Abstract
Purpose :
To define the time course and magnitude of remodeling of corneal cold sensory nerve fibers of adult mice in vivo.
Methods :
Mice expressing EYFP under the control of TRPM8 regulatory sequences (TRPM8-EYFP mouse) were anesthetized with an intraperitoneal injection of xylazine (16 mg/kg) followed by inhalation of isoflurane (1.5 %). In TRPM8-EYFP mice, only cold-sensitive fibers (roughly 20 percent of the total) display a green fluorescence, thus allowing their morphological identification. TRPM8+ sub-basal nerve leashes and intraepithelial terminals were imaged at 5x and 25x magnification by means of a confocal microscope and reconstructed in 3D using Imaris 8.2 software. Individual corneal leashes and intraepithelial terminals were monitored in the same animal at different time points over a week (day 0, day 2 and day 7). The total length of individual leashes was measured, and the length change rate calculated. The number of nerve terminals given by each sub-basal nerve fiber was also counted.
Results :
Points of penetration of a single stromal nerve into basal lamina to form a sub-basal leash were not homogeneously distributed throughout the cornea, being more abundant in its periphery than in the center. Five out of 7 leashes containing TRPM8 axons, measured in 3 mice, increased their total length at a rate of 34.56 ± 14.10 µm/day. Contrarily, total length decreased in another 2 leashes at a rate of -55.38 ± 34.60 µm/day. Additionally, the number, location and shape of nerve terminals given by the leashes changed with time (figure 1).
Conclusions :
Corneal nerve fibers in the living animal experience dynamic configuration changes involving increases and decreases of leashes’ total length and redistribution of their terminal endings, reflecting a continuous remodeling of corneal epithelium innervation.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.