Gastric dysreflexia after spinal cord injury

描述（由申请人提供）：脊髓损伤（SCI）最明显的后果是感觉和运动功能立即丧失。然而，绝大多数患者胃肠道（GI）功能严重受损，其中许多人胃动力严重抑制，需要肠内喂养。这些疾病的病理生理学仍不完全清楚，但在上一个资助期间收集的数据表明，从胃肠道到髓质孤束核（NTS）的迷走神经传入信号反应减弱。例如，SCI 导致 1) 餐后血清胆囊收缩素 (CCK) 表达减少； 2) 外周硫酸化 CCK (CCK-8s) 后 NTS 活化减弱； 3) 将 CCK-8 中央显微注射到 NTS 后，胃抑制作用减弱； 4) CCK-8s 浴后兴奋性突触后电流的体外全细胞记录减少。 NTS 神经元的一个亚类向迷走神经背运动核 (DMV) 的运动神经元提供强直抑制 (GABA) 输入，DMV 构成迷走神经胃肠道反射的迷走神经运动肢。 我们的新试验数据已发现与促胃肠道肽胃饥饿素类似的紊乱。我们假设 SCI 后肠脑轴内传入信号的减少可能会使 NTS-DMV 活性偏向于抑制性 GABA 能静息音。这种不受对抗的抑制信号可能是导致 SCI 后胃肠道运动障碍的机制之一。虽然临床对生长素释放肽的治疗潜力越来越感兴趣，但生长素释放肽模拟物用于 SCI 患者的治疗效果可能会降低。 在本提案中，我们将使用 T3-SCI 动物模型，结合体内生理（胃排空或蠕动和迷走神经）记录和分子（RT-PCR 和 ELISA）方法，旨在确定导致 SCI 后胃肠道功能丧失的机制。我们的总体假设是，脊髓损伤会减少迷走神经传入信号，并通过脑干迷走神经回路内不受调节的 GABA 信号传导引起胃动力障碍。 具体来说，我们将测试以下假设：1）胃脑干回路的迷走神经传入信号减少是由胃肠道肽释放减少介导的； 2) 胃脑干回路内突触前谷氨酸信号的减少是由迷走神经传入神经对胃肠肽的敏感性降低介导的； 3) 迷走神经传入和 NTS 神经元对进食相关肽的敏感性降低，使 GI 脑干回路偏向对 DMV 传出胃部流出的强直性 GABA 抑制。本提案产生的数据将提供关于减少 SCI 后胃肠道运动障碍的治疗策略的功效的新信息，从而改善消化过程的功能结果。该提案将为完善涵盖整个胃肠道长度的 SCI 后胃肠功能改变模型提供基础。最终这将有助于缓解 SCI 患者的胃肠道功能障碍。

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.