Strategies to maximize the functional benefit of regenerated corticospinal tract axons

项目摘要 再生神经科学的一个主要努力是改善中枢神经损伤后轴突的生长 系统（CNS）。然而，一旦实现了增长，改善功能的第二个障碍是再生的 轴突必须成功地与适当的突触后神经元组形成突触接触。的挑战 恢复有效回路的障碍在脊髓损伤后尤为严重，脊髓损伤损害了皮质脊髓束（CST）， 精细运动控制的关键途径。CST通过与特定的神经元突触连接来介导下行运动控制 脊髓神经元的子集，在人类和啮齿动物中同样包括一组不同的中间神经元， 与灵长类动物特有的CST-运动神经元直接接触有关。该领域取得了越来越大的成功 在促进CST轴突生长，但在行为恢复方面的进展滞后。这项工作将解决需要 监测再生的CST轴突的连接，并优化其行为输出。为此，我们将 采用啮齿动物模型的脊髓损伤，并利用组合的干细胞桥接和病毒表达， 一个名为KLF 6的促再生基因，我们最近发现它能引起强大的再生CST生长。在 此外，我们将利用最近开发的跨突触病毒标记技术， 前所未有的可视化突触后目标选择的能力。首先，我们将呈现KLF 6表达式 可控和可逆，以便在再生发生后使KLF 6沉默，以便确定是否 KLF 6表达延长本身干扰行为恢复。这将解决以下紧迫问题： 在某种程度上，促再生生长机制可能是以牺牲有效的突触 细化或目标选择。接下来，我们将测试康复训练雕刻目标选择的能力， 再生CST并改善其行为输出。最后，我们将同时使用电和化学发生 意味着慢性提高再生CST轴突的活性，我们假设这将增强CST 发芽和提高竞争突触领土。这些互补的方法将创造最佳的 策略，以最大限度地提高行为的好处，可以从再生的CST轴突提取。

PROJECT SUMMARY A major effort in regenerative neuroscience is to improve axon growth after injury to the central nervous system (CNS). Once growth is achieved, however, a second hurdle to improving function is that regenerated axons must succeed in forming synaptic contacts with appropriate sets of post-synaptic neurons. The challenge of restoring effective circuitry is especially acute after spinal injuries that damage the corticospinal tract (CST), a pathway critical for fine motor control. The CST mediates descending motor control by synapsing on specific subsets of spinal neurons, which in humans and rodents alike include a diverse set of interneurons in addition to the direct CST-motor-neuron contacts that characterize primates. The field has achieved increasing success in promoting CST axon growth, yet gains in behavioral recovery have lagged. This work will address the need to monitor the connectivity of regenerated CST axons, and to optimize their behavioral output. To do so we will employ rodent models of spinal injury and capitalize on combined stem cell bridging and viral expression of a pro-regenerative gene called KLF6, which we recently found to evoke robust regenerative CST growth. In addition, we will leverage a recently developed trans-synaptic viral labeling technique that enables an unprecedented ability to visualize post-synaptic target selection. First, we will render KLF6 expression controllable and reversible, in order to silence KLF6 after regeneration occurs in order to determine whether prolonged KLF6 expression itself interferes with behavioral recovery. This will address the pressing question of the degree to which pro-regenerative growth mechanisms may come at the expense of effective synaptic refinement or target selection. Next, we will test the ability of rehabilitative training to sculpt target selection by regenerating CSTs and improve their behavioral output. Finally, we will employ both electrical and chemogenetic means to chronically elevate activity in regenerating CST axons, which we hypothesize will both enhance CST sprouting and improve competition for synaptic territory. These complementary approaches will create optimal strategies to maximize the behavioral benefit that can be extracted from regenerated CST axons.