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Almudena Íñigo-Portugués, Omar Gonzalez Gonzalez, Ignacio Alcalde, Federico Bech, Juana Gallar, Jesus Merayo-Lloves, Carlos Belmonte; AGING EFFECTS ON CORNEAL COLD THERMORECEPTOR NEURONS AND CORNEAL NERVES ARE RELATED WITH CHANGES IN BASAL TEARING AND BLINKING RATES. Invest. Ophthalmol. Vis. Sci. 2016;57(12):402.
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© ARVO (1962-2015); The Authors (2016-present)
To determine in mice the effects of aging on morphometric, neurochemical and functional parameters of corneal cold sensory fibers and their relation with basal tearing and blinking rates
Corneas and trigeminal ganglia (TG) obtained from TRPM8BAC-EYFP and TRPM8-deficient mice of different ages (3 to 24 months) were studied. Blinking responses to chemical stimuli (osmolality and menthol) were measured in awake, restrained mice. Basal tearing was measured in anesthetized animals, using phenol red threads. Corneal nerves expressing EYFP protein were identified in whole mount corneas of mice using immunohistochemical techniques. Also, TGs were processed for immunofluorescence techniques against peripherin, NF20, TrkA and CGRP. Extracellular electrical activity of single sensory nerve endings of the corneal surface was recorded in excised and superfused eyes
The density, length and shape of corneal cold subbasal nerve fibers and terminals were altered by age in TRPM8BAC-EYFP mice corneas, resembling those found in young TRPM8-deficient mice. The density of TRPM8 axons in the subbasal plexus and of epithelial nerve terminals decreased with age. In young mice, two types of cold fibers, beaded (~50%) and smooth (~50%) and three types of terminal branches (“complex”, “ramifying” and “simple”) were found. In old mice, smooth axons predominated and their length was higher in comparison with young mice. The proportion of different types of terminals changed with aging and in old animals a new type (“collapsed terminal”) was identified. In the TG, two populations of TRPM8 corneal neurons with different neurochemical signature were identified. Their proportion and molecular pattern changed with age. Functionally, a large number of corneal cold nerve terminals in young mice were low-threshold-with a small number of high threshold terminals. This proportion changed with age, increasing markedly the number of high-threshold cold terminals. In parallel, basal tearing and blinking rates were altered in aged mice
Changes in the morphological, neurochemical and functional properties of corneal cold sensory neurons and their peripheral axons during aging appear to be associated with disturbances in basal tearing and blinking rates
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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