Microglia in the avian retina: Immunocytochemical demonstration in the adult quail

Abstract

Immunocytochemical techniques were used in conjunction with the QH1 antibody 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 plexiform layers throughout the entire retina, whereas a few microglial cells in the nerve fiber layer were seen only in the central zone of the retina, near the optic nerve head. In the outer plexiform layer, microglial cells were star-shaped, with processes that ramified profusely in the horizontal plane. Fine process tips extended outward radially, insinuating themselves among the photoreceptors. A regular mosaic-like arrangement of microglial cells was evident in the outer plexiform layer, with no overlapping between adjacent cell territories. Microglial cells in the inner plexiform layer ramified through the entire width of this layer, showing radial and horizontal processes. Microglia in the inner plexiform layer also tended to be regularly distributed in a mosaic-like fashion, although there was slight overlapping between adjacent cell territories. Microglia density in this layer was approximately twice that in the outer plexiform layer. This pattern of microglial distribution was similar to that described in vascular retinae of several species of mammals, a finding that suggest that blood vessels are not responsible for the final locations of microglia in the adult retina, and that microglial precursors must migrate through long distances before they reach their precise destination.

The Glial Design of a Teleost Optic Nerve Head Supporting Continuous Growth

“…We consider, taking as a reference those previous studies and the ultrastructural analysis of this glial cell type carried out in the present work, that we are able to precisely identify these elements as microglial cells. In the NFL of the quail retina a similar association has been observed between the microglial cells and the Müller cells' processes (Navascués et al 1994). These observations, and the proximity of the microglial cells to the optic nerve central artery, lead us to suggest that these cells may come from this vessel and enter the neural retina.…”

Genesis, Neurotrophin Responsiveness, and Apoptosis of a Pronounced Direct Connection between the Two Eyes of the Chick Embryo: A Natural Error or a Meaningful Developmental Event?

“…In the same manner, cells with collapsed cell bodies, degenerated dendrites, and apoptotic debris were determined at certain stages of development. Phagocytosing microglial cells were also identified by their typical ameboid or ramified morphologies (quail, Navascués et al, 1994Navascués et al, , 1995rat, Thanos et al, 1994) and counted in the same whole mounts. The absence of microglial cells at earlier stages of cell death (see Results) implies the involvement of other types of cells in the early phagocytosis.…”

Radial migration of developing microglial cells in quail retina: A confocal microscopy study

“…In addition, whole-mounted retinas facilitate the analysis of complete unsectioned cells, even of those with complex morphological features, such as ramified microglial cells. The adult quail retina contains a dense network of ramified microglia (Navascués et al, 1994), which derive from amoeboid microglial cells that enter the developing retina between 7 and 16 days of incubation (E7-E16). They enter from the optic nerve head and the base of the pecten and then migrate tangentially on its vitreal surface in contact with Mü ller cell endfeet in a central-to-peripheral direction (Navascués et al, 1995;Marín-Teva et al, 1998).…”