Ultrastructure of the corneal nerves after fixation with potassium permanganate

The innervation of the rat cornea was investigated electron microscopically after KMnO4 fixation. Myelinated nerve fibres were observed only in the limbal margin of the cornea, whereas the axons located in the stroma of the avascular cornea were surrounded by the Schwann cell cytoplasm. Axon profiles with small (300-500 A) granular vesicles and another type with agranular vesicles were seen among the non-vesiculated fibres in all parts of the cornea. After superior cervical ganglionectomy it was not possible to find any axons with small granular vesicles. On the other hand, sone degenerating axon profiles were observed in the stromal nerve trunks after ganglionectomy. In the epithelium-naked axons with an occasional mitochondrion and a few agranular vesicles penetrated between the epithelial cells. Moreover, axons filled with several mitochondria were rarely observed in the epithelium, but these were difficult to differentiate from the surrounding epithelial cells. The role of the different nerve types observed in the cornea is discussed. The results suggest that the rat cornea has a dual vegetative innervation.