旨在开发一种方法，利用最先进的跨突触病毒示踪物、基因表达和活性调节剂，在时间上将遗传通路扩展到特定的dIn群体，即dI1s，并允许识别和操纵从DRG到大脑的dI1特异性电路。可视化dI1细胞和特定功能类别的DRG神经元之间的突触联系，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，这项工作将为我们在疾病、神经性疼痛和脊髓损伤后的治疗方法提供实质性的信息。

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.