Abstract
Purpose: :
To describe the anatomy of cold sensitive nerve fibers in the cornea of a genetically modified mouse in which the cold transducing channel TRPM8 expression associated to a yellow-fluorescent protein (YFP).
Methods: :
TRPM8 promoter driven YFP-TRPM8 mice were used. Corneas were excised, whole mounted, fixed and stained with antibodies against neuronal class III beta-tubulin (Tuj-1) and against YFP.
Results: :
A scarce number of the axons (≈10%) exhibiting yellow-green fluorescence were identified within the main stromal nerve bundles entering the cornea at the corneoscleral limbus. YFP nerve bundles running in the stromal nerves branched repetitively contributing to the midstromal plexus and the subepithelial plexus. GFP nerves penetrated Bowman's membrane as curvilinear nerves to supply the corneal epithelium and ran longitudinally as part of the epithelial leashes that constitute the whorl-like subbasal nerve plexus. Intraepithelial terminals originated as branches of the scarce YFP subbasal nerves and terminated in the most superficial epithelial layers branching into a small number of short, bulbous endings.
Conclusions: :
Cold-sensitive sensory fibers in the mouse cornea represent a small percentage of the total number of sensory afferents. The reduced branching of the TPRM8 axons, the superficial location of their nerve terminals and the closeness and large size of the bulbous endings explain the reduced dimensions of corneal receptive fields of cold sensory afferents and the accessibility of cold-sensitive endings to extracellular recording.
Keywords: innervation: sensation • anatomy • cornea: basic science