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，其特征是由于受伤脊髓中交感神经元突然大量放电而导致的发作性高血压（高血压）。交感神经元使个体的“战斗或逃跑”反应（例如，更多的血液流向肌肉）成为可能。交感神经元如此敏感的原因是，由于脊髓损伤，来自较高脑中枢的下行抑制通路被中断了。在脊柱损伤患者中，自主神经反射障碍常由盆腔脏器（膀胱或肠道）的扩张或活动引起。因此，膀胱或肠道的膨胀通过感觉神经元向骶脊髓（下背部）发送信号。从这里，信号通过传递神经元传递到胸、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节影响，交感神经元的活动是不对抗的。因此，在内脏刺激后，它们的活动突然增加，导致血压突然升高（高达200毫米汞柱），这可能导致致命的脑出血或脊髓出血、癫痫发作，以及严重的头痛、发抖、出汗和焦虑。不幸的是，对于内脏感觉神经元、脊髓接力神经元和交感神经元之间的解剖或功能关系知之甚少。我们建议在一个定义良好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学联系，这些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脊髓的内脏感觉信息是如何传递到胸腰束中外侧细胞柱（IML）的交感神经节前神经元的。由于脊髓损伤后的伤害性传入神经萌芽依赖于神经生长因子，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、腰椎和骶脊髓以触发发芽，以确定哪些区域对引发自主神经反射障碍至关重要。与注射GFPAdts的损伤对照组相比，仅在T13/L1和L6/ s1段过表达NGFAdts可显著增加结肠膨胀引起的动脉血压。这表明，在脊柱横断后，骨盆内脏信息通过未识别的投射途径从腰骶背角的输入部位传递到内底肌。该提案有4个目标。首先，我们将利用L6/ s1脊髓生物素化右糖酐胺（BDA）的顺行示踪，以及交感椎前神经节伪狂犬病病毒（PRV）的逆行跨突触示踪来确定脊髓损伤后内脏信息从腰骶到胸脊髓传递的神经通路。其次，由于NGFAdts加剧了反射障碍，我们将确定这是否与通路发芽增加相关。第三，由于ngf独立事件可能在自主神经反射障碍中发挥作用，我们将把编码其他生长因子（FGF-2、NT-3、BDNF和GDNF）的Adts注射到腰骶索的多个水平。我们还将通过在胸远端脊髓注射它们来评估它们对腰椎本体脊髓神经元的直接影响。最后，基于我们最近的证据，我们将在损伤后向腰骶脊髓注射化学排斥信号蛋白3aadts，以试图阻止早期发芽事件和最小化反射障碍，并确定慢性注射是否能够诱导已建立的芽缩回。这一信息将为开发这种常见的、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.