Gastric dysreflexia after spinal cord injury

描述(申请人提供)：脊髓损伤(SCI)最明显的后果是感觉和运动功能的即刻丧失。然而，胃肠道(GI)功能的戏剧性损害发生在绝大多数患者中，他们中的许多人胃动力严重受抑，需要肠内喂养。这些疾病的病理生理学机制尚不完全清楚，但在之前的资助期间收集的数据表明，从胃肠道到延髓孤束核(NTS)的迷走神经传入信号的反应性减弱。例如，脊髓损伤的结果是：1)餐后血清中CCK的表达减少；2)外周硫酸CCK(CCK-8S)后NTS的激活减少；3)向NTS内微量注射CCK-8S后胃抑制减弱；以及4)体外全细胞记录的兴奋性突触后电流减少。NTS神经元的一个亚类向迷走神经背侧运动核(DMV)的运动神经元提供紧张性抑制(GABA)输入，DMV构成迷走神经-迷走神经GI反射的迷走神经运动肢。我们新的试点数据已经确定了类似于促动力GI肽Ghrelin的错配。我们推测，脊髓损伤后肠道-脑轴内传入信号的减少可能使NTS-DMV的活性偏向于抑制性GABA能静息音调。这种非相反的抑制信号可能是导致脊髓损伤后胃肠动力障碍的机制之一。虽然临床对Ghrelin治疗潜力的兴趣正在显现，但Ghrelin模拟物用于脊髓损伤患者的治疗效果可能会减弱。在目前的方案中，我们将使用T3-SCI动物模型，结合体内生理(胃排空或运动和迷走神经)记录和分子(RT-PCR和ELISA法)方法，目的是确定导致SCI后GI功能丧失的机制。我们的主要假设是，脊髓损伤减少了迷走神经传入信号，并通过脑干迷走神经回路中未调节的GABA能信号引起胃运动障碍。具体地说，我们将测试假设1)迷走神经传入信号减少到胃脑干回路是通过减少GI肽释放介导的；2)胃脑干回路内突触前谷氨酸能信号的减少是通过迷走神经传入对GI肽的敏感性降低介导的；3)迷走神经传入和NTS神经元对与喂养相关的肽的敏感性降低使GI脑干电路偏向强直的GABA能抑制DMV传出到胃的流出。本提案产生的数据将为减少脊髓损伤后胃肠动力障碍的治疗策略的有效性提供新的信息，从而改善消化过程的功能结果。这项建议将为完善脊髓损伤后胃肠功能改变的模型提供基础，该模型涵盖整个胃肠道长度。最终，这将有助于缓解脊髓损伤患者的胃肠道功能障碍。 公共卫生相关性：胃肠道传输延迟是脊髓损伤后的一种常见疾病。这项研究将有助于确定脊髓损伤后神经系统对消化信号处理的变化。这一认识对于开发胃肠动力障碍的有效治疗方法是必要的。

DESCRIPTION (provided by applicant): The most apparent consequence of spinal cord injury (SCI) is the immediate loss of sensation and motor function. However, a dramatic impairment of the functionality of the gastrointestinal (GI) tract occurs in the vast majority of the patients, many of whom have a severely depressed gastric motility that necessitates enteral feeding. The pathophysiology of these disorders remains incompletely understood, but data gathered during the previous funding period point toward diminished responsiveness of vagal afferent signaling from the GI tract to the nucleus tractus solitarius (NTS) in the medulla. For example, SCI results in 1) diminished postprandial serum expression of cholecystokinin (CCK); 2) diminished NTS activation following peripheral sulfated CCK (CCK-8s); 3) diminished gastroinhibition following central microinjection of CCK-8s into the NTS; and 4) diminished in vitro, whole cell recordings of excitatory post-synaptic currents following bath application of CCK-8s. A subclass of NTS neurons provide a tonic inhibitory (GABA) input onto motoneurones of the dorsal motor nucleus of the vagus (DMV), which composes the vagal motor limb of vago-vagal GI reflexes. Our novel pilot data have identified similar derangements to the prokinetic GI peptide, ghrelin. We hypothesize that a post-SCI reduction in afferent signaling within the gut-brain axis may bias NTS-DMV activity in favor of an inhibitory GABAergic resting tone. This unopposed inhibitory signal may be one mechanism leading to GI dysmotility following SCI. While clinical interest in the therapeutic potential of ghrelin is emerging, the therapeutic efficacy of ghrelin mimetics may be diminished for use in SCI patients. In the present proposal we will use an animal model of T3-SCI combined with in vivo physiological (gastric emptying or motility and vagus nerve) recording, and molecular (RT-PCR and ELISA) approaches with the aim of defining the mechanisms resulting in the loss of GI function after SCI. Our overarching hypothesis is that spinal cord injury reduces vagal afferent signaling and provokes gastric dysmotility through unregulated GABAergic signaling within brainstem vagal circuits. Specifically we will test the hypotheses that 1) reduced vagal afferent signaling to gastric brainstem circuits is mediated by diminished GI peptide release; 2) reduced presynaptic glutamatergic signaling within gastric brainstem circuits is mediated by reduced sensitivity of vagal afferents to GI peptides; 3) reduced vagal afferent and NTS neuronal sensitivity to feeding-related peptides biases GI brainstem circuits toward a tonic GABAergic inhibition of DMV efferent outflow to the stomach. The data generated by the present proposal will provide novel information regarding the efficacy of therapeutic strategies to reduce GI dysmotility following SCI, thereby improving functional outcome of digestive processes. This proposal will provide the basis to refine a model of post-SCI alterations in gastrointestinal function that encompasses the entire length of the GI tract. Ultimately this will help alleviate GI dysfunctions in SCI patients. PUBLIC HEALTH RELEVANCE: Delayed gastrointestinal transit is a common disorder following spinal cord injury. This study will help identify changes in the nervous system processing of digestive signals following spinal cord injury. This understanding is necessary in order to develop effective therapeutic treatment of gastrointestinal motility disorders.