A Flexible Circuit Design that Restores Locomotion after Injury

包括人类在内的哺乳动物受伤后恢复运动的一个巨大障碍是，启动和调节下游脊髓回路所需的下行脑输入无法在受损的脊髓上再生。不幸的是，从生物学上“欺骗”神经元与前目标重新连接的方法收效甚微。是否有其他方法可以激活损伤部位下方的运动脊髓回路？我们对药用水蛭的最新实验表明，在爬行行为的伸长和缩短阶段激活的拉伸敏感神经元的重塑可能是理解运动回路如何再次开启并促进协调运动的关键。我们的工作提供了一个罕见而独特的机会来探索一种新的基于感觉的电路设计如何取代基于中央的运动启动和协调的控制系统。重要的是，随着时间的推移，我们可以检查同一个体中这种转换的细胞基础。这种设计上的灵活性对于创造运动机器人系统，尤其是那些像水蛭一样的软体机器人系统，具有重要的影响。我们的研究是高度跨学科的，将涉及使用创新的分子和解剖学方法来理解神经元的可塑性；我们的目标还包括让全球的公民科学家和其他志愿者参与我们的研究。PI和Co-PI将继续在实验室中为女性、第一代大学生和代表性不足的科学家提供支持，并通过各自的科学组织制定新的包容性和多样性倡议。我们的跨学科团队将探索药用水蛭中新颖的神经回路是如何在神经索和大脑分离后出现并协调运动恢复的。当大脑神经元R3b-1的下行输入被移除时，爬行完全消失，但在大约2周后令人惊讶地恢复。我们的目标是研究导致这种恢复爬行的潜在电路设计。爬行恢复的关键是分布在每个体壁段的本体感觉拉伸受体（SRs）。这些本体感受器虽然本身没有受伤，但会产生新的位于中心（和节段间）的输出分支，这些分支预计会针对爬行相关的回路，特别是在神经索损伤部位正下方的“先导”神经节。我们将使用电生理记录，电压敏感染料成像和电子显微镜来询问铅神经节和SRs在建立爬行恢复中的作用。为了研究导联神经节和邻近神经节以及SR神经元中基因表达的变化，我们将使用空间转录组学，通过这种方法，全基因组表达分析将被映射回特定神经节和SR过程中从组织学切片获得的精确位置。我们的方法和仪器，在我们各自的机构，将允许mRNA分子在体细胞，神经元过程（内在和外在）和突触终端的亚细胞定位。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A huge barrier for restoring locomotion after injury in mammals, including humans, is that the descending brain inputs needed to initiate and regulate downstream spinal circuits are unable to regrow across the damaged spinal cord. Unfortunately, biologically ‘tricking’ neurons to reconnect with former targets has been met with limited success. Might there be another way of activating locomotor spinal circuitry below the site of injury? Our newest experiments in the medicinal leech indicate that the remodeling of the stretch-sensitive neurons, activated during the elongation and shortening phases of crawling behavior, are likely key to the understanding of how locomotor circuits are once again turned on and contribute to coordinated locomotion. Our work provides a rare and unique opportunity to explore how a novel sensory-based circuit design replaces a centrally-based governing system for the initiation and coordination of locomotion. Importantly, we can examine the cellular basis of this switch in the same individuals over time. This flexibility in design should have significant ramifications for the creation of locomoting robotic systems, especially those that are soft-bodied like the leech. Our research is highly interdisciplinary and will involve the use of innovative molecular and anatomical approaches to understanding neuronal plasticity; we also aim to include citizen-scientists and other volunteers around the globe in our research. The PI and Co-PI will continue to develop ways to support women, first-generation college students, and underrepresented scientists in their labs, and through the development of new inclusion and diversity initiatives through their respective scientific organizations.Our interdisciplinary team will explore how novel neural circuits, in the medicinal leech, emerge and orchestrate a recovery of locomotion after the nerve cord and brain become separated. When descending inputs from the brain neuron R3b-1 are removed, crawling is completely lost, yet surprisingly returns after about 2 weeks. Our goal is to study the underlying circuit design that accounts for this restored crawling. Key to crawl recovery are the proprioceptive stretch receptors (SRs) that pepper each body-wall segment. These proprioceptors, although not injured themselves, sprout new centrally-located (and intersegmental) output branches that are predicted to target crawl-related circuitry, especially in the ‘lead’ ganglion directly below the site of nerve cord injury. We will use electrophysiological recording, voltage-sensitive dye imaging, and electron microscopy to interrogate the role of the lead ganglion and SRs in establishing crawl recovery. To study changes in gene expression across neurons in the lead and adjacent ganglia, and in the SRs, we will use spatial transcriptomics, whereby genome-wide expression analysis will be mapped back to precise locations in specific ganglia and SR processes obtained from histological sections. Our methods and instrumentation, at our respective institutions, will allow for subcellular localization of mRNA molecules in somata, neuronal processes (intrinsic and extrinsic), and synaptic terminals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.