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的立即丧失。然而，胃肠道功能的严重损害发生在绝大多数患者中，其中许多患者胃运动严重抑制，需要肠内喂养。这些疾病的病理生理学仍不完全清楚，但在之前的资助期间收集的数据表明，迷走神经传入信号从胃肠道到髓质的孤束核（NTS）的反应性减弱。例如，脊髓损伤导致1)餐后血清中胆囊收缩素（CCK）表达降低；2)外周硫酸化CCK （CCK-8s）后NTS激活减弱；3)中枢微量注射CCK-8s后胃抑制减弱；4)体外，CCK-8s浸泡后突触后兴奋性电流的全细胞记录减少。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性抑制（GABA）输入，后者构成迷走-迷走神经GI反射的迷走运动肢体。我们的新试点数据已经确定了类似的紊乱，促胃肠肽，饥饿素。我们假设脊髓损伤后肠-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能静息张力。这种非对抗抑制信号可能是脊髓损伤后导致胃肠道运动障碍的机制之一。虽然临床对胃饥饿素治疗潜力的兴趣正在出现，但在脊髓损伤患者中使用胃饥饿素模拟物的治疗效果可能会降低。在本研究中，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）方法，旨在确定导致SCI后GI功能丧失的机制。我们的主要假设是脊髓损伤减少迷走神经传入信号，并通过脑干迷走神经回路中不受调节的gaba能信号引起胃运动障碍。具体来说，我们将测试以下假设：1)迷走神经传入信号减少是由胃肠道肽释放减少介导的；2)胃脑干回路突触前谷氨酸能信号的减少是由迷走神经传入神经对GI肽的敏感性降低介导的；迷走神经传入和NTS神经元对摄食相关肽的敏感性降低，使GI脑干回路倾向于对DMV向胃输出的进行性gaba能抑制。本提案产生的数据将为减少脊髓损伤后胃肠道运动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。该建议将为完善包括整个胃肠道长度的脊髓损伤后胃肠道功能改变模型提供基础。最终，这将有助于减轻脊髓损伤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.