寒冷环境刺激诱导咳嗽高反应性的机制：TRPA1的作用

The generally accepted conception that the exacerbation of chronic cough induced by cold environment is ascribed to the inhalation of cold air and then the direct stimulation of cough receptors in the lower airway is not consistent with the fact that cold air is usually unable to enter the lower airway. Based on our preliminary studies, we hypothesize that under the condition of the increased cough reflex sensitivity, the stimuli in the cold environment activate TRPA1 and TRPV1 co-expressing cough receptors located in the lower airway through TRPA1 expressing sensory afferents in the skin, then cause cough hyperreactivity to the cold environment. In the guinea pigs with chronic cough, the effects of cold environments and cold air inhalation on cough reactivity mediated by TRPA1 and TRPV1 will be compared, and their relationship with airway inflammation, eclectic diacharge of neuron in jugular ganglia and the number or distribution of nerve fibers expressing TRPA1, TRPV1, TRPM8 and substance P in the skin, tracheobronchi, jugular ganglia and nucleus of the solitary tract located in brainstem will be analyzed. By doing these，we will investigate the effects of TRPA1 on cough hyperreactivity induced by cold environment and its underlying mechanisms, and finally provide the evidence for more appropriate prevention and therapy of chronic cough in the future.

寒冷环境诱导慢性咳嗽加重由冷空气吸入直接刺激下气道咳嗽感受器引起的普遍认识不符合冷空气通常无法进入下气道的事实。在前期预实验的基础上，本课题提出咳嗽敏感性增高时，寒冷环境可经皮肤传入神经纤维的瞬时受体电位阳离子通道蛋白TRPA1激活下气道共表达TRPA1和TRPV1的咳嗽感受器诱导咳嗽高反应性的假说。拟在慢性咳嗽模型豚鼠上，比较寒冷环境和冷空气吸入对TRPA1和TRPV1介导的咳嗽反应性变化，探讨其与气道炎症、颈神经节纤维放电和皮肤、气管支气管、颈神经节、脑干孤束核组织表达TRPA1、TRPV1、TRPM8、P物质的神经纤维数量和分布改变的关系，阐明TRPA1在寒冷环境诱导咳嗽高反应性中的作用及机制，为今后采取更恰当的慢性咳嗽防治措施提供依据。

慢性咳嗽患者在寒冷环境下咳嗽加重是其典型特征，普遍认为这一现象的原因是患者直接吸入冷空气刺激下气道的咳嗽感受器。然而正常情况下，上气道对吸入空气有加湿保温作用，冷空气无法直接接触到下气道。在前期预实验的基础上，本课题提出咳嗽敏感性增高时，寒冷环境可经皮肤传入神经纤维的瞬时受体电位阳离子通道蛋白TRPA1激活下气道TRPA1咳嗽感受器诱导咳嗽高反应性的假说。为此，我们在反复吸入柠檬酸诱导的慢性咳嗽模型豚鼠上比较了寒冷环境和冷空气吸入对咳嗽反应性的影响，观察皮肤TRPA1拮抗剂HC-030031预处理后慢性咳嗽模型豚鼠咳嗽反应性、皮肤和气管神经纤维表达TRPA1数量和分布以及肺泡灌洗液中P物质浓度的变化，以证实寒冷刺激是通过皮肤TRPA1通路引起咳嗽反应性升高，并探讨其机制。.研究结果显示1）柠檬酸反复吸入诱导的慢性咳嗽模型豚鼠咳嗽反应性与正常豚鼠相比明显升高；2）慢性咳嗽模型豚鼠接受寒冷刺激后咳嗽反应性进一步增高，但整体寒冷与躯干四肢寒冷暴露表现出相似的咳嗽高反应性，而头部寒冷暴露后并未见咳嗽反应性的明显变化，表明寒冷环境诱导咳嗽高反应性是通过皮肤冷感受器诱导，而不是直接吸入冷空气所致。3）皮肤TRPA1拮抗剂预处理能明显阻断慢性咳嗽模型豚鼠寒冷暴露后增高的咳嗽反应性，抑制皮肤和气管TRPA1的表达，伴有肺泡灌洗液中P物质浓度的降低，证实皮肤TRPA1通路的重要作用。4）共聚焦显微镜显示寒冷刺激后皮肤和气管黏膜内神经纤维上TRPA1表达明显增高，并且被TRPA1拮抗剂阻断，进一步确立皮肤感觉神经上TRPA1通路在寒冷环境诱导咳嗽高反应性中的作用。.本研究通过实验首次证实寒冷环境是通过皮肤寒冷刺激诱导慢性咳嗽豚鼠的咳嗽高反应，其机制可能与皮肤感觉神经纤维上TRPA1通路激活有关。这些发现为阐述寒冷环境下慢性咳嗽的加重提供理论支持，但可能的中枢机制尚有待进一步的探讨。