Sensory nerve terminals are highly distributed in the cornea, and regulate ocular surface sensation and homeostasis in response to various endogenous and exogenous stimuli. However, little is known about mediators regulating the physiological and pathophysiological activities of corneal sensory nerves. The aim of this study was to investigate the presence of cholinergic regulation in sensory nerves in the cornea. Localization of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (vAChT) was evaluated using western blotting and immunohistochemical analysis. The synthesis and liberation of acetylcholine from the cornea were assessed using corneal segments pre-incubated with [H]choline. The responsiveness of corneal neurons and nerves to cholinergic drugs was explored using calcium imaging with primary cultures of trigeminal ganglion neurons and extracellular recording from corneal preparations in guinea pigs. ChAT, but not vAChT, was highly distributed in the corneal epithelium. In corneal segments, [H] acetylcholine was synthesized from [H]choline, and was also released in response to electrical stimuli. In cultured corneal neurons, the population sensitive to a transient receptor potential melastatin 8 (TRPM8) agonist exhibited high probability of responding to nicotine in a calcium imaging experiment. The firing frequency of cold-sensitive corneal nerves was increased by the application of nicotine, but diminished by an α4 nicotinic acetylcholine receptor antagonist. The corneal epithelium can synthesize and release acetylcholine. Corneal acetylcholine can excite sensory nerves via nicotinic receptors containing the α4 subunit. Therefore, corneal acetylcholine may be one of the important regulators of corneal nerve activity arranging ocular surface condition and sensation.

中文翻译：

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角膜乙酰胆碱通过烟碱受体调节感觉神经活动

感觉神经末梢高度分布在角膜中，调节眼表感觉和体内平衡以响应各种内源性和外源性刺激。然而，人们对调节角膜感觉神经生理和病理生理活动的介质知之甚少。本研究的目的是调查角膜感觉神经中胆碱能调节的存在。使用蛋白质印迹和免疫组织化学分析评估胆碱乙酰转移酶（ChAT）和囊泡乙酰胆碱转运蛋白（vAChT）的定位。使用与[H]胆碱预孵育的角膜片段评估角膜中乙酰胆碱的合成和释放。利用三叉神经节神经元原代培养物的钙成像和豚鼠角膜制剂的细胞外记录，探讨了角膜神经元和神经对胆碱能药物的反应性。 ChAT（而非 vAChT）高度分布在角膜上皮中。在角膜节段中，[3H]乙酰胆碱是由[3H]胆碱合成的，并且也会因电刺激而释放。在培养的角膜神经元中，对瞬时受体电位褪黑素 8 (TRPM8) 激动剂敏感的群体在钙成像实验中表现出对尼古丁做出反应的高可能性。冷敏感角膜神经的放电频率因尼古丁的应用而增加，但因α4烟碱乙酰胆碱受体拮抗剂而减少。角膜上皮可以合成和释放乙酰胆碱。角膜乙酰胆碱可以通过含有α4亚基的烟碱受体兴奋感觉神经。因此，角膜乙酰胆碱可能是调节眼表状况和感觉的角膜神经活动的重要调节剂之一。