Post-SCI effects of BDNF and epidural stimulation on inhibitory RORb interneurons

摘要 患有脊髓损伤(SCI)的人数持续上升，但康复策略 功能性运动恢复仍不充分。脊髓回路保持完好和功能，即使在 缺乏降压控制，可作为治疗靶点。神经营养因子已被证明可以 增强脑源性神经营养因子(AAV-1)的神经可塑性和实验性病毒过表达 脑源性神经营养因子)足以激活运动回路，以在完成后诱发后肢交替的足底踏步 啮齿动物的脊髓损伤。然而，病毒的BDNF效应也会导致反射亢进和后肢痉挛。次级马达 硬膜外阈值刺激(ES)可减少脊髓损伤患者的反射亢进，但其机制 这种效应背后的行动仍然难以捉摸。我们最近将病毒BDNF治疗与日常ES结合在一起 一种完全性脊髓损伤的小鼠模型，以确定这两者之间的协同效应 治疗策略和我们的初步发现表明ES可能在减轻BDNF诱导的作用中发挥作用 反射亢进，同时保持运动能力的改善。除了慢性残疾外，还有大量的 患有脊髓损伤的人也患有反射亢进，我们的方法允许探索治疗和 机械装置并联。脊髓中间神经元是损伤水平以下抑制控制的主要来源， 我们将使用精确的生理学和遗传学方法来识别具有可塑性的神经成分 在脊髓损伤和随后的病毒性脑源性神经营养因子干预后，伴或不伴ES。在本提案中，我们将重点放在 表达视黄醇孤儿核受体(RORB)的抑制性中间神经元(INS)群 最近被证明通过初级传入去极化(PAD)来选通低阈值感觉传入信号 突触前抑制的脊髓机制。Rorb INS可能会受到我们的组合方法的影响，因为 它们表达BDNF的同源受体TrkB受体，并在本体感觉激活时被招募 纤维，低强度ES的潜在效应神经元。我们的中心假设是：1)BDNF增加了 Rorb INS的细胞兴奋性和增强PAD途径的活性，但这不足以抵消其他 脑源性神经营养因子的作用导致反射亢进，2)ROBB介导的PAD通路在 并发ES以限制BDNF诱导的反射亢进并促进术后后肢踏步的改善 完全的SCI。我们将研究Rorb INS在突触前抑制回路中兴奋性的变化， 与行为学一起确定脊髓损伤的影响以及BDNF单独和联合治疗的效果 埃斯。这一建议将提供对脊髓损伤诱导的可塑性的机械性洞察，并确定治疗相互作用。 与功能性运动恢复以及潜在的功能丧失有关，这两者都将 有益于康复努力，以解决超出运动障碍的顽固性神经障碍。

ABSTRACT The number of individuals living with a spinal cord injury (SCI) continues to rise but rehabilitative strategies for functional locomotor recovery remain inadequate. Spinal circuits remain intact and functional even in the absence of descending control and serve as therapeutic targets. Neurotrophic factors have been shown to enhance neuronal plasticity and experimental viral overexpression of brain-derived neurotrophic factor (AAV- BDNF) is sufficient activate locomotor circuits to elicit alternating plantar stepping of hindlimbs after complete SCI in rodents. However, viral BDNF effects also induce a hyperreflexive state and hindlimb spasms. Sub-motor threshold epidural stimulation (ES) can reduce hyperreflexia in individuals living with SCI but the mechanism of action underlying this effect remains elusive. We have recently combined viral BDNF treatment with daily ES in a mouse model of complete SCI to identify synergistic effects between these two potentially complementary therapeutic strategies and our preliminary findings suggest a possible role for ES in mitigating BDNF-induced hyperreflexia while maintaining locomotor improvements. In addition to chronic disability, a large number of individuals living with SCI also suffer from hyperreflexia and our approach allows for exploration of treatment and mechanism in parallel. Spinal interneurons are the primary source of inhibitory control below the level of injury, and we will use precise physiological and genetic methods to identify the neural components subject to plasticity after SCI and subsequent intervention with viral BDNF, with or without ES. In this proposal, we focus on a population of inhibitory interneurons (INs) expressing the retinoid orphan nuclear receptor (RORb) which has recently been shown to gate low threshold sensory afferent signals via primary afferent depolarization (PAD), a spinal mechanism of presynaptic inhibition. RORb INs are likely to be affected by our combinatorial approach as they express TrkB receptors, the cognate receptor for BDNF, and are recruited upon activation of proprioceptive fibers, potential effector neurons of low intensity ES. Our central hypotheses are that: 1) BDNF increases the cellular excitability of RORb INs and enhances PAD pathway activity but this is insufficient to counteract other actions of BDNF leading to hyperreflexia, 2) the RORb-mediated PAD pathway is acutely enhanced during concurrent ES to limit BDNF-induced hyperreflexia and promote improvements in hindlimb stepping after complete SCI. We will investigate changes in the excitability of RORb INs at the presynaptic inhibitory circuit, together with behavior to determine the effects of SCI and treatment with BDNF alone and in combination with ES. This proposal will provide mechanistic insight into SCI-induced plasticity and identify therapeutic interactions that are associated with functional motor recovery as well as those underlying loss of function, both of which will benefit rehabilitative efforts to address intractable neurological disorders that extend beyond locomotor disability.