Fine structure of sensory nerves in the rat cornea: an experimental nerve degeneration study

Fine structure of nerve fibres and terminals in the rat cornea was studied after fixation with glutaraldehyde and osmium tetroxide or with potassium permanganate. Superior cervical and/or ciliary ganglionectomy as well as ophthalmic neurotomy were performed in order to verify the origin of the corneal nerves. In the control corneas axon profiles with granular vesicles were observed in the stroma. Other axons containing agranular vesicles were found both in the stroma and in the epithelium. Superior cervical ganglionectomy abolished only the axons containing granular vesicles but did not affect the corneal blink reflex. Ciliary ganglionectomy induced more conspicuous changes in both stromal and intraepithelial axon profiles. The corneal reflex was, however, normal. Some of the axons containing agranular vesicles also showed degenerative changes. However, intact axon profiles with agranular vesicles were seen even after extirpation of both the ciliary ganglion and the superior cervical ganglion (combined autonomic ganglionectomy). On the other hand, all axon profiles with agranular vesicles disappeared after coagulation of the ophthalmic and maxillary nerves (sensory denervation). This operation destroyed most of the axons in all parts of the cornea and abolished the blink reflex. It is concluded that the axon profiles in the corneal epithelium, containing agranular vesicles, are sensory axons of the trigeminal nerve. A possible role of the vesicles in sensory nerves is discussed.