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Shawntay Chaney, Anton Delwig, Andrea Bertke, Todd P Margolis, Douglas Yasumura, Ethan Buhr, Russell Van Gelder, Laura Cammas, David R Copenhagen; Melanopsin expression in the cornea. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4913.
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© ARVO (1962-2015); The Authors (2016-present)
Expression of melanopsin in the anterior eye has been documented in reports of melanopsin in the iris and projections from melanopsin ganglion cells into the ciliary body. Patients with corneal abrasions often suffer from photophobia suggesting the possibility that light activates nociceptors in the cornea. Furthermore, light directly potentiated trigeminal-mediated blink reflexes in rat eyes with lesioned optic nerves suggesting photosensitivity mediated by non-retinal photoreceptors. We therefore sought to test the hypothesis that melanopsin expression might also reside within fibers, possibly trigeminal fibers, innervating the cornea.
We used melanopsin IHC and Western blotting (F1006) to search for melanopsin protein in the cornea and trigeminal ganglia (TG). We used RT-PCR to look for gene expression in TG and cornea. We used cre;lox genetic system to liberate intracellular markers in melanopsin cells (Opn4cre::Ai14 mice and AAV-flex-plap injections into Opn4cre mice).
TdTomato and placental alkaline phosphatase (PLAP) was localized to both the corneal nerve plexus and terminal arborizations in the corneal epithelium. Melanopsin antibody staining of fibers in the cornea were observed in WT but not melanopsin null mice. TdTomato (Opn4cre::Ai14) localized to a subset of neurons in the trigeminal ganglia (TG). PLAP signal was detected in a subset of cultured TG neurons infected with AAV-flex-plap. Melanopsin mRNA was detected in TG cultures. Expression of PLAP in the iris and the mRGC fibers in the ciliary body confirms previous reports on melanopsin expression in the anterior region of the eye.
We report evidence of modest melanopsin expression in the cornea and in the neurons of the trigeminal ganglia. We have not yet shown directly that melanopsin is expressed in TG fibers within the cornea. It is alternatively possible that the melanopsin fibers in the cornea could be projections from mRGCs in retina or from non-retinal structures such as the iris. Functionally, light activation of melanopsin could be directly activating TG fibers in the cornea or it could be modulating responses to other stimuli sensed by the TG fibers such as pH, cold or touch.
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