Mechanisms of sensitzation in a rat model of chronic visceral hypersensitivity

描述(申请人提供)：肠易激综合征(IBS)影响高达15%的美国人口，对生活质量、工作效率和巨额医疗费用产生显著的负面影响。IBS的定义是间歇性腹痛和排便习惯改变的出现，以及没有可观察到的生物异常。虽然致病机制尚未确定，但人类研究表明，IBS与慢性内脏高敏感状态有关。IBS患者内脏高敏感性的产生和维持机制尚不清楚。我们已经建立了一种大鼠模型，该模型由一种传递到新生大鼠结肠的有害刺激启动，导致持久的内脏敏化。成年后(8-12周)，这些大鼠表现出对结直肠扩张的敏感性增加，外源性结肠特异性感觉神经元的兴奋性增加，以及S1背根神经节的基因可塑性。这些变化发生在没有炎症或其他解剖异常的组织学证据的情况下，提示外周敏化的伤害性信号特征重新编程。这项建议将评估TRPV1、p38和ERK MAPK在该模型外周敏化发展中的作用。TRPV1是一种表达在大多数伤害性感觉神经传入上的阳离子通道，可被酸和各种伤害性和炎症性刺激激活。我们的初步结果表明，在新生儿注射醋酸之前拮抗TRPV1可以减弱对结直肠扩张的持续敏感性的发展。我们还表明，新生儿醋酸处理激活了含有结肠传入胞体的DRG中的p38和ERK MAP激酶。我们推测，醋酸激活新生感觉神经元的TRPV1可能通过激活ERK1/2和p38MAPK通路，导致结肠背根神经节神经元兴奋性增强和基因表达改变。这一假设将通过内脏敏感性的行为测试、分离的结肠背根神经节神经元的膜片钳研究、定量RT-PCR的基因表达分析、Western印迹和免疫荧光研究来验证。我们的长期目标是确定导致IBS致敏状态启动和持续的关键分子事件，并为治疗这种综合征的新的药理学方法提供靶点。

DESCRIPTION (provided by applicant): Irritable bowel syndrome (IBS) affects up to 15% of the U.S. population, produces significant negative effects on quality of life, work productivity and significant health care costs. IBS is defined by the occurrence of intermittent periods of abdominal pain and altered bowel habits and the absence of observable biological abnormalities. Although no pathogenic mechanisms have been defined, human studies demonstrate that IBS is associated with a state of chronic visceral hypersensitivity. The mechanisms responsible for the generation and maintenance of visceral hypersensitivity in IBS patients are not known. We have developed a rat model initiated by a noxious stimulus delivered to the colon of neonatal rats that result in long-lasting visceral sensitization. As adults (8-12 weeks), these rats display an increased sensitivity to colorectal distention, increased excitability of extrinsic colon-specific sensory neurons, and gene plasticity in the S1 dorsal root ganglia. These changes occur in the absence of histological evidence of inflammation or other anatomical abnormalities and suggest a reprogramming of nociceptive signaling characteristic of peripheral sensitization. This proposal will evaluate the contributions of TRPV1 and p38 and ERK MAPK to the development of peripheral sensitization in this model. TRPV1 is a cation channel expressed on the majority of nociceptive sensory afferents that is activated by acid and various noxious and inflammatory stimuli. Our preliminary results show that antagonism of TRPV1 prior to neonatal administration of acetic acid attenuates the development of the persistent sensitivity to colorectal distention. We also show that neonatal acetic acid treatment activates p38 and ERK MAP kinases in DRG containing the soma of colon afferents. We hypothesize that TRPV1 activation by acetic acid in neonatal sensory neurons produces increased excitability and changes in gene expression in colon DRG neurons via activation of the ERK 1/2 and p38 MAPK pathways. This hypothesis will be tested using a behavioral assay for visceral sensitivity, patch clamp studies on isolated colon DRG neurons, gene expression analysis by quantitative RT-PCR, western blot and immunofluorescence studies. Our long-term objective is to identify key molecular events responsible for the initiation and perpetuation of the sensitized state in IBS and provide targets for new pharmacological approaches for the treatment of this syndrome.