Glial hyaluronate-binding protein (GHAP) in optic nerve and retina

The distribution of glial fibrillary acidic protein (GFAP) and of glial hyaluronate-binding protein (GHAP) was studied by indirect immunofluorescence with monoclonal and polyclonal antibodies in dog, rat and rabbit optic nerve. In dog and rabbit, myelination extends into the optic nerve head inside the eye, while in the rat myelination of the optic nerve ceases abruptly at its entry into the eye. Outside the eye the distribution of the two proteins was similar. Both antigens formed a delicate mesh surrounding myelinated optic nerve axons. In all 3 species GFAP immunoreactivity continued uninterrupted into the optic nerve head inside the eye. Conversely, in both dog and rat, GHAP immunoreactivity ceased abruptly in the region of the lamina cribrosa, a sieve-like structure continuous with the sclera through which bundles of optic nerve axons pass. No staining was observed in the myelinated optic nerve head of the dog nor in the non-myelinated optic nerve head of the rat. In the rabbit lacking a lamina cribrosa, GHAP immunoreactivity did not cease abruptly at the optic nerve entry into the eye, but the staining intensity was reduced in the optic nerve head.