Role of Intraspinal Plasticity in Autonomic Dysreflexia

描述(由申请人提供)：自主神经反射障碍是脊髓损伤(SCI)的一种潜在的危及生命的并发症，其特征是由于受损脊髓中的交感神经元突然大量放电而导致发作性高血压(高血压)。交感神经元使个体能够做出“战斗或逃跑”的反应(例如，更多的血液流向肌肉)。交感神经元如此敏感的原因是，由于脊髓损伤，来自高级大脑中心的下行抑制通路被中断。在脊柱损伤患者中，自主神经反射障碍通常是由盆腔内脏(膀胱或肠道)的扩张或活动引起的。因此，膀胱或肠道的扩张通过感觉神经元将信号发送到骶髓(下背部)。从这里，信号通过中继神经元传递到胸腰交感神经元(脊髓的胸部区域)。因为没有来自高级大脑的调制影响，交感神经元的活动是不受对抗的。因此，在内脏刺激后，他们活动的突然增加会导致血压突然上升(高达200毫米汞)，这可能会导致潜在的致命脑或脊髓出血、癫痫发作，以及严重的头痛、颤抖、出汗和焦虑。不幸的是，对内脏感觉神经元、脊髓中继神经元和交感神经元之间的解剖或功能关系知之甚少。我们建议在一个明确的自主神经反射障碍大鼠模型中使用各种组织学和生理学技术来发现这三种类型的神经元之间的解剖联系，这三种类型的神经元对自主神经反射障碍的发展至关重要。目前尚不清楚进入腰骶段脊髓的内脏感觉信息如何传递到胸腰段脊髓中间外侧细胞柱(IML)的交感节前神经元。由于脊髓损伤后伤害性传入发芽依赖于NGF，并与自主神经反射障碍的发生率相关，我们将编码神经生长因子(NGFAdts)的温度敏感腺病毒(Adts)注射到胸、腰和骶髓以触发发芽，以确定哪些区域对引发自主神经反射障碍至关重要。仅在T13/L1和L6/S 1节段过表达的NGFAdts使结直肠扩张引起的动脉血压显著高于注射GFP Adts的损伤对照组。这表明，在脊髓横断后，盆腔内脏信息通过未知的投射路径从其在腰骶背角的输入部位传递到IML。这项提议有4个目标。首先，我们将利用L6/S 1脊髓生物素化葡聚糖胺顺行追踪和交感神经节伪狂犬病病毒逆行跨突触追踪的方法识别脊髓损伤后将内脏信息传递到胸髓的神经通路。其次，由于NGFAdts加剧了反射障碍，我们将确定这是否与增加的通路萌芽有关。第三，由于NGF非依赖性传入神经在自主神经反射障碍中可能起作用，我们将编码其他生长因子的Adts，如成纤维细胞生长因子-2、神经营养因子-3、脑源性神经营养因子和胶质细胞源性神经营养因子，注射到腰骶髓的多个水平。我们还将通过将它们注射到远端胸髓来评估它们对腰椎固有脊髓神经元的直接影响。最后，根据我们最近的证据，我们将在损伤后将化学斥力信号素3aAdts注射到腰骶脊髓，试图阻止早期发芽事件，最大限度地减少反射障碍，以及确定长期注射是否能够诱导已建立的发芽回缩。这些信息将为开发治疗这种常见的、使人衰弱的脊髓损伤并发症的潜在治疗方法奠定基础。

DESCRIPTION (provided by applicant): Autonomic dysreflexia is a potentially life-threatening complication of spinal cord injury (SCI) that is characterized by episodic hypertension (high blood pressure) due to sudden, massive discharge of the sympathetic neurons in the injured spinal cord. The sympathetic neurons enable the 'fight or flight' response of an individual (e.g. more blood flow to the muscles). The reason the sympathetic neurons are so sensitive is that descending inhibitory pathways from higher brain centers are interrupted as a result of the SCI. In spinal injured patients, autonomic dysreflexia is frequently triggered by distension of, or activity within pelvic viscera (bladder or bowel). Therefore, distension of the bladder or bowel sends a signal via sensory neurons to the sacral spinal cord (the lower back). From here, the signal is relayed to thoracic and lumbar sympathetic neurons (chest region of the cord) by relay neurons. Because there is no modulating influence from the higher brain, the action of the sympathetic neurons is unopposed. As a result, the sudden increase in their activity following visceral stimulation causes a sudden rise in blood pressure (up to 200 mmHg) that can cause potentially fatal brain or spinal hemorrhage, seizures, as well as severe headache, shivering, sweating and anxiety. Unfortunately, little is known about the anatomical or functional relationships between the visceral sensory neurons, the spinal relay neurons, and the sympathetic neurons. We propose to use a variety of histological and physiological techniques in a well-defined rat model of autonomic dysreflexia to discover the anatomical connections between these three types of neurons that are critical for the development of autonomic dysreflexia. It is currently not known how visceral sensory information entering the lumbosacral spinal cord is relayed to sympathetic preganglionic neurons in the intermediolateral cell column (IML) of the thoracolumbar cord. Since nociceptive afferent sprouting after SCI is NGF-dependent and is correlated with the incidence of autonomic dysreflexia, we have injected temperature sensitive adenoviruses (Adts) encoding nerve growth factor (NGFAdts) into thoracic, lumbar and sacral spinal cord to trigger sprouting to determine which regions are critical for eliciting autonomic dysreflexia. Overexpression of NGFAdts only in the T13/L1 and L6/S 1 segments produced significant increases in arterial blood pressure evoked by colorectal distension versus injured controls injected with GFPAdts. This suggests that following spinal transection, pelvic visceral information is relayed from its input site in the lumbosacral dorsal horn to the IML via unidentified projection pathways. This proposal has 4 goals. Firstly, we will use anterograde tracing of biotinylated dextran amine (BDA) from the L6/S 1 cord, and retrograde transsynaptic tracing of pseudorabies virus (PRV) from sympathetic pre-vertebral ganglia to identify the neural pathways that transmit visceral information from lumbosacral to thoracic cord after SCI. Secondly, since NGFAdts exacerbate dysreflexia, we will establish whether this correlates with increased pathway sprouting. Thirdly, since it is possible that NGF-independent afferents play a role in autonomic dysreflexia, we will inject Adts encoding other growth factors, FGF-2, NT-3, BDNF and GDNF, into multiple levels of the lumbosacral cord. We will also assess their direct influence on lumbar propriospinal neurons by injecting them in the distal thoracic cord. Finally, based on our recent evidence, we will inject chemorepulsive semaphorin3aAdts after injury into the lumbosacral spinal cord in an attempt to thwart early sprouting events and minimize dysreflexia, as well as establish whether chronic injections are capable of inducing retraction of established sprouts. This information will form the basis for developing potential treatments for this common and debilitating complication of SCI.