Cell-Cell Adhesion in the Prelaminar Region of the Optic Nerve Head: A Possible Target for Ionic Stress

Abstract

Purpose: This paper aims to study the anterior surface of the optic nerve in relation to its ability to support a source of stress acting from the vitreous cavity. The intercellular junctions of the lining astrocytes mediated by cellular adhesion molecules (CAMs) may be the main targets for ionic stress. Methods: The optic nerve of the domestic pig was prepared for light, confocal laser and transmission electron microscopy. Immunostaining was performed for antibodies against glial fibrillary acidic protein, neural cadherin (N-cadherin) and neural CAM (N-CAM). Results: Only 1 type of intercellular junction was found among the bordering astrocytes, which was characterized as a zonula adherens. Unions between lining cells showed a positive immunogold effect and immunofluorescence against N-cadherin in the zonula adherens and membrane apposition. N-CAM was also present in areas of nonjunctional cellular adhesion. Conclusion: The stability of intercellular junctions of the nerve-vitreous boundary is sensitive to altered concentrations of Ca²⁺. Since aqueous humor has half the Ca²⁺ concentration of plasma, any contact of aqueous humor with the optic nerve head can interfere with the ionic concentration of calcium in the extracellular spaces. This mechanism may contribute to age-related changes and some types of glaucoma.