Mechanisms of sensitzation in a rat model of chronic visceral hypersensitivity

描述（由申请人提供）：肠易激综合征（IBS）影响多达15%的美国人口，对生活质量、工作效率和大量医疗保健成本产生重大负面影响。IBS的定义是间歇性腹痛和排便习惯改变，没有可观察到的生物学异常。虽然尚未确定致病机制，但人体研究表明肠易激综合征与慢性内脏过敏状态有关。肠易激综合征患者产生和维持内脏超敏反应的机制尚不清楚。我们已经开发了一种大鼠模型，通过将有害刺激传递到新生大鼠的结肠，导致长期的内脏致敏。成年后（8-12周），这些大鼠对结肠膨胀的敏感性增加，外源性结肠特异性感觉神经元的兴奋性增加，S1背根神经节的基因可塑性增强。这些变化发生在没有炎症的组织学证据或其他解剖异常的情况下，提示外周致敏特征的伤害性信号重编程。该提案将评估TRPV1和p38以及ERK MAPK在该模型中外周敏化发展中的贡献。TRPV1是一种在大多数伤害性感觉传入中表达的阳离子通道，可被酸和各种有害和炎症刺激激活。我们的初步结果表明，在新生儿给药醋酸之前，TRPV1的拮抗作用减弱了对结直肠膨胀的持续敏感性的发展。我们还发现，新生儿醋酸处理激活了含有结肠传入体的DRG中的p38和ERK MAP激酶。我们假设新生儿感觉神经元中TRPV1被醋酸激活，通过激活ERK 1/2和p38 MAPK通路，导致结肠DRG神经元的兴奋性增加和基因表达改变。这一假设将通过内脏敏感性的行为分析、分离结肠DRG神经元的膜片钳研究、定量RT-PCR的基因表达分析、western blot和免疫荧光研究来验证。我们的长期目标是确定肠易激综合征致敏状态启动和延续的关键分子事件，并为治疗该综合征的新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.