Müller glial cells of the goldfish retina are phagocytic in vitro but not in vivo.

The role of Müller glial cells in the process of degeneration and regeneration of the goldfish retina is poorly understood. One potential role is phagocytosis of neuronal debris in degenerating retinas. We investigated the phagocytic capacity of Müller glial cells of the goldfish retina both in vitro and in vivo. Müller glial cells from primary or first passage cultures were incubated with latex beads to assess their phagocytic ability, and acridine orange staining was used to identify phagolysosomes in living Müller glial cells. These experiments showed that Müller glial cells are phagocytic in culture. Cell identity was verified with an antibody raised against glial fibrillary acidic protein (GFAP). For the in vivo experiments fluorescent latex beads alone or in combination with the metabolic poison ouabain were injected into the posterior chamber. At various intervals (4 days to 8 weeks) after injection the retinas were prepared for immunocytochemistry. Polyclonal anti-GFAP and NN-1, a monoclonal antibody which recognizes macrophages and microglia within the goldfish retina, were used to identify the phagocytic cells. When the beads were injected into the eye, they were phagocytosed by macrophages/microglia cells but not by Müller cells.