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

摘要 脊髓损伤（SCI）患者的数量持续上升，但 功能性运动恢复仍然不足。脊髓回路保持完整和功能，即使在 缺乏下行控制并作为治疗靶点。神经营养因子已被证明 增强神经元可塑性和脑源性神经营养因子（AAV-1）的实验性病毒过表达， 脑源性神经营养因子（BDNF）足以激活运动回路，以在完成后引起后肢的交替足底踏步 啮齿类动物中的SCI。然而，病毒性BDNF的作用也会引起过度反射状态和后肢痉挛。子电机 阈值硬膜外刺激（ES）可以减少SCI患者的反射亢进，但 这种影响背后的行动仍然难以捉摸。我们最近将病毒性BDNF治疗与每日ES相结合， 完全SCI的小鼠模型，以确定这两种潜在互补之间的协同作用 治疗策略和我们的初步研究结果表明，ES在减轻BDNF诱导的 反射亢进同时保持运动能力的提高。除了慢性残疾之外， SCI患者也患有反射亢进，我们的方法允许探索治疗方法， 机制并行。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可塑性神经成分 在SCI和随后的病毒性BDNF干预后，有或没有ES。在本建议中，我们重点关注一个 一群抑制性中间神经元（IN）表达类维生素A孤儿核受体（RORb）， 最近被证明通过初级传入去极化（PAD）门控低阈值感觉传入信号， 突触前抑制的脊髓机制。RORb IN可能会受到我们的组合方法的影响， 它们表达TrkB受体，BDNF的同源受体，并在本体感受神经元激活后被招募。 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 IN的细胞兴奋性，并增强PAD途径活性，但这不足以抵消其他 BDNF的作用导致反射亢进，2）RORb介导的PAD通路在 同时ES限制BDNF诱导的反射亢进，并促进后肢步行的改善， 完整SCI我们将研究突触前抑制回路中RORb INs兴奋性的变化， 与行为一起确定SCI和单独用BDNF治疗以及与 ES.这项提议将提供SCI诱导的可塑性机制的见解，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，两者都将 有益于康复工作，以解决超出运动障碍的顽固性神经系统疾病。

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.