MICROGLIA IN THE AVIAN RETINA - IMMUNOCYTOCHEMICAL DEMONSTRATION IN THE ADULT QUAIL

Immunocytochemical techniques were used in conjunction with the QH1 an tibody to study the morphological characteristics and distribution of microglia in the avascular retina of an avian species (the quail). The majority of microglial cells appeared in the outer and inner plexifor m layers throughout the entire retina, whereas a few microglial cells in the nerve fiber layer were seen only in the central zone of the ret ina, near the optic nerve head. In the outer plexiform layer, microgli al cells were star-shaped, with processes that ramified profusely in t he horizontal plane. Fine process tips extended outward radially, insi nuating themselves among the photoreceptors. A regular mosaic-like arr angement of microglial cells was evident in the outer plexiform layer, with no overlapping between adjacent cell territories. Microglial cel ls in the inner plexiform layer ramified through the entire width of t his layer, showing radial and horizontal processes. Microglia in the i nner plexiform layer also tended to be regularly distributed in a mosa ic-like fashion, although there was slight overlapping between adjacen t cell territories. Microglia density in this layer was approximately twice that in the outer plexiform layer. This pattern of microglial di stribution was similar to that described in vascular retinae of severa l species of mammals, a finding that suggests that blood vessels are n ot responsible for the final locations of microglia in the adult retin a, and that microglial precursors must migrate through long distances before they reach their precise destination. (C) 1994 Wiley-Liss, Inc.