Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America; Department of Health Sciences, Gettysburg College, Gettysburg, PA 17325, United States of America.
Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America.
Exp Neurol. 2020 Jan;323:113092. doi: 10.1016/j.expneurol.2019.113092. Epub 2019 Nov 5.
Dramatic impairment of gastrointestinal (GI) function accompanies high-thoracic spinal cord injury (T3-SCI). The vagus nerve contains mechano- and chemosensory fibers as well as the motor fibers necessary for the central nervous system (CNS) control of GI reflexes. Cell bodies for the vagal afferent fibers are located within the nodose gangla (NG) and the majority of vagal afferent axons are unmyelinated C fibers that are sensitive to capsaicin through activation of transient receptor potential vanilloid-1 (TRPV1) channels. Vagal afferent fibers also express receptors for GI hormones, including cholecystokinin (CCK). Previously, T3-SCI provokes a transient GI inflammatory response as well as a reduction of both gastric emptying and centrally-mediated vagal responses to GI peptides, including CCK. TRPV1 channels and CCK-A receptors (CCKar) expressed in vagal afferents are upregulated in models of visceral inflammation. The present study investigated whether T3-SCI attenuates peripheral vagal afferent sensitivity through plasticity of TRPV1 and CCK receptors. Vagal afferent response to graded mechanical stimulation of the stomach was significantly attenuated by T3-SCI at 3-day and 3-week recovery. Immunocytochemical labeling for CCKar and TRPV1 demonstrated expression on dissociated gastric-projecting NG neurons. Quantitative assessment of mRNA expression by qRT-PCR revealed significant elevation of CCKar and TRPV1 in the whole NG following T3-SCI in 3-day recovery, but levels returned to normal after 3-weeks. Three days after injury, systemic administration of CCK-8 s showed a significantly diminished gastric vagal afferent response in T3-SCI rats compared to control rats while systemic capsaicin infusion revealed a significant elevation of vagal response in T3-SCI vs control rats. These findings demonstrate that T3-SCI provokes peripheral remodeling and prolonged alterations in the response of vagal afferent fibers to the physiological signals associated with digestion.
高位胸段脊髓损伤(T3-SCI)会显著影响胃肠道(GI)功能。迷走神经包含机械和化学感觉纤维以及运动纤维,这些纤维是中枢神经系统(CNS)控制 GI 反射所必需的。迷走神经传入纤维的细胞体位于结状神经节(NG)内,大多数迷走神经传入轴突是无髓 C 纤维,通过激活瞬时受体电位香草酸 1(TRPV1)通道对辣椒素敏感。迷走神经传入纤维还表达胃肠道激素的受体,包括胆囊收缩素(CCK)。先前的研究表明,T3-SCI 会引发短暂的 GI 炎症反应,以及胃排空和中枢介导的对包括 CCK 在内的 GI 肽的迷走神经反应的减少。在内脏炎症模型中,迷走神经传入纤维中表达的 TRPV1 通道和 CCK-A 受体(CCKar)会被上调。本研究旨在探讨 T3-SCI 是否通过 TRPV1 和 CCK 受体的可塑性来减弱外周迷走神经传入的敏感性。T3-SCI 会显著减弱 3 天和 3 周恢复期时胃分级机械刺激引起的迷走神经传入反应。免疫细胞化学标记 CCKar 和 TRPV1 显示,分离的胃投射 NG 神经元上有表达。qRT-PCR 定量评估显示,T3-SCI 后 3 天恢复期时整个 NG 中的 CCKar 和 TRPV1 mRNA 表达水平显著升高,但 3 周后恢复正常。损伤后 3 天,与对照组大鼠相比,T3-SCI 大鼠给予 CCK-8 后胃迷走神经传入反应明显减弱,而给予辣椒素后 T3-SCI 大鼠的迷走神经反应明显升高。这些发现表明,T3-SCI 会引发外周重塑和迷走神经传入纤维对与消化相关的生理信号的反应的长期改变。