Date of Award

Winter 12-31-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

Advisor

Ian Meng

Second Committee Member

Tamara King

Third Committee Member

Ling Cao

Additional Committee Members

Stephen Pelsue

Geoffrey Ganter

Abstract

Dry eye can result from multiple causes, including a reduction in the quantity or altered composition of tears. The lacrimal gland is the major supplier of the aqueous tear components, including water, electrolytes, and proteins. Reduced output from the lacrimal glands results in aqueous tear deficiency, a specific subclass of dry eye disease (DED) marked by inadequate tear volume. The prevalence of DED is 1.5-2 times greater in women than men, yet a comprehensive comparison of dry eye symptoms in male and female animals in an animal model of DED has not been performed. We excised the lacrimal gland to compare the effects of aqueous tear deficiency on male and female mice. We found that aqueous tear deficiency engendered greater epithelial damage and immune cell infiltration in female animals that is consistent with epidemiological reports indicating a greater prevalence of dry eye in women. Signs of ocular discomfort and pain are the most common symptoms of dry eye disease. Furthermore, the ability of the corneal afferents to sense potentially damaging stimuli and monitor dryness by controlling reflexive secretions and blinking is altered in dry eye. Utilizing lacrimal gland excision as a mouse model of DED, we assessed pain and anxiety-like behaviors in male and female animals. We found that female animals displayed a greater irritation and pain phenotype in response to tear deficiency produced by lacrimal gland excision and demonstrated an ongoing pain state that was exacerbated in moderate dry eye only in female mice. An analysis of nerve fiber density showed no difference between male and female mice in the moderate dry eye state, suggesting that nerve fiber density is not a good marker for the ongoing pain state. Using a mouse transgenic approach, ArchT, a light sensitive proton pump that acts as a neural inhibitor, was expressed in Nav1.8 expressing primary afferent neurons, which includes the majority of corneal afferents. In this way, corneal nerve fibers were selectively and transiently inhibited. After lacrimal gland excision, ArchT/Nav1.8-cre mice showed a significant conditioned place preference for the chamber illuminated with the ArchT-activating light. This effect was long lasting, as animals continued to prefer the chamber even after the light was turned off. Topical application of the anesthetic QX-314 plus lidocaine to the cornea mitigated the conditioned place preference. These studies provide evidence of sexual dimorphism in a mouse model of dry eye that is consistent with epidemiological data in humans. Furthermore, we were able to demonstrate an ongoing pain state in dry eye using an approach that can be utilized in assessing potential treatments for ocular pain.

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