The Glial Organization of an Optic Nerve Head that Supports Continuous Growth

Abstract

Abstract: : Purpose: The visual system of fish supports continuous growth during the animals life. In the optic nerve head (ONH), all the ganglion cells' axons formed in the retina must change their orientation to enter the optic nerve. This event makes the ONH a very important region for the correct organization of the newly formed and growing ganglion cells' axons. Due to this, glial cells located in this region could be important elements for the guiding of these new axons to their correct position. Methods: To analyze the peculiarities of the glial organization of the optic ONH of the tench (Tinca tinca), we used both immunohistochemical and electron microscopic approaches. We employed antibodies specific for the macroglial cells: glutamine synthetase (GS), glial fibrillary acidic protein (GFAP) and S100. We also employed the N518 antibody to specifically label the new ganglion cells' axons and the anti-proliferating cell nuclear antigen (PCNA) antibody to detect dividing cells. Results: The immunohistochemical and ultrastructural analyses demonstrated a particular regional adaptation of the Müller cells' vitreal processes, strongly labeled with the anti-GFAP antibody, around the optic disc. In direct contact with these Müller cells' vitreal processes and their end feet around the ONH there were S100 positive cells with ultrastructural characteristics of astrocytes and S100 negative cells, whose ultrastructural analysis distinguished them as microglial cells. Moreover, we found for the first time a population of proliferating PCNA labeled cells with ultrastructural features of glioblasts in the limit between the retina and the optic nerve in a region similar to the Kuhnt intermediary tissue of mammals. Finally, in the intraorbital portion of the optic nerve, by using electron microscopy we detected differentiating oligodendrocytes arranged in rows. Conclusion: By using immunohistochemical and electron microcopy we have demonstrated a particular organization of astrocytes and Müller cells around the optic disc of a teleost, that could be useful for the guiding of the newly formed ganglion cells' axons. Furthermore, we have identify a population of proliferating glioblasts, which could serve as a pool of glial cells during the continous growth of the visual system in these animals.

Keywords: 498 optic disc • 472 microscopy: electron microscopy • 479 Muller cells