Microglial cells in the retina of Carassius auratus: Effects of optic nerve crush

To study the morphology and distribution of the retinal microglial cells of the goldfish retina in normal conditions and after optic nerve crush, we h ave used the nucleoside diphosphatase (NDPase) technique, applied to whole- mounts or sections, for light and electron microscopy. In normal retinas, t wo populations of NDPase-positive cells were identified: compact cells asso ciated with the retinal vessels on the vitreal surface of the retina and mi croglial cells in various retinal layers. The microglial cells had a bipola r or multipolar morphology. Bipolar cells were observed in the nerve fibre layer, and multipolar cells were visualised in the ganglion cell layer (GCL ), inner plexiform layer (IPL), and outer plexiform layer. The highest dens ities of multipolar cells were observed in the IPL layer, where they adopte d a regular mosaic-like arrangement in which the occasional spaces were occ upied by cells of the GCL. After optic nerve crush, we observed an increase in the number of compact cells associated with the vessels and changes in NDPase activity, morphology, and distribution of the retinal microglial cel ls. These cells showed an increase in NDPase activity in all retinal layers from day 1 to day 15 after axotomy, and retraction of their processes from day 1 to day 7. In addition, the densities of microglial cells increased i n the GCL between 2 and 15 days after axotomy, and decreased in the IPL by day 4 after axotomy. These microglial changes resemble those observed in ot her regenerating and nonregenerating neuronal systems and may reflect a gen eral response of microglia directed to help the regeneration process. (C) 2 000 Wiley-Liss, Inc.