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。因此，DES患者会遭受眼部疼痛，在某些情况下还会出现严重的视力问题。DES影响了多达20%的人口，治疗往往仍然不足。干眼症的一个原因可能是感觉神经元无法通过对角膜干燥的反应来正确评估眼表液体状态。通过基础泪液的产生来维持正常泪膜的神经调节机制尚不清楚。我们最近发现，一类角膜初级传入神经元，冷细胞，已知对无害冷却有反应，也被眼表干燥、高渗溶液和薄荷醇激活。这些特性在参与基底撕裂调节的神经元中是可以预料到的，因为泪液从角膜表面蒸发会导致冷却和泪液膜渗透压的增加。据推测，这些干反应性冷细胞代表反射弧的传入肢，而反射弧驱动无害的基底撕裂而不产生眼痛。这一假设将在四个具体目标中进行检验。第一个目的是确定眼表干燥激活的角膜初级传入神经元的编码特性。特别关注高渗和TRPM8依赖性诱发反应；薄荷醇和无害冷却均可激活TRPM8通道。角膜初级传入事件将在大鼠三叉神经节的体内单单位电生理学表征。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TRPM8激动剂改变角膜初级传入神经元冷诱发和干诱发反应的能力。目的3将确定三叉神经脊髓核（Vsp）神经元的编码特性和投影目标激活眼表干燥。Vsp中的单个单元记录将用于评估接受角膜初级传入直接输入的神经元的特性，电刺激将用于测试它们在涉及撕裂调节的区域的投射状态。最后，Aim 4将确定三叉脊髓核内参与大鼠眼表TRPM8和TRPA1激动剂引起的流泪和有害行为的电路。在接受角膜输入的两个不同Vsp区域的病变将被执行，以确定它们对眼睛刺激的撕裂和伤害反应的相对贡献。增加对眼表干燥作出反应的神经元的敏感性和活性的能力代表了DES潜在治疗的一种新策略。

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.