Macroglial alterations after isolated optic nerve sheath fenestration in rabbit.

PURPOSE: To study the modifications undergone by the macroglial cells after meningeal breach of the optic nerve in the rabbit, without optic neuropathy. METHODS: The optic nerve sheath fenestration technique carried out in humans was adapted to rabbit without axonal injury in the optic nerve. The effects of meningeal fenestration on glial cells were examined by immunocytochemical procedures (day 15) using the antibodies against two astrocyte markers: glial fibrillary acidic protein (GFAP) and vimentin. Proliferation of glial cells was evaluated with single 5-bromodeoxyuridine (BrdU) labeling or double GFAP and BrdU labelings. Qualitative data on glial cells were evaluated with the electron microscope. RESULTS: Optic nerve sheath fenestration on healthy adult rabbits resulted in a decrease of volume of the subarachnoid space located at the level of the meningeal scar, with a significant increase of the optic nerve area. The meninges presented a fibrous scar. In the optic nerve parenchyma, astrocytes appeared hypertrophic in the vicinity of the fenestration. The whole nerve contains numerous BrdU-labeled mitotic cells, a number of which double-labeled for both BrdU and GFAP belong to the astrocyte line. There was no loss of optic nerve axons. CONCLUSIONS: The inflammation produced by the surgical breach of the peri-optic meningeal sheaths induces a significant reactivity, including proliferation of astrocytes in the optic nerve. Reactive astrocytes may interact positively with axons and may modify the extracellular environment in the optic nerve.