Dry-responsive corneal afferents, TRPM8, and regulation of tears

描述（由申请人提供）：干眼综合征（DES）是由角膜表面泪膜不足引起的。结果，DES患者遭受眼部疼痛，在某些情况下严重的视力问题。DES影响多达20%的人口，治疗往往仍然不足。干眼的一个原因可能是感觉神经元不能通过响应角膜的干燥来正确地评估眼表面流体状态。通过基础泪液产生维持正常泪膜的神经调节机制仍然未知。我们最近发现，一类角膜初级传入神经元，冷细胞，这是已知的非有害的冷却，也被激活的眼表干燥，高渗溶液，和薄荷醇。这些特性是参与调节基底流泪的神经元所预期的，因为泪液从角膜表面蒸发会导致泪膜的冷却和渗透压增加。据推测，这些干反应冷细胞代表反射弧的传入分支，其驱动无害的基底流泪而不产生眼痛。这一假设将在四个具体目标中进行审查。第一个目标将确定角膜初级传入神经元的编码特性激活眼表干燥。特别关注高渗和TRPM 8依赖性诱发反应; TRPM 8通道被薄荷醇和无害冷却激活。将使用大鼠三叉神经节中的体内单单位电生理学表征角膜初级传入。将检查对眼表干燥的反应，以及由热、化学和渗透刺激引起的反应。目的2将确定TRPM 8激动剂改变角膜初级传入神经元中的冷和干诱发反应的能力。目的3研究眼表干燥激活三叉神经脊束核神经元的编码特性和投射靶点。将使用Vsp中的单个单位记录来评估从角膜初级传入神经接收直接输入的神经元的特性，并将使用电刺激来测试它们对参与流泪调节的区域的投射状态。最后，目的4将确定在大鼠中由施加到眼表面的TRPM 8和TRPA 1激动剂诱发的流泪和伤害反应行为中涉及的三叉神经脊束核内的回路。将进行接收角膜输入的VSP的两个不同区域中的病变，以确定它们对眼睛刺激的流泪和伤害反应的相对贡献。增加对眼表干燥有反应的神经元的敏感性和活性的能力代表了DES潜在治疗的新策略。 公共卫生相关性：干眼症（DES）影响多达20%的人口，导致不适和疼痛的感觉，并可能导致严重的视力问题。药物洗脱支架的治疗往往仍然不足。这项拟议中的研究检查了特定感觉神经元在不产生疼痛的情况下增加流泪的能力。这一系列研究可能会为治疗DES的新方法开辟道路。

DESCRIPTION (provided by applicant): Dry eye syndrome (DES) results from an inadequate tear film on the corneal surface. As a result, patients with DES suffer from ocular pain and in some cases serious vision problems. DES affects as much as 20% of the population and treatment often remains inadequate. One cause of dry eye may be an inability of sensory neurons to properly assess the ocular surface fluid status by responding to drying of the cornea. The neural regulatory mechanisms involved in maintaining a normal tear-film, via basal tear production, are still unknown. We have recently discovered that a class of corneal primary afferent neurons, cold cells, which are known to respond to non-noxious cooling, are also activated by drying of the ocular surface, hyperosmotic solutions, and menthol. These properties would be expected of neurons that participate in the regulation of basal tearing, as evaporation of tears from the corneal surface causes both cooling and increased osmolarity of the tear film. It is hypothesized that these dry-responsive cold cells represent the afferent limb of the reflex arc that drives non- noxious basal tearing without producing ocular pain. This hypothesis will be examined in four specific aims. The first aim will determine the encoding properties of corneal primary afferent neurons activated by drying of the ocular surface. A particular focus will be on hyperosmotic and TRPM8 dependent evoked responses; TRPM8 channels are activated by both menthol and innocuous cooling. Corneal primary afferents will be characterized using in vivo single-unit electrophysiology in the rat trigeminal ganglion. Responses to drying of the ocular surface will be examined, as well as responses evoked by thermal, chemical, and osmotic stimuli. Aim 2 will determine the ability of TRPM8 agonists to alter cold- and dry-evoked responses in corneal primary afferent neurons. Aim 3 will determine the encoding properties and projection targets of spinal trigeminal nucleus (Vsp) neurons activated by drying of the ocular surface. Single unit recordings in Vsp will be used to assess properties of neurons that receive direct input from corneal primary afferents, and electrical stimulation will be employed to test for their projection status to regions involved in the regulation of tearing. Finally, Aim 4 will determine the circuitry within the spinal trigeminal nucleus involved in lacrimation and nocifensive behaviors evoked by TRPM8 and TRPA1 agonists applied to the ocular surface in rats. Lesions in two distinct regions of Vsp that receive corneal inputs will be performed to determine their relative contribution to tearing and nocifensive responses to ocular stimulation. The ability to increase the sensitivity and activity of neurons that respond to drying of the ocular surface represents a novel strategy for the potential treatment of DES. PUBLIC HEALTH RELEVANCE: Dry eye syndrome (DES), which affects as much as 20% of the population, causes feelings of discomfort and pain and can lead to serious vision problems. Treatment for DES often remains inadequate. The proposed research examines the ability of specific sensory neurons to increase tearing without producing pain. This line of research could lead the way to new methods for treating DES.