A light microscopic demonstration of amoeboid microglia and microglial cells in the retina of rats of various ages.

The retinae from rats of various ages were stained using the weak silver carbonate method of del Rio-Hortega. In newborn and early postnatal (3-day-old) rats, silver-impregnated round and amoeboidic cells displaying thick stout pseudopodial processes were distributed in the nerve fiber and ganglion cell layers. In 10-day-old rats, the cell bodies were rod-shaped bearing pseudopodia or fusiform showing slender and branching processes. The majority of the cells were found in the ganglion cell layer with occasional ones in the inner plexiforn layer. By 20 days of age, the cells became smaller and exhibited long branching processes. They were located predominantly in the inner plexiform or bipolar cell layer. In the adult animals, all the silver-impregnated cells appeared small and flattened with long branching processes. Based on their morphological features, it was concluded that they were in fact amoeboid microglia and microglial cells present in the developing retina which probably function as macrophages as described in the brain tissues.